G729 How much bandwdth ?

[hassepedro50]

Hi

Can someone please clarify these issues

The gatekeeper manuals say that G729 uses 16Kbps bandwidth

IS The G729 voice payload is 8 bytes and the overhead can go up to 24 bytes if we are not using cRTP or 4 or 2 bytes with RTP ?

Is it true that in spite of the packet size, G729 just needs 16kbps bandwidth or do we need to take in account other factors? Which ones?

I would appreciate very much this clarification. Thanks

[alessandro.dona · Accepted solution]

About your second question!

It's false

the formula to calculate bandwith is:

[(layer2header+(ip_head+udp_head+rtp_header)+samplesize)/samplesize]*speed codecs

EX:g729 l2=framerelay no CRTP

[(6+40+20)/20]*8000=26,400 bit per second

[alessandro.dona · Accepted solution]

To clarify:

If you mean only the codec bandwith the only think you have to keep into account is codec speed and samplesize

there is a g729 version whose cedec speed is 16

[alessandro.dona]

About your first question

paylod should be:

(sample_size*codec speed)/8=0.02*8000/8=20

overhead with crtp is (2 without udp crc checksum and four with crc checksum)

[PETER NEGUS]

The bandwidth figures used by the Gatekeeper are quite arbitary, and do not reflect real life - only the rather silly H323 v3 series recommendation. In real life, a G729 call will take 24K of level3 bandwidth, and about 27K of level 2, and a G711 will take 80K of level3, corresponding to 83K of level2. So in planning your system bandwidth requirements, you need to use the real life figures. In setting up your gatekeeper call admission control, you need to estimate the ratio of G.729 to G.711 (and fax bypass) calls, and work out the "gatekeeper" view of this bandwidth.

It's mad, I know, but it keeps us all employed...

[jamesfeely]

Call Admission Control only uses the payload size. If you're creating bandwith limitations for zones in a gatekeeper, g729 = 8k, g711 = 64k.

http://www.cisco.com/en/US/partner/tech/tk652/tk701/technologies_white_paper09186a00800da467.shtml#903519

If you're trying to do capacity planning or QoS, you have to consider payload, layer 3 overhead, and layer 2 overhead.

the bandwidth calculator may help: http://tools.cisco.com/Support/VBC/do/CodecCalc1.do