advanced computer network - tsinghua...

Advanced Computer Network

2012/11/23 1

Dan LI

CS Department, Tsinghua University

About Me

Research area

Internet architecture design

Cloud computing and data center networks

Green networking

Office

4-104, FIT Building

Homepage

http://www.netlab.edu.cn:8080/netlab/teacher/lidan/lidan.html

Email

[email protected] 2012/11/23 2

Teaching Assistant

Yirong Yu

1th year master student

Research direction

Future Internet architecture

Transport layer design

Email

[email protected]

2012/11/23 3

About You

Whether I pronounce your name correctly

The name you like to be called

Make sure about your registration for the

course

2012/11/23 4

Administrative Trivia

You are NOT required to buy any books

Reference materials

Computer Networks, Andrew. S. Tanenbaum

Reading list of papers

Course Web page

http://www.netlab.edu.cn:8080/netlab/teacher/lid

an/FIA.htm

Web learning system

Check it periodically to get the latest information

2012/11/23 5

http://www.netlab.edu.cn:8080/netlab/teacher/lidan/FIA.htm

http://www.netlab.edu.cn:8080/netlab/teacher/lidan/FIA.htm

Course Goals

Graduate Course

Research driven

Understand

How does the Internet work?

What are the Internet’s design principles and

architectures?

What are the current Internet research efforts?

Where is the future Internet architecture heading to?

2012/11/23 6

Course Goals (Cont.)

Appreciate what is good networking research

Real and important problem

Sound solution

Valid research methodology

Attractive presentation

Apply what you learned into a course project

2012/11/23 7

Course Format

9 lectures Please read at least 1 paper for every lecture topic

after the lecture

Paper presentation and discussion

Two times

Course Project

2012/11/23 8

Course Schedule

Week 1: Introduction

Week 2: Local Area Network and Ethernet

Week 3: Data center network

Week 4: Internetworking & IPv6

Week 5: Intra-domain routing

Week 6: Inter-domain routing

Week 7: Multicast

Week 8: TCP and congestion control (1)

2012/11/23 9

Course Schedule (Cont.)

Week 9: TCP and congestion control (2)

Week 10: P2P and overlay network

Week 11: Mobile & wireless network

Week 12: Network security

Week 13: Future Internet

Week 14: Paper presentation and discussion

Week 15: Course project report

Week 16: Examination

2012/11/23 10

Paper Presentation & Discussion

Tell the whole story of a research paper

Background, motivation, solution, evaluation,

conclusion

Prepare slides

30-minute presentation

Rehearsal one week before presentation

10-minte discussion

Everyone gives a score for your presentation

2012/11/23 11

Course Project

Two options

A survey paper on a certain topic

Problem, existing solutions, comparison

A paper on novel research idea

Problem definition, solution design, evaluation

Report two times

First time: problem, motivation and basic idea

Second time: solution, evaluation, documentation

Try to publish

2012/11/23 12

Class Disciplines

Keep your mobile phones silent

Do not need to take notes

Ask questions

2012/11/23 13

Grading

More important is what you realize/learn

than the grade

Class participation 20%

Presentation 30%

Course project 50%

2012/11/23 14

Review on Computer Networks

Networking Taxonomy

Internet Overview

Internet Layering Architecture

Important Issues in Future Internet Design

2012/11/23 15

Networking Review

What is a network?

2012/11/23 16

A system of lines/channels that interconnect

nodes

E.g., railroad, highway, telephony network,

computer network

What is a computer network?

A form of communication network —

moves information

Nodes are general-purpose computers

A Taxonomy of Communication

Networks

Communication Network

Switched Communication Network

Broadcast Communication Network

2012/11/23 17

Broadcast vs. Switched

Broadcast communication networks

Information transmitted by any node is received by

every other node in the network

Problem: coordinate the access of all nodes to the

shared communication medium (Multiple Access

Problem)

2012/11/23 18

A B C D E

Broadcast vs. Switched (Cont.)

