You are wong my friend. L3 codec bandwidth means - (Payload + L3) x PPS x 8 L2 Codec bandwidth means - (Payload + L3 + L2) x PPS x 8
So here is an example for G711 and G729 for L3 BW calculations: G711 20ms Payload - 160 Bytes L3 - 40 bytes PPS - 50 (160 + 40) x 50 x 8 = 80000 bps = 80kbps G729 20ms Payload - 20 bytes L3 - 40 Bytes PPS - 50 (20 + 40) x 50 x 8 = 24000 bps = 24 kbps Now copressed RTP G711 20ms Payload - 160 Bytes L3 - 2 bytes PPS - 50 (160 + 2) x 50 x 8 = 64800 bps = 64.8kbps G729 20ms Payload - 20 bytes L3 - 2 Bytes PPS - 50 (20 + 2) x 50 x 8 = 8800 bps = 8,8 kbps On Thu, Feb 2, 2012 at 2:51 AM, Nathan Silvers <silver...@gmail.com> wrote: > Whoops started my own private convo with datucha... thought i would copy > everyone else just to get more eyes on it and hopefully bring some > clarification... > > From my understanding and using the Cisco doc the default g.711 packet > size is 206bytes(including 2 - 10ms 80 byte voice samples = 160bytes or > 1028bits) and using crtp is 168bytes using the calculations the pps is > 64kbps/1028 bits = 50pps which using the same calculations of packet size > is 1648 * 50pps = 82.4kbps total... and the same calculation using crtp > same voice load so 50 pps bw calculation is total packet 1344bits * 50pps = > 67.2kbps which is well below your layer 3 base of 80kbps and includes the > same voice payload as the non-compressed packets at 82.4... the 64 and 8 > kbps are the base layer 3 bandwidth for just the audio, not including any > headers... > > If anyone sees it differently please let me know, i would hate to walk > into the test and have this whole concept wrong... > > > On Wed, Feb 1, 2012 at 2:05 PM, datucha123 datucha123 < > datucha...@gmail.com> wrote: > >> >> G711 64kbps and G729 8kbps are not the L3 Bandwidth for those codecs. >> These are the Payload Bandwidths for those codecs. >> >> G711 and G729 on L3 are using 80 and 24 kbps respectavely. >> >> Here is the easy way to calcualte the Codec bandwidth: >> >> (Payload_Size + L3_Header + L2_Header) x PPS x 8 >> >> Where >> *Payload_Size* - is the Codec Sample Size (Bit Rate). G711 at 20ms has >> 160 bytes. G729 at 20ms has 20 Bytes and etc (you can find Sampling Rate >> info on Cisco.com) >> *L3 Header* - is the IP/UDP/RTP, which is 40 bytes, unless compressed >> RTP is used. If the UDP checksum is used then the L3 Header is compresesd >> up to 4 bytes, and if not used then up to 2 bytes. (UDP checksum is enabled >> on a VoIP Dial-peer: "ip udp checksum" command. By default is disabled) >> *L2 Header* - for Ethernet it is 18 bytes, for Frame Relay is 4 bytes >> (based on QoS SRND). >> *PPS* - Packets per Second. This is based on the Sampling Rate as well >> in the following way: PPS = 1000 / Sample_Size in ms. >> *8* - this is just bits. To convert Bytes into bits. >> >> >> >> On Thu, Feb 2, 2012 at 1:39 AM, Nathan Silvers <silver...@gmail.com>wrote: >> >>> Hi Everyone, >>> >>> Just starting out on my CCIE path and had a revelation that might not be >>> huge to anyone else but if it helps one person understand I've done a good >>> job... >>> >>> So I was struggling with Codecs how to calculate bandwidth required and >>> all the header and crtp if that is involved and then Cisco throws on Layer >>> 3 Bandwidth vs Overall bandwidth and from a humble voice guy who has >>> focused mainly on LAN connections I am lost... >>> >>> http://www.cisco.com/en/US/tech/tk652/tk698/technologies_tech_note09186a0080094ae2.shtml#topic1 >>> Using the above Cisco document which can help and confuse(as they use >>> median BW when it comes to the CRTP compression as it can be a 2 or 4 byte >>> header depending on if you are using the UDP checksum) so my exact >>> calculations were always off a few bytes.. >>> >>> So I was thinking about this logically and looking at the different >>> pieces of the puzzle, >>> Layer 3 is going to ultimately be the voice packets which is defined by >>> the codec.. 711 = 64kbs, 729 = 8kbs, etc... >>> Layer two includes my headers and such which add to the needed bandwidth >>> depending on if they are compressed >>> So if you use CRTP you only need and additional 3.6kbs for 711 which is >>> the 67.6kbs bandwidth, or 11.6kbs for 729 >>> Now if uncompressed the headers can add quite a bit more requiring the >>> need for 18.8kbs more to put 711 at 82.8kbs and 729 at 26.8kbs >>> >>> So if you see a question regarding layer 3 bandwidth it is always the >>> codec kbs, ie 711 is 64 and 729 is 8 regardless of any compression, the >>> type of connection etc.. more of a no brainer question >>> They Layer 2 bandwidth is where the savings are by chopping the 40byte >>> IP/UDP/RTP header into 2 byes (or 4 bytes if UDP Checksum is enabled.) >>> >>> Gotta love white boards and running through a few situations.. the cisco >>> doc has the calculations to go through and how changing the payload size >>> can adjust the Packets Per Second which affects the required Bandwidth. If >>> anyone else is struggling with this I highly recommend just writing it all >>> out and trying hypothetical situations. >>> >>> Hope this helps someone! >>> >>> >>> -- >>> "The biggest mistake people make in life is not trying to make a living >>> at doing what they most enjoy." >>> >>> - Malcolm Forbes >>> >>> Nathan Silvers >>> >>> >>> _______________________________________________ >>> For more information regarding industry leading CCIE Lab training, >>> please visit www.ipexpert.com >>> >>> Are you a CCNP or CCIE and looking for a job? Check out >>> www.PlatinumPlacement.com <http://www.platinumplacement.com/> >>> >> >> > > > -- > "The biggest mistake people make in life is not trying to make a living at > doing what they most enjoy." > > - Malcolm Forbes > > Nathan Silvers > >
_______________________________________________ For more information regarding industry leading CCIE Lab training, please visit www.ipexpert.com Are you a CCNP or CCIE and looking for a job? Check out www.PlatinumPlacement.com
