title: BBC Two

text: The BBC also offers audio description on some popular programmes for visually impaired-viewers as well as sign language interpretation on some of its programmes for deaf and hard-of-hearing viewers. The percentage of the BBC's total television output with audio description available is 10%, having been increased from 8% in 2008.


title: BBC Two

text: Originally, programmes from BBC Two were shown in high definition on the dedicated BBC HD channel, alongside programmes from BBC Three and BBC Four, as well as some select series from CBBC and CBeebies. However, in plans outlined by the director general Mark Thompson on 6 October 2011, BBC HD would close to be replaced by "BBC Two HD", a high-definition simulcast of BBC Two that would work much the same way as BBC One HD. This move allowed the corporation to save £2.1 million, used to count towards its budget deficit following the freezing of the licence fee and the additional financial responsibility of addition services.


title: BBC Two

text: On 19 February 2013, it was announced that BBC Two HD would replace BBC HD from 6.05 a.m. on 26 March 2013. Channel numbers for the BBC's HD channels also changed on Sky, to allow BBC One HD and BBC Two HD to sit side-by-side on channels 141, and 142 respectively on the EPG.


title: BBC Two

text: On 16 July 2013, the BBC indicated that it wants to launch Northern Irish, Scottish and Welsh variations of BBC Two HD; however, this would require the approval of the BBC Trust, with a proposal due to be presented within six months.


title: BBC Two

text: On 10 December 2013, BBC Two HD was swapped with the SD channel in England on Sky's EPG for HD subscribers.


title: BBC Two

text: In October 2018, the BBC announced that regional variants of BBC Two HD in Wales and Northern Ireland would launch at the end of November that year on terrestrial, satellite (Wales only) and iPlayer. BBC Two HD in these regions were swapped with the SD channel on Sky's EPG for HD subscribers. A Scotland variant was not launched, as BBC Two Scotland was discontinued in February 2019 in favour of the new BBC Scotland channel.


title: Suresh Gopi

text: Suresh Gopi (born 26 June 1958) is an Indian actor, politician, playback singer and television presenter. He works predominantly in Malayalam cinema and has also appeared in some Tamil, Telugu, Kannada and Bollywood films. Suresh made his acting debut as a child in the 1965 film "Odayil Ninnu". He made his debut as an adult in 1986 and since then, he has acted in more than 250 films. Suresh Gopi is a recipient of the National Film Award and the Kerala State Film Award in 1998 for his performance in "Kaliyattam". He was a nominated member of the Rajya Sabha, the upper house of the Parliament of India.


title: Suresh Gopi

text: Suresh Gopi was born on 26 June 1958 in Kollam, Kerala, India to K. Gopinathan Pillai, a film distributor, and V. Gnanalekshmi Amma, as their eldest son. He has three younger brothers—Subhash Gopi, Sunil Gopi and Sanil Gopi (the latter two are twins). Suresh was brought up in Kollam. He completed his school education from Infant Jesus Anglo-Indian Higher Secondary School in Kollam. Suresh joined Fatima Mata National College in Kollam for higher studies. He holds a Bachelor of Science degree in Zoology and Master of Arts degree in English literature.


title: Suresh Gopi

text: Suresh Gopi made his debut as a child artist in 1965 by playing a small role in "Odayil Ninnu". Later he made his debut as an adult in 1986 with an uncredited role in "Niramulla Raavukal". He gained attention through the minor role of a prospective groom in "T. P. Balagopalan M. A." (1986). Suresh Gopi went on to play few antagonistic and numerous supporting roles throughout the late 1980s and early 1990s. He was noted for his villain role in "Irupatham Noottandu" (1987). It was the highest grossing Malayalam movie of that time. He had a major supporting role as "Harry" in "Oru CBI Diary Kurippu" (1988), which was also the highest grossing film at the time. Gopi's comic role as Sub Inspector "Minnal Prathapan" in "Manu Uncle" (1988) has over the years attained a cult status. His portrayal of Dr. Narendran in Padmarajan's 1990 film "Innale" (1990) was critically acclaimed and is considered by fans and critics to be one of the best performances of his career. Gopi also gained lot of appraisal for his portrayal of Aromal Chekavar in 1989 classic "Oru Vadakkan Veeragatha". He played another memorable cameo comic role as Christopher Luke, a professional killer in "Nagarangalil Chennu Raparkam" (1989). His other notable movies during the late 1980s include "Bhoomiyile Rajakkanmar", "New Delhi" (1987), "Moonnam Mura", "1921" (1988), "Varnam", "Douthyam", "Nair Saab" (1989). His notable films during the early 1990s includes "In Harihar Nagar" and "Thoovalsparsham" both released in 1990.


title: Suresh Gopi

text: After acting in more than 80 movies, Suresh Gopi finally got a breakthrough by playing the lead role in Shaji Kailas's "Thalastaanam" (1992), which was written by Renji Panicker. Suresh Gopi established himself as a lead actor in Malayalam cinema through "Ekalavyan" (1993). This crime thriller was also written by Renji Panicker and directed by Shaji Kailas. Ekalavyan broke many records at the box office and successfully completed 150 days in theaters. Shaji-Renji combination films turned Suresh Gopi into an overnight star in 1990s especially through police and army roles. In 1993 itself, he played the lead role in "Mafia", another Shaji-Renji crime thriller which was very successful at box office. The same year, he played the role of "Nakulan" alongside Mohanlal and Shobhana in Fazil's psychological thriller Manichitrathazhu, which is considered one of the best Malayalam movies ever made. He played the role of a NSG commando in Kashmeeram (1994) which was a commercial hit. It is probably the film "Commissioner" (1994), which helped Suresh Gopi to gain a super-star status in Malayalam Cinema. He played the role of "Bharath Chandran I.P.S" in this another Shaji-Renji crime thriller, which is treated as a cult classic film. He played the role of a RAW officer in Highway (1995) which ran for more than 100 days in theatres.


title: Suresh Gopi

text: Suresh Gopi's high budget film Yuvathurki (1996) failed to create expected results at box office. The same year, he appeared in a different avatar by playing the role of a wildlife photographer in Rajaputran. It became one of the highest grossing Malayalam movies in 1996.


title: Suresh Gopi

text: One of his popular and career best character "Anakkattil Chackochi" came out through "Lelam" in 1997. Scripted by Renji panicker and directed by Joshiy, it was one of the highest-grossing movies of the year. The role of Kannan Perumalayan in Jayaraj's "Kaliyattam" (1997) won him the National Film Award for Best Actor and the Kerala State Film Award for Best Actor. His other notable movies in 1997 were Janathipathyam and Guru. In Guru, he played a supporting role. Suresh Gopi's played a lead role alongside Jayaram in the comedy drama Summer in Bethlehem (1998). He played the character "Dennis" and received wide appreciation from the critics. It was also the third highest-grossing movie in 1998. His other notable movies in 1998 were Thalolam and Pranayavarnangal.


title: Suresh Gopi

text: Suresh Gopi's action thriller film Pathram (1999) directed by Joshiy was the highest grossing Malayalam movie in 1999. The film, which ran over 275 days in theatres is also considered by many fans to be one of the best in his career. The same year he starred in another Joshiy action thriller Vazhunnor which was also a commercial hit. In 1999, two of his popular crime investigation thrillers Crime File and F. I. R came out. Both films were commercially successful.


title: Suresh Gopi

text: In 2000, Suresh Gopi starred in Mark Antony and Cover Story, an action film and a crime thriller. He played a lead role, with comic elements, in the comedy drama Thenkashippattanam (2000) alongside Lal. The film was one of the highest grossers at the box office and ran for more than 275 days in theatres. Suresh Gopi played the lead role in Rajasenan's horror film Meghasandesham (2001). His other notable movies in 2001 are the comedy drama Sundara Purushan and investigation thriller Nariman. In 2003, he appeared in a lead role alongside Kunchako Boban in Rajasenan's family drama Swapnam Kondu Thulabharam. In 2005, he did the lead role in Renji Panicker's Bharathchandran I.P.S, a sequel to the 1994 film Commissioner. The film was a major hit at the box office. His performance is Makalkku (2005) was critically acclaimed.


title: Suresh Gopi

text: Suresh Gopi's fanbase slowly started to diminish during the mid-2000s with many of his movies released in 2006 becoming a failure at the box office. This includes films such as Lanka, Rashtram, Pathaaka, Ashwaroodan, Bada Dosth and Smart City. However, his legal thriller Chinthamani Kolacase directed by Shaji Kailas was a blockbuster at the box office in 2006. Suresh Gopi played the lead role of a psychotic lawyer, who enforces the law in his style.


title: Suresh Gopi

text: Most of his movies released after "Chinthamani Kolacase" were failures at the box office. It includes movies such as Detective, Paranju Theeratha Visheshangal, Black Cat Kichamani MBA and Time all of which released in 2007. The same year he had a special appearance in the science fiction film Bharathan Effect. His only commercially successful film in 2007 was the crime investigation thriller Nadiya Kollappetta Rathri. In 2008, Suresh Gopi did a lead role in the multi-starrer blockbuster . In 2009, he was praised for his role as "Ramesh Menon" in the anthology film Kerala Cafe in the segment "Lalitham Hiranmayam".


title: Suresh Gopi

text: In 2010, he played the role of a father seeking revenge upon those who raped his daughter in Janakan which earned him appreciation. In 2011, he appeared in the multi-starrer film "Christian Brothers". The same year, Suresh Gopi acted in the film "Melvilasom" which received wide critical acclaim upon its release. Suresh Gopi reunited with Shaji Kailas and Renji Panicker in 2012 through "The King & the Commissioner". In the film, which is a crossover of Commissioner (1994) and The King (1995), Suresh Gopi reprised his role as "Bharathchandran I.P.S" along with Mammooty reprising his role as "Joseph Alex" from "The King". The film, mostly panned by the critics was commercially successful. He was praised for his role as "Dr. Vijay Nambiar" in Apothecary (2014). He was nominated for the Best Actor award at the Filmfare Awards South for his performance in the movie. Suresh Gopi played the villain role in the Tamil film action thriller film I (2015). His role as "Dr. Vasudevan" in the movie was acclaimed. My God (2015) was his last film before going to a 4-year hiatus from acting.


