CSIS TAC-TOI-01 Quality of Service & Traffic Engineering (QoS & TE) Khaled Mohamed Credit: some of the sides are from Cisco Systems

CSIS TAC-TOI-01 Agenda QOS and TE in IP Network The QoS and TE Architectures QOS and TE Service Types The Technical Scenarios Reasons The Applications and Their Needs Q&A

CSIS TAC-TOI-01 QoS in IP Networks Thus far: “making the best of best effort” Future: next-generation Internet with QoS guarantees –Differentiated Services: differential guarantees –Integrated Services: firm guarantees Example: guarantees an audio application 1Mbps; the remaining to 0.5Mbps to Web transfer

CSIS TAC-TOI-01 Principles for QoS Guarantees packet classification: router can distinguish between different classes

CSIS TAC-TOI-01 Principles for QoS Guarantees prevents applications from misbehaving (e.g., multimedia app. sends higher than declared rate) scheduling and policing: provide protection (isolation)

CSIS TAC-TOI-01 Principles for QoS Guarantees Allocating fixed (non-sharable) bandwidth to flow: inefficient use of bandwidth if flows doesn’t use its allocation high utilization: while providing isolation, it is desirable to use resources as efficiently as possible

CSIS TAC-TOI-01 Principles for QoS Guarantees Basic fact of life: cannot support traffic demands beyond link capacity call admission: flow declares its needs, network may block call (e.g., busy signal) if it cannot meet needs

CSIS TAC-TOI-01 Summary of QoS Principles

CSIS TAC-TOI-01 Traffic Specification Three common-used criteria: (Long term) Average Rate: how many pkts can be sent per unit time (in the long run) –crucial question: what is the interval length: 100 packets per sec or 6000 packets per min have same average! Peak Rate: e.g., 6000 pkts per min. (ppm) avg.; 1500 ppm peak rate (Max.) Burst Size: max. number of pkts sent consecutively (with no intervening idle)

CSIS TAC-TOI-01 Traffic Specification Token Bucket: limit input to specified Burst Size and Average Rate. bucket can hold b tokens tokens generated at rate r token/sec unless bucket full over interval of length t: number of packets admitted less than or equal to (r t + b).

CSIS TAC-TOI-01 Scheduling Mechanisms scheduling: choose next packet to send on link FIFO (first in first out) scheduling: send in order of arrival to queue –discard policy: if packet arrives to full queue: who to discard? tail drop: drop arriving packet priority: drop/remove on priority basis random: drop/remove randomly

CSIS TAC-TOI-01 Scheduling Policies: more Priority scheduling: transmit highest priority queued packet multiple classes, with different priorities –class may depend on marking or other header info, e.g. IP source/dest, port numbers, etc..

CSIS TAC-TOI-01 Scheduling Policies: still more round robin scheduling: multiple classes cyclically scan class queues, serving one from each class (if available)

CSIS TAC-TOI-01 Scheduling Policies: still more Weighted Fair Queuing: generalized Round Robin each class gets weighted amount of service in each cycle.

CSIS TAC-TOI-01 Delay Guarantees token bucket, WFQ combine to guarantee upper bound on delay, i.e., QoS guarantee! WFQ token rate, r bucket size, b assigned flow rate, R D = b/R max arriving traffic

CSIS TAC-TOI-01 QOS Type of Services  Integrated services Differentiated services

CSIS TAC-TOI-01 IETF IntServ Services Architecture for providing QoS guarantees in IP networks for individual application sessions Assumptions –use a common infrastructure for both real-time and non-real-time communications –resource must be explicitly managed in order to meet the requirements of real-time applications resource reservation: routers maintain state info (a la VC) of allocated resources, QoS req’s

CSIS TAC-TOI-01 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 Controlled link sharing: Sharing link among different classes

CSIS TAC-TOI-01 Reference Architecture Admission Control Data In Data Out Control Plane Data Plane Scheduler Routing Messages RSVP messages Classifier RSVP Route Lookup Forwarding Table Per Flow QoS Table

CSIS TAC-TOI-01 Classifier Buffer management Scheduler flow 1 flow 2 flow n … Per-flow State A Closer Look at the Data Path

