LM CCN Section 1.1: History of Networking
Computer and Communication Networks
History of Networking John Easton
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Session Overview
o Network basics
– What is a communications network? – Evolution of network architectures
– Network addressing
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What is a Communications
Network?
o A set of equipment and facilities that provide a communications service
– Radio, phone, TV, data o Equipment
– Routers, servers, switches, hubs, modems
o Facilities
– Coaxial cable, optical fibre, conduits, masts etc.
o Business models often split facilities from equipment – Openreach
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LM CCN Section 1.1: History of Networking
What is a Communications
Network? (Cont.)
o Computer networks are a specialisation of communication networks
o Range of uses:
– Business, home, mobile
o Social and technical issues: – Scalability, privacy, social
o Connect end users (hosts) – Client / server
– Peer-to-peer / mesh
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What is a Communications
Network? (Cont.)
o Networks can be classified by scale
– Edge devices connect to local networks
– Edge networks connect to trunk networks via edge
routers
Scale Type
Vicinity PAN (Personal Area Network)
Building / site LAN (Local Area Network)
City MAN (Metropolitan Area Network)
County / Country WAN (Wide Area Network)
Planet Internet (Network of networks)
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Evolution of Computer Networks
o 1950s: Adaptation of telegraph technology to computers
o 1960s: Dumb terminals connect to shared host (SABRE airline reservations)
o 1970s: Direct connections between individual computers
– ARPANET, Ethernet, TCP/IP
o 1980s onwards: New applications, rise of the Internet
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LM CCN Section 1.1: History of Networking
General Purpose Computing
o ENIAC (1946)
– Electronic Numerical Integrator And Computer – University of Pennsylvania
– Original tasks:
o Artillery tables
o Feasibility of H-bomb o Circa 100s of multiplications
per second
o Not hugely reliable
– Vacuum tube technology
o General arithmetic units with a specific function
– Switched together to form a processing chain / program
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Rapid Development
o ENIAC (1946)
o Ferranti Mk. 1 (1951)
o LEO 1 – Lyons Tearooms (1951)
o Harwell CADET – First fully transistor-driven
computer (1955)
o Magnetic disk-based storage (1956)
o Development of integrated circuits (1959) o Atlas “supercomputer” (1962)
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Personal Computers
o Early machines all mainframe or minicomputers o “Personal Computing” originated in mid-70s
o Early pioneers were Olivetti
(1975), Apple (1976), and Commodore (1977)
o Common programming languages and some applications
– Re-implement on each hardware platform
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LM CCN Section 1.1: History of Networking
IBM PC (1981)
o Rapid path to market
– Compete with Apple 2
o Open standards with COTS parts
– Only basic input/output software (BIOS) was custom
o Licensed software
– Microsoft MS-DOS
o “Clone” PCs with similar components could run the same software
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Ethernet LANs
o Ethernet is the standard for high-speed wired access on LANs
– Interconnect local workstations
– Access shared resources (storage,
printing etc.)
o Low-cost, high-speed, comparatively low error rates
o Bandwidth on coaxial cables / twisted pair limited by interference
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Ethernet Medium Access Control
o Physical layer
o Network Interface Cards (NICs) connect
machines to a LAN
o Each NIC has globally unique address o Frames of data are broadcast into cable o NICs listen for frames with their address o Transmitting NICs listen for collisions
with other messages, and abort / reschedule communications as needed
Image by Barcex (Own work) CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0)], via Wikimedia Commons https://upload.wikimedia.org/wikipedia/commons/6/6c/ForeRunnerLE_25_ATM_Network_Interface_%281%29.jpg
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LM CCN Section 1.1: History of Networking
Network Protocols
o Run over physical media
o Protocols govern how communicating parties interact
– Internet Protocol (IP)
– Transmission Control Protocol (TCP) – Hypertext Transfer Protocol (HTTP)
– File Transfer Protocol (FTP)
– Simple Mail Transfer Protocol (SMTP)
o Set by standards bodies
– Internet Engineering Taskforce
– International Telecommunications Union
– IEEE
– Industry organisations (World Wide Web Consortium)
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The Big Picture (the Internet)
o An Internet is a network of networks o Hosts prepare Internet Protocol (IP)
packets and transmit them onto their
local network
o Routers act as interconnects
between networks, storing information on routes to other networks
Sender Router
Destination
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The Internet (Cont.)
o Gartner estimate 11 billion connected devices in use in 2018 – Growth rate around 1/3 per annum
o IP provides “best effort” service
– No guarantee a packet will arrive
– Connection vs. connectionless service
o UDP
– Connectionless, unreliable transfers, no flow control, fast for sender
o TCP
– Connection oriented
– Reliable, in-order byte stream transfer
– Flow control & acknowledgement of receipt
– Much greater overhead https://www.gartner.com/newsroom/id/3598917
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LM CCN Section 1.1: History of Networking
Packet vs. Circuit Switching
o Two approaches to data transfer: – Circuit switching
o Dedicated connection between machines (like a phone call)
– Packet switching
o Data sent in chunks over a shared connection
Circuit Switching Packet Switching
Often used for voice comms Normally used for data comms (although VoIP uses this method)
Dedicated resources mean Shared resources may mean poor guaranteed performance performance at busy times
Call setup required for each session Better overall utilisation of available bandwidth
Expensive Packets move one hop at a time, may have to queue
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Packet Switching
o Data split into packets
o Ethernet (physical transmission) header contains
source and destination MACs, and trailer contains
checksums
o Ethernet “payload” is the IP packet
o IP header includes source and destination addresses, versioning and protocol information, time to live etc.
o Packet also contains information on sequencing,
enabling the packets to be reassembled in the correct order (or to indicate missing packets)
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Store and Forward Delay
o Packet switched networks must wait for an entire packet to arrive before passing it on
– This introduces delays relative to circuit switching
o Assume a packet length of L bits, and a bit rate of R bps
– Time for packet to traverse a single link in then L/R seconds – Multiplies with number of hops
– In the network below delay = 3L/R
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LM CCN Section 1.1: History of Networking
IP Addressing
o IP uses hierarchical addressing
– Address consists of Network ID + Host ID
o IPv4 has 32-bit addresses
– 4 8-bit values separated by dots (dotted decimal notation) – 128.253.0.17
– Easy translation into binary
o Port numbers can be added to refer to specific services local to a machine
o Easy to remember domain names can be mapped to IP addresses
– The Domain Name System (DNS) stores the mappings o IPv6 uses 128 bit addresses
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IP Address Classes
o IP addresses traditionally split into classes to allow easy management based on expected size
– Subnet masks used to further sub-divide space within a range
Class Range
Major Original Users
A 0.0.0.0 to 127.255.255.255
Large companies (e.g. Xerox)
B 128.0.0.0 to 191.255.255.255
Universities / education
C 192.0.0.0 to 223.255.255.255
Other Users
D 224.0.0.0 to 239.255.255.255
Multicast groups
E 240.0.0.0 to 255.255.255.255
Reserved for future use
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Summary
o Network basics
– What is a communications network? – Evolution of network architectures
– Network addressing
o There’s plenty of self-study time on this course, so please do read more!
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