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Networks

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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Networks

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  1. Networks

  2. Common Xmit Media

  3. Shared Media • Networks are a shared communication resource • Only one user can access at a time

  4. 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

  5. Time-Division Multiplexing

  6. 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.

  7. Frames • Header and trailer indicates beginning and end of frame.

  8. 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...

  9. 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

  10. Point-to-Point Networks

  11. LAN’s • Reduce complexity and cost by sharing communication channel • TDM • Synchronization • Effective because of locality of reference • Spatial • Temporal

  12. Topologies • Star, Ring, Bus

  13. 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

  14. 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

  15. Hardware Adresses • Identify destination on shared channel • Hardware or physical address • Included in frame

  16. Ethernet Frame

  17. WAN • Packet Switch: Moves complete packets from one connection to another

  18. 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.

  19. ISO 7 Layer Model

  20. 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

  21. Nested Headers

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