Posts Tagged ‘gateway’


Over the coming weeks I will be running a new series here on Troubleshooting Voice. I often have students in class that report to me that one of the most difficult parts of their CCIE Voice exam experience was having to deal with the inner workings of some of the protocols and how to read and decipher them accurately. I have also begun to see this more and more across the various mailing lists and forums, and so I decided it was time to start an entire series on these not-to-be-feared topics. Since these protocols are covered quite in-depth in the CCNP Voice course (most specifically in the CVOICE portion), I highly encourage people starting out in Unified Communications, not to skip the lower level courses, and to really dig in at that CCNA Voice and then CCNP Voice level, before going into the CCIE Voice. At each level something is presented that is not explained at the next level, so it really is crucial to go through each progression of the track in a sequential and systematic order. This goes especially for those who might already have a CCIE, and think they understand what the CCIE is all about. They probably understand very well what the exam itself is all about, however the underlying Voice technologies are quite vastly different than the data world they may be used to. In fact, I hear this quite a lot from people making the jump from a R&S IE to the Voice side of the realm – “Man, this Voice stuff is totally different!“.

To begin with, we will start out a bit easy, and go over the basics of everyone’s favorite client/server gateway protocol – MGCP or “Media Gateway Control Protocol”.

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People constantly have troubles understanding the Gatekeeper-based call routing model. In this post, we are going to discuss the basic call-routing logic. Reader is assumed to understand the most fundamental gatekeeper configuration commands.

Basic Concepts

The first concept is the gatekeeper technology-prefix, which is the core of the gatekeeper dynamic call-routing process. Look at the tech-prefix as a special label used to group together a set of VoIP gateways. The gateways may register their technology prefixes with the gatekeeper dynamically, or you can map the prefixes to the VoIP gateways statically. The gatekeeper looks at the gateways registered under the same tech-prefix to be members of a single “gateway pool”. Now, recall that tech-prefix is just a part of the dialed number. Whether the called number prefix is actually a technology prefix, is decided by the gatekeeper, when it matches the dialed number against the database of the local registered/configured prefixes. There is nothing in the dialed number itself, that designates the part of the dialer string as a technology prefix.
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