Browse Prior Art Database

A System to Provide Highly Available Strictly Time Constraint Session Management

IP.com Disclosure Number: IPCOM000016390D
Original Publication Date: 2002-Dec-06
Included in the Prior Art Database: 2003-Jun-21
Document File: 4 page(s) / 95K

Publishing Venue

IBM

Abstract

Published here is a method and system to provide robust time constraint session management under distributed environment. This system is composed of the Timer Manager, State Manager and State Consumers. All these components are distributed and there is no "Single Point of Failure".

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  A System to Provide Highly Available Strictly Time Constraint Session Management

Background:

Delivering messages over IP network reliably has always been a desirable feature of Internet applications. A lot of methods have been designed to tackle the problem of reliably send/receive messages over IP networks, among them "Round Robin DNS" algorithm for Load Balance and AFS (Advanced File System from IBM) for replicating distributed states on the backend are examples of such methods. After IP telephony applications become popular, there come the requirements of reliably access session states under some specific time sequence.

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Figure 1 SIP INVITE client transaction

E.g. Figure 1 shows a standard transaction in SIP[1] (Session Initiation Protocol) - state transitions for INVITE methods. There're totally 4 states "Calling", "Proceeding", "Completed", "Terminated". Key points (as defined by SIP) are ,
(1) accompanying the transition into some states there'll be some timers initiated. e.g. as shown in figure 1, when entering "Calling" state, timer A will initiate.
(2) when timer A fires some time later, retransmission of message is required and "Calling" state remains.
(3) under some circumstances, e.g. when timer B fires, state will be transited from "Calling" to "Terminated".
(4) some state transition happened when a specific message is received at current state, e.g. state will be transited from "Calling" to "Proceeding" after receiving "INVITE" messages.

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In order to provide robust time constraint session management under distributed environment there are two basic requirements,
(1) Whenever a new message comes (request messages such as INVITE/ACK, response messages such as 1xx/2xx/300-699 ...) a stateless session will begin to serve this message, instead of memorizing the current state of the transaction that the message belongs to, it will retrieve current state from a distributed (remote) state manager, then depending on current state and latest received message it will decide what's the next state. This issue has been solved in a number of ways, such as OLD (OnLine Directory) in Lotus Sametime, so that you can be sure of reliable state management/retrieval in a transparent way.
(2) The second requirement is that state should be separated from processing and if the state consumer (who has been triggered previously when some timer fires) also fails, we need to find out a way to notify a backup state consumer of that failure. This second requirement is especially important be...