Switched communication networks

Information is transmitted to a sub-set of

designated nodes

Example: WAN

Problem: how to forward information to intended

node(s)

2012/11/23 19

A

B

A’

B’

Multiplexing in Switched Network

Need to share network resources

Conversation 1: A->B

Conversation 2: C->D

How?

Con. 1 gets the forwarding resource of A’ sometimes

Con. 2 gets the forwarding resource of A’ sometimes

2012/11/23 20

A

B C

D

A’

Taxonomy of Switched

Communication Networks


Circuit-Switched Communication Network

Packet-Switched Communication Network

2012/11/23 21

Circuit Switching

Source first establishes a connection (circuit)

to the destination

Source sends the data over the circuit

Then the connection is torn down

Example: telephony network

Early versions: human-mediated switches

Later versions: end-to-end electrical connection

2012/11/23 22

Timing in Circuit Switching

DATA

Circuit Establishment

Data Transmission

Circuit Termination

Host 1 Host 2 Node 1 Node 2

propagation delay

between Host 1

and Node 1

propagation delay

between Host 2

and Node 1

processing delay at Node 1

2012/11/23 23

Circuit Switching

A node (switch) in a circuit switching network

incoming links outgoing links Node

2012/11/23 24

Circuit Switching (Cont.)

What about many connections?

Many wires

E.g., those big 200-pair cables you sometimes see

A more practical approach is to multiplex

multiple circuits over a single “fast” wire

2012/11/23 25

Circuit Switching:

Multiplexing/Demultiplexing

Time divided in frames and frames divided in slots

Relative slot position inside a frame determines which conversation the data belongs to

Needs synchronization between sender and receiver

In case of non-permanent conversations

Needs to dynamically bind a slot to a conservation

2012/11/23 26


Networks


Circuit-Switched Communication Network


2012/11/23 27

Packet Switching

Data divided into multiple packets

At each node the entire packet is received, stored,

and then forwarded to the next node

Store-and-Forward Networks

incoming links outgoing links Node

Memory

2012/11/23 28

Packet Switching (Cont.)

Data from any conversation can be

transmitted at any given time

How to tell them apart?

Use meta-data (header) to describe packet

2012/11/23 29

Packet-Switching vs. Circuit-

Switching

Advantage of packet-switching over circuit switching

Efficient bandwidth usage

Disadvantage

More complex routers

Harder to provide good network services (e.g., delay and bandwidth guarantees)

In practice they are combined

IP over SONET, IP over Frame Relay

2012/11/23 30


Networks


Datagram Network

Virtual Circuit Network

2012/11/23 31

Datagram Packet Switching

Each packet is independently switched

Outgoing link of the packet is determined by the

switching node in per-packet granularity

No pre-allocated (reserved) path in advance

The paths for packets from the same

conversation can be different

Example: IP networks

2012/11/23 32

Timing of Datagram Packet

Switching

Packet 1

Packet 2

Packet 3

Packet 1

Packet 2

Packet 3

Packet 1

Packet 2

Packet 3

processing delay of Packet 1 at Node 2


propagation

delay between

Host 1 and

Node 2

transmission

time of Packet 1

at Host 1

2012/11/23 33


Networks


Datagram Network

Virtual Circuit Network

2012/11/23 34

Virtual-Circuit Packet Switching

Hybrid of circuit switching and packet switching Data is transmitted as packets

All packets from one conversation are sent along a pre-established path (=virtual circuit)

Guarantees in-sequence delivery of packets within a virtual circuit

However: Packets from different virtual circuits may be interleaved

Example: ATM networks

2012/11/23 35

Virtual-Circuit Packet Switching (Cont.)

Communication with virtual circuits takes

place in three phases

VC establishment

Data transfer

VC disconnect

2012/11/23 36

Timing of Virtual-Circuit Packet Switching

Packet 1

Packet 2

Packet 3

Packet 1

Packet 2

Packet 3

Packet 1

Packet 2

Packet 3


propagation delay

between Host 1

and Node 1 VC

establishment

VC

termination

Data

transfer

2012/11/23 37

Circuit Switching vs. Virtual-Circuit

Packet Switching

Both establish a path before data transfer

Guarantee in-sequence packet delivery

Difference

Whether using packet (header)

Resource multiplexing

The reserved slot for a circuit in circuit switching

cannot be used by other circuits

But no slot reservation in virtual-circuit packet

switching

2012/11/23 38

Today’s Lecture

Networking Taxonomy

Internet Overview



2012/11/23 39

The Simplest Network

Node Link Node

2012/11/23 40

More than Two Nodes

… But what if we want more hosts?

