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Traffic Shaping


Limitations of Isochronous Shaping. Easy to implement. Easy description ... 3. Isochronous Shaping with Priority Schemes. Uses bit patterns for priority ... – PowerPoint PPT presentation

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Title: Traffic Shaping

Traffic Shaping
  • Why traffic shaping?
  • Isochronous shaping
  • Isochronous shaping with Priority schemes
  • Shaping Bursty Traffic Patterns
  • Conclusions

1.Why traffic shaping?
  • Network knows what traffic to expect
  • Network can determine if the flow should be
    allowed to send
  • Network monitor the flows traffic - confirm the
    flows behavior as promised

1.Why traffic shaping?
  • 1. Regulating traffic
  • - 100 MB / 1 s vs 1 KB / 10 µs
  • 2. Deciding weather to accept the flows data
  • - can buffer 100 MB ?
  • 3. Policing a flow
  • - detect misbehaving flows

1.Properties of good traffic shaping scheme
  • Shaping scheme should describe wide range of
  • Shaping rules should make it easy to describe
    traffic patterns
  • Shaping scheme should be easy to police

2. Isochronous Shaping
  • regular amounts of data emitted at regular

2.1. Simple Leaky Bucket
  • Each flow has its own bucket
  • send rate ?
  • bucket size ß
  • Cell datagram traffic
  • Easy to implement to describe.
  • ex FIFO Timer

2.2. (r,T) Smooth Traffic
  • Based on stop and go algorithm
  • Send no more than r bits in any T time period
  • Limitation 2r sized datagram cant be sent
  • Implementation -simple
  • Bit counter, refreshed every T bit times

2.3. Limitations of Isochronous Shaping
  • Easy to implement
  • Easy description traffic policing
  • The range of behavior limited to fixed rate data
    flow. Var. rate flows request the peak rate -gt
    wasting network capacity - peak values occurs

3. Isochronous Shaping with Priority Schemes
  • Uses bit patterns for priority
  • How prioritizing is done
  • application knows less important data
  • network marks the incoming cells at exceeding

3. Isochronous Shaping with Priority Schemes
  • Limitations of priority schemes
  • low priority packets dont get through
  • bandwidth reservation for low priority traffic
  • selectively discard packets
  • many com. devices uses FIFOs - continuous memory
  • sufficiently flexible
  • used in first generation cell switches

4. Shaping Bursty Traffic Patterns
  • Token Bucket
  • Token Bucket with Leaky Bucket Rate Control

4.1. Token Bucket
  • Tokens inserted at rate ? into bucket
  • if bucket is full -gt token is dropped
  • send allowed if there are b tokens in bucket,
    bsize packet-size
  • ßt/? tokens worth data at any t time interval
  • long term transmission rate is ?

4.1. Token bucket - limitations
  • No need for discard priority policy
  • discards tokens and leaves to the flow the
    managing transmission queue if the flow
    overdrives the regulator
  • easy to implement (counter timer)
  • policing -gt bit more difficult - possibility for
    cheating in data rate

4.2. Token Bucket with Leaky Bucket Rate Control
Token bucket
Leaky bucket
4.2. Token Bucket with Leaky Bucket Rate Control
  • Token bucket combined with a simple leaky bucket
  • C gtgt ?
  • behaves like token bucket
  • permits bursty traffic - but regulates max.
    traffic to rate C
  • long term transmission rate is ?

5. Conclusions
  • More accurate description of flows rate help
    network to effectively manage its resources
  • Simplest shaping - leaky bucket - for fixed data
  • priority schemes - more general, combines H/L
    priority traffic in the same flow
  • token bucket (with leaky bucket) -gt more diverse
    traffic patterns

Flow Setup and Routing

Flow Setup and Routing
  • The Hosts role in flow setup
  • Protocols to establish a flow - ST II
  • Routing - Multicasting flow

1. The Hosts role in flow setup
  • Some mechanism/ protocol/data structure needed to
    ask the network for particular performance
  • Two main ways
  • few variables identify a general class of req.
  • video, voice, big file transfer flows
  • routers preconfigured - new apps -gt new classes
  • multivalued explicit specification of flow spec.
  • bustiness, delay requirements, sensitivity to
    loss etc.

2. Network answers to requests
  • Three main modes
  • simply yes / no answer
  • establish the best service available currently -
    if the best case is not acceptable the
    application can end the flow
  • negotiations should be interactive - complexity
    at network application

3.Protocols to establish a flow
  • General requirements
  • setup protocol should accommodate multiple
    receivers for a single flow
  • set up flows quickly
  • result in robust reservations
  • change the flow properties after flow is
  • support advance reservations

3.1. Strawman proposal
  • Enhance an existing internet protocol like IP by
    adding a flow ID field, and a flow spec option
    that can be sent as part of IP header
  • Routers forward IP datagrams as before, only if
    flow id is set forward based on information about
    flow requirements.
  • If has no info forwards normally ask sender for

3.2. Version 2 of the Stream Protocol
  • Most sophisticated / complex /complicated flow
    setup protocol
  • Two protocols
  • a datagram forwarding protocol ST
  • connection management protocol ST Control Message
    Protocol SCMP
  • 17 SCMP messages
  • flow setup is done hop-by-hop

3.3. RSVP
  • Resource ReSerVation Protocol
  • not the sender is managing the flow but each
  • filters are used
  • provide support for heterogeneity - receivers
    with slow links still can participate on flows
  • dynamic filtering allows receivers to modify flow
    properties - switching btw. listening of A and B
  • try to reduce load improve bandwidth management.

4. Routing
  • Historically routing determining if path exists
    btw. two points in a network
  • Routing supporting flows (more difficult)
    determining if a path exists so to achieve a
    flows requirement

4.1. Routing
  • Bellman-Ford
  • tries to minimize routing information by
    requiring routers to pass along information only
    about best routes
  • Implemented in RIP
  • Dijkstras alg.
  • distributes complete routing information to all
    routing agents
  • Implemented in OSPF, IS-IS

4.2. Multicasting and Multiobjective Routing
  • not only finding a path but finding a delivery
  • sender or receiver based routing ?
  • Q.E.D.