Multiplexing
Rick Graziani
graziani@cabrillo.edu
Rick_Graziani@csumb.edu
1
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, graziani@cabrillo.edu
2
Multiplexing
Adtran TSU (T1) Multiplexer
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)
Rick Graziani, graziani@cabrillo.edu
3
Multiplexing
Adtran T3SU 300 (T3)
Multiplexer
http://www.adtran.com
Blackbox Multiplexer
http://www.blackbox.com
Rick Graziani, graziani@cabrillo.edu
4
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, graziani@cabrillo.edu
5
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, graziani@cabrillo.edu
6
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, graziani@cabrillo.edu
7
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, graziani@cabrillo.edu
8
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, graziani@cabrillo.edu
9
LAN Topology
Rick Graziani
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Rick_Graziani@csumb.edu
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Direct Point-to-Point Communications
Nodes Connections
2
1
4
6
8
28
16
120
32
496
64
2,016
128
8,128



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!
Rick Graziani, graziani@cabrillo.edu
11
Direct Point-to-Point Communications
Rick Graziani, graziani@cabrillo.edu
12
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, graziani@cabrillo.edu
13
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, graziani@cabrillo.edu
14
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, graziani@cabrillo.edu
15
Topologies
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16
Topologies
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17
Topologies
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History of Ethernet
Bob Metcalfe





Volume 2
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
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19
Ethernet Transmissions and Manchester Encoding


Ethernet frames are sent out using Manchester Encoding.
Note: Token Ring uses Differential Manchester Encoding.
Rick Graziani, graziani@cabrillo.edu
20
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, graziani@cabrillo.edu
21
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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22
Sharing on an Ethernet
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6.2.1 Media Access Control (MAC)
Non-Deterministic
(1st come 1st served)
Deterministic
(taking turns)
Rick Graziani
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6.2.2 MAC rules and collision detection/backoff
The devices that were
involved in the collision do
not have priority to
transmit data.
(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.
1.
2.
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
Rick Graziani
3.
Detecting errors within data packets or on the network
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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.
Rick Graziani
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Rick_Graziani@csumb.edu
26
6.1.1 Introduction to Ethernet
DIX Ethernet is essentially the same as 802.3
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Designation
Description
10Base-2
10 Mbps baseband Ethernet over coaxial cable with a maximum distance of 185 meters. Also referred to as Thin
Ethernet or Thinnet or Thinwire.
10Base-5
10 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-FP
10 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-36
10 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.
Rick Graziani
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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-LX
1000 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.
Rick Graziani
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Rick_Graziani@csumb.edu
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6.1.3 Ethernet and the OSI model
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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
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Rick_Graziani@csumb.edu
31
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.
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7.1.3 10BASE2
Thin Net
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7.1.4 10BASE-T
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7.1.4 10BASE-T
Signal leaves the cable and enters the NIC on the SPLIT
Green pair. White-Green is +ve, solid Green is negative.
568B
Signal leaves the NIC and enters the cable on the Orange
is +ve, solid Orange is negative.
Rick Graziani
pair. White-Orange
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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.
Rick Graziani
•
The 100 m distance starts over at a Switch.
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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
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3rd Frame
4th Frame
37
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
Rick Graziani
cross-connects, and general infrastructure needs.
graziani@cabrillo.edu
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38
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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41
L=Long Wave
Length 1300nm
5000
550
S=Short Wave
Length 850 nm
550
error
multimode
550
275
•
100
25
Rick Graziani
graziani@cabrillo.edu
Rick_Graziani@csumb.edu
•
•
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.
42
Rick Graziani
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43
Broadcast Domain vs Collision Domain
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7.2.7 Future of Ethernet
1.
2.
3.
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
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Rick_Graziani@csumb.edu
45