QoS ( Intserv & Diffserv)

BYANJALI KULKARNI

YI-AN CHEN

QoS

• Current Internet offers best effort service only

• As the Internet is the ubiquitous communications infrastructure, there is a clear need for providing differentiated classes of service to network traffic

What is Intserv• Service differentiation in the Internet• Focuses on individual packet flows• Each flow requests specific levels of service from

network• Levels of service quantified as a minimum service rate,

or a maximum tolerable end-to-end delay or loss rate• Network grants or rejects the flow requests, based on

availability of resources and the guarantees provided to other flows

Interserv

• Best effort service• Real time service• Controlled link sharing

Multi-entity link-sharing

Multi-protocol link-sharing

Multi-service sharing

Framework of IS Model

• Packet scheduler• Admission control• Classifier• Reservation setup protocol(RSVP)

RSVP

• Path messages

• Resv messages

• PathErr, PathTear, ResvErr, ResvTear, ResvConf Messages

Phop, Sender template, Tspec, Adspec

Reservation style, Filter specification, Rspec, Tspec

Processing and Propagation of Path Messages by Network Routers

• Update the path state entry• Set cleanup timer• Create and forward Path message

Any change to stored path state or a change in the set of outgoing interfaces in the data forwarding path

Every refresh period timeout interval

RSVP

Appli-cation RSVP

proc. Polcyctrl

class-ifier

PacketScheduler

Admissionctrl

Classifier packetscheduler

admissionctrl.

RoutingProcess

RSVPPocess Polcy

ctrl.

Data

RSVP RSVP

Data Data

RouterHost

RSVP Filters

Sender Selection Distinct Shared

Explicit Fixed-Filter (FF) Style Share-Explicit (SE) Style

Wildcard None Defined Wildcard-Filter (WF) Style

Factors Impeding Deployment of Intserv/RSVP

• Use of per-flow state and per-flow processing raises scalability concerns for large network

• The necessary policy control mechanisms have only recently become available

What is Diffserv

• Based on a model where traffic entering a network is classified , possibly conditioned at the boundaries of the network, and assigned to different service classes

• Here, we avoid complexity and maintenance of per-flow state information in core nodes and push unavoidable complexity to the network edges

What is Diffserv

• Provide scalable service differentiated in the internet that can be used to permit differentiated pricing of internet service

• Separate packet forwarding model from routing model

Terminology

• Per Hop Behavior(PHB)• DS Domain( e.g. ISP, intranet)• DS Boundary Node(Egress & Ingress)• DS Interior Node• DS Codepoint(DSCP)• DS Behavior Aggregate

Terminology

• Bandwidth Broker (BB)Logical entity, can be mapped to a single or multiple physical entity

A logical entity residing in each administrative domain managing internal demands & resources according to some policy database (who can do what where and when)

Setting up & maintaining bilateral agreement with neighbor domains

Terminology

• SLA(SLS) & TCA(TCS)Customer/Provider boundariesService Level Agreement A set of parameters and their values which together define the service offered to a traffic stream by a DS domainTraffic Conditioning Agreement A set of parameters and their values which together specify a set of classifier rules and traffic profile

SLA

Logical View of Packet Classifier and Traffic Conditioner

classifier

Meter

Marker Shaper/Dropper

Packets

Terminology

• Classifier

• Traffic Profile Specifies the temporal properties of a traffic stream

selected by a classifier. It provides rules for determining whether a particular packet is in-profile or out-of-profile

•BA Classifier

•MF Classifier

Terminology• Traffic Conditioner

•Meter

•Marker

•Shaper

•Dropper

•Host Marking

•Router Marking

Service Taxonomy

• Quantitative Service

• Qualitative Service

• Relative Quantification Service

Traffic offered at service level A will be delivered with low latency

90% of in profile traffic delivered at service level B will experience of no more than 50 msec latency

Traffic with drop precedence AF12 has a higher probability of delivery than traffic with drop precedence AF13

Assured Forwarding (AF) Class• As long as aggregate traffic from some sites

connecting to internet does not exceed the subscribed information rate, forward packets with high probability

• AF PHB group - Forwarding of IP packets in N independent AF classes. Within each class, an IP packet is assigned M different levels of drop precedence

• Queuing and discard behavior

Expedited Forwarding (EF) Class• Providing low loss, low latency, low jitter,

assured bandwidth, end-to-end service through DS domains

• EF PHB A router uses policing and shaping

mechanism to ensure that the maximum arrival rate of a traffic aggregate is less than its minimum departure rate

Working within a Domain

BB

Source

Dest.

