Network Media and
Layer 1 Functionality
BSAD 146
Dave Novak
Dean, Chapter 3, pp 93-124
Objectives
Introduction to transmission media
 Basic cabling

Coaxial
 Twisted pair
 Optical fiber

Basic wireless
 Network Interface Card (NIC)
 Basic Physical Layer (layer 1) functionality

Background
Different parts of the electromagnetic
frequency spectrum can be used for data
transmission depending on the medium
used and the communications standards
being followed
 Properties of specific media affect

Bandwidth
 Attenuation
 Noise
 Distortion

Background
Bandwidth – range of frequencies
occupied or used by a carrier wave
 Attenuation – strength of signal
decreases as it propagates
 Noise – unwanted electromagnetic
energy that degrades the signal
(crosstalk, background interference)
 Distortion – original shape or
characteristic of waveform is altered

Transmission

Computer communication at basic level
involves the transfer of signals over media
Layer 1 functionality
 Examples

•
•
•
•
•
Electrical current over wire
Radio waves through air
Microwave through air
Infrared through air
Light rays through glass fibers
Source: http://mynasadata.larc.nasa.gov/images/EM_Spectrum3-new.jpg
Transmission Media

Directed
Coaxial cable
 Twisted pair
 Fiber-optic


Undirected

Radio Frequency (RF)
Coaxial Cable

At one time, coax was the most widely used
copper networking cable
Coaxial Cable

“Legacy Ethernet” LAN implementation
supports two IEEE 802.3 standards
RG 58 cable “Thinnet” supports 10Base2
 RG 8 cable “Thicknet “ supports 10Base5

Coaxial Cable

RG 8 cable “Thicknet “ supports 10Base5
Transceiver
 AUI
 Vampire taps

Coaxial Cable

RG 58 cable “Thinnet “ supports 10Base2
Twisted Pair Cable

Currently the most widely used LAN cabling

Two physical copper circuits (wires) are
twisted together to filter out EMI and reduce
cross talk

Each wire carries an equal, but opposite
signal
Twisted Pair Cable

1) UTP - unshielded

2) STP - shielded
Source: http://www.howtogeek.com/70494/what-kind-of-ethernet-cat-5e6a-cable-should-i-use/
Twisted Pair Cable
Source: http://www.howtogeek.com/70494/what-kind-of-ethernet-cat-5e6a-cable-should-i-use/
Twisted Pair Cable

Cable reduces interference and supports
higher bandwidth through twisting and
isolation
Cat 6 UTP
has more
twists/cm
and has
thicker
sheathing
than Cat 5
UTP
Source: http://www.howtogeek.com/70494/what-kind-of-ethernet-cat-5e6a-cable-should-i-use/
Twisted Pair Cable
Source: http://www.howtogeek.com/70494/what-kind-of-ethernet-cat-5e6a-cable-should-i-use/
Twisted Pair Cable

Different types of cable have different
performance characteristics
Network Cable Specification Comparison
Specification
CAT5
CAT5e
CAT6
CAT6a
CAT7
100 MHz
100 MHz
250 MHz
500 MHz
600 MHz
24 dB
24 dB
19.8 dB
18.4 dB
20.8 dB
100 ohms
±15
100 ohms
±15
100 ohms
±15
100 ohms
±15
100 ohms
±15
27.1 dB
30.1 dB
44.3 dB
59 dB
62.1 dB
PS-NEXT *
N/A
27.1 dB
42.3 dB
59.1 dB
59.1 dB
ELFEXT *
17.9 dB
17.4 dB
27.8 dB
43.1 dB
Not Specified
PS-ELFEXT *
14.4 dB
14.4 dB
24.8 dB
41.8 dB
Not Specified
Return Loss *
16 dB
20.1 dB
20.1 dB
32 dB
14.1 dB
Delay Skew *
50 ns
45 ns
45 ns
45 ns
20 ns
Frequency
Attenuation (Insertion Loss)*
Characteristic Impedence
NEXT *
Twisted Pair Cable

Different types of cable may be needed to
support different Ethernet standards
10BASE-T, 100BASE-TX, 100BASE-FX,
1000BASE-T
 10GBASE-T

Cat5e supports most common standards
 One could potentially use Cat 6, 6a, or 7 –
why wouldn’t you?

