networks Of the approximately four billion addresses defined in IPv4, about 18 million addresses in three ranges are reserved for use in private networks. Packets addressed in these ranges are not routable on the public Internet; they are ignored by all public routers. Therefore, private hosts cannot directly communicate with public networks, but require network address translation at a routing gateway for this purpose. {| class="wikitable" |+ Reserved private IPv4 network ranges |- !Name!!CIDR block!!Address range!!Number of addresses!!Obsolete classful description |- |24-bit block||10.0.0.0/8||10.0.0.0 – 10.255.255.255||align="right"|||Single Class A. |- |20-bit block|||172.16.0.0/12||172.16.0.0 – 172.31.255.255||align="right"|||Contiguous range of 16 Class B blocks. |- |16-bit block||192.168.0.0/16||192.168.0.0 – 192.168.255.255||align="right"|||Contiguous range of 256 Class C blocks. |} Since two private networks, e.g., two branch offices, cannot directly communicate via the public Internet, the two networks must be bridged across the Internet via a virtual private network (VPN) or other form of IP tunnel that encapsulates packets, including their headers containing the private addresses, for transmission across the public network. Additionally, encapsulated packets may be encrypted to secure their data. Connection technology Many technologies are available for wide area network links. Examples include circuit-switched telephone lines, radio wave transmission, and optical fiber. New developments have successively increased transmission rates. In ca. 1960, a line was normal on the edge of the WAN, while core links of 56 or 64 kbit/s were considered fast. Today, households are connected to the Internet with dial-up, asymmetric digital subscriber line (ADSL), cable, WiMAX, cellular network or fiber. The speeds that people can currently use range from 28.8 kbit/s through a 28K modem over a telephone connection to speeds as high as 100 Gbit/s using 100 Gigabit Ethernet. The following communication and networking technologies have been used to implement WANs. Asynchronous Transfer Mode Cable modem Dial-up internet Digital subscriber line Fiber-optic communication Frame Relay ISDN Leased line SD-WAN Synchronous optical networking X.25 AT&T conducted trials in 2017 for business use of 400-gigabit Ethernet. Researchers Robert Maher, Alex Alvarado, Domaniç Lavery, and Polina Bayvel of University College London were able to increase networking speeds to 1.125 terabits per second. Christos Santis, graduate student Scott Steger, Amnon Yariv, Martin and Eileen Summerfield developed a new laser that potentially quadruples transfer speeds with fiber optics. See also Cell relay Internet area network (IAN) Label switching Low-power wide-area network (LPWAN) Wide area application services Wireless WAN References External links Cisco - Introduction to WAN Technologies What is