Edge Router

Core Router

DS Domain

Working within a Domain

• Step 1 Source sends request message to first hop router • Step 2 First hop router sends request to BB, which sends

back either a accept or reject• Step 3 If accept, either source or first hop router will mark

DSCP and start sending packets

Working within a Domain

• Step 4 Edge router checks compliance with SLA and

does policing. Excess packets are either discarded or marked as low priority to comply with the SLA

• Step 5 Core routers will just look at DSCP and decide

PHB

Intra-Domain Resource Allocation Architecture

Edge Router-BB Communication

• BB contains the flow database containing information regarding flows requesting increased level of service . It contains ingress/egress interface, resources requested, start/finish time

• BB sends the TCA to the domain’s edge routers

Edge Router-BB Communication

• COPS is used for this. BB’s COPS server TCA to COPS client residing at edge router

• COPS client translates these commands to parameters understood by forwarding path via the Forwarding path driver(FPD)

Interdomain Communication

Functions of BB

• Negotiation of SLAs with BBs of neighboring domains

• Translation of SLAs into one or several TCAs for edge devices

• Delivery of the TCAs to the edge routers of the administered domain, using one of many proposed protocols

Steps in Interdomain Communication

• Assumption Needs of domain 1 towards domain 3 are satisfied by

a 64kb/s flow of premium traffic• Step 1 BB1 learns internally that a 64kb/s SLA is needed• Step2 BB1 requests the SLA from BB2, BB2 performs

admission control

Steps in Interdomain Communication

• Step 3 If the request is admitted, BB2 sends a TCA

derived from the SLA requested to R2( it’s administered edge router)

• Step 4 BB2 responds positively to BB1. This TCA

models the traffic to be transferred from domain1 via R2

Steps in Interdomain Communication

• Step 5 A similar TCA is sent by BB1 to it’s administered

edge router R1 instructing it to allow the given traffic to flow out to domain 2

• Step 6 BB2 may request more premium resources from

BB3 to aggregate the new premium traffic demand to the existing SLA between BB2 and BB3

Multicasting in DS Domain

• Neglected Reservation Subtree Problem (NRS)• Heterogeneous Multicasting Groups• Dynamic of Arbitrary Sender Change

NRS

Ingress

ingress

egress

egress

Routing

replication

Interface A

Interface B

Interface C

Interface D

Multicast packet replication in a DS router

NRS cont.

Sender

DS domain DS domain

Interior Router

Boundary Router

Receiver

Multicast branch with reservd bandwidthMulticast branch without reserved

NRS cont.

Sender

DS domain DS domain

Interior Router

Boundary Router

Receiver

Multicast branch with reservd bandwidthMulticast branch without reserved

Heterogeneous Multicasting Groups

• Participants requesting a best effort quality only should also be able to participate in a group communication which otherwise utilises a better service class

• Support heterogeneous groups with different service classes in a consistent way

Dynamics of Arbitrary Sender Change

• A sender resource must be reserved seperately if simultaneous sending delivery trees are used

Security Consideration

• Theft of service• Denial of service

2 Bit Differentiated Services Architecture for the Internet

• Premium service Premium service levels are specified as a d

esired peak bit rate for a specific flow• Assured service• Best-effort service

Block Diagram of First Hop Router Input Functionality

Markers to Implement the 2 Different Services

Border Router Input Interface Profile Meters

Router Output Interface for 2-bit Architecture

Statically Configured Example with no BB Messages Exchanged• All allocations are statically preallocated thr

ough purely bilateral agreements between users. This negotiation is done by human repreentatives of each domain

• BBs perform function to allocate profile within their local domain

End-to-End Example with Static Allocation

End-to-End Static Allocation eg. with no Remaining Allocation

First Step in End-to-End Dynamic Allocation Example

Second Step in End-to-End Dynamic Allocation Example

Third Step in End-to-End Dynamic Allocation Example

Fourth Step in End-to-End Dynamic Allocation Example

Final Step in End-to-End Dynamic Allocation Example

Intserv Operation over Diffserv

IS Domain DS Domain IS DomainS D

Intserv Operation over Diffserv

• Selecting an appropriate PHB for the requested service

• Performing appropriate policing at the edges of Diffserv region

• Exporting Intserv parameters from the Diffserv region

• Performing admission control on the Intserv requests

Statically Provisioned Diffserv Network Region

• RSVP messages carried transparently through the Diffserv network region

• The corresponding service level is determined by the Intserv to Diffserv mapping discussed previously

RSVP -Aware Diffserv Network Region

• Signaling between the Diffserv network region and network elements outside it

Comparison of Intserv & Diffserv Architectures

Intserv DiffservGranularity of servicedifferentiation

Individual Flow Aggregate offlows

State in routers(e.g.scheduling, buffermanagement)

Per Flow Per Aggregate

Traffic ClassificationBasis

Several header fields DS Field

Type of servicedifferentiation

Deterministic orstatistical guarantees

Absolute orrelativeassurance

Admission Control Required Required forabsolutedifferentiation

Signaling Protocol Required(RSVP) Not required forrelative schemes

Comparison of Intserv & Diffserv Architectures

Intserv Diffserv Coordination for service differentiation

End-to-End Local (Per-Hop)

Scope of Service Differentiation

A Unicast or Multicast path

Anywhere in a Network or in specific paths

Scalabilty Limited by the number of flows

Limited by the number of classes of service

Network Accounting Based on flow characteristics and QoS requirement

Based on class usage

Network Management Similar to Circuit Switching networks

Similar to existing IP networks

Interdomain deployment

Multilateral Agreements

Bilateral Agreements