Introduction 1 Introduction 2

WhatWhats s DataData CommunicationsCommunications ??Data Communications ~ the transfer of data or informationbetween a source and a receiver.

Concerning directly-connected information exchange (hop-by-hop)Generation of the information is not part of data communications

Interested in the transfer of data, the method of transfer and the preservation of the data during the transfer process.Purpose to provide the rules (protocols) and regulations (standards) that allow computers to exchange information and share resources.Networking focuses on the connectivity via data

communications technologies.

Introduction 3

Model of Networking CommunicationsModel of Networking Communications

Goal of Computer communications

via

communication networks

(physical communication)

Client(SRC/DEST)

Server(DEST/SRC)

Real

data

flowReal data flow

(logical communication)

cloud

Since 1970s . . .

Computernetworks

(to hide the complexity)

Introduction 4

Network Structure Network Structure A Closer LookA Closer Look

Communication linksi.e., Physical media(selective discussion later)

Network core: Switches/Routers,

network of networks Switching techniques

Network edge:- applications and hosts

(end systems)- CO/CL services

wireless

AP

so-called backbone

(())

So

Access networks

Introduction 5

Network Network CoreCoreMesh ()of interconnected routers(mostly) or switchesThe fundamental question:

How do data be transferred through How do data be transferred through network(s)?network(s)?

Circuit-switching: dedicated circuit/path per call(?), e.g., telephone network (Plain Old Telephone Service)

Packet-switching:data sent through net in discrete chunks

AP

Introduction 6

End systems (hosts):run application programse.g., WWW, emailat edge of network

Client/serverClient/server model (CS):client host requests, receives service from servere.g., WWW client (browser)/ server; email client/server

PeerPeer--toto--peerpeer model (P2P):host interaction symmetricSince Napster, 1999e.g., (video) teleconferencing, file-sharing (New Internet Directory Service) eDonkey, eMule, Gnutella, KaZaA, ezPeer, Kuro

Network Network EdgeEdge Edge device

(named w.r.t. core device)

AP

Introduction 7

AccessAccess NetworksNetworks

Q: How to connect end systems to edge router?residential access netsinstitutional access networks (school, company)mobile access networks

AP

Keep in mind: the connection- bandwidth (bits per second) ?

(which is media-dependent) - shared or dedicated ?(which is topology-dependent)

AP access point

dedicatedshared

Introduction 8

Residential Access : point to point accessResidential Access : point to point access

Dialup via modem

- up to 56Kbps direct access to router (conceptually)

ISDN:- Integrated Services Digital Network- BRI~64x2+16, PRI~1544 Kbps all-digital connect to router

xDSL: digital subscriber line (e.g., Asymmetric ADSL)

up to 1 Mbps home-to-routerup to 8 Mbps router-to-home

(Speed is continuously enhancing.)

SubscribersLocal loop

(so-called last mile)* All over a given telephone line

Introduction 9

Splitter

Ex: : 64Kbps - 6Mbps; : 1.5Mbps - 4.1 w/ 26AWG

: 64Kbps 640Kbps (())

ATUATU--RR

Filter

ATUATU--RR

Filter

ATUATU--RR

Filter

...

Hinet ISP

DSLAM DSLAM 62006200

ATM

Data STM-1 STM-1

TANET

ATMATM

,

PSTN

POTS

POTS: 0 ~ 4KHzUplink: 25 ~ 170KHz Downlink: 200KHz ~ 1.1MHz

POTS

,

1.1MHz

Ex: ADSL(Asymmetric Digital Subscriber Loop)Ex: ADSL(Asymmetric Digital Subscriber Loop)

Introduction 10

Network Architecture EvolutionNetwork Architecture EvolutionNetwork Architecture EvolutionTelegraph Networks - Telegram

Message Switching & digit(al) transmissionTelephone Networks - PSTN

Circuit SwitchingAnalog transmission (SL) digital transmission (DSL)Mobile communications (WLP)

Computer Networks - InternetPacket Switching & computer applications

Next-Generation InternetMultiservice, Mobile, Plug&Playpacket switching network Switching

TechniquesSwitching

Techniques

Introduction 11

Network ComponentsNetwork ComponentsNetworks are COMPLEX

Consists of MANY pieces : devices (computers/hosts/peripherals/IA)nodes (repeaters/switches/routers/computers)links (various media: wired or wireless)Lots of Protocols (layered in stack, standarization) Various of Applications

(FTP/Web/Videoconferencing/)* Miscellaneous hardwares and softwares

Two key elements:- Network topology ()- Protocols () and Network architecture

Sooooo

Introduction 12

Calls for Calls for protocols for communicationprotocols for communication??

