Traffic calculation examples

Branch office configuration - 1000 Avaya G700 Media Gateway IP phones

An existing DEFINITY^� system with 4000 DCP stations is being expanded to connect to a new building across town via data WAN facilities. The new building will support 1000 IP telephones, and all PSTN trunking over T1 facilities. For all phones in the existing and new facilities, the call mix is (1/3, 1/3, 1/3), with 4 calls per station and 1.5 CCS per call. Trunk and local intercom calls use G.711, while intercom across the WAN uses G.729, all with 30 ms frames. Assume all IP endpoints send silence.

Step 1. Avaya MM710 Media Module calculation for PSTN trunks

The PSTN trunk load is:

(2/3)(1000)(4)(1.5)/36 = 111.11 Erlangs

EBC(111.11) = 134 trunks for P01 grade of service. This means that 134/24 = 5.58, or six Avaya MM710 T1/E1 Media Modules are required.

Step 2. Avaya MM712 Media Module calculation

Step 2 is not necessary in this configuration.

Step 3. Avaya MM711 Media Module calculation

Step 3 is not necessary in this configuration.

Step 4. DSP Resource calculation

For trunk calls, the G.711 usage is 111.11 Erlangs. For intercom, we can assume that 4/5 of the calls are to the main facility over the WAN (G.729), and that 1/5 is local (G.711). We also assume all intercom calls shuffle. The intercom G.711 DSP usage is

(1/3)(1000)(4)(10/3600)(2 x 4/5 + 1 x 1/5) = 6.67 Erlangs

The total G.711 use is

111.11 + 6.67 = 117.78

The number of DSP resources required, using the more conservative, or TS centric, calculation is

(117.78/43.0) = 2.74, or 3.

Steps 5 and 6. Initial and final G700 Media Gateway calculation

To meet the requirements of Steps 1 and 2, two configurations are possible:

• Two G700s, each with three Avaya MM710 T1/E1 Media Modules

In this case, the DSP G.711 port usage is

117.78/2 = 58.9 Erlangs

Since this number is greater than the 43.0 Erlang design criteria, an Avaya MM760 Media Module is required in each of the G700s, for a total of four DSP resources, even though only three were required from the Step 2 calculation. With this configuration, there are no spare slots.

• Three G700 Media Gateways, each with two G700s

Since each G700 has an embedded DSP resource, no Avaya MM760 Media Modules are required. There are six spares (two per G700) for future expansion.

Step 7. The tone detection calculation

Tone detectors are required on incoming PSTN trunk calls. Suppose the average hold time is 4 seconds. The total tone detector usage is

(1/3)(1000)(4)(4) / 3600 = 1.48 Erlangs

The number of G700s required is

1.48/2.05 =.72, or 1

Step 8. The data network impact calculation

Since silence is sent, an active G.711 call uses 2 x 79.5 = 159.0 Kbps, and an active G.729 uses 2 x 23.5 = 47.0 Kbps. There are 111.11 Erlangs of IP station to T1 trunk traffic, all of it G.711. There 55.56 Erlangs of IP-IP traffic, 4/5s is G.729, 1/5 is G.711, and all of it shuffles. The calculation is:

[(111.11)(159.0) +(55.6)((4/5)(47.0) + (1/5)(159.0)) / 2] / 1000 = 19.6 Mbps half duplex or 9.8 Mbps full duplex