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6-6 DISTRIBUTED 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 6-3 shows 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 6-4 shows 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.
SWITCH
NETWORK
CALL
PROCESSOR &
MEMORY
NODE 1
D
C
I
U
DCIU LINK
1
3
4
D
I
CALL
PROCESSOR &
NODE 2
TIE TRUNKS
TIE TRUNKS
TIE
TRUNKS
SYSTEM 85
1
2
3
4
5
6
7
8
2
C
U
MEMORY
SWITCH
NETWORK
1
3
4
I
CALL
PROCESSOR &
2
P
MEMORY
SWITCH
NETWORK
SWITCH
NETWORK
CALL
PROCESSOR &
MEMORY
D
C
I
U
SYSTEM 85
1
2
3
4
5
6
7
8
DCIU LINK
"DIMENSION" SYSTEM
FP8 (ISSUE 3)
NODE 3 ENDPOINT
SYSTEM 75
DCIU/PI LINK
Figure 6-4. Minimized Link Connections