Terminology - HP ProCurve 5300xl Series Management Manual

Terminology

Term Use in This Document
802.1p priority A traffic priority setting carried by a VLAN-tagged packet moving from one device to another through
ports that are tagged members of the VLAN to which the packet belongs. This setting can be from 0 -
7. The switch handles an outbound packet on the basis of its 802.1p priority. However, if the packet
leaves the switch through a VLAN on which the port is an untagged member, this priority is dropped,
and the packet arrives at the next, downstream device without an 802.1p priority assignment.
802.1Q field A four-byte field that is present in the header of Ethernet packets entering or leaving the switch through
a port that is a tagged member of a VLAN. This field includes an 802.1p priority setting, a VLAN tag, or
ID number (VID), and other data. A packet entering or leaving the switch through a port that is an
untagged member of the outbound VLAN does not have this field in its header and thus does not carry
a VID or an 802.1p priority. See also "802.1p priority".
codepoint Refer to DSCP, below.
downstream A device linked directly or indirectly to an outbound switch port. That is, the switch sends traffic to
device downstream devices.
Differentiated Services Codepoint. (Also termed codepoint.) A DSCP is comprised of the upper six bits
DSCP
of the ToS (Type-of-Service) byte in IP packets. There are 64 possible codepoints. In the default QoS
configuration for the 5300xl switches, some codepoints are configured with default 802.1p priority
settings for Assured-Forwarding and Expedited Forwarding. In the default QoS configuration for the
3400cl/6400cl switches, one codepoint (101110) is set for Expedited Forwarding. All other codepoints
are unused (and listed with No-override for a priority).
DSCP policy A DSCP configured with a specific 802.1p priority (0- 7). (Default: No-override). Using a DSCP policy,
you can configure the switch to assign priority to IP packets. That is, for an IP packet identified by the
specified classifier, you can assign a new DSCP and an 802.1p priority (0-7). For more on DSCP, refer
to "Details of QoS IP Type-of-Service" on page 8-46. For the DSCP map, see figure 8-23 on page 8-47.
edge switch In the QoS context, this is a switch that receives traffic from the edge of the LAN or from outside the
LAN and forwards it to devices within the LAN. Typically, an edge switch is used with QoS to recognize
packets based on classifiers such as TCP/UDP application type, IP-device (address), Protocol (LAN),
VLAN-ID (VID), and Source-Port (although it can also be used to recognize packets on the basis of ToS
bits). Using this packet recognition, the edge switch can be used to set 802.1p priorities or DSCP policies
that downstream devices will honor.
inbound port Any port on the switch through which traffic enters the switch.
IP Options In an IPv4 packet, optional, these are extra fields in the packet header.
IP-precedence The upper three bits in the Type of Service (ToS) field of an IP packet.
bits
IPv4 Version 4 of the IP protocol.
outbound A packet leaving the switch through any LAN port.
packet
outbound port Any port on the switch through which traffic leaves the switch.
Quality of Service (QoS): Managing Bandwidth More Effectively
Introduction
8-5