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Bob Braden USC Information Sciences Institute 30th Anniversary Sept 9, 2002

Internet Quality of Service -- Fantasy and Reality. Bob Braden USC Information Sciences Institute 30th Anniversary Sept 9, 2002. What is QoS?. “Qwoss” -- No, it’s not an exotic vegetable...

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Bob Braden USC Information Sciences Institute 30th Anniversary Sept 9, 2002

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  1. Internet Quality of Service -- Fantasy and Reality Bob Braden USC Information Sciences Institute 30th Anniversary Sept 9, 2002 ISI 30th -- Bob Braden -- QoS

  2. What is QoS? • “Qwoss” -- No, it’s not an exotic vegetable... • Fundamental network capability:Allowing an end user (or collection of users, e.g., a campus or corporation) to control the attributes of communication service. • It sounds like almost a no-brainer, but it is actually exceedingly difficult and a bit fuzzy. • It cuts across many basic technical and economic aspects of the Internet. ISI 30th -- Bob Braden -- QoS

  3. Early History • Internet designers called it Type of Service(TOS) • 1981: Jon Postel defined Internet Protocol (IP) [RFC 791] • He took a SWAG to define a TOS byte in the IP header: • 3 bits of priority (Mandated by DoD -- “precedence”) • 3 bits of TOS attributes: • Low delay? • High throughput? • High reliability? • This sounded plausible, but ... ISI 30th -- Bob Braden -- QoS

  4. But... • What do these 3 TOS attributes MEAN? • How can routers implement them? • How/when should they be set? • Is this the “right” set of attributes? • Need quantifiers? • How can you prevent a tragedy of the commons? • Administrative control (e.g., military/corporation), or • Economic control -- charging $$$ ISI 30th -- Bob Braden -- QoS

  5. Why do We Need QoS? • To match network service to application requirements? • Resolve conflicts when network is overloaded, e.g., • Interactive services want minimum delay • File transfer & email want maximum throughput • Web users want both (!?) • Or to make some users more equal than others? ISI 30th -- Bob Braden -- QoS

  6. Making Users Unequal • Basic Internet design: all users are equal! • DoD said: “No way!” • Required service priority, linked to military hierarchy. • ISPs want to sell premium service to corporations and government agencies that can afford it. • Free-market approach -- “QoS Knob”. • Download too slow? Move the slider up, increase your cost per minute. ISI 30th -- Bob Braden -- QoS

  7. Why is QoS Hard (1)? 1.How do you define the service? • By its effect? Service attributes observable by users in end systems • ISPs want to write contracts, called “Service-level agreements” (SLAs), and charge money. • Or by mechanism? Specific queueing mechanisms in routers • Users and providers care about effect, not mechanism -- need to pick a service model. ISI 30th -- Bob Braden -- QoS

  8. Service Model... • User-observable attributes might be: • Reliable delivery of data? (How reliable?) • Ordered delivery of data? • Max bandwidth (measured over what interval?) • Max end-to-end [queueing] delay • Max jitter (delay variation) • Which ones matter? ISI 30th -- Bob Braden -- QoS

  9. Effect vs. Mechanism • Suppose your ISP says: “For an extra $10/month I will give your packets priority over packets from users who don’t pay extra.” • Priority is a mechanism; what would its serviceeffectbe? • It’s quite hard to connect: effect <=> mechanism; many academic papers have been generated on this topic. ISI 30th -- Bob Braden -- QoS

  10. Service Model... • It’s quite hard to connect: service <=> mechanism • Internet traffic does not follow any simple statistical laws; it can be very BURSTY. • Generally, to build a mechanism matching a useful service model requires traffic shaping/policing mechanisms to place a bound on the burstiness. • Delay or drop non-conformant packets in each user stream • Most common: token bucket shaper/policer. ISI 30th -- Bob Braden -- QoS

  11. Why is QoS Hard (2)? 2. You can build mechanisms that operate strictly packet/packet, butto make any QoS guarantee requires per-flow state in routers. • Violates the Internet religion: “Thou shalt forward IP datagrams using stateless routers.” • This religion provided simplicity, robustness, generality, and scalability -- not to be given up lightly. • There are also resource and scalability issues. ISI 30th -- Bob Braden -- QoS

  12. Why is QoS Hard (3)? 3. QoS requires accounting/feedback (e.g., charging) to avoid a tragedy of the commons. • Many technical, business, legal, social problems... ISI 30th -- Bob Braden -- QoS

  13. A Case Study of QoS • 1991: Internet research community believed that multimedia teleconferencing would become the 1000 pound gorilla (“killer app”) on the Internet. (The Web had not happened yet!). • ISI research had played a significant role... • Packet speech experiments on ARPAnet [Danny Cohen @ISI]. • VTC research @ ISI [Steve Casner] & @ BBN. • VTC technology -- the “MBONE tools” -- developed on DARPA Research Testbed Network (DARTnet) built & operated @ ISI. ISI 30th -- Bob Braden -- QoS

  14. Realtime... • Packet voice, and to a lesser extent packet video, require “realtime” service -- bounded E2E delay. • The Internet research community set to work on the technical problems ... • Developed: Internet Integrated Service. • Mostly DARPA-funded. • 1994: “Integrated Services in the Internet Architecture”[RFC 1633: Braden@ISI, Clark@MIT, Shenker@PARC] ISI 30th -- Bob Braden -- QoS

  15. Internet Integrated Service (IIS) • How define service? • Two service models: • Guaranteed [tight bound on E2E Q delay] • Controlled Load [loosely defined “good service”] • How do users request IIS? • RSVP: signaling protocol to request and set up QoS state in routers. • Initial design: Zhang & Shenker @PARC • Prototyping and standardization: Estrin, Braden, Berson, Lindell, Herzog @ ISI. ISI 30th -- Bob Braden -- QoS

  16. What Happened to IIS? • The Web happened, and it became the Internet gorilla, not VTC. • Some IETF opinion-leaders excommunicated IIS as heretical to the Internet religion. • Microsoft bought into IIS • Windows 2000 implements it. • The RSVP signaling protocol component has been widely adopted/adapted to other Internet signaling applications. ISI 30th -- Bob Braden -- QoS

  17. What Happened? • ISPs ignored IIS. • No business case or other incentive. • E2E IIS requires more collaboration than ISPs can muster • Another problem, which I have no time to discuss: Multicast! • The payment problem is not much closer to solution. ISI 30th -- Bob Braden -- QoS

  18. What Happened? • ISPs have pushed another QoS approach: Differentiated Service. • Redefine 6 bits of TOS byte to select 64 service classes. • QoS within ISP clouds rather than E2E. • Classify packets in boundary routers between ISPs, set these bits for use by the interior routers. • They can charge large customers for preferred service. ISI 30th -- Bob Braden -- QoS

  19. Current Status of Internet QoS • We know much more than we did 20 years ago about QoS service models and mechanisms. • There is still no Internet-wide deployment of QoS. • However, some forms of QoS are implemented by router vendors and are deployed in private intranets. • The IP telephony gorilla is crashing in the underbrush ... ISI 30th -- Bob Braden -- QoS

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