DCN286
INTRODUCTION TO DATA COMMUNICATION
TECHNOLOGY
Network Physical Layer
Connection
Purpose of Physical Layer
The role of the OSI physical layer is to encode the
binary digits that represent data link layer frames
into signals and to transmit and receive these
signals across the physical media---- cooper
wires, optical fiber, and wireless that connect
network devices.
Network Access Layer
 The network access layer is concerned with all of the
issues that an IP packet requires to actually make a
physical link to the network media.
 It includes the LAN and WAN technology details, and all
the details contained in the OSI physical and data link
layers.
Popular Copper Media Standards
TIA (Telecommunications Industry
Association) and EIA (Electronic Industries
Alliance) work together to publish
commercial building telecommunications
cabling standards TIA/EIA-568-B which
defines how to use the pins on the
connectors on the ends of the cables.
IEEE (Institute of Electrical and Electronic
Engineers) publishes LAN standards such
as IEEE802.3 which will define cable
requirement.
Coaxial cable
Gradually outdated from LAN
Can run for longer distances than either
STP or UTP
Less expensive than fiber-optic cable
though it is expensive than STP or UTP
Still popular for TV and home internet
service
STP (Shielded Twisted Pair) cable
 Shielding provides better electrical
signals by reducing noise and
attenuation.
 Shielding makes the cable more
expensive, heavier and hard to
bend.
UTP (Unshielded Twisted Pair)
Flexible and easy install
Offer the same data speeds
Inexpensive
RJ45 connector (RJ11 is for phone cable).
UTP Implementation
UTP Implementation
Straight-through Cable
Switch to Router
Switch to PC or Server
Hub to PC or Server
Cross-over Cable
Switch to Switch; Switch to Hub; Hub to Hub
Router to Router; PC to PC; Router to PC
Roll-over Cable (Configuration Purposes)
PC to Router; PC to Switch
UTP Implementation
Straight-Through cable
A cable that maintains the pin connection all the
way through the cable.
Cat 5 and Cat5e: Only wires 1, 2, 3, and 6 are
used
Gigabit Ethernet uses all the wires
To connect devices such as PC or routers to
other devices as hub or switches.
UTP Implementation
Cross-over cable
A cable that crosses the critical pair to properly
align, transmit, and receive signals on the device
with line connections
Pin 1 at one end and Pin 3 at the other end
Pin 2 at one end and Pin 6 at the other end
Used to connect similar devices:
Switch to switch
Hub to hub
TIA/EIA568-A and B pin outs
Pin #
1
2
3
4
5
6
7
8
Function
TD+
TDRD+
Unused
Unused
RDUnused
Unused
568A wire color
White/Green
Green
White/Orange
Blue
White/Blue
Orange
White/Brown
Brown
568 B wire color
White/Orange
Orange
White/Green
Blue
White/Blue
Green
White/Brown
Brown
Straight through cable
Can be used to connect PC and other
network equipments to LAN hub/switch
Wire 1 and 2 are used to transmit data
Wire 3 and 6 are used to receive data
Cross-over cable
It is used to connect two same equipments
such as PC-to-PC.
Both ends need to send data on pin 1 and
2; receive data on pin 3 and 6.
In 568B, one end has white/orange and
orange on pin 1 and 2; another has
white/orange and orange on pin 3 and 6.
In 568B, one end has white/green and
green on pin 3 and 6; another end has
them on pin 1 and 2.
Rollover cable
Usually used as console cable.
Change the sequence on another end.
Rollover or Console Cable
The cable used between a terminal and a
console port is a rollover cable with RJ-45
connectors.
Rollover cable (or Console cable) has a
different pinout than the straight-through or
crossover cable.
The pinout for a rollover cable is:
1 to 8, 2 to 7, 3 to 6, 4 to 5, 5 to 4, 6 to 3, 7 to 2,
and 8 to 1.
Connector and Adapter
The 8 Position 8 Contact
(8P8C) (often called
RJ45) connector
Cross over adapter
Optic media
 Fiber-optic cable has the strongest ability to resist
EMI (electromagnetic interference), RFI (Radio
Frequency Interference)
 Fiber’s bandwidth is much higher than any other
media.
