t turn-around and transit delays (e.g. word-processing). This is a classical form of 40.8.5 Traffic requirements asynchronous traffic. 'Forms' traffic where a small amount of data travels in one Obviously the different traffic types mentioned above place differ- direction on an ad hoc basis, but it is answered with a stream of ing requirements on the network equipment. traffic in the other direction (database enquiry). A transaction system (such as a booking system) will require fast 3. Block mode traffic, where there is a stream of large full packets call establishment and termination, high call capacity, but not travelling in one direction with short packets travelling in the necessarily fast data throughput as it will only be the occasional other (file transfer). screen. 4. Transaction traffic where there are high numbers of calls with A network with a large community of stop-start terminal applica- limited data transfer, often done with the Fast Select facility tions (typically the CCITT triple X PAD) require fairly low transit (e.g. credit card checks, holiday booking lounges). delays and low hop counts, but again not necessarily high data Optimised traffic, where many users are sharing a single con- performance. nection (often using a Transport connection). Optimisation is Block mode traffic, such as file transfer or database enquiry achieved by filling the packets as full as possible without systems, probably do not require low transit delays but do require degrading the class of service below the user requirements high data performance. (OSI). 6. Priority traffic. This may be any of the traffic types described Certainly, as technology progresses, users are becoming more and above but takes precedence over the normal data flowing in the more aware of the different jobs that IT can do for them and network. consequently the dumb terminal is being replaced by the intelligent 7. Management traffic, which is an overhead in any network. terminal which in turn is being replaced by the personal worksta- tion. A co