Cisco Systems IGX 8400

4-14 Cisco IGX 8400 Series Reference

Universal Switching Module Enhanced

This section introduces the connections that a UXM-E trunk supports. The context of each

description is the trunk rather than the connection endpoints. The purpose of these descriptions is

notonly to inform but also help you plan the network. Some deﬁnitions overlap because a connection

may qualify as more than one type.

•A Cell connection carries information that exists in ATM cell format throughout the path. On a

UXM-E trunk, therefore, the only cell connections are those that have originated on a UXM-E

port at one end and remain in cell format throughout the connection.

•AGateway connection carries information that normally exists in ATM cell format but is

translated to FastPacket format for some purpose at some point along the path. Reason for the

translation could be that the connection terminates on a FastPacket-based card, is a network

connection, or includes a FastPacket-based trunk card in the route.

•ANetworkingconnection carries network messages between nodes and terminate as FastPackets

(and therefore are also gateway connections).

•AUser-connection is a connection that a user has added at the current node. User-connections

can be cell connections or gateway connections. User connections are mutually exclusiveof via

connections and network connections.

•AViaconnection passes through a node and does not terminate on the node. Youcan neither view

nor alter a via connection because the connection does not terminate on the node (the node that

owns the connection has made the via node and trunk a part of the route).

•An Interworking connection is a service or network interworking connection in which one end

terminates as ATM and the other as Frame Relay. Interworking connections are a subset of

gateway connections.

Operating as a trunk, the UXM-E carries up to 8000 connections. A via connection can be either a

cell-type or a gateway-type.

Because network messages use gateway channels, they subtract from the total number of available

gateway connections. For eachactive port, the UXM-E reserves 270 gateway connections for

networking regardlessof the interface type. Therefore, with a fully-utilized 8-E1 or 8-T1 back card,

the UXM-E reserves up to 2160 connections. Because these numbers potentially represent a very

signiﬁcant reduction in the number of gateway connections for user-data, switch software lets you

specify a maximum number of activeports on the back card. The most applicable interfaces for this

capability are the T1 and E1 ports, especially with InverseMultiplexing Over ATM (IMA). See the

section “Inverse Multiplexing over ATM on IGX Trunks” for the description of IMA.

You can specify the maximum number oflogical trunks that can be active on a card through Cisco

WANManager or the CLI. The applicable CLI command is cnftrkport. For example, if you intend

an eight-port card to havetwo logical (IMA) trunks, you can use cnftrkport to specify a maximum

number of two trunks. Software would therefore reserve 540 connections for network messages

rather than the 2160 connections if you did not specify a maximum.

InverseMultiplexing over ATM(IMA) lets you group physical T1 or E1 lines to form a logical trunk.

A logical trunk consisting of more than one T1 or E1 line supports connections with data rates that

are much higher than the T1 or E1 rate. System software lets you specify IMA so that one or more

physical lines within the logical trunk can serve as backup if a line fails.