Download Brad`s Lecture on networks

Guided Transmission Media

twisted pair wires
• Shielded- STP
• Unshielded- UTP


coaxial cables
optical fiber
Twisted Pair Wires

consists of two insulated copper wires
twisted around each other
• twisting minimizes the electromagnetic
interference between adjacent pairs



Use RJ-45 connector, which has eight wires
inexpensive, readily available, flexible, light
weight, easy to install
susceptible to noise and signal attenuation
Twisted Pair Wires

UTP: Unshielded Twisted Pair
• Categories 1 through 5 (5 is fastest)
• Category 3: data rates up to 16 Mbps
• Category 5: data rates up to 100 Mbps
• more tightly twisted than Category 3 cables
• more expensive, but better performance

STP Shielded Twisted Pair
• extra metallic shield results in less electrical
interference than unshielded TP
• More expensive, harder to work with
Coaxial Cable (or Coax)




has an inner conductor surrounded by a
braided mesh
both conductors share a common center
axial, hence the term “co-axial”
higher bandwidth, much less susceptible to
interference than twisted pair
bulky
Coax Layers
outer jacket
(polyethylene)
shield
(braided wire)
insulating material
copper or aluminum
conductor
Types of coax

Thicknet
•
•
•
•

used in 10Base5 Ethernet
half-inch in diameter
bulky and expensive
devices connected via vampire tap
Thinnet•
•
•
•
used in 10Base2 Ethernets
easier to work with, cheaper than Thicknet
RG-58
BNC connectors on coax attach to T connectors
Fiber Optics




greater capacity, very fast, very reliable
can be used over longer distances
immune to electrical interference, small size
but very expensive and hard to install
Fiber consists of three concentric sections
plastic jacket
glass or plastic fiber core
cladding
LAN Topologies: Bus





All PCs connected on single cable
Each PC attaches to bus cable
Transmission from any stations travels
entire medium (both directions)
Terminators required at ends of bus
Stations take turns sending messages
Bus LAN Diagram
•Very flexible- easy to add new computers
•If one cable breaks, network goes down
CSMA/CD


Carrier sense multiple access with
collision detection- used in Ethernet
Four step procedure
• If medium is idle, transmit
• If medium is busy, listen until idle and
then transmit while still listening
• If collision is detected, cease transmitting
• After a collision, wait a random amount of
time before retransmitting
LAN Topologies: Ring


All PCs connected on single cable in a ring
If one cable in ring breaks, entire network
goes down!
Ring LAN Diagram

Token passing:
• Token constantly circulates through ring in one
direction
• If PC wants to send message, it gets token,
attaches message to token, and sends token
back out on the ring
• Other PCs must wait until free token comes
around
LAN Topologies: Star

Each station connected
directly to central hub
 Hub can broadcast
info to all attached
PCs or just to
individual PCs
 Better reliability- if
one cable fails, rest of
network not affected
 limited expandability
10BASE-T Ethernet




Uses UTP (unshielded twisted pair)
Star-shaped topology is well-suited to
existing wires terminating in a closet
Stations attach to central hub via two
twisted pairs
Physical star, but logical bus
OSI 7 layers
Open Systems Interconnection







Physical Layer
Data Link Layer
Network Layer
Transport Layer
Session Layer
Presentation Layer
Application Layer







Please
Do
Not
Tell
Secret
Passwords
Anytime
Network Protocols

TCP/IP- Transmission Control
Protocol/Internet Protocol
• backbone of the Internet
• used for addressing, tranporting, and delivering
messages on the Internet
• TCP part divides message into packets that can
be sent over the network
• IP part is responsible for addressing, sending,
and assembling the packets and for errorchecking
More Network protocols

PPP- Point-to-Point Protocol
• modem communications for sending data
packets over telephone lines
• used in dial-up networking (e.g., ERA account)

IPX/SPX - Internetwork Packet
Exchange.Sequenced Packet Exchange
• used in Novell networks
Network protocols continued

NetBEUI- NetBIOS Extended User
Interface
• used in Microsoft LANs

FTP: File Transfer Protocol
• send and receive files via Internet

HTTP: Hypertext Transfer Protocol
• protocol used to send Web pages over Web
More network protocols

NFS- Network File Services
• for accessing network drives

SMTP- Simple Mail Transfer Protocol
• Sending email over network

Telnet- terminal emulation
• connecting to remote host and emulating
terminal
Network Interface Cards (NIC)


Network adapter occupies PCI or ISA slot
Works as translator between network and
PC • NIC converts between networks, which
transmit serial data (1 bit at a time) and PCs,
which transmit parallel data (8 bits at a time)

NIC must match network architecture being
used (Ethernet, Token ring, etc.)
• some cards can support more than one
architecture and have connectors for both
Network hardware

Repeaters• amplify digital signal
• 2 types:
• amplifier repeater- amplifies signal and sends it
on (so if signal contains noise, the noise gets
amplified too)
• signal-regenerating repeater- actually regenerates
the digital signal, so noise gets removed

Hub
• clustering point for nodes on an Ethernet
network
Network hardware

Bridge
• connects two or more LANs or LAN segments
that use the same protocol

Router
• determines best path to send message to its
destination- examines addresses of network
traffic and decides which route to send it by

Gateway
• connects networks that use different protocols,
e.g., Ethernet to token ring network