Whats the differnec between a gatekeeper and a Call Agent?

Bosefus

I am working on my ONT and in the first chapter they talk about the different parts of a packet based phone network.

The definitions they give for a gatekeeper and call agent are identical except the book states that a call agent is used on centralized setups.

However, the diagrams they use show both.

I am thoroughly confused, can anyone clarify what the difference between the two is?

Thanks!

Edit: Sorry, did not realize I was in the CCIE board, and I am unable to move the post or delete and repost.

networker050184

I think in the ONT material it refers to them as follows.

A Call Agent is the central processing device in an MGCP set up.

A Gatekeeper provide centralized dial plans, translations, and some CAC in an H.323 environment.

dynamik

The gate keeper is like the manager. It handles the logistics and takes care of the call agent.

The call agent is the one you physically interact and what does the actual work.

Oh wait, you guys are talking about networking...

accely

I'm also on the ONT and this is confusing me as well ;P

Bosefus

What networker saying makes sense to me. Later on in the chapter they say that only the centralized protocol/model uses a CA and the other two use a gatekeeper.

I just wish they would not include both in the introductory diagram in the book as it is very confusing.

Cucumber

Yeah networker is spot on.

I dont remember the ONT book specifics but I have worked with gatekeepers and voice gateways for the last 3 years.

I use Gatekeepers for managing the dial-plan and signaling for H.323 gateways.

Imagine having hundreds of routers, each router having analog phones attached to them using FXS cards. I.e. the network I work for has more than 1000 routers having analog extensions.

Now picture yourself having to create/update the voip dial-peers on every single router in order to have people making extra-site calls for the 1000 sites. It would drive you mad on day one (you would have to administer about 1000 voip dial peers on every router).

So thats why the gatekeepers come into picture, you create/update the voip dial-peers for the whole network in a couple of gatekeepers and you are set (that way you need only 1, yes 1 voip dial-peer per router). Notice I said voip dial-peers, you still have to create pots dial-peers on each router for each analog phone attached to said router. Ie. if you have two phones on a router, you would need two pots dial-peers and 1 voip dial-peer and thats all.

So in summary you specify extension numbers on each router (pots dial-peers) and you have several gatekeepers for extra-site calls (voip dial-peers). That sounds very distributed to me, although you have some sort of centralized administration points. (the gatekeepers). Even if your gatekeepers die, you still can pick up any phone and you would get a dial tone, because the dial tone is gnerated locally at each router.

On the other hand if you attach phones into a cisco box that acts as a MGCP gateway, you need some other box that tells that MGCP gateway what to do with them (a Call Agent), i.e. you need CallManager for that. In that scenario, you configure the extension numbers in CallManager, not even in the MGCP gateway! In other words, if you had many MGCP gateways with lots of phones attached to them you would not have to configure extension numbers on the gateways, you would do everything on CallManager. If the CallManager cluster dies, your phones completely die too. That sounds very centralized to me.

Bosefus

Thank you for the excellent explanation and great example.