Microsoft KB Archive/156149

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MSDLC32 May Not Receive All Packets in Heavy Traffic

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Q156149

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The information in this article applies to:


 * Microsoft Windows 95

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SYMPTOMS
Programs using the Microsoft 32-bit DLC protocol may not be able to connect to the host over the network, especially when first starting up.

CAUSE
If the client receives a large number of DLC packets in an extremely short period of time, the MSDLC32 protocol may be unable to dynamically allocate additional buffers quickly enough to successfully receive all incoming packets.

RESOLUTION
This issue is resolved by the following updated file for Windows 95 and OEM Service Release 2 (OSR2), and later versions of this file:

  DLC.VXD  version 4.10.991  dated 8/27/96  241,566 bytes

STATUS
Microsoft has confirmed this to be a problem in Microsoft Windows 95 and OEM Service Release 2 (OSR2). An update to address this problem is now available, but is not fully regression tested and should be applied only to computers experiencing this specific problem. Unless you are severely impacted by this specific problem, Microsoft does not recommend implementing this update at this time. Contact Microsoft Technical Support for additional information about the availability of this update.

This issue is resolved in Microsoft Windows 98.

MORE INFORMATION
When MSDLC32 initializes, it allocates a certain number of buffers (specifically, Read CCB2 buffers) for incoming DLC packets. Over time, as additional buffers are needed, they are allocated dynamically. In the original release of MSDLC32, the initial number of Read CCB2 buffers allocated is 16. In this update, that number is increased to 64. By allocating more buffers initially, the buffers are available to be used immediately, without the delay incurred with dynamic allocation. Additional buffers are dynamically allocated later as needed.

This problem may occur in an environment using multiple DLC hosts with multiple routes to each host. In such environments, a very large number of packets may be received by the client nearly simultaneously in response to a single query. Under such high-stress situations, packets could be dropped during the time new buffers are being allocated to receive them.

This problem is more likely to occur when first starting a DLC session, because the buffer pool typically grows during the course of normal usage to be sufficient to accommodate surges in received packets.

For additional information about Windows 95 updates, please see the following article in the Microsoft Knowledge Base:

"Q161020 Implementing Windows 95 Updates" Additional query words: attachmate 3270 sna

Keywords : kbnetwork kbpolicy win95 kbAPI kbDLC kbSDKPlatform kbGrpDSNet

Issue type : kbprb

Technology : kbWin95search kbWin95