network protocols handbook.pdf

149Protocols GuideWide Area Network and WAN ProtocolsDescriptionA Wide Area Network (WAN) is a computer network covering multiple distanceareas, which may spread across the entire world. WANs often connectmultiple smaller networks, such as local area networks (LANs) or metro areanetworks (MANs). The world’s most popular WAN is the Internet. Some segmentsof the Internet are also WANs in themselves. A wide area networkmay be privately owned or rented from a service provider, but the term usuallyconnotes the inclusion of public (shared user) networks.A virtual private network (VPN) riding on the public switched data network(PSDN) is often used by organizations for their private and secured communications.VPN uses encryption and other techniques to make it appear thatthe organisation has a dedicated network while making use of the sharedinfrastructure of the WAN.WANs generally utilize different networking technologies and equipment thando LANs. Key technologies often found in WANs include SONET, Frame Relay,X.25, ATM, and PPP.WAN technologies and protocols are mostly data link layer (layer 2) protocolswhich are defined by many organizations over time. The key organizationsin this space are IETF for PPP, ITU-T for ATM, Frame Relay, ISO forX.25 and SONET.Key ProtocolsThe key WAN protocols are listed as follows:WANWide Area NetworkATM: Asynchronous Transfer Mode ReferenceATMModelATM LayerAAL: ATM Adaptation Layer Type 0-5 reservedfor variable bit rate video transfer.LANE-NNI: LAN Emulation - Network toNetwork InterfaceLANE-UNI: LAN Emulation - User to NetworkInterfaceMPOA: Multi Protocol Over ATMPNNI: Private Network-to-Network InterfaceQ.2931: ATM Signalling User InterfaceSynchronous Optical Network and SynchronousDigital HierarchySONET/SDHDOCSIS: Data Over Cable Service InterfaceBroadband AccessSpecificationBISDN: Broadband Integrade Service DigitalNetworkISDN: Integrated Services Digital NetworkQ.931: ISDN network layer interface protocolLAPD: ISDN Link Access Protocol ChannelD (Q.921)