Transcript RSVP and Integrated Services in the Internet: A Tutorial

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 networklayer service.
 IP delivery model is often referred to as “besteffort” .
 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
bounded 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
to 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-toend 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 controlledload 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.
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