Advanced Computer Networks

1
Advanced Computer Networks

• IntServ and RSVP
• Lan Wang
• lanwang_at_memphis.edu
• http//www.cs.memphis.edu/lanwang

Based in part upon the slides of Shriv
Kalyanaraman (RPI), Bruce Maggs (CMU), Lixin Gao
(Umass), Raj Jain (OSU), J.Kurose (Umass), S.
Keshav (Cornell)), I.Stoica (UCB), S. Deering
(Cisco).
2
Motivation

• Internet currently provides only single class of
  best-effort service.
• No admission control and no assurances about
  delivery
• Existing applications are elastic.
• Tolerate delays and losses
• Can adapt to congestion
• Future real-time applications may be inelastic.
• Should we modify these applications to be more
  adaptive or should we modify the Internet to
  support inelastic behavior?

3
Application Types

• Elastic applications.
• Wide range of acceptable rates, although faster
  is better
• E.g., data transfers such as FTP
• Continuous media applications.
• Lower and upper limit on acceptable performance
• Sometimes called tolerant real-time since they
  can adapt to the performance of the network
• E.g., changing frame rate of video stream
• Network-aware applications
• Hard real-time applications.
• Require hard limits on performance intolerant
  real-time
• E.g., control applications

4
A Short History of Internet QoS

• Lots of initial research in the late 80s and
  early 90s.
• Often takes a telecommunications view of the
  network.
• ATM QoS and Integrated services (IntServ) were
  developed based on these results.
• Focus on per-flow, hard QoS.
• Effort was driven by perceived application needs.
• In late 90s, the focus has shifted towards
  Differentiated services.
• Focus is on QoS for flow aggregates, e.g., all
  the flows belonging to one customer.

5
IntServ (Integrated Services)

• Focus on per-flow QoS.
• Provide hard and statistical guarantees.
• Many concerns
• Complexity
• Scalability
• Business model
• Charging

6
Components of Integrated Services

• Type of service model
• What does the network promise?
• Service interface
• How does the application describe what it wants?
• Packet scheduling
• How does the network meet promises?
• Establishing the guarantee
• How is the promise communicated to/from the
  network?
• How is admission of new applications controlled?

7
Service Models

• Guaranteed service
• Targets hard real-time applications.
• User specifies traffic characteristics and a
  service requirement.
• Requires admission control at each of the
  routers.
• Can mathematically guarantee bandwidth, delay,
  and jitter.
• Controlled load.
• Targets applications that can adapt to network
  conditions within a certain performance window.
• User specifies traffic characteristics and
  bandwidth.
• Requires admission control at each of the
  routers.
• Guarantee not as strong as with the guaranteed
  service.
• e.g., measurement-based admission control.
• Best effort

8
Service Interface

• Session must first declare its QoS requirement
  and characterize the traffic it will send through
  the network
• R-spec defines the QoS being requested by
  receiver (e.g., rate r)
• T-spec defines the traffic characteristics of
  sender (e.g., token bucket with rate r and buffer
  size b).
• A signaling protocol is needed to carry the
  R-spec and T-spec to the routers where
  reservation is required RSVP is a leading
  candidate for such signaling protocol.

9
Packet scheduling

• Guaranteed service
• Use token bucket filter to characterize traffic
• Described by rate r and bucket depth b
• Use WFQ (Weighted Fair Queuing) at the routers
• Parekhs bound for worst case queuing delay b/r

10
Admission Control

• Admission Control routers will admit flows based
  on their R-spec and T-spec and based on the
  current resource allocated at the routers to
  other flows.

11
Components of Integrated Services

• Type of service model
• What does the network promise?
• Service interface
• How does the application describe what it wants?
• Packet scheduling
• How does the network meet promises?
• Establishing the guarantee
• How is admission of new applications controlled?
• How is the promise communicated to/from the
  network

12
Role of RSVP

• Independent of unicast/multicast routing
  protocols.
• Must be present at sender(s), receiver(s), and
  routers.
• Carries resource requests all the way through the
  network.
• At each hop consults admission control and sets
  up reservation. Informs requester if failure.

13
Reservation Protocol RSVP
Upper layer protocols and applications
IP service interface
IP
ICMP
IGMP
RSVP
Link layer service interface
Link layer modules
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RSVP Goals

• Used on connectionless networks.
• Should not replicate routing functionality.
• Should adapt to route changes.
• Support for multicast.
• Different receivers have different capabilities
  and want different QOS.
• Changes in group membership should not be
  expensive.
• Should be able to switch allocated resource to
  different senders.
• Modular design should be generic signaling
  protocol.
• Result
• Receiver-oriented
• Soft-state

B
C
A
P
D
S
R
E
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Receiver-Initiated Reservation

• Receiver initiates reservation by sending a
  reservation to the source.
• If multicast, assumes multicast tree has been set
  up previously.
• Hooks up with the reserved part of the tree.
• How far the request has to travel to the source
  depends on the level of service requested.
• Uses existing routing protocol, but routers have
  to store the reverse path.
• Properties
• Can have parallel independent reservation and
  release actions.
• Supports receiver heterogeneity reservation
  specifies receiver requirements and capabilities.

