Lucent Technologies Release 8.2 manual Definity Switch Connectivity Networking Overview, Networks

DEFINITY Switch Connectivity 1 Networking Overview

Networks

When two or more switches are connected via tie trunks, they form a private network.

There are two basic types of networks for Lucent switches:

• Main-satellite/tributary (MS/T) — A network of switches in which a main switch is fully functional and provides attendants and CO trunks for connected satellite switches. Tributary switches are connected to the main and may have their own attendant and CO trunks. The main switch may be connected to one or more Electronic tandem networks (ETNs).

•Electronic tandem network (ETN) — A wide-area network of switches in which a call can tandem through one or more switches on its way from the originating switch to the destination switch. ETNs have a uniform dial plan (UDP), automatic alternate routing (AAR), and automatic route selection (ARS).

AT&T provides a service called software-defined network (SDN) that allows you to build a private network through the AT&T public network facilities. An ETN can be combined with an SDN to form a hybrid (ETN/SDN) network.

The switches in MS/T or ETN networks need to be provisioned with special

DEFINITY networking software packages.

DCS

Distributed Communications System (DCS) is a messaging overlay for ETN or MS/T networks. The overlay provides signaling connections between network nodes that enable certain key call features to operate transparently across the DCS network. That is, the transparent features appear to operate as if the switches in the DCS network were a single switch. For example, the DCS Call Coverage feature enables calls to an extension on one switch to be covered by extensions on a remote switch in the network.

DCS consists of two components — routing and message signaling. Routing the message requires one of several networking software packages. Typically, UDP is used singe it is included with DCS at no additional charge.

Although DCS is actually a messaging overlay for an existing network, it is commonly thought of as a type of network itself. In this document, we will refer to DCS in this way — DCS network will refer to a cluster of switches that are part of an existing ETN or MS/T network and are also administered for DCS.

In addition to the normal tie-trunk connections for the transmission of voice and call-control data, DCS requires a special signaling connection to carry the information needed to make the DCS features work. This signaling connection, or link, between two switches in a DCS network can be implemented in one of three ways:

•over a processor interface (PI) channel (on the si model) or a packet gateway (PGATE) channel (r model) using the X.25 protocol

•over an ISDN-PRI D-channel (csi, si, or r models)

•over a TCP/IP (either PPP or 10Base-T Ethernet) connection (csi, si, or r models)

Note: The csi model does not support X.25 connections.

		Administration for Network Connectivity
2	CID: 77730	555-233-504 — Issue 1 — April 2000