INTERNET QOS: A BIG PICTURE
XIPENG XIAO AND LIONEL M. NI, MICHIGAN STATE UNIVERSITY
Jinyoung You
CS540, Network Architect
Motivation
2

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
Motivation
3

What’s the QoS?
 Guarantee
a certain level of performance
 e.g.)
Packet dropping probability , Delay, Jitter, Out-oforder delivery, Error, Congestion

Why QoS?
 The
network capacity is insufficient
 Real-time streaming
 e.g.)
multimedia applications
VoIP, IPTV
 Requires fixed bit rate and are delay sensitive
Motivation
4

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
Motivation
5

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?
Outline
6
1.
2.
3.
4.
5.
6.
7.
IntServ/RSVP
DiffServ
MPLS
Traffic Engineering/CBR
Comparison of ATM Networks
Conclusion
Q&A
IntServ/RSVP
7

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-ef
fort service
IntServ/RSVP
8
IntServ/RSVP
9

Components
 Signaling
protocol
 Admission control routine
 Classifier
 Packet scheduler
IntServ/RSVP
10

Limitations
 Scalability
 State
information is proportional to amount of flow
 Overhead
on routers
 Should
have all components; RSVP, admission control, MF c
lassification, packet scheduling
 Ubiquitous
deployment is required
DiffServ
11

Motivation


DS is essentially a relative-priority scheme


The difficulty in implementing and deploying IntServ and R
SVP
Using DS fields of packet header to indicate service classes
Process complexity
core network → edge network
 More scalable

DiffServ
12

Customer

Have a Service Level Agreement (SLA) with its ISP



Mark the DS field according to the service class
Router


Which service class to provide?
Classification, policing, shaping, scheduling occur at only in
gress routers
Domain

DF field is remarked by SLA between the domains
DiffServ
13

Possible services of DiffServ

Premium service


Assured service


For better reliability than best-effort service
Olympic service


For low-delay and low-jitter 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

DiffServ
14

Assured Service
 Provide
reliable services even in times of network con
gestion
 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
DiffServ
15

Premium Service
 SLA
specifies a peak bit-rate
 Provide low delay and low jitter
 e.g.)
 More
 Be
Internet Telephony, Video Conferencing, VPN
expensive, But more prior than Assured Service
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
DiffServ
16

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
DiffServ
17
DiffServ
18
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
 Moves
 Core
encryption
processing to edge routers
did forwarding only, Scalable
Traffic Engineering/CBR

Motivation
 IntServ/RSVP
and DiffServ has degradation of
performance when traffic load is heavy.

Major goal
 Provide
efficient and reliable network operation
 Optimize network resource utilization
 To efficiently manage
 Optimize
bandwidth resources
traffic performance
 To enhance
QoS of traffic stream
Traffic Engineering/CBR

The factor of Congestion
 Lack
of network resource
 Upgrade
 Uneven
infrastructure
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, reliability, 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


However, New application will be invented to consume it


QoS will be automatically delivered
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