computer networking

Shaowen Yao, School Of Software, YNU 1

Computer Networking

— — A Top-Down ApproachFeaturing the Internet

By Shaowen Yao


Foreword: Before The lecture begin Lecturer and tutorial assistant:

Dr. Yao Shaowen （姚绍文）, Mr. Tian Kebin（田克斌）

Prof. Of School of Software

Tel: 5038650（O），5032263（L），Email: [email protected]

Text Book and Reference Books:

Computer Network -- James F. Kurose

Computer Networks -- Andrew S. Tannenbaum - 3rd Edition

Internetworking with TCP/IP, Volume 1; Protoco1s, and Architecture -2nd Edition

Operating Systems -Internals and Design Principles - William Stallings

计算机网络 –谢希仁 –2nd and 3rd Edition（In Chinese）

Etc.

Assessment Procedure:

Exam — — 70%

Middle-term examination — — 20%

Exercise — — 10%

Some Experiment, Practice and Exercise will be assigned during the tutorial hours


Foreword: Before The lecture begin

Some Requirements:

Not necessary to present but must keep silent.

Questions and good suggestions are encouraged to be given out in time

during lecturing hours.

Self-study with the help of Internet are greatly encouraged. After tutorial hours,

you can find and learn some useful protocols, such as HTTP, LDAP, SOAP,

IIOP of CORBA, NAT and something else. section 1.1.3 list some useful

hyperlinks.

Experiment and Practice:

Experiment: to configure network and some network equipments, such as

Firewall, Switch;

Practice: Programming in Java, C++ or ANSI C to implement core protocols,

and analyzing the implementation of some protocols with free source codes.

Lecture Notes Download:

URL: ftp：//202.203.32.52

Username: seinetwork（password：seiynu）


After the course, you should: Learn architecture of computer network, Master TCP/IP suite;

Master computer network protocol, network layering and key protocols of

each layer;

Master typical transmission media, data switch principle;

Master protocols of application layer and programming of some typical

application layer protocols;

Master functionality of transport layer, particularly TCP and UDP

programming;

Master functionality of network layer, particularly IP address and routing;

Master functionality of DLL and LAN, focusing on some basic concepts,

protocol, error control and IEEE standard for LAN;

Learn multi-media transmission;

Learn core concepts, key issues and foundation of network information

security;

Learn other key issues of computer network, such as Network

Management, C/S computing, Distributed computing, PKI and so on.


Chapter 1— —Computer Networksand the Internet


Goal:

get context, overview,

“feel” of networking

more depth, detail

later in course

approach:

descriptive

use Internet as

example

Overview:

what’s the Internet

what’s a protocol?

network edge

network core

access net, physical media

performance: loss, delay

protocol layers, service models

backbones, NAPs, ISPs

history

ATM network


Computer Network, internet and Internet

1、 What is network?— — Human network as an example.

Computer Network: the collection of computers:Computer Network: the collection of computers:

Via communication linksVia communication links

With the target to share resourceWith the target to share resource

Resource include: hardware/software/Resource include: hardware/software/

information/data and something useful to othersinformation/data and something useful to others

2、What is computer network?

3、What is internet?

3、What is Internet?


internet and Internet

1、In computer network— — Computer is theelement of the set.

Internet is one special internet;Internet is one special internet; Internet is a worldInternet is a world--wide computer network;wide computer network;

2、What is internet?

3、What is Internet?

the internet is the interconnection ofthe internet is the interconnection of ““ComputerComputerNetworkNetwork””, internet can be seen as: the collection of, internet can be seen as: the collection ofcomputer networks, i.e. Network of networks.computer networks, i.e. Network of networks.

4、What support the network and Internet to run well:Various protocols;Various protocols;


What’s the Internet: “nuts and bolts” view

millions of connected

computing devices: hosts,

end-systems

pc’s, workstations, servers

PDA’s, phones, toasters

running network apps

communication links

fiber, copper, radio, satellite

routers: forward packets

(chunks) of data thru

network

local ISP

companynetwork

regional ISP

router workstation

servermobile


What’s the Internet: “nuts and bolts” view

protocols: control sending,

receiving of msgs

e.g., TCP, IP, HTTP, FTP, PPP

Internet: “network of networks”

loosely hierarchical

public Internet versus private

intranet

Internet standards

RFC: Request for comments

IETF: Internet Engineering Task

Force

local ISP

companynetwork

regional ISP

router workstation

servermobile


Some concepts

1、Hosts or end systems: the computing deviceshooked up to the Internet.

2、TCP/IP: TCP/IP suite are the Internetprincipal protocols.

3、ISP: Internet Service Provider.

