Enhanced Transmission Selection; 802.1P Priority Values - Lenovo Flex System Fabric CN4093 Application Manual

Enhanced Transmission Selection

802.1p Priority Values

278
CN4093 Application Guide for N/OS 8.2
Enhanced Transmission Selection (ETS) is defined in IEEE 802.1Qaz. ETS provides
a method for allocating port bandwidth based on 802.1p priority values in the
VLAN tag. Using ETS, different amounts of link bandwidth can specified for
different traffic types (such as for LAN, SAN, and management).
ETS is an essential component in a CEE environment that carries different types of
traffic, each of which is sensitive to different handling criteria, such as Storage Area
Networks (SANs) that are sensitive to packet loss, and LAN applications that may
be latency‐sensitive. In a single converged link, such as when implementing FCoE,
ETS allows SAN and LAN traffic to coexist without imposing contrary handling
requirements upon each other.
The ETS feature requires CEE to be turned on (see "Turning CEE On or Off" on
page 265).
Under the 802.1p standard, there are eight available priority values, with values
numbered 0 through 7, which can be placed in the priority field of the 802.1Q
VLAN tag:
16 bits
Tag Protocol ID (0x8100)
0
Servers and other network devices may be configured to assign different priority
values to packets belonging to different traffic types (such as SAN and LAN).
ETS uses the assigned 802.1p priority values to identify different traffic types. The
various priority values are assigned to priority groups (PGID), and each priority
group is assigned a portion of available link bandwidth.
Priority values within in any specific ETS priority group are expected to have
similar traffic handling requirements with respect to latency and loss.
802.1p priority values may be assigned by the administrator for a variety of
purposes. However, when CEE is turned on, the CN4093 sets the initial default
values for ETS configuration as follows:
Figure 32. Default ETS Priority Groups
Typical Traffic Type
LAN
LAN
LAN
SAN
Latency-Sensitive LAN
Latency-Sensitive LAN
Latency-Sensitive LAN
Latency-Sensitive LAN
3 bits 1
Priority C
FI
15 16
802.1p Bandwidth
PGID
Priority Allocation
0
1 0 10%
2
1 50%
3
4
5
2 40%
6
7
12 bits
VLAN ID
32