On 6 April 2011 15:19, McKown, John <[email protected]> wrote:
> I don't know what hardware the phone switches run on. But, from what I've > been told, the software is usually written in Erlang. If we're talking about "traditional" circuit-switching digital switches, i.e. those that ran the North American public system from around the time of the AT&T breakup to the time when VOIP quite suddenly became the backbone of the phone system, then really the hardware is dedicated to circuit-switching tasks, and a general purpose CPU (with failover) treats the switching fabric as I/O devices to be directed. The CPU can be rebooted without affecting calls in progress. Of the two big vendors in North America, AT&T wrote most of their code in C, while Nortel used their own proprietary language called Protel. I don't know what the European vendors did. The current phone system is a lot harder to differentiate from the Internet we all know, since it's really a matter of packet switching of arbitrary data, some of which happens to represent phone calls. And the endpoints are much more variable than the traditional analogue desk telephone. But as with the Cisco or 3Com or Juniper router in your datacentre, or the bigger one at the ISP, there is specialized hardware directed by general purpose CPUs, and the hardware generally stays up despite program failure on the CPUs. You can even see this in a small way on the typical little home cable or DSL router; it's not uncommon for the program to crash, thus losing the firewall and NAT functions, but the switch portion of the box will happily keep switching those packets. We digress, and it's not yet Friday. Tony H. ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [email protected] with the message: GET IBM-MAIN INFO Search the archives at http://bama.ua.edu/archives/ibm-main.html