title: Suresh Gopi

text: In March 2019, he made a comeback announcement in acting by joining Vijay Antony starrer Tamil film Thamilarasan. The film is expected to release in late 2021 after getting delayed due to COVID-19 pandemic in India. Suresh Gopi made his comeback in Malayalam cinema by playing a pivotal role in Varane Avashyamund in 2020, after a five year long hiatus. The movie also saw the reunion of Suresh Gopi and Shobana after a span of 15 years. The movie was a major success at box office and was critically acclaimed. In June 2020, Tomichan Mulakuppadam announced to produce Suresh Gopi's 250th movie. The film titled as Ottakkomban would see Suresh Gopi playing the role of "Kuruvachan". On 14 February 2021, Suresh Gopi announced that he will be reuniting with director Joshiy for the film titled Paappan. His other upcoming movie is Kaaval, an action thriller directed by "Nithin Renji Panicker" which would also feature Renji Panicker playing a pivotal role.


title: Suresh Gopi

text: In 2012, he hosted the game show "Ningalkkum Aakaam Kodeeshwaran" on Asianet, which was the Malayalam version of "Who Wants to Be a Millionaire?". He continued to host it four more seasons.


title: Suresh Gopi

text: During his college days, Suresh was an active member of the Students' Federation of India (SFI), the students' wing of the Communist Party of India (Marxist) (CPIM). Later in his life, he developed an admiration for stateswoman Indira Gandhi and the Indian National Congress (INC). In the 2006 Kerala Legislative Assembly election, he campaigned for both Left Democratic Front (LDF) and United Democratic Front candidates. He campaigned for LDF candidate V. S. Achuthanandan in Malampuzha constituency and UDF candidate M. P. Gangadharan in Ponnani constituency.


title: Suresh Gopi

text: On 29 April 2016, Suresh Gopi was sworn in as a Member of Parliament (MP) in the Rajya Sabha, nominated by the President of India in the category of eminent citizens as per the provisions of Article 80 of the Constitution of India. He opted Thiruvananthapuram district as the nodal district of operation under the Members of Parliament Local Area Development Scheme. In May 2016, he was enlisted as a member in the standing committee for Information Technology and in the Consultative Committee for the Ministry of Civil Aviation (India). In October 2016, Suresh officially joined the Bharatiya Janata Party.


title: Suresh Gopi

text: He contested in the 2019 Indian general election in Kerala as a candidate of BJP in Thrissur constituency. During the election campaign he invoked the name of the Sabarimala deity Ayyappan and hence District Collector of Thrissur, T. V. Anupama issued notice to actor and report to the CEO of Kerala, Teeka Ram Meena. Meena found that Mr.Gopi has violated the model of conduct (MCC). He lost in this election to the Congress candidate T.N. Prathapan and secured third position behind the CPI candidate Rajaji Mathew Thomas who came second.


title: Suresh Gopi

text: During the 2020 Kerala local body elections, Gopi advised the local BJP representatives about his stance on accepting requests from people. He said that people from all over Kerala write to him about different requests, and he only accepts the letters of request from individuals if they are attached to letters of recommendation from BJP district party chiefs. This was described by Gopi as a move that would strengthen the party. This controversial statement was shared widely on social media.


title: Suresh Gopi

text: On 8 February 1990, Suresh married Radhika Nair, the granddaughter of actress Aranmula Ponnamma. They have five children—Lakshmi Suresh, Gokul Suresh, Bhagya Suresh, Bhavni Suresh, and Madhav Suresh. Lakshmi died in a car accident while she was one-and-a-half years old. Gokul Suresh is a young actor in Malayalam cinema. Suresh resides with family in Sasthamangalam, Thiruvananthapuram.


title: Suresh Gopi

text: Gopi made headlines in 2015, when he gave his support to Maharashtra's controversial ban on beef while he was talking to the media. He said he never tasted beef in his life, and he never cooked it in his home and nobody in his home eats beef. He also added that if such a ban comes to the state, he would obey the government. However, a new video appeared online which captured Gopi, conversing on a radio show and speaking about his weight gain after a latest trip to Zurich. He shared how he had eaten beef continuously for 4 days when there was only pork and beef available, which led him to gain weight.


title: Suresh Gopi

text: In December 2017, The Kerala state police arrested Suresh Gopi on charges of forging documents to register his luxury vehicle. The state police alleged that Gopi had used fraudulent home address to register his luxury vehicles in Pondicherry to escape the 20% vehicle-tax in Kerala on cars costing over ₹20 lakh. In January 2020, the Crime branch reported that Gopi had registered his two Audi cars at a price of ₹60 lakh and ₹80 lakh each and evaded paying a tax of ₹3.6 lakh and ₹16 lakh for each of the cars. He was later released on anticipatory bail.


title: Doctor Who missing episodes

text: Several portions of the long-running British science-fiction television programme "Doctor Who" are no longer held by the BBC. Between 1967 and 1978 the BBC routinely deleted archive programmes for various practical reasons—lack of space, scarcity of materials, and a lack of rebroadcast rights. As a result, 97 of 253 episodes from the programme's first six years are currently missing, primarily from seasons 3, 4 and 5, leaving 26 serials incomplete. Many more were considered lost until recovered from various sources, mostly overseas broadcasters.


title: Doctor Who missing episodes

text: "Doctor Who" is not unique in its losses, as many broadcasters routinely cleared their archives in this manner. Until the BBC changed its archiving policy in 1978, thousands of hours of programming in all genres were deleted. Other affected BBC series include "Dad's Army", "Z-Cars", "The Wednesday Play", "Till Death Us Do Part", "Steptoe and Son" and "Not Only... But Also". ITV regional franchisees, such as Rediffusion Television and Associated Television, also deleted many programmes, including early videotaped episodes of "The Avengers".


title: Doctor Who missing episodes

text: "Doctor Who" is unusual, however, in that each of its 97 missing episodes survives in audio form, recorded off-air by fans at home. Most episodes are also represented by production stills, tele-snaps, or short video clips. Furthermore, after careful restoration, all 1970s episodes are available in full colour, which is not always the case for other series.


title: Doctor Who missing episodes

text: Efforts to locate missing episodes continue, both by the BBC and by fans of the series. Recovered episodes have been extensively restored for release on VHS and DVD; surviving soundtracks have been released on cassette and compact disc. Many missing episodes have had their visuals reconstructed, either through specially commissioned animation or use of surviving footage and photographs.


title: Doctor Who missing episodes

text: Between approximately 1967 and 1978, large quantities of videotape and film stored in the BBC's Engineering department and film libraries, respectively, were wiped or destroyed to make way for newer programmes. This happened for several reasons, primarily the belief that there was no practical value to its retention.


title: Doctor Who missing episodes

text: The actors' union Equity had actively fought against the introduction of TV recording since the 1950s, when it first became a practical proposition. Before workable television recording was developed, if a broadcaster wished to repeat a programme (usually a one-off play), they had to re-hire the actors to perform it again, live, for additional fees. Equity's concern was that if broadcasters kept recordings of the original performances, they would be able to re-broadcast them indefinitely, which would reduce the amount of new production and threaten the livelihoods of its members. Although Equity could not prevent recording altogether, it added standard clauses to its members' contracts that stipulated that recordings could only be repeated a limited number of times within a specific timeframe, and deliberately set the fees for further use so high that broadcasters would consider it unjustifiable to spend so much money repeating an old programme rather than making a new one. Consequently, recordings whose repeat rights had expired were considered to be of no further domestic use to the broadcasters.


title: Doctor Who missing episodes

text: Most "Doctor Who" episodes were made on two-inch videotape for initial broadcast and then telerecorded onto 16 mm film by BBC Enterprises for further commercial use. Enterprises used 16 mm for overseas sales as it was considerably cheaper to buy and easier to transport than videotape. It also circumvented the problem of different countries' incompatible video standards, as film was a universal medium whereas videotape was not. The BBC had no central archive at the time; the Film Library kept programmes that had been made on film, while the Engineering Department was responsible for storing videotapes. BBC Enterprises only kept copies of programmes that they deemed commercially valuable. They had little dedicated storage space, and tended to place piles of film canisters wherever they could find space for them at their Villiers House property.


title: Doctor Who missing episodes

text: The Engineering Department had no mandate to archive the programme videotapes they held, although typically they would not be wiped or junked until the relevant production department or BBC Enterprises indicated that they had no further use for the tapes. The first "Doctor Who" master videotapes to be wiped were those for the serial "The Highlanders", which were erased on 9 March 1967, a mere two months after Episode 4's original transmission. Further erasing of "Doctor Who" master videotapes by the Engineering Department continued into the 1970s. Eventually, every master videotape of the programme's first 253 episodes (1963–69) was destroyed or wiped. The final 1960s master tapes to be erased were those for the 1968 serial "Fury from the Deep", in late 1974.


title: Doctor Who missing episodes

text: Despite the destruction of these masters, BBC Enterprises held an almost complete archive (bar the possible exception of a single episode of "The Daleks' Master Plan") of the series in the form of their 16 mm film telerecording copies until approximately 1972. From around 1972 to 1978, BBC Enterprises also disposed of much of their older material, including many episodes of "Doctor Who."


title: Doctor Who missing episodes

text: Enterprises' episodes were usually junked because their rights agreements with the actors and writers to sell the programmes abroad had expired. With many broadcasters around the world now switching to colour transmission, it was not deemed worthwhile extending agreements to sell the older black-and-white material.


title: Doctor Who missing episodes

text: The BBC Film Library, meanwhile, had no responsibility for storing programmes that had not originated on film, and there were conflicting views between the Film Library and BBC Enterprises over which party held the responsibility for archiving programmes. As each body believed it the other's responsibility to archive the material, each thought nothing of destroying its own copies as necessary. This lack of communication contributed to the erasure of much of the Corporation's film archive of older black-and-white programming. While thousands of other programmes have been destroyed in this way around the world, the missing "Doctor Who" episodes are probably the best-known example of how the lack of a consistent programme archiving policy risks permanent loss.


title: Doctor Who missing episodes

text: Following the purges and subsequent recoveries, gaps in the "Doctor Who" archive are spread unevenly through its first 11 seasons. Major losses mostly affect First and Second Doctor serials; although two stories are missing just one episode each ("The Tenth Planet", Episode 4 and "The Web of Fear" Episode 3), other stories are lost altogether. Patrick Troughton's era as the Second Doctor is particularly affected; of the 14 stories comprising his first two seasons, only "The Tomb of the Cybermen" and "The Enemy of the World" are complete, and these only exist due to telerecordings later returned from Hong Kong and Nigeria, respectively.


title: Doctor Who missing episodes

text: All stories starring Jon Pertwee as the Third Doctor are complete, though many episodes no longer survive on their original videotapes and were only available from black-and-white overseas prints upon recovery; these episodes have subsequently been restored to colour using a variety of methods. In order of original transmissions, the very last "Doctor Who" master videotapes to be wiped were the first episodes of the 1974 serials "Invasion of the Dinosaurs" and "Death to the Daleks". The latter was recovered from overseas, initially from a tape in the NTSC format, and later in the original PAL format on a tape returned from Dubai.