Scalability?

Wires for everybody!

2012/11/23 41

Small Network

LAN

2012/11/23 42

Grow bigger

WAN

2012/11/23 43

And bigger

Today’s Internet

2012/11/23 44

The Internet

Public, global-scale, general-purpose,

heterogeneous-technologies, computer

network

Internet Protocol

Open standard: Internet Engineering Task Force

(IETF) as standard body ( http://www.ietf.org )

Technical basis for other types of networks

Intranet: enterprise IP network

Driven by the research community

2012/11/23 45

http://www.ietf.org/

History of the Internet

ARPANET 1969, built by DARPA

Started as a research project for the military, < 100 computers , 56 kbps

Mid of 70’s, using TCP/IP

1983, ARPANET and MILNET split

NSFNET NSF builds NSFNET in 1986

Links 6 Supercomputer centers

1.5 Mbps, 10,000 computers

Replaces ARPANET as the backbone of Internet

2012/11/23 46

History of the Internet (Cont.)

1990 NSFNET moves to 45 Mbps, 16 mid-level networks

1994 NSF backbone dismantled, multiple private backbones

1994 Birth of WWW

2005 Backbones run at 10 Gbps

>300 millions users from allover the world

2011 Backbone speed reaches 100s Gbps

>2 billion users in the world, among which 0.48 billion from China

2012/11/23 47

Services Provided by the Internet

Shared access to computing resources Telnet (1970’s)

Shared access to data/files FTP, NFS (1980’s)

Communication medium over which people interact Email (1980’s), on-line chat rooms (1990’s) Instant messaging, IP Telephony (2000’s)

A medium for information dissemination WWW (1990’s) Audio, video (2000’s): peer-to-peer systems

2012/11/23 48

Technological Requirements of Internet

Cost

Evolvability

Manageability

Security

Deployment

Accountability

Scalability

2012/11/23 49

Today’s Lecture

Networking Taxonomy

Internet Overview



2012/11/23 50

Layering

Layering is a particular form of modularization

The system is broken into a vertical hierarchy of logically distinct entities (layers)

The service provided by one layer is based solely on the service provided by the layer below

Rigid structure

2012/11/23 51

Why Layering?

Without layering Each new application has to be re-implemented for

every network technology

Each new network tech requires changes on all apps.

High cost

2012/11/23 52

Telnet FTP NFS

Packet

radio

Coaxial

cable

Fiber

optic

Application

Transmission

Media

HTTP

Why layering? (Cont.)

Solution: introduce an intermediate layer that provides a unique abstraction for various network technologies

2012/11/23 53

Telnet FTP NFS

Packet

radio

Coaxial

cable

Fiber

optic

Application

Transmission

Media

HTTP

Intermediate

layer

Pros. & Cons.

Advantages

Modularity – protocols easier to manage and maintain

Abstract functionality – lower layers can be changed without affecting the upper layers

