Ace ACE-3205, Инструкция по установке и эксплуатации

Страница: 42 / 418

Chapter 1 Introduction Installation and Operation Manual
1-14 Functional Description ACE-3105, ACE-3205 Ver. 5.2
ATM over PSN Functionality
This section describes the unit's ATM over PSN capabilities in terms of:
• Queues and Buffers
• PSN Buffer Allocations
• Timeout Mechanism.
Queues and Buffers
The traffic sent by the Gigabit Ethernet interface is mapped to four strict priority
transmit queues, as follows:
ƒ Queue 1 (highest) – Reserved for clock distribution traffic; can store up
to 50 frames.
ƒ Queue 2 – Reserved for management traffic and highest priority data;
can store up to 500 frames.
ƒ Queue 3 – Used for the second priority data; can store up to 500 frames.
ƒ Queue 4 – Used for the lowest priority data; can store up to 500 frames.
Figure 1-11. Ethernet Queue Priority
PSN Buffer Allocations
• In the PSN to ATM direction –
ƒ Frames are received on the Ethernet port and are mapped to a VPC/VCC
based on the incoming PW label.
ƒ Each frame is stored in a buffer of 1600 bytes.
ƒ
Each VPC/VCC transmit channel can store up to 50 buffers.
ƒ The Tx priority of each Tx channel is determined by the connection service
category.
ƒ If a frame is received for a specific VCC/VPC that already occupies 50
buffers, the frame is dropped and the Rx congestion counter is increased.
•
In the ATM to PSN direction –
ƒ
Cells are received on the VCC/VPC and are mapped to a PW based on the
incoming VPI/VCI.
ƒ
Each incoming cell is either concatenated to an existing PW packet or
starts a new PW packet.
ƒ
Each PW packet is stored in a 1600 byte buffer.