Microsoft KB Archive/910879

= FIX: You may experience random increases in application response times when an application communicates with an IBM mainframe through an IP-DLC connection in Host Integration Server 2004 =

Article ID: 910879

Article Last Modified on 12/4/2007

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APPLIES TO


 * Microsoft Host Integration Server 2004 Standard Edition

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SYMPTOMS
You may experience random increases in application response times when an application communicates with an IBM mainframe through an IP data link connection (IP-DLC) connection. The IP-DLC connection is configured in Microsoft Host Integration Server 2004.

The increases in application response times are not deterministic. Normal response times may resume without intervention.



CAUSE
The increases in application response times occur when the IP-DLC link service issues false Adaptive Rate-Based (ARB) Flow/Congestion Control responses that include a slowdown indicator. The slowdown indicator informs the receiver of the ARB responses that the data send rate must be reduced. This causes data to be sent at a slower rate. The slower rate causes the increases in application response times.

The false ARB responses are most likely to occur on a lossy network.



Hotfix information
A supported hotfix is now available from Microsoft. However, this hotfix is intended to correct only the problem that is described in this article. Apply this hotfix only to systems that are experiencing this specific problem. This hotfix might receive additional testing. Therefore, if you are not severely affected by this problem, we recommend that you wait for the next service pack that contains this hotfix.

To resolve this problem, submit a request to Microsoft Online Customer Services to obtain the hotfix. To submit an online request to obtain the hotfix, visit the following Microsoft Web site:

http://go.microsoft.com/?linkid=6294451

Note If additional issues occur or any troubleshooting is required, you might have to create a separate service request. The usual support costs will apply to additional support questions and issues that do not qualify for this specific hotfix. To create a separate service request, visit the following Microsoft Web site:

http://support.microsoft.com/contactus/?ws=support

File information
The English version of this hotfix has the file attributes (or later file attributes) that are listed in the following table. The dates and times for these files are listed in Coordinated Universal Time (UTC). When you view the file information, it is converted to local time. To find the difference between UTC and local time, use the Time Zone tab in the Date and Time tool in Control Panel.

Note Because of file dependencies, the most recent hotfix that contains these files may also contain additional files.



STATUS
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the &quot;Applies to&quot; section.



MORE INFORMATION
The IP-DLC link service uses an algorithm that is called ARB-R. ARB-R stands for Adaptive Rate-Based Flow/Congestion Control - Responsive Mode. The ARB-R algorithm detects congestion on the network by looking at changes in the time a packet takes to be sent from the remote node to the local node. This is achieved by periodically sending timing information in network layer packets (NLPs). This timing information is held in the optional ARB segment. Specifically, each ARB segment contains the number of microseconds that have passed since the sending node sent the last ARB segment (sender_interval). When the local computer receives the ARB segment, the local computer calculates the number of microseconds that have passed since the local computer last received an ARB segment (receiver_interval). Then, the local computer compares the receiver_interval value to the sender_interval value.

On a stable network, the receiver_interval value is the same as the sender_interval value. If the network becomes slower, the network propagation delay for the first packet is smaller than the network propagation delay for the second packet. This causes the receiver_interval value to be larger than the sender_interval value. Conversely, if the network becomes faster, the receiver_interval value is smaller than the sender_interval value. The ARB-R algorithm maintains a cumulative sum that is determined by subtracting the sender_interval value from the receiver_interval value. This is referred to as the delay change sum (DCS). Every time that an ARB segment arrives, the ARB-R algorithm adds the value of the following expression to the DCS:

(receiver_interval - sender_interval)

If the network becomes faster, the DCS decreases. If the network becomes slower, the DCS increases.

If the DCS exceeds a certain value, the ARB-R algorithm sends a slowdown indicator to the remote node. This causes the remote node to send data at a slower rate in an attempt to relieve network congestion.

