Dominating technologies in the past three centuries

1
Introduction

• Chapter 1

2
Dominating technologies in the past three
centuries

• The 18th century the time of the great
  mechanical systems accompanying the Industrial
  Revolution.
• The 19th century the age of the steam engine.
• The 20th century the key technology has been
  information gathering, processing, and
  distribution. E.g., telephone, radio, TV,
  computer, and satellites.

3
The Trends

• The differences between collecting, transporting,
  storing, and processing information are quickly
  disappearing.
• The merging of computers and communications has
  had a profound influence on the way computer
  systems are organized.
• The concept of the computer center' is rapidly
  being replaced by one in which a large number of
  separate but interconnected computers do the job.
  These systems are called computer networks.

4
What is a computer network?

• The term of computer networks means an
  interconnected collection of autonomous
  computers. Two computers are said to be
  interconnected if they are able to exchange
  information.
• The key difference between a computer network and
  a distributed system
• A distributed system is a collection of
  independent computers appears to its users as a
  single coherent system. Usually, it has a single
  model or paradigm that it presents to the users,
  which is often implemented by a layer of software
  on top of OS, called middleware. E.g. WWW is a
  distributed system.
• In a computer network, this coherence, model, and
  software are absent. A user must explicitly log
  onto one machine (e.g., rlogin), submit jobs
  remotely (e.g., rsh), move files around (e.g.,
  rcp, ftp, uucp), and generally handle all the
  network management personally.

5
Uses of Computer Networks

• Why are people interested in computer networks
  and what can they be used for?
• Business Applications
• Home Applications
• Mobile Users
• Social Issues

6
Business Applications of Networks

• Resource sharing A network is needed because of
  the desire to make all programs, data, and
  equipment available to anyone on the network
  without regard to the physical location of the
  resource and the user.
• High reliability A network may have alternative
  sources of supply (e.g., replicated files,
  multiple CPUs, etc.). In case of one resource
  failure, the others could be used and the system
  continues to operate at reduced performance.
  This is a very important property for military,
  banking, air traffic control, and many other
  applications.
• Saving money A network may consist of many
  powerful small computers, one per user, with
  data kept on one or more shared file server
  machines, which offers a much better
  price/performance ratio than mainframes.In this
  model, the users are called clients, and the
  whole arrangement is called the client-server
  model.

7
A network with two clients and one server
8
The client-server model involves requests and
replies
9

• Powerful communication medium Networks make
  cooperation among far-flung groups of people easy
  where it previously had been impossible.
  In the long run, the use of networks
  to enhance human-to-human communication may prove
  more important than technical goals such as
  improved reliability. E.g., Email, real-time
  collaborative editors/word-processors, and video
  conferencing.
• E-business (B2B), or e-commerce (B2C)

10
Home Network Applications

• Access to remote information
• Person-to-person communication
• Interactive entertainment
• Electronic commerce

11
Access to remote information

• Starting in the 1990s, computer networks began to
  start delivering services to private individuals
  at home.
• Home reservations for airplanes, trains, hotels,
  restaurants, theaters, and so on, anywhere in the
  world with instant confirmation.
• Home banking and shopping.
• On-line and personalized electronic newspapers,
  journals, and libraries.
• Digital library.
• All these applications involve interactions
  between a person and a remote database.

12
Person-to-person communication

• The 21st Century's answer to the 19th Century's
  telephone.
• Electronic mails for everyone, which may contain
  digitized voice, pictures, moving TV and video
  images (and even smell !).
• Instant messaging, or chat room.
• Worldwide newsgroups for the population at large,
  and cover every conceivable topics.
• Internet phone, video phone, Internet radio.
• It is sometime said that transportation and
  communication are having a race, and whichever
  one wins will make the other obsolete.

13
Peer-to-peer systems

• In peer-to-peer system there are no fixed
  clients and servers.

