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Beginner

Bandwidth - SCCP IP Phone Registration Process

Hello, all

I have a question regarding bandwidth requirements for Cisco IP Phones to register on CUCM using SCCP protocol. I was able to find a document, which clearly describes network interfaces for CUCM - http://www.cisco.com/c/en/us/td/docs/voice_ip_comm/cucm/srnd/8x/uc8x/netstruc.html , but my question is a bit specific.

See, we have a remote site and our ISP is using policing to provide some QoS mechanics: for all voice traffic - audio and signalling one policy-map is used to police and LLQ traffic with bandwidth allocation: 368 Kbps . Exceed and violation actions is set to drop. To my mind it is a bit strange setup, but anyway my question is: is there any bandwidth requirements for IP Phone to register on CUCM? Due to as it is trying to access TFTP server, UDP is used and in case of policing a traffic this packets will be simply cut off and phone won't be able to register at all?

Thank you in advance.

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VIP Advisor

Hi,

 

Yes there is a bw required for phones to register. This is available in SRND

The formulas for calculating the bandwidth required for SCCP and SIP with and without Encryption are as listed below. It is assumed that the average call per hour per phone is 10.

 

Equation 1A: Recommended Bandwidth Needed for SCCP Control Traffic without Signaling Encryption.

Bandwidth (bps) = 265 (Number of IP phones and gateways in the branch)

 

Equation 1B: Recommended Bandwidth Needed for SIP Control Traffic without Signaling Encryption.

Bandwidth (bps) = 538 (Number of IP phones and gateways in the branch)

 

Equation 2A: Recommended Bandwidth Needed for SCCP Control Traffic with Signaling Encryption.

Bandwidth with signaling encryption (bps) = 415 (Number of IP phones and gateways in the branch)

 

Equation 2B: Recommended Bandwidth Needed for SIP Control Traffic with Signaling Encryption.

Bandwidth with signaling encryption (bps) = 619 (Number of IP phones and gateways in the branch)

 

To get a more accurate value, the average calls per hour per IP phone can be varied and the following formulas will need to be applied:

 

Equation 3A: Recommended Bandwidth Needed for SCCP Control Traffic for a Branch with No Signaling Encryption.

Bandwidth (bps) = (53 + 21 CH) (Number of IP phones and gateways in the branch)

 

Equation 3B: Recommended Bandwidth Needed for SIP Control Traffic for a Branch with No Signaling Encryption.

Bandwidth (bps) = (138 + 40 CH) (Number of IP phones and gateways in the branch)

 

Equation 4A: Recommended Bandwidth Needed for SCCP Control Traffic for a Remote Branch with Signaling Encryption.

Bandwidth with signaling encryption (bps) = (73.5 + 33.9 CH) (Number of IP phones and gateways in the branch)

 

Equation 4B: Recommended Bandwidth Needed for SIP Control Traffic for a Remote Branch with Signaling Encryption.

Bandwidth with signaling encryption (bps) = (159 + 46 CH) (Number of IP phones and gateways in the branch)

 

Regarding TFTP, policing won't stop TFTP but will reduce the transfer rate which means that your phones will take more time to register. However, TFTP transfer won't take place very frequent. It will only trigger when you have upgrades, performed factory reset on a phone, or installed new phone with old firmware version.