6 4 0 CM 3 2 0 160 Number of nodes
Figure 4.6 Total traffic that can be carried by a V C - 12 managed STM -4 M S-SPR ing or SNCP-ring under the 3 ideal traffic patterns
3 2 0 0 2 5 6 0 CM 1 2 8 0 6 4 0 14 1 6
Num ber of nodes
Figure 4.7 Total traffic that can be carried by a V C - 12 managed S T M - 16 M S-SPR ing or SNCP-ring under the 3 ideal traffic patterns
In figure 4.7, t4 represents the uniform traffic pattern and t3 represents both the hub and the node to the adjacent node traffic pattern in the SNCP-ring.
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4.3.4 Results on Limits of Ring Sizes
The maximum number of nodes on a ring is one of the impacts of different ideal traffic patterns in rings. This has already been discussed, but without taking into consideration the effect of an optimum routing algorithm proposed [78]. In the case of a VC-4 managed STM-16 MS-SPRing or SNCP-ring under an ideal uniform traffic pattern, the number of nodes that can participate on the ring is limited. The uniform traffic pattern represents a high density of traffic demand and large amounts of total traffic even with small number of nodes on the ring. Therefore the maximum number of nodes that can participate in a VC-4 managed STM -16 MS-SPRing under an ideal uniform traffic pattern, even if L = 1 VC-4, is 7 and in an STM -16 SNCP-ring is 6. This numbers increase to 15 and 11 for STM-64 VC-4 managed MS-SPRings and SNCP-rings respectively, where for a uniform traffic pattern that represents a high traffic density. The minimum traffic unit (1 VC-4) is again not insignificant compared to the total capacity of the ring. In neither case can the maximum number of 16 nodes, supported by the MS-SPRing protocol, be obtained. These constraints are especially important in understanding the applicability of MS-SPRings, since in tier 1 backbone networks, where VC-4 managed MS-SPRings are usually deployed, the traffic pattern resembles the uniform one. Therefore, it is rare for a 16 node MS-SPRing to be able to be formed in core SDH networks even if that would be desirable by the planner. For the other types of traffic patterns in VC-4 managed STM -16 or STM-64 MS- SPRings, with 1 VC-4 exchanged between each pair of nodes, the maximum number of nodes of 16, can be achieved. In VC-4 managed STM-16 or STM-64 SNCP-rings the maximum number of nodes can be even larger than 16 constrained only by the total traffic on the ring.
As the number of VC-4s exchanged between node pairs in VC-4 managed rings increases, the maximum number of nodes forming the ring decreases for both the uniform and the hub traffic pattern in MS-SPRings and for all traffic patterns in SNCP-rings. Only in a node to adjacent node traffic pattern in an MS-SPRing can the
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number of 16 nodes forming a ring, supported by the MS-SPRing protocol, be achieved for all traffic loads between node pairs up to the ring working capacity (8 VC-4s for the STM-16 MS-SPRing and 32 VC-4s for the STM-64 MS-SPRing). When we consider VC-12 management, we find that the maximum number of nodes which can participate in an SNCP-ring increases to the point where it is not an issue. For the (theoretical) VC-12 managed MS-SPRings the situation is similar, but the protocol induced limit of 16 nodes still applies.
4.3.5 Capacity Utilisation Comparison
The total traffic carried by a ring under different ideal traffic patterns, provides the best view of the capacity utilisation performance of a ring and a clear basis of comparison. As it can be seen in the figures produced, MS-SPRings have under any traffic pattern, the same or better capacity utilisation than SNCP-rings. Only under a hub traffic pattern and when n is even, can SNCP-rings have a theoretically better capacity utilisation than MS-SPRings.
The total traffic that can be carried by an STM-N SNCP-ring, under any traffic pattern, cannot exceed the total capacity of the ring (N STM-Is). In real traffic patterns, up to N STM-Is total capacity can be carried by an STM-N SNCP-ring independent of the number of nodes and the relative granularity. The curves shown for SNCP-rings in the figures 4.4-4.V show some differences in the total traffic carried for the three ideal traffic patterns, depending on the relative granularity and the number of nodes, but that has no real meaning for real traffic patterns, where an SNCP-ring can be loaded up to its limit.
For a hub traffic pattern in an STM-N MS-SPRing, the total traffic that can be carried cannot exceed the ring capacity (N STM-Is) as well. The capacity utilisation of an MS-SPRing under the hub traffic pattern is similar or worst (in theory) to an SNCP- ring under any traffic pattern. With a fine granularity (VC-12 management) the total