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New Member

Call Control Traffic SRND Calculations

Hi,

I am confused with the calculations for SCCP Call Control Traffic in the CUCM v8 SRND.

An equation of Bandwidth (bps) = 265 X (Number of IP phones and gateways in the branch) is provided with the assumption implied of 10 calls per hour per phone, this equation this matches the table provided, which for example states 100 phones using non-encrypted SCCP requires 27kbps for signalling.

The confusion comes when I look at the advanced formulas which allow you to specify a calls per hour (CH) per phone ratio. The equation provided is Bandwidth (bps) = (53 + 21 X CH) X (Number of IP phones and gateways in the branch), if we use the CH ratio of 10 (as per the above formula) I would assume this should mean (53+21 X 10) X  (No of Phones) however this would suggest 74k would be required for 100 phones, how can the two formulas vary so much?

Also can someone confirm the different requirements for call signalling between the CUCM the phone is actively registered too compared with the Standby CUCMs.

If anyone has a link to the relevant documents with the above formulas or can explain the method behind the SRND ones it is appreciated.

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Hall of Fame Super Silver

Call Control Traffic SRND Calculations

It is correct, (53 + 21 x CH) --> 53 + 21 x 10 --> 53 + 210 = 263, it must not be exactly 10 for CH hence 265.

Chris

3 REPLIES
Hall of Fame Super Silver

Call Control Traffic SRND Calculations

It is correct, (53 + 21 x CH) --> 53 + 21 x 10 --> 53 + 210 = 263, it must not be exactly 10 for CH hence 265.

Chris

New Member

Re: Call Control Traffic SRND Calculations

Thanks, that makes sense, the formula should be written as (53 + (21 * CH)) * (No of Phones).

I was reading it as (53 + 21 = 74 * 10 = 740) * 100 phones = 74000 bps rather than (53 + (21 *10)) * 100 phones = 26300 bps, obvious when you related it back to the actual figures.

Can anyone comment on Inactive Subscriber signalling, do you just remove the CH multiple from the equation as it isnt handling the call setup traffic just the keepalives etc? 

Hall of Fame Super Silver

Call Control Traffic SRND Calculations

Well, not really as this is simple algebraic equation, multiplication is done first with no need for parenthesis :-)

You don't need to worry about standby servers as all they receive from the phone is the keepalive every 30 seconds which is negligible, 4 bytes every 30 seconds even for thousands of phones does not add up to a lot.

HTH,

Chris

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