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Multiplexing

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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

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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)

Multiplexing

Adtran TSU (T1) Multiplexer

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Adtran T3SU 300 (T3) Multiplexerhttp://www.adtran.com

Blackbox Multiplexer

http://www.blackbox.com

Multiplexing

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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 solutions1. Build 5 sets of tracks2. Build 1 set of tracks and have 5 separate trains3. Build 1 set of tracks and share a single train (multiplexing)

Time Division Multiplexing

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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.

Time Division Multiplexing

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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.

Time Division Multiplexing

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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.

Time Division Multiplexing

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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.

Frequency Division Multiplexing

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LAN Topology

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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!

Nodes Connections 2 1 4 6 8 28 16 120 32 496 64 2,016 128 8,128

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Direct Point-to-Point Communications

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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.

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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.

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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.

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Topologies

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Topologies

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Topologies

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History of Ethernet

Bob Metcalfe

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

Volume 2

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Ethernet Transmissions and Manchester Encoding

Ethernet frames are sent out using Manchester Encoding. Note: Token Ring uses Differential Manchester Encoding.

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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.

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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)

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Sharing on an Ethernet

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6.2.1 Media Access Control (MAC)

Deterministic(taking turns)

Non-Deterministic(1st come 1st

served)

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6.2.2 MAC rules and collision detection/backoff

1. Transmitting and receiving data packets 2. Decoding data packets and checking them for valid addresses before

passing them to the upper layers of the OSI model 3. Detecting errors within data packets or on the network

(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.

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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.

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6.1.1 Introduction to Ethernet

DIX Ethernet is essentially the same as 802.3

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Designation Description

10Base-210 Mbps baseband Ethernet over coaxial cable with a maximum distance of 185 meters. Also referred to as Thin Ethernet or Thinnet or Thinwire.

10Base-510 Mbps baseband Ethernet over coaxial cable with a maximum distance of 500 meters. Also referred to as Thick Ethernet or Thicknet or Thickwire.

10Base-36 10 Mbps baseband Ethernet over multi-channel coaxial cable with a maximum distance of 3,600 meters.

10Base-F 10 Mbps baseband Ethernet over optical fiber.

10Base-FB 10 Mbps baseband Ethernet over two multi-mode optical fibers using a synchronous active hub.

10Base-FL 10 Mbps baseband Ethernet over two optical fibers and can include an optional asynchronous hub.

10Base-FP10 Mbps baseband Ethernet over two optical fibers using a passive hub to connect communication devices.

10Base-T 10 Mbps baseband Ethernet over twisted pair cables with a maximum length of 100 meters.

10Broad-3610 Mbps baseband Ethernet over three channels of a cable television system with a maximum cable length of 3,600 meters.

10Gigabit Ethernet

Ethernet at 10 billion bits per second over optical fiber. Multimode fiber supports distances up to 300 meters; single mode fiber supports distances up to 40 kilometers.

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Designation Description

100Base-FX 100 Mbps baseband Ethernet over two multimode optical fibers.

100Base-T 100 Mbps baseband Ethernet over twisted pair cable.

100Base-T2 100 Mbps baseband Ethernet over two pairs of Category 3 or higher unshielded twisted pair cable.

100Base-T4 100 Mbps baseband Ethernet over four pairs of Category 3 or higher unshielded twisted pair cable.

100Base-TX 100 Mbps baseband Ethernet over two pairs of shielded twisted pair or Category 4 twisted pair cable.

100Base-X A generic name for 100 Mbps Ethernet systems.

1000Base-CX 1000 Mbps baseband Ethernet over two pairs of 150 shielded twisted pair cable.

1000Base-LX1000 Mbps baseband Ethernet over two multimode or single-mode optical fibers using longwave laser optics.

1000Base-SX 1000 Mbps baseband Ethernet over two multimode optical fibers using shortwave laser optics.

1000Base-T 1000 Mbps baseband Ethernet over four pairs of Category 5 unshielded twisted pair cable.

1000Base-X A generic name for 1000 Mbps Ethernet systems.

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6.1.3 Ethernet and the OSI model

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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.

6.1.3 Ethernet and the OSI model

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• 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.

 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

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7.1.3 10BASE2

Thin Net

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7.1.4 10BASE-T

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Signal leaves the NIC and enters the cable on the Orange pair. White-Orange is +ve, solid Orange is

negative.

Signal leaves the cable and enters the NIC on the SPLIT Green pair. White-Green is +ve, solid Green is

negative.

568B

7.1.4 10BASE-T

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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.

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1st Frame

2nd Frame

3rd Frame

4th Frame

• 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.

Because Gigabit Ethernet is inherently full-duplex, the Media Access Control method views it as a point-to-point

link.

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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.

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7.1.8 100BASE-FX

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7.1.8 100BASE-FX

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7.1.8 100BASE-FX

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L=Long Wave Length

1300nm

S=Short Wave Length 850

nm

• 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.

multimode

error

5000

550

550

550

275

100

25

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Broadcast Domain vs Collision Domain

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7.2.7 Future of Ethernet

1. Copper (up to 1000 Mbps, perhaps more) 2. Wireless (approaching 100 Mbps, perhaps more) 3. Optical fiber (currently at 10,000 Mbps and soon to be more)