Internet QOS: A Big Picture Xipeng Xiao and Lionel M. Ni, Michigan State University
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Transcript of Internet QOS: A Big Picture Xipeng Xiao and Lionel M. Ni, Michigan State University
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INTERNET QOS: A BIG PICTUREXIPENG XIAO AND LIONEL M. NI, MICHIGAN STATE UNIVERSITY
Jinyoung YouCS540, Network Architect
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Motivation
Today’s Internet Best-effort service No guarantee as to timeliness or actual delivery No guarantee of low-delay and low-jitter services No service classes No abundant and cheap bandwidth
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Motivation
What’s the QoS? Guarantee a certain level of performance
e.g.) Packet dropping probability , Delay, Jitter, Out-of-order delivery, Error, Congestion
Why QoS? The network capacity is insufficient
Real-time streaming multimedia applications e.g.) VoIP, IPTV Requires fixed bit rate and are delay sensitive
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Motivation
Misunderstanding of QoS Cannot provide nonexistent bandwidth Cannot make the network faster Cannot cure poorly performing network
Contribution of QoS Provide relative prioritization of traffic
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Motivation
Service Models and Mechanisms of IETF Integrated Services/Resource Reservation Protocol (RSVP)
Model Differentiated Services (DS) model Multi Protocol Label Switching (MPLS) Traffic engineering Constrained Based Protocol
How they differ from and relate to each other? Which system they fit?
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Outline
1. IntServ/RSVP2. DiffServ3. MPLS4. Traffic Engineering/CBR5. Comparison of ATM Networks6. Conclusion7. Q&A
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IntServ/RSVP
Resource reservation For real-time service, before data are transmitted, Apps must first set up paths and reserve resources
Service classes Guaranteed service: fixed delay bound Controlled-load service: reliable and enhanced best-
effort service
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IntServ/RSVP
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IntServ/RSVP
Components Signaling protocol Admission control routine Classifier Packet scheduler
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IntServ/RSVP
Limitations Scalability
State information is proportional to amount of flow
Overhead on routers Should have all components; RSVP, admission control, MF
classification, packet scheduling
Ubiquitous deployment is required
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DiffServ
Motivation The difficulty in implementing and deploying IntServ and
RSVP
DS is essentially a relative-priority scheme Using DS fields of packet header to indicate service classes
Process complexity core network → edge network More scalable
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DiffServ
Customer Have a Service Level Agreement (SLA) with its ISP
Which service class to provide? Mark the DS field according to the service class
Router Classification, policing, shaping, scheduling occur at only ingress
routers
Domain DF field is remarked by SLA between the domains
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DiffServ
Possible services of DiffServ Premium service
For low-delay and low-jitter service Assured service
For better reliability than best-effort service Olympic service
gold, silver, and bronze, with decreasing quality
Differences between DiffServ and IntServ State information is proportional to the number of classes Process complexity is only at the edge router
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DiffServ
Assured Service Provide reliable services even in times of network
congestion
Be implemented as follows: Classification and policing are done at the ingress routers All packets, in and out, are put into an AQ The queue is managed by a RED or RIO
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DiffServ
Premium Service SLA specifies a peak bit-rate Provide low delay and low jitter
e.g.) Internet Telephony, Video Conferencing, VPN More expensive, But more prior than Assured Service
Be implemented as follows: Use P-bit on DS field If P-bit is on, the packet goes to Premium Queue Uneven distribution of traffic may cause a problem
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DiffServ
Service Allocation in Customer Domains How to decide services; Assured or Premium Service
Each host makes its own decision Bandwidth Broker(BB) makes decision
Resource Allocations in ISP Domains How boundary routers handle incoming traffic
Static SLAs, Manually configured. Dynamic SLA, RSVP
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DiffServ
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DiffServ
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DiffServ
Requirements on Routers Edge router: MF classifications, marking, and shaping ISP ingress router: policing, re-marking ISP egress routers: re-shaping BA classification, Assured Queue, Premium Queue For dynamic SLA, BB at the customer domain
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MPLS
MPLS: Multi Protocol Label Switching Incoming packets are assigned a “label” by edge router
Packets are routed according to the label By a label switch router(LSR)
The path a packet traverses is called label switched path(LSP) Network protocol independent
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MPLS
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MPLS
MPLS is strategically significant Provides faster packet classification and forwarding Provides an efficient tunneling mechanism
without encryption Moves processing to edge routers
Core did forwarding only, Scalable
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Traffic Engineering/CBR
Motivation IntServ/RSVP and DiffServ has degradation of perfor-
mance when traffic load is heavy.
Major goal Provide efficient and reliable network operation Optimize network resource utilization
To efficiently manage bandwidth resources Optimize traffic performance
To enhance QoS of traffic stream
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Traffic Engineering/CBR
The factor of Congestion Lack of network resource
Upgrade infrastructure Uneven distribution
Because of Shortest Path problem Constraint Based Routing
Automatically Traffic Engineering
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Traffic Engineering/CBR
Shortest Path Problem
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Traffic Engineering/CBR
Constrained Based Routing Compute QoS route
May select longest lightly-loaded path rather than heavily shortest path
Improve network resource utilization
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Traffic Engineering/CBR
Distribution of Link State Information Needs of link available bandwidth, buffer space information Link state advertisement of OSPF, IS-IS
Route Computation Various algorithm for distinct metrics; cost, hop-count, bandwidth, re-
liability, delay, jitter Let d(i, j) be a metric for link (i, j). For any path P = (i, j, k, …,l, m), metric d is:
Additive if d(P) = d(i, j) + d(j, k) + … + d(l, m) e.g.) delay, jitter, cost and hop-count
Multiplicative if d(P) = d(i, j) * d(j, k) * … * d(l, m) e.g.) reliability (1-loss rate)
Concave if d(P) = min{d(i, j), d(j, k), …, d(l, m)} e.g.) bandwidth
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Traffic Engineering/CBR
Pros Meeting the needs for QoS requirement of flows Improved network utilization
Cons Increased communication and computation overhead Increased routing table size Longer path may consume more resources Potential routing instability
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Traffic Engineering/CBR
The Position of CBR DiffServ: Not for replacing, but helping DiffServ RSVP: Independent with RSVP
CBR just determines the path of RSVP messages MPLS
MPLS: forwarding scheme, CBR: routing scheme Work together for traffic engineering
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Comparison of ATM Networks
ATM Network Use Virtual Circuit Switching Pros
Fast Provide QoS
Cons ATM cell header overhead Switch can not work at the boundary of network
ATM Network with DiffServ or MPLS Provide QoS on the router network Reduce ATM cell header overhead
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Conclusion
QoS is hotly debated issue Fibers and WDM will make bandwidth so abundant and cheap
QoS will be automatically delivered However, New application will be invented to consume it
Thus, Mechanism will be needed to provide QoS
Many mechanisms are provided but they not solve QoS problem There is little hope for success But, Way to go
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Q&A