Ieee 802.1Q Cos And Ip Tos Queuing; Table 24-1 Ip Tos Priority Queue Mappings; Table 24-2 Cos Priority Queue Mappings - Cisco ONS 15454 SDH Configuration Manual

Chapter 24 CE-100T-8 Ethernet Operation

IEEE 802.1Q CoS and IP ToS Queuing

The CE-100T-8 references IEEE 802.1Q class of service (CoS) thresholds and IP type of service (ToS)
(IP Differentiated Services Code Point [DSCP]) thresholds for priority queueing. CoS and ToS thresholds
for the CE-100T-8 are provisioned on a per port level. This allows the user to provide priority treatment
based on open standard quality of service (QoS) schemes already existing in the data network attached
to the CE-100T-8. The QoS treatment is applied to both Ethernet and POS ports.
Any packet or frame with a priority greater than the set threshold is treated as priority traffic. This
priority traffic is sent to the priority queue instead of the normal queue. When buffering occurs, packets
on the priority queue preempt packets on the normal queue. This results in lower latency for the priority
traffic, which is often latency-sensitive traffic such as voice-over-IP (VoIP).
Because these priorities are placed on separate queues, the priority queuing feature should not be used
to separate rate-based CIR/EIR marked traffic (sometimes done at a Metro Ethernet service provider
edge). This could result in out-of-order packet delivery for packets of the same application, which would
cause performance issues with some applications.
For an IP ToS-tagged packet, the CE-100T-8 can map any of the 256 priorities specified in IP ToS to
priority or best effort. The user can configure a different ToS in CTC at the card-level view under the
Provisioning > Ether Ports tabs. Any ToS class higher than the class specified in CTC is mapped to
the priority queue, which is the queue geared towards low latency. By default, the ToS is set to 255,
which is the highest ToS value. This results in all traffic being treated with equal priority by default.
Table 24-3
settings span the full 0 to 255 range, but only selected settings are shown.)
Table 24-1
ToS Setting in CTC ToS Values Sent to Priority Queue
255 (default)
250
150
100
50
0
For a CoS-tagged frame, the CE-100T-8 can map the eight priorities specified in CoS to priority or best
effort. The user can configure a different CoS in CTC at the card-level view under the Provisioning >
Ether Ports tabs. Any CoS class higher than the class specified in CTC is mapped to the priority queue,
which is the queue geared towards low latency. By default, the CoS is set to 7, which is the highest CoS
value. This results in all traffic being treated with equal priority by default.
Table 24-3
Table 24-2
CoS Setting in CTC CoS Values Sent to Priority Queue
7 (default)
6
5
shows which values are mapped to the priority queue for sample IP ToS settings. (ToS
IP ToS Priority Queue Mappings
None
251–255
151–255
101–255
51–255
1–255
shows which values are mapped to the priority queue for CoS settings.
CoS Priority Queue Mappings
None
7
6, 7
Cisco ONS 15454 and Cisco ONS 15454 SDH Ethernet Card Software Feature and Configuration Guide, R8.0
IEEE 802.1Q CoS and IP ToS Queuing
24-5