Bypassing Broken SIP ALG Implementations

The SIP protocol is commonly used for IP telephone communications. Unfortunately it’s notorious for having issues with NAT traversal. Even some major vendors can’t seem to get it right. [Stephen] had this problem with his Cisco WRVS4400N router. After a bit of troubleshooting, he was able to come up with a workaround that others may find useful.

The router had built in SIP ALG functionality, but it just didn’t work. [Stephen] was trying to route SIP traffic from a phone to an Asterisk PBX system behind the router. The router just couldn’t properly handle these packets regardless of whether SIP ALG was enabled or disabled.

[Stephen] first tried to change the SIP port on the external VOIP phone from the default of 5060 to something else. Then he setup port forwarding on the router to the Asterisk box to forward the traffic to the Asterisk system on the original port. This sort of worked. The calls would go through but they would eventually drop after about 20 seconds.

The only thing that [Stephen] could get to work completely was to change the SIP port in Asterisk’s sip.conf file using the “bindport” directive. He changed it to some random unused high port number. Then he setup port forwarding on the router to forward incoming UDP packets on that port to the Asterisk system. This worked fine, but now all of the original phones behind the router stopped working because they were configured to use the default port of 5060.

Rather than re-configure all of the phones in the organization, [Stephen] made one change on the Asterisk system. He setup an iptables rule to forward all incoming traffic on UDP port 5060 to the new SIP port. Now all of the phones are working with minimal changes across the organization. It’s a lot of hassle to go through just because the router couldn’t handle SIP correctly, but it gets the job done.

Breathe New Life Into Payphones with Asterisk

Payphones used to be found on just about every street corner. They were a convenience, now replaced by the ubiquitous mobile phone. These machines were the stomping grounds for many early computer hackers, and as a result hold a place in hacker history. If you’ve ever wanted to re-live the good ol’ days, [hharte’s] project might be for you.

[hharte] has been working to make these old payphones useful again with some custom hardware and software. The project intends to be an interface between a payphone and an Asterisk PBX system. On the hardware side, the controller board is capable of switching various high voltage signals required for coin-line signaling. The controller uses a Teensy microcontroller to detect the hook status as well as to control the relays. The current firmware features are very basic, but functional.

[hharte] also wrote a custom AGI script for Asterisk. This script allows Asterisk to detect the 1700hz and 2200hz tones transmitted when coins are placed into the machine. The script is also in an early stage, but it will prompt for money and then place the call once 25 cents has been deposited. All of the schematics and code can be found on the project’s github page.

[Thanks mies]

Hacking a Pogoplug into a $20 PBX

The Pogoplug Series 4 is a little network attached device that makes your external drives accessible remotely. Under the hood of this device is an ARM processor running at 800 MHz, which is supported by the Linux kernel. If you’re looking to build your own PBX on the cheap, [Ward] runs us through the process. Since the Pogoplug 4 is currently available for about $20, it’s a cheap way to play with telephony.

Step one is to convert the Pogoplug to Debian, which mostly requires following instructions carefully. After the Pogoplug is booting Debian, the Incredible PBX bundle can be installed. We’ve seen this bundle running on a Raspberry Pi in the past. Incredible PBX’s preconfigured setup based on Asterisk and FreePBX gives a ton of functionality out of the box.

With your $20 PBX running, there’s a lot that can be done. Google’s Voice service allows unlimited free calling to the USA and Canada. With Internet connectivity, you get email notifications for voicemails, and can query WolframAlpha by voice.

Get Phone Calls Answered with the Moshi Moshi

Moshi Moshi

Have a significant other that isn’t the best at picking up the phone? [Aaron] was having a hard time reaching his wife, so he hacked up a solution. The Moshi Moshi detects calls from [Aaron], and plays music to get her attention.

A remote server running Asterisk picks up the call and uses a Ruby script to log the call. Every ten seconds, an Arduino Due with an Ethernet shield polls a Sinatra web server to see if a call has arrived. If a new call has come in, a music loop is played. Getting the Due to loop audio was a bit of a challenge, but the end result sounds good.

Quite a bit of tech is brought together to make the Moshi Moshi, and all the code is provided in the write up. This could be helpful to anyone looking to combine hardware with the Asterisk PBX. After the break, [Aaron] shows us how the system works.

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Building a PBX setup around the Raspberry Pi

We’re not sure why this use didn’t immediately come to mind when we got our hands on a Raspberry Pi board, but the hardware is almost perfect as a PBX system. PBX, or Private Branch Exchange, is basically an in-house phone system. This guide which [Ward] put together shows you how to do some interesting things with it.

When talking about PBX setups the most common software package is Asterisk. That’s what’s at work here, rolled up with a bunch of other helpful software in an RPi targeted distro called Incredible PBX. All it takes to get up and running is to partition and burn the image to an SD like any other RPi distro. The configuration ends up being most of the work, starting with changing the default password, and moving on to customizing the environment to match your phone numbers and your needs. As with PBX setups on other embedded Linux devices, Google Voice is your best friend. The service will set you up with a free phone number.

This guide doesn’t delve into hardware connected hand sets. You’ll need to use a SIP phone. But that’s easy enough as there are free apps for most smart phones that will do the trick.

[Thanks Jamie]

Free home phone method uses parts we’re familiar with

[Headsheez] found a way to get his home phone service for free. He’s using a set of tools that we’re familiar with to route service from a typical analog phone system (which involves the extensions wired into your home) through a server to the Internet. On the hardware side of things this starts out with an Analog Telephone Adapter which translates the analog signal for use in a PBX system. He uses a copy of the open source PBX project called Asterisk which we’ve also seen used on devices like routers and the SheevaPlug. The actual telephone number comes from a Google voice account which for now is a free service but there’s no guarantee that it will remain that way in the future.

This should provide seamless service just like you’re used to with a traditional home phone line. There’s even caller ID for the number – but not the name – for incoming calls. The one big feature that is missing from this setup is the ability to call 911 for emergencies.

[via Reddit]

Pi phone lulls you to sleep with the digits of Pi

As you well know, today is March 14th – aka “Pi Day”.

Celebrated in math classrooms around the country, this truly is a celebration that belongs to the geeks. Here at Hack-a-Day, we too love Pi day, though we might not outwardly celebrate it with as much gusto as expressed by some of our readers.

[Chris Poole] is one Hack-a-Day fan who knows how to make the most of this mathematical holiday. He has put together a neat SIP-based phone service that reads Pi aloud to anyone who calls. He is running Asterisk in combination with Perl to read off the numbers, and is using a free SIP DID number to accept the calls. We gave it a shot earlier today, and were greeted by a gentle synthesized voice reading off the numbers of Pi. We’re not sure how many digits it is programmed to handle, as we stopped after about 20, so give him a call and let us know how many digits you make it through.

As a parting note, no Pi Day would be complete without a few obligatory Pi-related (albeit old) web comics and pastry concoctions, so here you go!

XKCD – Pi Equals…

XKCD – e to the Pi Times i

XKCD – E to the Pi Minus Pi

Spherical Pi Pie