Scaling of a VOCAL system

From table 3-1 of Practical VoIP: Using VOCAL
Server types	6-host system	14-host system	26-host system
Redirect servers	1	2	5
Feature servers	1	2	5
Marshal servers	2	4	10
Call Detail Record servers	½	2	2
Provisioning servers	1	2	2
Policy servers	½	2	2
Total number of hosts	6	14	26
Capacity in calls per second	35	70	175
Capacity in busy-hour call attempts (BHCA)	125,000	250,000	630,000

Each host is a 700MHz Pentium III with 512 MB or RAM.

Note that unlike a PBX or Public Exchange, the capacity in calls per second (or BHCA) is independent of the call durations, since the call traffic is carried directly between the endpoints via RTP and does not use the VOCAL system!

Transcript

[slide520] And they said, gee, we could deploy this on PCs, commodity PCs. In their case at the time, 700 megahertz Pentium 3s. And they said, if we took six systems, and we split them up this way, one for redirect, one for features, two for marshaling, half a server for call detail records, half a server for policy, one for provisioning, we could handle 35 calls per second. You might say, well, that doesn't sound like very much. But if you translate it to traditional PBX terms, that means 125,000 busy hour call attempts. So that's the most calls that you would be getting per hour if you were a public switch. That's a pretty substantial volume. The really interesting thing is by just going from six hosts to 14 such hosts, they could double it. And going up to 26 hosts, they could support 630,000 busy hour call attempts. Now, somebody might say, who cares? Well, the key feature here is unlike a normal PBX or exchange, the call capacity is independent of the call duration. Because the media traffic is flowing just between the endpoints that are communicating. These systems are only ever being invoked for the signaling. So it scales up very, very well.