Fundamental Concepts and Issues Lecture II IIITMK

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Fundamental Concepts and IssuesLecture
IIIIITM-K
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FUNDAMENTAL CONCEPTS

• What is a network?
• In its simplest form, networking is defined as
  two computers being linked together, either
  physically through a cable or through a wireless
  device.
• Recently developed benefit of networks
• -remote access of email and
  files using technology known as Virtual Private
  Networking (VPN)
• - an organization can access
  its network remotely via a secure, encrypted
  channel by means of either a dialup or Internet
  connection.

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Digital etiquette bursts, bits, and packets

• A computer network requires two hosts and a wire.
  Now we must examine how the hosts use this wire
  to communicate.
• The term "digital" means that a device uses
  bursts of electricity in discrete values.
• one discrete burst represent a bit set to one. A
  low voltage burst of zero represents a bit set to
  zero.
• A bit belongs to a binary number system whose
  values consist of 0s and 1s.

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• A packet is a discrete number of bursts onto the
  wire whose contents are understood by the hosts
  connected on the network.
• Exchanging of packets between computers on a
  network is referred to as a packet-switched
  network.
• The breaking up of data into pieces, packets, is
  the fundamental concept of network operation.

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PROTOCOLS

• Specifies common set of rules and signals which
  computers on the network use to communicate.
• Proprietary protocols Are standards developed
  and protected by hardware manufacturers.
• Open protocols Are nonproprietary protocols.
  They are established by independent
  organizations.
• Protocol suiteThe total package of protocols.

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NETWORK TOPOLOGY

• specifies the geometric arrangement of the
  network or a description of the layout of a
  specific region.
• The complete physical structure of the cable (or
  data-transmission media) is called the physical
  topology .
• The way data flows through the network (or
  data-transmission media) is called the logical
  topology.

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TYPES OF CONNECTIONS

• POINT-TO-POINT
• provides a direct link between two
  devices for example, a computer connected
  directly to a printer .
• MULTI-POINT
• provides a link between three or more
  devices on a network.

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NETWORK ARCHITECTURE

• Peer-to-Peer
• Client/Server
• a peer-to-peer network does not have a central
  server and consists of 2 or more computers
  connecting through a device called a Hub.
• Client/server networks are networks that connect
  individual computers, known as clients, and one
  or more central computers, called servers.

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Local Area Networks (LANs)

• LANs connect computers and peripherals within a
  building or group of buildings.
• Users can access software, data, and peripherals.
• LANs require special hardware and software.
• Computers connected to a LAN are called
  workstations or nodes.
• Different types of LANs
• Peer-to-peer
• Client-server

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Switching Strategies

• circuit switching dedicated circuit
  send/receive a bit stream
• packet switching store-and-forward send/receive
  messages (packets)

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Addressing and Routing

• Address byte-string that identifies a node
  usually unique
• Routing process of determining how to forward
  messages towards the destination node based on
  its address
• types of addresses
• unicast node-specific
• broadcast all nodes on the network
• multicast some subset of nodes on the network

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Common Multiplexing Strategies

• Time-Division Multiplexing (TDM)
• Used for telephony or other applications where
  there is a constant bit rate
• Frequency-Division Multiplexing (FDM)
• Frequencies on the physical media are used for
  different channels

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Application Modes

• Network supports common process-to-process
  channels
• sockets, ping, etc
• Request/Reply for file access and digital
  libraries
• ftp, telnet
• Message Stream for video applications

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What Goes Wrong in the Network?

• Bit-level errors (electrical interference)
• bit errors 10-7 for copper, 10-12 for fiber
• With Gbps line, 10/second with copper
• Packet-level errors (congestion)
• Adjust to match bit error rate
• Link and node failures
• Redundant equipment switches over on the order of
  days

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Failure Modes

• Messages are delayed
• Messages are corrupted
• Messages are delivered out-of-order
• Third parties eavesdrop
• The key problem is to fill in the gap between
• what applications expect and what the
• underlying technology provides.

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Performance measures

• 1.Bandwidth (throughput)
• Amount of data that can be transmitted per time
  unit. Example 10Mbps
• link versus end-to-end
• Notation
• --KB 210 bytes
• --Mbps 106 bits per second
• Bandwidth related to bit width

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Latency (delay)

• Time it takes to send message from point A to
  point B
• Example 24 milliseconds (ms)
• Sometimes interested in in round-trip time (RTT)
• Components of latency
• Latency Propagation Transmit Queue
• Propagation Distance / Speed Of Light
• Transmit Size / Bandwidth