14
Interactive entertainment

• Video on demand (the killer application) the
  user can select any movie or TV program ever
  made, in any country, and have it displayed on
  his screen instantly.
• Interactive films the user may choose
  alternative scenarios for the story direction.
• Live and interactive TV audience may
  participate in quiz shows, and so on.
• Multi-person real-time games (maybe the
  alternative killer application)
  hide-and-seek, flight simulators, etc. If done
  with goggles and 3-dimensional real-time,
  photographic-quality moving images, we have a
  kind of worldwide shared virtual reality.
• The ability to merge information, communication,
  and entertainment will surely give rise to a
  massive new industry based on computer
  networking.

15
Some forms of e-commerce
16
Mobile Network Users

• Combinations of wireless networks and mobile
  computing.

17
Network Hardware

• Local Area Networks
• Metropolitan Area Networks
• Wide Area Networks
• Wireless Networks
• Home Networks
• Internetworks

18
Networks classification

• Two important dimensions for classifying
  networks
• transmission technology, and
• scale.
• Two types of transmission technology
• Broadcast links
• Point-to-point links

19
Broadcast networks

• Broadcast networks have a single communication
  channel shared by all the machines on the
  network. They work as follows
• Packets sent by any machine are received by all
  the others.
• An address field within the packet specifies for
  whom it is intended.
• Upon receiving a packet, a machine checks the
  address field. If it is intended for itself, it
  processes the packet otherwise, it is just
  ignored.
• It is also possible to address all (broadcasting)
  or a subset of the machines (multicasting). A
  common scheme
• The address consisting of all 1 bits is reserved
  for broadcast.
• All addresses with the high-order bit set to 1
  are reserved for multicasting.
• The remaining addresses bits form a bit map
  corresponding to groups.
• Each machine can subscribe'' to any or all of
  the groups.

20
Point-to-point networks

• Point-to-point networks consist of many
  connections between individual pairs of machines.
  
• Multiple routes and intermediate machines may
  exist between a pair of machines, so routing
  algorithms play an important role here.
• A general rule (with many exceptions) smaller
  and localized networks tend to use broadcasting,
  whereas larger networks usually are
  point-to-point.

21
Classification of interconnected processors by
scale
22
Local Area Networks

• Three distinguishable characteristics for LANs
• Size usually a diameter of not more than a few
  kilometers, with bounded and known worst-case
  transmission time, making special design and
  simple management possible.
• Transmission technology usually a shared cable
  running at speeds of 10 to 100 Mbps (and even
  higher, up to 10Gbps), with delay of tens of
  microseconds and few errors.
• Topology bus (e.g., Ethernet), ring (e.g., IBM
  token ring), etc.

23
Two broadcast networks. (a) Bus. (b) Ring.

• Two broadcast networks
• (a) Bus
• (b) Ring

• Allocation of the shared channel
• Each machine is statically allocated a time slot
  to transmit, and gets its turn by round robin.
• Each machine is dynamically allocated a time slot
  on demand.
• Centralized method uses an arbitration unit to
  determine who goes next.
• Decentralized method allows each machine to
  decide for itself.

24
Metropolitan Area Networks
MAN uses one or two cables but does not contain
switching elements. It covers an entire city and
may be related to the local cable TV network.

• A metropolitan area network based on cable TV.

25
Wide Area Networks

• A WAN spans a large area, often a country or
  continent. A WAN consists of two parts
• Application part Machines for running user
  programs are called hosts.
• Communication part The hosts are connected by
  the communication subnet, or just subnet, whose
  job is to carry messages from host to host.
• The subnet consists of two components
• Transmission lines (circuits, channels, or
  trunks) move bits between machines.
• Switching elements (routers) are specialized
  computers used to connect two or more
  transmission lines.

26
Relation between hosts on LANs and the subnet
27
Main characters of WANs

• A WAM contains numerous cables or telephone
  lines, each one connecting a pair of routers.
• For those without direct connection,
  communication takes place indirectly via other
  routers.
• When a message (a packet) is sent from one router
  to another, it is received at each intermediate
  router in its entirety, stored there until the
  required output line is free, and then forwarded.
  A subnet using this principle is called
  point-to-point, store-and-forward, or
  packet-switched subnet.
• WANs may also use broadcast channels, such as
  satellites or ground radio systems.

