Its been a while since I updated. We completed some work on MGCP, H323 and SIP, but I felt they were incomplete for use on the blog. I will get those up as soon as I get the rest of the info. I may also do it in a part 2, but for now lets talk about gatekeepers.
What are they?
In MMA they are refered to guys who can beat any other fighter in there weight class on any given night, but for some reason or another they can't muster up enough win's to get the title shot. O
Any other definition.
Well in the world of Voice/Video they can be used for a few task.
Address resolution
Admission Control
Bandwidth management
Zone Management
Call Authorization
Address Resolution
the number you dial has to be turned into a IP address so we can reach the distant endpoint, so it does "Resolution" kinda similar to DNS.
Admission Control.
You can't just make a call when a gatekeeper is in town. Gateways have to go out to the gatekeeper and request for a call to be placed
Bandwidth Management.
When we are using multiple clusters the location function doesn't work as we have different call managers around so the gatekeeper can provide CAC, by keeping track of the calls being made. This gets pretty funky with how G711 under uses the bandwidth and G729 over uses the bandwidth and we will cover this later on.
Zone Management.
Gatekeepers keep track of all the gateways in there zone through a registration process. Gateways just can't come online with talking to the gatekeeper 1st.
Call Authorization
Gatekeepers can control access to certain gateways. You can use a AAA server with Radius to get this to work.
Gatekeeper signalling
H323 uses a H225 setup messages before it send the H245 messages for capabilities. When using gatekeepers for signalling we still use H225, but we use a form called Ras. So H225 Ras is used for the signalling between gateways and gatekeepers. and there are several sub messages when using them. Stay tuned as we break down the gatekeeper signalling and call flow in the next post.
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