Lack of WAN Bandwidth

Probably the most memorable installation that went awry because of bandwidth issues occurred very early in the evolution of IP telephony. In 1999, a company installed IP phones between two locations, as shown in Figure 7-1.

Figure 7-1. WAN Considerations for IP Telephony

Figure 7-1. WAN Considerations for IP Telephony

A couple of points are key in this diagram. First of all, this installation occurred before Cisco CallManager control servers could be centralized to support an entire enterprise network. So CallManager servers are at both locations to handle call control. The second point is this installation occurred during the early days of compression, and this company was not using any compression on the WAN.

There were about 30 users at Location A and another 70 or so users at Location B. The company WAN supported 56 K transmissions between the two locations. So, the question one might ask is, "How could people make calls between locations?" The answer was simple: They couldn't.

A single call, uncompressed, on the WAN would use 64 K of bandwidth plus overhead. This came out to approximately 80 K of bandwidth. Because of insufficient bandwidth on the WAN to accommodate calls between locations across the company network, the company had to continue paying for long-distance calls between these two locations until they added capacity to their WAN.

A logical question to be asked is why didn't they add capacity before the installation? That is not an easy question to answer, but it was clear that this customer had bought into the concept that IP telephony was going to save them a lot of money.

As previously discussed, IP telephony is most likely going to result in cost savings across many functions—but it is going to require an investment, and therefore, in many cases, the cost savings will occur over a period of time—hence an ROI calculation is in order. This customer, however, wasn't prepared to make that investment up front. After all, everything he had read in trade publications and technical write-ups talked about the tremendous (and immediate) savings associated with IPT. So the idea of adding bandwidth (and costs) to the network was not an acceptable decision at that time.

As a result, this company ended up with a system that made local, internal calls wonderfully, but still needed to pass calls between the two locations out through the PSTN.

A simple WAN analysis would have shown this customer that its current WAN could not support voice calls. Remember: In a converged environment, the company WAN has to carry both voice and data calls, and do so simultaneously.

Was this article helpful?

0 0

Post a comment