what’s data communicationskwke/dc2006/introduction.pdf · communication networks ... telephone...
TRANSCRIPT
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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
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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
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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
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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
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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
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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)
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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
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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
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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)
. . .
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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
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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.
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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
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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
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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
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Introduction 57
THE END
Introduction 58
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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)
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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
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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
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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