CSIS TAC-TOI-01 Intserv: QoS Guarantee Scenario Resource reservation –call setup, signaling (RSVP) –traffic, QoS declaration –per-element admission control –QoS-sensitive scheduling (e.g., WFQ) request/ reply

CSIS TAC-TOI-01 RSVP Protocol A flow needs performance guarantee 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

CSIS TAC-TOI-01 RSVP: Soft-state Receiver-initiated End-to-End Reservation Sender periodically sends PATH messages to receiver R, each router updates the PATH message by increasing hop count and adding its propagation delay When receiver R gets the PATH message, it knows –Traffic characteristics (tspec): (r,b,R) –Number of hops, propagation delay introduced by the routers Receiver R sends back this information + required worst-case delay in RESV Each router along path provides a per-hop delay guarantee and forwards RESV with updated info –In the simplest case, the routers can just split the delay –State timed out if not refreshed R1 R2 R3 S S R R (b,r,R,0,0) (b,r,R,2,D-D 3 ) (b,r,R,1,D-D3-D2) (b,r,R,0,0) (b,r,R,3,D) delay budget PATH RESV (b,r,R,1,d 1 ) (b,r,R,2,d 1 +d 2 ) (b,r,R,3,d 1 +d 2 +d 3 )

CSIS TAC-TOI-01 Implementing IntServ Use WFQ to implement controlled link sharing among different organizations WFQ provides guaranteed service Controlled-load and best-effort flows are separated by priority WFQ guaranteed flow n priority 10% 30% controlled flows best effort flows WFQ guaranteed flow 1 CS department gets 50%

CSIS TAC-TOI-01 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

CSIS TAC-TOI-01 The DiffServ Traffic Conditioner Block (TCB) Classifier: Identifies packets for assignment to Classes Meter: Checks compliance to traffic parameters (Token Bucket) and passes result to Marker and Shaper/Dropper to trigger particular action for in/out-of-profile packets Marker: Writes/rewrites the DSCP value Shaper: Delays some packets for them to be compliant with the profile Dropper: Drops packets that exceed the profile (Bc or Be)

CSIS TAC-TOI-01 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 scheduling... r b marking

CSIS TAC-TOI-01 Edge-router Packet Marking class-based marking: packets of different classes marked differently intra-class marking: conforming portion of flow marked differently than non-conforming one profile: pre-negotiated rate A, bucket size B packet marking at edge based on per-flow profile Possible usage of marking: User packets Rate A B

CSIS TAC-TOI-01 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

CSIS TAC-TOI-01 Classification and Conditioning may be desirable to limit traffic injection rate of some class: user declares traffic profile (eg, rate, burst size) traffic metered, shaped if non-conforming

CSIS TAC-TOI-01 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

CSIS TAC-TOI-01 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 –each with three drop preference partitions

CSIS TAC-TOI-01 Direction of Data-Flow 100Mbps WAN 2Mbps Why QoS? Congestion Scenario #1—Speed Mismatch The #1 Reason for Congestion! Possibly Persistent when going from LAN to WAN Usually Transient when going from LAN to LAN! 1000Mbps 100Mbps

CSIS TAC-TOI-01 Direction of Data-Flow Choke Point Choke Points Why QoS? Congestion Scenario #2—Aggregation Transient Congestion fairly typical! HQ Hub i Remote 2Mbps 512Kbps N*56Kbps FR/ATM 1000Mbps S1S2

CSIS TAC-TOI-01 STM-64/OC-192c Core1 Core2 STM-16/OC-48c Net-1 Net-2 Net-n Why QoS?? Congestion Scenario #3—Confluence Always need mechanisms to provide guarantees! Transient Congestion occurs!

CSIS TAC-TOI-01 Voice FTP ERP and Mission-Critical Bandwidth Low to Moderate Moderate to High Low Random Drop Sensitive Low High Moderate To High Delay Sensitive High Low Low to Moderate Jitter Sensitive High Low Moderate Typical Application QoS Requirements

CSIS TAC-TOI-01 Q & A Thank You