SIP Telephony
A lot of people have asked me about my home network configuration and VoIP telephone setup, so I thought I'd illustrate it here:
In the illustration, all blue arrows represent SIP communication with the annotation on the arrow representing the link layer. The black arrows carry non IP voice traffic, potentially over GSM/UMTS or the fixed line PSTN.
At the center of everything is of course the VoIP server. In my case I'm running Asterisk on there, along with a Jabber server and a mail configuration making my mailboxes available over IMAP. A plugin installed in my OpenFire Jabber server is able to identify whether I'm on the phone or not and set my IM status accordingly. If I'm logged in to my Jabber account, I also get an IM message with extra details about incoming calls. Voicemails are stored in my IMAP mailbox and I get notified via SMS.
The top left part of the diagram illustrates the many SIP DIDs which I have registered against my server. You can often get free DIDs from providers such as SIPGate, IPKall, etc. People can thus call a local DID number and contact me, no matter where I might happen to be. There are two other possible routes for incoming calls - the Sipura 2000 and the MV370 - but we'll look at those in more detail later.
I also have multiple outgoing channels over which I can place calls into the PSTN, shown in the top right of the diagram. Then there's pure VoIP calls which are originating and terminating in the VoIP world in the right-middle of the diagram. These might be calls from VoIP networks such as Gizmo, other SIP calls, and ENUM routed calls. You can use ENUM (RFC 3761) to identify whether PSTN numbers you're trying to call might have a VoIP equivalent. If a mapped number exists, one can bypass the PSTN and route the call completely over VoIP.
Looking at the basic networking at home, I have a 25MBit Cable Modem connection to the outside world. This is connected to a WRT54GL running OpenWRT. Since the WiFi point is in the living room, I have a WET54G WiFi bridge in my study which I use to bridge the WiFi connection back to an Ethernet connection, made available through a Gigabit switch to the rest of the equipment in my study. I’ve got several VoIP devices interacting in interesting ways. First of all, all my computers are running softphone software such as X-Lite or SJPhone. Fine, softphones work, and they're available whenever you're at your computer, but sometimes you just need a real phone unit which is independent of your computer. That's where the Avaya 4620SW comes in - it's a very solid phone with a lot of functionality and it works fairly well against my Asterisk server except for the fact that the MWI indicator, as well as several other features of the phone, only work when connected against an Avaya SIP server. The Sipura SPA 2000 is a SIP ATA which lets one bridge SIP VoIP and the PSTN. Thus, incoming calls on PSTN are routed over VoIP to my server, and my server can also route calls over VoIP to the PSTN line on the Sipura. It also has an FXO port so that you can plug any standard telephone into the Sipura and have it connect to both the VoIP and PSTN lines. The PORTech MV370 is a similar device except that you place a GSM SIM in it and it bridges SIP VoIP with the GSM/UMTS network.
Finally, there's my mobile phone - a Nokia N95. The N95 has WiFi networking capabilities, and comes with a native SIP stack built-in. When I'm at home, my mobile is registered over WiFi as a standard extension to my SIP network. If I'm not at home but if there might be a WiFi network I can log on to, I can place and receive calls over my VoIP server. The N95 is my favourite phone so far. I used to be a very firm Siemens follower starting with the Siemens S25, but having used the N95 for close to a year I really have come to love this phone.
This equipment configuration lends itself to a number of interesting scenarios:
- On an incoming call, all registered extensions ring allowing me to answer the phone on any device.
- I don't need a cordless phone at home - my mobile phone is already my cordless phone for home.
- I can place calls over my home telephone line even when I'm not at home
- Calls to my home numbers can be answered from anywhere my mobile phone is logged on to a WiFi network.
- Place and receive calls over a second SIM, and not have to worry with the hassle of constantly changing SIMs. The reason for the second SIM here is due to a mobile communications company here in Switzerland called Lebara who provide very competitive international call rates whereas Orange provides a good deal for local calls.
There's a lot of potential here, limited only by your imagination in how you hook everything up.
