CHAPTER 11 ( FRAME RELAY )

             Frame Relay is a standardized wide area network technology that specifies the physical and logical link layers of digital telecommunications channels using a packet switching methodology. Network handles the transmission over a frequently-changing path transparent to all end-users. Has become one of the most extensively-used WAN protocols. Its cheapness (compared to leased lines) provided one reason for its popularity. The extreme simplicity of configuring user equipment in a Frame Relay network offers another reason for Frame Relay's popularity.

             Frame Relay aimed to provide a telecommunication service for cost-efficient data transmission for intermittent traffic between local area networks (LANs) and between end-points in a wide area network (WAN). Frame Relay puts data in variable-size units called "frames" and leaves any necessary error-correction (such as re-transmission of data) up to the end-points. This speeds up overall data transmission. For most services, the network provides a permanent virtual circuit (PVC), which means that the customer sees a continuous, dedicated connection without having to pay for a full-time leased line, while the service-provider figures out the route each frame travels to its destination and can charge based on usage.

          Packet switching is a store and forward switching technology for queuing networks where user messages are broken down into smaller pieces called packets. Each packet has its own associated overhead containing the destination address and control information. Packets are sent from source to destination over shared facilities and use a statistical time−division multiplexing (TDM) concept to

share the resources.

           Fast packet switching is a combination of packet switching and faster networking using high−speed communications and low−delay networking. Fast packet is a "hold and forward" technology designed to reduce delay, reduce overhead and processing, improve speed, and reduce costs. It is designed to run on high−speed circuits with low (or no) error rates.

Frame Relay Speeds
          It is appropriate to discuss the speed that can be achieved with the use of Frame Relay. It was stated that Frame Relay was designed for speeds up to T−1/E−1 (1.544—2.048 Mbps); it later evolved to speeds of up to 50 Mbps. Actually, few end users have ever implemented Frame Relay at the higher speeds; this is more of a speed for the carrier community, but the need for stepped increments has always been a requirement for data transmission.


Frame Relay Access
         A link is installed between the end−user location and the network carrier's node. The normal link speed is T−1, although many locations can and do use Integrated Services Digital Network (ISDN) or leased lines at lower rates. Some customers may choose to install a local loop at speeds up to T−3(45Mbps approximately) to support higher−speed access and faster data throughput. The use of the T−3 will also allow for consolidation on the same link. Many of the carriers (and in particular the LECs) will offer the T−3 access and enable Frame Relay throughput atrates up to 37 or 42 Mbps.


   Provisioning PVCs and SVCs

        The primary difference between PVCs and switched virtual circuits (SVCs) is whether the connections are provisioned or established. Both types of connections need to be defined. The difference is when the connections are defined and resources allocated.The network operator typically provisions PVCs. The network operator can be the carrier (public services) or the MIS manager (private networks). Once the PVC is provisioned, the connection is available for use at all times unless there is a service outage.  

               

        SVCs are ideal for networks with highly meshed connectivity, highly intermittent applications, remote site access, and interenterprise communications. Each of these applications will be discussed in more detail in the succeeding slides. SVCs are also ideal for networks that are not primarily dependent on resources housed at a single location such as the headquarters site or at regional offices. In a nonhierarchical networking environment where there is a need to communicate
with many locations, SVCs can offer a viable solution.
       
  Advantages of SVCs
- magnified as the number of locations and the degree of connectivity requirements increase.
-Highly meshed networks are becoming more common as more and more companies deploy intranets.
-It isconceivable that all end users will have their own Web page within the corporation. This will
increase the amount of peer−to−peer intracompany traffic.



http://en.wikipedia.org/wiki/Frame_Relay