Low, Adam
2004-Mar-02 04:00 UTC
[Asterisk-Users] Small office requirements - Can this be done ?
I've done a fare amount of analysis on codec bandwidth requirements and you should remember that you typically will require more bandwidth over ADSL than you would over any other technology. I estimate a requirement of around 108Kb (on the wire) per G.711 channel rather than 86kb over straight PPP/HDLC based connections. Why I hear you ask ? The following calculations are based on G.711 PCM running at 20ms samples resulting in 200 byte packets (default for most codec implementations). 200 bytes G.711 packet + 8 bytes AAL5 overhead = 208 bytes 208 bytes fit in 5 cells of 48 bytes payload 5 cells are 265 bytes. VoIP over ATM AAL5MUX thus has an overhead of 21.51% VoIP G.711 conversation sends 50 packets per second. This uses 250 cells per second. This causes approximately 10 OAM5 cells to be sent over the duration. The total bitrate is thus (250 + 10) * 53 bytes * 8 bits = 110240 bits/second = 107.66Kbit/s Steve Kennedy wrote:>On Mon, Mar 01, 2004 at 07:08:29PM -0600, Michael Graves wrote: > > > >>I have disagree about the ADSL. I have a1.5 Mbit/512kbit service from >>Covad (in the US Southwest) and I have sustained 4 calls without a >>problem. I prefer to use GSM over G.711to squeeze it down, but that is >>my choice. I don't feel that call quality is substandard. >> >> > >That's the crunch (1.5/512) ... it's actually the 512 which is relevent. >Virtually all DSL in the UK is a wholesale product from BT (they have >about 2 million customers, Easynet who local loop unbundle may have >20,000, the rest of the providers maybe another 10,000 between them). > >All BT ADSL is 256K upstream, all BT DSL is contented (in theory 20:1 >and 50:1, but actually a lot less than that), there are a few providers >doing their own contention over BT's product. > >However the 256K upstream is still the limiting factor, so you can get >one, and MAYBE two VoIP lines over it. If BT would up the upstream to >512, you could probaly get 4 out of it .... > > >Steve > > >On the UK DSL using G.711 you should easily get 2 concurrect calls, G.711 uses about 84k(incl overhead) in each direction, so 2 calls would be 168K (of the 256k) If you switch o GSM or iLBC you should get 6 concurrent calls, and if you were to use IAX2 trunking you could *maybe* squeeze another one.. Other codecs could offer even more but I haven't tested them.. Later.. ********* DISCLAIMER ********* This message and any attachment are confidential and may be privileged or otherwise protected from disclosure and may include proprietary information. If you are not the intended recipient, please telephone or email the sender and delete this message and any attachment from your system. If you are not the intended recipient you must not copy this message or attachment or disclose the contents to any other person
David Uzzell
2004-Mar-02 04:20 UTC
[Asterisk-Users] Small office requirements - Can this be done ?
Low, Adam wrote:> I've done a fare amount of analysis on codec bandwidth requirements and you should remember that you typically will require more bandwidth over ADSL than you would over any other technology. I estimate a requirement of around 108Kb (on the wire) per G.711 channel rather than 86kb over straight PPP/HDLC based connections. > > Why I hear you ask ? > > The following calculations are based on G.711 PCM running at 20ms samples resulting in 200 byte packets (default for most codec implementations). > > 200 bytes G.711 packet + 8 bytes AAL5 overhead = 208 bytes > 208 bytes fit in 5 cells of 48 bytes payload > 5 cells are 265 bytes. VoIP over ATM AAL5MUX thus has an overhead of 21.51% > VoIP G.711 conversation sends 50 packets per second. This uses 250 cells per second. > This causes approximately 10 OAM5 cells to be sent over the duration. > > The total bitrate is thus (250 + 10) * 53 bytes * 8 bits = 110240 bits/second = 107.66Kbit/sSo for us Dummies out here :) who just know it works. This would mean that if you had a 512/256 aDSL and a 256 ISDN connection you would be able to have more channels over the ISDN? David> > > Steve Kennedy wrote: > > >>On Mon, Mar 01, 2004 at 07:08:29PM -0600, Michael Graves wrote: >> >> >> >> >>>I have disagree about the ADSL. I have a1.5 Mbit/512kbit service from >>>Covad (in the US Southwest) and I have sustained 4 calls without a >>>problem. I prefer to use GSM over G.711to squeeze it down, but that is >>>my choice. I don't feel that call quality is substandard. >>> >>> >> >>That's the crunch (1.5/512) ... it's actually