3Com 3C15500 - Network Director - PC, User Manual, Page: 628 / 924

624 C
HAPTER
15: P
RIORITIZING
N
ETWORK
T
RAFFIC
Key Concepts
Traffic prioritization has three basic aims:
■
To ensure that traffic defined as being more important flows through
the network quicker than other types of traffic.
■
To ensure that important traffic is less likely to be dropped if there is
congestion on the network.
■
To prevent traffic that has been blocked from flowing on the network.
In order to achieve the aims of traffic prioritization across the network,
each Switch in the network must provide facilities for:
■
Performing identification of the most important traffic and traffic that
should be blocked. This is known as
classification .
■
Performing suitable actions as a result of classification to meet the
needs of the particular traffic type that classification identified. There
are three actions that can be performed;
marking , queuing and
dropping .
Classification Classification identifies different types of traffic by examining the
contents of a packet or set of packets. For example, a packet received by
a device can be identified as traffic to and from your database server if
the destination or source IP address in the packet matches the IP address
of the database server.
There are many fields in a packet that a device may use to classify traffic,
including:
■
Ethernet type
■
Source or destination MAC address
■
IP protocol
■
Source or destination TCP port
■
Source or destination UDP port
Classification can also be much more complex than simply examining a
field in a packet. It can involve examining multiple fields in a packet,
parsing and analyzing the contents of a packet, or even analyzing flows
of traffic rather than a single packet.