ProCurve 5300xl Specifications download pdf (Page 17)

If the DSCP is remapped, the 802.1p priority associated with the new DSCP is used to

determine the priority queue on the outbound port. In addition, these 802.1p bits will be

included in the outgoing packet if VLAN tagging is specified for the outbound port.

IEEE 802.1p Priority Support

IEEE 802.1Q packet tagging supports both designation of VLAN membership (see the VLAN

section below) and packet priority (up to 8 levels and often referred to as 802.1p). Since 802.1p

has 8 levels of priority possible, but the switch has only 4 physical priority levels, the following

mappings are used:

802.1p priority Switch priority queue

1, 2 1 (low)

0, 3 2 (normal)

4, 5 3

6, 7 4 (highest)

Diffserv / TOS Support

As mentioned in the Classifiers section above, the ProCurve 5300xl Switch Series provide very

flexible control of the diffserv (DSCP) bits. Mapping of each of the 64 possible DSCPs can specify

an 802.1p priority, as well as a new DSCP for the outbound packet.

Diffserv code points are in their early acceptance for use in networks. Their importance will

grow as more networks and applications take advantage of them.

Since TOS IP Precedence and DSCP are mutually exclusive (they use the same set of bits in the

IP header), the switch will allow only TOS IP Precedence definitions or only DSCP definitions to

be active at any one time.

End-to-End QoS

QoS capabilities in the switch allow it to deal with two different concerns that arise in Ethernet

networks: congestion control and latency. In the past, controlling traffic congestion was viewed

as the primary reason for QoS. But with Ethernet prices dropping substantially year after year it

has been easier and lower cost to deal with congestion, at least in the local network, by

increasing the bandwidth available to traffic through higher speed connections.

While QoS for congestion control in the local local network has had marginal value, the ability of

QoS to deal with applications that are sensitive to varying latencies through a network is of

value. Delay sensitive applications depend on isochronous, or time-dependent, data.

Applications of this type include VoIP, streaming voice or video, data storage backups, or

network control in the form of SNMP packets, Spanning Tree BDPU packets, etc.

When trying to make overall packet latency as low as possible or minimize latency jitter, end-

to-end control becomes important. The 802.1p priority specification that is contained in each

tagged packet, as well as the DSCP, can provide this end-to-end continuity. As the packet

travels from source to destination, it is given the proper priority in each switch it travels through

based on its 802.1p value. The ProCurve 5300xl Switch Series maintain the 802.1p tags across

routed interfaces, allowing end-to-end QoS in routed environments.

The DSCP can also be used for QoS categorization of the packet. The ProCurve 5300xl Switch

Series can assign priorities based on the DSCP. Packets that are not 802.1p tagged can

nonetheless have a priority assigned to them through the DSCP alone.

The ability of the ProCurve 5300xl Switch Series to control not only the 802.1p priority, but also

read and/or re-write the DSCP bits to set QoS policy provides the network manager with an

even finer degree of control. Priority can be tailored to specific areas of the network, and the

DSCPs can be used eventually for parts of QoS policy other than priority. There is also room in

the DSCP definition for new QoS services that have not yet been defined.

Security

Virus Throttling

Virus-Throttling is based on the detection of anomalous behavior of network traffic that differs

from a normal activity. Under normal activity, a computer will make fairly few outgoing

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ProCurve 5300xl Specifications Page 17

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