title: Doctor Who missing episodes

text: For four years, Episode 1 of "Invasion of the Dinosaurs" was the only Pertwee episode to be entirely missing from the archives, until a black-and-white 16 mm copy was returned to the BBC in June 1983. The story was released on DVD with a partially recolourised version of Episode 1, alongside a higher-quality monochrome transfer of the episode, in "The UNIT Files" box set. With the exception of the final shot of episode 3 of "The Deadly Assassin" (1976), archival holdings from "Death to the Daleks" Episode 2 onwards are complete on the original broadcast videotapes.


title: Doctor Who missing episodes

text: Unrelated to the regular archive purges, the final shot of "The Deadly Assassin" Episode 3 (1976) has been excised from the master copy. The shot was removed after its initial UK transmission, following complaints from Mary Whitehouse of the National Viewers' and Listeners' Association. Subsequent repeats and commercial releases have restored the shot from off-air video copies.


title: Doctor Who missing episodes

text: Internally, the wiping policy officially came to an end in 1978, when the means to further exploit programmes by taking advantage of the new market for home videocassette recordings started to become apparent. The prevailing view had also begun to shift toward the attitude that archive programmes should, in any case, be preserved for posterity and historical and cultural reasons.


title: Doctor Who missing episodes

text: The BBC Film Library was turned into a combined Film & Videotape Library for the preservation of both media. The Film Library at the time held only 47 episodes of 1960s "Doctor Who"; they had once held 53, but six episodes had either been junked or gone missing. Junkings at BBC Enterprises, however, continued until the intervention of Ian Levine, a record producer and fan of the programme. Following the transfer of episodes still held by Enterprises, there were 152 episodes of "Doctor Who" no longer held by the BBC, although subsequent efforts have reduced that number to 97.


title: Doctor Who missing episodes

text: Among the most sought-after single lost episode is Episode 4 of the final William Hartnell serial, "The Tenth Planet", which ends with the First Doctor's regeneration into the Second. The only portion of the episode still in existence, bar a few poor-quality silent 8mm clips, is the final 27 seconds, comprising the regeneration itself and a few seconds leading up to it. The sequence had been shown in a 1973 episode of "Blue Peter" and was retained in that show's archive.


title: Doctor Who missing episodes

text: Even after the end of the purge, other archive issues persist. Serials from Seasons 22–26 were shown in Germany, with soundtracks dubbed into the German language; some of these episodes no longer exist in German television archives.


title: Doctor Who missing episodes

text: On 20 April 2006, it was announced on "Blue Peter" that a life-sized Dalek would be given to anyone who found and returned one of the missing episodes.


title: Doctor Who missing episodes

text: In January 2007, ITV began a campaign called "Raiders of the Lost Archive" and although the campaign was run by ITV, they were also looking to find "Doctor Who" episodes and other BBC shows. One episode of the Raiders of the Lost Archive show aired in January 2007 and a further two episodes in July 2009.


title: Doctor Who missing episodes

text: In December 2012, the "Radio Times" listings magazine announced it was launching the hunt for more "Doctor Who" episodes, to tie-in with the show's 50th anniversary. The "Radio Times" issued its own list of missing episodes. The magazine has also set up an email address specifically for "Doctor Who" missing episodes that the public can use to contact it if they have any information.


title: Doctor Who missing episodes

text: Compared with other BBC series broadcast in the 1960s, "Doctor Who" is well-represented in surviving episodes. Of the 253 episodes broadcast during the 1960s, 156 still exist – mainly due to copies produced for overseas sales. For example, Seasons 1 and 2, the most widely sold abroad of the 1960s era, are missing only nine and two episodes, respectively. By contrast, the less well-sold Season 4 has no complete serials, while Season 5 has only two complete serials ("The Tomb of the Cybermen" and "The Enemy of the World"). "Doctor Who"s high-profile have also helped to ensure the return of episodes which, for other less well-remembered programmes, might never have occurred.


title: Doctor Who missing episodes

text: Of all ongoing BBC series from the 1960s, only "Steptoe and Son" and "Maigret" have a similar survival record, with all episodes from both series existing in some form. "Doctor Who" is also comparatively rare amongst contemporaries in that all of its 1970s episodes exist as masters or telerecordings, while other series such as "Z-Cars" and "Dixon of Dock Green" are missing episodes from as late as 1975.


title: Doctor Who missing episodes

text: , there were 97 episodes unaccounted for. The missing episodes span 26 serials, including 10 full serials. Most of the gaps are from seasons 3, 4, and 5, which currently lack a total of 79 episodes across 21 (out of 26) serials. By contrast, seasons 1, 2, and 6 are missing just 18 episodes, across 5 (out of 26) serials. Of these missing stories, all but three – "Marco Polo", "Mission to the Unknown", and "The Massacre of St Bartholomew's Eve" – have surviving clips. All episodes also have full surviving audio tracks.


title: Doctor Who missing episodes

text: , many of these missing serials have been officially "completed" by using animation and/or telesnap reconstruction, and then subsequently released commercially by BBC Worldwide.


title: Doctor Who missing episodes

text: While the Patrick Troughton era is missing more episodes (53 as compared to 44 for William Hartnell), there are more Hartnell stories completely missing (6 as compared to 4). Serials highlighted in are missing all episodes.


title: Doctor Who missing episodes

text: Serials that are over 50% complete (e.g., "The Reign of Terror", "The Tenth Planet") have been issued as standalone releases, with the missing episodes bridged using animation, visual reconstructions, or narration to the camera. Surviving episodes which form 50% or less of a complete story – referred to as "orphaned" episodes – have been released by the BBC in compilations (e.g., "Lost in Time"), or as extras on releases of complete serials. A few four-episode serials of which 50% remain (e.g., "The Underwater Menace", "The Moonbase") have also been issued as standalone releases.


title: Doctor Who missing episodes

text: "Planet of Giants" was directed by Mervyn Pinfield and Douglas Camfield, and originally recorded as four episodes. To create a faster-paced climax, Episodes 3 and 4 were combined and reduced to form a single episode. The serial's 2012 DVD release features a reconstruction of the original episodes, directed by Ian Levine. The production rebuilds the deleted scenes using CGI, footage from elsewhere in the serial, and re-recorded dialogue from Carole Ann Ford, William Russell, and actors impersonating the rest of the cast.


title: Doctor Who missing episodes

text: When the BBC's complete holdings (both the BBC Film & Videotape Library and the BBC Enterprises) were first audited in 1978, the following episodes were absent from their collective archives, but have subsequently been returned to the Corporation through various methods. The 16 stories have all episodes existing as a result. Except where indicated, all episodes were returned as 16 mm telerecording negatives or prints:


title: Doctor Who missing episodes

text: In the years since the BBC archive was first audited in 1978, a number of episodes then absent have been returned from various sources.


title: Doctor Who missing episodes

text: When the BBC audited its Film Library in 1977, only 47 episodes were found to exist. These Film Library copies were a random sampling of viewing prints for various episodes, along with seven of the nine episodes that had originally been telerecorded onto film for editing and/or transmission, rather than recorded to videotape. These film-originated masters were stored in the Film Library, rather than in the Engineering Department with the videotapes. The presence of the viewing prints is less easily explained.


title: Doctor Who missing episodes

text: The Film Library's remit covers material originated on film, not on videotape – yet two of the film-originated episodes of "Doctor Who" ("The Power of the Daleks" Episode 6 and "The Wheel in Space" Episode 5) were junked by the Film Library, while it held such unexplained material as 16 mm copies of "The Tenth Planet" Episodes 1–3, presumably viewing prints which were mistakenly returned to them at some point instead of BBC Enterprises. Most surprisingly of all, they also retained a 16 mm telerecording copy of the original untransmitted pilot, presumably a viewing print made in 1963 and subsequently lodged at the Library.


title: Doctor Who missing episodes

text: The Film Library also held high-quality original film sequences made for insertion into videotaped episodes. Some of these, such as those from Episodes 1–2 of "The Daleks' Master Plan", survive to this day. Other junked sequences were mistakenly entered into a film library computer system, leading to an impression that they had existed for some years afterward, and inaccurate speculation that the BBC was still destroying clips well into the early 1980s.


title: Doctor Who missing episodes

text: Following the establishment of the Film and Videotape Library, an audit of the Engineering Department found 60 of the 128 Third Doctor episodes starring Jon Pertwee, which in addition to the Film Library's copies of the film-originated "Spearhead from Space", brought that Doctor's episode count up to 64 out of 128.


title: Doctor Who missing episodes

text: In 1978, Ian Levine located another 65 episodes from the show's first six seasons (plus 14 previously existing episodes), at the BBC Enterprises film vault at Villiers House in London. The episodes comprise 17 full serials, mostly from seasons 1 and 2. According to Levine, the prints of "The Daleks" were flagged to be junked that very day.


title: Doctor Who missing episodes

text: Levine alerted the new Film and Videotape Library's archive selector, Sue Malden, who paid her own visit to Villiers House and found every remaining Jon Pertwee episode (albeit as a 16 mm black-and-white telerecording), except for two from his final season: "Death to the Daleks" and "Invasion of the Dinosaurs", Episodes 1.


title: Doctor Who missing episodes

text: In August 1988, 10 years after Levine's and Malden's visits, Episodes 1 and 4–6 of the six-part story "The Ice Warriors" were discovered in a cupboard at Villiers House when the Corporation was in the process of moving out of the building.


title: Doctor Who missing episodes

text: Shortly after the junking process was halted and the BBC established its Film and Videotape Library for the purpose of storage and preservation, archive selector Sue Malden began to audit what material remained in the BBC's stores. When investigations revealed large gaps in the collection, Malden turned her inquiries to the National Film and Television Archive – which promptly returned three full Second Doctor serials – "The Dominators", "The Krotons", and "The War Games", adding seven more episodes and completing two of those serials. These all were standard 16 mm film telerecordings with the exception of "The Dominators" Episode 3, which was a 35 mm print.


title: Doctor Who missing episodes

text: Episodes 4 and 5 of "The Dominators" originated from a foreign broadcaster, and had been slightly edited; the missing footage was restored later, through a mix of censor clips and more complete prints held by private collectors.


