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Introduction to Management Information Systems
Chapter 5 Data Communications
and Internet Technology
HTM 304
Fall 07
Content
1. 5-layer Architecture for Communication
2. Internet
3. Enterprise Network
4. Wireless
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Fundamental Networking Concepts
Computer network
– collection of computers that communicate over
transmission lines
3 main type of networks
LANs – Local Area Network
WANs – Wide Area Network
internets – interconnected networks, e.g. the “Internet”
An Internet uses varied communication methods
and conventions
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Interconnected Networks
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Telecomm Network – Circuit Switching
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PSDN: Packet Switching Data Network
Demo: How a file is sent over PSDN
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Packet Switching Technology
Packet switching breaks transmissions into messages
(or packets, frames)
When a packet arrives at a router, the router must
decide which of several paths to use to send the
packet on
Complex algorithm
Computation done by each router
Some packets may be lost during transmission.
Only those packets that are lost will be resent
Won’t ruin the whole conversation
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Layered Protocol
A set of layered protocols provide seamless communication
between computers
What is protocol?
-- A standardized means for coordinating an activity between two
or more entities.
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Computer Protocol
Communications protocol
coordinates activity between
two or more computers
Two machines must agree on protocol and follow it to send
messages
There are many levels of coordination: e.g. MacOS ↔
Windows, Wireless network ↔ Wired LAN, etc.
A set of layered protocols provide seamless communication
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Three different network architectures
7-layer OSI model (developed by ISO)
ISO (International Organization for Standardization)
OSI (Open System Interconnection)
4-layer TCP/IP model (developed by IETP)
TCP/IP (Transmission Control Program / Internet Protocol)
IETP (Internet Engineering Task Forece)
5-layer blend model: TCP/IP – OSI model
The most commonly used model
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The 5-Layer Model
Require:
Remember the name of
these five layers
Describe the general
functions of each layer
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Layers, Protocols, and Analogy to Mail
Email:
How are you doing?
Deal with app.
software
Deal with how
to transport
(e.g. confirmation?)
Deal with how to
route packets
(e.g. next relay?)
Deal with physical
transportation
(e.g. network
medium, CRC)
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Layer 1 Physical Layer
Question: what is the very first step to connect two computers?
Concerned with transmitting data bits over a communication
circuit.
Example questions concerned:
What voltages to represent 0-1s?
How many bits per seconds to be sent?
What kind of cable to be used?
Reflect to the physical post office example:
The post office vehicle, the staff, the mailbox, the road condition…
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Layer 1 – Types of Cables
Type
Use
Maximal Speed
Dail-up Modem, DSL
Modem and T1 (leased line)
56kbps ~ 1.544mbps
Telephone Line
(Twisted pair copper)
Coaxial Cable
Cable modem
Upstream: 256kbps
Downstream: 10mbps
UTP
(Unshielded Twisted Pair)
LAN
100mbps
LAN, T3 (leased line), etc.
40 Gbps or more
Optical Fiber Cable
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The speed measurement
bps: stands for bit per second
Why use bits not bytes?
Other units:
Symbol
Name
Value
kbps (kbit/s)
kilo bit per second
1,000 bps
mbps (mbit/s)
mega bit per second
1,000,000 bps
Gbps (gbit/s)
Giga bit per second
1,000,000,000 bps
Remember the set of units for capacity storage: B, KB,
MB, GB.
Know the difference
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Calculation
How long does it take to send 10MB data using dial-up modem?
Speed: 54kbps = 54,000 bit per second
Data amount: 10MB = 10 * 1024 * 1024 * 8 bit = 83,886,080 bit
Time:
83,886,080 bit / 54,000 bit per second
 1553.46 second  25.89 minute
Why?
Ask for effective communication rate!
