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Adrian Georgescu, 06/16/2011 03:01 pm

<acronym title="SipDeveloperGuide*, depth=3">TOC</acronym>

= SIP SIMPLE SDK Integration Guide =

SIP SIMPLE client SDK is a Software Development Kit with a Python API useful for development of real-time communications end-points based on SIP and related protocols with multimedia like Audio, Instant Messaging, File Transfers, Desktop Sharing and Presence. Other media types can be easily added by using an extensible high-level API. The library has cross platform capabilities on Linux OS, Mac OSX and Microsoft Windows. The library works with no or minimal changes on any platform that supports Python and provides direct access to the input and audio devices using one of the supported backends.

Current Status

SIP SIMPLE client SDK is reliable for production use and is used today in finished products that are downloaded daily more than 300 times. The products work on Linux, Mac and Windows desktop OS and Linux Servers.

Installation Instructions

SIP SIMPLE client SDK is ready packaged for latest Ubuntu Linux distributions (Lucid, Maverick and Natty), Debian Linux distributions (Stable and Unstable) and can be manually installed on MacOSX 10.5, 10.6 and Microsoft Windows XP, Vista and 7 by following the documentation provided with the source code. To install the SDK on Debian or Ubuntu, configure your deb repository as described [http://www.ag-projects.com/projects-products-96/683-software-repositories here], then:

{{{
sudo apt-get update
sudo apt-get install python-sipsimple
}}}

Complete building instructions from source for the SDK and its dependencies are available [http://sipsimpleclient.com/wiki/SipInstallation here]

API Documentation * Online documentation is available at http://sipsimpleclient.com/wiki/SipMiddlewareApi * Printable documentation in PDF format is available at http://download.ag-projects.com/SipClient/SIPSIMPLE-Manual.pdf Usage Instructions

Using SIP Simple SDK library is no different than using any other Python library, by installing it in the system manually from the source code with 'sudo python setup.py install' command or from a ready made package when available for the target OS then import its modules into the program and use it.

To setup a simple audio call and hangup one has to write as little as 10 lines of code. A complete wide-band conferencing application has been written in only 300 lines of code. Developing a complete end-point like Skype is the most complex example of what the SDK may be used for. Blink on Mac has about 25,000 lines of code.

The complexity grows once one needs to interact with the end-user for more actions like creating conferences, interacting with telephony like applications, adding chat or handle presence messages. The complexity is dictated by the GUI design, the library provides easy to understand high-level functions and the develeper does not need to understand SIP or other related protocols used inside the kit to achieve his goal.

=== Deployment Scenarios ===

The SDK can be used to build real-time communications end-points that operates in the following scenarios:

  • On a LAN by using Bonjour discovery mechanism or on the public Internet by using the Server of a SIP Service provider, next hop lookup is based on DNS as described in RFC 3263
  • In a P2P overlay network like a DHT that provides routing and lookup service. For this, the SIP end-point must publish its Address of Records (AoR) address:port:protocol where it listens for incoming requests into the overlay and must implement a lookup function to obtain the peer end-points addresses from the overlay so that it can establish outbound sessions with them. For NAT traversal there must be a set of super-nodes that provide media relay functions based on ICE methodology
Sample Code

=== Hello World Program ===

This is the hello world example that establish a wideband audio call. After installing the SDK, paste this code into a console and run it using Python.

{{{
#/usr/bin/python

from application.notification import NotificationCenter

from sipsimple.account import AccountManager
from sipsimple.application import SIPApplication
from sipsimple.core import SIPURI, ToHeader
from sipsimple.lookup import DNSLookup, DNSLookupError
from sipsimple.storage import FileStorage
from sipsimple.session import Session
from sipsimple.streams import AudioStream
from sipsimple.threading.green import run_in_green_thread

from threading import Event

class SimpleCallApplication(SIPApplication):

def init(self):
        SIPApplication.__init__(self)
        self.ended = Event()
        self.callee = None
        self.session = None
        notification_center = NotificationCenter()
        notification_center.add_observer(self)
def call(self, callee):
        self.callee = callee
        self.start(FileStorage('config'))
@run_in_green_thread
    def _NH_SIPApplicationDidStart(self, notification):
        self.callee = ToHeader(SIPURI.parse(self.callee))
        try:
            routes = DNSLookup().lookup_sip_proxy(self.callee.uri, ['udp']).wait()
        except DNSLookupError, e:
            print 'DNS lookup failed: %s' % str(e)
        else:
            account = AccountManager().default_account
            self.session = Session(account)
            self.session.connect(self.callee, routes, [AudioStream(account)])
def _NH_SIPSessionGotRingIndication(self, notification):
        print 'Ringing!'
def _NH_SIPSessionDidStart(self, notification):
        audio_stream = notification.data.streams[0]
        print 'Audio session established using "%s" codec at %sHz' % (audio_stream.codec, audio_stream.sample_rate)
def _NH_SIPSessionDidFail(self, notification):
        print 'Failed to connect'
        self.stop()
def _NH_SIPSessionDidEnd(self, notification):
        print 'Session ended'
        self.stop()
def _NH_SIPApplicationDidEnd(self, notification):
        self.ended.set()
  1. place an audio call to the specified SIP URI in user@domain format
    target_uri="sip:"
    application = SimpleCallApplication()
    application.call(target_uri)
    print "Placing call to %s, press Enter to quit the program" % target_uri
    raw_input()
    application.session.end()
    application.ended.wait()
    }}}

=== Full Demo Programs ===

Full sample programs are available in 'sipclients' package available in the [http://www.ag-projects.com/projects-products-96/683-software-repositories same repository] as python-sipsimple. These programs operate in a Linux or MacOSX terminal and implement most of the functions provided by the the SDK.

