Packet prioritization

Because communication between the branch office and the main office varies in importance, packets must be differentiated based on their priority, and accorded preferential use of the limited bandwidth accordingly. Microsoft Internet Security and Acceleration (ISA) Server 2006 supports bandwidth control by providing packet prioritization using the Differentiated Services (DiffServ) protocol. The DiffServ protocol provides a framework that enables deployment of scalable service discrimination over the Internet. DiffServ uses a tab in the IP header of each packet to label its priority.

Packet prioritization is a global Hypertext Transfer Protocol (HTTP) policy setting. It applies to all browser traffic that passes through ISA Server, rather than to traffic handled by a specific rule. The packet prioritization functionality is provided by the DiffServ Web filter, which scans the Uniform Resource Locator (URL) or domain and assigns the packet priority using DiffServ bits. You can create priorities in ISA Server whose DiffServ bits match those of the priorities on your corporate routers.

This filter has a high priority, and is high in the ordered list of Web filters. This is because the DiffServ Web filter must be aware of the size of the request or response that is being sent, and therefore must inspect the data at the point that it is sent or received by ISA Server. Do not change the default priority and order settings of this filter.

Notes

• ISA Server does not add DiffServ bits to traffic on protocols other than HTTP or HTTPS. ISA Server may not transmit existing DiffServ bits for traffic on other protocols.
• Packet prioritization using DiffServ works in networks whose routers support Quality of Service (QoS) functionality.

After you enable DiffServ, you configure the URLs and domains which will be subject to prioritization. You can configure packet prioritization for specific URLs or domains. For instructions, see Assign a priority to a URL and Assign a priority to a domain.

When ISA Server forwards requests for these URLs or domains to a router that supports Quality of Service, it also forwards the DiffServ value that you specify for the priority assigned to the specific URL or domain. For instructions on configuring priorities, see Configure priorities to apply to DiffServ values.

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