A Window to Real-Time Communication

Microsoft debuts support for Session Initiation Protocol in Windows XP.

The Session Initiation Protocol (SIP) may not be a familiar technology term to many corporate users. But that might change now that Microsoft Corp. has built support for the lightweight protocol into the Windows XP desktop operating system that it officially launches this week. In the coming months, more users may learn about SIP and find out if it lives up to its promise to bring more innovative and cost-effective real-time communications to their companies.

SIP, which became an Internet Engineering Task Force (IETF) standard in 1999, lets a user initiate any type of real-time communication session—such as text-based messaging, voice, video or even application-sharing—with another user over an Internet Protocol (IP) network. Extensions to SIP enable instant messaging.

Because SIP is lightweight, it can work not only with PCs but also with other devices, such as mobile phones or personal digital assistants. For instance, a PC user equipped with the right software could make a voice call to a colleague on a cell phone.

How SIP Works The Session Initiation Protocol (SIP) lets one user initiate any type of real-time communication session—such as text-based messaging, voice, video or even application-sharing—with another user over an IP network. Here’s an example of how a typical corporate scenario might work: Alice, who works at Company A, needs to speak with Bob, who works at Company B. Each company has a SIP proxy server, and Alice and Bob can be using any of a variety of clients, including a PC software phone, or softphone; a SIP hardware phone; an analog phone with an adapter; or a SIP-enabled cell phone. 1. When Bob turns on his client, his phone automatically sends a register message to his company’s SIP proxy server. The register message tells the SIP proxy server: If you get a call for Bob, send it to this IP address. 2. Alice decides to call Bob via her PC softphone. She types, “I want to call Bob at Company B.” Her invite request is sent to Company A’s SIP proxy server. 3. Company A’s SIP proxy server uses the Domain Name System to look up Bob’s domain, and the invite request is forwarded to Company B’s SIP proxy server. 4. The Company B SIP proxy server sees that Alice wants to call Bob and forwards her invite request to Bob’s IP address, which it obtained from the registration process. 5. Bob’s phone rings, or a screen pops up, and Bob is asked if he wants to accept the call. His affirmative response, called a 200 OK, is sent to his company’s proxy server. 6. The Company B SIP proxy server forwards the 200 OK to Company A’s SIP proxy server, which sends the 200 OK to Alice’s client. 7. An acknowledgment message, or ACK, is sent directly to Bob’s client. Alice and Bob begin communicating. Note: If either party used an ordinary telephone, a voice-over-IP gateway would be needed between the SIP proxy server and the client device for the connections to be made. Source: Jonathan Rosenberg, chief scientist at Dynamicsoft Inc., co-author of the SIP specification and former co-chairman of the IETF’s SIP Working Group.

Vendors are already making SIP phones and proxy servers, but Microsoft's support is "an important milestone in terms of SIP gaining momentum," says Peter O'Kelly, an analyst at Patricia Seybold Group Inc. in Boston.

Microsoft is so bullish on SIP that it's putting a SIP stack and application programming interface into its entire Windows family, including XP for PCs and embedded devices, CE for the Pocket PC and the Windows .Net Server operating system, says Mark Lee, a lead project manager with the company's Windows team.

In June, Microsoft held a Windows design review event that drew approximately 90 companies to learn about implementing SIP. Microsoft also plans to support Internet-based services that an individual or a company can use for SIP-based messaging: authentication through its .Net Passport service and presence and notification through its .Net Messenger service. But corporations may elect to use their own servers to authenticate users, maintain the "presence" information about when and where users are available, and enable notification between clients, Lee says.

Reuters Group PLC took the latter approach, working with Microsoft on a SIP-based instant messaging system for the financial community. The London-based news and financial information provider got the idea from the instant messaging services that are popular among consumers and corporate users.

"We thought, 'Boy, could that play a role in the financial market,' " says Lewis Knopf, managing director of collaboration services at Reuters. But, Knopf says, his company recognized that existing instant messaging services were too insecure and unreliable and didn't provide the logging mechanisms that financial firms need.

So, working with Microsoft, Reuters approached 25 financial institutions, including Citigroup Inc., Deutsche Bank AG and Morgan Stanley Dean Witter & Co., about creating a high-security, SIP-based instant messaging service and contacts directory. Because Windows XP has yet to gain mainstream usage, Reuters must distribute to its partners SIP-enabled clients that will run on various Windows versions.

