[Asterisk-Users] Need help understanding SIP phones

[Lee Cremeans]

>How would/do vendor specific phones like cisco 7900's and 3Com VCX 3100
>series phones work SIP to SIP if they download the protocol from the
>Vendor call centers?

At least in the 79xx's case, the phone actually downloads firmware updates
from a TFTP server; by changing the name of the image to use, you can make
it run SCCP/CallManager, SIP, MGCP (on the 7940/7960) or H.323 (on the
7905G) firmware. Note that you can't have multiple firmware images running
at once; you have to pick one. The phones have internal flash memory so they
don't have to download firmware every time, only when it's updated or
changed; they always download their configuration info from a set of text
files (SIPDefault.cnf, SIP<macaddr>.cnf) every time they boot, though. Also
note that Cisco's super-low-end phones like the 7902G and 7910G only support
SCCP, and can't be changed; Asterisk has rudimentary support for SCCP, but I
don't know how functional it is.

I haven't looked at the 3Com phones, so I'm not sure exactly how they
operate, but I imagine it'd be similar to the Ciscos.

-lee