614_2_qos control by

QoS control by means of COPS to SupportSIP-based applications

S. Salsano, L. Veltri

IEEE Networks, March/April 2002

R93944010賈　立 R93922011黃文彬R93922053陳育成 R93922095陳奕安

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Contents

Introduction The COPS role for Dynamic DiffServ resource al

location Definition of the COPS Interfaces IP Telephony : A COPS Based QoS model Implementation Testbed conclusion

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What is QoS

What is quality of service? What does it take for the Internet to

support QoS? Existing Internet QoS architectures:

Integrated services, differentiated services, and MPLS overview.

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What is QoS User point of view:

Assurance of end-to-end service. E.g. Guaranteed delay (VoIP), Guaranteed bandwidth (VPN)

Relaxed definition: Service differentiation: different packets is treated

differently. end-to-end service guarantees may be achieved by

provisioning. e.g. only a small portion of high priority packets.

Existing IP networks only support best effort service. Adding service differentiation is non-trivial.

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Applications that need QoS VoIP: bounded delay VPN: bounded bandwidth Video conferencing: bounded delay and bounded

loss rate

Common QoS parameters: delay/delay variation (jitter) Bandwidth error rate

What is QoS(Cont.)

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Per flow QoS guarantees and aggregate QoS guarantees

Statistical QoS guarantees .vs. deterministic QoS guarantees

What is QoS(Cont.)

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Between the network and its clients: Traffic contract. Traffic specification/desired QoS/supported QoS

At network edge: Signaling and admission control Packet classification/marking Traffic shaping Packet classification/marking and traffic shaping is

also called traffic conditioning. Traffic policing

What is needed to support QoS

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What is needed to support QoS: At routers:

classification and scheduling: FCFS won't work, need more advanced packet scheduling scheme (Fair Queuing)

Routing algorithm need to improve: find a path that satisfies QoS constraints (QoS/policy/constraint based routing).

Buffer management. Traffic monitoring: find problems as early as possible Traffic reshaping (at merge and fork points)

What is needed to support QoS

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Alternative: buy excessive bandwidth Everything is simple in the Internet without QoS, everything

seems to be much harder in the Internet with QoS support.

What is the main problem? Complexity and scalability of QoS mechanisms Which is cheaper: higher network speed or network with QoS

support.

Where is the balance? A guess: Some form of QoS support will be there, per flow QoS

guarantee may or may not ever be deployed.

QoS in the Internet: Do we really need it?

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Trying to match the user demand by providing per flow QoS guarantees.

Signaling protocol: RSVP IntServ is a reservation based approach

Main problem: Router complexity (scalability)

Intergrated Services (IntServ)

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Define per-hop behavior instead of end-to-end service model

Support a small number of forwarding classes at each router.

Forwarding class is encoded in the packet header.

Problems with DiffServ:end-to-end service guaranteed is hard to

maintain.

Differentiated Services (Diffserv)

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Originally designed for IP over ATM A short (fixed length) label is encoded for the

packet header for packet forwarding Allow Label switched path (LSP) to be setup

(explicit routing). allow datagram and virtual circuit to be

coexisted in an IP network. MPLS can be combined with IntServ and

DiffServ to support QoS.

Multi-Protocol Label Switching (MPLS):

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Comparison of IntServ and DiffServ

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 a specific path

Scalability Limitation 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 network

Similar to existing IP networks

Interdomain deployment Multilateral Agreements Bilateral Agreements

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COPS

DefinitionCommon Open Policy Service protocol IETF RAP working groupTo support policy control in an IP QoS environ

mentPolicy servers v.s. policy clients

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The COPS Role for Dynamic DiffServ Resource Allocation

COPS protocol A simple query Response protocol that allows policy servers (PDPs, Policy

Decision Point ) to communicate policy decisions to network devices (PEPs, Policy Enforcement Point )

To support multiple types of policy clients Uses to TCP to provide reliable exchange of messages Provides the means

To establish and maintain a dialogue between the client and the server

To identify the requests

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The COPS Role for Dynamic DiffServ Resource Allocation(2)

Two main model

Outsourcing and provisioning models in COPS

Outsourcing model Provisioning modelEvents

Notifications

Configuration commands

Trigger Events (1)Query (2)

Response (3)

Trigger events generate queries and responses

Trigger events, notifications, and configuration commands are asynchronous

Bandwidth broker(policy decision point)

Edge router(policy enforcement point)

Edge router(policy enforcement point)

Bandwidth broker(policy decision point)

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The dynamic scenario for DiffServ QoSAn admission control framework

To use server to control the admission of traffic within a DiffServ domain Bandwidth Broker

The use of COPS for the communication between the edge device and the BB

COPS extensions for DiffServ resources allocation under outsourcing model

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Signaling mechanism The QoS client to make resource reservation requ

ests to the network RSVP

End-to-end protocol to support multicast sessions spanning the whole Internet with receiver-oriented reservations

More complex

The European IST project AQUILA More systematic approach to address this problem

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COPS support to dynamic DiffServ-based IP QoS

PDP

PDP PEP

PEP

COPS

COPS

QoS client(H323

gatekeeper,SIP server…)

Edge router

QoS-enabled network

Bandwidth broker

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Definition of the COPS Interface

The extension of COPS For dynamic DiffServ QoS scenario

COPS-DRA : DiffServ Resource AllocationCOPS-ODRA : Outsourcing DRA

Based only on the outsourcing model For flexibility and efficiency In combination with providing model

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The PEP always explicitly asks the PDP/BB for a given amount of resources

