Hi Friends, Something I'd like to shed some light on if possible - how is it that a single ISDN conversation only uses 64K for bidirectional communication (using ulaw, correct?), but on several occasions now have seen references to ulaw voip conversations using 64K per side of the conversation, plus packet overhead (http://www.zytrax.com/tech/protocols/voip_rates.htm - seems to be down now - plus other references) for a total of over 128K per ulaw 'full duplex' voice conversation? Thanks Tim
I assume ISDN accomplishes this since the PRI is set to use channel 24 for signaling. Your 64K channels is data and the control overhead is sent on the signaling channel. Actually, everything I have seen is around 80K full duplex for a uLaw channel with overhead. That is point to point... W -----Original Message----- From: asterisk-users-bounces@lists.digium.com [mailto:asterisk-users-bounces@lists.digium.com] On Behalf Of Tim Pushor Sent: Monday, July 18, 2005 9:22 AM To: Asterisk Users Mailing List - Non-Commercial Discussion Subject: [Asterisk-Users] Codecs and bandwidth Hi Friends, Something I'd like to shed some light on if possible - how is it that a single ISDN conversation only uses 64K for bidirectional communication (using ulaw, correct?), but on several occasions now have seen references to ulaw voip conversations using 64K per side of the conversation, plus packet overhead (http://www.zytrax.com/tech/protocols/voip_rates.htm - seems to be down now - plus other references) for a total of over 128K per ulaw 'full duplex' voice conversation? Thanks Tim _______________________________________________ Asterisk-Users mailing list Asterisk-Users@lists.digium.com http://lists.digium.com/mailman/listinfo/asterisk-users To UNSUBSCRIBE or update options visit: http://lists.digium.com/mailman/listinfo/asterisk-users
Tim Pushor wrote:> Hi Friends, > > Something I'd like to shed some light on if possible - how is it that a > single ISDN conversation only uses 64K for bidirectional communication > (using ulaw, correct?), but on several occasions now have seen > references to ulaw voip conversations using 64K per side of the > conversation, plus packet overheadISDN, like T1, is full duplex. So your 64K channel is 64K in each direction, up and down. B.
Of course - ISDN is bi-directional. I guess saying that ULAW takes 130K+ bandwidth depending on the framing type (local lan, w/1 hop, vlan, etc) is not very clear. Thats total bandwidth. With lots of us at home and small business using asynchronous connections - we need to keep that in consideration. Thanks for helping clear that up. Tim Steve Kennedy wrote:>On Mon, Jul 18, 2005 at 11:28:57AM -0600, Tim Pushor wrote: > > > >>>ulaw is 64Kb/s over a p2p link (or circuit switched in the PSTN world). >>>If you then convert to IP there's at least a 20% overhead, can be more >>>depending on the situation. >>>Might take 100Kb/s >>> >>> >>Thats what I thought as well, so I was wondering why ISDN is 64K, but >>VOIP RTP/ulaw has been documented to be 64K per direction + packet >>overhead (132K+) >> >> > >ISDN is 64K per direction too, on a synchronous link i.e. 64K in both >directions. > >I guess if you packetise etc then you've got to worry about both >directions and the bandwidth to supoort it ... > > >Steve > > >