Transcript Slides

The Integrated Services in the
Internet: State of the Art
Paul P. White
Jon Crowcroft
Advanced Computer Networks
1
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
2
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.
Advanced Computer Networks
3
What are typical old
applications?
• Telnet
• FTP
• http
etc…..
Advanced Computer Networks
4
What are new emerging
applications ?
• Real Audio
• Real video
• Net Meeting/ conferencing
• White board
etc……
Advanced Computer Networks
5
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
6
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,
Advanced Computer Networks
7
cont..
• Mbone (multicast backbone), for group
communication. Advantage – massive
reduction in load.
Advanced Computer Networks
8
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
9
What do these new applications
require?
Commitment to have
• Real time delivery i.e. bounded jitter-no
retransmission allowed.
• Certain Bandwidth
• Packet loss
So, they are very sensitive to QOS their packet
receives.
• Also, these new applications are multipoint to
multipoint.
Advanced Computer Networks
10
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.
Advanced Computer Networks
11
Two main classed of multimedia
applications
• Adaptive applications – guarantee for
minimum capacity with reasonable
probability.
• Legacy constant rate applications – strong
guarantee of service.
Advanced Computer Networks
12
IETF (Internet Engineering Task
Force)
• Standardizing body.
• Has Integrated Services Working group.
http://www.ietf.org/html.charters/intservcharter.html
• Defined several services classes – provides
certain QOS commitments
• QOS is programmable on per flow basis by
end applications.
Advanced Computer Networks
13
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
14
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
15
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.
Advanced Computer Networks
16
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.
Advanced Computer Networks
17
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)
Advanced Computer Networks
18
What is Rspec ?
• Reservation characteristics.
R bandwidth, I.e. service rate (bytes/sec)
S slack term (ms)
Advanced Computer Networks
19
Classes of services:
• Best effort Services
And two Integrated Services:
• Guaranteed service
• Controlled load service
• Predictive load service
Advanced Computer Networks
20
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.
Advanced Computer Networks
21
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
22
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
23
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
24
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
25
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.
Advanced Computer Networks
26
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
27
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 …..
Advanced Computer Networks
28
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
Advanced Computer Networks
29
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.
Advanced Computer Networks
30
cont…
- merge points in the distribution tree for
sources sharing the same reservation.
- reshaping incurs additional delay –
slowing down early packets.
Advanced Computer Networks
31
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
32
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 ????
Advanced Computer Networks
33
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)
Advanced Computer Networks
34
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
35
cont…
- maintaining soft state in the network.
- protocol overhead control/
- modularity.
Advanced Computer Networks
36
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
37
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
38
RSVP is – is not
Is
• 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
39
cont….
Is not
• A routing protocol.
• Not duplex.
• Not a sender oriented approach.
• Does not use hard-state.
Advanced Computer Networks
40
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
41
What are Directions of RSVP
messages ?
Resv
ResvTear
PathErr
S1
R1
RCV1
R2
Path
PathTear
ResvErr
ResvConf
Rn
R3
RCV2
R4
RCV3
router
Advanced Computer Networks
42
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
43
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
44
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
45
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
46
Reserve
S1{4B}
S2{3B}
S4{5B}
incoming reservation requests
FF(S1{2B}, S2{3B}, S4{5B})
FF(S1{4B}, S2{2B})
I
S2{6B}
S4{4B}
S6{2B}
FF(S4{4B})
FF(S2{6B}, S4{2B}, S6{2B})
I
S2{3B}
S3{2B}
S5{4B}
Outgoing requests after merging
FF(S1{4B},S2{6B})
I
Towards S1, S2
FF(S3{2B},S4{5B})
Towards S3, S4
FF(S5{4B},S6{6B})
Towards S5, S6
FF(S2{3B}, S3{2B}, S5{4B})
FF Reservation example
Outgoing requests after merging
Reserve
WF(* {5b})
I
Towards S1, S2
WF(* {5b})
Towards S3, S4
WF(* {5b})
(* {5B})
I
I
(* {3B})
I
I
(* {4B})
I
incoming reservation requests
WF(* {5B})
WF(* {2B})
WF(* {3B})
WF(* {2B})
WF(* {4B})
Towards S5, S6
WF Reservation example
Advanced Computer Networks
47
Outgoing requests after merging
Reserve
SE((S1,S2){5B})
I
Towards S1, S2
SE((S3, S4){5B})
Towards S3, S4
SE((S5, S6{5B})
Towards S5, S6
I
I
(S1, S2, S4){5B}
I
(S4, S6){3B}
I
(S2, S3, S5){4B}
I
incoming reservation requests
SE((S2, S4){5B})
SE((S1, S2){2B})
SE((S4{3B})
SE((S4, S6{2B})
SE((S2, S3, S5){4B})
SE Reservation example
Advanced Computer Networks
48
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
49
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.
Advanced Computer Networks
50
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
51
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.
Advanced Computer Networks
52
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
53
cont..
• Guaranteed service fragment includes
- Ctot
- Dtot
- Csum
- Dsum
-
Guaranteed service break bit
Guaranteed service general parameters values
Advanced Computer Networks
54
cont..
• Controlled load service fragment include
- controlled load service break bit
- controlled load service general
parameters values.
Advanced Computer Networks
55
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
56
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
57
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
58
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
59
Available bandwidth
in router
Sender
5Mb/s
4Mb/s
2Mb/s
4Mb/s
3.5Mb/s
R1
R2
R3
R4
R5
Resv(R1, S1)
Resv(R1, S1)
Receiver
Resv(R1, S1)
ResvErr
R = 2.5 Mb/s, S1 = 0 Reservation request denied
Available bandwidth
in router
Sender
Resv(R2, S2)
5Mb/s
4Mb/s
2Mb/s
4Mb/s
3.5Mb/s
R1
R2
R3
R4
R5
Resv(R2, S2)
Resv(R2, S2)
Resv(R1, S1)
Resv(R1, S1)
Receiver
Resv(R1, S1)
R = 3 Mb/s, S1 > 0, R2 = 2Mb/s, S2<S1. Reservation accepted
Advanced Computer Networks
60
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 ?
Advanced Computer Networks
61