Twisted Pair Cable

Refers to copper conductor in wire pairs

Solid – uses single piece copper strand
• Not flexible, but more durable

Stranded – uses multiple smaller copper
strands woven together
• Flexible
Twisted Pair Cable

Most “common” UTP and STP cables use 8
pin RJ45 connectors
Optical Fiber Cable

Supports high bandwidth, long distance
transmission by sending pulses of light over
very thin, pure glass (or plastic) strands
Source:
https://www.google.com/search?q=image+of+fiber+optic+cable&tbm=isch&tbo=u&source=univ&sa=X&ei=XijpUvbnCpStsQTQh
YFg&sqi=2&ved=0CDwQsAQ&biw=1129&bih=842/
Optical Fiber Cable

Two types of cable / transmission

1) Multi-mode

2) Single-mode
Source:
https://www.google.com/search?q=fiber+optic+cable&tbm=isch&tbo=u&source=univ&sa=X&ei=TAzoUviwLue0sAThgYHoDw&v
ed=0CFAQsAQ&biw=1129&bih=842/
Multi-Mode Fiber

Mostly used for communication over short
distances – within building, around campus

High bandwidth, but higher dispersion

Bandwidth-distance product limit is lower than
single mode

Has larger core diameter (and larger wave
length) than single mode

Less complex equipment than single mode

LED versus laser
Single-Mode Fiber

Has higher bandwidth than multi-mode and is
effective over very large distances

High bandwidth, low dispersion

Carries only a single ray

Equipment is complex and expensive

Specific types of lasers
Optical Fiber Connectors
Source: http://www.telegaertner.de/en/karl-gaertner/data-voice/office/artikel/images/lwl-patchkabel.jpg
Optical Fiber Connectors
Source: http://www.arcelect.com/fibercable%20connectors.gif
Wired Cable Design
Wireless Transmission

A WLAN (wireless LAN) is a LAN that does
not rely on physical cabling to transmit data
between devices

WLANs use radio frequencies (RF) to
transmit data

The goal of wireless communication is to
transmit large amounts of data as fast as
possible without wires
Wireless Transmission

Wireless communication follows the IEEE
802.11 specification which defines halfduplex transmission using the same
frequency for send and receive

Let’s talk about this a bit
Wireless Transmission

RF transmission does not require licensing
but it is regulated by the government!

The regulating agencies are the FCC in the
US and the ETSI in Europe

802.11 provides standards for RF operation
within FCC rules (frequencies and power
levels)
Wireless Transmission

There tend to be more difficulties achieving
high speed transmission with RF than with
wired technologies for a number of reasons
Wireless Transmission

To send an RF signal, the use of a
modulation technique is required

How did we define modulation?
Wireless Transmission

Spread Spectrum technique used to
modulate data by “spreading” the bandwidth
available for transmission

Signal is transmitted on bandwidth larger than
the frequency content of the transmission
• Security; increased resistance to noise,
interference, and jamming…
• Lower power per frequency band
• Redundancy
Spread Spectrum Examples

Direct Sequence Spread Spectrum (DSSS)

An RF modulation technique where data are
multiplied by a pseudo noise (PN) signal to
“spread” the signal, the modified signal is
transmitted over various frequencies
according to the PN sequence, original signal
reconstructed by receiver

As long as PN sequence is different than the
PN sequence of other transmissions the
signal to noise ratio is positive
Spread Spectrum Examples

Frequency Hopping Spread Spectrum
(FHSS)

Subdivides bandwidth on a particular channel
(say channel 1) into separate 1 MHz channels

Switch rapidly (pseudo-randomly) between
the different 1 MHz frequency bands (min of
75 frequencies every 30 sec) broadcasting for
only a few milliseconds over any particular
band
Electromagnetic Spectrum
FCC controls the available spectrum and WLANs can operate
in only 3 ranges: 1) 900 MHz, 2) 2.4 GHz, or 3) 5 GHz
Electromagnetic Spectrum

900-MHz band (902 – 928 MHz)

