AT&T 7400 series, 7500 series, 7100 series, 2500 series Linkage Design, Minimized Link Connections

6-6DISTRIBUTED COMMUNICATIONS SYSTEM (DCS)

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Linkage Design

Signaling links between DCS nodes can be designed with an underlying direct linkage or minimized linkage philosophy.

Direct Linkage. When a DCS cluster is designed using direct linkage, every DCS node is directly connected to every other DCS node. Figure 6-3shows a DCS cluster with direct linkage. The advantage of direct signaling links is reliability. If the signaling link between Node 1 and Node 2 fails, feature transparencies are only lost between these two nodes.

Minimized Link Connections. When a DCS cluster is designed using minimum linkage, one DCS node is chosen as a cluster hub. The cluster hub communicates with all DCS nodes. For communications to reach nodes other than the cluster hub, they must "hop" through the hub’s DCIU or PI. Figure 6-4shows a DCS cluster using a minimum signaling linkage configuration. Because nondirect linkage requires less hardware and fewer ports, it is more economical than direct linkage. However, minimum linkage is less reliable than direct linkage. Moreover, in figure 6-4,failure of node 2 will cause loss of feature transparency in the remainder of the cluster.

TIE TRUNKS

SYSTEM 85

	CALL	D
SWITCH		C
	PROCESSOR &
NETWORK		I
	MEMORY
		U
	NODE 1

1DCIU LINK

2

3

4

5

6

7

8

DCIU LINK

		"DIMENSION" SYSTEM
		FP8 (ISSUE 3)
1
	D
2		CALL
	C		SWITCH
3		PROCESSOR &
	I		NETWORK
		MEMORY
4	U
		NODE 2
			TIE
			TRUNKS

SYSTEM 85

	CALL	D
SWITCH		C
	PROCESSOR &
NETWORK		I
	MEMORY
		U

	DCIU/PI LINK
1		1		SYSTEM 75
2
3		2		CALL
4			P		SWITCH
	3			PROCESSOR &
5			I		NETWORK
6				MEMORY
7	4
8

NODE 3 ENDPOINT

TIE TRUNKS

Figure 6-4.Minimized Link Connections