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Information Science Institute of Sripatum University
IS516
Computer Communication and Networks
ื่ สารคอมพิวเตอร์และเครือข่าย
การสอ
Asst.Dr.Surasak Mungsing
[email protected]
[email protected]
http://www.spu.ac.th/teacher/surasak.mu
Sripatum University
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Lecture 04
Networking Devices and Software
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LAN: Local Area Network
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Local Area Network
Star Network
Ring Network
Bus Network
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Tiered Local Area Networks
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Single-Cell Wireless LAN
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Multiple-Cell Wireless LAN
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Wireless LAN Configurations
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Media
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Electromagnetic Spectrum for Telecommunication
ELF - Elementary Low Frequency
VF - Voice Frequency
VLF - Very Low Frequency
LF - Low Frequency
MF - Medium Frequency
HF - High Frequency
VHF - Very High Frequency
UHF - Ultrahigh Frequency
SHF - Superhigh Frequency
EHF - Extremely Frequency
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Comparison of Shielded and Unshielded Twisted Pair
Attenuation (dB per 100m)
Frequency
(MHz)
Category
3
UTP
Category
5
UTP
1
2.6
4
Near-end Crosstalk(dB)
STP
Category
3
UTP
Category
5
UTP
STP
2.0
1.1
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62
58
5.6
4.1
2.2
32
53
58
16
13.1
8.2
4.4
23
44
50.4
25
-
10.4
6.2
-
41
47.5
100
-
22.0
12.3
-
32
38.5
300
-
-
21.4
-
-
31.3
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Twisted Pair Categories and Classes
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Structured Cabling Elements
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Cable Distances Specified in EIA-568-A
Telecommunications
D
Outlet
Main
A
Horizontal
Cross-connect
Cross-connect
Telecommunications
D
Outlet
C
Horizontal
B
Cross-connect
Media Type
UTP (Voice Transmission
Intermediate
Cross-connect
A
B
C
D
900 m
500 m
300 m
90 m
Category 3 UTP up to 16 MHz
90 m
90 m
90 m
90 m
Category 5 UTP up to 100 MHz
90 m
90 m
90 m
90 m
STP up to 300 MHz
90 m
90 m
90 m
90 m
02.5 mm Optical Fiber
2000 m
500 m
1500 m
90 m
Single-mode Optical Fiber
3000 m
500 m
2500 m
90 m
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IEEE 802 Protocol Models Compared to OSI Model
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LAN Protocol in Context
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LLC PDU in a MAC Frame
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Internetworking Devices
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Internetworking Devices

When two or more computers connect in order to
communicate to each other or to use shared
resources, they are a computer network

When two or more networks connect for
communication or resource sharing purpose, they
are an internetwork or internet

Connecting two or more networks requires
networking device(s) such as Repeater, Bridges,
Switches, Routers, Gateway
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OSI VS Internetworking Devices

Each networking device communicates with network
layers in the OSI reference model

Lower layers of the OSI reference model describe
functionalities of main networking device and type of
device classified by network layer of the OSI

Devices in physical layer, e.g. MODEM, Hub, PBX,
repeater

Devices in data link layer, e.g. Bridge, Switch

Devices in network layer, e.g. Router

Devices in network layer, e.g. Gateway
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Internetworking Devices and the OSI Model
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MODEM : MOdulation and DEModulation

Main functions of a MODEM are to convert analog
signal to digital signal and to digital signal to
convert analog signal

Signals used in telephone network are analog but
Signals used in computers are digital
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Dial-up line and a Dedicated line

Dial-up line is temporary connection using
telephone line for communications

Dedicated line is line always connected between
two communications devices
Advantages of dial-up line
Advantages of dedicated line
1. Costs no more than making
regular call
1. Quality and consistency of
connection are better
2. Computers at any two locations
can establish a connection using
modems and telephone network
2. Computer locations are fixed
3. Can be digital or analog
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HUB

A device that broadcasts signals. Normally used to
expand network as tree structure topology based on
10Base-T standard

Main responsibility of a hub is to broadcast signals
through or within a network, therefore it is a physical
layer device of the OSI reference model

Today’s hub can manage ports and evolved to
switched hub, which support layer 2 and layer 3
functions
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Switched Hub
N
10
10
Mbps
Mbps
10
A
x 10Mbps
Mbps
B
10
Mbps
C
D
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Repeater

An electronic device that only works in the physical
layer of the OSI reference model

Used to repeat and amplify signals so that they
can travel farther, which solved attenuation
problem

Repeater dose not change or modify signals, it just
repeats and retransmit the signals, therefore it
joins two portions of the same network to become
one larger network
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A Repeater in the OSI Model
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Repeater
 does not change but retransmit signals to
another segment of the network
 makes two segments become one network
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Bridge

A device than link same type of networks, such
as Ethernet to Ethernet, or token ring to token
ring

Broadcasting signals within same network

if destination address is in other network, there
will be no broadcasting within the sender
network, and packets will be send to bridge and
then to the other network
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A Bridge in the OSI Model
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A Bridge
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Switch
•
•
Many types of switches: Cell switch or ATM switch,
Ethernet switch, frame relay
Switching devices are developed with new
technology and capable of transmitting and receiving
data at very high speed (many hundred million bits
per second), such as frame relay and ATM switch
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Router
•
•
•
A device that connects networks, such as Ethernet, frame
relay (LAN-to-WAN) with specific protocols to be used by
routers
Router receives packets and examines destination of each
packet then compare with routing table to choose a route and
forward the packet via that route
If the forward route uses different network standard it then
transform to the new standard
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A Router in the OSI Model
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Routers in an internet
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Gateway

Device or software for connecting networks, same or
different type of networks

If networks use different protocols, gateway acts as a
protocol converter so that they can communicate

Supports from application layer downward

Facilitates distributed applications
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A Gateway in the OSI Model
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A Gateway
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Communication software
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Communication Software

Software that connects and exchanges
data between communication system in a
network, e.g. Telnet, FTP (File Transfer
Protocol), Web Browser (IE/Netscape…),
E-Mail, Instant Messaging and
Internet Telephony
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Telnet

Service software for remote login

telnet can run on Windows OS by using “run” menu and type
telnet <ip address > for example telnet 202.44.68.3
or specifies the domain name to be connected, such as
telnet spu.ac.th
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Telnet
Type
telnet 202.44.68.3
Enter username and password
display after successfully
connected to spu.ac.th
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Benefit of Telnet

using resources of a remote computer

Searching and transfering data between computers,
even in different system

Checking e-Mails or other services in case of using
other computer, in particular, in text mode
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FTP (File Transfer Protocol)

Use for file transfer between computers, within
same network or different network, and same
type or different type of computers

FTP programs that work in text mode require
typing and those that work in Graphic mode are
easier to use
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Instant Messaging : ICQ, MSN
1: Login to the IM server
2: Server checks if any
established friends, family,
or co-workers, called
buddies, are online
3: Send instant messages to
online buddy
Step
Step
2
1
IM
server
4: Instant message travels
through messaging server
and then to online buddy
Step
messaging
3
server
Step
4
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Next Lecture:
Guided Networks
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