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ECE 466/566 Advanced Computer Networks

This article explores resource reservation and quality of service guarantees in multimedia networking, focusing on the integrated services and differentiated services architectures. It discusses the challenges of admitting new flows while maintaining QoS guarantees for already admitted flows. It also covers topics such as call admission control, signaling protocols, RSVP, and guaranteed services.

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ECE 466/566 Advanced Computer Networks

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  1. ECE 466/566 Advanced Computer Networks Thinh Nguyen Email: thinhq@eecs.orst.edu Electrical Engineering and Computer Science Oregon State University 7: Multimedia Networking

  2. Integrated Services and Differentiated Services 7: Multimedia Networking

  3. IETF Integrated Services • architecture for providing QOS guarantees in IP networks for individual application sessions • resource reservation: routers maintain state info (a la VC) of allocated resources, QoS req’s • admit/deny new call setup requests: Question: can newly arriving flow be admitted with performance guarantees while not violated QoS guarantees made to already admitted flows? 7: Multimedia Networking

  4. Resource reservation call setup, signaling (RSVP) traffic, QoS declaration per-element admission control • QoS-sensitive scheduling (e.g., WFQ) Intserv: QoS guarantee scenario request/ reply 7: Multimedia Networking

  5. Call Admission Arriving session must : • declare its QOS requirement • R-spec: defines the QOS being requested • characterize traffic it will send into network • T-spec: defines traffic characteristics • signaling protocol: needed to carry R-spec and T-spec to routers (where reservation is required) • RSVP 7: Multimedia Networking

  6. Guaranteed service: worst case traffic arrival: leaky-bucket-policed source simple (mathematically provable) bound on delay [Parekh 1992, Cruz 1988] token rate, r arriving traffic bucket size, b per-flow rate, R WFQ D = b/R max Intserv QoS: Service models [rfc2211, rfc 2212] Controlled load service: • "a quality of service closely approximating the QoS that same flow would receive from an unloaded network element." 7: Multimedia Networking

  7. IETF Differentiated Services Concerns with Intserv: • Scalability: signaling, maintaining per-flow router state difficult with large number of flows • Flexible Service Models: Intserv has only two classes. Also want “qualitative” service classes • “behaves like a wire” • relative service distinction: Platinum, Gold, Silver Diffserv approach: • simple functions in network core, relatively complex functions at edge routers (or hosts) • Don’t define service classes, provide functional components to build service classes 7: Multimedia Networking

  8. marking r b scheduling . . . Diffserv Architecture • Edge router: • per-flow traffic management • marks packets as in-profile and out-profile • Core router: • per class traffic management • buffering and scheduling based on marking at edge • preference given to in-profile packets • Assured Forwarding 7: Multimedia Networking

  9. Rate A B Edge-router Packet Marking • profile: pre-negotiatedrate A, bucket size B • packet marking at edge based on per-flow profile User packets Possible usage of marking: • class-based marking: packets of different classes marked differently • intra-class marking: conforming portion of flow marked differently than non-conforming one 7: Multimedia Networking

  10. Classification and Conditioning • Packet is marked in the Type of Service (TOS) in IPv4, and Traffic Class in IPv6 • 6 bits used for Differentiated Service Code Point (DSCP) and determine PHB that the packet will receive • 2 bits are currently unused 7: Multimedia Networking

  11. Classification and Conditioning may be desirable to limit traffic injection rate of some class: • user declares traffic profile (e.g., rate, burst size) • traffic metered, shaped if non-conforming 7: Multimedia Networking

  12. Forwarding (PHB) • PHB result in a different observable (measurable) forwarding performance behavior • PHB does not specify what mechanisms to use to ensure required PHB performance behavior • Examples: • Class A gets x% of outgoing link bandwidth over time intervals of a specified length • Class A packets leave first before packets from class B 7: Multimedia Networking

  13. Forwarding (PHB) PHBs being developed: • Expedited Forwarding : pkt departure rate of a class equals or exceeds specified rate • logical link with a minimum guaranteed rate • Assured Forwarding : 4 classes of traffic • each guaranteed minimum amount of bandwidth and buffering. • each with three drop preference partitions 7: Multimedia Networking

  14. Traffic and Service Characterization • To quantify a service one has two know • Flow’s traffic arrival • Service provided by the router, i.e., resources reserved at each router • Examples: • Traffic characterization: token bucket • Service provided by router: fix rate and fix buffer space 7: Multimedia Networking

  15. Token Bucket • Characterized by three parameters (b, r, R) • b – token depth • r – average arrival rate • R – maximum arrival rate (e.g., R link capacity) • A bit is transmitted only when there is an available token • When a bit is transmitted exactly one token is consumed r tokens per second bits slope r b*R/(R-r) b tokens slope R <= R bps time regulator 7: Multimedia Networking

  16. Characterizing a Source by Token Bucket • Arrival curve – maximum amount of bits transmitted by time t • Use token bucket to bound the arrival curve bps bits Arrival curve time time 7: Multimedia Networking