16
Soft State

• Routers keep state about reservation.
• Periodic messages refresh state.
• Non-refreshed state times out automatically.
• Alternative Hard state
• No periodic refresh messages.
• State is guaranteed to be there.
• State is kept till explicit removal.
• Why could there be a problem?
• Properties of soft state
• Adapts to changes in routes, sources, and
  receivers.
• Recovers from failures
• Cleans up state after receivers drop outs

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RSVP Service Model

• Make reservations for simplex data streams.
• Receiver decides whether to make reservation
• Control messages in IP packets (proto 46).
• PATH/RESV messages sent periodically to refresh
  soft state.
• One pass
• Failed requests return error messages - receiver
  must try again.
• No end to end ack for success.

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Basic Message Types

• PATH message
• RESV message
• CONFIRMATION message
• Generated only upon request.
• Unicast to receiver when RESV reaches node with
  established state.
• TEARDOWN message
• ERROR message (if PATH or RESV fails)

19
PATH Messages

• PATH messages carry senders T-spec.
• Token bucket parameters
• Routers note the direction PATH messages arrived
  and set up reverse path to sender.
• Receivers send RESV messages that follow reverse
  path and setup reservations.
• If reservation cannot be made, user gets an error.

20
RESV Messages

• RESV messages carry receivers R-spec.
• Forwarded via reverse path of PATH.
• Queuing delay and bandwidth requirements.
• Source traffic characteristics (from PATH).
• Filter specification
• Which transmissions can use the reserved
  resources?
• Reservation style.
• Router performs admission control and reserves
  resources.

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Router Handling of RESV Messages

• If new request rejected, send error message.
• If admitted
• Install packet filter into forwarding dbase.
• Pass flow parameters to scheduler.
• Activate packet policing if needed.
• Forward RESV message upstream.

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RSVP reservations

• Reservations from multiple receivers for a single
  sender are merged together at branching points.
• Reservations for multiple senders may be added
  up
• Video conference
• Reservations for multiple senders may not be
  added up
• Audio conference, not many talk at same time.
• Only subset of speakers (filters).

23
Reservation Styles

• Three styles
• Wildcard/No filter does not specify a
  particular sender for group.
• Fixed filter sender explicitly specified for a
  reservation.
• Video conference
• Dynamic filter valid senders may be changed
  over time.
• Audio conference

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Example

• Senders S1, S2, S3
• Receivers R1, R2, R3
• Router interfaces A,B,C,D

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Wildcard Filter Reservation

• R1, R2, and R3 want to reserve 4b, 3b, and 2b,
  respectively (b is given rate).

A
C
S1
R1
B
D
R2
S2, S3
R3
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Fixed Filter Reservation

• R1 wants to reserve 4b for S1 and 5b for S2.
• R2 wants to reserve 3b for S1 and b for S3.
• R3 wants to reserve b for S1.

A
C
S1
R1
B
D
R2
S2, S3
R3
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Dynamic Filter Reservation

• R1 wants to reserve b for S1 and S2 (shared).
• R2 wants to reserve 3b for S1 and S3 (shared).
• R3 wants to reserve 2b for S2.

A
C
S1
R1
B
D
R2
S2, S3
R3
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Changing Reservation

• Receiver-oriented approach and soft state make it
  easy to modify reservation.
• Modification sent with periodic refresh.

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Routing Changes

• Routing protocol makes routing changes.
• In absence of route or membership changes,
  periodic PATH and RESV messages refresh
  established reservation state.
• When change, new PATH messages follow new path,
  new RESV messages set reservation.
• Non-refreshed state times out automatically.

30
State in Switches

• Have to keep sink tree information.
• No such thing as inverse multicast routing.
• Also have to keep information on sources if
  filters are used.
• Selected in path message.
• Used in aggregation and propagating information
  to switches.
• Also used in limiting protocol overhead.
• Switches do not propagate periodic reservation
  and path messages.
• They periodically regenerate copies that
  summarize the information they have.
• Raises concerns about scalability.

31
RSVP - Review

• Supports unicast and multicast.
• Unicast considered as special case of multicast.
• Receiver initiation handle negotiation at
  application level.
• Receiver heterogeneity
• how can low-capability receiver benefit from
  video sent at high bandwidth? Layered encoding
• Soft state

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Differentiated Services

• Intended to address the following difficulties
  with Intserv
• Scalability maintaining per-flow states by
  routers in high speed networks is difficult due
  to the very large number of flows
• Flexible Service Models Intserv has only two
  classes, want to provide more qualitative service
  classes want to provide relative service
  distinction (Platinum, Gold, Silver, )

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Assignments

• Reading Assignment
• Chap 14 of Huitema (Scheduling)
• Paper Summary, due Apr. 14, 2005
• Marjory S. Blumenthal and David D. Clark,
  Rethinking the design of the Internet The end to
  end arguments vs. the brave new world.
• Project Presentation Apr. 21 and Apr. 26
• Project Demo Apr. 28
• Final Report May 3