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SIP: The Glue for IP Communications, Redefining Voice and Data Convergence Based on SIP

SIP: The Glue for IP Communications

by Anne L. Coulombe, Head of SIP-Based Solutions
www.mitel.com

[Published on SIP Center Newletter, March 2003 ]

Look around you, glue is critical, it transforms parts into assemblies, yet it is mostly invisible. SIP is both a glue and a chameleon, it provides the strength of epoxy, yet it functions as a catalyst. It bonds IP and multimedia communications between disparate systems when you need it, and then it let's you disconnect and start all over again.

We say that SIP is to VoIP, what HTTP is to the Net, and what SMTP is to linking disparate email systems. HTTP is the navigation and linking mechanism on the Net, while SMTP is the protocol that revolutionized corporate and inter-company communications in the early '90s. SIP is now revolutionizing packetized voice. SIP allows us to easily converge voice, video and data, which we commonly call multimedia, on broadband IP networks. Frankly, given SIP's invisibility, the usage rate is higher than reported.

Should a customer see SIP? Should they see the glue? End-users, IT and telecom people want to know that SIP bonds systems together, ensures packetized voice and multimedia functions properly and transparently. Although the bottom line is that users really just want their system to work, and don't really care if SIP as the underlying protocol is red, blue, purple or green. Users want the ability to go beyond traditional telephony in an IP environment and SIP provides the conduit to make this happen.

SIP works today: Two hour conference calls between continents using the Internet (which is by design a best effort network), using a combination of different vendor phones, dialing direct, gateways, and disparate systems all work together now. SIP is the glue that holds and links this all together.

Redefining Voice and Data Convergence Based on SIP
By A.J. Gillette and Anne L. Coulombe
Mitel Networks Corp

[Published on SIP Centre's SIP Cognition pages, May 2003]

Mitel has been hard at work for the past 12 months creating the next generation of office products based on open standards including Linux, Java and SIP. The 3050ICP made its first public appearance in the spring of 2002, and has continued to evolve to its present state. Consider a distributed voice and data system, that assumes using a best-efforts network called the Internet, yet makes dialing by extension and dial plans transparent to the user. It is natively SIP.

The basics:

The 3050 is written in Java making it possible to deploy the system on a selection of operating systems. It ships on Mitel's 6000 MAS platform (Linux), and we also have this working on Red Hat Linux and Windows 2000. Targeting networked offices up to 20 users each, the basic hardware config is the equivalent to a standard P3/450 with 128Meg of RAM. The unit has a laptop 20Gig hard disk and has been configured with and without a local CDROM. The 3050 hardware has two network interfaces where the second NIC is either integrated into the box or provided as a USB/Ethernet dongle. This particular hardware has one expansion slot that can be used for an Ethernet NIC or ISDN BRI card today, and soon for T1/E1. We use external PSTN to SIP gateways that connect via SIP/Ethernet and provide both FXO and FXS connections in a variety of port sizes.

Why Java? Mitel picked Java because of its ability to support multiple OS's and a belief that Java has matured to a point where it was possible to create world class, real time applications.

Under the hood:

This version operates on the Mitel 6000 MAS, a Linux distribution that provides most of the traditional components Linux users expect. The firewall, user account management, file server, DHCP server, DNS server, SMTP server (Mail), Print server, NTP server (Time), TFTP server and HTTP server (Web) are all part of the distribution. We also have a scripted user interface that simplifies the installation and configuration of the system to 10 easy questions. The 3050 adds the Sun JDK1.3.1, and Tomcat4 to the basic OS to support the additional 3050 components.

What is in the telephony part of the solution? A Back to Back User Agent (B2BUA), a separate call router, a voicemail sub system an auto-attendant and configuration servlets to configure and maintain the system from low overhead web pages. The B2BUA is the core application that controls the Linux IPTables firewall and provides a SIPUA that all of the other applications use to communicate within the system. Having a centralized UA has enabled Mitel to track the SIP standard making changes in one place that are leveraged through out the rest of the product. The B2BUA and call router handle routing SIP calls both internally and externally, setting up the connection, performing NAT, where necessary and dynamically controlling the built in firewall to allow SIP traffic to setup UDP media streams. The B2BUA maintains knowledge of peer systems to make it possible to track network IP address changes. This enables a network of 3050's connected via ADSL, Cable and other network infrastructures to dynamically adjust routes as DHCP network addresses change.

Basic features are configured via a standard web browser using servlets in order to avoid overhead associated with traditional applets. The servlets allow users to setup toll restriction and routing rules using regular expressions that range from the most simple of rules to very complex system interactions. Other configuration tables include Auto-attendant configuration, Voicemail configuration, Password/Level management, SIP Authentication, PSTN Gateway management, Backup/Restore, Peer configuration, Phone replacement, auto configuration and Phone Management.

The level of complexity of the management interface varies depending on the level of the user accessing the system. Mitel's 5055 SIP phones have been integrated with the 3050, so that a system administrator manages both local and remote phones from the 3050 web pages. All 5055 phones features can be setup and downloaded to sets. For non-sophisticated users, the system will auto-configure connected phones with default extensions and features to insure the system powers up working.

The voicemail sub-system is a stand-alone SIP component that uses the system SIPUA to perform the traditional voicemail functions. Voicemail is recorded and stored as email with audio enclosures on the local or on an external SMTP server. This makes it possible for users to receive voicemail in the traditional way or as email. The voicemail sub-system is implemented using Sun's Java Mail extension to the basic JDK, therefore is OS independent.

The 3050 is completely SIP standard compliant and has been tested with over 40 other vendors for interoperability. Speaking of interop, Mitel is pleased to be hosting SIPit 13, August 18-24, 2003 in Ottawa, Canada. Join us!

For further information please email me at: Anne_Coulombe@mitel.com, Head of SIP-Based Solutions, Mitel Networks.
www.mitel.com >>