28
A stream of packets from sender to receiver
29
Wireless Networks

• Categories of wireless networks
• System interconnection
• Wireless LANs
• Wireless WANs

30
Wireless Networks (2)

• Bluetooth configuration
• Wireless LAN

31
Wireless Networks (3)

• (a) Individual mobile computers
• (b) A flying LAN

32
Home Network Categories

• Computers (desktop PC, PDA, shared peripherals)
• Entertainment (TV, DVD, VCR, camera, stereo, MP3)
• Telecomm (telephone, cell phone, intercom, fax)
• Appliances (microwave, fridge, clock, furnace,
  airco)
• Telemetry (utility meter, burglar alarm, babycam).

33
Distinctive Properties of Home Networks

• The network and devices have to be easy to
  install.
• The network and devices have to be foolproof in
  operation.
• Low price is essential for success.
• The main application is likely to involve
  multimedia, so the network needs sufficient
  capacity.
• It must be possible to start out with one or two
  devices and expand the reach of the network
  gradually.
• Security and reliability will be very important.

34
Internetworks
A collection of interconnected networks is called
an internetwork or just internet. The Internet
refers to a specific worldwide internet that is
widely used to connect universities, government
offices, companies, and private individuals.
Both the general internet and the specific
Internet will be extensively covered by this
course.
35
Network Software

• Protocol Hierarchies
• Design Issues for the Layers
• Connection-Oriented and Connectionless Services
• Service Primitives
• The Relationship of Services to Protocols

36
Protocol Hierarchies

• To reduce their design complexity, most networks
  are organized as a series of layers or levels.
  
• Each layer offers certain services to the higher
  layers, shielding those layers from the details
  of how the offered services are actually
  implemented.
• Layer on one machine carries on a conversation
  with layer on another machine. The rules and
  conventions used in this conversation are
  collectively known as the layer protocol.
• The entities comprising the corresponding layers
  on different machines are called peers, which
  communicate using the protocol.

37
A Five-layer Protocol Hierarchy

• Between each pair of adjacent layers there is an
  interface, which defines primitive operations and
  services the lower layer offers to the upper one.
  
• The set of layers and protocols is called the
  network architecture, which must contain enough
  information to allow a software/hardware
  implementation which correctly obey the
  appropriate protocol.
• Neither the details of the implementation nor the
  specification of the interfaces are part of the
  architecture because they are not visible from
  the outside.

38
The philosopher-translator-secretary architecture
39
The philosopher-translator-secretary architecture

• Two philosophers (peer processes in layer 3), one
  speaking English and the other speaking French,
  want to communicate.
• Each one has to use a translator (peer processes
  at layer 2).
• Each translator contacts a secretary (peer
  processes at layer 1) for message transmission.
• For the philosopher 1 to convey his message to
  his peer, he passes his message in English to his
  translator, who may translate it into Dutch, or
  other language, depending on the layer 2
  protocol.
• The translator then gives the message to his
  secretary to transmit, by fax, telephone, email,
  or some other means, depending on layer 1
  protocol.
• When the message arrives, the peer secretary
  hands the message to the peer translator, who
  translates it into French and passed across the
  2/3 interface to philosopher 2.