For scalability Per-flow state is not stored in PDP/BB Resource allocation requests are properly aggregated Aggregate state information is kept in PDP/BB

Provisioning model More scalable Inflexibility : difficult to handle modification of config. Not explicitly customized to handle dynamic DiffSer

v QoS

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Requirements for a combined model The capability of provisioning resource to local

nodes, in order to avoid high signaling burden Easy for the local node to request the modification

of the provisioned resource Possible to handle specific requests under the

outsourcing model

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Three components of the reserv. Requests The scope and amount of reservation

Where the reservation applies How much bandwidth

The type of requested service Possibly including a set of QoS parameters

The flow identification To which IP flow or aggregate of flows the reservation applies

More complex scenarios may require more parameters

Ex : timing

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An example information exchange using COPS-DRA

PDP

PDP PEP

QoS-enabled network

Bandwidth broker

PEP PDP(3)

(6)

(1)

(2)(4)

(5)

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IP telephony : A COPS Based QoS model SIP protocol

Defined within the IETF Initiate voice, video, and multimedia sessions Candidate for call setup signaling in IP telephony

IntServ-based approaches Client is customized for specific QoS mechanism. Terminal has to implement SIP and QoS reservation

protocol.

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IP telephony : A COPS Based QoS model The main idea

To eliminate the need for a specific QoS protocol in the terminals

To use SIP as the sole call setup protocolAll the QoS-related functions can be moved fr

om the terminal to local SIP proxy servers To relieve the terminals of unneeded complexity an

d preserving backward compatibility

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Q-SIP Architecture

No specific QoS protocol required. Terminal implementation is simplified.

QoS SIP architecture

Client network

COPS/Other

Q-SIPproxy server

Q-SIP

QoS Access PointQoS Access Point

Client network

SIP SIP

Q-SIP proxy server

COPS/Other

SIP terminal SIP

terminal

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Asymmetric Q-SIP Architecture

Variant scenarios


Client network

COPS/Other

Q-SIPproxy server

Q-SIP

QoS Access Point

QoS Access Point

Client network

SIP SIP

SIP proxy server

COPS/Other

Q-SIP terminal

SIP terminal

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A Q-SIP Architecture using COPS Based QoS model


PDP PEP PEP PDP

PDP

Client network

COPS-DRA

COPS-DRA

Bandwidth Broker(BB)

Q-SIP

Access edge router Access edge router

Client network

SIP SIP

Qos-enablednetwork

Qos signaling (COPS)

Application signaling (SIP)

COPS-DRA

Q-SIP proxy server

Q-SIP proxy server

SIP terminal

SIP terminal

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A COPS Based QoS model

QoS SIP architectureThe edge routers

Implement all mechanisms needed to perform admission control decision and policing function

COPS protocol Used to make QoS reservation requests to the Qo

S access points

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A COPS Based QoS model(Cont.)

SIP server To exchange message between the clients To add QoS related information in the SIP messag

es To negotiate QoS parameters among them Interact with the network QoS mechanisms

Q-SIP Enhanced SIP ( QoS-enable SIP server )

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Message Flow

INVITE INVITE(With QoS-Info) INVITE

180 ringing180 ringing180 ringing

Cops REQCops REQ

Cops DEC Cops DEC

(With QoS-Info)200 OK

Cops REQ Cops REQ

Cops DECCops DEC200 OK

ACK ACK ACK

<Traffic stream>

200 OK

DiffServ network

Called user Q-SIP serverCalled user Q-SIP server

SIP terminalCalled user ERCalled user ER

Bandwidth broker

SIP terminal

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QoS Info recorded in Q-SIP

QoS info. is inserted into new INVITE messages or 200 OK response message: QoS-Info: <qos-param> *(;<qos-param>) Same info can also be carried by “Record-Route”

header.

Example of QoS-Info: QoS-Info: qos-domain=coritel.it;

er-ingress=192.168.77.5; qos-mode=unidirectional

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QoS Info recorded in Q-SIP(Cont.)

<qos-mode> Either “unidirectional” or “bidirectional”

<er-ingress> & <er-egress> The edge router on caller/callee side

<qos-domain> Identify the domain where resource reservation is done

<caller-media-addr> & <caller-media-port> Caller address

<other>

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Implementation Testbed

The overall testbed scenario

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the QoS and call setup aspects two Ethernet based client networks Based on Linux OS COPS clients/servers

A DiffServ core network Two ERs & one core router PDP/BB

Access network One SIP terminal & one Q-SIP server

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Q-SIP server, ER, and BB internal architecture

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Conclusions

Signaling mechanismResource admission control within DiffServResource requests to a QoS providerQoS-aware call setups for SIP-based applicati

ons

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Conclusions (Cont.)

Resource admission control within DiffServPEP (Edge Router)

Handles resource & policy enforcement

PDP (Bandwidth Broker) Handles resource allocation pecisions

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Conclusions (Cont.)

Resource requests to a QoS providerPEP (SIP proxy server)

Asks for QoS reservation

PDP (edge router) Typically edge routers of the DiffServ network

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Conclusions (Cont.)

QoS-aware call setups for SIP-based applications Integrating the SIP signaling with DiffServ Qo

S mechanismsPreserving backward compatability.

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Reference

S. Salsano, L. Veltri, Qos Control by Means of COPS to Support SIP-Based Applications

X. Xiao, L. M. Ni, Internet QoS: A Big Picture S. Mallenius, The COPS (Common Open Policy

Service) Protocol S. Salsano, L. Veltri, SIP Extensions for QoS

support, <draft-veltri-sip-qsip-01.txt> http://www.coritel.it/projects/cops-bb

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