A Computer Network interconnects computers over a wide geographical area

Communications between computers requires very specificunambiguous rules in every tier

A protocolprotocol is a set of rulesa set of rules that governs how two or more communicating parties are to interact, e.g.,

Transport/delivery rules: Internet Protocol (IP) Transmission Control Protocol (TCP)

Even Application rules: HyperText Transfer Protocol (HTTP) ~ for web services Simple Mail Transfer Protocol (SMTP) ~ for E-mail services

Introduction 13

A familiar protocol A familiar protocol -- ProceduralProcedural

Do you have a first name or street?

Caller

What name?Y-Bein

Caller replies

System replies with number

System replies

System replies

System replies

Operator replies

Thank you, please hold

Pan-Green Road

Caller replies

Taipei

Dials 104

What city?

Caller replies

Operator replies

Caller waits

Thank you, please holdCaller waitsCaller dials

please dial . . .

Introduction 14

Data Communications ProtocolsData Communications ProtocolsData Communications ProtocolsConnection-Oriented (CO) Protocol

Sending and receiving station establish a real/virtual connectionbefore data is transmitted All frames/packets are guaranteed to arrive and are to arrivein orderEx: VCPS(at NL), TCP(at TL), FTP(at APL), ATM(at DLL)

(between end-systems)

(with respect to end-users)

Introduction 15

Connectionless (CL) Protocol- Sending station sends a sequence of independent frames/packets to

the receiving station with no dedicated/fixed path- Intermediate nodes are forwarding packets with their best-effort- can be acknowledged (with retransmission) or no acknowledged

(with no retransmission) ACK by the receiver- Ex: DGPS(at NL), UDP(at TL), SNMP(at APL), IP (at NL)

Introduction 16

Protocols ~ a set of (standard) rules that specifies- Format of messages- Meaning of messages- Rules of exchange- Procedures for handling problems

~ Designed in Layers (layered communications)- separation of networking functions to simplify

network design (reducing complexity and more ) Layers + Protocols form a Protocol stack/suite

( several software modules)~ called Network Architecture

Protocols ~ a set of (standard) rules that specifies- Format of messages- Meaning of messages- Rules of exchange- Procedures for handling problems

~ Designed in LayersLayers (layered communications)(layered communications)-- separation of networking functions to simplify

network design (reducing complexity and more ) Layers + Protocols form a Protocol stack/suite

( several software modules)~ called Network ArchitectureNetwork Architecture

Introduction 17

- above ~ to provide services- below ~ to ask for (receive) services

(2) peer layer entity via peer protocols protocols ()~ to logically transfer messages for a session to be built-up

* ServiceService interface ~ define the physical data flow between layers* Peer protocolprotocol ~ define the logical data exchange and

peer-to-peer logicallogical communications(Q: How to approach this goal ?)

In LayeredIn Layered communicationscommunications- an entityentity of a particular layerlayer can only communicate with :

(1) adjacent layer entities via serviceservice interfacesinterfaces

(service viewpoint) or Service Access Point, SAPSAP)

?

??

Introduction 18

Layer and Peer Protocol InteractionLayer and Peer Protocol Interaction For each layer , it will communicate

to above service provider; to below service user;and adjacent through service interface point (SAP) address

protocolprotocol

Layer N/(N-1) interface

Introduction 19

Reducing complexity~ divide interrelated aspects of networking

Standardizing interfaces (physical)~ define interfaces for PnP compatibility and multivendor integration

Facilitating modular engineering~ specialize development/implementation efforts on modular functions

Accelerating technique evolution~ prevent change dependency, so each layer can evolve quickly

Simplifying teaching and learning~ divide internetworking into discrete and easily learned subsets

Why a layered Network Model ? (advantages ?)Why a layered Network Model ? (advantages ?)Why a layered Network Model ? (advantages ?)