40
Information flow supporting virtual communication
in layer 5
The important thing to understand about the
above Figure is the relation between the virtual
and actual communication and the difference
between protocols and interfaces. The lower
layers of a protocol hierarchy are frequently
implemented (in whole or in part) in hardware or
firmware.
41
Design Issues for the Layers

• Addressing a mechanism for identifying senders
  and receivers -- some form of addressing for both
  machines and processes.
• Directions for data transfer simplex,
  half-duplex, full-duplex communication.
• Logical channels at least two per connection.
• Error control both sides must use the same
  error-detecting and error-correcting codes.
  Besides, some way is needed to tell which
  messages have been correctly received and which
  have not.
• Message sequencing or ordering message pieces
  are numbered, but what should be done with pieces
  out of order ?
• Flow control keep a fast sender from swamping a
  slow receiver with data. Some kind of feedback
  from receiver is needed.
• Mechanisms for disassembling, transmitting, and
  reassembling messages. A related issue is what to
  do when processes insist upon transmitting data
  in very small units.
• Multiplexing using the same connection for
  multiple, unrelated conversations. E.g., a few
  physical circuits are used for all virtual
  connections.
• Routing which path should be chosen ? The
  decision may be split over several layers.

42
Connection-Oriented and Connectionless Services

• Connection-oriented service is modeled after the
  telephone system. The essence of a connection is
  that it acts like a tube the sender pushes
  objects in at one end, and the receiver takes
  them out in the same order at the other end.
  Connection-oriented services are suitable for
  communicating for a long time between two
  parties.
• Connectionless service is modeled after the
  postal system. Each message carries the full
  address and is routed independently. The order is
  not guaranteed. Connectionless services are
  suitable for sending short messages.

43
Quality of service

• Reliable services guarantee they never lose
  data. This can be implemented by
  acknowledgements. The overhead introduced are
  often worth it, but sometimes undesirable
  (unreliable services).
• A reliable connection-oriented service is
  appropriate for file transfer.
• An unreliable connection-oriented service is
  appropriate for digitized voice traffic.
• A reliable connectionless service (acknowledged
  datagram service) is appropriate for registered
  mails.
• An unreliable connectionless service (datagram
  service) is appropriate for electronic junk mail
  (with a high probability of arrival, but no
  guarantee).
• Another connectionless service is the
  request-reply, commonly used to implement the
  client-server model.

44
Six different types of services
45
Service Primitives
A service is formally specified by a set of
primitives available to a service user to
interact with the service provider. These
primitives tell the service provider to perform
some action or report on an action taken by a
peer entity.

• Five service primitives for implementing a simple
  connection-oriented service.

46
Service Primitives (2)

• Packets sent in a simple client-server
  interaction on a connection-oriented network.

47
Services to Protocols Relationship

• Services and protocols are distinct concepts.
• A service is a set of primitives (operations)
  that a layer provides to the layer above it.
  The service defines what operations (not the
  format and meaning of the exchanged data) the
  layer is prepared to perform on behalf of its
  users.
• A protocol is a set of rules governing the format
  and meaning of the frames, packets, or messages
  that are exchanged by the peer entities within
  the same layer. Entities use
  protocols in order to implement their service
  definitions. The change of protocols may not be
  visible to the service users (the service remain
  the same).
• Many older protocols (e.g., TCP/IP) did not
  distinguish the service from the protocol, which
  is now regarded as a serious blunder.

48
Reference Models

• The OSI Reference Model
• The TCP/IP Reference Model
• A Comparison of OSI and TCP/IP
• A Critique of the OSI Model and Protocols
• A Critique of the TCP/IP Reference Model

The OSI model was proposed by the International
Standards Organization. It is also called ISO OSI
(Open System Interconnection) Reference Model.
49
The OSI Reference Model
50
Design principles of OSI model

• The principles that were applied to arrive at the
  seven layers are
• A layer should be created where a different level
  of abstraction is needed.
• Each layer should perform a well defined
  function.
• The function of each layer should be chosen with
  an eye toward defining internationally
  standardized protocols.
• The layer boundaries should be chosen to minimize
  the information flow across the interfaces.
• The number of layers should be large enough that
  distinct functions need not be thrown together in
  the same layer out of necessity, and small enough
  that the architecture does not become unwieldy.
• Note the OSI model itself is not a network
  architecture because it does not specify the
  exact services and protocols to be used in each
  layer. It just tells what each layer should do.

