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4. Frame RelayFrame Relay is a packet switching technology, which uses a synchronous HDLC (High Level Data Link Control) protocol for transporting packets between LANs over a WAN. Data is sent in variable-size HDLC packets, referred to as "frames". It operates at the physical and data link layers of the OSI reference model. Frame Relay originally was designed for use across Integrated Services Digital Network (ISDN) interfaces. Today, it is used over a variety of other network interfaces as well. The protocol is similar to that of an X.25 network. Frame relay and X.25 networks uses circuits known as "Virtual Circuits (VC)" and statistical multiplexing. Frame Relay virtual circuits fall into two categories: Switched Virtual Circuits (SVCs) and Permanent Virtual Circuits (PVCs). Statistical multiplexing accommodates more flexibility and more efficient use of bandwidth. As the network became more reliable, switched in frame relay simply pass packets without performing error correction. The customer equipments perform end-to-end error correction.
The initial proposals for standardization were submitted the ITU. Work on frame relay was also undertaken in the American National Standards Institute (ANSI)-accredited standards committee in the U.S. A major development in Frame Relay's history occurred in 1990 when companies formed a consortium to focus on Frame Relay technology development and extended the protocol with features that provide additional capabilities for complex internetworking environments. These Frame Relay extensions are referred to collectively as the Local Management Interface (LMI). Figure 5-1 illustrates components of the frame relay network.
FR Related Standards ANSI Standards: ANSI T1.606-1990: Integrated Services Digital Network (ISDN) - Architectural Framework and Service Description for Frame Relay Bearer Service. T1.606 and T1.618 define the frame relay core procedures ANSI T1.617-1991: Integrated Services Digital Network (ISDN) - Signaling Specification for Frame Relay Bearer Service for Digital Subscriber Signaling System #1. T1.617 defines maintenance procedures for frame relay networks. Annex D of this standard defines procedures applicable to permanent virtual circuits (PVCs) ANSI T1.618-1991: Integrated Services Digital Network (ISDN) - Core Aspects of Frame Protocol for use with Frame Relay Bearer Service ITU Recommendations: I.233.1: ISDN frame relaying bearer service. This recommendation describes the frame relaying bearer service and the method of its provision in an ISDN. I.233.2: ISDN frame switching bearer service I.370: Congestion Management for the ISDN Frame Relaying Bearer Service. This Recommendation describes U-plane based congestion management strategy and mechanisms for ISDN frame relay bearer services. It covers both network and end user mechanisms and responsibilities to avoid or recover from periods of congestion. Q.922: ISDN data link layer specification for frame mode bearer services. This Recommendation specifies the frame structure, elements of procedure, format of fields and procedures of the data link layer to support frame mode bearer services in the user plane as defined in Recommendation I.233.1. Q.933: ISDN Digital Subscriber Signaling System No. 1 (DSS1) - Signaling specifications for frame mode switched and permanent virtual connection control and status monitoring. This recommendation specifies the signaling to establish, maintain and release circuit-switched bearers between ISDN users and Remote Frame Handlers. Q.933bis: Abstract test suite - Signaling specification for frame mode basic call control conformance testing for permanent virtual connections (PVCs) Q.2933: Digital Subscriber signaling System No. 2 (DSS 2) ??Signaling specification for frame relay service. This Recommendation specifies the procedures for the establishing, maintaining and clearing of Broadband Integrated Services Digital Network (B-ISDN) Frame Relaying connections at the User-network interface. X.76: Network-to-network interface between public networks providing PVC and/or SVC frame relay data transmission service. This Recommendation describes the frame relay network-to-network interface intended for the interconnection of public networks providing PVC and/or SVC frame relay data transmission service. MFA Specifications: Normally, the MFA (MPLS, Frame Relay, and ATM) Forum adapts the standards defined by standard setting organizations such as ITU and creates implementation agreements. FRF.1.2: PVC User-to-Network Interface (UNI) Implementation Agreement FRF.2.2: Frame Relay Network-to-Network Interface (NNI) Implementation Agreement FRF.3.2: Frame Relay Multiprotocol Encapsulation Implementation Agreement FRF.4.1: SVC User-to-Network Interface (UNI) Implementation Agreement FRF.5: Frame Relay/ATM PVC Network Interworking Implementation FRF.6: Frame Relay Service Customer Network Management Implementation Agreement FRF.7: Frame Relay PVC Multicast Service and Protocol Description FRF.8.2: Frame Relay/ATM PVC Service Interworking Implementation Agreement FRF.9: Data Compression Over Frame Relay Implementation Agreement FRF.10.1: Frame Relay Network-to-Network SVC Implementation Agreement FRF.11.1: Voice over Frame Relay Implementation Agreement FRF.12 Frame Relay Fragmentation Implementation Agreement FRF.13 Service Level Definitions Implementation Agreement FRF.14 Physical Layer Interface Implementation Agreement FRF.15 End-to-End Multilink Frame Relay Implementation Agreement FRF.16.1 Multilink Frame Relay UNI/NNI Implementation Agreement FRF.17 Frame Relay Privacy Implementation Agreement FRF.18 Network-to-Network FR/ATM SVC Service Interworking Implementation Agreement FRF.19.1 Frame Relay Operations, Administration and Maintenance Implementation Agreement FRF.20 Frame Relay IP Header Compression Implementation Agreement |
