[c-nsp] ISDN to Mauritius / change bearer to speech onoutgoingcalls

[John Edwards]

Michael Markstaller wrote:

> sure, but it looks like they don't get a single packet from each other..

> Oct 29 18:37:21 MEST: ISDN BR0 Q931: TX -> SETUP pd = 8  callref = 0x09
>         Bearer Capability i = 0x8090A3
>                 Standard = CCITT
>                 Transer Capability = Speech
>                 Transfer Mode = Circuit
>                 Transfer Rate = 64 kbit/s
>         Channel ID i = 0x83
>         Called Party Number i = 0x80, '000230xxxxxxx'
>                 Plan:Unknown, Type:Unknown

The bearer cap  0x8090a3 means that the call is designated as being 
humans talking to each other, and specifically allows the signal to be 
munged by a compression codec that expects to deal with voice. If the 
connection to Mauritius is via a Satellite this is almost certainly the 
case.

The one you want is 0x9090a3, or 'audio' which specifies a 64K digital 
bearer end to end. This is usually used by analogue-to-isdn interfaces, 
or some kinds of DOV routers and linux boxes that aren't Cisco. Cisco 
routers can accept such a call, but there was no dialer-map to make one 
last time I looked.

One of the ways you could test this out is to try a 56K modem call 
across the circuit - if it can negotiate a V.90 connection faster than 
33.6K then it's probably a real ISDN channel (although latency may also 
interfere). If it cannot, then chances are it's being compressed or even 
a VoIP service in the middle somewhere.

John Edwards