51
The physical layer

• The physical layer is concerned with transmitting
  raw bits over a communication channel.
• The major goal making sure that when one side
  sends a 1 bit, it is received by the other side
  as a 1 bit, not as a 0 bit.
• Typical questions (main design issues)
• How many volts should be used to represent a 1
  and how many for a 0.
• How many microseconds a bit lasts.
• Whether transmission may proceed simultaneously
  in both directions.
• How the initial connection is established and how
  it is torn down when both sides are finished.
• How many pins the network connector has and what
  each pin is used for.
• These issues belong to the domain of the
  electrical engineer.

52
The data link layer

• It takes a raw transmission facility from the
  physical layer and transforms it into a line that
  appears free of undetected transmission errors to
  the network layer.
• Main design issues
• Break the input data up into data frames and
  transmit the frames sequentially.
• Process the acknowledgement frames sent back by
  the receiver.
• Retransmit lost or damaged frames, and solve the
  problem of possible duplicate frames.
• Offer several different service classes to the
  network layer, each of a different quality and
  price.
• Use some traffic regulation mechanism to let the
  transmitter know how much buffer space the
  receiver has at the moment. This flow regulation
  is frequently integrated with error handling.
• A Medium ACcess (MAC) sublayer is introduced to
  deal with the access control over the shared
  channel in broadcast networks.

53
The network layer

• The main task of this layer is to control the
  operation of the subnet.
• Routing from source to destination static,
  dynamic (per session or per packet). Congestion
  control.
• Allowing heterogeneous networks to be
  interconnected (internetworking) different
  addressing, length of packet, and protocols.
  
• Accounting count the number of packets or
  character per customer.
• In broadcast networks, the routing problem is
  simple, so the network layer is often thin or
  even nonexistent.

54
The transport layer

• The basic function of this layer is to
• accept data from the session layer,
• split it up into smaller units if need be,
• pass these to the network layer, and
• ensure that the pieces all arrive correctly at
  the other side.
• Type of services
• An error-free point-to-point channel that
  delivers messages in the order in which they were
  sent.
• Isolated messages with no guarantee about the
  order of delivery.
• Broadcasting of messages to multiple
  destinations.
• The type of service is determined when the
  connection is established.
• The transport layer is a true source-to-destinatio
  n or end-to-end layer. Flow control between hosts
  is also needed but different from between routers
  (similar principles will apply to both).

55
The session and presentation layers

• The session layer provides enhanced services
  useful in some applications, e.g., remote login,
  remote file transfer.
• The presentation layer is concerned with the
  syntax and semantics of the information
  transmitted. Typical services
• Encode data in a standard agreed upon way to
  facilitate information exchange among
  heterogeneous systems using different codes for
  strings (e.g., ASCII and Unicode), integers
  (e.g., one's complement and two's complement),
  and so on.
• Data compression for reducing the number of bits
  to be transmitted.
• Cryptography for privacy and authentication.

56
The application layer

• This layer contains a variety of commonly needed
  protocols.
• Typical services
• Domain Name Service.
• Transfer files among different file systems.
• Electronic mails among different systems.
• Telnet.
• World Wide Web.

57
The TCP/IP reference model

• The TCP/IP model was used in the grandparent of
  all computer networks, the ARPANET, and its
  successor, the worldwide Internet.
• Major design goals
• The ability to connect multiple networks together
  in a seamless way.
• The ability to survive loss of subnet hardware,
  with conversations not being broken off.
• A flexible architecture for supporting
  applications with divergent requirements, ranging
  from transferring files to real-time speech
  transmission.
• All these goals led to the choices of a
  packet-switching network based on a
  connectionless internetwork layer, called the
  internet layer.
• The internet layer the official packet format
  and protocol at this layer is called IP (Internet
  Protocol). Its job is to inject IP packets into
  any network and have them travel independently to
  the destination (potentially on a different
  network).
• The TCP/IP internet layer is similar in
  functionality to the OSI network layer.

