ITT550 - Chapter05-RY-Physical Network Design
ITT550 - Chapter05-RY-Physical Network Design
ITT550 - Chapter05-RY-Physical Network Design
ITT550
Chapter 5:
Physical
Network Design
Overview of the Physical Design Phase
Objectives
DEC DEConnect
Building Entrance
There is one point of entry and exit for all
telecommunications lines, incl. telephone, data
backbones to other premises, and other WAN
transmission facilities
Within the building entrance, a cross-connect
device provides a convenient termination point for
cables, and allows the interconnection of devices in
a clean and systematic way
Cross-Connect Devices
Equipment Room
Large office buildings may have a centralized
equipment room to house devices e.g.
telephone system PBX, banks of modems,
servers and all other network devices
This room will include a main cross-connect,
sometimes referred to as a main distribution
frame (MDF)
The MDF provides a central interconnection
point for the network cabling
Vertical Backbone
The backbone cabling is usually referred to as
vertical cabling
E.g., vertical cabling may run from an
equipment room in the basement to a wiring
closet on an upper floor
A separate backbone cable will often run from
the MDF cross-connect to each wiring closet.
In other cases, wiring closets may be directly
connected to each other with backbone cable
Wiring Closets
One or more cross-connect devices
interconnect the rack-mounted hub to the
backbone cable(s) and to individual cables that
run to wall plates at each user work area
The short cables used to interconnect the hub
and cross-connects are called patch cables
Equipment in the wiring closet is known as
intermediate distribution frame (IDF) equipment
Horizontal Wiring
Horizontal wiring connects the wiring closet to
each wall plate near a user's station
It is typically UTP or STP
Work Area
Consists of the cable and other devices
connecting the user station to the wall plate
Usually have RJ-45 plugs at both ends, to
insert into the adapter card port and wall plate
outlet
Fiber
Subsystem UTP STP
Optic
Backbone 2,000 m 800 m 700 m
Intercloset link 2,000 m 800 m 700 m
Horizontal Wiring
Closet to wall plate N/A 90 m 90 m
Wall plate to adapter N/A 10 m 10 m
Voltage Buildup
To avoid damage to network devices,
excessive direct current (DC) voltage must not
be allowed to build up on the line
E.g. if a line code represented a binary 1 with a
positive voltage and a binary 0 with zero
voltage, a signal like that depicted on the
Voltage Buildup Diagram would result
Voltage Buildup
Manchester Encoding
Timing Synchronization
timing circuitry of the receiving NIC must be
synchronized with the signal pulses
E.g. Manchester encoding makes it easy for
receiving devices to synchronize to the
numerous voltage transitions
techniques are used with other line encoding
systems, including differential Manchester
encoding (used with FDDI)
Signal Strength
For a bit stream to be recognizable, the voltage
pulses must be strong enough to be detected
by the receiving circuitry
However, as a signal travels along a conductor,
it loses strength, or amplitude
This process of amplitude loss is referred to as
attenuation
◦ Impedance
◦ Continuity and polarity
◦ Cable length
Each of these characteristics is measurable
and testable, according to EIA/TIA’s standards
and Underwriter's Laboratories (UL)
cable installations should be tested and verified
to ensure they meet the standards
Transmitter
A transmitter includes the following
components:
◦ Encoder that converts the input data signal into
digital electrical pulses
◦ Light source that converts the digital electrical
signal to light pulses
◦ Connector that couples the light source to the
fiber through which the light rays travel
Receiver
A receiver converts the modulated light pulses
back to electrical signals and decodes them
The receiver, contained within the destination
computer system, includes:
◦ Photodetector that converts the light pulses into
electric signals
◦ Amplifier, if needed
◦ Message decoder
= 10 * 0.699
= 6.99 dB
Spread Spectrum
Wireless Comparison