Location/Physical Bandwidth question

[g.grier]

I found the following in a CCO doc:

http://www.cisco.com/en/US/products/sw/voicesw/ps556/products_administration_guide_chapter09186a008011b432.html

"For purposes of location bandwidth calculations only, assume that each call stream consumes the following amount of bandwidth:

G.711 call uses 80 kbps

G.723 call uses 24 kbps

G.729 call uses 24 kbps

GSM call uses 29 kbps

Wideband call uses 272 kbps

Note Each call comprises two call streams. To improve voice quality, lower the bandwidth setting, so fewer active calls are allowed on the link to this location. Entering a value of zero allocates infinite bandwidth and allows an unlimited number of calls on the link."

***Do the statements "each call stream consumes the following amount of bandwidth" & "each call comprises two call streams" mean that a G.729 call can take up more that 24kbps (48kbps) in physical bandwidth?

I have done testing in a lab and confirmed that I can make G.729 calls with a location set to 24k and a G.711 call with 80k, but based on the information above this is only for one call stream.

Thank you in advance!

[dgahm]

Your testing tells you what you need to know -- the doc is wrong. I have done similar testing myself with the same results. Call Manager locations look at each G711 call as requiring 80kb. It is true that any call is comprised of a stream in each direction, but it makes little sense to say that a G711 call needs 160kb. That would be like saying a T1 is 3mb of bandwidth because you have 1.5 full duplex. It is worth noting that true bandwidth depends on layer 2. As an example G711 really takes 87kb over Ethernet, and G729 31kb.

The main thing is to understand how many calls your QOS can handle, based on real bandwidth requirements, and set the CAC accordingly. If you follow this basic rule you won't be adjusting the location bandwidth to improve voice quality.

[dweiner]

Actually, the doc is not wrong. These are the amounts CCM deducts from the value set for Location bandwidth for each call. As noted - 'For purposes of location bandwidth calculations only...'. Even though the actual bandwidth over the LAN/WAN is greater due to L2 headers, you should NOT deviate from these numbers when setting locations bandwidth in CallManager. You SHOULD be aware of actual bandwidth requirements in your LAN/WAN and then adjust the locations bandwidth accordingly. CallManager doesn't know what kind of network the calls will go over, so uses payload values for each call.

The SRND goes into good detail on actual bandwidth required in the LAN/WAN -

http://www.cisco.com/go/srnd

Look at the CallManager 4.0 SRND under "Bandwidth Consumption with Layer 2 Headers Included" in the WAN QOS Bandwidth Provisioning section.

The general guideline in the SRND is that voice bandwidth should not normally consume more than 33% of the WAN link, except in very low bandwidth situations. Whatever bandwidth value you use in locations, you should make sure that your priority queue (with LLQ) is at or above that value so that all voice bearer traffic is prioritized acros the LAN/WAN.

[dgahm]

These statements in the doc are very misleading:

"For purposes of location bandwidth calculations only, assume that each call stream consumes the following amount of bandwidth:

G.711 call uses 80 kbps

Note Each call comprises two call streams"

That appears to be saying that Call Manager would deduct 160kb for a G711 call, which is wrong.

Call Manager is not using payload values as you stated, that would be be 64kb for G711, and 8kb for G729. The locations value includes the IP and UDP headers, but leaves off the layer 2 header.