How to change the Hello World Asterisk example to use TCP instead of UDP?

Asterisk Asterisk SIP
1

I setup Asterisk on a server. I set up the basic “Hello, World” example (direct from the docs here) which entails having my extensions.conf file as:

[from-internal]
exten = 100,1,Answer()
same = n,Wait(1)
same = n,Playback(hello-world)
same = n,Hangup()

and my pjsip.conf file as:

[transport-udp]
type=transport
protocol=udp
bind=0.0.0.0

[6001]
type=endpoint
context=from-internal
disallow=all
allow=ulaw
auth=6001
aors=6001

[6001]
type=auth
auth_type=userpass
password=unsecurepassword
username=6001

[6001]
type=aor
max_contacts=1

I have a simple Python script to make a call to the extension 100. This is direct from the docs here, where I call this script passing in the sip address sip:100@:

import sys
import pjsua as pj

# Logging callback
def log_cb(level, str, len):
    print str,

# Callback to receive events from Call
class MyCallCallback(pj.CallCallback):
    def __init__(self, call=None):
        pj.CallCallback.__init__(self, call)

    # Notification when call state has changed
    def on_state(self):
        print "Call is ", self.call.info().state_text,
        print "last code =", self.call.info().last_code, 
        print "(" + self.call.info().last_reason + ")"

    # Notification when call's media state has changed.
    def on_media_state(self):
        global lib
        if self.call.info().media_state == pj.MediaState.ACTIVE:
            # Connect the call to sound device
            call_slot = self.call.info().conf_slot
            lib.conf_connect(call_slot, 0)
            lib.conf_connect(0, call_slot)
            print "Hello world, I can talk!"


# Check command line argument
if len(sys.argv) != 2:
    print "Usage: simplecall.py <dst-URI>"
    sys.exit(1)

try:
    # Create library instance
    lib = pj.Lib()

    # Init library with default config
    lib.init(log_cfg = pj.LogConfig(level=3, callback=log_cb))

    # Create UDP transport which listens to any available port
    transport = lib.create_transport(pj.TransportType.UDP)

    # Start the library
    lib.start()

    # Create local/user-less account
    acc = lib.create_account_for_transport(transport)

    # Make call
    call = acc.make_call(sys.argv[1], MyCallCallback())

    # Wait for ENTER before quitting
    print "Press <ENTER> to quit"
    input = sys.stdin.readline().rstrip("\r\n")

    # We're done, shutdown the library
    lib.destroy()
    lib = None

except pj.Error, e:
    print "Exception: " + str(e)
    lib.destroy()
    lib = None
    sys.exit(1)

This all works fine, I call the SIP server, and hear the “Hello, World” recording.

What do I need to change so that I can have this communication occur over TCP? So far I have tried changing my pjsip.conf file by changing the protocol to tcp in the following part:

[transport-udp]
type=transport
protocol=udp
bind=0.0.0.0

, adding ;transport=tcp to the URI of my server that I pass in to the Python script, and also changing the line in the Python script that creates a Transport to

# Create UDP transport which listens to any available port
transport = lib.create_transport(pj.TransportType.UDP)

What happens is in the Python script I get

pjsua_acc.c !...SIP registration failed, status=408 (Request Timeout)

And on the server I don’t see the request at all.

2

Changing the “protocol” to “tcp” on the Asterisk side will have it listen to TCP. As for the pjsua side, I don’t have experience there.

3

I have a feeling this might be related to me being behind a NAT. In this case it appears it would not be as simple as changing the protocol to tcp, correct? The PJSUA side is working fine actually, at least I can see the SIP REGISTER message being sent. It isn’t reaching the server however.

4

Which is behind NAT? If Asterisk is behind NAT you need to ensure that the port is opened and that the options for NAT are set[1]. If the remote is behind NAT you need to ensure the options for that are set (rewrite_contact and rtp_symmetric).

[1] https://wiki.asterisk.org/wiki/display/AST/Configuring+res_pjsip+to+work+through+NAT

5

I am not yet sure, I am new to this networking stuff, and am in the process of finding out.

A question: does it make sense that if I am having issues with TCP communication with Asterisk due to the presence of NAT, that I don’t have the issues when I use UDP?

6

It is possible, yes. Without knowing the network layout it’s impossible to say with certainty where the problem areas would be.