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RSVP and Integrated Services in the Internet: A Tutorial

Paul P. White, University College London

IEEE Communications Magazine,

May 1997

Members:劉佳妮、陳駿元、魏君竹

Presenter:劉佳妮Date:2002/12/10

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Outline

Introduction IETF integrated services Guaranteed service Controlled-Load service RSVP(Resource reservation protocol) Path messages Reservation styles and merging Slack Term Summary

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Introduction

The current Internet consists of a multitude of networks built from various link-layer technologies and relies on the Internet Protocol (IP) to interwork between them.

IP offers an unreliable, connectionless network-layer service.

IP delivery model is often referred to as “best-effort” .

Transmission Control Protocol (TCP) required to provide end-to-end reliability.

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Introduction(cont.)

For non-real-time Internet traffic such as File Transfer Protocol (FTP) data, the best-effort delivery model of IP has not been a problem.

Many real-time applications are delay sensitive to the point where the best-effort delivery model of IP can be inadequate.

Quality of service (QoS) with regard to bandwidth, packet delay, and loss through the RSVP.

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IETF integrated services

In response to the growing demand for an integrated services Internet, the Internet Engineering Task Force (IETF) set up an Integrated Services (intserv) Working Group .

RSVP is one kind of QoS and the resource must be reserved along with the transmission schedling behavior.

The Intserv architecture defines two major classes of service: Guaranteed service Controlled-load service

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Guaranteed service

Guaranteed Service provides an assured level of bandwidth,a firm end-to-end delay bound, and no queuing loss for conforming packets of a data flow.

It is intended for applications with stringent real-time delivery requirements, such as certain audio and video applications.

The token bucket model

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Guaranteed service(cont.)

Leaky Bucket parameters (r,b) r :Token bucket rate b :Token bucket size

Tspec: p : Peak data rate m :Minimum policed unit M :Maximum packet size

Rspec: R: Reserved rate ( R>>r) S: slack term (Signify the difference between the desired delay and the delay

obtained by using reservation level R)

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Guaranteed service(cont.)

Rspec: describes service requested from network controlled-load: none guaranteed: delay target

Tspec: describes flow’s traffic characteristics average bandwidth + burstiness: token bucket filter token rate r bucket depth B must have a token to send a byte must have n tokens to send n bytes start with no tokens accumulate tokens at rate of r per second can accumulate no more than B tokens

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Guaranteed service(cont.)

Simple Delay bound : b/R Request guarantee transmission rate is R The amount of traffic generated over interval t is bo

unded by rt+b The maximum queueing delay experienced by any

packet will be bound by b/R Multiplex Delay bound:b/R+C/R+D

The delay which depends on flow transmission rate is C.

Non-rate-dependent delay is D

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Controlled-load service

Provides approximately the same QoS under heavy loads as under light loads.

Intended for applications that can tolerate a certain amount of loss or delay to a reasonable level.

Controlled-load service simply prioritizes the packets in the flow, ensuring that they do not wait too long in router queues as they cross the network.

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RSVP

Resource ReSerVation Protocol. Allows applications running in hosts to reserve resources

in the Internet for their data flows. RSVP software must be present in the receivers, sender,

and routers. Two principle characteristics of RSVP

It provides reservations for bandwidth in multicast trees(unicast is handled as a special case).

It is receiver-oriented. RSVP is not a routing protocol and sometimes referred t

o as a signaling protocol that allows hosts to establish and tear-down reservations for data flows.

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RSVP(cont.)

RSVP depends on an underlying routing protocol(unicast or multicast) to determine the routes for the flows.

Operation

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RSVP(cont.)

訊息種類 功能PATH  從傳送端的電腦中傳送資料流資訊給接收端電腦。

RESV 從接收端電腦中傳送保留項目的請求，其中的內容包括了頻寬大小、服務層級以及來源的 IP位址

PATHErr 這是用來回應 PATH訊息所產生的錯誤

RESVErr  這是用來回應 RESV訊息所產生的錯誤

PATH-TEAR  沿著運作的路徑移除PATH的狀態。

RESV-TEAR  沿著運作的路徑移除保留項目

RESV-CONF  選項設定。假如接收端需要一個確認訊息，那麼傳送端就會發出這個訊息給接收端

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Path Message

Originate at the senders and flow downstream towards the receivers.

The principle purpose of the path messages is to let the routers know on which links they should forward the reservation messages.

Each Path message includes the following information: Phop Sender Template Sender Tspec Adspec

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Reservation styles and merging

A reservation message specifies whether merging of reservations from the same session is permissible.

A reservation style also specifies from which senders in a session the receiver desires to receive data.

There are currently three reservation styles Fixed-filter style(FF) Wildcard-filter style(WF) Shared-explicit style(SE)

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Fixed-filter style(FF)

It specifies a list of senders from which it wants to receive a data flow along with a single bandwidth reservation. These reservation are distinct, i.e., they are not to be shared.

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Wildcard-filter style(WF)

It is telling the network that it wants to receive all flows from all upstream senders in the session and that its bandwidth reservation is to be shared among the senders.

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Shared-explicit style(SE)

It specifies a list of senders from which it wants to receive a data flow along with a single bandwidth reservation. This reservation is to be shared among all the senders in the list.

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Slack Term

Slack Term which S(ms) as well as the amount of bandwidth, R to be installed in each router along the path.

S represents the amount by which the end-to-end delay bound .

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Slack Term(cont.)

R3 can only reserve a value of 2Mb/s which if used as the new reservation value in the propagated Resv message will cause an increase in the end to end delay bound di.

The request can be accepted and a reservation of 2Mb/s installed in R3.(R=2Mb/s, S2=S1-di)

R2 and R1 also reserving 2Mb/s.

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Summary

In this tutorial we have looked at the controlled-load and guaranteed service classes that can provide end applications with enhanced QoS commitments over conventional best-effort delivery.

RSVP can be used by end applications to select and invoke the appropriate class and QoS level.