HELLO & WELCOME

[WelshPaul]

So, I have been using the Andrews & Arnold SIP2SIM service for a few days now and overall, I like it. Unfortunately, I encountered an annoying issue that took some time to figure out.

Let’s imagine we have the following PBX setup:

• FreePBX server is hosted in the cloud and has the following extensions setup:
  
  • Ext: 200 <--- Snom phone
  • Ext: 201 <--- Zoiper softphone
  • Ext: 202 <--- Yealink phone
  • Ext: 203 <--- Snom phone
  • Ext: 204 <--- Zoiper softphone
  • Ext: 205 <--- SIP2SIM

The problem:
The Andrews & Arnold SIP2SIM phone would only ring when called internally from extension 201, call from any other extension and the Andrews & Arnold SIP2SIM phone wouldn’t ring.

Example:
Caller picks up the Snom phone handset registered against extension 200 and dials “205” (the extension SIP2SIM is registered to), caller hears the internal ringing tone in the earpiece of the Snom phone but the SIP2SIM phone doesn’t ring. After 25 seconds or so the caller is forwarded to extension 205’s unavailable voicemail where they are prompted to leave a message.

So, I send an email over to Andrews & Arnold support explaining the problem and ask if this was a known issue.
(I didn’t want to waste time running SIP traces, grabbing PCAP files and altering settings server side just to be told later on that it’s a known issue or a limitation of the SIP2SIM service – Been there, done that!)

Few minutes later, I received the following reply:

Has this always been the case?

What device is the SIM in?

We have limited logs on the SIM, the CDRs show the SIP error 480 which means 'Temporarily Unavailable - Callee currently unavailable.’

https://en.wikipedia.org/wiki/List_of_S ... onse_codes

There’s no SIP logs as it’s within your network. Does you Asterisk have any logs or are you able to get a PCAP?

I guess it’s not a known problem or a limitation of the service then.
Time to look at some SIP traces and grab some PCAP files...

204>203-Flow_Seq.png (31.39 KiB) Viewed 4407 times

Hmm, PCAP shows that it's the Andrews & Arnolds Voiceless server returning the “480 Temporarily not available” error and not mine. Play the stream and I hear a BT recorded message:

Sorry the number you have called is not available. Sorry the number you have called is not available. This number is not accepting calls at present. Please try later. This number is not accepting calls at present. Please try later.

After several more emails between myself and Andrews & Arnold support and getting knowhere I was ready to give up and call it a day when out of the the blue I received the following email from someone higher up the support chain at Andrews & Arnold:

Thanks for all the details reports and PCAPs (they were helpful)

Manx (our upstream provider) are expecting us to add PA-ID which must be
a valid number which seems really odd when this is in effect an internal
call

They made a change very recently and despite our valid reasoning they
are not willing to look at this again

We have had no choice but to contact Ofcom about this and we'll be using
the responses we get back to fire back at MANX

From: <sip:201@voiceless.aa.net.uk>;tag= 2021000000321500001 vs From:
<sip:204@voiceless.aa.net.uk>;tag=2021000000321500001

According to MANX both are not valid so it makes little sense that from
201 is working

It may be that you can get around this as it seems to validate things
like the area code, e.g. +44 0000 0000000
doesn't work but +44 1344 000000 should get through

So I wonder whether you can change the outgoing CLI to the format of +44
1344 000000 and see if that works

Interesting, let’s give it a try!

To change the extensions caller ID for internal calls in FreePBX we need to enter a CLI of our choosing here: Applications > Extensions > 200 > Advanced > CID Num Alias

I entered my landline CLI in the following format “01792000000” as special characters are not allowed here. Clicked “Save”, then “Apply changes” and it works! I can now receive internal calls on my SIP2SIM phone.

If you want to retain the extension number as the CLI, use 0200 for extension 200, 0201 for extension 201 etc.
CLI will be displayed as 0200 or 0201 but it helps identify from what extension the call originated from.