advanced computer networks1 the integrated services in the internet: state of the art paul p. white...
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Advanced Computer Networks 1
The Integrated Services in the Internet: State of the Art
Paul P. White
Jon Crowcroft
Advanced Computer Networks 2
Motivation of the paper
• To Study the Evolution of the Internet from a simple Data only Network into a true multiservice Network that supports multimedia applications and their protocols with appropriate performance and cost.
Advanced Computer Networks 3
What is traditional services and what was the goal behind it ?
• Point to point best effort service.• Goal – highly fault tolerant data network for the defense
community. • So….. most of the attention was paid to dynamic route
calculation, thus not too much attention was paid to performance of packet forwarding.
• Assumptions…… not to share network with other users and let it become overloaded.
• the amount of state shared between the network and end systems is minimized, just enough to calculate set to routes and determine best route. More importance given to dynamic and distributed route calculation.
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What are typical old applications?
• Telnet
• FTP
• http
etc…..
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What are new emerging applications ?
• Real Audio
• Real video
• Net Meeting/ conferencing
• White board
etc……
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What do we need ?
• A new service model
• Applications that need higher assurance for bandwidth, packet loss and delay can ask for it.
• Implies that we need networks to treat some packets differently from others.
Advanced Computer Networks 7
What led the internet evolution and how ?
• Traffic management for different applications.
• Different users.Stages in internet evolution:• TOS (Type of Service) forwarding, obtained by spying at TCP port numbers.• TCP, enhances inherently unreliable IP, to
provide ordered and reliable delivery,
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cont..
• Mbone (multicast backbone), for group communication. Advantage – massive reduction in load.
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How do we enhance internet to support various applications, users
without overloading ?• Overengineering – always will be some
applications that can exceed network capacity.
• Resource Reservation – received most attention.
• Usage based charging – very complex, hard to deploy and not global agreement on traffic.
Advanced Computer Networks 10
What do these new applications require?
Commitment to have• Real time delivery i.e. bounded jitter-no
retransmission allowed. • Certain Bandwidth• Packet lossSo, they are very sensitive to QOS their packet
receives.• Also, these new applications are multipoint to
multipoint.
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How to fulfill these requirement ?
• Not use the applications due to pricing and
network congestion.
• Use congestion avoidance RED, DEC bit …
• Use congestion control and WFQ.
None of above guarantee minimal packet forwarding rate, so…… dynamic specification of a source req. is preferable.
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Two main classed of multimedia applications
• Adaptive applications – guarantee for minimum capacity with reasonable probability.
• Legacy constant rate applications – strong guarantee of service.
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IETF (Internet Engineering Task Force)
• Standardizing body.• Has Integrated Services Working group.http://www.ietf.org/html.charters/intserv-charter.html• Defined several services classes – provides
certain QOS commitments• QOS is programmable on per flow basis by
end applications.
Advanced Computer Networks 14
How is it done ?
• End applications makes requests.• Requests pass to routers by network
management protocols or through Reservation Protocols (RSVP).
• Requests dictate level of resources to e reserved and transmission scheduling behavior in the routers……. Thus providing end-to-end QOS.
Advanced Computer Networks 15
Does having QOS between router provide end to end QOS ?
• No…. Why ? • What about link layer technologies ?• Link layer to ensure that the link layer installs
appropriate QOS support.• Defined by Integrated Services over Specific Link
Layers Working Group of IETF(issll).
http://www.ietf.org/html.charters/issll-charter.html
Advanced Computer Networks 16
What is admission control and why is it required ?
• Control mechanism.• Admission control looks at the Tspec and Rspec of
the flow to determine if desired service can be provided to a flow given its currently available resources.
• Not causing previously admitted flow to suffer.• If it can provide the service flow is admitted• Otherwise denied.
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cont…
• Also look at the maximum datagram size, it should not be greater than MTU maximum transmission unit of the link.
• Assumption: Datagram receiving enhanced QOS are never fragmented.
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What is Tspec ?
• Traffic characteristics of the flow.
