Ch.4. Networking and the Internet

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Ch.4.Networking and the Internet

• Sec (4.1)Network Fundamentals

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Network classifications

1. Local Area Network (LAN)
2. Metropolitan Area Network (MAN)
3. Wide Area Network (WAN)

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Network classifications

• A LAN normally consists of a collection of
  computers in a single building or building
  complex, for ex. The computers in the university
  campus or those in a manufacturing plant might be
  connected by a LAN
• A MAN is a network of intermediate size, such as
  one spanning a local community
• A WAN links machines over a greater
  distance-perhaps in neighboring cities or on
  opposite sides of the world

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Network classifications

• There are another classifying networks is based
  on whether the network's internal operation is
  based on designs that are in the public domain or
  on innovations owned and controlled by a
  particular entity such as an individual or a
  corporation
• a network of former type is called a Open network
• a network of a latter type is called a Closed or
  Proprietary network
• an Internet is an open system TCP/IP
• Company like Novell Inc. is closed system

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There are another classification is based on the
topology of the network

1. Ring in which the machines are connected in a
   circular fashion
2. Bus in which the machines are all connected to a
   common communication line called a bus
3. Star in which one machine serves as central
   focal point to which all the others are connected

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There are another classification is based on the
topology of the network

• the star network is perhaps the oldest, having
  evolved from the paradigm of a large central
  computer serving many users.
• As the simple terminals employed by these users
  grew into small computers themselves, a star
  network emerged.
• Today, however, the bus topology, having been
  popularized under the standards known as
  Ethernet, is probably the most popular network
  topology.

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Network topology
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Network topology
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It is important to remember that a network's
topology might not be obvious from its physical
appearance

• For instance, a bus network might not appear as a
  long bus from which computers are connected over
  short links
• Each computer connected to each other by central
  location called Hub
• Hub which are the central location where are the
  computers connected in bus network
• The hub is little more than a very short bus
• All hubs is relay any signal it receives back out
  to all the machines connected to it

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There are difference between stars and bus
network

• the central device in star network is a computer
  that receives and often process messages from the
  other computers
• but the central device in the bus networks is a
  hub that merely provides a common communication
  path to all the computers

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It is important to remember that a network's
topology might not be obvious from its physical
appearance

• wireless network, using radio broadcast
  technology are becoming quite common
• hub in many of today's bus networks is
  essentially a radio relay station

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Protocols

• For a network to function reliably, it is
  important to establish rules by which network
  activities are conducted
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  ?? ????? ????? ????? ???? ?????? ???????? ???
  ??????
• Let us consider the problem of coordinating the
  transmission of messages among computers in a
  network.
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  ??????? ?? ???? ???? ?????????
• Without rules governing this communication, all
  the computers might insist on transmitting
  messages at the same time or might fail the relay
  messages when that assistance is required
• ??? ??? ??????? ???? ????? ???? ??????? ???? ??
  ??? ??????? ??? ?? ??????? ?? ??? ????? ?? ????
  ?? ????? ??????? ?????? ???? ????? ????????

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token ring protocol

• One approach to solve this problem is the token
  ring protocol, which was developed by IBM in the
  1970s and continues to be a popular protocol in
  network based on the ring topology
• ???? ??? ??????? ??? ???? token ring protocol
  ????? ?? ?????? ?? ???? ??????
• In this protocol, all the machines in the network
  transmit messages in only one common direction ,
  meaning that all messages sent over the network
  move around the ring in the same direction by
  being forwarded from computer to computer.
• ???? ?????? ???? ??????? ??? ???? ?????? ?? ?????
  ????

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token ring protocol

• and forwards a copy on around the ring, when the
  forwarded copy reaches the originating computer,
  that machine knows that the message must have
  reached its destination and removes the message
  from the ring
• Of-course, this system depends on inter machine
  cooperation
• ?????? ??? ?????? ???????? ??? ??????? ???? ??
  ??? ?? ??????? ?? ???? ??? ????????? ????? ??? ??
  ???? ???? ?????? ?? ??????
• ??? ????? ??? ??????? ?? ??? ???????

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token ring protocol

• To solve this problem, a unique bit pattern,
  called a token, is passed around the ring
• ???? ??? ??????? ????? ???? bit pattern ????
  ???? token ??????? ??? ??????
• Possession of this token gives the machine the
  authority to transmit its own message
• ?????? ??? ?? token ???? ?????? ?????? ????
  ??????? ?????? ??
• Without the token, a machine is only allowed to
  forward messages.
• ??? ??? ??? ?? token ?????? ????? ?? ?? ??? ???
  ??? ???????
• Normally, each machine merely relays the token in
  the same manner in which it relays messages.