TheThe topologytopology of the Internet;of the Internet;

Access network;Access network;

Regional ISP;Regional ISP;

National and international ISP;National and international ISP;


Some concepts

Voice communication vs. packet switching.

TeleTele--communication: before transmission, a physical linkcommunication: before transmission, a physical linkconnection is established;connection is established;

The Internet and Network employ a technique named asThe Internet and Network employ a technique named as ““packetpacketswitchingswitching”” instead of a dedicated path, e.g., IP packetinstead of a dedicated path, e.g., IP packet

Packet switching allows multiple communicating end systems toPacket switching allows multiple communicating end systems toshare a path, even parts of a path at the same time.share a path, even parts of a path at the same time.

5、With protocols, how can the information or data besent on network or Internet:

4、Communication links: to connect every kinds of endsystem together.

Links are made up of different types of physical media, includinLinks are made up of different types of physical media, includingg

coaxial cable, copper wire, fiber optics, radio spectrum;coaxial cable, copper wire, fiber optics, radio spectrum;

Link bandwidth: the link transmission rate in bits/sec.Link bandwidth: the link transmission rate in bits/sec.


Some concepts

7、Intranet.

Private Networks;Private Networks;

Use the same Internet Technology (the same typesUse the same Internet Technology (the same typesof host, routers, links, protocols, and standards).of host, routers, links, protocols, and standards).

Packet switching allows multiple communicating endPacket switching allows multiple communicating endsystems to share a path, even parts of a path atsystems to share a path, even parts of a path atthe same time.the same time.

6、Who take the responsible to standardize theprotocol for network.

There are many organizations with high reputationThere are many organizations with high reputationto produce protocols: IEEE, ITUto produce protocols: IEEE, ITU--T(CCITT), ISO,T(CCITT), ISO,IETFIETF… …… …


IETF and RFC documentations

Internet Engineering Task Force (IETF)

Open organization - anyone may join

Primarily dedicated to development of the Internet

protocols.

Ideas are presented as RFCs and go through a

review process

RFC standards described in RFC 1602

Proposed

Draft

Standard


IETF and RFC documentations

Requests For Comment (RFC)

Describe formally (and sometimes not soformally) everything about the Internet;;

Actually, RFCs are really a form of Memo;

All RFC docs are available on-line:www.ietf.org/rfc.html;

We use RFCs to learn about SMTP (821),

HTTP (2616), for example.


What’s the Internet: a service view

Communication infrastructure

enables distributed

applications:

WWW, email, games, e-

commerce, databases, voting,

more?

To enable distributed apps.,

the Internet must provide

one or more services to make

distributed apps. transparent

across the underlied physical

network.



communication services

provided:

Connection－Oriented: to

guarantee Quality of Service

(QOS) of data transmission

between two peers. Peer can be

host, component, computing

entity like process or object.

connectionLess: without any

guarantees on QOS of data

transmission.

Do you give some examples in

real life like the services?



Internet and applications:

Internet is an infrastructure to

allow various applications to be

invented and deployed, e.g.,

early email, ftp, and etc.

Advance and new development is

the eventual power to make the

Internet grow up.


What’s a protocol?

human protocols:

“what’s the time?”

“I have a question”

Run different protocols,

e.g., different languages.

… specific msgs sent

… specific actions takenwhen msgs received, orother events

… Without protocol, withoutcommunication.

network protocols:

machines rather than

humans

all communication activity

in Internet governed by

protocols

protocols define format, order

of msgs sent and received

among network entities, and

actions taken on msg

transmission, receipt


What’s a protocol?

a human protocol and a computer network protocol:

Q: Other human protocol?

Hi

Hi

Got thetime?

2:00

TCP connectionreq.

TCP connectionreply.

Get http://cs.smith.edu/Welcome.html

<file>time

Protocol is very important, learning computer network isfocused on learning network protocols, to understandingthe what, why, and how of networking protocols.


A closer look at network structure:

network edge:

applications and

hosts

network core:

routers

network of networks

access networks,

physical media:

communication links


Another view of computer Network

Computer Network =Computer Network =

Communication subnet + Resources subnetCommunication subnet + Resources subnet

or Communication subnet + User subnetor Communication subnet + User subnet

ResourcesResourcesSubnetSubnet

CommunicationSubnet

CommunicationCommunicationSubnetSubnet

HostHost

Host

Host

HostHost

Host


The network edge:

end systems (hosts):

run application programs

e.g., WWW, email

at “edge of network”

client/server model

client host requests, receives

service from server

e.g., WWW client (browser)/

server; email client/server

peer-peer model:

host interaction symmetric

e.g.: teleconferencing


Network edge: connection-oriented service

Goal: data transfer between end

sys.

handshaking: setup (prepare

for) data transfer ahead of

time

Hello, hello back human

protocol

set up “state” in two

communicating hosts

TCP Connection: like reg. letter

In a very loose manner;

Only the end systems is aware;

Virtual Connection: vs. physical

connection in circuit switching.

