Integrated and Differentiated Services Architecture

for Multimedia Applications over the Internet

• Approaches for providing QoS on the Internet

• Two different service types IntServ and DiffServ : implementation and problems

• Two-bit differentiated services architecture

• Problems with end-end bandwidth allocation based on level of marked traffic

• Discussion

Presentation Plan

Presentation Plan

• Focus on concepts and reasoning• Discuss issues & challenges• Offer personal opinions stimulating

thinking

Two Approaches for Providing QoS on the Internet

1. “Freeway model” – Integrated Services (IntServ)– Build a dedicated highway or “circuit”

between communicating points2. “Doctor’s model” – Differentiated Services

(DiffServ)– Mark a doctor’s vehicle (e.g. ambulance)

or “packet” to get priority on the road and limit the percentage of such high-priority vehicles in the total traffic mix

Integrated Services (IntServ)

• A connection-oriented solution• QoS on a per-flow basis• Depends on resource

reservation (RSVP)

7

Information Network : Scale of Network

LAN

SD2

SD1

RC1

Ingres Egress

BW1 BW2 BW3

S S

RC2

SD = sender, RC = receiver, S = server, LAN = Local Area Network, BW = Bandwidth

Node1

Node2

Node3

ack

Ingress

8

Quality of Service: View at a glance

Multimedia applications: network audio and video

network provides application with level of performance needed for application to function.

QoS

9

Multimedia QoS Requirements

• live sources, stored sources• requirements: deliver data in timely manner

– short end-end delay for interactive multimedia• e.g., IP telephony, teleconf., virtual worlds

– in time for “smooth” playout • relaxed reliability

– 100% reliablity not always required

10

Why is QoS so hard?

need session’s input traffic• must know app’s traffic

demand(resources, delivery-time constraint, reliability of information transfer)

To provide performance (delay, jitter, loss) guarantees:

compute session’s output• Priority of scheduling

(scheduling discipline)

11

12

RSVP – Reservation Protocol

• Reservation is done in one direction• Receiver-initiated• The sender sends QoS wanted to the

receiver which sends an RSVP message back to the sender

• The sender does not need to know the capabilities along the path or at the receiver

13

RSVP : logical frame work

LAN

SD2

SD1

RC1

Ingres Egress

BW1 BW2 BW3

S S

RC2

SD = sender, RC = receiver, S = server, LAN = Local Area Network, BW = Bandwidth

Node1

Node2

Node3

Forward resourceRequest along the Communication path

Backward responseTo resource request

Ingress

14

Intserv: QoS guarantees• Resource reservation

– call setup, signaling (RSVP)– traffic, QoS declaration– admission control

– QoS-sensitive scheduling (e.g., WFQ)

request/reply

15

QoS Routing

• QoS Routing = Multiple parameter routing subject to constraints– Link metrics are vectors– NP-complete (good heuristics needed)

A

B C D

EF G

H J

K

delay: 10 msbandwidth :100 Mb/scell loss ratio: 1.0e-6

I

Difficulties with IntServ & RSVP

• Scalability– Keeping a state (and using it!) for each flow

overloads the router– Periodic messages to refresh the states creates

more traffic

• Router complexity increases (more computing capabilities required)

• How to satisfy heterogeneous QoS requirements for different receivers

• Ambitious signaling is not practical

Differentiated Services (DiffServ)

• Motivations: no end-to-end signaling and per-flow state, for scalability, complexity and quick-to-deploy reasons.

• Diff-Serv approach: use the TOS field to sort packets into classes and treat them differently.– e.g., one TOS bit to indicate the delay

requirement of the packet, and another to indicate the drop precedence

IP Header (V4)8 bits

19

Type of Service (TOS) Routing

“low delay”

“high throughput”

Originally does not support real QoS

Principles of DiffServ• Connectionless mode• QoS for aggregates of traffic, such as

primary/premium, assured and best-effort• Keep the forwarding path simple to

allow easy and early deployment; push complexity to network edge

• Avoid strong assumptions about traffic types; assume the dominant Internet traffic will be the best-effort traffic in a massive amount, so there is ample headroom to provide priority for a relatively small set of packets

How to describe a service• What is provided to the customer

– E.g., 1 Mbps, continuously available

• To where is this service provided– A single destination– A group– All nodes on local provider– Everywhere

• Level of assurance provided to service– What level of performance uncertainty can

user tolerate

Premium service

• Provides guaranteed peak bandwidth service with negligible delay/jitter

• “Virtual leased lines”: don't waste bandwidth when circuits are unused

• Useful for voice• is given its own high-priority queue in

routers; takes a small portion of network bandwidth

• Shaped and hard-limited to its provisioned peak rate

Mechanism for premium service

Host First-hop

Intra-network

Router

H-Q: premium, no dropping L-Q: best effort, dropping on

congestion

Assured service

• Provides an expected level of bandwidth with delay

• Characteristic slightly better than best-effort

• Useful for e.g., connections to search engines

• Permits flows to use any additional available bandwidth

• Requires buffer management, e.g., RED

Mechanism for assured service

Host First-hop Cou

nte r

Cou

nte r

Out- and in- dropper

RIO scheme, packets are treated preferentially

Marking packets according to the service profile

RIO algorithm

• RED - Random Early Detection– Packets dropped with low but

increasing probability as queue grows; instead of waiting until it is full and dropping all new packets

• RIO– Run two RED algorithms for “in” and

“out” with different dropping frequencies

Usage Example of DiffServ

Components of DiffServ

(1) Edge node algorithmsClassification, policing, shaping,

metering, marking, etc.

(2) Router algorithmsPacket discard algorithms: RED-like methods for in-profile and outof-

profile trafficPriority, low-latency queueing

Forwarding Path

Access Router

• Packet Classifier: classifies the packets based on their flow-id

• Marker:– being implemented as tocken bucket– checks the conformance of arriving packets and marks

them accordingly

Marker Implementation

Premium Marker Assured Marker

Core Router

Illustration of Discard Policy

Closure

• DiffServ is sort of a gamble. It may actually work in the market place. We are all learning!

• Initially, probably only few traffic classes will need to be deployed. Deployment can start when ISP routers have been made TOS aware

• Access and boundary routers need processing power per packet

• Network management is needed for resource control (on-going work)

Assignment

• Compare ATM’s CBR with DiffServ’s Premium Service

• Compare ATM’s ABR with DiffServ’s Assured Service

We are all learning, so keep improving your knowledge