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IEEE P802.1p was a task group active from 1995 to 1998, responsible for adding traffic class expediting and dynamic
multicast In computer networking, multicast is group communication where data transmission is addressed to a group of destination computers simultaneously. Multicast can be one-to-many or many-to-many distribution. Multicast should not be confused with ...
filtering to the
IEEE 802.1D IEEE 802.1D is the Ethernet MAC bridges standard which includes bridging, Spanning Tree Protocol and others. It is standardized by the IEEE 802.1 working group. It includes details specific to linking many of the other 802 projects including t ...
standard. The task group developed a mechanism for implementing
quality of service Quality of service (QoS) is the description or measurement of the overall performance of a service, such as a telephony or computer network, or a cloud computing service, particularly the performance seen by the users of the network. To quantitat ...
(QoS) at the
media access control In IEEE 802 LAN/MAN standards, the medium access control (MAC, also called media access control) sublayer is the layer that controls the hardware responsible for interaction with the wired, optical or wireless transmission medium. The MAC sublay ...
(MAC) level. Although this technique is commonly referred to as IEEE 802.1p, the group's work with the new priority classes and
Generic Attribute Registration Protocol Multiple Registration Protocol (MRP), which replaced Generic Attribute Registration Protocol (GARP), is a generic registration framework defined by the IEEE 802.1ak amendment to the IEEE 802.1Q standard. MRP allows Network bridge, bridges, Network ...
(GARP) was not published separately but was incorporated into a major revision of the standard, IEEE 802.1D-1998, which subsequently was incorporated into IEEE 802.1Q-2014 standard. The work also required a short amendment extending the frame size of the Ethernet standard by four bytes which was published as IEEE 802.3ac in 1998. The QoS technique developed by the working group, also known as
class of service Class of service (COS or CoS) is a parameter used in data and voice protocols to differentiate the types of payloads contained in the packet being transmitted. The objective of such differentiation is generally associated with assigning prioritie ...
(CoS), is a 3-
bit The bit is the most basic unit of information in computing and digital communications. The name is a portmanteau of binary digit. The bit represents a logical state with one of two possible values. These values are most commonly represente ...
field called the Priority Code Point (PCP) within an
Ethernet frame header In computer networking, an Ethernet frame is a data link layer protocol data unit and uses the underlying Ethernet physical layer transport mechanisms. In other words, a data unit on an Ethernet link transports an Ethernet frame as its payload. ...
when using
VLAN A virtual local area network (VLAN) is any broadcast domain that is partitioned and isolated in a computer network at the data link layer ( OSI layer 2).IEEE 802.1Q-2011, ''1.4 VLAN aims and benefits'' In this context, virtual, refers to a ph ...
tagged frames as defined by
IEEE 802.1Q IEEE 802.1Q, often referred to as Dot1q, is the networking standard that supports virtual local area networking (VLANs) on an IEEE 802.3 Ethernet network. The standard defines a system of VLAN tagging for Ethernet frames and the accompanying proce ...
. It specifies a priority value of between 0 and 7 inclusive that can be used by QoS disciplines to differentiate traffic.


Priority levels

Eight different classes of service are available as expressed through the 3-bit PCP field in an
IEEE 802.1Q IEEE 802.1Q, often referred to as Dot1q, is the networking standard that supports virtual local area networking (VLANs) on an IEEE 802.3 Ethernet network. The standard defines a system of VLAN tagging for Ethernet frames and the accompanying proce ...
header added to the frame. The way traffic is treated when assigned to any particular class is undefined and left to the implementation. The IEEE, however, has made some broad recommendations: Note that the above recommendations have been in force since IEEE 802.1Q-2005 and were revised from the original recommendations in IEEE 802.1D-2004 to better accommodate
differentiated services Differentiated services or DiffServ is a computer networking architecture that specifies a mechanism for classifying and managing network traffic and providing quality of service (QoS) on modern IP networks. DiffServ can, for example, be used t ...
for
IP network The Internet protocol suite, commonly known as TCP/IP, is a framework for organizing the set of communication protocols used in the Internet and similar computer networks according to functional criteria. The foundational protocols in the suit ...
ing.


See also

*
IEEE 802.1 IEEE 802.1 is a working group of the IEEE 802 project of the IEEE Standards Association. It is concerned with: * 802 LAN/MAN architecture * internetworking among 802 LANs, MANs and wide area networks * 802 Link Security * 802 overall network manage ...
* IEEE 802.11e * IEEE 802.3 * Type of service (ToS) * Ethernet priority flow control


References

{{IEEE standards


External links


IEEE 802.1D-2004
(contains original 802.1p changes - now part of 802.1Q-2014)
IEEE 802.1Q-2014
(incorporates 802.1D) Quality of service IEEE 802.1p Working groups Ethernet standards