TVOICE – Multisite Bandwidth- Call Admission Control – Dial-Peer Limitations and CUCM Locations

Intro: While QoS protects voice from data, what if you have to protect voice from voice? The journey of bandwidth management has led us to Call Admission Control (CAC). This Nugget focuses specifically on dial-peer based restrictions and CUCM Locations (both basic and RSVP-Enabled Locations). 


Voice will always win over data with QoS. LLQ is a particularly common configuration for voice.

How do we deal with ‘voice vs voice’ in these situations? Protect voice… from voice! Hence CAC!

Simple Way – Dial-Peer Limitations

Simple command entered under dial-peer to limit them.

dial-peer voice 10 pots
max-conn 23

More Complex – CUCM Locations

  • Simple – Create Locations… Assign bandwidth value and then put devices inside! Designed for centralised model.
  • Device – Phone/Gateway Assigned to Location (BW Unlimited)
  • Interlocation calling has bandwidth restrictions assigned
  • Works well in ‘Hub and Spoke’ toplogies
  • RSVP Aware Locations Solve more complex topologies


Reservation for bandwidth (end to end)

Two key messages: PATH and RESV

CUCM sends message to Gateway ‘Hey I need 100Kbps!’

A PATH message is sent across the chain, all routers reply back with a RESV to confirm the reservation. Or possibly NO, I don’t have the bandwidth.

  • CUCM looks at Location configuration, relevant to destination call.
  • MTP point will now kick in… (Terminates/bridges audio)
  • 1st Leg between IP Phone and GW, 2nd Leg = Router to Router, 3rd Leg = Router to Destination IP Phone
  • Passthrough CODEC
  • Implement Reservation end to end!
  • Routers must be configured for this. DSPFarm must be setup for MTP and also registered with UCM. *Same concept as previous XCODE example – Use a MRGL/MRG to set your MTP resource. MTP is required on hardware IOS for this to work.
  • Interface level commands on routers for RSVP values.
  • Relies on Routing Table/Protocol is topology aware!

RSVP Configuration

  • RSVP Service Parameters (Cisco CallManager Service->RSVP 1st 4 items…Default Interlocation RSVP Policy – No Reservation/Optional/Mandatory etc.. Retry Timer – 60, Mid-call Retry Counter – 1, Mid-call error handle option – If Retry Counter Exceeds)
  • RSVP Voice Gateway Configuration
    (Almost same as XCODE example)


  • MTP Addition
  • RSVP Location Configuration