the 512 which is relevent. >>Virtually all DSL in the UK is a wholesale product from BT (they have >>about 2 million customers, Easynet who local loop unbundle may have >>20,000, the rest of the providers maybe another 10,000 between them). >> >>All BT ADSL is 256K upstream, all BT DSL is contented (in theory 20:1 >>and 50:1, but actually a lot less than that), there are a few providers >>doing their own contention over BT's product. >> >>However the 256K upstream is still the limiting factor, so you can get >>one, and MAYBE two VoIP lines over it. If BT would up the upstream to >>512, you could probaly get 4 out of it .... >> >> >>Steve >> >> >> > > On the UK DSL using G.711 you should easily get 2 concurrect calls, > G.711 uses about 84k(incl overhead) in each direction, so 2 calls would > be 168K (of the 256k) > > If you switch o GSM or iLBC you should get 6 concurrent calls, and if > you were to use IAX2 trunking you could *maybe* squeeze another one.. > > Other codecs could offer even more but I haven't tested them.. > > Later.. > > > ********* DISCLAIMER ********* > > This message and any attachment are confidential and may be privileged or otherwise protected from disclosure and may include proprietary information. If you are not the intended recipient, please telephone or email the sender and delete this message and any attachment from your system. If you are not the intended recipient you must not copy this message or attachment or disclose the contents to any other person > > > _______________________________________________ > 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 > >
Low, Adam
2004-Mar-02 04:43 UTC
[Asterisk-Users] Small office requirements - Can this be done ?
> So for us Dummies out here :) who just know it works.Yep, it sure does, I thought it was something people might find interesting. Its certainly been a challenging subject for me to try and provide reliable and high quality voice service over ADSL. In my experience it seems to depend a hell of a lot on the QoS deployed on the ATM network behind the DSLAM's. Obviously a single cell being dropped every 5 cells would effectively cause every G.711 IP packet to be lost. Here in Holland I ported my KPN (legacy incumbent) telephone number to my home VoIP service about 4 months ago. It has been running over a BBNED ADSL service and works great 99.9% of the time. Although during recently virus/worm outbreaks I have found people complain they hear my voice choppy, probably due to the contention of all the other ADSL connection upstreams as they propagate those viruses/worms.> This would mean that if you had a 512/256 aDSL and a 256 ISDN connection > you would be able to have more channels over the ISDN?Thats right, I am not aware of any ADSL providers that actually provide their stated service level at an IP layer rather than at the ATM layer but maybe they are out there ... The exact calculation depends on how your encapsulating IP over the 256k ISDN connection. I will assume your actually getting 4x B channels with either multi-link PPP (haven't calculated the overhead for this one) or a CSU/DSU converting to X.21/V.35 (preferable). You should be able to push 3 concurrent G.711 channels over that 256k ISDN service assuming 86Kbps per channel.> DavidHere's a little table I put together for our capacity planning team: G.711 over Ethernet = 95 Kbps per channel G.711 over IP/PPP = 86 Kbps per channel G.711 over ADSL/ATM = 108 Kbps per channel G.729 over Ethernet = 39 Kbps per channel G.729 over IP/PPP = 30 Kbps per channel G.729 over ADSL/ATM = 45 Kbps per channel ********* DISCLAIMER ********* This message and any attachment are confidential and may be privileged or otherwise protected from disclosure and may include proprietary information. If you are not the intended recipient, please telephone or email the sender and delete this message and any attachment from your system. If you are not the intended recipient you must not copy this message or attachment or disclose the contents to any other person
John Fraizer
2004-Mar-02 06:34 UTC
[Asterisk-Users] Small office requirements - Can this be done ?
David Uzzell wrote:> > So for us Dummies out here :) who just know it works. > > This would mean that if you had a 512/256 aDSL and a 256 ISDN connection > you would be able to have more channels over the ISDN? > > DavidIt all depends on what excapsulation your aDSL uses. It boils down to encapsulation overhead with "overhead" being the number of bits _in_addition_to_your_payload_ that are required to transit your payload. John