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 (910879)

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.

RESOLUTION

Hotfix information

A supported hotfix is now available from Microsoft, but it is only intended to correct the problem that is described in this article. Only apply it to systems that are experiencing this specific problem. This hotfix may receive additional testing. Therefore, if you are not severely affected by this problem, we recommend that you wait for the next Host Integration Server 2004 service pack that contains this hotfix.

To resolve this problem immediately, contact Microsoft Product Support Services to obtain the hotfix. For a complete list of Microsoft Product Support Services telephone numbers and information about support costs, visit the following Microsoft Web site:

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

Note In special cases, charges that are ordinarily incurred for support calls may be canceled if a Microsoft Support Professional determines that a specific update will resolve your problem. The usual support costs will apply to additional support questions and issues that do not qualify for the specific update in question.

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.

File name	File version	File size	Date	Time	Platform	SP requirement
Snaipdlc.dll	6.0.1998.0	960,000	16-Nov-2005	21:56	x86	SP1
Snaservr.exe	6.0.1998.0	407,552	16-Nov-2005	21:56	x86	SP1
Trcipdlc.dll	6.0.1998.0	2,945,024	16-Nov-2005	21:56	x86	SP1
Trcservr.exe	6.0.1998.0	847,360	16-Nov-2005	21:56	x86	SP1

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

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.

REFERENCES

For more information about Advanced Peer-to-Peer Networking (APPN), High Performance Routing (HPR), and the ARB-R algorithm that is implemented in APPN/HPR networks, visit the following IBM Web site:

http://publib-b.boulder.ibm.com/Redbooks.nsf/RedbookAbstracts/sg243669.html

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