chapter 18 protocols for qos support 1 89-850 communication networks: protocols for qos support:...

Chapter 18 Protocols for QoS Support1

89-850 Communication Networks: 89-850 Communication Networks: Protocols for QoS Support: Protocols for QoS Support: RSVP and MLPSRSVP and MLPS

Source and ©: Stallings Hi-Speed Networks and Internets, Ch. 18Source and ©: Stallings Hi-Speed Networks and Internets, Ch. 18

Last updated: Tuesday, April 18, 2023

Prof. Amir HerzbergDept of Computer Science, Bar Ilan Universityhttp://AmirHerzberg.com


Resource Reservation: RSVPResource Reservation: RSVP

Dynamic routing, WFQ, diff-serv (RED, ECN): use available resources for existing traffic

RSVP: reserve resources to ensure QoS Unicast: appl reserves resources (@routers)

– If QoS unavailable: wait or try at reduced QoS Multicast: ditto, plus…

– Some recipients may not want to `tune in`

– Others may want only some of the traffic E.g. basic and enhanced video components, select channel


Resource Reservation Resource Reservation Problems on an InternetProblems on an InternetMust interact with dynamic routing

– Reservations must follow changes in route– Implicit assumption: new route is `better`

would usually have resourcesSoft state – a set of state information at a

router that expires unless refreshed– End users periodically renew resource

requests


Resource ReSerVation Resource ReSerVation Protocol (RSVP) Design GoalsProtocol (RSVP) Design Goals Enable receivers to make reservations

– Allow different reservations in same multicast group Deal gracefully with changes in group membership

– Dynamic reservations, separate for each member of group Aggregate for group should reflect resources needed

– Take into account common path to different members of group Receivers can select one of multiple sources

– E.g. to select `channel` to view Deal gracefully with changes in routes

– Re-establish reservations Minimize, aggregate control protocol overhead Independent of routing protocol


RSVP CharacteristicsRSVP Characteristics

Unicast and Multicast Simplex

– Unidirectional data flow– Separate reservations in two directions

Receiver initiated– Receiver knows which subset of source transmissions it wants

Maintain soft state in internet– Responsibility of end users

Providing different reservation styles– Users specify how reservations for each group are aggregated

Transparent operation through non-RSVP routers Support IPv4 (ToS field) and IPv6 (Flow label field)


Data Flows - SessionData Flows - Session

Data flow identified by destinationResources allocated by router for duration of

sessionDefined by

– Destination IP addressUnicast or multicast

– IP protocol identifierTCP, UDP etc.

– Destination portMay not be used in multicast


Flow DescriptorFlow Descriptor

Reservation Request issued by destination– Flow spec

Desired QoSUsed to set parameters in node’s packet schedulerService class, Rspec (reserve), Tspec (traffic)

– Filter specSet of packets for this reservationSource address, source UDP/TCP port


Treatment of Packets of One Treatment of Packets of One Session at One RouterSession at One Router


RSVP Operation DiagramRSVP Operation DiagramG1, G2sent filter specw/o S2

G3sent filter specw/ogrey


Reservation StylesReservation Styles

How resource requirements from members of group are aggregated

Reservation attribute– Reservation shared among all senders (shared)

Characterizing entire flow received on multicast address

– Allocated to each sender (distinct) Simultaneously capable of receiving flow from each sender

Sender selection– List of sources (explicit)– All sources, no filter spec (wild card)


Reservation Styles in RSVPReservation Styles in RSVP

Reservation Attribute:– Distinct

Sender selection explicit = Fixed filter (FF) styleSender selection wild card = none

– SharedSender selection explicit= Shared-explicit (SE) styleSender selection wild card = Wild card filter (WF)


Fixed Filter StyleFixed Filter Style

Distinct reservation for each senderExplicit list of sendersFF(S1{Q1}, S2{Q2},…)

– Q = flow specE.g. nB for n units of resource B

Example usage: video distribution


Shared Explicit StyleShared Explicit Style

Single reservation shared among specific list of senders

SE(S1, S2, S3, …{Q})Multicast data sourcesUnlikely to transmit simultaneouslyE.g. primary and backup sources


Wild Card Filter StyleWild Card Filter Style Single reservation shared by all senders If used by all receivers: shared pipe whose

capacity is largest of resource requests from receivers downstream from any point on tree

Independent of number of senders using it Propagated upstream to all senders WF(*{Q})

