SIP Development Tools

By Richard "Zippy" Grigonis, Feature Articles

SIP has become the premier the call control/signaling protocol for IP Communications, unseating its predecessor, H.323. Developing products that rely on SIP is less difficult than with H.323, and working with SIP code, while not a walk in the park, is nevertheless relatively straightforward compared to other types of protocols.

SIP is the core signaling protocol of the upcoming IMS (IP Multimedia Subsystem) network, which will unite wireless and wireline networks, enable fixed-mobile convergence (FMC) and allow for a multitude of services to be developed almost willy-nilly. The SIP protocol and SIP servers are the enablers for IMS advanced services. However, developers have discovered that there’s a big difference between SIP compliance and IMS SIP compliance. Basic SIP with all of its extensions is fairly complex and IMS SIP is an even more complex signaling protocol. Many changes and a large number of complex extensions to the original IETF SIP standard were introduced for IMS, making IMS extended SIP even more complicated than ever before. Moreover, some of the IMS SIP interfaces are still under discussion. It’s a major challenge to developing SIP systems containing advanced features for IMS deployment.

The differences between IMS SIP and non IMS SIP are as follows:

First there are the IMS SIP extensions on the access level:

• SigComp (RFC 3320)

• P-headers (RFC 3455/3325) — P-preferred-identity, P-access-network-info, P-asserted-identity, P-calledparty- id. When discussion IMS SIP, many vendors think that IMS 3GPP has defined a bunch of P-headers needed for the IMS network to be capable of providing specific services that the IMS network should bring to the world, but the P-headers are a minor issue in being IMS compliant. Many P-headers were defined to pass relevant information in the network, but having these capabilities is not enough to give you the capability to develop IMS compliant elements.

• AKA-MD5 (RFC 3310)

• Security agreements (RFC 3329)

• IPsec

• Media authorization (RFC 3313)

• Service-route mechanism (RFC 3608)

• Reg-event package (RFC 3680)

• IPv6

Then there are security extensions (too numerous to list here) and miscellaneous extensions such as IMS resource reservation (RFC 3312), path headers (RFC 3327), SDP extensions (more attributes, grouping of media lines, more codec support, etc.), XML schemas usage including those in SIP message bodies (registration event package, XCAP, PIDF etc.). Finally, there are extensions by the IETF SIMPLE group with their work on presence and IM optimization (partial notifications/publications, notifications filtering, resource lists (RLS)/SIP exploders, and MSRP). Fortunately, vendors have evolved their SIP development tools to keep pace with transitions in both basic IETF SIP and IMS SIP.

One of the major vendors of SIP and SIP IMS-based development tools is RADVISION (news - alert) (http://www.radvision.com). Sagi Subocki, head of the company’s IMS Segment in the Technology Business Unit and Manager of the SIP, Megaco and DIAMETER toolkits, says: “We are focusing on building developer tools, including SIP Toolkits and Megaco / H.248 and DIAMETER toolkits too. We provide a framework, both to the client side with our multimedia terminal framework and a SIP server development platform. We have a set of testing tools, both for H.324M technology [the mobile version of ITU H.324, defined for visual PSTN phone terminals] and for SIP. IMS [IP Multimedia Subsystem] is a strategic vertical of the business unit on which we have focused for a few years now.”

“We also now have a full IMS Developer Suite, developed to focus on the IMS market,” says Subocki. “The IMS Developer Suite consists of various components; each of which is dedicated to a different protocol, and has IMS, Megaco / H.248, DIAMETER, and testing tools designed for IMS network elements. As part of this Developer Suite, we have a SIP Developer Toolkit which of course involves the SIP side of the IMS network. It has the basic SIP stack with a complementary RTP and SDP stack and add-ons to the SIP stack which give the specific capabilities that each customer might need. There are also complementary toolkits such as a NAT [Network Address Translation] Traversal Toolkit for developers who need capabilities of dealing with network borders and firewalls.”

“Basically, the SIP Developer Toolkit, it really focuses on SIP tools for developing SIP network elements,” says Subocki. “We also offer a larger SIP Developer Suite, or which comes with an IMS package [See Figure 1].”

To be precise, the RADVISION Developer Suite offers the following:

• The Presence and Instant Messaging add-on — RADVISION calls it the SIMPLE add-on.

• The IMS add-on

• An XML schema package that gives support for specific XML schemas needed for more advanced services.

• The NAT Traversal Toolkit, which has both STUN and ICE capabilities.

