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  1. Multiplexing Rick Graziani

  2. Multiplexing Multiplexing and WAN (Wide Area Networks) • The ability to establish, maintain and terminate multiple wide area system-to-system connections over a single wide area link. • Data/Voice systems to Data/Voice systems • LAN to LAN • Terminal to Host Rick Graziani,

  3. Multiplexing Multiplexer (mux) = A device which allows several devices to share the same communications circuit (cable, airwaves, etc.). Common Types of Multiplexing • Time Division Multiplexing (TDM) • Statistical Time Division Multiplexing (STDM) • Frequency Division Multiplexing (FDM) Adtran TSU (T1) Multiplexer Rick Graziani,

  4. Multiplexing Adtran T3SU 300 (T3) Multiplexer Blackbox Multiplexer Rick Graziani,

  5. Time Division Multiplexing Time Division Multiplexing = A multiplexer which allows devices to transmit information (data/voice) over the circuit by quickly interleaving information. Train Example: • Five Accordion Manufacturers with 20 box cars of accordions needed to get to their destination ASAP • SF to New York • Three solutions 1. Build 5 sets of tracks 2. Build 1 set of tracks and have 5 separate trains 3. Build 1 set of tracks and share a single train (multiplexing) Rick Graziani,

  6. Time Division Multiplexing 3. Build 1 set of tracks and share a single train with the box cars lined up as: Company Box Car A 1 B 2 C 3 D 4 E 5 A 6 B 7 etc. Rick Graziani,

  7. Time Division Multiplexing • Each source connected to the TDM mux has the entire bandwidth for a portion of time. • TDM constructs a “frame” consisting of one or more time slots for each input source. • TDM scans each input source for data during its designated time slot. If the source has no data to transmit, TDM mux inserts null data and the time slot is wasted. Rick Graziani,

  8. Time Division Multiplexing • The TDM channel or circuit must be able to handle the sum of the data rates of all its input sources plus overhead (later). • TDM can handle input sources with different data rates. • A slower device may be assigned one time slot, where a faster device may be assigned two or more time slots. Rick Graziani,

  9. Frequency Division Multiplexing • Multiplexing where input devices share the bandwidth of the circuit by dividing the link into many separate frequencies. • Involves modulating the signal from digital to analog and any other modulation techniques such as TCM. • Each user has the full bandwidth of the circuit at all times. Rick Graziani,

  10. LAN Topology Rick Graziani

  11. Direct Point-to-Point Communications • The total number of connections grows more rapidly than the total number of connections. • Full mesh formula: Connections = (N2-N)/2 • Could you imagine 8,128 separate connections for 128 PC LAN! NodesConnections 2 1 4 6 8 28 16 120 32 496 64 2,016 128 8,128 Rick Graziani,

  12. Direct Point-to-Point Communications Rick Graziani,

  13. Shared Communication Channels • LAN networks allow multiple computers to share a communcations medium, used for local communications. • Point-to-point connections are used for long-distance and a few other special cases. Rick Graziani,

  14. Shared Communication Channels • Why are shared networks used only for LANs? • Technically: Shared networks require coordination and having timing restrictions (later). • Economically: Much more expensive over long distances. Rick Graziani,

  15. Shared Communication Channels • LANs operate under the principle of locality of reference. • Locality of Reference: Computer communication follows two distinct patterns: • First, a computer is more likely to communicate with computers that are physically nearby than with computers that are far away. • We will see this later with Ethernet frame sizes and cable distances. • Second, a computer is more likely to communicate with the same set of computers repeatedly. (Temporal Locality of Reference) • We will see this later with ARP tables. Rick Graziani,

  16. Topologies Rick Graziani,

  17. Topologies Rick Graziani,

  18. Topologies Rick Graziani,

  19. History of Ethernet • Developed at Xerox PARC (Palo Alto Research Center) in early 1970’s. • One of three technologies Steve Jobs saw before developing the MacIntosh (Ethernet, OOP, and GUI), • Bob Metcalfe, founder of 3Com, was one of the developers • Digitial Equipment Corporation, Intel and Xerox later produced the DIX standard. • IEEE now controls Ethernet standards, IEEE 802.3 Bob Metcalfe Volume 2 Rick Graziani,

  20. Ethernet Transmissions and Manchester Encoding • Ethernet frames are sent out using Manchester Encoding. • Note: Token Ring uses Differential Manchester Encoding. Rick Graziani,

  21. Ethernet Transmissions and Manchester Encoding • A digital encoding technique in which each bit period is divided into two complementary halves to provide timing information. • A negative-to-positive voltage (0-to-1) transition in the middle of the bit period designates a binary “1” while a positive-to-negative transition represents a “0.” (Newton) • The data is included in the direction of the transition. Rick Graziani,