title: Doctor Who missing episodes

text: An appeal to broadcasters in other countries who had shown the programme (notably Canada and African nations such as Nigeria) produced "lost" episodes from the archives of their television companies. "The Tomb of the Cybermen", for example, was recovered in this manner from Rediffusion Television in Hong Kong in 1992. Of the 50 episodes recovered since the original BBC audit of its holdings, 24 have been returned from overseas broadcasters:


title: Doctor Who missing episodes

text: Note that on occasion some broadcasters purchased "Doctor Who" telerecordings (usually 16 mm) but subsequently cancelled the order.


title: Doctor Who missing episodes

text: Nigerian television has been a particularly fruitful source for episode recovery; a total of 15 out of the 50 episodes recovered since 1978 have been reclaimed from Nigeria, leading to the completion of three full serials ("The Time Meddler", "The War Machines", and "The Enemy of the World").


title: Doctor Who missing episodes

text: In October 1984, copies of "A Land of Fear", "Guests of Madame Guillotine", and "A Change of Identity", along with another copy of "Prisoners of Conciergerie" (which was already found in 1982), were found in Cyprus. They were duly returned early in 1985 and the recovery was formally announced in July of that year. Cyprus did not screen" The Reign of Terror" (broadcasts ended with the showing of episode 6 of "The Sensorites" on 25 November 1966). As a result of these episode recoveries only two episodes (parts 4 and 5, "The Tyrant of France" and "A Bargain of Necessity") remain missing; although copies of these episodes had also been held in Cyprus, they were destroyed during the 1974 Turkish invasion of Cyprus. For the 2013 DVD release, episodes 4 and 5 were animated by Planet 55 Studios and Big Finish Productions.


title: Doctor Who missing episodes

text: "The Tomb of the Cybermen" was prepared for release in early 1992 on cassette as part of the "Missing Stories" collection, with narration by Jon Pertwee. Then in late 1991, telerecordings of all four episodes were returned to the BBC from the Hong Kong-based Rediffusion company. In May 1992, the serial was released on VHS with a special introduction from director Morris Barry.


title: Doctor Who missing episodes

text: Between 1991 and 2013, the serial was believed to be the only complete story from Season 5 (and the only complete serial to feature Deborah Watling as Victoria Waterfield) before the complete run of "The Enemy of the World" was returned from Nigeria in 2013.


title: Doctor Who missing episodes

text: Following months of rumours, in October 2013 a BBC press conference announced the return of 11 episodes (including two previously existing) from a television relay station in the city of Jos, Nigeria. In the course of his work abroad, Philip Morris of Television International Enterprises Archives had discovered episodes 1–6 of "The Enemy of the World" and episodes 1–6 of "The Web of Fear" and returned 11 of these to the BBC. Episode 3 of "The Web Of Fear" had been part of the find, but by the end of protracted negotiations for the return of the film cans, the episode had disappeared from the cache, with the presumption that it was sold to a private collector.


title: Doctor Who missing episodes

text: The return of the nine missing episodes was the single largest recovery of "Doctor Who" episodes in 25 years, resulting in only the second full serial from Troughton's first two seasons to be restored to the BBC.


title: Doctor Who missing episodes

text: Both serials were promptly released on iTunes, with DVD releases following over the next few months. On both the iTunes and the DVD release, episode 3 of "The Web of Fear" was represented by a tele-snap reconstruction, edited by John Kelly.


title: Doctor Who missing episodes

text: Several episodes have been returned by private film collectors, who at some point acquired 16 mm film prints intended for sale to foreign broadcasters.


title: Doctor Who missing episodes

text: Roger Stevens was working for the BBC as a film editor in the 1980s, and one morning, as he was travelling to work by train, he bumped into a BBC colleague and they began to talk about "Doctor Who" episodes. The BBC projectionist mentioned that he had nine episodes of "Doctor Who" that Stevens could buy for £25. In the summer of 1981, Stevens bought "The Space Museum" episode 1, "The Abominable Snowmen" episode 2, "The Moonbase" episode 4, "Invasion of the Dinosaurs" episode 1, and three episodes of "Carnival of Monsters". Stevens then contacted Ian Levine to find out what was missing from the BBC archive; Levine confirmed that "The Abominable Snowmen" episode 2 and "Invasion of the Dinosaurs" episode 1 were currently missing.


title: Doctor Who missing episodes

text: Stevens gave these prints to Levine, who returned "The Abominable Snowmen" to the BBC in February 1982, although he held back "Invasion of the Dinosaurs" from the BBC for a while. This was later returned to the BBC by Levine in June 1983, who then made a copy and returned the original to Levine.


title: Doctor Who missing episodes

text: "The Reign of Terror" was recovered by Bruce Campbell when he attended a film fair in the 1980s and began chatting to a stall holder who informed him that one of his regular customers had in their possession "The Reign of Terror" episode 6. Campbell got in contact with the customer, bought the missing episode for £50, and then, in May 1982, donated it to the BBC through Ian Levine.


title: Doctor Who missing episodes

text: In 1984 "Doctor Who Magazine" (issue #87) ran a story about a rumour of a missing "Doctor Who" episode that was in Portsmouth; this led to episode 3 of "The Wheel in Space" being loaned to the BBC in April 1984 by David Stead to allow for a copy to be made. It was released on VHS in 1992, with poor results. Later, the print was borrowed again, and a new copy made, using D3 videotape. Stead recollects that he had purchased the episode for £15.


title: Doctor Who missing episodes

text: In 1982, novice film collector Gordon Hendry purchased 16 mm copies of "The Faceless Ones", episode 3, and "The Evil of the Daleks", episode 2, from a film fair in Buckingham. At that time Hendry was unaware of the episodes' value (only one episode of "The Faceless Ones" and none of "The Evil of the Daleks" were known to exist).


title: Doctor Who missing episodes

text: In 1985, a cinema owner in Brighton persuaded Hendry to lend him the films, so as to screen the episodes for profit while the Panopticon VI convention was being held in the town. Saied Marham, an associate of Hendry's, visited Panopticon to generate interest in the showing, only to be dismissed as a hoaxster, and the screening did not go ahead. So Marham kept the films to himself.


title: Doctor Who missing episodes

text: After the event, Paul Vanezis spent 15 months attempting to retrieve the episodes from Marham. Eventually, in 1987, after Vanezis got the episodes back from Marham, a charity fundraising convention called Tellycon aired "The Faceless Ones", episode 3, in tribute to the recently deceased Patrick Troughton.


title: Doctor Who missing episodes

text: In the following weeks, Vanezis and Ian Levine negotiated the return of both episodes to the BBC archive.


title: Doctor Who missing episodes

text: Although the New Zealand Broadcasting Corporation received copies of "The Crusade", it never broadcast the story due to a prohibitive rating from the censor board. After rejecting the serial, NZBC never returned its film prints to the BBC or actively destroyed them.


title: Doctor Who missing episodes

text: In 1998 collector Bruce Grenville purchased a 16 mm copy of "The Crusade" episode 1 from a stall at a New Zealand film fair, containing various material previously rescued from a rubbish tip. Through a series of chance meetings, the episode eventually was returned to the BBC in January 1999.


title: Doctor Who missing episodes

text: In 1975, the Australian Broadcasting Corporation returned all eight broadcast prints of "Galaxy 4" and "The Underwater Menace" to the BBC to be disposed of. In the mid-1980s, former ITV engineer Terry Burnett purchased episode 3 of "Galaxy 4" and episode 2 of "The Underwater Menace" from another collector, unaware of their value (the only extant episode of the former serial, and one of just two from the latter). In December 2011, after a chance encounter with Doctor Who Restoration Team member Ralph Montagu, Burnett returned the episodes to the BBC.


title: Doctor Who missing episodes

text: "The Daleks' Master Plan" was never sold abroad; only Australia requested viewing copies (excepting Episode 7, "The Feast of Steven"), and eventually declined to purchase the serial.


title: Doctor Who missing episodes

text: Three out of the serial's 12 episodes have been recovered. 16 mm copies of episodes 5 and 10 were returned to the BBC in 1983. Episode 2 was returned in 2004 by former BBC engineer Francis Watson. He had come across the film in the 1970s, while clearing a projector testing room at the BBC's Ealing Studios. Instead of disposing of the film as instructed, he brought it home – eventually to return it to the BBC when he realised the value of the material.


title: Doctor Who missing episodes

text: Of the 50 recovered episodes, several are missing short segments – due either to overseas censorship or to damage to the surviving film print. The following table shows all affected episodes, and the total duration of missing material.


title: Doctor Who missing episodes

text: Of the 97 missing episodes, 36 are represented by short "orphan" clips, recovered from various sources. These clips span 17 of the 26 serials affected by missing episodes, seven of which are otherwise completely missing. The only serials lacking any footage whatsoever are "Marco Polo", "Mission to the Unknown", and "The Massacre of St Bartholomew's Eve". The following table shows all recovered excerpts, together with pertinent episodes, format of the clips, and the source of recovery. Otherwise-missing serials are in red.


title: Doctor Who missing episodes

text: Some overseas viewing prints were physically edited for content by local censor boards before transmission, for reasons such as excessive violence, fright-inducing material, and, in some cases, the conservative personal views of the censors. Additionally, episodes might occasionally receive minor edits for timing reasons as well, in order to fill their allocated broadcast slot along with advertising. Hence, episodes recovered from these sources (Australia, New Zealand) are missing these segments.


title: Doctor Who missing episodes

text: Later discoveries turned up a large number of excised clips, held by interested parties as proof of the edits. In October 1996, Australian "Doctor Who" fans Damian Shanahan and Ellen Parry discovered a collection in the records of the National Archives of Australia, provided as evidence by the Commonwealth Film Censorship Board (now the Classification Board). These clips include: "The War Machines", episodes 2–4; "The Smugglers", episodes 1, 3–4; "The Highlanders", episode 1; "The Underwater Menace", episodes 1, 4; "The Macra Terror", episodes 2–3; "Fury From The Deep", episodes 2, 4–5; and "The Wheel In Space", episode 4.


title: Doctor Who missing episodes

text: The clips from "The Underwater Menace", episode 2 were later found to precisely match the edits to the print discovered in late 2011, suggesting that the recovered episode was exactly the same print that had been censored decades before.


title: Doctor Who missing episodes

text: In an interview for the fanzine "The Disused Yeti", Shanahan stated that although he and Parry had found paper records relating to the censoring of early to mid William Hartnell stories, the excised portions for all stories from "An Unearthly Child" to "The Gunfighters" had been destroyed some time before Shanahan and Parry's investigation.


title: Doctor Who missing episodes

text: In 2002, New Zealand fan Graham Howard uncovered excised clips from episodes 2, 4 & 5 of "The Web of Fear" and episode 5 of "The Wheel in Space".