58
The TCP/IP reference model

• The transport layer It is the same in
  functionality as the OSI transport layer. Two
  official end-to-end protocols
• TCP (Transmission Control Protocol) a reliable
  connection-oriented protocol.
• UDP (User Datagram Protocol) an unreliable
  connectionless protocol.
• The application layer The TCP/IP model does not
  have session or presentation layers, which are of
  little use to most applications. The top
  application layer contains all the higher-level
  protocols. Many other protocols, such as HTTP
  used on the World Wide Web, have been added over
  the years.
• The host-to-network layer The layer below the
  internet layer is a great void. The TCP/IP model
  just points out that the host has to connect to
  the network using some protocol so it can send IP
  packets over it. This protocol is not defined and
  varies from host and network to network.

59
The TCP/IP reference model
60
Protocols and networks in the TCP/IP model
initially
61
Comparing OSI and TCP/IP Models

• Fundamental similarities
• The same concept of a stack of independent
  protocols.
• Similar functionality of the layers.
• The three central concepts to the OSI model
• Services which tell what the layer does, not how
  entities above it access it or how the layer
  works.
• Interfaces which tell the processes above it how
  to access it (i.e., what the parameters and
  results are), not how the layer works inside.
• Protocols which are used between peer entities
  to implement the offered services.
• The biggest contribution of the OSI model is to
  make the distinction between these three concepts
  explicit. The TCP/IP model did not clearly
  distinguish them.

62
Major differences

• The OSI model was devised before the protocols
  were invented, but the reserve was true with the
  TCP/IP model.
• The OSI model has seven layers, but the TCP/IP
  model has only five layers.
• The OSI model supports both connection-oriented
  and connectionless communication in the network
  layer, but only connection-oriented communication
  in the transport layer. The TCP/IP model has only
  connectionless mode in the internet layer, but
  has both modes in the transport layer.

63
A Critique of the OSI Model and Protocols

• Why OSI did not take over the world
• Bad timing
• Bad technology
• Bad implementations
• Bad politics

64
Bad Timing

• The apocalypse of the two elephants.

65
A Critique of the TCP/IP Reference Model

• Problems
• Service, interface, and protocol not
  distinguished
• Not a general model
• Host-to-network layer not really a layer
• No mention of physical and data link layers
• Minor protocols deeply entrenched, hard to replace

66
Hybrid Model

• The OSI model minus the session and presentation
  layers is exceptionally useful for discussing
  computer networks, but the OSI protocols have not
  become popular.
• The TCP/IP model is practically nonexistent, but
  the protocols are widely used.
• The following hybrid reference model to be used
  in this course.

67
Example Networks

• The Internet
• Connection-Oriented Networks X.25, Frame
  Relay, and ATM
• Ethernet
• Wireless LANs 80211

68
An early proposal

• (a) Structure of the telephone system.
• (b) Barans proposed distributed switching system.

69
The ARPANET

• It is the creation of ARPA (later DARPA, now
  ARPA), the (periodically Defense) Advanced
  Research Projects Agency of the US Dept. of
  Defense.
• Much of our present knowledge about networking is
  a direct result of the ARPANET project.
• ARPANET technologies
• IMP (Interface Message Processor) Originally
  Honeywell DDP-316 mini. with 12K 16-bit words
  memory. Replaced several times by more powerful
  machines. Some IMPs allow direct terminal
  connection. They were called TIPs (Terminal
  Interface Processors).
• IMPs were connected by 56 kbps or 230.4 kbps
  leased lines. Each IMP could originally handle
  only one to four hosts, and subsequently tens of
  hosts and hundreds of terminals simultaneously.

70
The original ARPANET design
ARPANET did not follow the OSI model at all (it
predates OSI by more than a decade). The original
ARPANET design is shown below.
71
ARPANET in its first three years

• Growth of the ARPANET (a) December 1969. (b)
  July 1970.
• (c) March 1971. (d) April 1972. (e)
  September 1972.

