Frame Relay, part 1
From Cisco Press' Network Consultants Handbook we present Chapter 15, serialized in its entirety -- all you need to know about Frame Relay on a Wide Area Network.
Network Consultants Handbook - Frame Relay
by Matthew Castelli
Frame Relay is a Layer 2 (data link) wide-area networking (WAN) protocol that operates at both Layer 1 (physical) and Layer 2 (data link) of the OSI networking model. Although Frame Relay internetworking services were initially designed to operate over Integrated Services Digital Network (ISDN), the more common deployment today involves dedicated access to WAN resources.
NOTE: ISDN and Frame Relay both use the signaling mechanisms specified in ITU-T Q.933 (Frame Relay Local Management Interface [LMI] Type Annex-A) and American National Standards Institute (ANSI) T1.617 (Frame Relay LMI Type Annex-D).
Frame Relay is considered to be a more efficient version of X.25 because it does not require the windowing and retransmission features found with X.25. This is primarily due to the fact that Frame Relay services typically are carried by more reliable access and backbone facilities.
Frame Relay networks are typically deployed as a cost-effective replacement for point-to-point private line, or leased line, services. Whereas point-to-point customers incur a monthly fee for local access and long-haul connections, Frame Relay customers incur the same monthly fee for local access, but only a fraction of the long-haul connection fee associated with point-to-point private line services. The long-haul charges are typically usage-based across the virtual circuit (VC).
NOTE: The long-haul fee associated with point-to-point private (leased) line services is sometimes known as the inter-office connection fee. Service providers generally file a tariff with the FCC regarding these fees, comprising a base cost plus a per-mile charge.
NOTE: X.25 was designed for use over less reliable transmission medium than what is available in the marketplace today. Due to this unreliable nature, X.25 took on the error detection and correction (windowing and retransmission) mechanisms within the protocol stack. This resulted in higher overhead on the network, yielding less available bandwidth for data throughput.
NOTE: Frame Relay is a packet-switched technology, enabling end nodes to dynamically share network resources.
Frame Relay was standardized by two standards bodiesinternationally by the International Telecommunication Union Telecommunication Standardization Sector (ITU T) and domestically by ANSI.