  17. d Per-hop Reservation • Given b,r,R and per-hop delay d • Allocate bandwidth ra and buffer space Ba such that to guarantee d slope ra slope r bits Arrival curve b Ba 7: Multimedia Networking

  18. num hops (b,r,R,3) (b,r,R,3,D) worst-case delay End-to-End Reservation • Source S sends a message containing traffic characteristics • r,b,R • This message is used to computes the number of hops • Receiver R sends back this information + worst-case delay (D) • Each router along path provide a per-hop delay guarantee and forwards the message • In simplest case routers split the delay D S2 R (b,r,R) S (b,r,R,2,D-d1) S1 S3 (b,r,R,1,D-d1-d2) (b,r,R,0,0) 7: Multimedia Networking

  19. Diffserv Architecture • Ingress routers • Police/shape traffic • Set Differentiated Service Code Point (DSCP) in Diffserv (DS) field • Core routers • Implement Per Hop Behavior (PHB) for each DSCP • Process packets based on DSCP DS-2 DS-1 Egress Ingress Egress Ingress Edge router Core router 7: Multimedia Networking

  20. Differentiated Service (DS) Field • DS filed reuse the first 6 bits from the former Type of Service (TOS) byte • The other two bits are proposed to be used by ECN 0 5 6 7 DS Field 0 4 8 16 19 31 Version HLen TOS Length Identification Flags Fragment offset IP header TTL Protocol Header checksum Source address Destination address Data 7: Multimedia Networking

  21. Examples of Differentiated Services • Two types of service • Assured service • Premium service • Plus, best-effort service 7: Multimedia Networking

  22. Assured Service [Clark & Wroclawski ‘97] • Defined in terms of user profile, how much assured traffic is a user allowed to inject into the network • Network: provides a lower loss rate than best-effort • In case of congestion best-effort packets are dropped first • User: sends no more assured traffic than its profile • If it sends more, the excess traffic is converted to best-effort 7: Multimedia Networking

  23. Premium Service[Jacobson ’97] • Provides the abstraction of a virtual pipe between an ingress and an egress router • Network: guarantees that premium packets are not dropped and they experience low delay • User: does not send more than the size of the pipe • If it sends more, excess traffic is delayed, and dropped when buffer overflows 7: Multimedia Networking

  24. Edge Router Ingress Traffic conditioner Class 1 Marked traffic Traffic conditioner Class 2 Data traffic Classifier Scheduler Best-effort Per aggregate Classification (e.g., user) 7: Multimedia Networking

  25. Assumptions • Assume two bits • P-bit denotes premium traffic • A-bit denotes assured traffic • Traffic conditioner (TC) implement • Metering • Marking • Shaping 7: Multimedia Networking

  26. TC Performing Metering/Marking • Used to implement Assured Service • In-profile traffic is marked: • A-bit is set in every packet • Out-of-profile (excess) traffic is unmarked • A-bit is cleared (if it was previously set) in every packet; this traffic treated as best-effort r bps User profile (token bucket) b bits assured traffic in-profile traffic Set A-bit Metering out-of-profile traffic Clear A-bit 7: Multimedia Networking

  27. TC Performing Metering/Marking/Shaping • Used to implement Premium Service • In-profile traffic marked: • Set P-bit in each packet • Out-of-profile traffic is delayed, and when buffer overflows it is dropped r bps User profile (token bucket) b bits premium traffic Metering/ Shaper/ Set P-bit in-profile traffic out-of-profile traffic (delayed and dropped) 7: Multimedia Networking

  28. Scheduler • Employed by both edge and core routers • For premium service – use strict priority, or weighted fair queuing (WFQ) • For assured service – use RIO (RED with In and Out) • Always drop OUT packets first • For OUT measure entire queue • For IN measure only in-profile queue Dropping probability 1 OUT IN Average queue length 7: Multimedia Networking

  29. Scheduler Example • Premium traffic sent at high priority • Assured and best-effort traffic pass through RIO and then sent at low priority yes high priority P-bit set? no yes low priority A-bit set? RIO no 7: Multimedia Networking

  30. Control Path • Each domain is assigned a Bandwidth Broker (BB) • Usually, used to perform ingress-egress bandwidth allocation • BB is responsible to perform admission control in the entire domain • BB not easy to implement • Require complete knowledge about domain • Single point of failure, may be performance bottleneck • Designing BB still a research problem 7: Multimedia Networking

  31. 3 2 7 5 1 profile profile 6 4 profile 8 9 Example • Achieve end-to-end bandwidth guarantee BB BB BB receiver sender 7: Multimedia Networking

  32. Comparison to Best-Effort and Intserv 7: Multimedia Networking

  33. Summary • Diffserv more scalable than Intserv • Edge routers maintain per aggregate state • Core routers maintain state only for a few traffic classes • But, provides weaker services than Intserv, e.g., • Per aggregate bandwidth guarantees (premium service) vs. per flow bandwidth and delay guarantees • BB is not an entirely solved problem • Single point of failure • Handle only long term reservations (hours, days) 7: Multimedia Networking

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