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RSVP questions

Hello All

I am starting out new with RSVP and have read some documents on Cisco's website regarding the RSVP configuration. I have to say I still feel a bit lost with RSVP.

Firstly a description of my network. I have a 6 site WAN. Every site has a VoIP phone. Each Cisco 1841 at every site has hard QoS enabled where a specific amount of b/width had been assigned to the QoS and the remaining bandwidth is used for data. The head office has the internet connection which is used for external calls via the PBX. That said I would now like to configure RSVP but there are a few config questions.

From the Cisco doc it seems I can only have 2 sites to use RSVP? Is that correct? I don't think I believe that, but I would like to confirm this.

looking at the following command:

ip rsvp bandwidth interface-kbps single-flow-kbps ->

  1.) If I have a multi site, do I need to configure the single-flow-kbps?

  2.) How will this affect traffic flow? (ie will it slow down multiple sites or not)

ip rsvp reservation command has session-dport & sender sport. However the VoIP phones use rtp & sip, so that means I have multiple destination & source ports. Can I go ahead and put this command in several times for each port used by rtp & sip?

A problem I noticed on my RSVP reservation command is that the router changes the sender-address to Why is that? How can I fix that and prevent it from happening?


Hall of Fame Super Silver

Re: RSVP questions

Hello Willemvw,

if your IP PBX is a Cisco Call Manager with appropriate release you may want to consider location based Call Admission Control with RSVP.


as you have noted IP Phones are not able to perform reservations.

The idea with RSVP agent is to deploy media termination points MTP so that a call between phone1 in HQ and phone2 in siteM actually uses 3 VoIP call legs: phone1 to RSVP agent of HQ, RSVP agent of HQ to RSVP agent of site M, RSVP agent of site M to phone2.

In this case RSVP is used just to check BW availability between a pair of locations/sites, if RSVP does not succeed depending on some call manager settings the call can fail or it can be classified as best effort (with DSCP marking down to 00 instead of EF).

In an hub and spoke solution, the ip rsvp bandwidth configured on the branch site allows to control how you divide the bandwidth between sites and allows also to take in account calls between branch sites.

on HQ side the RSVP agent will have an ip rsvp bandwidth configured for the aggregate bandwidth.

Doing so the first RSVP agent to deny a call should be the branch router.

CUCM allows to enable RSVP enabled CAC between pairs of sites.

In your case you should deploy locations and regions in a way that all branch offices have theri own region and their own locations.

each phone has to be able to reach the local RSVP agent in its MRGL (media resource group list) in order to use it.

The CUCM coordinates all the signalling and instructs the phone to setup an RTP stream with the MTP / RSVP agent


SRND CAC chapter

Hope to help