Nortel Networks CG030601 manual Address resolution for PVCs, Committed information rate

Configuration Guide

Contivity Secure IP Services Gateway

Frame Relay on Contivity Secure IP Services Gateway

Address resolution for PVCs

Address resolution for PVCs maps a remote network address such as an IP address to a local DLCI number. IP uses the Address Resolution Protocol (ARP). ARP dynamically generates an ARP table of addresses and DLCI numbers by sending messages back and forth to each network node to gather address information. This process increases broadcast traffic across the network.

Committed information rate

The committed information rate (CIR) is the rate at which the network supports data transfer under normal operations. Its name is descriptive: you have a contract with your carrier, who has committed to providing a given throughput, here called the committed information rate. The CIR is measured in bits per second. You configure this value that the carrier provides per virtual circuit.

When configuring the CIR, consider the following:

CIR of 0

You can contract with a carrier for a CIR of 0, which yields best-effort service at low cost. The carrier transmits data, but does not commit to providing a specified throughput. To configure a CIR of 0, set both the throughput (which is the CIR) and the committed burst (Bc) to 0, and set the excess burst (Be) to a value greater than 0. For more information about burst rates, see the next section, “Committed burst rate and excess burst rate.”

Maximum CIR

The maximum CIR should not be greater than the speed of the access line on the slower end of a virtual circuit. In a big pipe/little pipe topology likely CIRs at the remote sites would be 32 Kb/s, 56 Kb/s, or 64 Kb/s. If you configure CIRs for these virtual circuits at the central site, you can use CIR enforcement (described in the next section) to prevent the big pipe from sending traffic that exceeds the PVC CIRs.

Committed burst rate and excess burst rate

The committed burst rate (Bc) defines the number of bits that the CES can transmit over a specified time interval (Tc) when congestion is occurring. The excess burst (Be) defines the number of extra bits that the CES attempts to send over the Tc when there is no congestion. Both the Bc and the Be are values that you configure.

The sum of the Bc and the Be is the maximum amount of traffic that can travel across the network per Tc when there is no congestion. If you set the Be to a value greater than zero, the CES can send traffic exceeding the CIR. To enforce the CIR, that is, to limit traffic that the CES can send to the amount of the CIR, set the Be to 0.