In Chapter 2, the working of H.323 and SIP protocols was explained.This chapter explains how to set up an infrastructure including H.323 and/or SIP components and gives real-world examples of configuration for popular equipment.The focus will be on setting up basic services, meaning the equipment that is necessary to provide basic call services, authentication and billing.
~ 4.1 General concepts
Before giving examples on how to set up SIP or H.323 zones using equipment from specific vendors, this section introduces the general concepts.With these concepts in mind, it will be easier to understand the vendor-specific parts that follow.
~ 4.1.1 Architecture
Chapter 2 introduced us to the architectures of pure H.323 and SIP environments. Basically, there is one central server and multiple telephony endpoints registering with that server.The server's task, among others, is to resolve a dialled address to an IP target. However, when we talk about real-world set-ups, this server infrastructure tends to be more complicated.The reasons for this are:
- usage of redundant servers to increase availability or provide load balancing (see Section 4.1.2);
- usage of multiple servers, e.g., for branch offices;
- more than one signalling protocol.
There are two possibilities to support multiple signalling protocols within one zone: have servers with built-in support for every protocol or have dedicated servers for each protocol and signalling gateways between them.
A server that supports more than one signalling protocol (see Figure 4.1) is the best solution. It is easier to manage since there is just one configuration to take care of and there will not be any problems with server-to-server interaction.
Unfortunately, there seems to be no equipment that provides fully-featured SIP and H.323
support on the same machine. 1
If a zone includes both a SIP Proxy as well as an H.323 Gatekeeper, then call routing inside the domain becomes an issue. A signalling gateway is required to enable an H.323 endpoint to call a SIP endpoint and vice versa (see Figure 4.2).
1. Actually there is a product that claims support for both SIP and H.323 protocols: the Asterisk PBX.
See: http://www.asterisk.org/. How well it supports SIP and H.323 is not yet known.
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Figure 4.1 SIP/H.323 zone using a multi-protocol server
Signalling