2.4 GHz band (2.4 – 2.4835 GHz)

Most widely used frequency range used in
WLANs

Used by 802.11 (base, b, g, n) standards

11 channels, each 22 MHz wide
Electromagnetic Spectrum

5 GHz band (complicated regs vary by
country)

23 non-overlapping channels

Used by 802.11 (a, h, j, n, ac) standards
Electromagnetic Spectrum

If you are interested see

http://en.wikipedia.org/wiki/List_of_WLAN_channels
Electromagnetic Spectrum

2.4 GHz band

11 overlapping channels

1, 6, and 11 non overlapping
Electromagnetic Spectrum
Electromagnetic Spectrum
Wireless Transmission

Potential drawbacks to wireless
Reliability
 IEEE 802.11 technologies have historically
been slower than wire-based technologies
 Limited range
 Security concerns

Network Interface Card

Provides a physical connection between a
networked device and the network medium

Also provides an interface between layers 1
and 2 of the OSI

Separate cards are needed to support
different layer 2 networking technologies
(Ethernet, Wi-Fi, dialup, etc.)
Network Interface Card
Network Interface Card
Generally plugs right into PCI (Peripheral
Component Interconnect) slots
 Most modern NICs are PCI


Have different network cable connectors
depending on types of cable supported

RJ-45 connector most common
Basics of data transfer

Data move through devices along paths
called buses

Several paths side by side (parallel)
• Data moves in lateral groups as opposed to single
(serial) data stream
• 32-bit bus means 32 bits moving along side by
side

Data move over network channel in a single
streams called serial transmission

One lane highway with data ALWAYS
traveling in same direction
Network Interface Card

1) Data transmission and reception

Primary function of NIC is to generate and
transmit signals of the appropriate type over
network and to receive incoming signals

Signal type depends on network medium and
Data Link Layer (2) protocol used

On legacy Ethernet LAN, every computer
receives all packets transmitted over network
 NIC must examine MAC destination
address in each packet to see if it is intended
for the local host
Network Interface Card

2) Signal encoding and decoding


Converts binary data encapsulated in a frame
into electrical voltage, light pulses, or other
signal
3) Data buffering

Since NIC transmits and receives data in
serial manner, it must be able to store data
until outgoing frames can be sent and
incoming frames can be processed by CPU
Network Interface Card


4) Data encapsulation

Building frame around data in preparation for
transmission

Read contents of incoming frames, strips off
frame, and pass data up to Network Layer (3)
5) Serial / parallel conversion


Usually 64 bits at a time
6) Media access control

Regulates how device access network
medium
Layer 1 hardware
functionality
Recognize / work with basic signals
 Little to no management capabilities
 Examples

Repeaters
 Hubs

Does not understand frames or MAC
addresses
 Does not understand network level
addresses and routing

Layer 1 hardware
functionality

Hubs –vs- repeaters


I’ll discuss this from a functionality / historical
perspective as no one really makes or uses
“layer 1 hubs” anymore
The concept of how a “layer 1 hub” works
is important with respect to our
discussion of legacy versus switched
Ethernet though…
Layer 1 hardware
functionality

Center discussion on hubs
Used to connect devices to a star or ring LAN
 Send copies of electrical signals to next
segment, do not reconstruct frames

• Regenerate and forward ALL electrical signals
• Multiple ports
• Do not understand frame formats
• Do not understand physical address
• Do not understand higher level network addresses
Token Ring MAU
Look like Ethernet hubs/switches, but are
NOT the same
 Passive device


Acts like a ring, even if topology is a star
Do not retransmit incoming traffic out other
ports simultaneously
 Transmits to each connected device in roundrobin manner

Token Ring MAU
PC on port 5
transmits packet
Hub receives packet and
forwards a copy out
each port
MAU receives incoming
packet from port 5 and
transmits out port 6 
MAU waits for packet
to return through port 6
before transmitting
packet out port 7 
Summary
Introduction to transmission media
 Basic cabling

Coaxial
 Twisted pair
 Optical fiber

Basic wireless
 Network Interface Card (NIC)
 Basic Physical Layer (layer 1) functionality
