Dropper / Marker
Based on the indication of the rate controller, and the rate control mode for the flow,
the dropper/marker will do the following:
No rate control Oversubscription mode Strict policing mode
Incoming rate < CIR mark “green” mark “green” mark “green”
Incoming rate > CIR mark “green” mark “yellow” drop
In the dropper function a decision is made whether to drop or forward a packet. On a
TransLAN
®
card a deterministic dropping from tail when the queue is full is
implemented. Packets that are marked red are always dropped. If WAN Ethernet link
congestion occurs, frames are dropped. Yellow packets are always dropped before any
of the green packets are dropped. This is the only dependency on queue occupation
and packet color that is currently present in the dropper function. No provisioning is
needed.
Default user priority
A default user priority can be configured for each customer-role port. Possible values
are 0 (lowest priority) { 7 (highest priority) in steps of 1. The default setting is 0.
Provisioning of the default user priority does not apply to network-role ports.
The default user priority is treated differently depending on the taggging mode:
• LAN-VPN (M-LAN) mode
Incoming frames without a user priority encoding (untagged frames) are treated as
if they had the default user priority.
• IEEE 802.1Q VLAN tagging mode and provider bridge mode
Incoming frames without a user priority encoding (untagged frames) get a default
user priority assigned. This C-UP may be equal to a user priority given by one of
the provisioned flow descriptors. The subsequent traffic class assignment for this
flow, however, will overwrite this C-UP bits again.
Traffic classes
At each ingress port, the traffic class (TC) for each frame is determined. At
customer-role ports, this is done via the flow identification and the related provisioned
traffic class. At network-role ports, the traffic class is directly derived from the p-bits
of the outermost VLAN tag.
Depending on the operation mode, these traffic classes exist:
Provider bridge mode and IEEE
802.1Q VLAN tagging mode
with encoding of the dropping
precedence
The traffic class is encoded in the user priority bits
using p2 and p1. Thus, 4 traffic classes are defined:
0, 1, 2, 3.
Ethernet Overview
Classification, queueing and scheduling
....................................................................................................................................................................................................................................
365-312-801R7.2
Issue 3, May 2007
Alcatel-Lucent - Proprietary
See notice on first page
11-59
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