Modify Remote Procedure Call Compression in Exchange Server 2003

By default, all remote procedure call (RPC) data that moves between Microsoft Outlook 2003 and Exchange Server 2003 is compressed, regardless of its size. The algorithms that are used by the Exchange 2003 RPC compression code produce very little overhead on the server, and at the same time, they greatly reduce the number of bytes that are sent. The algorithms therefore help to speed up communication between the client and the server. Even though there are advantages, you may want to control RPC compression. To give you this flexibility, you can add three new registry key values to the system settings:

• Rpc Compression Minimum Size
• Rpc Compression Enabled
• Rpc Packing Enabled

Even though the compression algorithms that are used by Exchange make compression cheap in terms of processor cycles when you compare them to other compression schemes, compression is still an expensive operation. Therefore, packets that are under a specific size do not justify the high cost to compress the data. Because the relationship between the cost to compress and the level of compression is not a linear relationship, it is more expensive to compress the first byte than it is to compress any subsequent bytes. Because Transmission Control Protocol (TCP) packets have a limit of 1.4 kilobytes, the cost to compress a packet that is less than 1 kilobyte outweighs any benefits of making a single packet smaller. By not compressing packets that are 1 kilobyte or smaller, you can regain some processor cycles.

Sometimes you may not want to use any compression at all. If you are trying to troubleshoot connectivity problems and you are using Network Monitor to view the packets that are being sent over the network, RPC compression may make analysis difficult because you only see the compressed data in the trace.

By using these registry keys to modify RPC compression, you can control Exchange 2003 RPC to your advantage.

WARNING: If you use Registry Editor incorrectly, you may cause serious problems that may require you to reinstall your operating system. Microsoft cannot guarantee that you can solve problems that result from using Registry Editor incorrectly. Use Registry Editor at your own risk.

You can use the following registry keys control RPC compression on your Exchange Server:

• Location: HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\MSExchangeIS\ParametersSystem
  Parameter: Rpc Compression Enabled
  Type: REG_DWORD
  Value: 0x00000001 means enabled (default)
• Location: HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\MSExchangeIS\ParametersSystem
  Parameter: Rpc Compression Minimum Size
  Type: REG_DWORD
  Value: Minimum number of bytes required in the RPC packet before compression is activated (defaults to 1024)
• Location: HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\MSExchangeIS\ParametersSystem
  Parameter: Rpc Packing Enabled
  Type: REG_DWORD
  Value: 1 is enabled (default) , 0 is disabled