IEEE 802.1p
Encyclopedia
IEEE P802.1p is the name of a task group active during 1995–98 responsible for adding traffic class expediting and dynamic multicast filtering to the IEEE 802.1D
standard. Essentially, they provided a mechanism for implementing Quality of Service
(QoS) at the Media Access Control
(MAC) level. The group's work with the new priority classes and Generic Attribute Registration Protocol (GARP) was not published separately but was incorporated into a major revision of the standard, IEEE 802.1D-1998. It 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 (CoS), is a 3-bit
field called the Priority Code Point (PCP) within an Ethernet frame
header when using tagged frames on an 802.1 network. It specifies a priority value of between 0 and 7 inclusive that can be used by QoS disciplines to differentiate traffic. Although this technique is commonly referred to as IEEE 802.1p, there is no standard or amendment by that name published by the IEEE.
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 were revised in IEEE 802.1Q-2005 and differ from the original recommendations found in IEEE 802.1D-2004.
IEEE 802.1D
802.1D is the IEEE MAC Bridges standard which includes Bridging, Spanning Tree 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 the widely deployed 802.3 , 802.11 and 802.16 standards.VLANs are not...
standard. Essentially, they provided a mechanism for implementing Quality of Service
Quality of service
The quality of service refers to several related aspects of telephony and computer networks that allow the transport of traffic with special requirements...
(QoS) at the Media Access Control
Media Access Control
The media access control data communication protocol sub-layer, also known as the medium access control, is a sublayer of the data link layer specified in the seven-layer OSI model , and in the four-layer TCP/IP model...
(MAC) level. The group's work with the new priority classes and Generic Attribute Registration Protocol (GARP) was not published separately but was incorporated into a major revision of the standard, IEEE 802.1D-1998. It 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 (CoS), is a 3-bit
Bit
A bit is the basic unit of information in computing and telecommunications; it is the amount of information stored by a digital device or other physical system that exists in one of two possible distinct states...
field called the Priority Code Point (PCP) within an Ethernet frame
Ethernet frame
A data packet on an Ethernet link is called an Ethernet frame. A frame begins with Preamble and Start Frame Delimiter. Following which, each Ethernet frame continues with an Ethernet header featuring destination and source MAC addresses. The middle section of the frame is payload data including any...
header when using tagged frames on an 802.1 network. It specifies a priority value of between 0 and 7 inclusive that can be used by QoS disciplines to differentiate traffic. Although this technique is commonly referred to as IEEE 802.1p, there is no standard or amendment by that name published by the IEEE.
Priority levels
Eight different classes of service are available as expressed through the 3-bit PCP field in an IEEE 802.1QIEEE 802.1Q
IEEE 802.1Q is the networking standard that supports Virtual LANs on an Ethernet network. The standard defines a system of VLAN tagging for Ethernet frames and the accompanying procedures to be used by bridges and switches in handling such frames...
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:
| PCP | Network priority | Acronym | Traffic characteristics |
|---|---|---|---|
| 1 | 0 (lowest) | BK | Background |
| 0 | 1 | BE | Best Effort |
| 2 | 2 | EE | Excellent Effort |
| 3 | 3 | CA | Critical Applications |
| 4 | 4 | VI | Video, < 100 ms latency |
| 5 | 5 | VO | Voice, < 10 ms latency Latency (audio) Latency refers to a short period of delay between when an audio signal enters and when it emerges from a system... |
| 6 | 6 | IC | Internetwork Control |
| 7 | 7 (highest) | NC | Network Control |
Note that the above recommendations were revised in IEEE 802.1Q-2005 and differ from the original recommendations found in IEEE 802.1D-2004.
See also
- IEEE 802.1IEEE 802.1IEEE 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 other wide area networks* 802 Link Security* 802 overall network management...
- IEEE 802.11eIEEE 802.11eIEEE 802.11e-2005 or 802.11e is an approved amendment to the IEEE 802.11 standard that defines a set of Quality of Service enhancements for wireless LAN applications through modifications to the Media Access Control layer. The standard is considered of critical importance for delay-sensitive...
- IEEE 802.3IEEE 802.3IEEE 802.3 is a working group and a collection of IEEE standards produced by the working group defining the physical layer and data link layer's media access control of wired Ethernet. This is generally a local area network technology with some wide area network applications...
- Type of ServiceType of ServiceThe type of service field in the IPv4 header has had various purposes over the years, and has been defined in different ways by five RFCs...
(ToS) - DiffServ