{{{
sudo apt-get install sipclients
}}}

  • sip-register - REGISTER a SIP end-point with a SIP Registrar or detect Bonjour neighbors
  • sip_audio_session - Setup a single SIP audio session using RTP/sRTP media
  • sip_session - Complete client supporting multiple sessions with Audio (RTP/sRTP), IM and File Transfer (MSRP)
  • sip_message - Send and receive short messages in paging mode using SIP MESSAGE method
  • sip_publish_presence- PUBLISH presence to a Presence Agent
  • sip_subscribe_winfo - SUBSCRIBE to the watcher list for given SIP address on the Presence Agent
  • sip_subscribe_presence - SUBSCRIBE to Presence Event for a given SIP address
  • sip_subscribe_rls - SUBSCRIBE for Presence Event to a list managed by a Resource List Server
  • sip_subscribe_xcap_diff - SUBSCRIBE for xcap-diff Event to monitor changes to XCAP documents
  • sip_subscribe_mwi - SUBSCRIBE for Message Waiting Indicator

For a description of the sample programs see http://sipsimpleclient.com/wiki/SipTesting

=== Finished Products ===

The SDK is used in several products since end of 2009. These are end-products that use the SDK and provide excellent examples for how the SDK was used to achieve the goals.

1. Multiparty Conference Application with Wideband Audio, IM and File Transfer: http://sylkserver.com
 1. SIP client implementation for MacOS X available in the Mac App Store: http://itunes.apple.com/us/app/blink-pro/id404360415?mt=12&ls=1 
 1. SIP Client for Linux: Blink for Ubuntu, and Debian, use same repositories from AG Projects and do 'sudo apt-get install blink' 
 1. SIP client for MS Windows: https://blink.sipthor.net/download.phtml?download&os=nt
Non-Python environments

As the programming choice was Python this SDK will appeal to people that want to develop applications in Python. If one want to use the library into another environment it must check if is feasible or not as embedding a programming language into another is not a string forward process if at all possible.

=== Cocoa Objective C ===

MacOS platform is using Objective C for native development. But it also provide a bridge between Python and Objective C. This makes it possible to write pure Python programs that run into the native OS without much changes.

http://pyobjc.sourceforge.net/

The SDK was fully used without any problems to build Blink for MacOSX by using this bridge.

=== Qt Framework ===

Qt Framework from Nokia (formerly Trolltech) is using C for native development. But it also has Python bindings. This makes it possible to write pure Python programs that integrate with Qt framework.

http://qt.nokia.com/

The SDK was fully used without any problems to build Blink for Windows and Linux by using Qt Framework and its Python bindings.

=== Web Browser Plugin ===

Today, web browsers do not give direct access to the input and output audio devices to their plugins, which is required by a real-time audio application. Browsers do not support direct embedding of Python code either. If one looks for example at how Google Talk plugin in the browser works, it actually installs a regular server daemon into the system that performs similar functions to IP SIMPLE Client SDK and the web browser interacts with it by using a proprietary API running on the same host between the daemon and the browser plugin. The core software that does the media, signaling, integration with the audio device does not run in the browser itself, the browser is only used only as a GUI.

There is a recent initiative to form a work group in both W3C and IETF to address this important issue of accessing and processing audio data within the browser itself as today this is not possible. This requires cooperation from the browser manufacturers, third-party developers cannot do this on their own without cooperation from the web browser makers (like Adobe has obtained for its Flash product). This initiative is called RTCweb:

http://rtc-web.alvestrand.com.

Google published a first specification and code drop in May 2011 and IETF and W3C had a few initial conference calls to setup the future agenda but no more at this stage.

SIP SIMPLE Client SDK cannot run in the browser today as browsers won't support Python nor direct access to audio devices both required by the SDK to operate. However one could build a program that stays behind the browser in the same way as Google Talk.

=== C Language ===

Embedding C code into Python program is easy and feasible we do this in our Python library as well for some low level parts where we speed was needed. The other way around is not, as passing complex data structure from a high level language like Python to a low level one like C is quite a problem. How to possibly integrate Python into C is described here:

http://docs.python.org/extending/embedding.html

Is unlikely that the SDK can be used in such way because of data translation or multi-threading issues that could be impossible to solve, in any case nobody has ever tried.

=== Java Language ===

There is a bridge between Python and Java.

http://www.jython.org/

It is unknown if is feasible to use the SDK under this environment, as nobody has reported trying it yet.

=== Translating into other languages ===

There are currently 47,000 lines of code in SIP SIMPLE Client SDK.

The state machine for a multimedia real-time application is an order of magnitude more complex than protocols like BitTorent.

There are multiple-threads and the design is non-blocking by using asynchronous reactor and a notification system. SIP Simple SDK generates today 135 Notification on state changes, each of them carrying complex data structures.

When all combined together the final application is quite complex and achieving the same in a low level programming language like C for example would be a major undertaking. Expressing this complexity into a low level language like C requires many years of work with a large team of well qualified people.