User's Manual

DragonWave Inc.
46
Horizon Compact Release 1.01.01 Wireless Ethernet Product User Manual – Volume 1
11.3.1 Operation with 802.1P Priority Queuing Disabled
If 802.1P filtering is disabled in the Horizon Compact system, all incoming frames are treated equally and
are forwarded on a first-come first-served basis. The system operates in a FIFO (First In First Out) basis.
If the Pause Frames feature (see Section 11.4) is enabled, pause frames will be sent to the connected
switch when the input buffer is close to being full (internally set threshold). This allows time for the queue
to empty prior to more frames being received and thus avoids congestion.
11.3.2 Operation with 802.1P Priority Queuing Enabled
If 802.1P filtering is enabled in the Horizon Compact system, the scheduling mechanism can be
described as follows:
1. Select the highest priority queue which has a frame in it
2. Send that frame
If COS CIRs are set for the queues, then the scheduling mechanism can be described as follows:
1. Select the highest priority queue which has a frame in it, and hasn’t used up its CIR budget
2. Send that frame
The operation of the Scheduler is affected by both the user-configurable CIR and CoS Queue PBS
settings.
If the Pause Frames feature (see Section 11.4) is enabled, pause frames will be sent to the connected
switch when the input buffer is close to being full (internally set threshold).
The Horizon Compact system also allows any frames without a VLAN tag to be allocated an 802.1P CoS
level (“set untagged frame priority”). If the “set untagged frame priority” is not configured, then all
untagged frames will be forwarded through Queue 1.
Horizon Compact is also able to manage Q-in-Q or Super VLAN traffic. The system can be configured to
use either an encapsulated frame’s priority tag or the encapsulating frame’s priority tag, in determining
priority handling.
11.3.3 Expedite Queues
Expedite Queuing is a mechanism that allows one or more of the four Queues to transmit its data as
priority traffic, at the expense of the remaining Queues. When Expedite Queue is enabled, then as long
as there is data in the Expedite Queue, or Queues, that data will be transmitted first. This allows time
critical or error-sensitive traffic to have priority data delivery.
As network services increase, the need for multiple Expedite Queues becomes evident. A network
administrator may require three Expedite Queues and decide to send all network routing protocols
through the highest Expedite Queue; send IP Voice through the next highest Expedite Queue; send Video
over IP through the next highest Expedite Queue and send all other traffic to the remaining Queue, which
is not configured as an Expedite Queue. To do this, the administrator would configure Queues 4, 3 and 2
as Expedite Queues and configure Queue 1 as a standard Queue with a particular CIR. Configuring the
CIR for a particular queue to 100% enables the expedite function for that queue.
11.3.4 Management Traffic
Slow Ethernet services and multicast frames are handled by a special Queue inside the Horizon
Compact. The Queue is not user-accessible. It works similar to an Expedite Queue in that it ensures
management traffic is passed through in an “expedited” fashion. It does not affect, nor is related to the 4
Queues within Horizon Compact. This Queue does not impact the operation of the 4 user-configurable
802.1P Queues.