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

© Jörg Liebeherr, 1998-2002 1

Quality-of-Service Architectures for the Internet

Integrated Services (IntServ)


Components of a QoS architecture

Source: CMU, S. Seshan, B. Maggs


Granularity of 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


Integrated Services

1. At network entrance: Policing and Shaping

2. Somewhere in the network: Admission Control

3. At switches: Classification, Scheduling

4. Between hosts and routers: Signaling

FlowSpec (TSpec, RSpec)

Distributed or Centralized

Weighted Fair Queuing or

other latency-rate algorithm

RSVP

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


RSVP Functional Diagram

Application

RSVPD

AdmissionsControl

PacketClassifier

PacketScheduler

PolicyControl

DATA

DATA

RSVPD

PolicyControl

AdmissionsControl

PacketClassifier

DATA

RoutingProcess

Host Router

Source: Gordon Chaffee, UC Berkeley

PacketScheduler


RSVP Flowspec

Peak Data Rate [p]

Minimum Policed Unit [m]

Maximum Policed Unit [M]

Token Bucket Rate [r]

. . .

Token Bucket Size [b]

Guaranteed Flowspec

Rate [R]

Slack Term [S]


T-SPEC

R-SPEC


Guaranteed Service

• A flow must perform a reservation request during a flow setup phase– Uses RSVP

• Traffic Specification (T-SPEC):

(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, DRRNortel - CBQ


RSVP in IntServ

• Flow set-up: – advertisement with PATH message from source – contains TSPEC (p,M,r,b) of the source– contains ADSPEC (Ltot, Dtot) which is updated on the path

• ADSPEC contains: Ltot = i Li

Dtot = i Di – PATH does not result in reservations !– ADSPEC is used by receiver to select reservation

(p,M,r,b)

(p,M,r,b)

(p,M,r,b)( )

(L1, D1 )

(L1+L2, D1+D2)

Sender

Receiver

Source: P. Thiran

14

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.

(p,M,r,b)

(p,M,r,b)

(p,M,r,b)

( )

(L1, D1 )

(L1+L2, D1+D2)

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


Reservation Merging

Receiver#1

Receiver#2

Receiver#3

Reservations mergeas they travel up tree.

R6

R3

R1

R4 R7

(1) 50Kbs

(2) 50Kbs

(3) 50Kbs

(4) 100 Kbs

(5) 100 Kbs

(6) 100 Kbs

(7) 100 Kbs

(8) 60Kbs

(9) 60Kbs



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)

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