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token ring protocol

• ?? ????? ?????? ?? ???? ?????? ?? ?????? ??? ??
  token ???? ??????? ???? ?????? ?????? ?? token
  ????? ????? ?? ??? ????? ????? ???? ???? ?? token
  ???? ????? ??????? ?????? ??? ?????? ????? ??
  token ??? ?????? ????? ??????? ?? ??? ???
  ??????? ???? ???? ?? ??? ????? ???? ??? ????? ??
  token ??? ?????? ??????
• However, if the machine receiving the token has
  messages of its own to introduce to the network,
  it transmits one message while holding the token
• When this message has completed its cycle around
  the ring, the machine forwards the token to the
  next machine in the ring
• When the next machine receives the token it can
  either forward the token immediately or transmit
  its own new message before sending the token to
  the next machine

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token ring protocol
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Ethernet protocol

• Another protocol for coordinating message
  transmission is used in bus topology networks
  that are based on the Ethernet protocol
  collection.
• ???? ???????? ??? ???? ???? ??????? ??????? ?? ??
  topology bus ? ????? ?? Ethernet protocol
  collection ??? ???? ?? Ethernet ?????? ????
  ????? ?? ??? ??????? ???? (CSMA /CD)
• To transmit message is controlled by the protocol
  known as Carrier Sense Multiple Access with
  Collision Detection (CSMA/CD)
• This protocol dictates that each message be
  broadcast to all the machines on the bus
• ??? ?????????? ???? ?? ????? ???? ??? ??????? ??
  ?? bus

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Ethernet protocol

• Each machine monitors all the messages but keeps
  only those addressed to itself
• ?? ???? ????? ?? ??????? ???? ????? ??? ?????????
  ?????? ??
• To transmit a message, a machine waits until the
  bus is silent, and at this time it begins
  transmitting while continuing to monitor the bus
• ???? ????? ?????? ????? ??? ???? ?? bus ?????
  ??? ??? ????? ???? ?????? ?? ??????? ???????? ??
  bus
• If another machine also begins transmitting, both
  machine detect the clash and pause for a brief
  random period of time before trying to transmit
  again
• ??? ??? ???? ???? ??? ??? ?????? ??? ????????
  ????? ??????? ?????? ????? ?????? ????? ???????
  ??? ?????? ????? ??? ????

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Ethernet protocol

• Under the CSMA / CD protocol each machine merely
  tries again
• ??? ?????? ?? ???? ????? ???? ????? ?? ????
  ?????? ???????? ?? ??? ?????? ??????? ???????
• ???? ???????? ??? ?? ??????? ???????? ??
  ????????? ??? ??? CSMA / CD ?? ???? ??? ????? ??
  ????

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Ethernet protocol
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Combining Networks

• Sometimes it is necessary to connect existing
  networks to form an extended communication
  system, this can be done by connecting the
  networks to form a larger version of the same
  type of network. Like bus network based on the
  Ethernet protocols, it is often possible to
  connect the buses to form a single large bus.
  This is done by means of different devices known
  as
• repeater
• bridges
• switches

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1) Repeater

• which is little more than a device that connects
  two buses to form a single long bus. The repeater
  simply passes signals back and forth between the
  two original buses without considering the
  meaning of the signals

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2) Bridges

• a similar to, but more complex than a repeater.
  Like a repeater, it connected two buses, but it
  dose not necessarily pass all messages across the
  connection.
• Instead, it looks at the destination address that
  a companies each message and forwards a message
  across the connection only when that message is
  destined for a computer on the other side
• A bridge produces more efficient system than that
  produced by a repeater

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2) Bridges
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3) Switches

• is a bridge with multiple connections, allowing
  it to connect several buses rather than just two
  .
• switch produces a network consisting of several
  buses extending from the switch as spokes on a
  wheel
• As in the case of a bridge, a switch considers
  the destination address of all messages and
  forwards only those messages for other spokes.
• Each message that is forwarded is relayed only
  into the appropriate spoke, thus minimizing the
  traffic in each spoke

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internet

• note that the generic term internet is distinct
  from the Internet. The Internet with the capital
  I refers to a particular worldwide internet that
  we will study in the other section
• In which the original networks maintain their
  individuality and continue to function as
  independent networks
• Sometimes, the networks to be connected have
  incompatible characteristics ( connected
  differences network with several protocol)
• for instance, the characteristics of a ring
  network using the token ring protocol are not
  readily compatible with an Ethernet bus network
  using CSMA/CD

