Professor Jeffrey Robinson
August 20, 2013
In this discussion we look at some of the history around frame-relay. We then look at some of the equipment necessary to create the frame relay connections, as well as how the connections work both logically and physically. Some limiting factors are discussed as well as committed information rates, burst rates, an error handling. Some of the positive aspects of frame-relay are identified along with some options for the future of WAN technologies.
Operating at the physical and datalink layers of the OSI model, frame relay ...view middle of the document...
The DTE devices are usually located on the customer’s premises and is the equipment that terminates a specific network. DCE devices are usually owned by the carrier. This equipment provides switching and clocking services in the network which allow data to be transmitted through the WAN.
By providing connection oriented datalink layer communications, a defined communication is created between the devices which are linked with a connection identifier. This logical connection between a pair of DTE devices is created with a frame-relay virtual circuit and traverses a frame-relay packet-switched network (PSN). A datalink connection identifier the (DLCI) allow for bidirectional communications between DTE devices in these virtual circuits. By multiplexing multiple virtual circuits into single physical circuits reduces the complexity of the network and the amount of equipment necessary to connect many DTE devices. Inside the frame-relay PSN, one virtual circuit can traverse many intermediate DCE switches. There are two categories of frame-relay virtual circuits: permanent virtual circuits (PVCs) and switched virtual circuits (SVC’s). Switched virtual circuits are connections that are temporary and are created and terminated after each data transfer upon completion of the data transfer. Whereas permanent virtual circuits are connections that are permanent. A DLCI value is allocated to each of the virtual circuits DTE devices within the frame-relay WAN. The virtual connection on each side can have the same value inside the same frame-relay WAN. Cisco Kid (2010).
Some of the LMI enhancements that were developed by the consortium, also known as extensions, provide additional features for complex internetwork management such as multicasting, global addressing, and virtual circuit status messages. Cisco Kid (2010).
Because frame-relay is a technology based on bandwidth demand, the bandwidth is shared on a packet by packet basis with others in the same class. The permanent virtual circuit does not consume any bandwidth until it is needed. This may be cost effective when compared to paying for leased line services. This allows frame-relay to provide a low cost of ownership while adhering to standards and internetworking with other services. A highly reliable WAN may be achieved through frame-relay and a good service level agreement (SLA) from the provider.
Frame-relay can be thought of as a simple principle because it allows the higher-level protocols to deal with many of the problems. Although, it can include optional features such as congestion notification and signaling mechanisms. Ideally, a committed information rate (CIR) is selected that best meets the needs of the customer. This is the maximum burst rate, which when exceeded can cause the frames to be discard eligible (DE). In reality, the nature of frame-relay allows all bits to be discard eligible, but the error correction is handled by the upper layers. Some configurations allow speeds to...