INTERNET QOS: A BIG PICTUREXIPENG XIAO AND LIONEL M. NI, MICHIGAN STATE UNIVERSITY

Jinyoung YouCS540, Network Architect

2

Motivation

Today’s Internet Best-effort service No guarantee as to timeliness or actual delivery No guarantee of low-delay and low-jitter services No service classes No abundant and cheap bandwidth

3

Motivation

What’s the QoS? Guarantee a certain level of performance

e.g.) Packet dropping probability , Delay, Jitter, Out-of-order delivery, Error, Congestion

Why QoS? The network capacity is insufficient

Real-time streaming multimedia applications e.g.) VoIP, IPTV Requires fixed bit rate and are delay sensitive

4

Motivation

Misunderstanding of QoS Cannot provide nonexistent bandwidth Cannot make the network faster Cannot cure poorly performing network

Contribution of QoS Provide relative prioritization of traffic

5

Motivation

Service Models and Mechanisms of IETF Integrated Services/Resource Reservation Protocol (RSVP)

Model Differentiated Services (DS) model Multi Protocol Label Switching (MPLS) Traffic engineering Constrained Based Protocol

How they differ from and relate to each other? Which system they fit?

6

Outline

1. IntServ/RSVP2. DiffServ3. MPLS4. Traffic Engineering/CBR5. Comparison of ATM Networks6. Conclusion7. Q&A

7

IntServ/RSVP

Resource reservation For real-time service, before data are transmitted, Apps must first set up paths and reserve resources

Service classes Guaranteed service: fixed delay bound Controlled-load service: reliable and enhanced best-

effort service

8

IntServ/RSVP

9

IntServ/RSVP

Components Signaling protocol Admission control routine Classifier Packet scheduler

10

IntServ/RSVP

Limitations Scalability

State information is proportional to amount of flow

Overhead on routers Should have all components; RSVP, admission control, MF

classification, packet scheduling

Ubiquitous deployment is required

11

DiffServ

Motivation The difficulty in implementing and deploying IntServ and

RSVP

DS is essentially a relative-priority scheme Using DS fields of packet header to indicate service classes

Process complexity core network → edge network More scalable

12

DiffServ

Customer Have a Service Level Agreement (SLA) with its ISP

Which service class to provide? Mark the DS field according to the service class

Router Classification, policing, shaping, scheduling occur at only ingress

routers

Domain DF field is remarked by SLA between the domains

13

DiffServ

Possible services of DiffServ Premium service

For low-delay and low-jitter service Assured service

For better reliability than best-effort service Olympic service

gold, silver, and bronze, with decreasing quality

Differences between DiffServ and IntServ State information is proportional to the number of classes Process complexity is only at the edge router

14

DiffServ

Assured Service Provide reliable services even in times of network

congestion

Be implemented as follows: Classification and policing are done at the ingress routers All packets, in and out, are put into an AQ The queue is managed by a RED or RIO

15

DiffServ

Premium Service SLA specifies a peak bit-rate Provide low delay and low jitter

e.g.) Internet Telephony, Video Conferencing, VPN More expensive, But more prior than Assured Service

Be implemented as follows: Use P-bit on DS field If P-bit is on, the packet goes to Premium Queue Uneven distribution of traffic may cause a problem

16

DiffServ

Service Allocation in Customer Domains How to decide services; Assured or Premium Service

Each host makes its own decision Bandwidth Broker(BB) makes decision

Resource Allocations in ISP Domains How boundary routers handle incoming traffic

Static SLAs, Manually configured. Dynamic SLA, RSVP

17

DiffServ

18

DiffServ

DiffServ

Requirements on Routers Edge router: MF classifications, marking, and shaping ISP ingress router: policing, re-marking ISP egress routers: re-shaping BA classification, Assured Queue, Premium Queue For dynamic SLA, BB at the customer domain

MPLS

MPLS: Multi Protocol Label Switching Incoming packets are assigned a “label” by edge router

Packets are routed according to the label By a label switch router(LSR)

The path a packet traverses is called label switched path(LSP) Network protocol independent

MPLS

MPLS

MPLS is strategically significant Provides faster packet classification and forwarding Provides an efficient tunneling mechanism

without encryption Moves processing to edge routers

Core did forwarding only, Scalable

Traffic Engineering/CBR

Motivation IntServ/RSVP and DiffServ has degradation of perfor-

mance when traffic load is heavy.

Major goal Provide efficient and reliable network operation Optimize network resource utilization

To efficiently manage bandwidth resources Optimize traffic performance

To enhance QoS of traffic stream

Traffic Engineering/CBR

The factor of Congestion Lack of network resource

Upgrade infrastructure Uneven distribution

Because of Shortest Path problem Constraint Based Routing

Automatically Traffic Engineering

Traffic Engineering/CBR

Shortest Path Problem

Traffic Engineering/CBR

Constrained Based Routing Compute QoS route

May select longest lightly-loaded path rather than heavily shortest path

Improve network resource utilization

Traffic Engineering/CBR

Distribution of Link State Information Needs of link available bandwidth, buffer space information Link state advertisement of OSPF, IS-IS

Route Computation Various algorithm for distinct metrics; cost, hop-count, bandwidth, re-

liability, delay, jitter Let d(i, j) be a metric for link (i, j). For any path P = (i, j, k, …,l, m), metric d is:

Additive if d(P) = d(i, j) + d(j, k) + … + d(l, m) e.g.) delay, jitter, cost and hop-count

Multiplicative if d(P) = d(i, j) * d(j, k) * … * d(l, m) e.g.) reliability (1-loss rate)

Concave if d(P) = min{d(i, j), d(j, k), …, d(l, m)} e.g.) bandwidth

Traffic Engineering/CBR

Pros Meeting the needs for QoS requirement of flows Improved network utilization

Cons Increased communication and computation overhead Increased routing table size Longer path may consume more resources Potential routing instability

Traffic Engineering/CBR

The Position of CBR DiffServ: Not for replacing, but helping DiffServ RSVP: Independent with RSVP

CBR just determines the path of RSVP messages MPLS

MPLS: forwarding scheme, CBR: routing scheme Work together for traffic engineering

Comparison of ATM Networks

ATM Network Use Virtual Circuit Switching Pros

Fast Provide QoS

Cons ATM cell header overhead Switch can not work at the boundary of network

ATM Network with DiffServ or MPLS Provide QoS on the router network Reduce ATM cell header overhead

Conclusion

QoS is hotly debated issue Fibers and WDM will make bandwidth so abundant and cheap

QoS will be automatically delivered However, New application will be invented to consume it

Thus, Mechanism will be needed to provide QoS

Many mechanisms are provided but they not solve QoS problem There is little hope for success But, Way to go

Q&A