Comment 0 for bug 1505631

[Overview]
The IEEE 802.1p signaling standard defines traffic prioritization at Layer 2 of the OSI model. Layer 2 network devices, such as switches, that adhere to this standard can group incoming packets into separate traffic classes.The 802.1p standard is used to prioritize packets as they traverse a network segment (subnet).When a subnet becomes congested, causing a Layer 2 network device to drop packets, the packets marked for higher priority receive preferential treatment and are serviced before packets with lower priorities.

The 802.1p priority markings for a packet are appended to the MAC header.On Ethernet networks, 802.1p priority markings are carried in Virtual Local Area Network (VLAN) tags. The IEEE 802.1q standard defines VLANs and VLAN tags. This standard specifies a 3-bit field for priority in the VLAN tag, but it does not define the values for the field. The 802.1p standard defines the values for the priority field. This standard defines eight priority classes (0 - 7). Network administrators can determine the actual mappings, but the standard makes general recommendations. The VLAN tag is placed inside the Ethernet header, between the source address and either the Length field (for an IEEE 802.3 frame) or the EtherType field (for an Ethernet II frame) in the MAC header. The 802.1p marking determines the service level that a packet receives when it crosses an 802.1p-enabled network segment.

[Proposal]
Existing QoS [1]_ framework can be extend for supporting VLAN priority.

[Benefits]
- Enhancement to the existing QoS functionality.

[What is the enhancement?]
- Add VLAN tagging support to the QoS extension.
- Add additional command lines for realizing ECN functionality.
- Add OVS support.

[Related information]
[1] QoS
   https://review.openstack.org/#/c/88599/
[2] Specification
    https://blueprints.launchpad.net/neutron/+spec/vlan-802.1p-qos