Layers: each layer implements a service . . .- via its own internal-layer actions- relying on services provided by layer below

Introduction 20

OSI 7-Layer Reference ModelOSI 7OSI 7--Layer Reference ModelLayer Reference Model

Proposed by ISO for OSI (Open System Interconnection)Started in 1977; completed in 1983

ISO standard 7498A reference model for computer communication architecture and protocol development

Introduction 21

Application layer (Layer 7)

~ Provides network access to application programs and users~ Issues: everything is application specific~ Example: Telnet (Remote login), File Transfer Protocol (FTP)

Electronic mail service, X-terminal (terminal emulation)

OSI 7-layer : A Top-Down View

Introduction 22

Presentation layer (Layer 6)~ Responsible for the format/transformation of data to be

exchanged between applications~ Issues: - Syntax (character code) & semantics conversion

- Data compression(encoding)/decompression- Cryptography (Encryption & Decryption)

~ Example: ASN.1, OSI presentation protocol, data types

Introduction 23

Session layer (Layer 5)

~ Supports the dialog between cooperating application programs

~ Issues: - Session/dialog establishment/maintenance/termination- Synchronization of dialog- Recovery (from error) or backup via checkpoints

~ Example: ISO session protocol, RPC (Remote Procedure Call)

Introduction 24

Transport layer (Layer 4)

~ Controls the delivery of messages/data between the end stations

(at a pre-negotiated service quality) (e.g., reliable ?)~ Issues: - Connection establishment/management/termination

- Error control and/or flow/congestion control(if required)~ Example: TCP, UDP, SPX (Netwares Sequenced Packet eXchange)

Introduction 25

Network layer (Layer 3)

~ transfer of data between end systems across communication networks

~ Issues: - Addressing (locating a host in the network)- Routing (data packet forwarding) & Congestion control

~ Example: IP (Internet Protocol), IPX(InterPacket eXchangeProtocol), CCITT X.25 (network layer)

Introduction 26

Data Link layer (Layer 2)

~ Provides reliable transfer of block information (the frame) over a link(between two physically connected end system on a link basis)

~ Issues: - Synchronization (framing)- Error control*- Flow control

~ Example: ISO HDLC (High Level Data Control), IEEE 802.2 LLCCCITT LAPD (Link Access Procedure-D channel), X-modem

Switch/bridge

Introduction 27

Physical layer (Layer 1)

~ Concerned with (only) transmission of bits over a communication channel (transmission media)

~ Issues: - Conversion of bits into electrical or optical signal - Encoding & Decoding- Scrambling & Descrambling

~ Example: CCITT X.21, RS-232(unbalanced), RS-449 (balanced)

blue lines - linksIntroduction 28

Layer 4 and above (referred to higher layer) are end-to-end protocols (executed only on a host computer/end-system)The lower four layers provide reliable data exchange and quality of information transmission.Not all 7 layers are needed.

Define sublayers if necessary:DLL LLC (logic link control) & MAC (medium

access control)Many layered protocol architectures do not define the session or the presentation layer. ( Example )

Remarks

Introduction 29

MODEM ExampleMODEM Example

Introduction 30

Host A (FTP client) Host B (FTP server)

Internetwork

Control connection (at initial)

Data connection (by request)

Combining higher layers FTP Application

AP L.C.

PL L.C.

SL L.C.

LC ~ logic communication

Introduction 31

- Physical ~ transmission of bits over communicationchannel (transmission media)

- Data link ~ Provides reliable transfer of block information(the frame) over a link

- Network ~ packet forwarding (addressing + routing)- Transport ~ Controls the way of data delivery between

stations/nodes - Session ~ dialog between cooperating application programs

(login and password)- Presentation ~ data representation of information and

compatibility - Application ~ individual application program for users

Summary Summary -- OSI LayersOSI Layers

Introduction 32

OSI vs. Internet ArchitectureOSI vs. Internet Architecture

Introduction 33

Implementing Communication Between LayersImplementing Communication Between Layersin

tera

ctio

n

Adding control info at header/trailer

Introduction 34

OSI model in OSI model in PointPoint--toto--PointPoint CommunicationCommunicationHow are data transmitted under the OSI model ?