On the back end, Reuters is using a SIP-enabled real-time communications server from Microsoft, which has yet to announce the server software, to establish sessions between clients, manage communications and track presence information, Knopf says. Each partner also must have a SIP proxy server to enable messages and logging.

Reuters plans to launch the service with its 25 partners by year's end and make the service available to the rest of the financial industry early next year. Knopf notes that some partners and client companies may elect to host their own instant messaging systems and connect to Reuters' hosted service in federated fashion.

Right now, the firms are piloting text messages, but audio and video may be added in the future, Knopf says. "Our main worry is bandwidth," he says.

The potential for SIP is just starting to be explored. Cambridge, Mass.-based Lotus Software Group and Dulles, Va.-based America Online Inc. recently tested an extension to SIP—SIP for Instant Messaging and Presence Leveraging Extension—to get their proprietary instant messaging services to interoperate on a server-to-server basis.

Some companies are experimenting with replacing private branch exchange telephone systems with a single network that carries both data and voice traffic. For example, telecommunications software developer Webley Systems Inc. in Deerfield, Ill., and voice application network provider Tellme Networks Inc. in Mountain View, Calif., are in the process of equipping internal users with SIP phones.

SIP phones, which can be hardware or software, are configured with SIP proxy addresses. A user says the name of the individual he wants to call, and the request is sent to a voice-activated dialing application and then to a SIP proxy server, which routes the call to a voice-over-IP gateway, if necessary, and then to the intended recipient—even if the recipient is using an ordinary telephone connected to the public switched telephone network.

"A lot of companies are finding that maintaining a data network and voice network is a very expensive proposition," says Don Jackson, vice president of advanced telephony at Tellme Networks. "If you're already going to put in a data network for the PCs on everyone's desktops, why not make the network do double duty and provide voice access as well?"

Since new SIP proxy servers can register a number of devices for any end user, users have the advantage of being able to indicate their preferred choices for incoming calls at any point in time, if they have several device options.

"It's much easier to integrate new applications into these SIP-based networks because they're software-based and the protocol is open," Jackson explains.

Related Information:


New Technology, Features Supported in Windows XP

Some of the new features and technology that are expected to impact corporate users in Microsoft’s new Windows XP desktop operating system:

Application compatibility Allows applications built for older Windows operating systems to run on Windows XP. Operating system catches every application programming interface call and monitors what happens when an application tries to start up. A Program Compatibility Wizard has a set of fixes, or shims, that provide an application with the code that it needs to run. Corporations get an application-compatibility tool kit to test applications. Corporations should have less trouble getting their legacy applications to run on Windows XP than they did on Windows 2000. Microsoft claims that 12,000 commercial applications will run well on Windows XP, compared with approximately 6,000 for Windows 2000.
Remote Desktop/Remote Assistance Remote Desktop lets employees access their primary office desktops from the road. Remote Assistance lets IT staffers see and take control of the screens of mobile users they’re trying to help. Through the Remote Desktop Protocol, a Windows-based terminal or other Windows-based client communicates with a Windows-based Terminal Server, which a corporation must have installed to enable this feature to work. Corporations potentially can reduce costs associated with assisting remote users. Users could gain more flexibility to work from remotelocations.
Improvements to System Restore An administrator can pick a date on the calendar and restore a system to the way it was on that date. Operating system actively monitors system file changes and some application file changes to record or store versions created before the changes occurred. In the event of a problem, an administrator can restore an unlimited number of PCs to a previous state without losing personal data files, such as Word documents, graphics or e-mail. Windows Millennium Edition supported System Restore, but the operating system suffered a noticeable hit on performance when the feature was in use, said Microsoft product manager Tom Laemmel.
Enhanced support for wireless networking (802.1x) A “seamless roaming” feature automatically authenticates users to another wireless network when they change locations. A “zero configuration” feature allows wireless users to gain access to other wireless networks they’re permitted to use. Operating system detects when a user moves to a new wireless network access point and forces reauthentication to ensure appropriate network access. As users roam from one wireless network area to another, the operating system automatically configures itself to the nearest network. Users should find it much easier to stay connected when they’re working in a wireless state. This feature will eliminate the need to write code to enable users to switch from one network to another. All they’ll see is a sign-on screen.

Source: Microsoft Corp.

Copyright © 2001 IDG Communications, Inc.

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