Reuse – upper layers can reuse the functionality provided by lower layers

Disadvantages

Information hiding

Inefficient implementations

2012/11/23 54

Addressing

Error Control

Flow Control

Congestion Control

Fragmentation

Routing

2012/11/23 55

Design Issues in Each Layer

ISO/OSI Reference Models

Application

Presentation

Session

Transport

Network

Datalink

Physical

Application

Presentation

Session

Transport

Network

Datalink

Physical

Network

Datalink

Physical

Physical medium

Host A Host B

Router

• Seven layers

– Lower three layers are implemented everywhere

– Next four layers are implemented only at hosts

2012/11/23 56

Logical Communication

Layers interacts with corresponding layer on

peer

Application

Presentation

Session

Transport

Network

Datalink

Physical

Application

Presentation

Session

Transport

Network

Datalink

Physical

Network

Datalink

Physical

Physical medium

Host A Host B

Router

2012/11/23 57

Physical Communication

Communication goes down to physical

network, then to peer, then up to relevant

layer

Application

Presentation

Session

Transport

Network

Datalink

Physical

Application

Presentation

Session

Transport

Network

Datalink

Physical

Network

Datalink

Physical

Physical medium

Host A Host B

Router

2012/11/23 58

Encapsulation

• A layer can use only the service provided by the layer

immediate below it

• Each layer may change and add a header to data packet

data

data

data

data

data

data

data

data

data

data

data

data

data

data

2012/11/23 59

OSI Model Concepts

Service –says what a layer does

Interface –says how to access the service

Protocol –says how is the service implemented

A set of rules and formats that govern the communication between two peers

Term “protocol” is overloaded

specification of peer-to-peer interface

module that implements this interface

2012/11/23 60

OSI Model Concepts

Service and Protocol 2012/11/23 61

Layer k+1

Layer k-1

Layer k+1

Layer k-1

Service provided by layer k

Protocol

Physical Layer

Service

Move the information between two systems connected by a physical link

Interface

Specify how to send and receive a bit

Protocol

Make sure the correct transmission

Coding scheme used to represent a bit, voltage levels, duration of a bit

Examples

Coaxial cable, optical fiber links

2012/11/23 62

Data Link Layer

Service Transform a raw transmission facility into a line appearing

free of undetected transmission erros to the upper layer Framing, i.e., attach frames separator

Others (optional) Arbitrate the access to common physical media

Ensure reliable transmission

Provide flow control

Interface Send/receive a data unit (packet) to/from a machine

connected to the same physical media

Protocol Layer addresses, mechanisms for Medium Access Control

(MAC) (e.g., CSMA/CD)…

2012/11/23 63

Layer-2 Technologies

Ethernet

Dominate LAN technology

Listen to wire before transmission

Avoid collision with active transmission

InfiniBand

Primarily used in high-performance computing

Features: QoS, failover, Scalable

Fabre channel

Primarily used for storage networking

Gigabit-speed network technology

With active transmission 2012/11/23 64

Network Layer

Service Deliver a packet to specified destination

Perform segmentation/reassemble (fragmentation/ defragmentation)

Others Packet scheduling

Buffer management

Interface Send/receive a packet to a specified destination

Protocol Define global unique addresses

Construct routing tables

2012/11/23 65

Internet Protocol (IP)

Data communication across a packet-switched internetwork

Best effort delivery

Characterized as unreliable

Lack of reliability results in

Data corruption, data packet loss, duplicate arrival, out-of-order packet delivery

2012/11/23 66

host

host

router

router

router

router

router

router

IPv4

IPv4 address is too short

Many fields are useless 2012/11/23 67

Ver IHL ToS Total Length

Identifier Fragment

Offset

TTL Protocol Header Checksum

Source Address

Destination Address

Options and Padding

IPv4 Header

20 bytes

Header size can vary

if options are used

F

IPv6

Extension headers can be added after

the addresses

2012/11/23 68

IPv6 Header Ver

Traffic

Class Flow Label

Payload Length Next

Header

Hop

Limit

Source Address

(128 bits)

Destination Address

(128 bits)

Routing

Router Operation

When packet arrives at router

Examine header to determine intended destination

Look up in table to determine next hop in path

Send packet out appropriate port

2012/11/23 69

Router

How to generate the

routing table?

Routing (Cont.)

Graph model:

Represent each router as node

Direct link between routers represented by edge

Edge “cost” c(x,y) denotes measure of difficulty

of using link

2012/11/23 70

A

E

F

C

D

B

2

3

6

4

1

1

1

3

Transport Layer

Service Provide an error-free and flow-controlled end-to-end

connection

Multiplex multiple transport connections to one network path

Split one transport connection in multiple network paths

Interface How to send/receive a segment by user’s requirements

Protocol Implement reliability, flow control and congestion control

Examples TCP and UDP

2012/11/23 71

Transport Layer (Cont.)