  22. Ethernet Transmissions and Manchester Encoding • Rick’s Coding method (no standard – can go other direction) • draw lines in the middle of the bit cell • make a up arrow for a one bit • make an down arrow for a zero bit • connect the lines and make transition when necessary (i.e. consecutive 1’s or 0’s) Rick Graziani,

  23. Sharing on an Ethernet Rick Graziani,

  24. 6.2.1 Media Access Control (MAC) Non-Deterministic (1st come 1st served) Deterministic (taking turns) Rick Graziani

  25. 6.2.2 MAC rules and collision detection/backoff (JAM) When a collision occurs, each node that is transmitting will continue to transmit for a short time to ensure that all devices see the collision. The devices that were involved in the collision do not have priority to transmit data. • Transmitting and receiving data packets • Decoding data packets and checking them for valid addresses before passing them to the upper layers of the OSI model • Detecting errors within data packets or on the network Rick Graziani

  26. 6.1.2 IEEE Ethernet naming rules • In BASE band signaling, the data signal is transmitted directly over the transmission medium. • In BROADband signaling, not used by Ethernet, a carrier signal is modulated by the data signal and the modulated carrier signal is transmitted. Rick Graziani

  27. 6.1.1 Introduction to Ethernet DIX Ethernet is essentially the same as 802.3 Rick Graziani

  28. Rick Graziani

  29. Rick Graziani

  30. 6.1.3 Ethernet and the OSI model Rick Graziani

  31. 6.1.3 Ethernet and the OSI model All other stations in the same collision domain see traffic that passes through a repeater. Stations separated by bridges or routers are in different collision domains. Rick Graziani

  32.  7.1.2 10BASE5 The 5-4-3 rule. no more than 5 segments separated by more than 4 repeaters, and no more than three populated segments • Not more than five segments. • No more than four repeaters may be connected in series between any two distant stations. • No more than three populated segments. Rick Graziani

  33. 7.1.3 10BASE2 Thin Net Rick Graziani

  34. 7.1.4 10BASE-T Rick Graziani

  35. 7.1.4 10BASE-T Signal leaves the cable and enters the NIC on the SPLITGreen pair. White-Green is +ve, solid Green is negative. 568B Signal leaves the NIC and enters the cable on the Orange pair. White-Orange is +ve, solid Orange is negative. Rick Graziani

  36. 7.1.5 10BASE-T wiring and architecture The 5-4-3 rule still applies. • 10BASE-T links can have unrepeated distances up to 100 m. • Hubs can solve the distance issue but will allow collisions to propagate. • The 100 m distance starts over at a Switch. Rick Graziani

  37. Because Gigabit Ethernet is inherently full-duplex, the Media Access Control method views it as a point-to-point link. • Cat 5e cable can reliably carry up to 125 Mbps of traffic. • 1000BASE-T uses all four pairs of wires. • This is done using complex circuitry called a Hybrid to allow full duplex transmissions on the same wire pair. • This provides 250 Mbps per pair. • With all four-wire pairs, this provides the desired 1000 Mbps. • Since the information travels simultaneously across the four paths, the circuitry has to divide frames at the transmitter and reassemble them at the receiver. 1st Frame 2nd Frame 3rd Frame 4th Frame Rick Graziani

  38. 7.1.8 100BASE-FX 200 Mbps transmission is possible because of the separate Transmit and Receive paths in 100BASE-FX optical fiber. • The main application for which 100BASE-FX was designed was inter-building backbone connectivity • 100BASE-FX was never adopted successfully. This was due to the timely introduction of Gigabit Ethernet copper and fiber standards. • Gigabit Ethernet standards are now the dominant technology for backbone installations, high-speed cross-connects, and general infrastructure needs. Rick Graziani

  39. 7.1.8 100BASE-FX Rick Graziani

  40. 7.1.8 100BASE-FX Rick Graziani

  41. 7.1.8 100BASE-FX Rick Graziani

  42. L=Long Wave Length 1300nm 5000 550 S=Short Wave Length 850 nm 550 error multimode 550 275 • The Media Access Control method treats the link as point-to-point. • Since separate fibers are used for transmitting (Tx) and receiving (Rx) the connection is inherently full duplex. • Gigabit Ethernet permits only a single repeater between two stations. 100 25 Rick Graziani

  43. Rick Graziani

  44. Broadcast Domain vs Collision Domain Rick Graziani,

  45. 7.2.7 Future of Ethernet • Copper (up to 1000 Mbps, perhaps more) • Wireless (approaching 100 Mbps, perhaps more) • Optical fiber (currently at 10,000 Mbps and soon to be more) Rick Graziani