Bandwidth and Location

[Pramoth Sundaram]

Hi All

1 .Does any know what is the exact relation ship between Bandwidth available in the Circuit and Bandwidth allocation on Location parameters on CUCM.

2. How to scope the required bandwidth per site.

Thanks

[ronpatel]

HI Pramoth,

There is no relateion between actual BW used and BW allocated using Location parameter. In CUCM location parameter, we consider how many number of calls which we can pass using standard values for G711 or G729 calls.

8 kb/s for (G.729) and 64 kbps for G711 calls. So if we says 8kbps calls should go between two location, so location configuratoin will only allow only one call between two location but actualt BW taken by that call between actual physical location would be as per below link

Below is exact BW used by a Cisco VOIP calls. It hs formula related to it.

http://www.cisco.com/en/US/tech/tk652/tk698/technologies_tech_note09186a0080094ae2.shtml

Let me know if you need more details.

Regards

Ronak Patel

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[Marek Janecek]

@Ronak

Good answer but for Location calculatios is used little bit different BW for each codec ( in order to count with L2 and L3 overhead )

for example G.711 uses 80kb/s, G.729 24kb/s

If you want other codecs, refer to (for example):

http://www.cisco.com/en/US/docs/voice_ip_comm/cucm/admin/7_1_2/ccmsys/a02cac.html#wp1033331

HTH

[Robert Thomas]

CUCM takes into consideration some overhead and doesn't calculate based on the payload only. This is the reason for using 80kbps and 24kbps. This amount cannot be modified. You would need to base your calculations for amounts of calls based on this.

[Chris Deren]

Correct, so when calculating the bandwidth you cannot just use you LLQ values from QoS configuration. Consider an example of a site with T1 MPLS connection where 33% of it is assigned to voice in LLQ configuration.  Doing the math yileds:

1536 kbps / 3 = 512 kbps, which can support 512/ 32.8 (G729 call with overhead over MPLS) = 15.6 ~ 15 (round down) Calls

You cannot just plug in 512 as the bandwidth in CUCM Location, you need to convert to what CUCM thinks is needed for 15 G729 calls which is 15 * 24 = 360 kbps

Notice the significant discepency, if you were to plug in 512 you sure would cause quality issues.

HTH,

Chris