PDU

Data

Message

InformationEncapsulation Decapsulation

bits

Frame

Packet

Segment

Signal

100110101101010201101000010 . . .

Physical (transmission media)(via channel or network)

overhead

Introduction 35

Protocol Layering Protocol Layering NetworkedNetworked CommunicationCommunication

Transport

PresentationSession

Data LinkPhysical

Network

Application

Transport

PresentationSession

Data LinkPhysical

Network

Application

Station/Host A Station/Host B

IS or Node

network

IS (Intermediate System) :L7 Gateway*L3 RouterL2 Switch/BridgeL1 Hub/Repeater

Data LinkPhysical

Network

Data LinkPhysical

Network

Data LinkPhysical

Network

Data LinkPhysical

Network(protocol stack in One computer)

IS - so called Intermediate Message Processor, IMP (refer to ISO Network Hierarchy)

L3L2L1

datadata datadata

datadata

Introduction 36

Calls for Addressing ()Calls for Addressing Calls for Addressing (())

Mechanisms needed to distinguish among . . .

- multiple networks on the Internet (internetworking)

- multiple computers on a network

- multiple applications (software) on a computer

- multiple copies of specific single application ona computer

(entity,)End-point (in TCP/IP-based Internet)

. . .

Introduction 37

Addressing ConceptsAddressing Concepts

A SAP is unique only within a system but need not be globally unique.Introduction 38

Physical/MAC Address Physical/MAC Address the NICthe NICs IDs ID

RJ-45 Jack

DFE 540TX

NIC ~ Network Interface Card ()ID ~ identifier ()

uniquely identifies each physicalnetwork connection of a device also referred to as physical or hardware addressusually exist within a flat address

spacepreestablished and typically fixed

relationship to a specific device

Introduction 39

Check with your MAC Address via winipcfg

Manufacturers ID

* Alternate: ipconfig -all, netstat r command under MS NT/2000/XP

NICs ID/Serial number

242 's

IEEEs EIU-48 rule

Introduction 40

Network TopologyNetwork Topology

(f) hybrid(f) hybrid

(a) point to point(a) point to point (b) star(b) star

(c) bus(c) bus (d) ring(d) ring

(e) mesh(e) mesh

Introduction 41

Network ClassificationsNetwork ClassificationsLAN

PAN

according to geographic size/span of networking

WAN

MAN

GAN

future BAN

Introduction 42

xANxAN ExamplesExamples--IILAN

MAN

Introduction 43

xANxAN ExamplesExamples--IIII

WAN

GAN

Read: P.30-36, Tomasi

Introduction 44

Standard Organization for Data and Standard Organization for Data and Network Communications Network Communications

ISO (Institute of Standardization Organization)ITU-T (International Telecommunication Union Telecommunications sectors) formally the CCITTANSI (America National Standard Institute)IEEE (Institute of Electrical and Electronic Engineering)Electronic/Telecommunications Industrial AssociationsOthers: ATM forum, Gigabit/10GE Alliance, etc.

Introduction 45

Standard Organization for Internet Standard Organization for Internet

IAB - Internet Activities/Architecture Board IETF - Internet Engineering Task Force

(the most important one)IRTF - Internet Research Task Force

Introduction 46

Network of networks(inter-connected set of networks) To interconnect different computers used by various organizations via the same TCP/IP protocol it treats all networks (e.g., LAN, WAN, etc.) equally (i.e., a flat network)

What is the What is the InternetInternet ??

NBP A

NBP B

NAP NAP

regional ISP

regional ISP

localISP

localISPA(B,S)P ~ Access (Backbone,

Service) Providers

* roughly hierarchical

New computers added to the Internet > ONE per second Internet ~ Doubling in size every nine to twelve months

Introduction 47

Internet Society OrganizationsInternet Society Organizations

IANA ~ Internet Assigned Number Authority

NIC ~ Network Information CenterAPNIC (TWNIC, etc.), EURNIC, etc.

