QoS: Where, When, and Why? Ed Knightly ECE/CS Departments Rice University knightly (and without...
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Transcript of QoS: Where, When, and Why? Ed Knightly ECE/CS Departments Rice University knightly (and without...
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QoS: Where, When, and Why?
Ed Knightly
ECE/CS Departments
Rice University
http://www.ece.rice.edu/~knightly
(and without bankruptcy along the way)
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Ed Knightly
The Big Questions
• When do clients/customers want QoS?– Always! – No one wants unpredictable, poor performance
• How to deliver QoS?– Capacity planning?– Admission control (flow or aggregates)?– Adaptive algorithms and applications?– Marking/scheduling/AQM packet differentiation?
• Are we there yet?– NO! End-to-End service is lousy
Even the undergrads won’t use VoIP Video is useless match-box sized
– Applications can adapt, but users will not!
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Ed Knightly
Answers
Required mechanisms depend on
– QoS stringency: voice, live streaming media, …
– Traffic: predictability, aggregation level, …
– Economics: how can provider make $$ (or lose less)
– Deployability: ten-year scale for layer 3, six-months for layer 2/7
Case studies: Core, Enterprise, Metro Edge, Internet Data Centers, Wireless access
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Ed Knightly
I. Why QoS in NOT Needed In Today’s Core
1. Traffic is highly predictable and not bursty in the core
Operate here? Even QoS cannot save you
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Ed Knightly
Why QoS is NOT Needed in Today’s Core
1. Traffic is highly predictable and not bursty in the core because users are capped by– Abundance of low-rate access links
Ex. OC-3, T3, T1, DSL, modems, …– Abundance of rate limiters
Ex. Throttle dorm traffic; reduce ISP bill
2. There is no “production” real-time traffic– No VoIP, high-quality video, …
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Ed Knightly
With the Current Evolutionary Path
• Capacity planning is simple and sufficient – Traffic prediction = Time-of-day prediction (easy!)
• There are no research issues in the core – QoS or otherwise (why worry about ECN, AQM, multicast, …)
• More bankruptcies and junk bonds to come
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Ed Knightly
Disruptive Changes for the Future of the Core
• Economics? – Need to re-think;real costs to over-provisioning in line cards
• Integration of voice/video/new apps? – It’s happening at the edge
• Burstable high-speed packet access? – 1 and 10 Gigabit Ethernet access
Clients will burst, the traffic will change Contrast to today’s relatively low speed circuit access
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Ed Knightly
II. The Network Edge (Myth)
• Common, but unrealistic view– Hosts, network of switches (or routers), edge Internet
router
Internet B ac kb o neR o uter
S w itc hH o s t
...
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Ed Knightly
The Network Edge (Reality)
• Ring metro backbone– Rings are the dominant configuration for their fault tolerant
properties– Size ~ 100 nodes, ~ 10 km
InternetB ac kb o neM etro B ackbo ne
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Ed Knightly
SONET: the Dominant Metro Ring Technology
• Circuits between pairs of nodes. Problems:– Cannot re-use unused capacity (no statistical multiplexing)– Cannot burst to full link rate– Coarse bandwidth granularity (155 Mbps)– Up to N2 circuits
Inefficient!
InternetB ac kb o ne
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Ed Knightly
Emerging Approach: Packet Rings (GigE and RPR)
• Advantages– Statistical multiplexing, burstable access, efficiency
• Example Metro Provider: Phonoscope – 2 GigE rings spanning Houston with 400+ customers– 400 Mbps of data– 50 Mbps VoIP– 800 Mbps of streaming MPEG
InternetB ac kb o ne
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Ed Knightly
Challenges in Packet Rings
• Fairness– Closest node to the gateway gets the most bandwidth– Extent of unfairness depends on protocol (TCP/UDP), topology (RTT and
number of nodes) and traffic inputs– Goal: inter-node performance isolation
• Guaranteed QoS– Voice/Video require performance isolation (without circuits)
InternetB ac kb o ne
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Ed Knightly
Research Issues in Packet Rings
• Distributed priority scheduling and MAC– How to throttle at ingress, use simple transit path scheduling,
and achieve ring-wide QoS/fairness goals?
– Hot topic in ad hoc networking, equally challenging (and more relevant?) in packet rings
• Admission control, faster-time-scale capacity planning– Challenge in low-aggregation regime with (true) bursty traffic
• Potential impact is high– Aggressive and innovative edge service providers– Significant enterprise market– Fast innovation/deployment time at layer 2
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Ed Knightly
III. The Edge of the Network Edge:Internet Data Centers
• Many hosted sites at a shared physical location
– Share network bandwidth
– Share management facilities
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Ed Knightly
Problem with Today’s IDC’s
• Static Resource Model – Number of servers per
website is fixed
• Performance losses– Peak allocation poor
resource utilization– Mean allocation
performance degradation– Inability to deal with flash
crowds
• Result: inefficiency, poor QoS, bankruptcy
E-news.com
E-mart.com
Workload
Workload
Un-utilized servers
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Ed Knightly
QoS Research Problems in IDC’s: Infrastructure-on-Demand
• Migrate servers to hot spots
• Challenge: how to exploit efficiencies of resource sharing while providing QoS?
– When to migrate– By how many– Load prediction– SLA provisioning
Workload
Workload
Un-utilized servers
Server Migration
E-news.com
E-mart.com
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Ed Knightly
IV. QoS in the Other Edge: Wireless
• Yes, WiFi is in your future
• Applications: VoIP + multimedia + web + …
• Constraint: random access MAC’s are essential for low cost and simplicity
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Ed Knightly
QoS Challenges at the Wireless Edge
• Low aggregation regime with high burstiness: capacity planning won’t solve it
• Challenging QoS-aware MAC design problems– Unsolved under realistic channel models
exploit multi-rate physical layer directional antennas power aware
• Admission control/bandwidth allocation– Requires modeling/prediction of a complex system
(random access, multi-priority MAC, wireless channel, …)
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Ed Knightly
Summary
• QoS in the core is not needed in evolutionary path– Watch out: revolutions are possible in search of profit
• Challenging hot spots– Metro edge, IDC, wireless edge, Enterprise
• Why? – Traffic less predictable, not highly aggregated, not rate
limited– Can be more aggressive/innovative at layer 2/7