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Chapter 11 Avaya P330 Layer 2 Features
Avaya P332G-ML User’s Guide 55
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 networkl 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.
Avaya P330 switches supports two internal priority queues – the High Priority
queue and the Normal Priority queue.
• Packets tagged with priorities 4-7 are mapped to the High Priority queue;
packets tagged with priorities 0-3 are mapped to the Normal Priority queue.
This classification is based either on the packet’s original priority tag, or, if the
packet arrives at the port untagged, based on the priority configured for the
ingress port (set using the set port level CLI command).
In cases where the packet was received tagged, this priority tag is retained when the
packet is transmitted through a tagging port.
In cases where the priority is assigned based on the ingress priority of the port, then
on an egress tagging port the packet will carry either priority 0 or priority 4,
depending on the queue it was assigned to (High Priority=4, Normal Priority=0).
MAC Address
The MAC address is a unique 48-bit value associated with any network adapter.
MAC addresses are also known as hardware addresses or physical addresses. They
uniquely identify an adapter on a LAN.
MAC addresses are 12-digit hexadecimal numbers (48 bits in length). By
convention, MAC addresses are usually written in one of the following two formats:
• MM:MM:MM:SS:SS:SS