• The SigComp package, which is needed in IMS. This is mandatory and very important in the IMS network because of the issue of access through wireless and 3G where bandwidth is sometimes limited and is therefore a valuable resource. (This is why compression of the signaling protocol is mandatory.)

• An SCTP add-on

• The XDM toolkit.

“With our SIP Developer Suite, customers can basically mix-and-match the specific add-ons and toolkits they need for the specific network element which is being developed,” says Subocki. “You get our product in source code, very extensive documentation and of course sample code and GUI test applications.”

SIP Tool Potpourri

There are all kinds of SIP-related tools Yours Truly has run into in recent years, such as the following:

• The SIP-H.323 Converter by Cosystech (news - alert) (now CoSystems, http://www.cosystems.com),

• DC-SIP a complete package of portable source code, sample applications, full reference designs, test applications, and customization tools, by Data Connection (news - alert) (http://www.dataconnection.com).

• Various testing products by GL Communications (news - alert) (http://www.gl.com) that provide extensive SIPbased call emulation, analysis, SIP call trace, and call monitoring.

• The SIP Stack from HCL Technologies (news - alert) (http://voip.hcltech.com) that smoothes the progress of SIP-based VoIP product and solution development. It comprises SIP User Agent and SIP Server reusable components that have been tested and ported on to multiple platforms.

• An API to develop SIP-based applications from Hellosoft (news - alert) (http://www.hellosoft.com).

• Hotsip’s (news - alert) (http://www.hotsip.com) Service Creation Environment (SCE) for the their M2CE SIP application server with access to open APIs, making it relatively easy to add and customize new and existing applications.

• A full SIP Stack and SIP Lite from Hughes Software Systems (news - alert) (http://www.hssworld.com).

• A SIP stack from Mediatrix (news - alert) (http://www.mediatrix.com).

• Nine-9s (news - alert) (http://www.nine-9s.com); their TeleSoft product includes their CompactSIP SIP stack, 3GPP / WiMAX / IMS SIP stack, SIP-ISDN and SIP-PSTN interworking software.

• Netbricks (news - alert) (http://www.netbricks.com) offers SIP-BRICKS, a high-performance SIP implementation. Netbricks is a leading developer and supplier of Portable Protocol Stacks compliant with Protocol standards.

• The SIP Toolkit from ELUON (news - alert) (http://sip.eluon.com/index.jsp).

• The EmSIP embedded SIP Stack from Parrish Systems (http://www.parrishsys.com).

• PJSIP, an Open Source SIP Stack, supporting many SIP extensions/features (http://www.pjsip.org).

• MjSip is a complete java-based implementation of a SIP stack available as open source under the GPL license (http://www.mjsip.org).

• The VBVoice service creation environment from Pronexus (news - alert) (http://www.pronexus.com).

• The SIP control interface and a management agent from SandCherry (news - alert) (http://www.sandcherry.com).

• The HiPath Software Development Kit from Siemens (news - alert) (http://www.siemens.com).

• The High-Performance SIP Stack from Jugphoon (news - alert) (http://www.juphoon.com).

• VQmon from Telchemy (news - alert) (http://www.telchemy.com) is integrated into IP Phones, VoIP Gateways, Residential Gateways, SLA monitoring systems, routers, OSS, Probes and Analyzers,. and provides reporting metrics using SIP, RTCP, XR QoS Reports and other key protocols.

• The TsGATE software SIP to PSTN Gateway design kit from TeleSoft International (news - alert) (http://www.telesoft-intl.com).

• The VeriCall Edge is VoIP embedded software platform that offers the media processing; and SIP call control functionality needed to develop a video and VoIP enabled client device.

• The Fusion SIP Software Suite from Unicoi Systems (http://www.unicoi.com/fusion_net/fusion_sip.htm), designed for use in embedded devices, has a small footprint and is completely ROMable and re-entrant. The Fusion SIP stack provides a simplified API for quick integration with the application and transport stack (TCP/IP/UDP). (news - alert)

• The SIP Protocol stack from Wind River (news - alert) (http://www.windriver.com).

As developers create new communications services in existing wireline and wireless networks — as well as the upcoming IMS network — many of these tools will be getting quite a workout (and will doubtless evolve along with SIP and IMS). Even more new tools will appear as a plethora of mobile devices and technologies make their way into enterprises and consumer residences.

Richard “Zippy” Grigonis is Executive Editor of TMC’s IP Communications Group.