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Frame Relay

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a Frame Relay packet and send it to the source router, telling it to slow
down the rate at which it is transmitting packets.

Committed Information Rate (CIR)

Frame Relay provides a packet-switched network to many different custom-
ers at the same time. This is a great idea because it spreads the cost of the
switches among many customers. However, Frame Relay is based on the
assumption that not all customers need to transmit constant data all at the
same time. Frame Relay works best with bursty traffic.

Think of Frame Relay as a party line. Remember party lines? That's when

many people on your block had to share the same phone number. Okay, I'm
showing my age here, but understand that party lines were created on the
assumption that few people needed to use the phone each day. If you needed
to talk excessively, you had to pay for the more expensive dedicated circuit.
Frame Relay works somewhat on the same principle, except many devices
can transmit at the same time. However, if you need a constant data-stream
connection, then Frame Relay is not for you. Buy a dedicated, point-to-point
T-1 instead.

Frame Relay works by providing a dedicated bandwidth to each user,

who is committed to that bandwidth at any given time. Frame Relay provid-
ers allow customers to buy a lower amount of bandwidth than what they
really might need. This is called the committed information rate (CIR). What
this means is that the customer can buy bandwidth of, for example, 256K,
but it is possible to burst up to T-1 speeds. The CIR specifies that as long as
the data input by a device to the Frame Relay network is below or equal
to the CIR, then the network will continue to forward data for the PVC.
However, if data rates exceed the CIR, it is not guaranteed.

The CIR is the rate, in bits per second, at which the Frame Relay switch agrees

to transfer data.

It is sometimes possible to also purchase an excess burst (Be), which

allows customers to exceed their CIR for a specified amount of time. In this
situation, the DE bit will always be set.

Choose a CIR based on realistic, anticipated traffic rates. Some Frame

Relay providers allow you to purchase a CIR of zero. You can use a zero CIR
to save money if retransmission of packets is acceptable. However, under-
stand that the DE bit will always be turned on in every frame.

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