Week 5 lan topology

Media, LAN Technologies,
and Network Topologies
Lecture 5

Introduction to Media
Network traffic must flow through some
form of media, whether it is a cable, or
is wireless.
The most common forms of network
media are twisted-pair, coaxial, and
fiber-optic cable.

Twisted-Pair Cable
T-P cable is the most common of all of the
media types in the average local area
network (LAN) environment.
Different categories of T-P cable exist. The
different categories of cable specify the
maximum data bandwidth that the cable can
withstand.
T-P comes in two forms, Unshielded (UTP) or
Shielded (Plenum/STP).

Twisted-Pair Categories
Category
Maximum
Data Rate
Usual
Application
CAT-1 < 1 Mbps POTS & ISDN
CAT-2 4 Mbps
IBM Token
Ring
CAT-3 16 Mbps
Voice/Data
-10baseT

Twisted-Pair Categories
(cont.)
CAT-4 20 Mbps
16Mbps Token
Ring Networks
CAT-5 100 Mbps
100baseT,
155Mb ATM
CAT-7
(in progress)
1000 Mbps
1000baseT,
Gigabit
Ethernet

Twisted-Pair (cont.)
Twisted-pair cable
(CAT5 and up)
consists of 4
separate pairs of
wires, all wound
separately.

Coaxial Cable
Coaxial cable (coax) is almost the same
thing that carries your cable TV signal.
Data coax is just held to a higher
quality.
Historical Tidbit: Coax cable, although
not commonly seen nowadays, was
how Ethernet was developed!

Coax (cont.)
The physical
medium itself
consists of an inner
wire, surrounded by
an insulator, which
is also surrounded
by a shield.

Coax Applications
Local Area Networks
(LANs)
 Thinnet (10base2) –
200 meters
 Thicknet (10base5) –
500 meters
 Baseband
transmissions only
Wide Area Networks
(WANs)
 T3/DS3/E3
 Broadband
transmissions

Baseband v. Broadband
Baseband is where the medium only
carries one signal on the line.
Broadband carries multiple signals on a
single line.

Fiber Optic Cable
Fiber optic cable is
where the future of LAN
wiring exists.
Fiber comes in two
different types:
 Multimode – a
channelized fiber-optic
circuit. Multiple carrier
frequencies.
 Singlemode – a “clear
channel” circuit. One
carrier frequency.

Fiber Applications
High-bandwidth voice transmission.
“Backbone” applications.
Very fast data transfer between network
devices.

Other Media
Cellular
Infrared
Satellite
 Geosynchronous
 Low Earth Orbit
Packet Radio
Microwave

LAN Topologies
There are three main types of LAN
systems:
 Star Topology
 Ring Topology
 Bus Topology
Some topologies are actually hybrids of
the above!

Star Topology
All computers
connect to a
centralized point.
The central point is
called the hub.

Ring Topology
One computer is
connected to the
two computers
adjacent to it.
In the traditional
case, if a system is
disconnected from
the ring, the network
fails.

Bus Topology
A bus topology consists of a single
cable to which each network device
attaches.
Bus topology has the same problems
as a ring topology.

LAN Technology Options
o Ethernet
o Fast Ethernet
o Gigabit Ethernet
o 10 Gig Ethernet
LAN Technologies

Ethernet
Ethernet design by Bob Metcalfe in 1976.
The Ethernet specification details how
devices are supposed to interact on the
segment, distances between devices, and a
whole other multitude of other things.
Carrier Sense On Multi-Access Networks
(CSMA) with Collision Detection (CD) was the
most important part of the specification.

Ethernet
10 Base 5 (Thicknet) (Bus Topology)
10 Base 2 (Thinnet) (Bus Topology)
10 Base T (UTP) (Star/Tree Topology)
10 Base FL (Fiber) (Star/Tree Topology)
LAN Technologies

CSMA on Ethernet
CSMA indicates that computers wait
until the ether is free. In this case, no
electrical signal denotes when the ether
is “free.”

CSMA on Ethernet (cont.)
The “signal” is the carrier of the ether.
The act of waiting for the opportunity to
send on the ether is carrier sense.

