Avaya 555-245-600 manual Traffic engineering

Traffic engineering

Table 27: Outbound COI matrix for Uniform Distribution Model in Example 2: Uniform Distribution model

Outbound CUR			To trunks in Site __
		1	2	3
From stations in Site	1	49 Erlangs	0	0
____
	2	0	18 Erlangs	0
	3	0	0	8 Erlangs

Again, Table 26 and Table 27 are constructed without considering overflow traffic.These tables imply that the Site 1 PSTN trunks carry 98 Erlangs (49 inbound and 49 outbound) of traffic, the Site 2 trunks carry 36 Erlangs, and the Site 3 trunks carry 16 Erlangs. Applying the standard Erlang loss model with a P01 GOS to each of the three sites implies that at least 116 trunks are needed in Site 1, at least 49 trunks are needed in Site 2, and at least 26 trunks are needed in Site 3. Note that this constitutes a total of 191 trunks, as opposed to the estimate of 171 trunks that was obtained without sizing the three trunk groups separately. A total of 171 could be used to attain an overall grade of service of P01, but that would induce a large amount of intersite traffic. The use of 191 total trunks, distributed between the three sites as specified above, ensures that at least 99% of the calls are guaranteed to be intrasite.

In some cases, there might be factors that justify over-engineering the trunk groups. For example, a customer who is based in North America most likely leases T1 trunk facilities between each of its sites and the appropriate COs. In this example, it might be reasonable to use five T1 facilities (that is, 120 DS0 channels) for Atlanta, three T1 facilities (that is, 72 DS0 channels) for Boston, and two T1 facilities (that is, 48 DS0 channels) for Cleveland. This yields an overall GOS much better than P01, and at the same time, the use of standardized equipment reduces costs. In fact, the use of Erlang’s loss formula implies a blocking probability of 0.004 in Atlanta, and negligible blocking probabilities (that is, several orders of magnitude better than P01) for the other two sites. These extremely low-blocking probabilities justify the assumption that intersite trunk traffic (overflow traffic) is negligible in this example.

Finally, the entries for the intercom COI matrix must be determined. Of the 195 Erlangs of station usage in that site, 49 Erlangs are associated with inbound calls, and 49 Erlangs are associated with outbound calls. That leaves 195 - 49 - 49 = 97 Erlangs of station usage in the Atlanta site for intercom calls. Similarly, there are 72 - 18 - 18 = 36 Erlangs of station usage in the Boston site for intercom calls, and 34 - 8 - 8 = 18 Erlangs of station usage in the Cleveland site for intercom calls.

188 Avaya Application Solutions IP Telephony Deployment Guide