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Shumon Huque University of Pennsylvania MAGPI GigaPoP April 15th 2002 - NSF/ITR Scalable QoS Workshop. Some QoS Deployment Issues. University of Pennsylvania network. Large research university in Philadelphia, PA 22,000 students, 4,000 faculty, 10,000 staff 48,000 registered IP addresses

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Some qos deployment issues

Shumon Huque

University of Pennsylvania


April 15th 2002 - NSF/ITR Scalable QoS Workshop

Some QoS Deployment Issues

University of pennsylvania network
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

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, J&J Pharmaceuticals

Magpi gigapop cont
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

Who wants qos
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

What types of qos
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?


  • 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

Interdomain internet qos
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

Interdomain internet2 qos
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

Deployment challenges
Deployment Challenges

  • I2 backbone is an R&E 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

Deployment challenges 2
Deployment Challenges (2)

  • So, we need to be very careful about changes we introduce to the network to facilitate QoS

  • Don’t jeopardize existing production traffic

Router support for qos
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

Router code support cont
Router code support (cont)

  • Example: Juniper routers

  • 4.x release:

    • Can police DS BA’s 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

Parallel network infrastucture
Parallel Network Infrastucture

  • Deploy parallel network infrastructure

  • Place QoS enabled routers on this

  • Researchers are happy, but ..

  • Cost prohibitive

Qos policy issues
QoS policy issues

  • Where does marking occur?

    • Endstations

    • First hop routers or switches

    • Edge routers

  • Who’s allowed to mark? How to validate?

    • Complexity of deploying policies

    • Additional controls and checks to enforce the policies

      • Policy servers: COPS, bandwidth brokers etc

Inter domain signalling
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

What we do today
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 don’t mark or re-mark DSCP code points

Bandwidth management alternatives
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

Endstation problems
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


  • We’re 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