Microprocessor-based systems

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Microprocessor-based systems

• Course 11 Computer networks

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The need for communication networks

• The need for communication (data and program
  exchange) between computer systems
• Shared use of computing resources (computers,
  storage, peripheral devices)
• First networks
• DARPA-NET network for military purposes
• Academic networks (Americans)
• CERN inter-networks
• Today
• the network is a communication and cooperation
  infrastructure for the development of distributed
  applications
• A set of small computers (PCs), plus a network is
  more powerful than a computer and several
  terminals

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Classification of networks

• Based on the way it is used
• Point-to-point networks, dedicated connection
  between two devices
• Broadcasting networks communication medium for
  more equipment
• Unicast - one recipient
• Multicast - multiple recipients
• Broadcast - all network nodes are addressed
• Anycast at least one node is addressed
• After stretching area
• Personal Area Networks (PAN)
• Local Area Networks (LAN)
• Metropolitan Networks (MAN)
• Wide Area Networks (WAN)

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Personal area networks (PANs)

• Have a stretch of 1-2m
• Intended for interconnection of equipment at an
  individual phone, PDA, headphones, MP3 player,
  etc..
• Examples Bluetooth, ZigBee
• Low speed
• Wireless connectivity in the frequency of public

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Local Area networks (LAN)

• Interconnect equipment in the same building
• Belong to some organizations
• Distances 10m-1km
• Speed 10-100Mbs, 1Gbs
• Standard protocols
• Ethernet (CSMA / CD),
• Token Ring,
• Token Bus
• Low error rate
• Communication medium twisted pair or coaxial
  electrical cable

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Metropolitan area networks

• Interconnected local networks in the territory of
  a locality or region
• Can be private or public
• Example the metropolitan network of universities
  in Cluj
• Distances 1-10km
• Speed 100kbs-10Mbs-100Mbs
• Standard protocols
• DQDB (Double Queue Doubel bus),
• ATM,
• Frame Relay
• Communication medium fiber optics

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Wide Area Networks (WAN)

• allow transfer of information from very large and
  diverse places
• internet network of networks
• Distances thousand miles
• Protocol TCP / IP
• Speed 100kbs-10Mbs 100 Mbs
• Example
• Internet
• AOL
• Geant
• RoEduNet

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Network communication models

• the need for a model to ensure compatibility
  between equipment and networks, regardless of
  manufacturer, type, location
• ISO-OSI model - Open Systems Interchange
• Separating the functions of communication on
  several layers of abstraction
• 7 layers

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The OSI model
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Packaging the message
Header
Useful content
Footer
.
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Access to the communication services

• Each layer offers a set of communication services
• There are layers with one type of service (in the
  Internet the network layer is only IP), or layers
  with different types of services (e.g. for
  transport layer TCP - connection-oriented
  service and UDP service with no connection)
• Higher layers access lower layer services through
  access points (service access points)
• Two components of the same layer but from
  different computers communicate as if they are
  directly connected - logical connection
• A communication travels through the entire
  protocol stack

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The TCP/IP model compared with OSI
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ATM model
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Protocol layers

• Physical layer
• Physical layer deals with information
  transmission at the bit. A physical layer
  protocol must specify
• the nature of the signals used to encode binary
  data (eg voltage layers, currents, laser beam,
  etc..), and acceptance layers
• electrical characteristics, mechanical
  performance and transmission medium (electrical
  cables, optical, radio)
• methods to reduce noise and eliminate the
  influence of transmission errors
• type of connectors used
• Physical protocol must ensure efficient use of
  transmission medium, and a transfer rate as
  large.
• Depending on the nature of transmission medium
  can use different encryption methods and
  compaction of binary information.
• The transmission media used in digital
  communication are
• a. twisted pair cable - is cheap, with the
  frequency dependent transmission distance, may be
  shielded or unshielded (UTP - Unshielded Twisted
  Pair), twisting the two wires of the cable
  increases noise immunity.
• b. The coaxial cable - is high bandwidth and high
  noise immunity, transmission distance is
  relatively large, there are two ways of using
  the basic band (one channel / cable) or broadband
  (multi-channel / cable )
• c. optical fiber - is a transmission medium with
  high performance parameters (high bandwidth, low
  delay) has full immunity to electromagnetic
  noise, on a single optical wireless can transmit
  many channels

