Some QoS Deployment Issues

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Some QoS Deployment Issues

• Shumon Huque
• University of Pennsylvania
• MAGPI GigaPoP
• April 15th 2002 - NSF/ITR Scalable QoS Workshop

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University of Pennsylvania network

• Large research university in Philadelphia, PA
• 22,000 students, 4,000 faculty, 10,000 staff
• 48,000 registered IP addresses
• 200 switched subnets
• Central routing between them and out to Internet
  and Internet2

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MAGPI GigaPoP

• An Internet2 GigaPoP
• Value added services
• Commodity Internet transit
• Facilitator of regional edu/research initiatives
• Subscribers
• UPENN, Lehigh U, Princeton U, PA county school
  units, JJ Pharmaceuticals

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MAGPI GigaPoP (cont)

• External Connectivity
• Internet2
• OC-12c POS to Abilene
• Commodity Internet
• UUNET OC-3
• Cogent Gigabit Ethernet
• Yipes Gigabit Ethernet (rate limited)
• DCANet Fast Ethernet

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Who wants QoS?

• University researchers
• QoS researchers in CS department
• Research applications needing strict guarantees
  on latency, b/w, jitter etc
• Networking staff (Univ and gigaPoP)
• Manage exploding b/w needs
• Enable new classes of applications
• Eg. VoIP, video conferencing, streaming
• Run non-mission critical traffic at lower
  priority
• Eg. File sharing apps, dorm traffic, bulk
  transfers

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What types of QoS?

• DiffServ in routing core and gigaPoP
• Layer2 priority (802.1p) in the switched portions
  of the campus network
• Mapping L3 QoS to/from L2 QoS
• Signalling and admission control?
• RSVP intra-domain? Aggregate reservations map
  to Diffserv traffic class at edge?
• Bandwidth Broker signalling?

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DiffServ

• Types of forwarding behavior we are most
  interested in
• EF (Expedited Forwarding)
• BE (Best Effort - default PHB)
• LBE/Scavenger (eg. QBSS)
• ABE - low delay form

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Interdomain Internet QoS

• Not very optimistic
• Some ISPs are starting to offer services
• Multiplicity of providers
• Need for them to run interoperable QoS
  implementations
• Mechanisms to ask for QoS reservations across
  administrative domains
• Peering/SLA issues

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Interdomain Internet2 QoS

• More optimistic
• Typically one or a few QoS enabled I2 backbone
  networks (eg. Abilene)
• Agreed upon QoS architecture
• Common set of operational practices and
  procedures
• Some provisioning procedures in place
• Existing demand from researchers

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Deployment Challenges

• I2 backbone is an RE network, but ..
• Universities are using it to transport production
  traffic between them
• And not just traffic associated with meritorious
  research applications (one of the original ideas)
• GigaPoP is a production network providing access
  to I2 and Commodity Internet

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Deployment Challenges (2)

• So, we need to be very careful about changes we
  introduce to the network to facilitate QoS
• Dont jeopardize existing production traffic

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Router support for QoS

• Not mature or well tested
• Often the features are in experimental code
  trains, unsuitable for deployment in a production
  network
• Marking, re-marking, policing, traffic shaping,
  appropriate queue scheduling disciplines etc
• Insufficient queues to support large scale
  service differentiation
• Often software implementations of required
  queueing disciplines instead of hardware
• Obviously this situation will improve in the
  future

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Router code support (cont)

• Example Juniper routers
• 4.x release
• Can police DS BAs but not much more
• 5.x release
• More queue scheduling disciplines
• Per queue traffic shaping
• DSCP marking and re-marking
• DSCP based prioritization and forwarding
• Eg. Assigning EF BA to a high priority queue
• Mapping of 802.1p to Layer-3 QoS

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Parallel Network Infrastucture

• Deploy parallel network infrastructure
• Place QoS enabled routers on this
• Researchers are happy, but ..
• Cost prohibitive

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QoS policy issues

• Where does marking occur?
• Endstations
• First hop routers or switches
• Edge routers
• Whos allowed to mark? How to validate?
• Complexity of deploying policies
• Additional controls and checks to enforce the
  policies
• Policy servers COPS, bandwidth brokers etc

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Inter-domain signalling

• No suitable mechanisms today for end2end
  inter-domain signalling of QoS reservations, call
  admission control
• Manual/static provisioning
• Bandwidth brokers/SIBBS work ongoing

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What we do today

• To facilitate researchers doing wide-area QoS
  experimentation
• Conscious effort not to impede
• Provide research labs with an uncongested path
  though campus/gigapop to QoS enabled Abilene
  network
• Make sure intervening routers dont mark or
  re-mark DSCP code points

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Abilene QoS testbed
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Bandwidth Management Alternatives

• University has experienced rapidly increasing
  bandwidth requirements
• Overprovision the campus network
• Buy more commodity Internet bandwidth through the
  gigaPoP
• Employ rate limiting where appropriate
• Employ lightweight QoS, eg. LBE/Scavenger

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Endstation problems

• Network apps often unable to use available
  bandwidth because of problems on end-stations
• Poorly designed applications, application
  protocols
• Insufficiently sized socket buffers
• Inefficient, insufficiently tuned network stacks
• Duplex mismatch
• MTU mismatch
• Having QoS in the network does not address this
  class of performance problems

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Conclusion

• Were interested in QoS
• Too early to deploy end2end reservation based QoS
  in many production networks
• Intra-domain QoS a near-term possibility
• Both reservation based and lightweight
• VoIP, degrading non-mission critical traffic
• End2End Inter-domain QoS difficult
• Co-ordination, SLAs, inter-domain signalling