OECG – Chapter 14

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Assured forwarding – a DiffServ PHB defining 4 queueing classes and 3 probabilities that a packet with be dropped within a queue class.

Cell Loss Priority – when this bit is set to “1” in an ATM cell, it tells an ATM device that this cell should be dropped before others in times of congestion

class-based marking – classifying and marking packets on a IOS router using class-maps

class map – use to define a type of traffic that can be later used for QoS processing

Class selector – a DiffServ PHB defining 8 different classes of service. Intended to be compatible with IP Precedence

Differentiated Services – an RFC-based definition of QoS that breaks up the ToS byte in a different way that IP Precedence, and also provides an optional prioritization framework in the form of several “per hop behaviors”

Differentiated Services Code Point – the first 6 bits of what used to be the ToS byte, now the differentiated services field

discard eligible – when this bit is set to “1” in a frame-relay frame, it tells an frame device that this cell should be dropped before others in times of congestion

DS field – second byte of the IP header. Used to be the ToS byte.

Expedited Forwarding – a DiffServ PHB defining a DSCP value (46) for low-latency queuing, while at the same time making sure that the DSCP 46 packets don’t monopolize the pipe

IP Precedence – the first 3 bits of the ToS byte, mostly all of what’s used for QoS in the IPP model

Modular QoS CLI – IOS commands starting with the term “class-based”. Evolved from a need to unify and simplify disparate IOS QoS tools.

MPLS Experimental – a 3-bit field in the MPLS header used to mark frames; often used for QoS purposes, to prioritize traffic through the MPLS cloud.

Network Based Application Recognition – an IOS tool that classifies packets based on layer 7 inspection. Extensible by adding PDLM from cisco.com.

Per-Hop behavior – a group of DSCP values and QoS actions as related to those values.
policy map – tells a router how to handle certain classes of traffic

service policy – applies a QoS policy-map to an interface, thus putting that policy into action

ToS byte – a 1 byte field in the IP header used for QoS. Originally defined in RFC 791, supplanted by Differentiated Services.

User Priority – 3 bit field in an 802.1q header intended for marking frames, typically QoS

Ethan Banks writes & podcasts about IT, new media, and personal tech.
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