Setsockopt Is Unable to Mark the Internet Protocol Type of Service Bits in Internet Protocol Packet Header
ID: Q248611
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This article discusses a Beta release of a Microsoft product. The
information in this article is provided as-is and is subject to change
without notice.
No formal product support is available from Microsoft for this Beta
product. For information about obtaining support for a Beta release,
please see the documentation included with the Beta product files, or
check the Web location from which you downloaded the release.
The information in this article applies to:
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Microsoft Windows NT Server versions 4.0, 4.0 SP5
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Microsoft Windows NT Workstation versions 4.0, 4.0 SP5
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Microsoft Windows 2000 Professional
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Microsoft Windows 2000 Advanced Server
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Microsoft Windows 2000 Server
SUMMARY
Windows NT 4.0 and Windows 2000 do not support the marking of Internet Protocol (IP) Type of Service (ToS) bits with Setsockopt.
MORE INFORMATION
Typically the operating system subjects a program resource request for priority to policy and resource checks to determine the availability of resources along a network data path before actually determining whether to permit the prioritization. A program has no way to interact with the network elements to determine whether the resources are available.
The former ToS and precedence bits specified in Request For Comment (RFC) 1349 have been made obsolete by RFCs 2474 and 2475. These RFCs replaced ToS with Differentiated Services (DiffServ).
DiffServ Code Point (DSCP) enables packets that pass through network devices operating on layer 3 information, such as routers, to have their relative priorities differentiated from one another. DSCP is established by setting the first six bits of the ToS field in the IP header. DSCP has assumed the function of determining IP precedence, but maintains backward compatibility. With DSCP marking, layer 3 devices can establish aggregated precedence-based queues and provide better service to packets that have a higher relative priority.
The is particularly beneficial when packet services are subject to queuing, as is the case under significant network traffic loads associated with streaming media presentations and other real-time data streams. For DSCP to be effective, layer 3 devices must be DSCP-enabled.
Internet Protocol Type of Service (IP_ToS) changes the default value set by the Transport Control Protocol/Internet Protocol (TCP/IP) service provider in the ToS field of the IP header in outgoing datagrams. With the implementation of DSCP, using Setsockopt to modify the IP_ToS settings of an IP datagram is not required. To determine if IP_ToS is supported, a program may use the getsockopt parameter to obtain the current options in affect. If getsockopt does not work, the IP_ToS option is not supported.
For information about the use and application of the Quality of Service (QoS) Application Programming Interfaces (APIs) which have effectively replaced the IP_ToS option, see MSDN Online and search for QoS.
For additional information about traffic prioritization, click the article numbers below
to view the articles in the Microsoft Knowledge Base:
Q222102 Traffic Prioritization Using IP Precedence
Q222020 Description of 802.1P Signaling
Q233039 QoS Queuing Techniques
Additional query words:
Keywords : kbnetwork
Version : WINDOWS:2000; winnt:4.0,4.0 SP5
Platform : WINDOWS winnt
Issue type : kbinfo