Lowest level end-

to-end protocol

Header generated

by sender is

interpreted only by

the destination

Routers view

transport header

as part of the

payload

2012/11/23 72

7

6

5

7

6

5

Transport

IP

Datalink

Physical

Transport

IP

Datalink

Physical

IP

2 2

1 1

UDP(User Datagram Protocol)

“Best effort” service, UDP segments may be Lost

Delivered out of order to app

Connectionless No handshaking between UDP sender and receiver

Each UDP segment handled independently of others

Unreliable No flow control, no error control, no retransmission

Applications Streaming multimedia apps:

Loss tolerant Rate sensitive

DNS, SNMP Client can get the query result quickly

2012/11/23 73

TCP (Transmission Control Protocol)

UDP provides just integrity and demulplexing

TCP adds…

Connection-oriented

Reliable

Ordered delivery

Byte-stream

Flow control

Congestion control

2012/11/23 74

Top Three layers

Session and Presentation are seldom mentioned

Application layer

Service

Any service provided to the end user

Interface

Depends on the application

Protocol

Depends on the application

Examples

FTP, Telnet, WWW browser

2012/11/23 75

ISO/OSI Layers

Physical – sends individual bits

Data link – sends frames, handles access control to shared media

Network – delivers packets, using routing

Transport – demultiplexes, provides reliability & flow control

Session & Presentation – seldom used

Application – what end user gets, e.g., HTTP (web)

2012/11/23 76

TCP/IP Reference model

Application

Presentation

Session

Transport

Network

Datalink

Physical

Internet

Net access/

Physical

Transport

Application

IP

LAN Packet

radio

TCP UDP

Telnet FTP DNS

OSI (formal) Internet (informal)

• OSI: conceptually define services, interfaces, protocols

• Internet: provide a successful implementation

2012/11/23 77

OSI VS. TCP/IP

• OSI

• Bad timing

• Bad technology

• Bad implementations

• Bad politics

• TCP/IP

•Service, interface, and

protocol not distinguished

•Not a general model

•Host-to-network “layer” not

really a layer

•No mention of physical and

data link layers

•Minor protocols deeply

entrenched, hard to replace

2012/11/23 78

Current Model

This is “Hourglass” philosophy of Internet

Idea

If everybody just supports IP, can use many different

applications over many different networks

Technology

Applications

email WWW phone...

SMTP HTTP RTP...

TCP UDP…

IP

ethernet PPP…

CSMA async sonet...

copper fiber radio...

2012/11/23 79

The “Curse of the Narrow Waist”

IP over anything, anything over IP

Has allowed for much innovation both above and below the IP layer of the stack

An IP stack gets a device on the Internet

Drawbacks:

difficult to make changes to IP

But…people are trying (GENI)

Only a small amount of information available about lower levels (wireless)

2012/11/23 80

Today’s Lecture

Networking Taxonomy

Internet Overview



2012/11/23 81

Important issues

Multicast

P2P

Cloud computing

Data center networking

Green network

2012/11/23 82

Multicast- Efficient Data Distribution

2012/11/23 83

Src Src

P2P Networks

Client/server service model -> P2P service

model

Reduce the server burden

Client not only downloads, but also uploads to

other clients

Make better use of the end-system capability

Applications

File sharing

Multimedia streaming

2012/11/23 84

Cloud Computing

A new Internet service model

The other extreme is P2P

Users share computers and data In the cloud

Elasticity and Multiplexing Cost saving

Technologies Data center

Long-distance transport

Mobile + cloud

2012/11/23 85

Commercial clouds

2012/11/23 86

Data Center Networking

The core of cloud computing

Interconnect hundreds of thousands of computers and provide the routing service

A new environment of networking

Quite different from Internet

Technologies

Interconnection topology

Routing

Transport

2012/11/23 87

Green Network

2012/11/23 88

Beautiful

But, wasteful

Test

2012/11/23 89

advanced computer network - tsinghua...

Documents