Cisco Support Community
Showing results for 
Search instead for 
Did you mean: 
Community Member

CAC Question


in Cisco Unified CallManager System Guide, Release 5.0(1), p80 it says:

Each audio call includes two streams, one in each direction. Video calls have four or six streams (that is,

two or three streams in each direction).

Thus, if the link to the a remote location has 160 kbps of available bandwidth,

that link can support one G.711 call at 80 kbps (in each direction), three G.723 or G.729 calls at 24 kbps

each (in each direction),

please can any one explain what is the previous speak mean?

what is the story of (one stream in each direction?) is it really needed to account g.711 bandwidth as 160k (both directions) not as every one can get once he reads any document on codec bandwidth (which is 80k with overheads...)

please advise



Re: CAC Question

So this looks like Cisco's marketing calculator was used here. For example Cisco marketing has a history of calling 100/full duplex = 200Mbit/s of bandwidth. It is marketing/sales people at their best :)

I wouldn't rely on those numbers of 160k. Instead, I'd use the following pages for my calculations. if you want to see the math, or use if you just want the numbers.

Good luck!


-- -Mark Turpin
Community Member

Re: CAC Question

so, I used the calculator, my selections:

codec: g711

payload size: 160 byte

compression: off

media access: ppp

tunnel: none

number of calls: 2


BW per call + 5% additional overhead=86.94 kbps


total BW (w/overhead) = 173.88 kbps

so, my older understanding is true (according to BW per call)

now, how is the (one in each direction) in my previous post can be understood from technical point of view


Community Member

Re: CAC Question



Re: CAC Question

Right so 86.94k/s per call is what you should be using to budget. Since you plugged in two calls, that's 173.88k/s. The one in each direction math is pure marketing. As in my previous post, Cisco is famous for saying that on Ethernet, if you have a 100 full duplex configured on a switchport it is 200Mbit/s of bandwidth. They say this because it is 100Mbit/s in Transmit and 100Mbit/s in Receive. They add the transmit and receive values together. Technically, the port only does 100Mbit/s but they market it as doing 200Mbit/s - which is technically wrong, but from a sales perspective, good. Hope this makes sense!


-- -Mark Turpin
CreatePlease to create content