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

Integrated Services and Differentiated Services 7: Multimedia Networking

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

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

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

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

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

Diffserv Architecture Edge router: per-flow traffic management marks packets as in-profile and out-profile r b marking scheduling . 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

Edge-router Packet Marking profile: pre-negotiated rate A, bucket size B packet marking at edge based on per-flow profile Rate A B 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

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

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

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

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

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

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

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

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 d Ba 7: Multimedia Networking

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 (b,r,R,3) num hops S2 R S (b,r,R) (b,r,R,2,D-d1) (b,r,R,3,D) worst-case delay S1 S3 (b,r,R,1,D-d1-d2) (b,r,R,0,0) 7: Multimedia Networking

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 Ingress Egress Ingress Egress Edge router Core router 7: Multimedia Networking

Differentiated Service (DS) Field 5 6 7 DS Field 4 8 16 19 31 Version HLen TOS Length Identification Flags Fragment offset TTL Protocol Header checksum IP header Source address Destination address Data 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 7: Multimedia Networking

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

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

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

Edge Router Class 1 Marked traffic Class 2 Data traffic Classifier 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

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

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 Set A-bit in-profile traffic Metering Clear A-bit out-of-profile traffic 7: Multimedia Networking

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

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

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

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

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

Comparison to Best-Effort and Intserv Diffserv Intserv Service Connectivity No isolation No guarantees Per aggregate isolation Per aggregate guarantee Per flow isolation Per flow guarantee Service scope End-to-end Domain Complexity No setup Long term setup Per flow steup Scalability Highly scalable (nodes maintain only routing state) Scalable (edge routers maintains per aggregate state; core routers per class state) Not scalable (each router maintains per flow state) 7: Multimedia Networking

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