TCP service [RFC 793]

TCP - Transmission Control

Protocol

Internet’s connection-oriented

service

reliable, in-order byte-stream

data transfer

loss: acknowledgements and

retransmissions

flow control:

sender won’t overwhelm receiver

congestion control:

senders “slow down sending rate”

when network congested


Network edge: connectionless service

Goal: data transfer

between end systems

same as before!

UDP - User Datagram

Protocol [RFC 768]:

Internet’s connectionless

service - no handshaking

unreliable data transfer

no flow control

no congestion control

App’s using TCP:

HTTP (WWW), FTP

(file transfer), Telnet

(remote login), SMTP

(email)

App’s using UDP:

streaming media,

teleconferencing,

Internet telephony


The Network Coremesh of interconnected routers

the fundamental question: how is data transferred

through net?

circuit switching: dedicated

circuit per call: telephone

net

packet-switching: data sent

thru net in discrete “chunks”


Network Core: Circuit Switching

End-to-end resources

reserved for “call”

link bandwidth, switch

capacity

dedicated resources: no

sharing

circuit-like (guaranteed)

performance

call setup required


Visualized circuit switching: illustration

Switching in Telephone network:

Relay circuit-based circuit switching

Time-slot-based circuit switching

Circuit Switch

1

2

3

1 2 3

...

i

Input time-slot queue buffer

j

Output time-slot queue buffer

RAM buffering

Time-slot Switching


Network Core: Circuit Switching

network resources (e.g.,

bandwidth) divided into

“pieces”— — Multiplexing

pieces allocated to calls

resource piece idle if not used

by owning call (no sharing)

dividing link bandwidth into

“pieces”

frequency division：FDM

time division：TDM

some examples：cable TV,

satellite communication… …


Network Core: Packet Switching

each end-end data stream divided

into packets

Why we need packet;

user A, B packets share network

resources;

each packet uses full link

bandwidth;

resources used as needed,

resource contention:

aggregate resource

demand can exceed

amount available

congestion: packets

queue, wait for link use

store and forward:

packets move one hop

at a time

transmit over link

wait turn at next link

Bandwidth division into “pieces”

Dedicated allocation

Resource reservation


Network Core: Packet Switching

Packet-switching versus circuit switching: human

restaurant analogy

other human analogies?

A

B

C10 MbsEthernet

1.5Mbps

45 Mbs

D E

statistical multiplexing

queue of packets waitingfor output link

Primary Rate Interface (PRI):

E1:2.048Mbps;

T1:1.544Mbps.


Packet switching vs. circuit switching

1 Mbit link (1Mbps)

each user:

100Kbps when “active”

active 10% of time

circuit-switching:

10 users

packet switching:

with 35 users,

probability > 10 active

less that .0017

Packet switching allows more users to use network!

N users

1 Mbps link


Packet switching vs. circuit switching

Great for bursty data

resource sharing

no call setup

Excessive congestion: packet delay and loss

protocols needed for reliable data transfer, congestion control

Q: How to provide circuit-like behavior?

bandwidth guarantees needed for audio/video apps

still an unsolved problem (chapter 6)

Is packet switching a “slam dunk winner?”


Message switching

All kinds of messages are segmented into smaller on the source

host, and the receiver reassembles the packets back into

original message. Why do we need packet instead of app.

message?

The segmentation and reassembly may be an extra burden, is

such burden worthy of the advantage from doing that?

One comparison between packet switching and message

switching:

Assume: message with 7.5Mbits,

between source and destination are 2 packet switches and 3 links

with 1.5Mbps.

No congestion in the network

Do you wonder:


Packet switching vs. Message switching

Message switching costs: 5sec. in each hop, totally

takes 15sec.

MessageMessage

Packet switching: Segment into 5000 packets;

One packet cost 1ms;

Two switches works (instore and forward behavior)simultaneously;

Totally takes 5.002sec.


The advantages and disadvantages ofPacket switching

With obvious smaller end-to-end delays;

When bit errors occur, even only one bit is error,

the whole packet is corrupted and will be discarded,

the advantage of PS over MS is very obvious.

Sth. like FTP with “Resume” vs. traditional FTP.

Another potential advantage is that different

message with different size, and packet can be

specified with uniformed length, the PS and end-

system can process packets much simpler than msg.

packet switching’s disadvantage: overhead. Both

packets and msg need additional data as their header.


Have a Try !

On page 42 before subsection 1.4.2;

Download one Java Applet and try it;

Examine the effect of additional propagation delays

computer networking

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