Support / How the Products Work

Moving packets through a WiFi network uses significant overhead. Combine this with the relatively small packets for VoIP that must be sent at regular intervals, (e.g. every 20 ms) and the overall system becomes increasingly
inefficient. For example, with 64Kbps VOIP traffic, the frame size is 160 bytes but there are 40 bytes of IP overhead and 30 bytes for MAC layer overhead, for a total of 230 bytes per frame. The overhead is far less for a large data packet (2300 bytes).

As contention is added (multiple clients) and as packets traverse multiple hops, effective bandwidth is reduced far more so with competing mesh products than with Mesh City Mesh Net. Also, beyond bandwidth degradation (causing packet delay), latency and jitter degrade more with increased contention in the 1-radio backhaul products.

Mesh City Mesh Net multi-radio backhaul ensures deterministic latency and jitter by eliminating the effects of both single radio backhauls and involuntary contention.

Mesh City Mesh Net VoIP engine ensures the timely delivery of VOIP packets.

Let’s look at a wireless mesh solution to cover a number of square miles of city. For this analysis, let’s assume initially that only VoIP conversations are being supported. Of course, when data transfers are mixed into the analysis, the number of simultaneous VoIP conversations may be reduced.

Let’s assume that there are 5,000 subscribers per square mile, and that during the peak hour of the day, each makes one call of 5 min duration. This produces a peak traffic level of 0.083 Erlangs per subscriber, resulting in an average of 416 simultaneous conversations per square mile during the peak hour.

Assume also that mesh nodes are deployed on a 1/5 mile grid. There will be 25 nodes covering the first square mile. As the number of square miles increases, this number converges on an average of 16 per square mile (two sides of the square are shared).

Lastly, 802.11b AP radios on each node can support 29 simultaneous conversations with a G.711 64Kb voice codec and 60 conversations with a G.729 8Kb codec.

If we assume one DS3 connection per square mile and 64Kbps VoIP calls, then the 3-radio modules can support 464 simultaneous conversations needed for 5,000 subscribers and even leaves some bandwidth available for data traffic.

If the G.729 codec were used (8Kbps), 3-radio modules support up to 960 simultaneous conversations per square mile - essentially supporting a subscriber density of 10,000 per square mile given the same usage parameters.