Sip call over 2G network

i am using asterisk 11 and has set my asterisk over a public IP. i am making call from a android sip phone over another android sip client via asterisk , the quality is good with 3G network , but when i switch the network to 2g i get the following problems.

  1. some time my client don’t even register.
  2. if it gets register i cant hear sound properly on the phones.

i have to make this product over 2G network, please make any suggestion if i should use SIP or IAX or any other protocol which work over 2g network where bandwidth is limited to 8-9 kbps.

You trying to get SIP plus media into a bandwidth that is smaller than half rate GSM media only!

Your best solution would be to use half rate GSM and forget the SIP entirely.

I believe that IAX can be configured to stream media with minimal overhead, so a very aggressive codec might just get the media stream down to that sort of bandwidth. RTP bandwidth is about 10 times that for G.711, and still several times greater with more aggressive codecs, because of the per frame overhead.

The failure to register suggests you have a high packet loss rate. If you are sending media at the same time, this will just be contention with the media for bandwidth that is only a fraction of what the media requires. If you lose registers even when there is no media, you probably need to use a TCP based protocol. I’m not convinced there is a standard TCP VoIP protocol that also has low overhead for the media. TCP in a high loss environment will result in very large delays.

Basically 2G is trying to get data, and various overheads into the bandwidth used by an efficient digital voice system, with the exception that it is using codecs that are about three decades old. However modern codecs aren’t going to get that much better without loss of quality. VoIP is always going to use bandwidth less efficiently than a digital phone network designed from the start as a digital phone network.

Although you may think that the mobile company is grossly overcharging you for voice traffic, market forces mean that the cost of calls do have some relation to the cost of providing the service.

Hi David heartily thanks for your reply,

how can i use half rate GSM without SIP or iax, as far as i came out of googling that it is operating at 6.5 kbit/s which will serve my purpose but i really don’t understand how to use this with asterisk, and if i remove the SIP how my phones are going to communicate with each other.

Talk to you mobile network operator. All references to GSM refer to using the mobile network as a mobile phone network, not as a mobile data network with VoIP on top.

Actually, you will probably not care whether they use half or full rate GSM, in that case.