Class-based QoSClass-based QoS

Internet QoS model requires per session state Internet QoS model requires per session state at each routerat each router 1000s - 1000000s of flows1000s - 1000000s of flows

per session RSVP is complex per session RSVP is complex

=> reluctance on part of network admins to => reluctance on part of network admins to accept intservaccept intserv

Differentiated services (diffserv)Differentiated services (diffserv) scalable scalable and and flexibleflexible service differentiation service differentiation

Diffserv ArchitectureDiffserv Architecture

Two types of components:Two types of components: edge routersedge routers

classification, marking, and shaping classification, marking, and shaping

core routerscore routers forwarding according to classification and markingforwarding according to classification and marking

Classification, Marking, and Classification, Marking, and ShapingShaping

packet mark inpacket mark in Differentiated Services (DS) Differentiated Services (DS) field in IP pkt (supersedes type of service field)field in IP pkt (supersedes type of service field)

classifier and markerclassifier and marker

DSCP CU

6 bits

classifierclassifier markermarkershaper/droppershaper/dropper

forward

drop

profilemeter

packets

Per-Hops BehaviorPer-Hops Behavior

per-hop behavior results in deifferent service per-hop behavior results in deifferent service classes receiving different measurable classes receiving different measurable performanceperformance

two PHBstwo PHBs expedited forwarding: departure rate of an expedited forwarding: departure rate of an

aggregate class must exceed a configured rateaggregate class must exceed a configured rate

– policies that can provide this:policies that can provide this: prioritypriority WFQWFQ

assured forwardingassured forwarding

Assured ForwardingAssured Forwarding

four classes of servicefour classes of service ordering among delays between classes at router, ordering among delays between classes at router,

i.e., delay of a class 1 packet no greater than for i.e., delay of a class 1 packet no greater than for class 2 packetclass 2 packet

within each class three “drop preference” within each class three “drop preference” categoriescategories ordering among categories, i.e., packet with drop ordering among categories, i.e., packet with drop

preference 1 is less likely t be dropped than preference 1 is less likely t be dropped than packet with drop preference 2.packet with drop preference 2.

Where is Diffserv going?Where is Diffserv going?

PHBs are on their way to definitionPHBs are on their way to definition several marking schemes have been proposedseveral marking schemes have been proposed

two colortwo color three colorthree color

services combining PHBs and marking schemes yet services combining PHBs and marking schemes yet to be definedto be defined

the the hottesthottest Internet topic around Internet topic around

IETF Diffserv home page: IETF Diffserv home page: http://www.http://www.ietfietf.org/html.charters/.org/html.charters/diffservdiffserv-charter.html-charter.html

Quality of Service Guarantees: Quality of Service Guarantees: SummarySummary

various applications need QoS guarantees to be effective various applications need QoS guarantees to be effective QoS touches almost all layers of network architecture: QoS touches almost all layers of network architecture:

API, application API, application transport (end system policing, smoothing) transport (end system policing, smoothing) network network data link data link call admission, blocking call admission, blocking

call setup protocol need to actively engage switches call setup protocol need to actively engage switches importance of packet-level scheduling importance of packet-level scheduling area of active research area of active research