Collision Detection
Since networks are not instantaneous, it is
possible for two stations to check the ether,
deem it time to send, and both send at the
same time.
This is called a collision.
When a collision occurs, the sender
immediately stops transmission, and waits
some random length of time, and then begins
transmission again.

Collision Detection (cont.)
A busy segment will always have collisions.
Collisions do not damage the equipment, but
it forces the two machines that caused the
collision to wait, and therefore it slows down
the network.
Fewer machines on a segment, smaller
segments, can improve the collision count.

Ethernet Address
o End nodes are identified by their Ethernet
Addresses (MAC Address or Hardware
Address) which is a unique 6 Byte address.
o MAC Address is represented in Hexa Decimal
format e.g 00:05:5D:FE:10:0A
o The first 3 bytes identify a vendor (also called
prefix) and the last 3 bytes are unique for every
host or device

Ethernet Address
o MAC address allocation administered by IEEE
o manufacturer buys portion of MAC address space (to
assure uniqueness)
o Analogy:
(a) MAC address: like Social Security Number
(b) IP address: like postal address
o IP hierarchical address NOT portable
o depends on IP network to which node is attached

Ethernet
o Physical Media
 10 Base5 - Thick Co-axial Cable with Bus Topology
 10 Base2 - Thin Co-axial Cable with Bus Topology
 10 BaseT - UTP Cat 3/5 with Tree Topology
 10 BaseFL - Multimode/Singlemode Fiber with Tree
 Topology
o Maximum Segment Length
 10 Base5 - 500 m with at most 4 repeaters (Use Bridge to extend
the network)
 10 Base2 - 185 m with at most 4 repeaters (Use Bridge to extend
the network)
 10 BaseT - 100 m with at most 4 hubs (Use Switch to extend the
network)
AN Technologies

Fast Ethernet
o 100 Mbps bandwidth
o Uses same CSMA/CD media access protocol
and packet format as in Ethernet.
o 100BaseTX (UTP) and 100BaseFX (Fiber)
standards
o Physical media :
 100 BaseTX - UTP Cat 5e
 100 BaseFX - Multimode / Singlemode Fiber
o Full Duplex/Half Duplex operations.
LAN Technologies

Fast Ethernet
o Provision for Auto-Negotiation of media speed:
10 Mbps or 100Mbps (popularly available for
copper media only).
 100 Base TX - 100 m
 100 Base FX - 2 Km (Multimode Fiber)
 100 Base FX - 20 km (Singlemode
Fiber)
LAN Technologies

Gigabit Ethernet
o 1 Gbps bandwidth.
o Uses same CSMA/CD media access protocol as in
Ethernet and is backward compatible (10/100/100
modules are available).
o 1000BaseT (UTP), 1000BaseSX (Multimode Fiber) and
1000BaseLX (Multimode/Singlemode Fiber) standards.
 1000 Base T - 100m (Cat 5e/6)
 1000 Base SX - 275 m (Multimode Fiber)
 1000 Base LX - 512 m (Multimode Fiber)
 1000 Base LX - 20 Km (Singlemode Fiber)
 1000 Base LH - 80 Km (Singlemode Fiber)
LAN Technologies

10 Gig Ethernet
o 10 Gbps bandwidth.
o Uses same CSMA/CD media access protocol as in
Ethernet.
o Propositioned for Metro-Ethernet
 1000 Base-T - Not available
 10GBase-LR - 10 Km (Singlemode Fiber)
 10GBase-ER - 40 Km (Singlemode Fiber)
LAN Technologies

LocalTalk
LocalTalk is another form of a bus network.
LocalTalk differs from Ethernet in a few ways:
 When a machine senses the segment is free, it
holds it until the frame transmission is over. All
other machines know to wait for transmission to
complete.
 Bandwidth is quite small at ~230Kbps. That’s
2.3% of the earliest Ethernet specification!

IBM Token Ring
Access mechanism is
called token passing.
Once the sent
information makes a
complete turn around
the ring, the sender
passes the token to the
next machine.
This is a strict-
alternation scheme
where all machines
have the same chance
to transmit information.

Fiber Distributed Data
Interconnect (FDDI)

Week 5 lan topology

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Week 5 lan topology