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Can you explain in detail how IM works? And is it possible to develop your own IM B2B solution?

I read the previous answers you gave regarding using the Microsoft IM SDK. I would like to know, however, if you know where one could find more detailed information on how IM actually works. I played around with the Microsoft SDK. However, to my understanding, it still looks like you have to use its infrastructure. How do you think it's possible to develop your own IM B2B solution? And can it be done on your own, or is using the MSN platform the answer?
Here's how IM works in a nutshell. You have a virtual server component which runs under IIS on your Exchange 2000 server. You then have IM clients that connect to this virtual server. This is done using the RVP protocol, a proprietary protocol development by Microsoft that is essentially an extension to the HTTP 1.1 protocol. RVP extends HTTP 1.1 by adding additional command verbs which are used for presence information, subscription information and security/privacy. Because RVP is an extension of HTTP 1.1, all communication takes place over TCP port 80. However, unlike HTTP servers, this port cannot be changed. Exchange 2000's IM is hard-coded to use this port, and only this port.

If you are developing your own B2B solution for IM, and you want to use a Microsoft solution, you have two choices: create your own now using the IM SDK; or wait until after .NET Server is released and look for the release of a Microsoft product called RTC Server (Real-Time Communications Server). It may or may not be called this, but basically, there will be an server product that supports IM, although it will do so using SIP (Session Initiation Protocol) and not RVP. SIP is a new protocol supported by RFCs and it is not proprietary to Microsoft like RVP is.

If you do choose to go with Exchange 2000 and the current implementation of IM, you can still quickly and easily create a B2B solution. Basically, once you have IM running in each organization, the only remaining work that needs to be done is:

  1. Adding the proper RVP records to each businesses DNS server. If it cannot resolve the RVP record, an IM client won't know how to contact an IM server.

  2. Configuring your firewall, router, NAT, whatever, to allow inbound HTTP port 80 traffic to your IM server. Note that you'll want to make sure your network device(s) recognize RVP; some older firewalls and routers do not and will block access.
  3. To add contacts, you may be looking at something like MMS (Microsoft Metadirectory Services) or opening up LDAP requests.

For more information, see:

  • Exchange 2000 Instant Messaging Setup,
  • Exchange 2000 Instant Message Service
  • Instant Messaging Tip: Deploying Exchange 2000 Instant Messaging Software in an Environment Other Than Windows 2000
  • Instant Message Polling and Fixed Port Callback Delivery.
  • Dig Deeper on Microsoft messaging and collaboration services

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