Revision: take in to account that the effective communication rate is
30%
Effective Speed: 54kbps * 30% = 16,200 bit per second
Data amount: 10MB = 10 * 1024 * 1024 * 8 bit = 83,886,080 bit
Time:
83,886,080 bit / 16,200 bit per second
 5178.15 second  86.3 minute
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More exercise:
Estimate the time to download the following files under
different network conditions:
A)
reported speed: 30kbps,
effective rate: 25%
file size: 204KB – a JPEG file
B)
reported speed: 5.4 mbps,
effective rate: 30%
file size: 4 GB - DVD
C)
reported speed: 100 mbps,
effective rate: 15%
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file size: 605MB – a CD
Extended Cable: Hub
Operates on the physical layer: the first layer
A shared bus: an extended cable that
physically connects all the computers
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Another device - Modem
Stands for: modulator – demodulator
Modulation:
Covert digital signals to analog signals
Demodulation:
Covert analog signals to digital signals
Modem converts digital
signals to analog signals
so that the data can be
transferred via the analog
cable/equipments.
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Types of Modems
Dial-up Modems
Produces analog signals that can be carried on a regular
telephone line.
Point – to Point communication  circuit switch network
DSL Modems
DSL: digital subscriber line
Operate on the same telephone lines, but do not interfere with
voice telephone service.
Cable Modems:
High speed data transmission using cable television lines.
Operate in such a way that their signals do not interfere with TV
signals.
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How many ways to connect computers?
Three typical topologies
STAR
BUS
RING
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Pros: easy to add a new node; easy to access the
file server; If one node is down, it will not affect
others; Cons: the # of nodes has limit; slows down
when too many nodes;
Pros: in expensive, easy to install, easy to
add a new node; can add more nodes;
Cons: require coordination among the
nodes on when to use the bus
Pros: high bandwidth and span large distance;
Cons: relatively expensive and hard to install;
communication among the computers is difficult
(require a token – token ring)
Layer 2: Data Link Layer
Task: to establish a virtual line that appears free of
undetected transmission errors to the network layer.
Analogy:
How to send the mail from one station to another. Decision maker
on this lever doesn’t consider the physical layer specifics such as
what kind of car, road condition, car speed.
Use Google Map to figure out the direction
Traffic Lights
Damage control (car incidence)
Some main function of Data Link Layer:
Traffic control (not sending too fast)
Error control (collision detection, token management)
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Frame
Layer 2 receives data packets from above (i.e. layer 3,
Internet layer), and breaks them down into frames
A frame can be of a few hundreds or a few thousand bytes.
Frames are transmit sequentially.
Acknowledgement Frames are sent back by the receiver.
Frames contain the MAC address of the sender computer and the
receiver computer.
Here, the receiver computer is the computer in the next link (e.g. the
next post-office transition station)
MAC address: uniquely assigned with the NIC (network interface
card)
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Layer 2 Equipment
Network Interface Card (NIC)
Modern motherboard sometimes has NIC built-in
Each NIC has a unique identifier, the MAC address
MAC: Medium Access Control
The MAC address is assigned by the manufacturer, you cannot
change it.
Layer 2 protocols recognize the MAC addresses in the network,
and determine how to establish data link from one computer to
the other.
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Some Layer 2 Control Standards
Control error-less communication between two physical
computers based on different ways the computers are
connected. Two important standards need to know:
Ethernet: IEEE 802.3
IEEE (pronounced “ I triple E”: stands for the Institute for Electrical
and Electronics Engineers.
IEEE 802 committee: LAN standards committee
Used for control communication under bus topology.
Used for most of the PCs.
Token-Ring: IEEE 802.5
Advocated by IBM. Token circulates around the ring. Whoever gets
the ring talks.
Wireless Comm. IEEE 802.11 series
Will talk later in wireless session.
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Summary of Today
Basic concepts:
Computer networks
LAN / WAN / internet / Internet
PSDN: explain the difference with circuit switch network
Layered Protocols
What is protocol? Why protocols?
Names of three different architectures
The TCP/IP-OSI blend model: name of 5 layers?
The hardware layers: physical layer and data link layer
Functionalities
Devices: cables, Hub, Modem, NIC
Calculation: How to estimate transmission time?
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