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Getting started with SIP

An InteropNet Labs white paper.

By nobody,
May 11, 2004 09:29 AM ET -

Voice-over-IP (VoIP) networking comprises many components and network managers might find themselves treading on new and fragile ground as they investigate VoIP projects.  This white paper provides an inexpensive path that you can use to learn more about a particular VOIP technology, Session Initiation Protocol (SIP), get experience with the products and the market, and become more confident before building an enterprise-wide deployment.  The products and services mentioned in this white paper are representative based on our team's recommendations; others are available.

Start by using someone else's SIP server

You'll need a phone.  To start, get a free or demo version of a software-based phone for your desktop (Windows or Mac are common, but Linux soft phones exist as well).  X-Lite from Xten is a free, multi-platform soft phone with many features.  When using a soft phone you may also want to invest in an inexpensive headset if you don't have one already.

The two biggest components of a SIP network are the phones and the SIP proxy servers.  Start by getting a phone of your own and using someone else's SIP proxy server.  You can learn more about what kinds of phones are used in SIP and what a SIP proxy server is by reading our white paper "What is SIP?"  A number of free SIP-based telephony projects are alive and well on the Internet that will provide the SIP proxy server for you to test with.  You can start by getting a phone and hooking it up to someone else's SIP network.  That will help you to learn SIP terms and concepts, and give you an easy way to learn debugging.

Begin by signing up for a Free World Dialup (FWD) account.  FWD is, as the name suggests, free, and provides an Internet-wide SIP network with some limited Public Switched Telephone Network (PSTN) gateway capabilities.  You can hook multiple phones of your own up to FWD (and talk to each other using FWD) as well as other people who are connected to FWD.  Because FWD requires SIP technology, you'll mostly find other small businesses and technologists connected.  Nevertheless, you'll still want to be aware of the security issues involved---a good way to start is by leaving your test phone outside of your company firewall.  Make sure you read and follow the "Get FWD" Quick Start Guide.

Test your connection to FWD by calling 613 (FWD loopback number) to hear yourself talk. This is actually a very complete and worthwhile test that measures connectability.  Next, dial 411 to try something more interesting---a SIP call that terminates on the PSTN.  You can compare the quality by dialing direct to 800-555-TELL (which is the same number that FWD connects you to when you dial 411 on FWD via SIP).

Next, get an inexpensive "hard phone," such as the Grandstream Budgetone (about $65) and follow the FWD setup instructions.  You can get a second FWD account if you want, or just changeover your soft phone account to the hard phone. 

Begin learning how to debug SIP. You will need an Ethernet switch configured with a monitoring port, or an older hub/repeater that will copy all packets to your analyzer port.  Download a freeware protocol analyzer -- Ethereal has nice VoIP decodes, or you might already have a product like EtherPeek available, you can use that too.  Because SIP is easy to debug even without advanced protocol decodes, you don't need to start with a VoIP-specific product (but may want one as you become more advanced and work on more difficult problems).  Use your analyzer to watch VoIP streams.  Look at the call setup, audio streams, and call teardown.

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