Articles by Mark A. Miller 

Understanding SIP�Part III: Message Formats

Like HTTP, SIP operation is based on a request/response model. Like SMTP, each SIP message is headed by an email-address-like identifier. A series of methods and Status Codes specify purposes and procedures.

Understanding SIP�Part II: Protocol Capabilities

As a robust client/server application modeled on familiar IETF protocols, such as SMTP and HTTP, SIP would seem to have a simple, clearly defined role in a suite of IP tools. However, a number of variables add complexity to SIP's operation.

Understanding SIP�Part I: History and Architecture

Reflecting the IETF's pragmatic development mind-set, and built on other well-known protocols such as HTTP and SMTP, SIP is viewed by many as fundamentally simpler than H.323.

Understanding H.323�Part IV: Testing System Interoperability

The quirky evolution path taken by H.323 and related standards makes for some serious implementation challenges. Fortunately, there are tools to help.

Understanding H.323�Part III: Signaling

The communications—such as on/off-hook, dialtone, and busy signal—that set up and terminate calls on the PSTN are replaced by a complex set of protocols and procedures in the packet-based H.323 world.

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