72
TCP/IP

• The TCP/IP model and protocols were specifically
  designed to handle the interconnection of the
  vast number of WANs and LANs comprising the ARPA
  internet.
• TCP/IP protocols were then integrated in Berkeley
  UNIX by a convenient program interface to the
  network (sockets), which makes TCP/IP very
  widespread.
• To facilitate finding hosts in the ARPANET, DNS
  (Domain Naming System) was created to organize
  machines into domains and map host names onto IP
  addresses.
• By 1990, the ARPANET had been overtaken by newer
  networks that it itself had spawned, so it was
  shut down and dismantled

73
CSNET
By the late 1970s, the NSF (National Science
Foundation, USA) set up CSNET to provide
networking facilities to the computer science
community in USA as a whole (particularly those
without access to ARPANET).
CSNET was centered
around a single machine (CSNET-RELAY) at BBN that
supports dial-up lines (PHONENET) and had
connections to the ARPANET and other networks
(e.g., X.25, CYPRESS). Its major services
include emails, file transfer, and remote login.

74
The NSFNET backbone in 1988
By 1984, NSF began designing a high-speed
network, called NSFNET, that would be open to
all university research groups. NSFNET consists
of a backbone network connecting six
supercomputer centers, and about 20 regional
networks.
Software technology TCP/IP. Backbone speeds 56
kbps, 448 kbps, 1.5 Mbps, 45 Mbps (ANSNET)
75
The Internet

• After the interconnection of ARPANET and NSFNET
  (using TCP/IP as the only official protocol),
  many regional networks in the world joined up.
• Sometime in the mid-1980s, people began viewing
  the collection of networks as an internet, and
  later as the Internet.
• By 1990, the Internet consisted of 3000 networks
  and 200,000 computers.
• In Jan. 1992, the Internet Society was set up to
  promote the use of the Internet.
• By 1995, the Internet contained multiple
  backbones, hundreds of regional networks, tens of
  thousands of LANs, millions of hosts, and tens of
  millions of users.
• The size doubles approximately every year. The
  current number of Internet users is unknown, but
  is certainly hundreds of millions and will hit 1
  billion fairly soon.

76
The role of TCP/IP in the Internet

• The glue that holds the Internet together is the
  TCP/IP model and TCP/IP protocol stack.
• What does it actually mean for a machine to be on
  the Internet ?
• It runs the TCP/IP protocol stack,
• has an IP address, and
• has the ability to send IP packets to all other
  machines on the Internet.

77
Internet Usage

• Traditional applications (1970 1990)
• E-mail
• News
• Remote login
• File transfer
• By the early 1990, one new application, the WWW
  (World Wide Web) changed the picture and brought
  hundreds of millions of new, non-academic users
  to the Internet.

78
Architecture of the Internet

• Overview of the Internet.

79
Connection-oriented Networks

• A public network is a subnet owned by the network
  operator (government or private companies),
  providing communication service for the
  customers' hosts and terminals. Analogous to the
  public telephone system.
• Many old public networks use the OSI model and
  the standard CCITT or ISO protocols for all the
  layers.
• For the lowest three layers, CCITT has issued
  recommendations, known collectively as X.25
• The physical layer protocol (X.21) specifies the
  physical, electrical, and procedural interface
  between the host and the network.
• The data link layer protocol deals with
  transmission errors on the telephone line between
  the user's equipment (host or terminal) and the
  public network.
• The network layer protocol deals with addressing,
  flow control, delivery confirmation, interrupts
  and related issues.
• X.25 provides a reliable and
  connection-oriented packet (up to 128 bytes)
  delivery service, running at speeds up to 64
  kbps.

80
Broadband ISDN and ATM

• ISDN (Integrated Services Digital Network) is an
  international undertaking to replace the entire
  worldwide telephone system and all the
  specialized networks with a single integrated
  digital network for all kinds of information
  transfer services.
• The new B-ISDN service offersr
• video on demand,
• live TV from many sources,
• full motion multimedia electronic mail,
• CD-quality music,
• LAN interconnection,
• high-speed data transport, and
• many other services, all over the telephone line.
  
