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Chapter 11 Avaya P330 Layer 2 Features
Avaya P334T-ML User’s Guide 77
Speed
The IEEE defines three standard speeds for Ethernet: 10, 100 and 1000 Mbps (also
known as Ethernet, Fast Ethernet and Gigabit Ethernet respectively).
Flow Control
The process of adjusting the flow of data from one device to another to ensure that
the receiving device can handle all of the incoming data. This is particularly
important where the sending device is capable of sending data much faster than the
receiving device can receive it.
There are many flow control mechanisms. One of the most common flow control
protocols, used in Ethernet full-duplex, is called xon-xoff. In this case, the receiving
device sends a an xoff message to the sending device when its buffer is full. The
sending device then stops sending data. When the receiving device is ready to
receive more data, it sends an xon signal.
Priority
By its nature, network traffic varies greatly over time, so short-term peak loads may
exceed the switch capacity. When this occurs, the switch must buffer frames until
there is enough capacity to forward them to the appropriate ports.
This, however, can interrupt time-sensitive traffic streams, such as Voice and other
converged applications. These packets need to be forwarded with the minimum of
delay or buffering. In other words, they need to be given high priority over other
types of network traffic.
Priority determines in which order packets are sent on the network and is a key part
of QoS (Quality of Service). The IEEE standard for priority on Ethernet networks is
802.1p.
The Avaya P334T-ML supports two internal priority queues – the High Priority
queue and the Normal Priority queue – on its Gigabit Ethernet ports (51,52) and
four internal priority queues on its 10/100Mbps ports. The classification of packets
within the queues is as follows:
•Gigabit Ethernet ports:
— packets tagged with priorities 4-7 are assigned to the High Priority queue
— packets tagged with priorities 0-3 are assigned to the Normal Priority
queue.
• 10/100Mbps ports:
— packets tagged with priorities 0-1 are assigned to the Low Priority queue
— packets tagged with priorities 2-3 are assigned to the Normal Priority
queue;
— packets tagged with priorities 4-5 are assigned to the High Priority queue
— packets tagged with priorities 6-7 are assigned to the Highest Priority
queue.