Tspec parameters include:
p peak rate of flow (bytes/sec)
b bucket depth (bytes)
r token bucket rate (bytes/sec)
m minimum policed unit (bytes)
M maximum datagram size (bytes)
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What is Rspec ?
• Reservation characteristics.
R bandwidth, I.e. service rate (bytes/sec)
S slack term (ms)
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Classes of services:
• Best effort Services
And two Integrated Services:
• Guaranteed service
• Controlled load service
• Predictive load service
Advanced Computer Networks 21
What is controlled load service ?
• Provides approximately the same QOS under heavy loads as under light loads.
• Commits to offer a service equivalent to that seen by a best effort flow on a lightly loaded network.
• Tspec is required without peak rate parameter.
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How is it different from Best Effort Service ?
• Does not noticeably deteriorate as the network load increases.
• Best effort experiences worst services as the network load increases.
• Best effort uses simple FIFO buffering schemes while it uses simple priority queuing
Advanced Computer Networks 23
What are the applications that require controlled load services ?• Intended for class of applications that can
tolerate certain amount of loss or delay.
• Adaptive real-time applications
• Existing Mbone applications over intranet
• SNA or DEC local area terminal tunneling across a public internet service provider’s backbone network –both are delay sensitive.
Advanced Computer Networks 24
What is guaranteed load service ?
• Provides an assured level of bandwidth, a firm end-to-end delay bound.
• No queuing loss for conforming packets of data flow.
• Characterized by allocating a bandwidth R and buffer space B that flow consumes.
Advanced Computer Networks 25
How to get end to end delay ?
• In a perfect fluid model delay is bound by b/R provided R > r
where R is bandwidth of wire between src – dst.
b is depth of bucket.
r is token bucket rate.
Two errors arises due to finite packet sizes
Any packet experiences an excess delay in the forwarding due to its size in the same queue
Advanced Computer Networks 26
cont..
• Inaccuracies in the scheduling.
So delay bound becomes
b/R + C/R + D
In guaranteed service limit on peak rate p results in reduction of the delay bound
also due to packetization effect of the flow
consider the maximum packet size M.
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cont..
Qdelayend2end = (b-M) (p-R) + (M + Ctot) + Dtot
R(p-r)
R
(case p> R > r)
Qdelayend2end = (M + Ctot) + Dtot
R
(case R > P > r)
Advanced Computer Networks 28
What is policy control ? Why ?
• It is a function applied on a per-packet basis to make sure that a flow conforms to the Tspec that was used to make reservation.
• Policy control should be done at network access point to traffic does not interfere with other flows.
• Different from admission control …..
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cont..
• Non conforming flow should not be allowed to affect QOS if conforming flows.
• Non conforming data should be treated as best effort traffic.
• Routers should try to forward as many packets of nonconforming data as possible
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Why need traffic reshaping ? Where ?
• Requires the reshaping of traffic to the token bucket of the reserved Tspec.
• Should be applied at places where it is possible for a data to exceed the reserved Tspec. Occurrences is possible in two cases:- branch pt in distribution tree where the reserved tspecs of the outgoing branches are not the same.
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cont…
- merge points in the distribution tree for sources sharing the same reservation.
- reshaping incurs additional delay – slowing down early packets.
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Killer Reservation problem
• Occurs due to merging of heterogeneous reservation requests from receivers onto the tree from the same source.- large reservations made subsequent to an existing smaller reservation fails, and due to native implementation entire reservation fails- receivers continually making attempts to make large reservations, retrying quickly after failure block smaller reservation requests that might succeed.
Advanced Computer Networks 33
What are the applications that require guaranteed service ?
• Many military and commercial applications.
• Real-time stock quotes.
• Remote surgery using robotic arm.
Any more applications ????
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Does all link layer technology support QOS ?
• Token ring – yes (synchronous, asynchronous traffic)
• LAN switches – yes (multiple queue based on 802.1p header)
• Frame Relay - yes.• ATM – yes (CBR, VBR, ABR, GFR)• Ethernet – yes (802.1p header has 3 priority
bits)
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Why RSVP ?
• Setup necessary router state to support the Integrated Services.
