Quality-of-Service Architectures for the Internet Integrated Services (IntServ)

Quality-of-Service Architectures for the InternetIntegrated Services (IntServ)

Components of a QoS architecture Source: CMU, S. Seshan, B. Maggs

Granularityof QoS • Per-flow guarantees • Require per-flow reservations in the network • Require per-flow classification at routers

QoS Service Architectures for the Internet • Two QoS architectures have been defined for Internet. • Integrated Services (IntServ) • Proposed in 1994 • Per-flow Quality of Service • Resource reservation/admission control • Can support delay guarantees • Differentiated Services (DiffServ) • Proposed in 1998 • Class-based QoS • Resource reservation not always needed

Integrated Services IntServ specifies two types of services: Guaranteed Service • Guaranteed bandwidth • End-to-end delay bounds • No loss due to buffer overflows Controlled Load Service • Provides a service that is equivalent to a best effort service in a lightly loaded netework • Low loss • Low delay • No absolute guarantees

At network entrance: Policing and Shaping Somewhere in the network: Admission Control At switches: Classification, Scheduling Between hosts and routers: Signaling FlowSpec (TSpec, RSpec) Distributed or Centralized Weighted Fair Queuing or other latency-rate algorithm RSVP Integrated Services in IntServ

Resource ReSerVation Protocol (RSVP) • RSVP is a signaling protocol that enables senders, receivers, and routers of unicast or multicast sessions to communicate with each other for setting up state to support a service • Receiver-driven • Resource reservation is initiated by receivers • Unicast and multicast sessions • Soft-state: state information of RSVP must be periodically refreshed • Separate mechanisms required for authorization, authentication, and charging

RSVPD Routing Process Application Policy Control Policy Control Admissions Control Admissions Control Packet Classifier Packet Scheduler Packet Classifier Packet Scheduler RSVP Functional Diagram Host Router RSVPD D A T A DATA DATA Source: Gordon Chaffee, UC Berkeley

Source: Cisco

RSVP Flowspec Guaranteed Flowspec . . . Token Bucket Rate [r] T-SPEC Token Bucket Size [b] Peak Data Rate [p] Minimum Policed Unit [m] Maximum Policed Unit [M] R-SPEC Rate [R] Slack Term [S] Source: Gordon Chaffee, UC Berkeley

Guaranteed Service • A flow must perform a reservation request during a flow setup phase • Uses RSVP • Traffic Specification (T-SPEC): E(t) = min (M + pt, rt + b) • M is max. packet size • p is peak rate • r is average rate • b is burst size • Routers along a path accept or reject reservation

Latency-rate Schedulers • Guaranteed service assumes that routers implement a latency-rate service curve with delay T and rate R: S(t) = R · (t – T)+ with • T = L /R + D • L is the maximum packet size of this flow • D = Lall / C is the maximum packet transmission time (preemption delay) • Lall is maximum packet size at this link • C is the link capacity Router implementations (some in software): Cisco – WFQ Extreme Networks – WFQ, CBQ, DRR Nortel - CBQ

RSVP in IntServ • Flow set-up: • advertisement with PATH message from source • contains TSPEC (p,M,r,b) of the source • containsADSPEC(Ltot, Dtot)which is updated on the path • ADSPEC contains: Ltot = i Li Dtot = iDi • PATH does not result in reservations ! • ADSPEC is used by receiver to select reservation (p,M,r,b) (p,M,r,b) () Sender (p,M,r,b) (L1, D1 ) (L1+L2, D1+D2) Receiver Source: P. Thiran

() (p,M,r,b) (L1, D1 ) (p,M,r,b) (L1+L2, D1+D2) (p,M,r,b) RSVP in IntServ • Flow set-up: Receiver responds with a RESV message. • RESV messages make the reservations at the node • Receiver writes the service level requested by receiver in an R-SPEC • R-Spec specifies the reserved rate R’ • R’ is determined at the receiver using the formula: ((b-M)/R’) (p-R)+/(p-r) + (M + i Li)/R’ + i Di • This assumes that all nodes reserve the same rate Rn= R’. • R’ is computed so that end-to-end delay bound <= delay objective. R’ R’ R’ Source: P. Thiran

Call Admission • Call Admission: routers will admit calls based on their R-spec and T-spec and base on the current resource allocated at the routers to other calls. Source: CMU, S. Seshan, B. Maggs

(7) 100 Kbs Reservation Merging (3) 50Kbs R1 Reservations merge as they travel up tree. (6) 100 Kbs R3 (2) 50Kbs (5) 100 Kbs (9) 60Kbs R4 R6 R7 (1) 50Kbs (8) 60Kbs (4) 100 Kbs Receiver #1 Receiver #2 Receiver #3 Source: Gordon Chaffee, UC Berkeley

Summary of IntServ • Advantages: • Strong guarantees (bounded delays) • Disadvantages: • Requires that all routers implement IntServ • Scalability concerns since routers must maintain state information • Charging and authentication of reservations must be solved • Interdomain issues are difficult to resolve

Quality-of-Service Architectures for the Internet Integrated Services (IntServ)