swvlan

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E0 192.168.3.150

LAN - 192.168.3.0/24

BANGLORE OFFICE

E0 192.168.1.150

LAN - 192.168.1.0/24

HYDERABAD OFFICEE0 192.168.2.150

LAN - 192.168.2.0/24

CHENNAI OFFICE

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• Frame Relay is a data link layer

packet-switching protocol that uses digital circuits.

• It is used for medium to longer distances and for

longer connectivity.

• Leased lines also provide longer connectivity but a

physical circuit is used to make connection between

2 sites and the same circuit path is used always.

• Frame Relay connections use logical circuits to make

connections between 2 sites. These logical circuits are

referred to as Virtual Circuits(VCs).

• Multiple VCs can exist on the same physical

connection.

• VCs are Full duplex.

Frame Relay

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• VCs overcome the scalability problems of

leased lines by providing multiple logical circuits

over the same physical connection.

• Only one serial interface of a router is needed to

handle the VC connections to multiple sites Whereas

using leased lines multiple serial interfaces are needed

to connect to multiple sites.

• VCs provide full connectivity at a much lower price

compared to leased lines.

Advantages of Frame Relay

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• Sub-interfaces

• Uses Shared bandwidth

• Local Management interface(LMI):

– used between the Frame relay DTE(eg.Router) and the

Frame Relay DCE(eg. Frame Relay switch)

– Defines how the DTE interacts with the DCE

– Locally significant

– Provides VCs status information(a keep-alive

mechanism)

– LMI standards : Cisco, ANSI, Q933a

The DTE and DCE must have the same LMI signaling type

Frame Relay Terminology

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• Data Link Connection Identifier(DLCI) :

– used to identify each VC on a physical interface

(i.e.) Each VC has a unique local address called a DLCI

number.

– switch will map to the destination depending on the

DLCI number

– Inverse ARP is used to map DLCIs to next hop

addresses.

– Mapping can also be done manually.

– Its Locally significant.

– These numbers are given by the Frame relay

service providers, Service providers assign DLCIs in

the range of 16 to 1007.


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• Virtual circuits are of two types:

– Permanent Virtual Circuits – PVCs

– Switched Virtual Circuits –SVCs

• Permanent Virtual Circuit :

– similar to a dedicated leased line , permanent connection.

– used when constant data is being generated.

• Switched Virtual Circuit :

– also called as Semi-permanent virtual circuit

– similar to a circuit switched connection where the VC is dynamically built and then torn down once the data has been sent.

– used when data has to be sent in small amounts and at periodic intervals.


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• Committed Information Rate(CIR) :

– Average data rate measured over a fixed period

of time that the carrier guarantees for a VC.

– committed bandwidth

• Burst Rate(BR) :

– Average data rate provider guarantees for a VC.

– Excess bandwidth


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• FECN and BECN :

– Forward Explicit Congestion Notification

– Backward Explicit Congestion Notification

• When congestion occurs switch marks the FECN and

BECN bits in the frame header.

• FECN is sent to the destination

• BECN is sent to the source

• Thereby notifying both source and destination

about the congestion.

• FECN = 0 and BECN =0 implies no congestion.


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