In preparation of your CCNA exam, we want to make sure we cover the various concepts that we could see on your Cisco CCNA exam. So to assist you, below we will discuss one of the more difficult CCNA concepts; Frame Relay. As you progress through your CCNA exam studies, I am sure with repetition you will find this topic becomes easier. So even though it may be a difficult concept and confusing at first, keep at it as no one said getting your Cisco certification would be easy!
Frame Relay: WAN Protocol for Internetworking
Frame Relay is a WAN protocol for LAN internetworking which operates at the physical and data link layer to provide fast and efficient method of transmitting information from a user device to another across multiple switches and routers.
Frame Relay is based on packet-switched technologies similar to x.25, which enables end stations to dynamically share the network medium and the available bandwidth. It employs the following two packet techniques: a) Variable-length packets and b) Statistical multiplexing. It does not guarantee data integrity and discard packets when there is network congestion. In reality, it still delivers data with high reliability.
The Frame Relay frame is transmitted to its destination through virtual circuits, which are logical paths from an originating point in the network to a destination point. Virtual circuits provide bidirectional communication paths from one terminal device to another and are uniquely identified by a data-link connection identifier (DLCI). A number of virtual circuits can be multiplexed into a single physical circuit for transmission across the network. This capability often can reduce the equipment and network complexity required to connect multiple terminal devices. A virtual circuit can pass through any number of intermediate switches located within the Frame Relay packet switched network.
There are permanent virtual circuits (PVCs) or switched virtual circuits (SVCs). PVCs are set up administratively by the network manager for a dedicated point-to-point connection; SVCs are set up on a call-by-call basis using the same signaling for ISDN set up.
There are two flavors of Frame Relay, one is based on the Q.922 LAPF, which is the popular and standard deployment, and the other conforms to LMI specifications, which is less used.
Due to its bandwidth efficiency and high reliability, Frame Relay offers an attractive alternative to both dedicated lines and X.25 networks for the inter-connecting of LANs through switches and routers.
Protocol Structure – Frame Relay: WAN Protocol for Internetworking
The Frame Relay (LAPF Q.922 based) frame structure is as follows:
Frame Relay frames that conform to the LMI specifications consist of the fields as follows:
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I hope you found this article to be of use and it helps you prepare for your Cisco CCNA certification. I am sure you will quickly find out that hands-on real world experience is the best way to cement the CCNA concepts in your head to help you pass your CCNA exam!