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Networking Fundamentals
Data unit
Network process to application
6. Presentation
Data representation, encryption and
decryption, convert machine dependent data to
machine independent data
5. Session
Interhost communication, managing sessions
between applications
4. Transport
Reliable delivery of packets between points on
a network.
3. Network
Addressing, routing and (not necessarily
reliable) delivery of datagrams between points
on a network.
2. Data link
A reliable direct point-to-point data connection.
1. Physical
A (not necessarily reliable) direct point-to-point
data connection.
OSI Model
7. Application
Application (Layer 7)
• This layer supports application and end-user processes.
Communication partners are identified, quality of service is
identified, user authentication and privacy are considered,
and any constraints on data syntax are identified. Everything
at this layer is application-specific. This layer provides
application services for file transfers, e-mail, and
other network software services. Telnet and FTP are
applications that exist entirely in the application level. Tiered
application architectures are part of this layer.
Presentation (Layer 6)
• This layer provides independence from differences in
data representation (e.g., encryption) by translating
from application to network format, and vice versa.
The presentation layer works to transform data into
the form that the application layer can accept. This
layer formats and encrypts data to be sent across
a network, providing freedom from compatibility
problems. It is sometimes called the syntax layer.
• Mostly useless
Session (Layer 5)
• This layer establishes, manages and
terminates connections between applications.
The session layer sets up, coordinates, and
terminates conversations, exchanges, and
dialogues between the applications at each
end. It deals with session and connection
• Mostly useless.
Transport (Layer 4)
• This layer provides transparent transfer of data between end
systems, or hosts, and is responsible for end-to-end error
recovery and flow control. It ensures complete data transfer.
• Layer 4 data units are also called packets, but when you're
talking about specific protocols, like TCP, they're "segments"
or "datagrams" in UDP. This layer is responsible for getting
the entire message, so it must keep track of fragmentation,
out-of-order packets, and other perils. Layer 4 provides endto-end management of communication. Some protocols, like
TCP, do a very good job of making sure the communication is
reliable. Some don't really care if a few packets are lost--UDP
is the prime example.
Network (Layer 3)
• This layer provides switching and routing
technologies, creating logical paths, known as virtual
circuits, for transmitting data from node to node.
Routing and forwarding are functions of this layer, as
well as addressing, internetworking, error handling,
congestion control and packet sequencing.
• IP is part of layer 3, along with some routing
protocols, and ARP (Address Resolution Protocol).
Everything about routing is handled in layer 3.
Addressing and routing is the main goal of this layer.
Data Link (Layer 2)
• At this layer, data packets are encoded and decoded into bits.
It furnishes transmission protocol knowledge and
management and handles errors in the physical layer, flow
control and frame synchronization. The data link layer is
divided into two sub layers: The Media Access Control (MAC)
layer and the Logical Link Control (LLC) layer. The MAC sub
layer controls how a computer on the network gains access to
the data and permission to transmit it. The LLC layer controls
frame synchronization, flow control and error checking.
• Ethernet, among other protocols, lives on Layer 2.
• MAC address, switches, or network cards
Physical (Layer 1)
• This layer conveys the bit stream - electrical
impulse, light or radio signal -- through
the network at the electrical and mechanical
level. It provides the hardware means of
sending and receiving data on a carrier,
including defining cables, cards and physical
aspects. Fast Ethernet, RS232,
and ATM are protocols with physical layer
Characteristics of Fiber-Optic Cable
Immunity to Electromagnetic Interference
Weight and Size
Corrosion and Water Resistance
Greater Distances
No “Vampire” taps
hard to eaves-drop
I don’t think it’s impossible – just expensive
and requires specialized equipment
and know-how
Immune to EMP
Immunity to Electromagnetic
Immune to EMP
Motors and Generators do not cause
Garage Door
Hair Dryer
Weight and Size
Lighter than copper (1/10)
Smaller diameter than copper (10/1)
No current means no sparks
Light transmission safer
(and cheaper) than work
lamps in some hazardous
Compared to copper:
higher frequency means greater bandwidth
no impedance limitations
no inductive reactance (at high frequencies
copper can lose conduction)
Corrosion and Water Resistance
Glass and plastic do not rust or corrode easily
No tarnish or verdigris (oxidation/rust)
Greater Distances
Copper networks segments mostly limited to
100 meters or less.
fiber-optic can support distances over
20 kilometers.
FDDI applications can be
200 km (124 mi).
The Nature of Light
light energy waves - electromagnetic
electromagnetic waves need no carrier (can
travel through a vacuum) unlike sound waves
instead of frequency: wavelength
visible light roughly 400 - 800 nm
nano meter is meter/billion
fiber-optic commonly used 850nm - 1550nm
Glass or plastic core serves as medium for light
Cladding surrounds the core traps light in the core
Buffer physically protects core/cladding
Water proofing may be added
Oil or water resistant sheath coversall
Loose tube gel filled greater protection
Tight buffer less space more fragile
Attenuation can be through scattering, dispersion,
Fresnel reflection, or extrinsic loss due to bends
splices and connectors
Scattering due to impurities in the core,
cumulative over distance. Glass is better than
Dispersion distortion from cladding reflection.
primary limiter on distance
Fresnel reflection occurs at connectors
Multimode fiber optic cable - large core diameter
Single-mode fiber optic cable - small core diameter
- matched to wavelength to control dispersion allows greater distances
Micrometers - um - meter/million
Cable identified as core/cladding
multimode eg 50/125 65.5/125
single-mode eg 8.3/125
802.3 Standards
• Gigabit Ethernet
• 10 Gigabit Ethernet 10GBase ___
• 10GBaseW
Gigabit Ethernet
IEEE 802.3z
1000BaseSX - multimode fiber
1000BaseLX – single (5km)
or multimode fiber (550m)
1000BaseCX - copper core 25m
10 Gigabit Ethernet
IEEE 802.3ae
fiber only
10GBaseSR (short range) 26m-82m
10GBaseLR (long range) 10km single-mode
10GBaseER (extended range) 40km singlemode
Wide area networks and SONET
10GBaseSW Short Wavelength (850nm)
connect dist.= 33m
10GBaseLW Long Wavelength (1310nm)
connect dist.= 10km
10GBaseEW Extended Wavelength (1550nm)
connect dist.= 40km (25mi)
Fiber Distributed Data Interface
Backbone for MAN or WAN
Structured as dual rings (primary, secondary)
Fault tolerant – two ways
Rings transmit in opposite directions
Token ring
Fiber-Optic Cable Connectors
Proprietary designs abound
SC ST FC LC and MTRJ are most common
ST round insert like BNC (push and twist)
SC square plug
FC screw threads like coaxial connector
LC new small single or duplex dev. by Lucent
Technologies (formerly Bell Labs)
MTRJ - another small duplex design
See page 135
Installation and Troubleshooting
Installing Connectors
Making a Fusion Splice
Using Fiber-Optic Cable Meters
Not usually prepared in the field
Requires expertise to apply, certifications
(BICSI, FOA, Nortel Networks, Beldon )
• Cleaved not cut
Installing Connectors
Design/measure prior to installation/supply
Splicing difficulties include dirt and alignment
Glass cores must be cleaved carefully
Plastic cores must be cut carefully
Making a Fusion Splice
Fusion Splice
two ends melted/welded/fused together
Mechanical splicing
Ends clamped with
gel to mitigate
Fresnel effects
Using Fiber-Optic Cable Meters
Power meter and light source
OTDR optical time Domain Reflectometer
Can locate faults (distance to)
Rent don’t buy