Internet Information Services (IIS) enforces a limit on the maximum number of application pool requests that can be held in the queue at any given time. If this limit is reached, any new requests will be denied and users receive a "503 - Service Unavailable" error message. By default, IIS sets the queue length to 1,000 requests. That default value might be too low because, with a queue length of 1,000, Communicator Web Access (2007 R2 release) will only be able to handle approximately 650 concurrent users before new users began to be turned away.

To help ensure availability of the Communicator Web Access service, it is recommended that you set the value of the IIS queue length to the expected maximum number of users times 1.5. For example, suppose you expect that, at most, you will have 2,000 users logged on to Communicator Web Access at a given time. In that case, you should set the queue length to 3,000 (that is, 2,000 users multiplied by 1.5).

To change the queue length setting in IIS 7.0

  1. Click Start, point to Administrative Tools, and then click Internet Information Services (IIS) Manager.

  2. In IIS Manager, expand the name of the IIS server, and then click Application Pools.

  3. In the Application Poolspane, right-click the Communicator Web Access application pool and then click Advanced Settings.

  4. In the Advanced Settingsdialog box, under General, click Queue Length, and then type a value that is 1.5 times the maximum number of concurrent users in your Communicator Web Access deployment.

  5. Click OK.

To change the queue length setting in IIS 6.0

  1. Click Start, click All Programs, point to Administrative Tools, and then click Internet Information Services (IIS) Manager.

  2. In IIS Manager, expand the Sitesnode, right-click the Communicator Web Access Application pool and then click Properties.

  3. In the Propertiesdialog box, click the Performancetab.

  4. Under Request Queue Limit, click Limit the kernel request queue (Number of requests), and then type a value that is 1.5 times the maximum number of concurrent users in your Communicator Web Access deployment.

  5. Click OK.