VSC7440 datasheet(226/444 Pages) MICROSEMI

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Functional Descriptions

VMDS-10492 VSC7440 Datasheet Revision 4.2

209

The following illustration provides an overview of shared queue system.

Figure 53 •

Shared Queue System Block Diagram

Frames are stored in the packet memory and linked into the ingress queue for the logical source port

along with the analyzer result.

The analyzer result is then processed by a frame forwarder, frame by frame. Each of the frame

transmission requests are added to an egress queue in the queue system attached to a specific egress

port. A transmission request can be a normal switching request to another port, a mirror copy, for

stacking updates, and for a CPU connected to one of the egress ports. For VD0, it can do multiple copies

of the request. The frame forwarder can also request that a specific frame copy be discarded.

The frame forwarder is efficient, because only frame references are switched, giving a forwarding

bandwidth in the range of 67 Gbps (64 byte frames) to 2 terabits (Tbps) (1,518 byte frames). The frame

data itself is not moved within the queue system.

The forwarding request is passed through a queue mapper, which then selects an egress queue based

on the classified properties of the frame. For example, a simple switch may use the classified QoS class

only and an advanced carrier switch may use MPLS-classified traffic class (TC).

A congestion control system can decide to discard some or all copies of the frame. This decision is

based on consumption per QoS level. The queue mapper can be configured to change the drop decision

using a congestion control mechanism based on queue sizes rather than only QoS class.

Each destination port has a part of the total shared queue pool attached. Transmission is scheduled

towards the destination ports through a hierarchical scheduling system, where all queues belonging to

each port are arbitrated. On the way out, frames pass through the rewriter where the frame data can be

AFI loopback port (VD1).

When the queue system is requested to send to VD1, it sends the request to the AFI. The AFI stores the

request and can be configured to transmit the frame to any port in a programmed schedule. The AFI can

transmit the frame to any of the egress ports. If VD1 is selected as destination by the AFI, the frame is

looped back into the analyzer.

Table 134 •

Port Definitions in Shared Queue System (continued)

Ports

Connection

Ingress Queues

Congestion Control

Analyzer

Result

Buffer Control

Scheduling Configuration

Egress Queues, Destination

Transmit

commands

for port

Queue 0

Frame

Forwarder

Queue

Mapper

Queue 1

Queue

Queue 0

Queue 1

Queue

Scheduler

Hierarchy

Analyzed

Frames

Egress Queues, Destination 1

Queue 0

Queue 1

Queue

Scheduler

Hierarchy

Egress Queues, Destination 0

Transmit

commands

for port 0

Transmit

commands

for port 1

Queue 0

Queue 1

Queue

Scheduler

Hierarchy

Resource

Management

Packet

Memory

Data

Ref

Forwarding

Queue

Mapping

Queue

Limitation

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