AT&T 2500 series, 7500 series, 7100 series, 7200 series, 7400 series, 7300 series Transmission Media

6-4DISTRIBUTED COMMUNICATIONS SYSTEM (DCS)

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administrable amount of time elapses, the packet is retransmitted. The link can be reset and restarted if packets are not delivered or if the packets arrive out of sequence.

Transmission Media

Both analog and digital facilities can carry DCS signals between network nodes (see the DCS Signaling Link Connections section later in this chapter).

When multiplexed digital facilities are used, two scenarios are possible. One scenario is to multiplex DCS signaling onto a DS1 facility externally through an channel division multiplexer (CDM) (see chapter 1 for more details) that interfaces with the DCIU or PI link. The other scenario is to internally multiplex the signaling onto the DS1 facility through a DS1 port. DCS signaling channels can be redirected through DS1 ports through a dedicated connection. On the System 75 and Generic 1 communications system dedicated connections are set up through switch administration that connects the PI channel and the DS1 channel over an internal communications path. On a System 85 or Generic 2 communications system, the DS1 channel is permanently connected to a general purpose port (GPP). In turn, the GPP communicates with the DCIU over a MPDM. (See figure 6-2.)

SYSTEM 75/G1

SOFTWARE

CONNECTION D S 1

PI

AVD

SYSTEM 85/G2

		SOFTWARE
	CONNECTION
D			G
S			P
1			P

D

C

I

U

MPDM

Figure 6-2.Internally Connected DCS Signaling Channel Over a DS1

On the System 75 and Generic 1 communications systems these dedicated connections are called permanent switched connections (PSC); on the System 85 and Generic 2 communications systems, they are called dedicated switched connections (DSC).

Note:

∙When a dedicated connection must be implemented between a System 75 or Generic 1 endpoint, and a System 85 or Generic 2 endpoint, the connection should be implemented as a PSC on the System 75 or Generic 1 communications system. Because PSCs can be established across communications systems, no DSC is necessary on the System 85 or Generic 2 communications system when the PSC is defined on the System 75 or Generic 1.

∙On the System 75 and Generic 1 communications system, PSCs can be defined at either of two administration screens: the Permanent Switched Connection screen or the Interface Link screen. PSCs established through the Interface Link screen are more properly called software connections, rather than PSCs.