title: Doctor Who missing episodes

text: A fan in Australia has returned small excerpts of off-screen footage, recorded from repeat showings using an 8mm cine film camera. The missing episodes covered include "The Reign of Terror", episodes 4–5; "Galaxy 4", episode 1; "The Myth Makers", episodes 1–4; "The Savages", episodes 3–4; "The Tenth Planet", episode 4; "The Power Of The Daleks", episodes 1–2; "The Macra Terror", episode 3; and "The Faceless Ones", episode 2.


title: Doctor Who missing episodes

text: Due to the show's habit of repeating cliffhanger footage, sometimes missing episode material can be found in surviving neighbour episodes. Episode 2 of "The Daleks" uses a prefilmed reprise from the original recording of Episode 1, which later had to be remounted; the original version of Episode 1 is presumed to have been destroyed.


title: Doctor Who missing episodes

text: A brief clip from Episode 4 of "The Crusade" exists at the very start of "The Space Museum". Episode 1 of the latter serial begins with the characters in period costume, briefly frozen in place. An off-camera cough heard on both soundtracks shows that the clip was a filmed insert from the previous (and currently missing) episode.


title: Doctor Who missing episodes

text: In its lead-in to an upcoming repeat, "The Wheel in Space" episode 6 contains a short three-frame clip from "The Evil of the Daleks" episode 1, alongside a reprise from the existing episode 2 of that serial.


title: Doctor Who missing episodes

text: Other episodes contain straight excerpts from earlier serials, such as episode 10 of "The War Games", which employs model shots from the first episodes of "Fury from the Deep", "The Web of Fear" and "The Wheel in Space".


title: Doctor Who missing episodes

text: Clips from some missing episodes also survive due to their use in other surviving programmes. For example, excerpts from Episode 4 of "The Daleks' Master Plan" were used in a 1973 edition of "Blue Peter", and scenes from "The Power of the Daleks" in an Australian programme called "Perspective: C for Computer".


title: Doctor Who missing episodes

text: In 2005, two further short clips from "The Power of the Daleks" – along with a higher-quality version of one of the extant scenes – were discovered in a 1966 episode of the BBC science series "Tomorrow's World". The clips, lasting less than 10 seconds each and on film (as opposed to film recordings), came to light when the "Tomorrow's World" segment was broadcast as part of the edition of 11 September 2005 of the clip-based nostalgia show "Sunday Past Times" on BBC Two. After being alerted to the footage, Paul Vanezis of the Doctor Who Restoration Team tracked down the uncut version of the clip.


title: Doctor Who missing episodes

text: The 1977 documentary "Whose Doctor Who" indirectly led to a lengthy excerpt from "Four Hundred Dawns", episode 1 of the 1965 serial "Galaxy 4". The film's producers used an excerpt from a viewing print of the episode, which they further cut down in the editing. Rather than discard the unused portion, the film's advisor Jan Vincent-Rudzki asked to keep the film trims. Later in the 1990s, Vincent-Rudzki returned the clip to the archives. At a total of 5m 53s, this clip is the longest piece of surviving footage from an otherwise missing episode, accounting for a quarter of the total running time.


title: Doctor Who missing episodes

text: Apart from actual episode footage, rare behind-the-scenes material also was discovered for "The Smugglers", "The Evil of the Daleks", "The Abominable Snowmen", and "Fury from the Deep". Also from the latter serial exists some raw footage from the filming of Episode 6, featuring some alternative camera angles from what was eventually broadcast.


title: Doctor Who missing episodes

text: Although numerous episodes are still missing, full-length audio soundtracks for all missing episodes are held by the BBC. These come from off-air recordings made by fans, often made by use of a microphone attached to a tape recorder placed close to the television set. While the quality of these off-air recordings varies greatly, multiple fan recordings exist for every episode.


title: Doctor Who missing episodes

text: In November 1991, Jon Pertwee recorded link narration for a planned spring 1992 cassette release of the then-missing serial "The Tomb of the Cybermen". However, all four episodes of "The Tomb of the Cybermen" were found in Hong Kong in December 1991, and returned to the BBC archive in January 1992. With the serial no longer being lost, the cassette release of the soundtrack was then delayed for a year until mid-1993, and then released due to contractual obligations. In 1992, Colin Baker recorded link narration for a cassette release of "The Macra Terror", while Tom Baker recorded link narration for a cassette release of "The Evil of the Daleks". The two coffee bar scenes from Episode 1 of "The Evil of the Daleks" had to be removed due to songs by The Seekers and The Beatles playing in the background. The following year in the summer of 1993, Tom Baker did first person link narration (as the Fourth Doctor recalling earlier adventures) for the cassette releases of "The Power of the Daleks" and "Fury from the Deep", a style which he also did when narrating the never-recorded bits on the 1992 VHS release of "Shada". This first person style of link narration was in complete contrast to his previous narration on "The Evil of the Daleks" cassette release, which had been done in the third person as Tom Baker.


title: Doctor Who missing episodes

text: Beginning in 1999, the BBC started releasing all the serials with missing episodes on CD audiobook, with linking narration provided by former actors on the serials, such as William Russell, Peter Purves, Frazer Hines, Anneke Wills, Wendy Padbury and Carole Ann Ford, although Colin Baker's 1992 cassette link narration was reused for the 2000 CD release of "The Macra Terror", which left much more to the listener's imagination compared to all other CD releases of "Doctor Who" TV soundtrack audiobooks from 1999 to 2012. In 2012, "The Macra Terror" was re-released as part of the "Collections 4" boxset, and included new more detailed linking narration by Anneke Wills. By February 2006, the soundtracks for all of the then 108 missing episodes had been released, albeit with a copyright-uncleared music replacement of "Paperback Writer" by The Beatles with Hold Tight by Dave Dee, Dozy, Beaky, Mick & Tich in the second coffee bar scene during Episode 1 of "The Evil of the Daleks". On the CDs, there are also some slight pauses and slightly rejigged sequences for reasons of clarity, and with overdubbed linking narration.


title: Doctor Who missing episodes

text: From 2006 to 2009, BBC Audiobooks released many wholly existing stories on CD audiobook, such as "The Tomb of the Cybermen" and "The Ark". These releases ceased in 2009 with "The Ambassadors of Death" due to declining sales, before four serials from Tom Baker's era were released in late 2012 under BBC Audiobooks' successor, AudioGo. After the release of the "City of Death" audiobook in December 2012, there was a gap of over seven years before the next audiobook release of a TV soundtrack story, with "The Web Planet" in 2020.


title: Doctor Who missing episodes

text: Between 2010 and 2013, BBC Audiobooks collected the individual narrated soundtracks in a series of five CD box sets, entitled "Doctor Who: The Lost TV Episodes". For the sets, some serials (such as "The Evil of the Daleks") were re-released with improved audio restoration. In addition to the soundtracks, the sets include special features such as the "Archive on 4" documentary, "Doctor Who – The Lost Episodes" and high-quality scans of the original camera/rehearsal scripts in PDF format.


title: Doctor Who missing episodes

text: For the first 11 seasons of "Doctor Who", often the surviving materials are in a very different format or condition from their original broadcast masters. Surviving 1960s material is recorded on film stock of varying quality, while early 1970s material is available in a patchwork of professional and consumer formats. To present the material in a form approximating its original broadcast masters requires extensive technical work, and a certain amount of invention.


title: Doctor Who missing episodes

text: In its original form, the videotape used to record "Doctor Who" captures images at 50 interlaced fields per second, resulting in a smooth, "live" feel to motion. To transfer the episodes to film, the film camera is timed to combine two video fields in each frame, converting 50 fields to 25 frames per second; on playback, the omission of in-between images results in a choppier "film" style motion. To recreate the original "live" video feel, early telerecorded episodes are processed through a digital tool known as VidFIRE, which approximates the missing motion between film frames.


title: Doctor Who missing episodes

text: In addition to the telerecorded material, some early 1970s material survives only, or in colour only, on NTSC videotapes produced for North American transmission (e.g., TV Ontario and CKVU in Vancouver). NTSC runs at a different frame rate from PAL video, and has a different number of scan lines. The conversion process used in the 1970s was primitive by modern standards, resulting in a noticeable amount of picture and motion loss. Converting the NTSC tapes back to PAL ("Double Conversion") introduces more artefacts, creating a blurry picture and juddering motion. To rectify the problem, in 2005 a new Reverse Standards Conversion process, which attempts to unpick the original video conversion, was introduced for the DVD release of "The Claws of Axos".


title: Doctor Who missing episodes

text: Several early 1970s colour serials, starring Jon Pertwee, were retained only as black-and-white film prints. In addition to the motion issue shared by all telerecorded episodes, for years the loss of colour presented a major challenge for restoration.


title: Doctor Who missing episodes

text: Some of the telerecorded Pertwee episodes also survive on NTSC colour videotapes, recorded over-air on consumer hardware. In the early 1990s, an early form of the Doctor Who Restoration Team attempted to pair the low-resolution colour signal from these sources with the high-resolution black-and-white signal from the black-and-white film recordings. In this way, several Jon Pertwee stories were returned to a rough form of colour: "Doctor Who and the Silurians", "Terror of the Autons", and "The Dæmons". Off-air NTSC colour tapes were also recovered for all of "The Ambassadors of Death", but were considered of too poor a quality to permit more than a partial restoration.


title: Doctor Who missing episodes

text: In 2007, BBC archive specialist James Insell established the Colour Recovery Working Group, an online project to find new ways of restoring black-and-white telerecordings to colour. In 2008, Reverse Standards Conversion inventor Richard Russell developed a technique involving the use of chroma dots embedded in the black-and-white signal to recreate the missing colour. This technique was initially used as part of the recolouring process on episode 3 of "Planet of the Daleks"; the chroma dot process was used alongside a computer-based colourisation process to match together the differing qualities of colour recovery. The process was then used on an entire episode of "Dad's Army", showing that it was possible to use it on entire recordings.


title: Doctor Who missing episodes

text: Subsequently, chroma dots were used to restore the colour to Episodes 2–4, 6, and 7 of "The Ambassadors of Death" and episodes 2–6 of "The Mind of Evil". Episode 1 of "Invasion of the Dinosaurs" presented a unique challenge, in that the chroma dots only contained red and green colour filter information, requiring that the blue filter to be added manually. Given the rough result, the DVD includes both the reconstructed colour and the black-and-white version.


title: Doctor Who missing episodes

text: Episode 1 of "The Mind of Evil" contains no colour information. In principle, BBC engineers were supposed to filter out the chroma dots upon telerecording, to create a cleaner picture. In most cases they failed to do so properly, allowing the colour recovery process to work. For this one episode, the filter had been correctly applied – so there was no colour to recover. To complete the serial for DVD, the episode was manually colourised by Stuart Humphryes and Peter Crocker – thereby returning the final Pertwee episode to its original colour presentation.