RFC ~ Request For CommentsFYI ~ For Your Information (RFC # > 1500)

IRTF - Internet Research Task Force- Responsible for research and deve-lopment of the Internet protocol suite

IETF - Internet Engineering Task Force - Responsible for solving short-term engineering needs of the Internet.It has over 40 Working Groups.

IAB, 1983

IETF

Area 1 Area 8

IRTF

working groups

research groups

. . .

. . .

. . .

. . .

IAB ~ Internet Activities Board

IESG: Internet Engineering Steering Group

TWNIC

Introduction 48

Internet Protocol StackInternet Protocol StackInternet Protocol Stack

Application: supporting network applications

FTP, SMTP, HTTP, SMTP, POP3Transport: host-host data transfer

TCP, UDPNetwork: routing of datagrams from source to destination

IP,ICMP, IGMP, RIP,OSPF, BGP4Link: data transfer between neighboring network elements

PPP/SLIP, Ethernet, Token-RingPhysical: bits on the wire - transmission

Network Access

Physical Layer

Media Access Control Layer

Network (IP) Layer

Transport (TCP) Layer

Application Layer

Introduction 49Higher-layer see nothing pealed off; Lower-layer cannot see misunderstood

Protocol layering and dataProtocol layering and dataEach layer takes data from upper (lower)

Adds (take off) header information to create new data unitDoes what the action(s) indicated by the headerpasses new data unit to layer below (above)

applicationtransportnetwork

linkphysical

source

applicationtransportnetwork

linkphysical

destinationMMMM

HtHtHnHtHnHl

MMMM

HtHtHnHtHnHl

messagesegmentdatagramframe

Encapsulation Decapsulation

networks

Introduction 50

Some Protocols in TCP/IP SuiteSome Protocols in TCP/IP Suite

Introduction 51

IP headerTCP header

Protocol Data Unit (Protocol Data Unit (PDUPDU) in TCP/IP Architecture) in TCP/IP Architecture

Meaningful to appropriate peerprotocol software module

DLL Frame

InternetProtocol Stack

DLL header

Host A

NIC

Introduction 52

Windows> telnet 140.124.70.26 (showing the first packet transmitted by the src PC)

PDU Decomposition in TCP/IP Scenario

Protocol #: Network--Transport layer

Sources MAC addressDest.s MAC address

Protocol type: DLC--Network layer

Introduction 53

Src port # (randomly generated by the src PC)Dest port # (an well-known for well-known application)

Port #: Transport--Application layer

(PDU contd)

(More on Layer communication)Introduction 54

How to get RFC ?

Web sites: http://www.rfc-editor.org

Introduction 55

RFC ExamplesRFC Examples

topic

1. RFC1700 - assigned numbers (including all port numbers and constants)2. RFC2700 - State (standard, draft standard, proposed standard, experimental,

informational, or historic) of standardization of various internet protocols

Other RFCs:

RFC 1577

RFC 1700

Introduction 56

Some Important Some Important RFCsRFCs

Protocol Full Name RFC # Protocol Full

Name RFC # Protocol Full

Name RFC #

TCP* Transport Control Protocol

793 1323 BOOTP

Bootstrap Protocol

951 1048 1084

SNMP* Simple

Network Management

Protocol

1067 1448

UDP* User

Datagram Protocol

768 URL

Uniform Resource Location

1738 SMTP Simple Mail

Transfer Protocol

821 822

IP* Internet Protocol 791 DHCP* Dynamic Host Configuration

Protocol

1531 1541 2131

MIME Multipurpose

Internet Mail

Extensions

2045 2046 2047 2048

ICMP* Internet Control Message Protocol

792 Telnet* Telnet (Remote login) 764 854 POP3

Post Office Protocol V.3 1939

ARP* Address

Resolution Protocol

826 FTP* File

Transfer Protocol

959 IMAP Internet

Mail Access

Protocol 2060

RARP Reverse Address

Resolution Protocol

903 DNS* Domain Name

System

1034 1035 NNTP

Network News

Transport Protocol

977

HTTP Hypertext Transfer Protocol

2068 Cookies HTTP State

Management Protocol

2109 CIDR Classless

InterDomain Routing

1519

ISSP Internet Standard

Subnetting Procedure

950 PPP Point to Point Protocol 1661 NAT IP Network

Address Translator

1631

Introduction 57

THE END

Introduction 58

-

Introduction 59

Optical (Visual) TelegraphOptical (Visual) Telegraph

Claude Chappe invented optical telegraph in the 1790sSemaphore mimicked a person with outstretched arms with flags in each handDifferent angle combinations of arms & hands generated hundreds of possible signalsCode for enciphering messages kept secret (code book)Signal could propagate 800 km in 3 minutes!