• Why not ST-II or ST-II+ ? because RSVP has
- receiver initiated reservation.- separating reservations from packet filtering- providing different reservation styles
Advanced Computer Networks 36
cont…
- maintaining soft state in the network.
- protocol overhead control/
- modularity.
Advanced Computer Networks 37
Why receiver oriented ?
• To efficiently handle heterogeneous receivers.
• Allow dynamic group membership.
• Easier to commercial deployment - since receiver would pay for requested services.’
• similar to Deering’s Multicast routing approach.
Advanced Computer Networks 38
Why use softstate ?
• Tolerant to frequent routing changes.
• Adds robustness
• QOS routing can be deployed separately
• gives straight forward way to increase or decrease the level of resource allocation.
Advanced Computer Networks 39
RSVP is – is notIs• Signaling protocol• Is simplex – makes reservation for unidirectional flow only• Receiver –oriented approach• Maintains soft –state.• Traffic control and policy control parameters are opaque to
it.• Is dependent on present routing protocols• Provides transparent operation through routers that do not
support it.
Advanced Computer Networks 40
cont….
Is not
• A routing protocol.
• Not duplex.
• Not a sender oriented approach.
• Does not use hard-state.
Advanced Computer Networks 41
How RSVP works ?
• Senders originate PATH message to install routing state in each router in the path
• provide information to receiver of Sender’s traffic
• Receivers send RESV messages towards senders to request reservation in intermediate routers
• IP datagram protocol number is 46.
Advanced Computer Networks 42
R1 R2 R3
R4
S1
RCV1
RCV2
RCV3
Rn router
ResvResvTearPathErr
PathPathTearResvErrResvConf
What are Directions of RSVP messages ?
Advanced Computer Networks 43
What is filterspec and flowspec?
• Associated with reservations at the routers
• describes the packet to which reservation applies
• obtained from merging process applied to selected Resv messages
• style is (filterspec{flowspec}) used to summarize the request made by the Resv message.
Advanced Computer Networks 44
What are different merging and reservation styles ?
• Fixed Filter (Distinctive Reservation and Explicit sender selection)
- filterspec consists of single sender only
- effective flowspec of the reservation installed is the maximum of all FF reservation requests received for that particular sender.
Advanced Computer Networks 45
cont...
• Wildcard Filter (shared Reservation and Explicit Sender Selection)
- filterspec is a wildcard and matches on any sender from upstream
- effective flowspec installed is the maximum of all reservation requests received.
Advanced Computer Networks 46
cont...
• Shared Explicit (Shared reservation and explicit sender selection)
- filterspec contains a specific set of senders from upstream and is obtained by taking the union of individual filterspecs.
- effective flowspec installed is the maximum form all SE reservation requests received
Advanced Computer Networks 47
Towards S1, S2
Towards S3, S4
Towards S5, S6
FF(S1{4B},S2{6B})
FF(S3{2B},S4{5B})
FF(S5{4B},S6{6B})
WF(* {5b})
WF(* {5b})
WF(* {5b})
Towards S1, S2
Towards S3, S4
Towards S5, S6
Outgoing requests after merging
Outgoing requests after merging
incoming reservation requests
incoming reservation requests
FF(S1{2B}, S2{3B}, S4{5B})FF(S1{4B}, S2{2B})
FF(S4{4B})FF(S2{6B}, S4{2B}, S6{2B})
FF(S2{3B}, S3{2B}, S5{4B})
WF(* {5B})WF(* {2B})
WF(* {3B})WF(* {2B})
WF(* {4B})
I
I
I
I
I
I
ReserveS1{4B}S2{3B}S4{5B}
S2{6B}S4{4B}S6{2B}
S2{3B}S3{2B}S5{4B}
Reserve
(* {5B})
(* {3B})
(* {4B})
I
I
I
FF Reservation example
WF Reservation example
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SE((S1,S2){5B})
SE((S3, S4){5B})
SE((S5, S6{5B})
Towards S1, S2
Towards S3, S4
Towards S5, S6
SE((S2, S4){5B})SE((S1, S2){2B})
SE((S4{3B}) SE((S4, S6{2B})
SE((S2, S3, S5){4B})
I
I
I
Reserve
(S1, S2, S4){5B}
(S4, S6){3B}
(S2, S3, S5){4B}
I
I
I
SE Reservation example
incoming reservation requestsOutgoing requests after merging
Advanced Computer Networks 49
What information is in PATH messages ?
