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Networks. Common Xmit Media. Shared Media. Networks are a shared communication resource Only one user can access at a time. Packet and Circuit Switched. Circuit: Public Telephone Network Packet: Internet and US Mail Data divided into small units (packets) for transmission

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Presentation Transcript
shared media
Shared Media
  • Networks are a shared communication resource
  • Only one user can access at a time
packet and circuit switched
Packet and Circuit Switched
  • Circuit: Public Telephone Network
  • Packet: Internet and US Mail
  • Data divided into small units (packets) for transmission
  • More efficient use of shared resource
packets and frames
Packets and Frames
  • Packet: A small, self-contained parcel of data sent across a computer network. Each packet contains a header that identifies the sender and recipient, and data to be delivered.
  • Frame: The form of a packet that the underlying hardware accepts and delivers.
frames
Frames
  • Header and trailer indicates beginning and end of frame.
transmission errors
Transmission Errors
  • Error Detection and Error Correction
  • Both require additional information beyond data, appended to end of frame
  • Many Schemes
  • Parity checking, Check Sum, CRC codes
  • Error Correcting Codes: Hamming, Reed-Solomon, etc...
slide9

Parity refers to the number of bits set to 1 in the data item

    • Even parity - an even number of bits are 1
    • Odd parity - an odd number of bits are 1
  • A parity bit is an extra bit transmitted with a data item,
  • chose to give the resulting bits even or odd parity
    • Even parity - data: 10010011, parity bit 1
    • Odd parity - data: 10010111, parity bit 0
lan s
LAN’s
  • Reduce complexity and cost by sharing communication channel
  • TDM
  • Synchronization
  • Effective because of locality of reference
    • Spatial
    • Temporal
topologies
Topologies
  • Star, Ring, Bus
ethernet
Ethernet
  • Widely used LAN technology
  • Invented at Xerox PARC (Palo Alto Research Center) in 1970s
  • Defined in a standard by Xerox, Intel and Digital - DIX standard
  • Standard now managed by IEEE - defines formats, voltages, cable lengths, ...
  • Uses bus topology
  • Single coax cable - the ether
  • Multiple computers connect
  • One Ethernet cable is sometimes called a segment
  • Limited to 500 meters in length
  • Minimum separation between connections is 3 meters
slide14
Originally 3 Mbs
  • Then, 10 Mbs
  • Fast Ethernet, 100 Mbs
  • One computer transmits at a time
  • Signal is a modulated carrier which propagates from transmitter in both directions along length of segment
hardware adresses
Hardware Adresses
  • Identify destination on shared channel
  • Hardware or physical address
  • Included in frame
slide17
WAN
  • Packet Switch: Moves complete packets from one connection to another
protocols and layering
Protocols and Layering
  • A rule that specifies format and meaning of messages that computers exchange
  • Protocols organized in layers, each of which solves specific aspect of communication problem.
slide21

Layer 7: Application

    • Application-specific protocols such as FTP and SMTP (electronic mail)
  • Layer 6: Presentation
    • Common formats for representation of data
  • Layer 5: Session
    • Management of sessions such as login to a remote computer
  • Layer 4: Transport
    • Reliable delivery of data between computers
  • Layer 3: Network
    • Address assignment and data delivery across a physical network
  • Layer 2: Data Link
    • Format of data in frames and delivery of frames through network interface
  • Layer 1: Physical
    • Basic network hardware - such as RS-232 or Ethernet
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