CAC On Voice Gateway/CME part 1

To read part 1 , click here

To read part 2 , click here

To read part 3 , click here

To read part 4 , click here

Call Admission Control (CAC) is a concept that applies to voice traffic only—not data traffic.

CAC is therefore a deterministic and informed decision that is made before a voice call is established and is based on whether the required network resources are available to provide suitable QoS for the new call.

Connection Admission Control is defined as the set of actions taken by the network during the call set-up phase (or during call re-negotiation phase) in order to determine whether a connection request can be accepted or should be rejected (or whether a request for re-allocation can be accommodated)

Ref :
Cisco Web Site

Maximum connection on a dial-peer

suppose you have 2 ways for outgoing call (SIP provider and PST) . In general  SIP provider are less expensive than PSTN , so you want most of your calls to go out through your wan connection to your SIP provider

  1. Suppose that your WAN connection bandwidth is 1.5 Mbit/s = 1500 Kbps
  2. Codec being used is G711u
  3. The maximum you want to use at a time is 50% of the WAN bandwidth

G711 use 64 Kbps , but in reality and after adding all headers it reach 85 Kbps , to be in the safe side I will consider that G711 will consume 90 Kbps.

So let’s calculate the maximum calls we want to establish to the sip provider at a time,

90 Kbps X 8 calls = 720 Kbps , is will make almost 50 % of the bandwidth

The idea is to create 2 dial-peers  the first will direct calls to the SIP provider , the sconde will direct the calls to the PSTN

Cisco2821(config)#dial-peer voice 40 voip
Cisco2821(config-dial-peer)# destination-pattern 9.T
Cisco2821(config-dial-peer)#codec g711ulaw
!!we give the highest priority to this dial peer
Cisco2821(config-dial-peer)#preference 0
!!only 8 calls at a time can be established using this dial-peer
Cisco2821(config-dial-peer)#max-conn 8
Cisco2821(config-dial-peer)# session target

The dial-peer below will be used for PSTN connection

Cisco2821(config)#dial-peer voice 41 pots
Cisco2821(config-dial-peer)# destination-pattern 9.T
Cisco2821(config-dial-peer)#preference 1
Cisco2821(config-dial-peer)#port 0/0/0

There is no need to use the max-conn command in dial-peer 41 , whenever you reach the maximum calls allowed by your provider the caller will hear a busy tone

Resume :

Calls will go out to the SIP provider , we allow only 8 concurrent calls at the same time . the call number 9 will go to the PSTN provider

This entry was posted in CallManager Express, Gateway, LAB and tagged , , . Bookmark the permalink.

3 Responses to CAC On Voice Gateway/CME part 1

  1. Pingback: CAC On Voice Gateway/CME part 2 | elhallak

  2. Pingback: CAC On Voice Gateway/CME part 3 | elhallak

  3. Pingback: CAC On Voice Gateway/CME part 4 | elhallak

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