Transcript telecommunication basics

LIS508 lecture 7:
introduction to networks
Thomas Krichel
2003-11-19
Structure
•
•
•
•
General things about networks
History of Internet
LANs and Ethernet
The TCP/IP model
•
discussion mostly based on
Tanenbaum’s “computer networks”
classic book….
Computer network
• Definition:
– A computer network is a collection of autonomous
computers
– The distributed nature of the system is apparent to the
user
• Motivation
–
–
–
–
Resource sharing
Increase reliability
Improve scalability
Money savings through use of PCs
Progress in computers
• Moore’s law: the power of computers doubles
roughly every 18 months.
–
–
–
–
–
–
1985 - 386 Processor - 275,000 transistors
1989 - 486 DX Processor - 1,180,000 transistors
1993 - Pentium Processor - 3,100,000 transistors
1997 - Pentium II Processor - 7,500,000 transistors
1999 - Pentium III Processor - 24,000,000 transistors
2000 - Pentium 4 Processor - 42,000,000 transistors
Power input in networks
• The speed of network connections has
improved much faster than that.
• But since computer network links
computers, progress in network speed has
been held up by computers being slow!
• The conclusion should be that progress in
network technology will go on and will
affect more of our lives.
• We are only at the beginning of the wired
age!
Computer networks for communication
• Access to remote information
– Data sources
– Software
– E-commerce
– Video on demand
• Person to person communication
– Email
– Video conferencing
– Interactive television
Types of networks by technology
• Broadcasting network
– any message issued by one computer is
received by all computers on the network
• Point-to-point network
– Circuit switched: there is one physical link that
is being made between two machines that
need to communicate. ex.: telephone
– Packet switched: the communication is
broken into pieces. Each piece is sent
individually. ex: Internet
Types
• LAN
– Bounded size,
• bus topology: one cable from first to last machine
• ring topology: one cable in circular for
• star topology: all cables go to a central machine.
– High speed and reliability
• WAN
– Interconnection of a large number of hosts
– Has transmission lines and routers
– Has an irregular topology, often with subnets
WAN example
• The university campus it Westchester has
one LAN linking all the computers
together. Student and office facilities are
separate.
• At the center, there is a gateway machine
that send all the traffic to the Brooklyn
campus.
• There, there is another set of machines
that send out-of-campus traffic out of
campus
an internet
• An internet is a collection of networks that
can be used together.
– It does not have a known topology.
– Parts of it are controlled by different
organizations.
– It uses interconnects many types of networks.
• The most famous internet is the Internet.
Network modeling
• Usually networks are modeled as layers
• Purpose of layer is to carry out services for
the higher layer in a way that is
transparent to the higher layer.
– Layers communicate with their peers
according to known protocols
– Between layers in the same machine there is
an interface.
Service types
• Connection oriented / connectionless
– phone conversation
– datagram
• Reliable / non-reliable
– Online video
– File transfer
example
• http is an application protocol on the
Internet.
– It is the protocol that web servers and web
clients use
– It is also used in some other instances.
• http relies on a transport service to
transport data from one machine to
another. This transport protocol is called
TCP. This happens on a lower layer.
The Internet
• The Internet is kept together by two key
protocols
– The Internet protocol IP.
– And the transmission control protocol TCP.
• TCP relies on IP to provide services, thus
IP is on a lower layer than TCP.
• Both are commonly referred to as TCP/IP.
Origins of TCP/IP
• 1957: USSR launches the Sputnik
• US worried about command and control
structure after a nuclear attack
• Early 60s Paul Baran promotes packet
switching rather than circuit switching.
• Mid 60s: Pentagon says that it wants this,
gives grants to ARPA.
ARPAnet original design
• Network nodes have host computers and router
computer
• Hosts sends messages smaller than 8061 bits
• routers breaks it up into packets smaller than
1008 bits
• all router are connected by transmission lines
• each router connected to 2 others
• store and forward principle
implementation
• 12k times 16 bit words memory minicomputer
without hard disk as routers connected by
56kbps leased phone lines
• life with four hosts in 1969–12
• over 30 hosts in 1972–09
• protocol research leads to TCP/IP in 1974
• integrated into Berkeley UNIX, freely available
• Internet research group developing protocols
• 1979 Internet research group reorganized to
Internet Control and Configuration Board
More history
• 1980: MILNET split off the ARPAnet
• CSNET set up
– links researchers at non-ARPA contract institutions to
the ARPAnet
– ran on a single box with dial-up lines since late 70s
• 1984 NSF links adds a router to it
supercomputers, sets up NSFnet,
– the first purely TCP/IP network, on 56kbps.
– additional funding for (eventually 20) regional
networks connect to the backbone
• 1990 ANS (MERIT,MCI,IBM) take over NSFnet
The Internet now
• Connects millions of computers worldwide.
• Each computer is part of a local network.
This network is sometimes very small.
• If you have problems connecting to the
Internet, it is most likely a local problem,
rather than the Internet being “down”.
LAN
• A LAN generally operates a broadcasting
network.
• Something that is transmitted by one
station is heard by all other stations
• An individual message is called a frame.
• This creates a media access control
(MAC) problem. When one station issues
a frame, it destroys a frame from another
station, through frame collision.
Ethernet
• comes from the term "luminiferous ether".
• Today the name for a family of LAN
protocols implementing CSMA/CD
protocol for the MAC problem.
• CSMA/CD stands for carrier sensitive
media access with collision detection.
• Initially only referred to IEEE 802.3
standard
• Can run over a variety of physical devices.
IEEE 802.3 history
• 1980 first version following work by DEC,
Intel and XEROX
• 1982 version two released
• 1983 Novell creates its own version…
• 1990 support for twisted pair cable added
• Over time, a whole set of standards have
emerged to deal with other applications
such as wireless devices.
10baseT
• This is most widely used physical
infrastructure today.
• It runs over twisted-pair cable and RJ-45
jack.
• Cables are cheap, transmission is fast,
.59c
• Maximum length of cable about 150m,
thus not good for bus architecture.
Fiber optic cable
• This type of cable is a lot faster.
• It uses light to transmit signal, so it is
almost as fast as the speed of light.
• It has no problems of loss of signal over
long distances.
• But it its more expensive.
• Only used for transmissions of lots of data,
between hubs.
other devices
• “repeater” is a device that amplifies an electric
signal so that it can travel over some more wire.
• “hub” is a repeater with a lot of outgoing wires.
Hubs are dump, or smart. A smart hub can be
inspected by a monitoring device to see what the
traffic is doing there.
• A “bridge” or “switch” is a device that links
different LANs together. In normal “promiscuous”
mode, it receives signals from all LANs. It will
know which MAC address is on which LAN and
transmit echo signal to the right LAN.
MAC address
• A physical address burned onto each
network interface card used on a LAN.
• Forms an address for your computer on a
LAN
• It is 6 bytes long, written in hex, usually
written with each byte separated by “:”.
• 2 power 48 addresses, that is about 11000
addresses for every inhabitant of the
planet.