title: Doctor Who missing episodes

text: In addition to short video clips and audio soundtracks, for many episodes off-screen photographs − known as "tele-snaps" − exist, taken by photographer John Cura. From the 1940s to the 1960s, Cura was hired by various interested parties to document the transmission of many television programmes, including "Doctor Who". Typically the photographs were used for promotion, or as keepsakes for cast and crew in the days before home video recorders. In many cases, they form the only remaining visual record of missing television programmes.


title: Doctor Who missing episodes

text: Since the late 1990s, fan groups such as Loose Cannon Productions have reconstructed the missing episodes, using original camera scripts to match Cura's tele-snaps and other visual material to the surviving audio tracks. Although technically infringing copyright, these "recons" have generally been tolerated by the BBC, provided that they are not sold for profit.


title: Doctor Who missing episodes

text: Official high-quality recons have also been used on commercial releases, including cut-down reconstructions – "The Ice Warriors" VHS (a 12-minute "highlights" reconstruction bridging the missing Episodes 2 and 3); and "Marco Polo" (a 30-minute reconstruction on "The Beginning" DVD box set) – and full-length presentations, including "The Tenth Planet" VHS (containing a full reconstruction of the missing Episode 4); "Galaxy 4" (a reconstruction of the three missing episodes to accompany the recently recovered episode 3, "Air Lock," presented on "The Aztecs" Special Edition DVD); and "The Web of Fear" digital and DVD releases (containing a reconstruction of Episode 3, alongside the rest of the newly rediscovered serial).


title: Doctor Who missing episodes

text: In several cases, producers of the "Doctor Who" DVD range have commissioned original black-and-white animation, synced to the programme's original audio tracks. Early commissions served to "complete" serials with only one or two missing episodes, allowing the full serials to be sold as a commercial product. Later, BBC Worldwide and BBC America commissioned a full animation of "The Power of the Daleks" for broadcast and commercial release.


title: Doctor Who missing episodes

text: The first such effort, Cosgrove Hall's animation of "The Invasion" episodes 1 and 4, was released to DVD alongside the surviving episodes in November 2006. The animation had been paid for by an earlier surplus in the "Doctor Who" website budget, allowing it to be used in the DVD release as a test for the concept, at no extra cost. Despite the DVD's success, the sales were not high enough to offset the animation cost for any future collaboration.


title: Doctor Who missing episodes

text: Eventually other animation studios were commissioned to continue the reconstruction. In June 2011, 2 Entertain announced that the missing episodes 4 and 5 of "The Reign of Terror" would be animated by Planet 55 Studios, using the "Thetamation" process. The serial was released on DVD in January 2013. Planet 55 would later go on to animate Episode 4 of "The Tenth Planet" (November 2013), and episodes 1 and 3 of "The Moonbase" (January 2014).


title: Doctor Who missing episodes

text: In August 2013, BBC Worldwide announced that episodes 2 and 3 of "The Ice Warriors" would be animated by Qurios Entertainment for a DVD release later that month.


title: Doctor Who missing episodes

text: In December 2013, 2 Entertain commissioning editor Dan Hall mentioned that Planet 55 had again been commissioned to complete "The Underwater Menace", for what he hoped would be an early 2014 release. However, in September 2015 "Doctor Who" Magazine confirmed that the much-delayed DVD, now scheduled for 26 October, was instead to contain tele-snap reconstructions of the missing episodes 1 and 4.


title: Doctor Who missing episodes

text: In September 2016 it was announced that the completely missing serial "The Power of the Daleks" would be animated and released via the BBC Store on 5 November 2016, the 50th anniversary of the serial's first broadcast, before it was released on DVD (21 November) and Blu-ray (6 February 2017). This was the first wholly missing serial to be completely reconstructed using animation.


title: Doctor Who missing episodes

text: In 2008, after future collaboration with Cosgrove Hall had been rejected due to expense, 2 Entertain was approached by David Busch of US animation studio Titmouse, Inc., who offered to do the work more cheaply as a result of the favourable exchange rate between the UK and the US, and put together a test trailer of scenes animated from various missing serials, including "The Power of the Daleks", "The Moonbase", "The Macra Terror", "The Web of Fear", and "Fury from the Deep". While 2 Entertain decided not to commission anything from Titmouse, the trailer was eventually seen by Ian Levine, who offered to try and raise the money for a full episode reconstruction to serve as a prototype. The episode chosen was "Mission to the Unknown", as it was a self-contained episode featuring the Daleks with a limited number of characters and sets, thus keeping the budget down. Although completed, the animated version of "Mission to the Unknown" has never been officially released, although it has been posted on various video streaming sites.


title: Doctor Who missing episodes

text: With the advent of ever-more-powerful home computers and more specialist programs for them, many fans are also working on unofficial animations of the missing episodes, with many clips being shown online.


title: Doctor Who missing episodes

text: From 2010 to 2012, five audio box sets were released by BBC Audiobooks. The sets collected the full, unaltered soundtracks to the "Doctor Who" stories which did not exist in video form up to that point. These episodes included linking narration, and all of the five sets contained exclusive interviews with former cast members. The first collection was released on 5 August 2010 and the fifth was released on 1 August 2012. BBC Audiobooks–which later became AudioGo–went into administration in 2013 and ceased production officially in 2014.


title: Doctor Who missing episodes

text: In some cases missing episodes are bridged by narration to the camera – often by a surviving actor from the serial, occasionally in-character. For their VHS releases, "The Reign of Terror" and "The Crusade" were presented by actors Carole Ann Ford and William Russell – while Episodes 1 and 4 of "The Invasion" were bridged by Nicholas Courtney.


title: Doctor Who missing episodes

text: In 2012, a reimagined version of "The Power of the Daleks", written by, directed by, and starring Nick Scovell, was released on YouTube in three parts before it was shown complete at the "Power:Reimagined" convention in September 2012.


title: Doctor Who missing episodes

text: In addition, the BBC has invested in the reconstruction of episodes using animation and the recreation of parts of various serials, including the completely missing "Marco Polo", in the docudrama "An Adventure in Space and Time" produced for the 50th anniversary in 2013.


title: Doctor Who missing episodes

text: In 2019, the BBC released a recreation of "Mission to the Unknown", which was produced by a team of students, graduates and staff of the University of Central Lancashire.


title: Doctor Who missing episodes

text: Richard Molesworth's "Wiped! Doctor Who's Missing Episodes" (Telos Publishing, 2010) explores in detail the paper trail and recovery efforts surrounding the hunt for missing episodes. A revised edition was published in March 2013.


title: J. Bruce Ismay

text: Joseph Bruce Ismay (; 12 December 1862 – 17 October 1937) was an English businessman who served as chairman and managing director of the White Star Line. In 1912, he came to international attention as the highest-ranking White Star official to survive the sinking of the company's new flagship , for which he was subject to severe criticism.


title: J. Bruce Ismay

text: Ismay was born in Crosby, Lancashire. He was the son of Thomas Henry Ismay (7 January 1837 – 23 November 1899) and Margaret Bruce (13 April 1837 – 9 April 1907), daughter of ship-owner Luke Bruce. Thomas Ismay was the senior partner in Ismay, Imrie and Company and the founder of the White Star Line. The younger Ismay was educated at Elstree School and Harrow, then tutored in France for a year. He was apprenticed at his father's office for 4 years, after which he toured the world. He then went to New York City as the company representative, eventually rising to the rank of agent. Bruce was one of the founding team of Liverpool Ramblers football club in 1882.


title: J. Bruce Ismay

text: On 4 December 1888, Ismay married Julia Florence Schieffelin (5 March 1867 – 31 December 1963), daughter of George Richard Schieffelin and Julia Matilda Delaplaine of New York, with whom he had five children:


title: J. Bruce Ismay

text: In 1891, Ismay returned with his family to the United Kingdom and became a partner in his father's firm, Ismay, Imrie and Company. In 1899, Thomas Ismay died, and Bruce Ismay became head of the family business. Ismay had a head for business, and the White Star Line flourished under his leadership. In addition to running his ship business, Ismay also served as a director of several other companies. In 1901, he was approached by Americans who wished to build an international shipping conglomerate (the International Mercantile Marine Company) to which Ismay agreed to sell his firm.


title: J. Bruce Ismay

text: After the death of his father on 23 November 1899, Bruce Ismay succeeded him as the chairman of the White Star Line. He decided to build four ocean liners to surpass the built by his father: the ships were dubbed the Big Four: , , , and . These vessels were designed more for size and luxury than for speed.


title: J. Bruce Ismay

text: In 1902, Ismay oversaw the sale of the White Star Line to J.P. Morgan & Co., which was organising the formation of International Mercantile Marine Company, an Atlantic shipping combine which absorbed several major American and British lines. IMM was a holding company that controlled subsidiary operating corporations. Morgan hoped to dominate transatlantic shipping through interlocking directorates and contractual arrangements with the railroads, but that proved impossible because of the unscheduled nature of sea transport, American antitrust legislation, and an agreement with the British government. White Star Line became one of the IMM operating companies and, in February 1904, Ismay became president of the IMM, with the support of Morgan.


title: J. Bruce Ismay

text: In 1907, Ismay met Lord Pirrie of the Harland & Wolff shipyard to discuss White Star's answer to the and the , the recently unveiled marvels of their chief competitor, Cunard Line. Ismay's new type of ship would not be as fast as their competitors, but it would have huge steerage capacity and luxury unparalleled in the history of ocean-going steamships. The latter feature was largely meant to attract the wealthy and the prosperous middle class. Three ships of the were planned and built. They were in order , and RMS (later HMHS) . In a highly controversial move, during construction of the first two "Olympic"-class liners, Ismay authorised the projected number of lifeboats reduced from 48 to 16, the latter being the minimum allowed by the Board of Trade, based on the 's tonnage.


title: J. Bruce Ismay

text: Ismay occasionally accompanied his ships on their maiden voyages, and this was the case with the "Titanic". During the voyage, Ismay talked with either (or possibly both) chief engineer Joseph Bell or Captain Edward J. Smith about a possible test of speed if time permitted. After the ship collided with an iceberg 400 miles south of the Grand Banks of Newfoundland on the night of 14 April 1912, it became clear that it would sink long before any rescue ships could arrive. Ismay stepped aboard Collapsible C, which was launched less than 20 minutes before the ship went down. He later testified that as the ship was in her final moments, he turned away, unable to watch. Collapsible C was picked up by the "Carpathia" about 3–4 hours later.