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Physical Layer

• Communication media
• Twisted pair cable (UTP)
• Coaxial cable
• Fiber Optic
• Radio
• IR transmission
• Topology
• Star
• Ring
• Bus
• Tree
• graph

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Data Link Layer

• Role
• Structuring data within packages
• Providing a secure communication channel
• Detecting transmission errors
• The parity bits, checksum, CRC
• Types of services
• unconfirmed service without connection
• confirmed service without connection
• confirmed the connection-oriented service
• Examples
• HDLC protocol (High Data Link Control)
• SLIP protocol (Serial Line Internet Protocol)
• Unaltered IP packets for transmission (Internet)
• PPP (Point-to-Point Protocol)

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Access mechanisms to the communication
environment (MAC sub-layer)

• Layer used for local area networks where the same
  medium is shared by multiple nodes
• Access control
• Centralized
• Distributed
• Classification of access methods

Algorithm Centralized Distributed
Round-Robin Polling Token ring, Token bus
With reservation Central reservation Distributed reservation
With multiple access ----- CSMA/CD (Ethernet)
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Network layer

• Role routing messages
• Solutions
• Circuit switching - phone system
• Packet Switched
• Routing algorithms
• The shortest path routing
• Flooding algorithm (flooding)
• Flow-based routing
• Vector-distance routing
• Hierarchical routing
• Network layer on the Internet IP (Internet
  protocol)
• The network is organized around three
  hierarchical levels
• high-speed network that makes up the backbone of
  the system (backbone)
• regional networks (Europe, America, Asia, ..)
• academic networks, government, companies, ISPs,
  etc..
• The IP addresses 4 bytes, 232 possible addresses
  not enough

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Transport layer

• Role creates a secure channel of communication
  on an uncertain environment
• It makes a logical connection between remote
  applications (like a dedicated pipeline for the
  two applications)
• Transport layer on the Internet
• TCP connection-based transport protocol
• UDP - connectionless transport protocol
• Operations performed
• reordering messages in order to respect the
  initial order
• re-transmits erroneous messages
• eliminates duplicate messages
• It uses the message confirmation technique
• Packets are numbered to keep track of their order
• Connection is done through sockets (Socket)
• Socket port IP address

Ap1
Ap2
Apn
Internet
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Other OSI layers

• Session Layer
• responsible for controlling the sequence of
  dialogue between the two applications that
  communicate with each
• handles authentication dialog between partners by
  checking the access passwords
• Presentation Layer
• It deals with issues concerning coding-decoding
  for data security
• Application level
• offers various models and communication
  interfaces for user applications
• - Network virtual terminal (eg TELNET)
• - File transfer (eg FTP)
• - Email (eg SMTP)
• - Remote execution of procedures (RPT)
• - Network management (eg SNMP)
• - Web browsing, etc..

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Other Application layer protocols

• - DNS (Domain Name System) - is a service that
  allows addressing messages based on symbolic
  names, the protocol allows transformation of
  symbolic names for network addresses (IP
  addresses)
• - NFS (Network File System) - is a mapping
  service that allows remote file folders in your
  local directory, this service provides a uniform
  access to files regardless of their location
• - NIS (Network Information System) - is a service
  providing resource information contained in the
  network, such applications can be identified,
  gateway services, etc.., Resembles the "yellow
  pages" published to identify firms and services
  they provide
• - RPC (Remote Procedure Call) - is a protocol
  through which applications can be launched
  remotely or procedures, the Protocol provides the
  procedures and appeal mechanisms for transmitting
  call parameters, many network applications are
  based on an RPC mechanism
• - WWW (World Wide Web) - is a distributed
  information service that allows searching of
  information through various databases across the
  network in Internet, information is organized in
  the form of pages, a page can contain text,
  pictures, small applications ( applet's) and
  especially links to other sites containing
  similar information, search information is
  through programs of "navigation" (eg Netscape,
  Internet Explorer, etc.). is writing pages using
  HTML and protocol HTTP communication is used.