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router

• it is a machine using to connection between two
  networks to form an internet
• a router is computer belonging to both networks
  that forwards messages in one network into the
  other network
• note that the task of a router is significantly
  greater than that of repeater, bridges and
  switches because a router must convert between
  the idiosyncrasies of the two original networks

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router

• for ex.
• When transferring a message from a network using
  the token ring protocol to a network using
  CSMA/CD, a router must receive the message using
  one protocol and then transmit it to the other
  network using another protocol
• Another ex.
• Consider the problem posed when the two networks
  being connected use different addressing systems
  to identify the computers in the networks.
• When a computer in one network wants to send a
  message to a computer in the other

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router
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router

• The result is that each machine in an internet
  has two address
• ??? ??????? ???? ??? ???? ??????? ?? ????????
• Original network address
• New internet address
• To send a message from a computer in one of the
  original networks to a computer in the other,
• ???? ????? ?? ??????? ?? ???? ?????
• the computer at the origin bundles the
  destination's internet address with the message,
• ?????? ??????? ?? ??? ?????? ?? ?????? ?????
  ????? ?? ??? internet address ?? ??? ???????
  ????? ?????? ??? router ???????? ?????? ???????

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router

• and sends the bundle to the router using the
  local network's original addressing system
• the router looks inside the bundle, find the
  internet address of the message's ultimate
  destination
• ?? ???? ??? router ??? ???? ?????? ????? ??????
  ??????? ?????
• translates that address into the address format
  that is appropriate for the other network, and
  forwards the message to its destination
• ????? ???? ??? ??????? ??? ???address format
  ????? ???? ?????? ?????? ??? ?? ???? ??????? ?????

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Interprocess Communication

• The various activities executing on the different
  computers within a network must often communicate
  with each other to coordinate their actions and
  to perform their designated task. Such
  communication between process is called
  interprocess communication
• A popular convention used for IC is client /
  server model
• Client which make requests of other processes,
  or a server
• Server which satisfies the requests made by
  clients

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Continue

• In the LAN network there are two types of
  networking
• client / server network
• Where there is a specific computer called
  a server, which servers all common files and
  document so that other computers (client) can
  use, access, update and manipulate them at the
  same time.

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client / server network

• a) Server must be prepared to serve multiple
  clients at any time

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client / server network

• Other kinds of servers are
• print server
• communication server
• mail server

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client / server network

• ???? ?????? ????????
• ????? ????? ????? ???? server ???? ???????
  ??????? ??? ?????? ???? clients ????? ??? ???
  ???? ??? server ???? ??? ?? ?????? ????? ??
  ?????? ????? ????? ??? client ??? ????? ????????
  ?????????? ?????????. ??? ????? ??? server
• ???? ??????? (file server)
• ?????? ?? ????? ??????? ?????? ????????
  ???????? ??? ??? ??? ???? ????? ?????? ?????
  ????? ????? ????? ??????? ?? ?????? ??? ??????
  downloading ??? ????? ????? uploading
• ???? ??????? (printer server)
• ????? ????? ???????? ???????? ??? ?????
  ????? ?? ??????

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client / server network

• ???? ????????? (communication server)
• ????? ??????? ???????? ?????? ???????? ??
  ???????? ???? ???? ?????? ??? ????? ???????
  ?????? ??? modem ??????? ??????.
• ????? ?????? ?????? ?????? ?????? ?? ???? ?? ???
  ????????, ??? ??? ?????? ???? ?????? ???????
  Dedicate server ????? ??????? ??????? ?? ?????
  ????? ????? ??? ????? ????? ??????? ??????? ???
  ???, ??? ??????? ????????
• ???? ????? ????? ???? ???? ???? ????? ?????
  ???????? . ????? ????
• ???? ?????? ???????? ?? ????? ???????? ??????
  ??????? ??????????? ?????? ?????? ?????? ????????
  ?? ???????

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peer-to-peer network

• Does not use a server. Individual computers share
  data directly with others computers

b) Peers communicate as equals on a one-to-one
basis
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peer-to-peer network

• ???? ???? ?????
• ?? ??? ????? ?? ???????? ?? ??????? ???????
  ???????? ? ?????? ?? ???? ?? ?????? ?? ???? ?????
  ?? ????? ?? ??? ?????, ?? ??? ?? ???? ???? ????
  ?? ??????? ?????? ?? ??????
• ???? ??? ???? ?? ???? ?????? ???????? .
  ??????? ?? ??? ??????? ??? ??????? ???????

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Distributed Systems

• Meaning that they consist of software units that
  execute as processes on different computers