– * = used for (wild card) sender Audio teleconferencing with multiple sites

– Assuming one speaker at any given time


Reservation Style Examples Reservation Style Examples

If shorterroutefromS2, S3to R1

E


RSVP Protocol MechanismsRSVP Protocol Mechanisms

Two message types– Resv

Originate at multicast group receivers Propagate upstream Merged when appropriate Create soft states Reach sender

– Allow host to set up traffic control for first hop

– Path Provide upstream routing information Issued by sending hosts (to allow Resv to reach sources) Transmitted through distribution tree to all destinations


RSVP Host ModelRSVP Host Model

2

3

45

6

7

1


RSVP Router ModelRSVP Router Model

RSVP in Router

From multicast routing:N(group)

Rcv(m,u,style)(message m from neighbor u;

m{path(g),rsv(g,amt,)})


Multi-Protocol Label Switching Multi-Protocol Label Switching (MPLS) : Background(MPLS) : Background

Mid-1990s: Efforts to marry IP and ATM– Motivation: ATM switches were much faster than routers– IP switching (Ipsilon), Tag switching (Cisco), …

Routing (e.g. OSPF) define path between end points Assign packets to flow & path as they enter network

– Simpler, faster routing/switching of packets– Connection-oriented QoS support– Traffic engineering: choose and change path for each flow– Virtual private networks– Multi-Protocol support


MPLS: Connection Oriented MPLS: Connection Oriented QoS SupportQoS SupportGuarantee fixed capacity for specific

applicationsControl latency/jitter

– Ensure capacity for voiceProvide specific, guaranteed quantifiable

SLAsConfigure varying degrees of QoSMPLS imposes connection oriented

framework on IP based internets


MPLS Traffic EngineeringMPLS Traffic Engineering

Traffic Eng: select routes, reserve resources to optimize utilization based on known demands

Basic IP: per-packet routing/forwarding decision MPLS: aware of flow traffic, QoS req’

– Load-balance – select (different) route for flows

– Intelligent re-routing (of flows) when congested


MPLS OperationMPLS Operation

Label Switched Routers (LSR)– Forward packets based on appended label– IP header not examined

Labels define flow of packets between end points or multicast destinations

Connection oriented: each flow has…– Specific path through LSRs– Specific QoS requirements


MPLS Domain OperationMPLS Domain Operation


Explanation - SetupExplanation - Setup

Labelled Switched Path (LSP) established prior to routing and delivery of packets

QoS parameters established along LSP:– Resource commitment

– Queuing and discard policy at LSR (Per-Hop Behav.)

– Interior routing protocol e.g. OSPF used

– Labels assigned Local significance only Manually or using protocol


Explanation – Packet HandlingExplanation – Packet Handling

Packet enters domain through edge LSR– Edge LSR determines flow, LSP– Append label– Forward packet

LSR within domain:– Remove label from incoming packet– Attach outgoing label and forward

Egress LSR:– Strips label, reads IP header and forwards


MPLS Packet ForwardingMPLS Packet Forwarding


MPLS Labels StackMPLS Labels Stack

Packet may carry a stack of MPLS labels– Processing based on top label– Any LSR may push or pop label

Unlimited levels

– Push label of aggregate (tunnel) LSP, pop at exit – Fewer labels smaller, more efficient tables


Label Format DiagramLabel Format Diagram

Label value: Locally significant 20 bit Exp: 3 bit reserved for experimental use

– E.g. DS information or PHB guidance S: 1 for oldest entry in stack, zero otherwise Time to live (TTL): from (& to!) IP header


Constraint Based RoutingConstraint Based Routing

Take into account traffic requirements of flows and resources available along hops– Current utilization, existing capacity, committed

services

– Additional metrics over and above traditional routing protocols (e.g. OSPF, BGP)

Maximum link data rate Current capacity reservation Packet loss ratio Link propagation delay


Label DistributionLabel Distribution

Setting up LSP for a flow… each LSR:Assign in-label to incoming packetsInform all upstream LSRs of in-labelReceive out-label from downstream LSRManually or by label-setup protocol

– RFC 3031: enhanced RSVP/BGP or new


Summary - QOSSummary - QOS

Queuing to prefer/guarantee QoS (e.g. WFQ)Signal congestion to slow TCP (fairly)

– RED, ECNReserve resources – RSVP

– For unicast, multicast– Traditional IP dynamic routing or…

Fixed paths, label switching – MPLSMore… (e.g. RTP – in book)

chapter 18 protocols for qos support 1 89-850 communication networks: protocols for qos support:...

Documents

qos support

multicast slide

qos unavailable

reduced qos multicast

router slide

channel slide

different reservations

resource requests slide