Network composed of Avaya G700 Media
Gateways with IP tie and PSTN trunking

An enterprise has offices in five different states. Each office is to be configured to accommodate 100 DCP telephones and PSTN trunking in a stand alone system. Inter-office communication will be over H.323 tie trunks. The call mix is (1/2 enterprise, 1/4 incoming from the PSTN, and 1/4 outgoing to the PSTN), with 8 calls per hour per station and 2 CCS per call. Calls from a given station to another station in the enterprise are equally likely. Each office should have an LSP for backup. Local IP traffic is G.711, and WAN traffic is G.729, all with 30 ms frames. We can assume all IP endpoints send silence.

The following calculations are for each office.

Step 1. Avaya MM710 Media Module calculation for PSTN trunks

For each office, the PSTN trunk load is

(1/2)(100)(8)(2) / 36 = 22.22 Erlangs

EBC(22.22) = 34 trunks for P01 grade of service. This means that 34/24 = 1.42 or two Avaya MM710 T1/E1 Media Modules are required.

Step 2. DCP Station Avaya MM712 Media Module calculation

For each office, the DCP stations will require (100/8) = 12.5 or 13 Avaya MM712 Media Modules. Station usage is 22.22 Erlangs.

Step 3. Avaya MM711 Media Module calculation

Step 3 is not necessary in this configuration.

Step 4. The DSP resource calculation

For PSTN trunk calls, the G.711 usage is 22.22 Erlangs. For enterprise intercom, assume that 4/5 of the calls are over WAN IP trunks (G.729), and that 1/5 is local (G.711). The total G.711 use is

22.22 (for PSTN trunks) + 22.22 x (1/5 + 2 x 4/5) (for enterprise intercom) = 62.16 Erlangs.

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

(62.16/43.0) = 1.45 or 2

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

Fifteen Avaya Media Modules are required for T1s (2) and stations (13). This configuration then requires at least four G700 Media Gateways, which are more than enough to supply the number of DSPs required (2). Two more slots are required for the S8300 Media Server and the LSP. This brings the number of G700s to five, with three spare slots.

Step 7. Tone detection calculation

Tone detectors are required on all PSTN trunk calls, on intra-office intercom calls (1/5 of enterprise intercom), and on outgoing inter-office intercom calls (2/5 of enterprise intercom). The busy hour traffic load is 400 PSTN calls, and 400 enterprise intercom calls. If the average tone detector hold time is 4 seconds per call, the overall tone detector usage is

400 + 400(1/5 + 2/5)(4) / 3600 =.71 Erlangs

The total number of G700s required per office is.71/2.05 =.35 or 1.

Step 8. 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 22.22 Erlangs of T1 trunk traffic, all of it G.711 if converted to IP. There 22.22 Erlangs of enterprise intercom traffic, 4/5s is G.729, 1/5 is G.711, if converted to IP. To simplify, we assume 100% conversion. The calculation is

[(22.22)(159.0) +(22.22)((4/5)(47.0) + (1/5)(159.0))] / 1000 = 5.1 Mbps half duplex or 2.5 Mbps full duplex