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Subject: RE: [ws-rx] Issue i022, RM Assertions

Retransmission parameters as well as algorithms are problematic for the following reasons:

1)       The characteristics of the path from source to destination are often unknown and often are time-variant.

2)       2) Retransmissions if too frequent cause flooding and potential catastrophic degradation if the path is near saturation

3)       The Path may consist of not only transmission means, but also intermediaries with attendant processing delays

4)       Exponential backoff may be implemented many ways, there is more than one algorithm any they have different parameters

5)       Backoff algorithm selection may be implementation specific, what is good for cell phones may not be good for cluster interconnected nodes

6)       I have found no theoretical modeling available of the case of web services cum intermediaries

7)       Most published data concerning the behavior of backoff algorithms examine fairly simple network segment related saturation and do not address client, server, let alone intermediary saturation.

8)       Exponential backoff algorithms need a recovery mechanism for those situations where there is a high standard deviation of delay.

9)       TCP/IP experience has shown that efficiencies are improved with an adaptive mechanism as described in TCP Extensions for High Performance (see RFC 1323 RTTM)


Clearly a backoff mechanism is required; however implementation specific needs are not served well by the selection of any specific algorithm for all potential implementations of this specification.  It is recommended that implementers utilizing IP based transmission media consider the mechanism described in RFC 1323.  Delete all re-transmission parameters as described in the specification since they are unnecessary and unhelpful should the implementer use an algorithm with a different set of controls.




From: Vikas Deolaliker [mailto:vikas@sonoasystems.com]
Sent: Thursday, August 04, 2005 9:53 AM
To: ws-rx@lists.oasis-open.org
Subject: [ws-rx] Issue i022, RM Assertions





The RM policy assertions, specifically, InActivityTimeout, BaseRetransmissionInterval and ExponentialBackoff parameters need to be more finely specified.


The following are the areas which need finer specification


a)   Default Value for InActivityTimeout, BaseRetransmissionInterval and ExponentialBackoff:

There needs to be a default set for these parameters. Currently the specification says “If omitted, there is no implied value.” Since these parameters dictate the delivery of the message, an implementation is going to assume a default anyways. Not specifying this will make implementations assume a different default value and cause unwanted timeouts.


b)   Definition of InActivity

There needs to be a discussion of definition of inactivity. If RMS sends a sequence to RMD and is waiting for the response which is delayed for whatever reason, is that inactivity on the link between RMS and RMD counted towards InActivityTimeout? If yes, then it is entirely possible that while waiting for a sequence response, RMS could timeout due to InActivity.


c)   Applicability of InActivityTimeout:

It needs to be specified to which end this parameter is applicable. It seems like sequence creator starts the timer for InActivityTimeout. If the intention is that this timer exists on both ends of a sender and receiver engaged in a RM sequence, we need to define a method for synchronization of the timer value of this parameter between them. For example an KeepAlive message would need to be defined for keeping sequence alive.


d)   Corner Case Handling:

There needs to be a discussion of the corner case when the BaseRetransmissionInterval exceeds InActivityTimeout. This can happen when the RMD is indisposed and ExponentialBackoff drives up the value of BaseRetransmissionInterval. In this case my retransmission is schedule later than the timeout that I need to abide to. What state does the RMS enter in this situation?


e)   BaseRetransmissionInterval Needs an Upper Bound:

If an RMD is offline for extended period of time, one can expect the BaseRetransmissionInterval to be exponentially backed off i.e. become large enough to be not meaningful anymore. Having an upper bound on this parameter will enable the RMS to stop retransmitting and report a fault. 






1)   InActivityTimeout and BaseRetransmissionInterval can be merged into one i.e. BaseRetransmissionTimeout. Having just one counter on the RMS and RMD will reduce the run-time resources (much simpler state machine) required to implement RM-Assertions and avoid confusion (unknown states in state machine) caused by two timeouts. Having a separate timeout for sequence and retransmission may not be necessary as activity on the RM link is transmission/retransmission. I believe one timeout i.e. BaseRetransmissionTimeout does not change the behavior of the system. Once this timeout occurs the sequence has to timeout as the implication of the timeout is the destination is either congested or offline.


2)   If InActivityTimeout has to be there as a parameter, we need to fully specify it with mechanisms for synchronization and keepalive. In addition, we need to discuss how the corner cases and other conflicts that occur when one has two timeout (as discussed in a-e above) are handled.





Sonoa Systems, Inc.

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Santa Clara, CA 95054

(408) 748-1730 x100


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