Introduction 60

ChappeChappe TelegraphTelegraph

Principle of operation

The telegraph of the Chappebrothers is a 5 m height mechanical device made up: - of two wings or indicators, 2 meters length and 30 cm broad. - counterweight to ensure the balance of the unit. - of a manipulator to put moving the wings.

Claude Chappe(1763 - 1805)

Introduction 61

Electric TelegraphElectric TelegraphWilliam Sturgeon Electro-magnet (1825)

Electric current in a wire wrapped around a piece of iron generates a magnetic force

Joseph Henry (1830)Current over 1 mile of wire to ring a bell

Samuel Morse (1835, 1791-1872)Pulses of current deflect electromagnetPulses of current deflect electromagnetto generate to generate dotsdots & & dashesdashesExperimental telegraph line (wire) over 40 miles (1840)

Signal propagates at the speed of light (~ 2 x 108 m/s in cable)

Introduction 62

Morse code converts text message into sequence of dots and dashes

Use transmission system designed to convey dots and dashes

Morse Code: 1st Digital CommunicationsMorse Code: 1st Digital Communications

Introduction 63

Morse Electric TelegraphMorse Electric Telegraph

Morse register Introduction 64

Electric telegraph networks explodedMessage switching & Store-and-Forward operationKey elements: Addressing, Routing, Forwarding

Rate: 25~30words/min or 20bit/s20bit/s (5 char/word, 8bit/char)Optical telegraph networks disappeared since then (1832)

Electric Telegraph NetworksElectric Telegraph Networks

Q: How to increase the transmission rate over a telegraph circuit?

Switches

Message

Destination

SourceMessage

Message

Message

X

X

X

X

X

X

Introduction 65

BellBells Telephones TelephoneAlexander Graham Bell (1875) working on harmonic telegraph to multiplex telegraph signalsDiscovered voice signals can be transmitted directly

Microphone converts voice pressure variation (sound) into analogous electrical signalLoudspeaker converts electrical signal back into sound

Telephone patent granted in 1876Bell Telephone Company founded in 1877

Signal for ae as in cat

Microphone Loudspeakeranalog

electricalsignalsound sound

Introduction 66

!!

BellBells Sketch of Telephones Sketch of Telephone

Introduction 67

The NThe N22 ProblemProblem

For N users to be fully connected directlyRequires N(N 1)/2 connections Requires too much space for cablesInefficient & costly since connections not always on

N = 1000N(N 1)/2 = 499500

1

2

34

N

. . .

End up with . . .Introduction 68

Telephone Pole CongestionTelephone Pole Congestion

Solution?

Circuitswitching

Introduction 69

Computer Network Evolution OverviewComputer Network Evolution Overview

1950s: Telegraph technology adapted to computers 1960s: Dumb terminals access shared host computer

SABRE airline reservation system (terminal-oriented ntwk)1970s: Computers connect directly to each other

ARPANET (1970s) packet switching networkTCP/IP internet protocolsEthernet local area network

1980s & 1990s: New applications and Internet growthCommercialization of InternetE-mail, file transfer, Telnet, WWW, firewall, P2P, . . .Internet traffic surpasses voice traffic

Introduction 70

ARPANET ApplicationsARPANET Applications1957, ARPA(Advanced Research Project Agency) of DoD

in response to the Soviet Unions SputnikIntiated in the lat of 1970s, Introduced many new applications :Email, remote login, file transfer, Formed a committee, 1983 IAB (Internet Activity Board)Intelligence at the edge

UCLA RAND TINKER

USC

NBS

UCSB

HARV

SCD

BBN

STAN

AMES

AMES McCLELLAN UTAH BOULDER GWC CASE

CARN

MITRE

ETAC

MIT

ILLLINC

RADC

56kbps