ProCurve 5300xl Specifications download pdf (Page 16)

Prioritization / QoS

Quality of Service (QoS) mechanisms in the ProCurve 5300xl Switch Series provide the network

manager control over packet flows based on a number of factors. In addition, since the switches

can override the priority values in the incoming packets, the network manager can maintain

QoS control over inappropriate priority designations coming from users or applications at the

end nodes. Conversely, many applications can be given priority treatment through the switch

without the end node clients having to be aware of QoS, particularly valuable since client

operating systems and the applications themselves are generally not QoS aware at this time.

The primary means of control is through priority queues in the switch. Pieces of information in

the packet that can be used to determine priority queue placement are called classifiers. The

mechanism to actually store the priority based on the classifiers is through the 802.1Q tags or

through the IP TOS/Diffserv section in the IP header. The ProCurve 5300xl Switch Series do not

modify either of the packet fields when routing the packet (unless a QoS override is specified in

the port config) so the QoS status of a packet can be maintained as the packet travels

elsewhere in the network. Each of these is discussed in the following sections.

The final section, End-to-End QoS, briefly discusses the value of QoS in networks.

Priority Queues

Each port on a ProCurve 5300xl Switch Series module has four priority queues. A packet placed

into a particular queue will be processed according to the priority of that queue.

The priority queues are managed through a fair-weighted queuing algorithm that prevents any

priority queue from getting starved (the packets in it not being serviced by the switch) due to

high traffic levels in higher priority queues.

QoS Classifiers

Through user configuration, priority of packets can be specified based on the following

classifiers. This list is in order of precedence; if there are multiple classifiers that apply to a

specific packet, the one that is highest on this list takes effect.

• Layer 4 TCP/UDP port numbers: allows prioritization based on the application associated with

the packet. This allows, for instance, VoIP packets using fixed port numbers to be prioritized

higher than other traffic. It can also be used to downgrade packet flows, such as HTTP traffic.

Can also be used to remap the diffserv code points (DSCP).

• Device Priority (destination or source IP address) : up to 256 addresses can be specified per

chassis, destination address takes precedence over source address. it can also be used to

remap the DSCP.

• IP Type of Service (ToS) field (IP packets only): support for both the older TOS IP Precedence

definition, or the newer Differentiated Services (Diffserv) definition. If using the TOS IP

Precedence, the bits are mapped to packet priority queues using the same table as shown in

the next section “IEEE 802.1p Priority Support”. The 802.1p bits are also set for the outbound

packet if the packet goes out of the switch through a port that has 802.1Q tagging turned on.

For diffserv, each of the diffserv code points (DSCP) can have a priority set for it. It is also

possible to set a new DSCP and 802.1p priority based on the incoming DSCP, or set the

802.1p priority alone based on the incoming DSCP. The ability to re-write the DSCP allows the

network manager to:

Identify packets coming from a different area of the network, such as a remote site,

by changing the DSCP as it comes through the ProCurve 5300xl Switch Series and

treating this remote packet differently than packets originating in the local

environment.

Redefine an incoming DSCP to conform to the DSCP definitions defined in the local

environment.

• Protocol Priority (IP, IPX, ARP, DEC LAT, AppleTalk, SNA, and NetBEUI)

• VLAN ID: Allows a VLAN to be assigned a specific priority; can also remap the DSCP.

• Incoming source-port on the switch; can also remap the DSCP.

• Incoming 802.1p Priority (present in tagged VLAN environments)

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ProCurve 5300xl Specifications Page 16

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