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Frame Relay - Computer Network - Lecture Slides, Slides of Computer Networks

Chhattisgarh Swami Vivekanand Technical UniversityComputer Networks

Frame Relay, Introduction to Frame Relay, Link Access Procedure for Frame Relay, Frame Relay Terms, Frame Relay Layer Support, Frame Relay Bandwidth, Frame Relay Flow Control and many other topics of Computer Network can be find in my documents.

Typology: Slides

2011/2012

Uploaded on 11/09/2012

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Frame Relay
Semester 4 – Module 5
Students completing this module should be able to:
Identify the components of a Frame Relay network
Explain the scope and purpose of Frame Relay
Discuss the technology of Frame Relay
Compare point-to-point and point-to-multipoint topologies
Examine the topology of a Frame Relay network
Configure a Frame Relay Permanent Virtual Circuit (PVC)
Create a Frame Relay Map on a remote network
Explain the issues of a non-broadcast multi-access network
Describe the need for subinterfaces and how to configure them
Verify and troubleshoot a Frame Relay connection
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Frame Relay

Semester 4 – Module 5

Students completing this module should be able to: Identify the components of a Frame Relay network Explain the scope and purpose of Frame Relay Discuss the technology of Frame Relay Compare point-to-point and point-to-multipoint topologies Examine the topology of a Frame Relay network Configure a Frame Relay Permanent Virtual Circuit (PVC) Create a Frame Relay Map on a remote network Explain the issues of a non-broadcast multi-access network Describe the need for subinterfaces and how to configure them Verify and troubleshoot a Frame Relay connection

Overview

  • Frame Relay was developed as an extension to

ISDN

  • Offered Packet-Switched alternative
  • Now is a stand-alone WAN Technology
  • Frame Relay switches create virtual circuits to

connect remote LANs to a WAN.

  • Frame Relay has become one of the most

extensively used WAN protocols.

  • One reason for its popularity is that it is inexpensive compared to leased lines.
  • Another reason Frame Relay is popular is that configuration of user equipment in a Frame Relay network is very simple

Frame Relay Terms

  • A Virtual Connection (VC) is created by storing input-port to output-port mapping in the memory of each switch and thus linking one switch to another until a continuous path from one end of the circuit to the other is identified
  • Frame Relay provides no error recovery mechanism
    • Relies on upper layers for error recovery
    • If there is an error in a frame, as detected by any node, it is discarded without notification
  • The FRAD or router connected to the Frame Relay network may have multiple virtual circuits connecting it to various end points - This makes it a very cost-effective replacement for a mesh of access lines - With this configuration, each point needs only a single access line and interface - More savings arise as the capacity of the access line is based on the average bandwidth requirement of the virtual circuits, rather than on the maximum bandwidth requirement Docsity.com

Frame Relay Terms

• The various virtual circuits on a single

access line can be distinguished because

each VC has its own Data Link Channel

Identifier (DLCI)

• The DLCI is stored in the address field of

every frame transmitted

• The DLCI usually has only local

significance and may be different at each

end of a VC

Frame Relay Bandwidth & Flow Control

  • The serial connection or access link to the Frame Relay network is normally a leased line
  • The speed of the line is the access speed or port speed.
    • Port speeds are typically between 64 kbps and 4 Mbps.
    • Some providers offer speeds up to 45 Mbps
  • Usually there are several PVCs operating on the access link with each VC having dedicated bandwidth availability
  • This is called the committed information rate (CIR)
  • The CIR is the rate at which the service provider agrees to accept bits on the VC
  • Individual CIRs are normally less than the port speed
  • However, the sum of the CIRs will normally be greater than the port speed - Sometimes this is a factor of 2 or 3. - Statistical multiplexing accommodates the bursty nature of computer communications since channels are unlikely to be at their maximum data rate simultaneously

Frame Relay Bandwidth & Flow Control

  • Frame Relay switches incorporate a policy of dropping frames from a queue to keep the queues short
  • Frames with their DE bit set will be dropped first
  • When a switch sees its queue increasing, it tries to reduce the flow of frames to it
  • It does this by notifying DTEs of the problem by setting the Explicit Congestion Notification (ECN) bits in the frame address field
  • The Forward ECN (FECN) bit is set on every frame that the switch receives on the congested link
  • The Backward ECN (BECN) bit is set on every frame that the switch places onto the congested link
  • DTEs receiving frames with the ECN bits set are expected to try to reduce the flow of frames until the congestion clears

Frame Relay Address Mappings & Topologies

  • In any Frame Relay topology, when a single

interface is used to interconnect multiple sites,

there may be reachability issues

  • This is due to the nonbroadcast multiaccess

(NBMA) nature of Frame Relay

  • Split horizon is a technique used by routing

protocols to prevent routing loops

  • Split horizon does not allow routing updates to be sent out the same interface that was the source of the route information
  • This can cause problems with routing updates in a Frame Relay environment where multiple PVCs are on a single physical interface

Frame Relay Address Mappings & Topologies

  • Whatever the underlying topology of the physical

network, a mapping is needed in each FRAD or

router between a data link layer Frame Relay

address and a network layer address, such as

an IP address

  • The DLCI for each VC must be associated with

the network address of its remote router

  • This information can be configured manually by using map commands
  • The DLCI can also be configured automatically using Inverse ARP

Frame Relay LMI

  • There are several LMI types, each of which is

incompatible with the others

  • The LMI type configured on the router must

match the type used by the service provider

  • Three types of LMIs are supported by Cisco

routers:

  • Cisco - The original LMI extensions
  • Ansi - Corresponding to the ANSI standard T1. Annex D
  • q933a - Corresponding to the ITU standard Q Annex A

Stages of LMI and Inverse ARP

  • LMI status messages combined with Inverse

ARP messages allow a router to associate

network layer and data link layer addresses

  • When a router that is connected to a Frame

Relay network is started, it sends an LMI status

inquiry message to the network

  • The network replies with an LMI status message

containing details of every VC configured on the

access link

Configuring a static Frame Relay map

  • The local DLCI must be statically mapped to the network layer address of the remote router when the remote router does not support Inverse ARP.
  • This is also true when broadcast traffic and multicast traffic over the PVC must be controlled.
  • These static Frame Relay map entries are referred to as static maps.

Frame Relay Subinterfaces

  • Subinterfaces are logical subdivisions of a physical interface
    • When used, the physical interface does not get assigned an IP address
  • In split-horizon routing environments, routing updates received on one subinterface can be sent out another subinterface
  • In a subinterface configuration, each virtual circuit can be configured as a point-to-point connection, allowing each subinterface to act similarly to a leased line
  • Frame Relay subinterfaces can be configured in either point-to-point or multipoint mode - When using Point-to-point subinterface, each pair of the point-to-point routers is on its own subnet - Multipoint subinterfaces can be used to establish PVC connections to multiple physical interfaces on remote routers
  • The encapsulation frame-relay command is assigned to the physical interface. All other configuration items, such as the network layer address and DLCIs, are assigned to the subinterface