Microsoft KB Archive/198622

= XCON: Adjustment of MTA Reliable Transfer Service Values =

Article ID: 198622

Article Last Modified on 10/28/2006

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APPLIES TO


 * Microsoft Exchange Server 4.0 Standard Edition
 * Microsoft Exchange Server 5.0 Standard Edition
 * Microsoft Exchange Server 5.5 Standard Edition

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This article was previously published under Q198622



SUMMARY
The Microsoft Exchange Server's message transfer agent (MTA) uses Reliable Transfer Service Element (RTSE) values that you can manually edit. These values ensure reliable transfer of the information objects (messages) between MTAs. These settings determine:
 * How much information is transferred before a checkpoint is inserted (Checkpoint Size in Kilobytes).
 * How long to wait after an error to restart message transfer (Recovery Timeout in Seconds).
 * The number of checkpoints that can go unacknowledged before mail transfer is suspended. In other words, after X number of checkpoints, the remote server must acknowledge reception of recent checkpoints and request more (Window Size).

The default settings are sufficient for most networks. However, by adjusting these values you can improve message delivery, particularly over limited bandwidth and unreliable links.



MORE INFORMATION
The Reliable Transfer Service (RTS) settings are located in two different places in the Exchange Server Administrator program.
 * Intrasite RTS values are located in the properties of the MTA Site Configuration object, on the Messaging Defaults tab, in the RTS Values area. These settings also affect connections across a site connector. You must restart all MTAs in the site for any changes made here to take effect.
 * You can also change RTS values on an X.400 Connector's property page, on the Override tab, in the RTS Values area. These values override any MTA Site Configuration values; be sure they match at each end of the connector. You must also restart the MTA at each server for these changes to take effect.
 * Checkpoint Size (K): The amount of data to be transferred before a checkpoint is inserted. A checkpoint consists of one synchronization point (session level) inside an IP packet, about 59 bytes long. Inserting a checkpoint reduces transmission speed but increases the reliability of the connection. If an error occurs and the message must be transferred again, the process restarts from the most recent checkpoint.

If you specify 0, no checkpoint is set. Microsoft does not recommend a checkpoint size of 0. A checkpoint of 5 improves reliability over an unreliable network, but reduces transmission speed. A checkpoint of 1 requires that every packet be explicitly requested before you can send the next. The default value is 30.
 * Recovery Timeout in Seconds: The amount of time after an error occurs that the MTA waits for a reconnection (initiated locally or remotely) before it deletes checkpointed information and restarts the transfer from the beginning. The default value is 60.
 * Window Size: The number of checkpoints that can go unacknowledged before data transfer is suspended. The greater the window size, the greater the transfer rate. The lower the window size, the more reliable the transfer. Only specify window size if the checkpoint size is greater than 0. The default value is 5.

Additional query words: "rts values", "reliable transport service"

Keywords: kbinfo KB198622

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