Cs 5220: computer communications

Август 22, 2022

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Cs 5220: computer communications

Содержание

2. Computer Network Evolution 1960s: Terminals access shared host computer SAGE; SABRE airline reservation system Tree-topology terminal-oriented
3. Terminal-Oriented Networks Early computer systems very expensive; Time-sharing methods allowed multiple terminals to share local computer
4. Dedicated communication lines were expensive Terminals generated messages sporadically Frames carried messages to/from attached terminals Address
5. Multiplexing Multiplexer allows a line to carry frames to/from multiple terminals Frames are buffered at multiplexer
6. Error Control Protocol Communication lines introduced errors Error checking codes used on frames “Cyclic Redundancy Check”
7. Computer-to-Computer Networks As cost of computing dropped, terminal-oriented networks viewed as too inflexible and costly Need
8. Packet Switching Network should support multiple applications Transfer arbitrary message size Low delay for interactive applications
9. The ARPANET The vulnerability of the telephone system was a concern. (a) Telephone system structure; (b)
10. The ARPANET Design Connection-less packet transmission Packets are encapsulated in frames Error control uses check bits
11. ARPANET Applications ARPANET (NSF-NET) introduced new applications Email, remote login, file transfer, …
12. Ethernet Local Area Network In 1980s, affordable workstations available Need for low-cost, low error rate, high-speed
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Слайд 2

Computer Network Evolution
1960s: Terminals access shared host computer
SAGE; SABRE airline reservation

system
Tree-topology terminal-oriented networks
1970s: Computers connect directly to each other
ARPANET packet switching network
TCP/IP Internet protocols
Ethernet local area network
1980s - 2000s: New applications and Internet growth
Commercialization of Internet
E-mail, file transfer, web, P2P, . . .
Internet traffic surpasses voice traffic

Слайд 3

Terminal-Oriented Networks
Early computer systems very expensive; Time-sharing methods allowed multiple terminals

to share local computer
Remote access via telephone modems

Слайд 4

Dedicated communication lines were expensive
Terminals generated messages sporadically
Frames carried messages to/from

attached terminals
Address in frame header identified terminal
Medium Access Controls for sharing a line in arbitrated manner
Example: Polling protocol on a multi-drop line

Medium Access Control

Слайд 5

Multiplexing
Multiplexer allows a line to carry frames to/from multiple terminals
Frames are

buffered at multiplexer until line becomes available, i.e. store-and-forward
Header carries other control information for framing

Frame

Слайд 6

Error Control Protocol
Communication lines introduced errors
Error checking codes used on frames
“Cyclic

Redundancy Check” (CRC) calculated based on frame header and information payload, and appended
Header also carries ACK/NAK control information
Retransmission requested when errors detected

Слайд 7

Computer-to-Computer Networks
As cost of computing dropped, terminal-oriented networks viewed as too

inflexible and costly
Need to develop flexible computer networks
Interconnect computers as required
Support many applications
Application Examples
File transfer between arbitrary computers
Execution of a program on another computer

Слайд 8

Packet Switching
Network should support multiple applications
Transfer arbitrary message size
Low delay for

interactive applications
Store-and-forward operation could induce high delay on interactive messages
Packet switching introduced
Network transfers packets using store-and-forward
Packets have maximum length
Break long messages into multiple packets
By switching, packets delivered (and reassembled) at destination

Слайд 9

The ARPANET
The vulnerability of the telephone system was a concern.
(a) Telephone

system structure; (b) Distributed switching system structure

Слайд 10

The ARPANET Design
Connection-less packet transmission
Packets are encapsulated in frames
Error control uses

check bits
Destinations identified by unique addresses
Routing tables at the packet switches
Messages are segmented into packets
End-to-end congestion control
Flow control prevents buffer overflow

Слайд 11

ARPANET Applications
ARPANET (NSF-NET) introduced new applications
Email, remote login, file transfer, …

Слайд 12

Ethernet Local Area Network
In 1980s, affordable workstations available
Need for low-cost, low

error rate, high-speed network, possible using coaxial cable
Broadcasting, medium access control
Network interface card with a unique address
Ethernet is the standard for high-speed wired access to computer networks

Cs 5220: computer communications

Содержание

Computer Network Evolution1960s: Terminals access shared host computerSAGE; SABRE airline reservation

Terminal-Oriented NetworksEarly computer systems very expensive; Time-sharing methods allowed multiple terminals

Dedicated communication lines were expensiveTerminals generated messages sporadicallyFrames carried messages to/from

MultiplexingMultiplexer allows a line to carry frames to/from multiple terminalsFrames are

Error Control ProtocolCommunication lines introduced errorsError checking codes used on frames“Cyclic

Computer-to-Computer NetworksAs cost of computing dropped, terminal-oriented networks viewed as too

Packet SwitchingNetwork should support multiple applicationsTransfer arbitrary message sizeLow delay for

The ARPANETThe vulnerability of the telephone system was a concern.(a) Telephone

The ARPANET DesignConnection-less packet transmissionPackets are encapsulated in framesError control uses

ARPANET ApplicationsARPANET (NSF-NET) introduced new applicationsEmail, remote login, file transfer, …

Ethernet Local Area NetworkIn 1980s, affordable workstations availableNeed for low-cost, low

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