• phop - the address of the last RSVP capable node, updated at every RSVP capable router.
• Sender template - the filter specification identifying sender, IP addr, sender port
• sender Tspec - sender traffic characteristics
• adspec - OPWA information, updated at every RSVP capable router.
Advanced Computer Networks 50
How PATH messages are processed and propagated ?
• Update/Create its PATH state entry.• Setup cleanup timer equal to timeout interval and
restart timer.• Router generates the PATH messages based on its
PATH state and forwarding down the tree.• PATH messages forwarded on any change in
PATH state or on change of outgoing interfaces in the data forwarding path.
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cont..
• Also created and forwarded very refresh timeout interval.
• Refresh timeout interval is several times smaller than cleanup timeout interval.
• PATHTEAR messages expedite the tear down process (explicitly), generated when Path state is deleted.
Advanced Computer Networks 52
What is Adspec ?
• Optional object that sender may include in PATH message to advertise to receiver the characteristics of the end to end communication path.
• Receiver determines the level of reservation required for end to end QOS.
• Consist of message header, default general parameter fragment, and either guaranteed or controlled load service fragment.
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cont..
• General parameter fragment include
- minimum path latency.
- path bandwidth.
- global break bit.
- IS hop count.
- PathMTU
since IS requires that packet never be fragmented M in Tspec should never exceed MTU
Advanced Computer Networks 54
cont..
• Guaranteed service fragment includes
- Ctot
- Dtot
- Csum
- Dsum
- Guaranteed service break bit
- Guaranteed service general parameters values
Advanced Computer Networks 55
cont..
• Controlled load service fragment include
- controlled load service break bit
- controlled load service general parameters values.
Advanced Computer Networks 56
What is OPWA ?
• Refers to the reservation model where sender includes an adspec information in its PATH messages.
• Done to enable receiver to determine the end-to-end service as a result of this reservation
• helps minimize the handshaking latency between senders and recipient.
Advanced Computer Networks 57
What does Resv message include?
• Reservation style• filter specification, filterspec• flow specification, flowspec• reservation confirm object, ResvConf,
contains IP addr• Resv messages are merged in upstream
routers to obtain effective flowspec and filterspec.
Advanced Computer Networks 58
How does Resv message propagate ?
• Upward based on the PATH state.• Merges based on the rules discussed earlier• Effective flowspec is passed to the traffic control
module to apply both admission control and policy control.
• ResvErr message is send downstream if attempt is denied.
• If accepted reservation state is setup in accordance to flowspec and filterspec.
Advanced Computer Networks 59
What is slack term ?
• Represents the amount by which the end to end delay bound will be end to end delay bound required by the application.
• Inclusion of non zero slack term offers the individual routers greater flexibility to make reservation.
• Reservation is accepted, although unable to meet the deadline if slack term is larger than the excess delay.
Advanced Computer Networks 60
R1 R2 R3 R4 R5
R1 R2 R3 R4 R5
Sender
Sender
Receiver
Receiver
5Mb/s 4Mb/s 2Mb/s 4Mb/s 3.5Mb/s
3.5Mb/s4Mb/s2Mb/s4Mb/s5Mb/s
Available bandwidthin router
Available bandwidthin router
Resv(R1, S1)Resv(R1, S1)Resv(R1, S1)
Resv(R1, S1)Resv(R1, S1)Resv(R1, S1)Resv(R2, S2)Resv(R2, S2)Resv(R2, S2)
ResvErr
R = 2.5 Mb/s, S1 = 0 Reservation request denied
R = 3 Mb/s, S1 > 0, R2 = 2Mb/s, S2<S1. Reservation accepted
Advanced Computer Networks 61
Some areas of future research• Accounting and billing needs• Aggregation of nonspecifically related
reservations.• Authentication.• Usage account model etc….• To use IS or Diff services ????????? Is the big
question.• How to deploy them ?