title: J. Bruce Ismay

text: After being picked up by the "Carpathia", Ismay was led to the cabin belonging to the ship's doctor, Frank Mcgee. He gave Captain Rostron a message to send to White Star's New York office:


title: J. Bruce Ismay

text: Ismay did not leave Mcgee's cabin for the entire journey, ate nothing solid, and was kept under the influence of opiates. Another survivor, 17-year-old Jack Thayer, visited Ismay to try to console him, despite having just lost his father in the sinking.


title: J. Bruce Ismay

text: When he arrived in New York, Ismay was hosted by Philip Franklin, vice president of the company. He also received a summons to appear before a Senate committee headed by Republican Senator William Alden Smith. Ismay later testified at the "Titanic" disaster inquiry hearings held by both the U.S. Senate (chaired by Senator William Alden Smith) the following day, and the British Board of Trade (chaired by Lord Mersey) a few weeks later.


title: J. Bruce Ismay

text: After the disaster, Ismay was savaged by both the American and the British press for deserting the ship while women and children were still on board. Some papers called him the "Coward of the "Titanic"" or "J. Brute Ismay", and suggested that the White Star flag be changed to a yellow liver. Some ran negative cartoons depicting him deserting the ship. The writer Ben Hecht, then a young newspaperman in Chicago, wrote a scathing poem contrasting the actions of Captain Smith and Ismay. The final verse reads: "To hold your place in the ghastly face / of death on the sea at night / is a seaman's job, but to flee with the mob / is an owner's noble right."


title: J. Bruce Ismay

text: Some maintain Ismay followed the "women and children first" principle, having assisted many women and children himself. Ismay's actions were defended in the official British inquiry, which found "Mr. Ismay, after rendering assistance to many passengers, found "C" collapsible, the last boat on the starboard side, actually being lowered. No other people were there at the time. There was room for him and he jumped in. Had he not jumped in he would merely have added one more life—namely, his own—to the number of those lost."


title: J. Bruce Ismay

text: Ismay had boarded Collapsible C with first-class passenger William Carter; both said they did so after there were no more women and children near that particular lifeboat. Carter's own behaviour and reliability, however, were criticised by Mrs. Lucile Carter, who sued him for divorce in 1914; she testified Carter had left her and their children to fend for themselves after the collision and accused him of "cruel and barbarous treatment and indignities to the person". London society ostracised Ismay and labelled him a coward. On 30 June 1913, Ismay resigned as president of International Mercantile Marine and chairman of the White Star Line, to be succeeded by Harold Sanderson.


title: J. Bruce Ismay

text: Ismay announced during the United States Inquiry that all the vessels of the International Mercantile Marine Company would be equipped with lifeboats in sufficient numbers for all passengers. Following the inquiry, Ismay and the surviving officers of the ship returned to England aboard .


title: J. Bruce Ismay

text: During the congressional investigations, some passengers testified that during the voyage they heard Ismay pressuring Captain Smith to increase the speed of the "Titanic" in order to arrive in New York ahead of schedule and generate some free press about the new liner. The book "The White Star Line: An Illustrated History" (2000) by Paul Louden-Brown states that this was unlikely, and that Ismay's record does not support the notion that he had any motive to do so.


title: J. Bruce Ismay

text: Writing on the BBC News magazine website, Rosie Waites reports that Ismay was widely vilified in the United States after the sinking of the "Titanic" due to the hostility shown in the yellow press controlled by William Randolph Hearst, who had fallen out with Ismay. Waites writes "Ismay was almost universally condemned in America, where the Hearst syndicated press ran a vitriolic campaign against him, labelling him 'J. Brute Ismay'. It published lists of all those who died but in the column of those saved it had just one name – Ismay's."


title: J. Bruce Ismay

text: Following from the Hearst press depiction of Ismay, Waites writes that every subsequent film about the "Titanic" has depicted Ismay as a villain, starting with the 1943 Nazi propaganda film "Titanic" where he is depicted as "a power-mad Jewish businessman"; the 1996 miniseries "Titanic"; Julian Fellowes' 2012 miniseries "Titanic", and James Cameron's 1997 film "Titanic", in which Ismay is often villainized due to the film's inclusion of a scene based on the eyewitness account of First Class passenger Elizabeth Lines who, after the sinking, testified to overhearing Ismay seemingly urge Captain Smith to arrive in New York on Tuesday night, ahead of schedule. Louden-Brown, consultant to the Cameron film, has stated that he thought the antagonistic characterisation of Ismay was unfair, and he tried to challenge this. Louden-Brown said, "Apart from being told, under no circumstances are we prepared to adjust the script, one thing they also said is 'this is what the public expect to see'." The 1958 film "A Night to Remember" did not just blame Ismay for the disaster but also presented him in an unfavourable and cowardly light, while a "Titanic"-themed episode of the science fiction television series "Voyagers!" portrayed Ismay dressing as a woman in order to sneak into a lifeboat.


title: J. Bruce Ismay

text: Lord Mersey, who led the 1912 British inquiry into the sinking of the "Titanic", concluded that Ismay had helped many other passengers before finding a place for himself on the last lifeboat to leave the starboard side.


title: J. Bruce Ismay

text: Though cleared of blame by the official British inquiry, Ismay never recovered from the "Titanic" disaster. Already emotionally repressed and insecure before his voyage on "Titanic", the tragedy sent him into a state of deep depression from which he never truly emerged. He kept a low profile afterwards. He lived part of the year in a large cottage, Costelloe Lodge, in the townland of Derrynea (near Casla) in Connemara, County Galway, Ireland which he bought from Henry Rudolph Laing of Cadogan Gardens, London, in January 1913, less than a year after the sinking. The purchase also included the fishing rights for the river and lake adjoining it. Paul Louden-Brown, in his history of the White Star Line, writes that Ismay continued to be active in business, and that much of his work was for The Liverpool & London Steamship Protection & Indemnity Association Limited, an insurance company founded by his father. According to Louden-Brown:


title: J. Bruce Ismay

text: Ismay maintained an interest in maritime affairs. He inaugurated a cadet ship called "Mersey" used to train officers for Britain's Merchant Navy, donated £11,000 to start a fund for lost seamen, and in 1919 gave £25,000 (approximately equivalent to £ in ) to set up a fund to recognise the contribution of merchant mariners in the First World War.


title: J. Bruce Ismay

text: After the tragedy, Ismay's wife Florence ensured the subject of "Titanic" was never again discussed within the family. His granddaughter, historian and author Pauline Matarasso, likened her grandfather to a "corpse" in his later years:


title: J. Bruce Ismay

text: In his personal life, Ismay became a man of solitary habits, spending his summers at his Connemara cottage and indulging in a love of trout and salmon fishing. When in Liverpool, he would attend concerts by himself at St George's Hall or visit a cinema, at other times wandering through the Liverpool parks and engaging transients in conversation. A family friend observed the spectre of "Titanic" was never far from Ismay's thoughts, saying that he continually "tormented himself with useless speculation as to how the disaster could possibly have been avoided." At a Christmastime family gathering in 1936, less than a year before Ismay's death, one of his grandsons by his daughter Evelyn, who had learned Ismay had been involved in maritime shipping, enquired if his grandfather had ever been shipwrecked. Ismay finally broke his quarter-century silence on the tragedy that had blighted his life, replying: "Yes, I was once in a ship which was believed to be unsinkable."


title: J. Bruce Ismay

text: Ismay's health declined in the 1930s, following a diagnosis of diabetes, which worsened in early 1936 when the illness resulted in the amputation of his right leg below the knee. He was subsequently largely confined to a wheelchair. On the morning of 14 October 1937, he collapsed in his bedroom at his residence in Mayfair, London, after suffering a massive stroke, which left him unconscious, blind and mute. Three days later, on 17 October, J. Bruce Ismay died at the age of 74.


title: J. Bruce Ismay

text: Ismay's funeral was held at St Paul's Church, Knightsbridge, on 21 October 1937, and he is buried in Putney Vale Cemetery, London. He left a very considerable personal estate, which, excluding property, was valued at £693,305 (approximately equivalent to £ in ). In March 1939, his wife Florence conveyed the property in Connemara unto their son George Bruce Ismay (including the fishery rights extending from the sea to the Lake of Glenicmurrin via the River Casla). After his death, Florence renounced her British subject status in order to restore her American citizenship on 14 November 1949.


title: MQTT

text: MQTT (originally an initialism of MQ Telemetry Transport) is a lightweight, publish-subscribe, machine to machine network protocol for Message queue/Message queuing service. It is designed for connections with remote locations that have devices with resource constraints or limited network bandwidth. It must run over a transport protocol that provides ordered, lossless, bi-directional connections—typically, TCP/IP. It is an open OASIS standard and an ISO recommendation (ISO/IEC 20922).


title: MQTT

text: Andy Stanford-Clark (IBM) and Arlen Nipper (then working for Eurotech, Inc.) authored the first version of the protocol in 1999. It was used to monitor oil pipelines within the SCADA industrial control system. The goal was to have a protocol that is bandwidth-efficient, lightweight and uses little battery power, because the devices were connected via satellite link which, at that time, was extremely expensive.


title: MQTT

text: Historically, the "MQ" in "MQTT" came from the IBM MQ (then 'MQSeries') product line, where it stands for "Message Queue". However, the protocol provides publish-and-subscribe messaging (no queues, in spite of the name). In the specification opened by IBM as version 3.1 the protocol was referred to as "MQ Telemetry Transport". Subsequent versions released by OASIS strictly refers to the protocol as just "MQTT", although the technical committee itself is named "OASIS Message Queuing Telemetry Transport Technical Committee". Since 2013, "MQTT" does not stand for anything.


title: MQTT

text: In 2013, IBM submitted MQTT v3.1 to the OASIS specification body with a charter that ensured only minor changes to the specification could be accepted. After taking over maintenance of the standard from IBM, OASIS released version 3.1.1 on October 29, 2014. A more substantial upgrade to MQTT version 5, adding several new features, was released on March 7, 2019.


title: MQTT

text: MQTT-SN (MQTT for Sensor Networks) is a variation of the main protocol aimed at battery-powered embedded devices on non-TCP/IP networks, such as Zigbee.


title: MQTT

text: The MQTT protocol defines two types of network entities: a message broker and a number of clients. An MQTT broker is a server that receives all messages from the clients and then routes the messages to the appropriate destination clients. An MQTT client is any device (from a micro controller up to a fully-fledged server) that runs an MQTT library and connects to an MQTT broker over a network.