 Fiber is highly secure and it is easy to detect
intrusion.
 Fiber uses light signal transmission and its
attenuation is much less than electrical signals. Its
length could be very long
Optical fiber cable components
 Core: usually made by
silicon dioxide (from
sand)
 Cladding: coated on the
core to reflect light and
seal it inside
 Buffer: physical protect
cladding and core
 Jacket: prevent damage
from abrasion, solvents
and other contaminants
Optical Fiber Connector (Optional)
LC/PC connector and
SC/PC connectors
have caps covering
the ferrules
Other connectors are
ST, SC, MT, MT-RJ,
MU, etc, etc
Multimode fiber
Fiber with large (greater than 10 μm) core
diameter may allow light coming in with
different angles. (It must be in limit of
acceptance cone)
Single mode fiber
Fiber with a core diameter less than about
ten times the wavelength of the
propagating light and it can only allow light
coming in from one direction.
LAN Connectivity Devices
Repeaters
Hubs
Switches
Bridges
Routers
Repeaters
A repeater can be used to increase the length
of your network by eliminating the effect of
attenuation on the signal.
It connects two segments of the same network,
overcoming the distance limitations of the
transmission media.
Some repeaters also serve as transmission
media adapters, connecting two different types
of media.
Repeaters
Repeaters can connect segments that have the
same access method. (CSMA/CD, Token
Passing, Polling, etc.)
Disadvantages
Repeaters do not filter data
Its use is inappropriate when there is a heavy network
traffic.
Repeater
10base5 – 500meter cable length limit;
10base2 - 200meter cable length limit;
10BaseT - 100meter cable length limit;
Repeater is to amplify signal and extend the
cabling distance.
Working in layer 1 (Physical) of TCP/IP
model
Repeaters
Figure11-6
Hub
Central connection of Ethernet LAN.
Physically Star topology and could be
logically RING, Bus and/or Star
May have built-in repeater
Working in layer 1 (Physical) of TCP/IP
model
Hubs
A hub is used as a central point of
connection among media segments.
Cables from network devices plug in to the
ports on the hub.
Hubs are referred as Concentrators or multiport repeater
Hubs receive signals from connected
devices and transmit them to the other
connected devices
Hubs
Regenerate and repeat signals
Propagate signals through the network
Can not filter network traffic
Can not determine the best path
Are used as network concentration points.
Hubs
Types of Hubs
Passive Hubs
Active Hubs
Intelligent Hubs (Switches)
Passive Hub
It functions only as a connection point for
the signals
The signal pass through a passive hub
without regeneration or amplification.
Active Hub
It regenerates or amplifies the signal
before they are retransmitted.
Drawback:
The noise is also regenerated
Switch
Think switch as a hub with bridge functioning on
each port (interface):
1. Switch will offer central connection to all hosts.
2. Switch will only forward frame according to
destination MAC address on per-port base.
3. Will regenerate signals (repeater function)
4. Most switches are working in layer 2 (Data
Link) of TCP/IP model.
Switches
LAN Switch
broadcast
traffic
LAN switch
Broadcasts to all ports on LAN
sw itch.
Single Switch Virtual LANs
broadcast
source
Forwarding Frame based on Destination
MAC Address
 The switch maintain table, called a MAC table,
that maps destination MAC addresses with ports
used to connect to each node. For each
incoming frame, the destination MAC address in
the frame header is compared to the list of
addresses in the MAC table. If a match is found,
the port number in the table that is paired with
MAC address is used as exit port for the frame.
 The MAC table can be referred to by many
different name. It also called Switch table or
Bridge table.
Switch Operation
To accomplish Frame Forwarding, Ethernet LAN
switches use five basic operations:
Learning: The Mac table must be populated with
MAC addresses and their corresponding ports.
The learning process allows these mappings to
be dynamically acquired during normal
operation.
