Nortel Networks CG030601 - Manual (Page 3)

Configuration Guide
Contivity Secure IP Services Gateway
Frame Relay on Contivity Secure IP Services Gateway
CG030601 2.00 July 2003 Page: 3 of 14
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.