BT Broadband Voice with Asterisk

Introduction and Disclaimer

While I work for BT, none of this material is authorised, approved or in any way endorsed by BT. No BT internal documentation or information has been used when investigating it or writing it.

System Hacks

It is impossible to configure most 3rd party clients including Asterisk to work with BT Broadband. Asterisk requires the right side of a SIP address to resolve (so do most other SIP clients). That is not the case for BT Broadband voice.

The simple workaround for this is to dig for the current proxy addresses and put them in /etc/hosts as addresses for the domain portion of the SIP address. The proxy is: sp2.btsip.bt.net. Dig on this returns

;; ANSWER SECTION:
sp2.btsip.bt.net.       1       IN      A       62.239.169.132
sp2.btsip.bt.net.       1       IN      A       62.239.169.152
sp2.btsip.bt.net.       1       IN      A       62.239.169.168
sp2.btsip.bt.net.       1       IN      A       62.239.169.204
sp2.btsip.bt.net.       1       IN      A       62.239.169.212
sp2.btsip.bt.net.       1       IN      A       62.239.169.232
sp2.btsip.bt.net.       1       IN      A       62.239.169.240

As a BT employee I cannot say what I really think about this DNS TTL, regardless of how much I want to say it. In any case, in order for asterisk to work we will effectively hardwire this address locally so we toss a coin, take one address out of these and put it in /etc/hosts for btsip.bt.com

# /etc/hosts

X.X.X.X        btsip.bt.com

SIP Config

The SIP config will work only if the system has been hacked as in the previous section. The actual values for the password and username have to be obtained from the URL used by the BT Home Hub configurator.

register => PHONENUMBER:PASSWORD@btsip.bt.com/s

[btsip.bt.com]
secret=PASSWORD
fromdomain=btsip.bt.com
host=btsip.bt.com
outgoingproxy=sp2.btsip.bt.net
usereqphone=yes
call-limit=1
context=btline
canreinvite=no
disallow=all
allow=g729,ulaw,alaw,gsm
dtmfmode=info
nat=yes
type=peer                       ; we only want to call out, not be called
insecure=very
fromuser=PHONENUMBER
username=PHONENUMBER
authname=PHONENUMBER

-- AntonIvanov? - 21 Nov 2008