Aging: The entries in the MAC table acquired by
the learning process are time stamped. This time
stamp is used as a means for removing old
Continues Slide-37
entries in the MAC table. After it is made in the
MAC table, a procedure begins count down,
once it reaches count 0, the entry is aged out
and remove from the table.
Flooding: If a switch does not have a MAC address
entry in its MAC table that matches the
destination MAC address of received frame, the
switch will flood the frame. Flooding involves
sending a frame to all ports except the port on
which the frame arrived.
Switch Continues
Selective Forwarding:
Selective forwarding is the process of examining
the destination MAC address of a frame and
forwarding it out to the appropriate port.
Filtering: In some cases, a frame is not forwarded.
This process is called frame filtering e.g. a
switch does not forward a frame to the same
port on which it arrived. A switch will also drop a
corrupt frame. If a frame fails a CRC check, the
frame is dropped.
Ethernet Bridge
 Intelligent device to forward frame according to
destination Media Access Control (MAC)
address
 Forwarding: If the destination MAC address has
a port different to the originate port, the frame
will be sent.
 Filtering: If the destination MAC address is
reachable with the same interface when it
arrived, the frame will be discarded.
 Working in layer 2 (Data Link) of TCP/IP model
Layer 2 Bridging
Bridges
Segmentation
80% of LAN traffic stays on local LAN
20% of LAN
traffic travels
between LANs
LAN A
bridge
LAN B
Router
Redirect packets according to destination
logical address (IP address).
Can build routing path between different
network segments (subnets)
Can act as firewall
Can work as VPN (server) connection
Working in layer 3 (Network) of TCP/IP
model
Routers
Figure 11-7
Wireless tech introduction
 Infrared
 Bluetooth
 Microwave
 Radio
 Wi-Fi
In general, wireless network is secondary because
of two concerns: speed and security. But, it does
offer mobility and convenience.
Wireless Networking Media
Radio frequency (RF)
Laser
Infrared (IR)
Satellite/Microwaves
Wireless transmission techniques to carry
wireless signals
Wireless signals are electromagnetic waves
that travel through the air.
Wireless Networking Media
Infrared
Line of sight
Short distances
No obstacles between transmitter and receiver
Radiofrequency
Allows devices to be in different room or even
buildings
Limited radio
Can be single or multiple (Spread spectrum)
frequencies
Single Frequency
Is subject to outside interference and
geographic obstructions
Insecure (Easily monitored by others)
Spread Spectrum
Multiple frequencies
More secure
Security in the Wireless Environment
The first level of security in a wireless LAN
consists of protecting the radio frequency
waveform itself.
Security in the Wireless Environment
Wireless Access Points
Wireless Bridges
Encryption
WEP – Wireless Equivalence Privacy
EAP – Extensible Authentication Protocol
(IEEE 802.1X)
Wireless LAN Topology
Wireless Bridges
Wireless Security
If you think someone might eavesdrop on
your LAN radio links…..
Encryption is the key
Wireless Security Approaches
WEP – Wired Equivalency Privacy
IEEE 802.1X or Extensible Authentication
Protocol (EAP)
Wireless Equivalent Privacy
WEP
It is a security mechanism defined with the
IEEE 802.11 standard.
Designed to protect over the over-the-air
transmissions between wireless LAN access
points and NICs.
IEEE 802.11b requires 40-bit encryption keys
Cisco supports the optional 128-bit standard.
WEP Goals
Deny access to the network by
unauthorized users who do not possess
the appropriate WEP key.
Prevent the decoding of captured WLAN
traffic hat is WEP-encrypted without the
possession of the WEP key.
Should be supplemented with additional
higher-level security mechanisms such as
VPNs or Firewalls.
802.1X/EAP
Extensible Authentication Protocol
It is an alternative WLAN security approach
to WEP
802.1X/EAP focuses on providing:
Centralized authentication
Dynamic key distribution
It is a standard for port-based network
access control
Cabling the WAN
Wide Area Network (WAN) Services
To connect one network to a remote network
Provide different connection methods
Different cabling standards from those of LANs