OnSIP Tips from the SIP Maven: Customer Q&A
Mar
08
2010
OnSIP Tips from the SIP Maven: Customer Q&A Comments: 1
Question: I’m going to be traveling in the next week. Can I plug my Polycom phone into my computer and use a Wi-Fi network to make calls?
Answer: The short answer is no. Most VoIP phones have a simple switch that enables a computer to connect via Ethernet to a phone. You can’t reverse this process and connect a phone to a computer 'yes' the long answer is 'maybe' (See first comment below).
There are a few alternatives. You can use a softphone on your laptop and make and receive calls using a headset. Our favorite softphones are made by Counterpath. We have detailed instructions on configuring X-Lite and eyeBeam.
If you have an iPhone or Android OS smartphone you can use a SIP app to install your OnSIP user. Fring and iSIP work well.
If you are going to be staying somewhere where you can add a device to a Wi-Fi network you can also use an Apple Airport Express and plug your SIP desktop phone directly into that. The Airport Express connects to a WiFi broadband router that you have access to (so its not going to work in a Starbucks or a hotel, but its great if you are going to the parents or in-laws).
You can plug the Airport Extreme into any power outlet and then run your SIP phone from there. I use my Airport Express/Polycom combo to work in different rooms around the house (or even outside in the summer).
Share your laptop internet connection with your VoIP phone
During development of our SIP services we often need to inspect SIP packets being sent on BOTH sides of the router, i.e. packets as they leave the phone and packets as they arrive to our servers. In order to watch packets as they leave a phone often it is easiest for me to use my Mac's ability to NAT one network connection behind another. In order to do this simply connect your airport connection to a wifi network then go to:
System Preferences > Sharing > Internet Sharing
Once there, share FROM the AirPort TO Ethernet. Now plug your phone into the ethernet jack on your laptop and you've now shared your laptop's internet connection with your VoIP phone. Once at this point however a common issue you may face here is that now you have "double nat'd" your phone if your laptop is already behind another NAT (a router). Read the knowledgebase article on NAT traversal for more info on this.
With Windows - I believe (from here on it's all untested for me) - you can bridge two network connections. Effectively the difference from the Mac here is that there is no NAT anymore, your phone is getting it's own IP address on the same LAN as your laptop.