Chapter 11 Avaya P330 Layer 2 Features
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.