• The underlying technology that makes B-ISDN
  possible is called ATM (Asynchronous Transfer
  Mode) because it is not synchronous (tied to a
  master clock), as most long distance telephone
  lines are.

81
ATM Virtual Circuits

• A virtual circuit.

82
ATM cell
The basic idea behind ATM is to transmit all
information in small, fixed-size packets called
cells.

• ATM is both a technology (hidden from the users)
  and potentially a service (visible to the users).
  Main reasons for choosing cell switching
• It is highly flexible and can handle both
  constant rate traffic (audio, video) and variable
  rate traffic (data) easily.
• At the very high speeds envisioned (gigabits),
  digital switching of cells is easier than using
  traditional multiplexing techniques.
• It can provide broadcasting which is essential
  for TV distribution and many other applications.
  
• ATM networks are connection-oriented. Cell
  delivery is not guaranteed, but their order is.
  The most common speeds for ATM networks 155 Mbps
  (used by ATT's SONET for high definition TV),
  and 622 Mbps (for carrying four 155-Mbps
  channels).

83
The ATM Reference Model

• The ATM reference model.

84
The ATM Reference Model (2)

• The ATM layers and sublayers and their functions.

85
Ethernet

• Architecture of the original Ethernet.

86
Wireless LANs

• (a) Wireless networking with a base station.
• (b) Ad hoc networking.

87
Wireless LANs (2)

• The range of a single radio may not cover the
  entire system.

88
Wireless LANs (3)

• A multicell 802.11 network.

89
Network Standardization

• Benefits of standardization
• Allow different computers to communicate.
• Increase the market for products adhering to the
  standard.
• Two categories of standards
• De facto (Latin for from the fact'') standards
  are those that have just happened, without any
  formal plan. E.g., IBM PC for small office
  computers, UNIX for operating systems in CS
  departments.
• De jure (Latin for by law'') standards are
  formal legal standards adopted by some authorized
  standardization body.
• Two classes of standard organizations
• Organizations established by treaty among
  national governments.
• Voluntary, nontreaty organizations.

90
Who's who in the telecommunication world

• Key words (read the text for details)
• Common carriers private telephone companies
  (e.g., ATT, USA).
• PTT (Post, Telegraph Telephone )
  administration nationalized telecommunication
  companies (most of the world).
• ITU (International Telecommunication Union) an
  agency of the UN for international
  telecommuni-cation coordination.
• CCITT (an acronym for its French name) one of
  the organs of ITU (i.e., ITU-T), specialized for
  telephone and data communication systems.

91
ITU

• Main sectors
• Radiocommunications
• Telecommunications Standardization
• Development
• Classes of Members
• National governments
• Sector members
• Associate members
• Regulatory agencies

92
Who's who in the standards world

• ISO is a voluntary, nontreaty organization
  founded in 1946, with members from 89 member
  countries.
• The procedure for ISO to adopt standards
• First, one of the national standards organization
  feels the need for an international standard in
  some area.
• A working group is then formed to come up with a
  CD (Committee Draft).
• The CD is then circulated to all the member
  bodies, which get six months to criticize it.
• If a substantial majority approves, a revised
  document, called a DIS (Draft International
  Standard) is produced and circulated for comments
  and voting.
• Based on the results of this round, the final
  text of the IS (International Standard) is
  prepared, approved, and published.
• IEEE (Institute of Electrical and Electronics
  Engineers), the largest professional organization
  in the world, is another major player in the
  standards world, e.g., IEEE's 802 standard for
  LANs has been taken over by ISO as the basis for
  ISO 8802.

93
IEEE 802 Standards
The 802 working groups. The important ones are
marked with . The ones marked with ? are
hibernating. The one marked with gave up.
94
Metric Units

• The principal metric prefixes.

95
Who's who in the Internet standards world

• Read the text for information about the IAB
  (Internet Architecture Board).
• A famous remark about Internet standardization
  rough consensus and running code.