title: MQTT

text: Information is organized in a hierarchy of topics. When a publisher has a new item of data to distribute, it sends a control message with the data to the connected broker. The broker then distributes the information to any clients that have subscribed to that topic. The publisher does not need to have any data on the number or locations of subscribers, and subscribers, in turn, do not have to be configured with any data about the publishers.


title: MQTT

text: If a broker receives a message on a topic for which there are no current subscribers, the broker discards the message unless the publisher of the message designated the message as a retained message. A retained message is a normal MQTT message with the retained flag set to true. The broker stores the last retained message and the corresponding QoS for the selected topic. Each client that subscribes to a topic pattern that matches the topic of the retained message receives the retained message immediately after they subscribe. The broker stores only one retained message per topic. This allows new subscribers to a topic to receive the most current value rather than waiting for the next update from a publisher.


title: MQTT

text: When a publishing client first connects to the broker, it can set up a default message to be sent to subscribers if the broker detects that the publishing client has unexpectedly disconnected from the broker.


title: MQTT

text: Clients only interact with a broker, but a system may contain several broker servers that exchange data based on their current subscribers' topics.


title: MQTT

text: A minimal MQTT control message can be as little as two bytes of data. A control message can carry nearly 256 megabytes of data if needed. There are fourteen defined message types used to connect and disconnect a client from a broker, to publish data, to acknowledge receipt of data, and to supervise the connection between client and server.


title: MQTT

text: MQTT relies on the TCP protocol for data transmission. A variant, MQTT-SN, is used over other transports such as UDP or Bluetooth.


title: MQTT

text: MQTT sends connection credentials in plain text format and does not include any measures for security or authentication. This can be provided by using TLS to encrypt and protect the transferred information against interception, modification or forgery.


title: MQTT

text: The MQTT broker is a piece of software running on a computer (running on-premises or in the cloud), and could be self-built or hosted by a third party. It is available in both open source and proprietary implementations.


title: MQTT

text: The broker acts as a post office. MQTT clients don't use a direct connection address of the intended recipient, but use the subject line called "Topic". Anyone who subscribes receives a copy of all messages for that topic. Multiple clients can subscribe to a topic from a single broker (one to many capability), and a single client can register subscriptions to topics with multiple brokers (many to one).


title: MQTT

text: Each client can both produce and receive data by both publishing and subscribing, i.e. the devices can publish sensor data and still be able to receive the configuration information or control commands (MQTT is a bi-directional communication protocol). This helps in both sharing data, managing and controlling devices. A client can not broadcast the same data to a range of topics, and must publish multiple messages to the broker, each with a single topic given.


title: MQTT

text: With the MQTT broker architecture, the client devices and server application become decoupled. In this way, the clients are kept unaware of each other's information. MQTT, if configured to, can use TLS encryption with certificate, username and password protected connections. Optionally, the connection may require certification, in the form of a certificate file that a client provides and must match with the server's copy.


title: MQTT

text: In case of failure, the broker software and clients can automatically hand over to a redundant/automatic backup broker. Backup brokers can also be set up to share the load of clients across multiple servers on site, in the cloud, or a combination of these.


title: MQTT

text: The broker can support both standard MQTT and MQTT for compliant specifications such as Sparkplug. This can be done with same server, at the same time and with the same levels of security.


title: MQTT

text: The broker keeps track of all the session's information as the device goes on and off, in a function called "persistent sessions". In this state, a broker will store both connection info for each client, topics each client has subscribed to, and any messages for a topic with a QoS of 1 or 2.


title: MQTT

text: In 2019, OASIS released the official MQTT 5.0 standard. Version 5.0 includes the following major new features:


title: MQTT

text: Each connection to the broker can specify a quality of service (QoS) measure. These are classified in increasing order of overhead:


title: MQTT

text: This field does not affect handling of the underlying TCP data transmissions; it is only used between MQTT senders and receivers.


title: MQTT

text: Security of the MQTT protocol was compromised in 2020 by Italian researchers, executing Slow DoS Attacks on such protocol (see CVE-2020-13849).


title: Bog

text: A bog or bogland is a wetland that accumulates peat as a deposit of dead plant materials often mosses, typically sphagnum moss. It is one of the four main types of wetlands. Other names for bogs include mire, mosses, quagmire, and muskeg; alkaline mires are called fens. A baygall is another type of bog found in the forest of the Gulf Coast states in the United States. They are often covered in heath or heather shrubs rooted in the sphagnum moss and peat. The gradual accumulation of decayed plant material in a bog functions as a carbon sink.


title: Bog

text: Bogs occur where the water at the ground surface is acidic and low in nutrients. In contrast to fens, they derive most of their water from precipitation rather than mineral-rich ground or surface water. Water flowing out of bogs has a characteristic brown colour, which comes from dissolved peat tannins. In general, the low fertility and cool climate result in relatively slow plant growth, but decay is even slower due to low oxygen levels in saturated bog soils. Hence, peat accumulates. Large areas of the landscape can be covered many meters deep in peat.


title: Bog

text: Bogs have distinctive assemblages of animal, fungal, and plant species, and are of high importance for biodiversity, particularly in landscapes that are otherwise settled and farmed.


title: Bog

text: Bogs are widely distributed in cold, temperate climes, mostly in boreal ecosystems in the Northern Hemisphere. The world's largest wetland is the peat bogs of the Western Siberian Lowlands in Russia, which cover more than a million square kilometres. Large peat bogs also occur in North America, particularly the Hudson Bay Lowland and the Mackenzie River Basin. They are less common in the Southern Hemisphere, with the largest being the Magellanic moorland, comprising some in southern South America. Sphagnum bogs were widespread in northern Europe but have often been cleared and drained for agriculture. A paper led by Graeme T. Swindles in 2019 showed that peatlands across Europe have undergone rapid drying in recent centuries owing to human impacts including drainage, peat cutting and burning.


title: Bog

text: A 2014 expedition leaving from Itanga village, Republic of the Congo, discovered a peat bog "as big as England" which stretches into neighboring Democratic Republic of Congo.


title: Bog

text: Like all wetlands, it is difficult to rigidly define bogs for a number of reasons, including variations between bogs, the in-between nature of wetlands as an intermediate between terrestrial and aquatic ecosystems, and varying definitions between wetland classification systems. However, there are characteristics common to all bogs that provide a broad definition:


title: Bog

text: Because all bogs have peat, they are a type of peatland. As a peat-producing ecosystem, they are also classified as mires, along with fens. Bogs differ from fens in that fens receive water and nutrients from mineral-rich surface or groundwater, while bogs receive water and nutrients from precipitation. Because fens are supplied with mineral-rich water, they tend to be slightly acidic to slightly basic, while bogs are always acidic because precipitation is mineral-poor.


title: Bog

text: There are many highly specialized animals, fungi, and plants associated with bog habitat. Most are capable of tolerating the combination of low nutrient levels and waterlogging. Sphagnum is generally abundant, along with ericaceous shrubs. The shrubs are often evergreen, which may assist in conservation of nutrients. In drier locations, evergreen trees can occur, in which case the bog blends into the surrounding expanses of boreal evergreen forest. Sedges are one of the more common herbaceous species. Carnivorous plants such as sundews ("Drosera") and pitcher plants (for example "Sarracenia purpurea") have adapted to the low-nutrient conditions by using invertebrates as a nutrient source. Orchids have adapted to these conditions through the use of mycorrhizal fungi to extract nutrients. Some shrubs such as "Myrica gale" (bog myrtle) have root nodules in which nitrogen fixation occurs, thereby providing another supplemental source of nitrogen.


title: Bog

text: Bogs are recognized as a significant/specific habitat type by a number of governmental and conservation agencies. They can provide habitat for mammals, such as caribou, moose, and beavers, as well as for species of nesting shorebirds, such as Siberian cranes and yellowlegs. Bogs contain species of vulnerable reptilians such as the bog turtle. Bogs even have distinctive insects; English bogs give a home to a yellow fly called the hairy canary fly ("Phaonia jaroschewskii"), and bogs in North America are habitat for a butterfly called the bog copper ("Lycaena epixanthe"). In Ireland, the viviparous lizard, the only known reptile in the country, dwells in bogland.


title: Bog

text: The United Kingdom in its Biodiversity Action Plan establishes bog habitats as a priority for conservation. Russia has a large reserve system in the West Siberian Lowland. The highest protected status occurs in Zapovedniks (IUCN category IV); Gydansky and Yugansky are two prominent examples.


title: Bog

text: Bog habitats may develop in various situations, depending on the climate and topography (see also hydrosere succession).


title: Bog

text: Bogs may be classified on their topography, proximity to water, method of recharge, and nutrient accumulation .


title: Bog

text: These develop in gently sloping valleys or hollows. A layer of peat fills the deepest part of the valley, and a stream may run through the surface of the bog. Valley bogs may develop in relatively dry and warm climates, but because they rely on ground or surface water, they only occur on acidic substrates.


title: Bog

text: These develop from a lake or flat marshy area, over either non-acidic or acidic substrates. Over centuries there is a progression from open lake, to a marsh, to a fen (or, on acidic substrates, valley bog), to a carr, as silt or peat accumulates within the lake. Eventually, peat builds up to a level where the land surface is too flat for ground or surface water to reach the center of the wetland. This part, therefore, becomes wholly rain-fed (ombrotrophic), and the resulting acidic conditions allow the development of bog (even if the substrate is non-acidic). The bog continues to form peat, and over time a shallow dome of bog peat develops into a raised bog. The dome is typically a few meters high in the center and is often surrounded by strips of fen or other wetland vegetation at the edges or along streamsides where groundwater can percolate into the wetland.


title: Bog

text: In cool climates with consistently high rainfall (on more than c. 235 days a year), the ground surface may remain waterlogged for much of the time, providing conditions for the development of bog vegetation. In these circumstances, bog develops as a layer "blanketing" much of the land, including hilltops and slopes. Although a blanket bog is more common on acidic substrates, under some conditions it may also develop on neutral or even alkaline ones, if abundant acidic rainwater predominates over the groundwater. A blanket bog can occur in drier or warmer climates, because under those conditions hilltops and sloping ground dry out too often for peat to form – in intermediate climates a blanket bog may be limited to areas which are shaded from direct sunshine. In periglacial climates a patterned form of blanket bog may occur, known as a string bog. In Europe, these mostly very thin peat layers without significant surface structures are distributed over the hills and valleys of Ireland, Scotland, England, and Norway. In North America, blanket bogs occur predominantly in Canada east of Hudson Bay. These bogs are often still under the influence of mineral soil water (groundwater). Blanket bogs do occur north of the 65th latitude in the northern hemisphere.