Frame Relay – WAN Connection.
Frame Relay is a popular high-performance wide area network – WAN protocol that operates at the physical and data link layers of the OSI reference model. Frame relay is a type of WAN connection used to connect one site to many remote sites through a single physical circuit, this operation makes it easy to construct reliable and inexpensive networks.
Frame Relay network is very simple. Frame Relay connections are created by configuring network routers or other devices to communicate with a service provider Frame Relay switch. The service provider configures the Frame Relay switch, which helps keep end-user configuration tasks to a minimum.
Frame Relay has lower overhead than X.25 because it has fewer capabilities e.g., Frame Relay does not provide error correction; modern WAN facilities offer more reliable connection services and a higher degree of reliability than older facilities.
The Frame Relay node simply drops packets without notification when it detects errors. Any necessary error correction, such as re-transmission of data, is left to the endpoints. This makes propagation from the customer end to the customer end through the network very fast.
Frame Relay network uses permanent virtual circuits (PVCs). PVC is the logical path along with an originating Frame Relay link, through the network, and along with a terminating Frame Relay link to its ultimate destination. Compare this to the physical path used by a dedicated connection. In a network with Frame Relay access, a PVC uniquely defines the path between two endpoints.
Each virtual circuit is identified by a Data Link Connection Identifier (DLCI), which is simply a number between 0 and 1023. Cisco routers can only use DLCI numbers in the range 16 through 1007 to carry user data.
Benefits of Frame Relay.
1 Cost Effectiveness
Frame Relay reduces network costs by using less equipment, less complexity, and easier implementation. Frame Relay is a more cost-effective option for two reasons.
i. First, with dedicated lines, customers pay for an end-to-end connection. That includes the local loop and the network link. With Frame Relay, customers only pay for the local loop, and for the bandwidth they purchase from the network provider. Distance between nodes is not important. While in a dedicated-line model, customers use dedicated lines provided in increments of 64 kb/s, Frame Relay customers can define their virtual circuit needs in far greater granularity, often in increments as small as 4 kb/s.
ii. Frame Relay shares bandwidth across a larger base of customers. Typically, a network provider can service 40 or more 56 kb/s customers over one T1 circuit. Using dedicated lines would require more DSU/CSUs (one for each line) and more complicated routing and switching. Network providers save because there is less equipment to purchase and maintain.
2. Frame Relay provides greater bandwidth, reliability, and resiliency than private or leased lines.
3. Flexibility.
Virtual circuit provides considerable flexibility in network design. In Frame Relay, the end of each connection has a number to identify it called a Data Link Connection Identifier (DLCI). Any station can connect with any other simply by stating the address of that station and the DLCI number of the line it needs to use.
Summary of Establishing a WAN Connection with Frame Relay.
■ Frame Relay PVCs are identified with DLCIs, and the status of the PVCs is reported through the LMI protocol.
■ Frame Relay point-to-point subinterfaces require a separate subnet for each PVC, and multipoint subinterfaces share a single subnet with Frame Relay peers.
■ To display connectivity with the Frame Relay provider, use the show frame-relay lmi command. To display connectivity with the Frame Relay peer, use the show frame-relay pvc and show frame-relay map commands.
How Frame Relay Works
How To Configure Frame Relay on a Cisco Routers
