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Frame Relay Tutorial

September 7th, 2011 Go to comments

Let’s start this article with the question: Why do we need Frame Relay?

Let’s take a simple example. Suppose you are working in a big company and your company has just expanded to two new locations. The main site is connected to two branch offices, named Branch 1 & Branch 2 and your boss wants these two branches can communicate with the main site. The most simple solution is to connect them directly (called a leased line) as shown below:


To connect to these two branches, the main site router, HeadQuarter, requires two serial interfaces which a router can provide. But what happens when the company expands to 10 branches, 50 branches? For each point-to-point line, HeadQuarter needs a separate physical serial interface (and maybe a separate CSU/DSU if it is not integrated into the WAN card). As you can imagine, it will need many routers with many interfaces and lots of rack space for the routers and CSU/DSUs. Maybe we should use another solution for this problem? Luckily, Frame Relay can do it!

By using Frame Relay we only need one serial interface at the HeadQuarter to connect to all branches. This is also true when we expand to 10 or 50 branches. Moreover, the cost is much lesser than using leased-lines.


Frame Relay is a high-performance WAN protocol that operates at the physical and data link layers of the OSI reference model. It offers lower-cost data transfer when compared to typical point-to-point applications, by using virtual connections within the frame relay network and by combining those connections into a single physical connection at each location. Frame relay providers use a frame relay switch to route the data on each virtual circuit to the appropriate destination.

Maybe these terminologies of Frame Relay are difficult to understand so we will explain them in more detail in this article.


The first concept in Frame Relay you must grasp is about DTE & DCE:

+ Data terminal equipment (DTE), which is actually the user device and the logical Frame-relay end-system
+ Data communication equipment (DCE, also called data circuit-terminating equipment), which consists of modem and packet switch

In general, the routers are considered DTE, and the Frame Relay switches are DCE. The purpose of DCE equipment is to provide clocking and switching services in a network. In our example, HeadQuarter, Branch 1 & Branch 2 are DTEs while Frame Relay switches are DCEs.

Virtual Circuits

The logical connection through the Frame Relay network between two DTEs is called a virtual circuit (VC). The term “virtual” here means that the two DTEs are not connected directly but through a network. For example, the HeadQuarter & Branch 1 (or Branch 2) can communicate with each other as if they were directly connected but in fact they are connected through a Frame Relay network with many Frame Relay switches between them.


There are two types of VCs
+ switched virtual circuits (SVCs): are temporary connections that are only used when there is sporadic data transfer between DTE devices across the Frame Relay network. SVC is set up dynamically when needed. SVC connections require call setup and termination for each connection.
+ permanent virtual circuits (PVCs): A predefined VC. A PVC can be equated to a leased line in concept.

Nowadays most service providers offer PVC service only to save additional costs for signaling and billing procedures.

Comments (21) Comments
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  1. Anonymous
    August 2nd, 2016

    brief and
    nice explanation

  2. Anonymous
    August 2nd, 2016


  3. Anonymous
    August 3rd, 2016

    very nice explanation

  4. PowTown
    August 3rd, 2016

    You did a great job.

    August 6th, 2016


  6. bradm
    August 13th, 2016


  7. Lost Frame
    August 25th, 2016

    srs this tutorial was too useful thank you so much 9tut.com -_-

  8. AZIZ
    September 6th, 2016

    emm understand

  9. RAJ
    September 12th, 2016


  10. Tamil
    September 21st, 2016

    Nice !

  11. Anonymous
    October 2nd, 2016

    it was amazing tutorial!

    Thanks indeed. in cisco net academy there are many unused and impractical information.

    again thanks

  12. Anonymous
    October 4th, 2016

    a explosure

  13. Anonymous
    October 19th, 2016

    hi i understand that cisco removed frame relay from ccna ver 3.0 is that true??

  14. Anonymous
    November 22nd, 2016

    that’s what I heard as well.

  15. Anonymous
    November 27th, 2016


  16. Anonymous
    December 22nd, 2016

    so helpful thank so much.

  17. Anonymous
    January 4th, 2017

    Very good good elaboration…. keep it up

  18. Anonymous
    January 7th, 2017

    hi ,first i thank you very much for your great job
    but is this inculed in ccna 200 125


  19. Anonymous
    January 10th, 2017

    great thank you

  20. Thozhi
    February 4th, 2017

    very helpful….Thank u so much….

  21. Anonymous
    March 16th, 2017

    whats the relationf splithorizon

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