Transcript c12- Data Communication n Networkingx

Chapter 12
DATA COMMUNICATION
AND NETWORKING
Communication
sending or receiving information
Beating of drums
Mirrors reflecting sunlight
Homing pigeons
Telegraph, telephone
Computers …
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Data Communication
Data Communication
DATA COMMUNICATION
• Exchange of data between two devices
• wired or wireless transmission medium
Transfer of data
Method of transfer
Preservation of the
data during the
transfer process
Communication system (collection of hardware, software …)
Delivery
• The system must
deliver data to the
correct or the
intended
destination.
Accuracy
• The system must
deliver data
accurately (error
free).
Timeliness
• The system must
deliver data in a
timely manner
without enough
time lags.
Five components of a data
Communication System
1. Message
2. Sender
• It is the
information to be
communicated.
Popular forms of
information
include text,
pictures, audio,
video etc.
• It is the device
which sends the
data messages. It
can be a
computer,
workstation,
telephone
handset etc.
3. Receiver
• It is the device
which receives
the data
messages. It can
be a computer,
workstation,
telephone
handset etc.
4. Transmission
Medium
• It is the physical
path by which a
message travels
from sender to
receiver. Some
examples include
twisted-pair wire,
coaxial cable,
radio-waves etc.
5. Protocol
• It is a set of rules
that governs the
data
communications.
It represents an
agreement
between the
communicating
devices. Without
a protocol, two
devices may be
connected but
not
communicating.
Data Transmission Modes
Simplex
• Data in a simplex channel is always one way. Simplex
channels are not often used because it is not possible
to send back error or control signals to the transmit
end. An example of a simplex channel in a computer
system is the interface between the keyboard and the
computer, in that key codes need only be sent one
way from the keyboard to the computer system.
Half Duplex
• A half duplex channel can send and receive, but not at
the same time. Its like a one-lane bridge where two
way traffic must give way in order to cross. Only one
end transmits at a time, the other end receives.
Full Duplex
• Data can travel in both directions simultaneously.
There is no need to switch from transmit to receive
mode like in half duplex. Its like a two lane bridge on
a two-lane highway.
Analog & Digital Transmission
Analog
• information changes continuously
and can take on many different
values. An analog clock’s hands
move constantly, displaying time
on a continuous scale.
Digital
• information is characterized by
discrete states. A light bulb, for
example, is on or off. A digital
clock represents the time in oneminute intervals and doesn’t
change its numbers again until
the next minute. A digital clock
can represent exact minutes but
not the seconds that pass in
between.
Analog & Digital Transmission …
Analog to analog
Voice (Analog Data) Telephone  Analog Signal
Digital to analog
PC ( Digital Data) Modem  Analog Signal
Analog to digital
Voice ( Analog Data)  CODEC  Digital Signal
Digital to Digital
PC ( Digital Data) Digital Transmitter  Digital Signal
Analog
Signals- Sine waves
•Amplitude
•Frequency
•Wavelength
Data Communication Measurement
Narrowband Services
• 64 Kbps or less channels
Wideband Services
• 1.5 Mbps to 45 Mbps (North American)
• 2 Mbps to 34 Mbps (International)
Broadband Services
• 45 Mbps or greater (North American)
• 34 Mbps or greater (International)
Transmission Media
Radio Frequency Propogation
Modulation
Multiplexing
Multiplexing …
Synchronization- Controlling time
Asynchronous Transmission
Each character of data is treated independently
Synchronous Transmission
For sending large blocks of data
Control schemes
Character-oriented
Bit-oriented
Switching
4 Employee Office
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Direct Lines to each of them!
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Point to point communication
Impractical & Wasteful
Route calls by making temporary connection!
Use Switches or Exchanges
Some switches are directly connected to a comminication device while others
are dedicated to route/forward information
Circuit switching
Major Attributes
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Dedicated fixed BW channel
Data (sent/received) path is determined by the circuit
Data path does not change within the lifetime of
connection
Simple method. Used in Public Service Telephone
Network (PSTN)
Disadvantage?
Waste when there is no data flowing
Cannot change the circuit after it is established even if
there are other (cheaper) routes possible
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Packet Switching
Major Attributes
• Focuses on data communication (vs. voice)
• Break data into packets
• Package Assembler and Disassembler (PAD)
• Packets from a single message will not necessarily follow
the same route
• Packet Header
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Destination
Priority
…
Packet Switching Exchange (PSE)
Efficient?
“Message Switching” is obsolete
Computer Network
Standalone versus Networked Environment
How can we connect (physically)?
Network Operating Systems
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Manage multiple computers on a network
• Client/Server (NOS)
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Client request and server serves
Access to resources
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Equal peer nodes
• Peer to peer network (NOS?)
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Both server & client
Music/File sharing!
Client/Server
How it works
Client sends request for service to server
Server fulfills request and send results to client
Client and server may share processing
Benefits
Reduces volume of data traffic
Allows faster response for each client
Nodes can be less expensive computers
Attribute
P2P
Client/Server
Centralization of resource
and data
No
Yes
Maintenance cost
Low
High
Needs staffs, support
Installation Process
Simple
Requires experts
Cost
Low- no dedicated server
Requires a dedicated
server
Security
Low
High
Reliability
High- all independent
nodes
Server down- network
down
Standalone Vs. Networked Environment
Topology – Physical layout of components
Computer Network
LAN
MAN
WAN
CAN
LAN- Local Area Network
Connections over short distances through
communications media
Connecting LANs
Bridge – connects networks with similar protocols
Router – directs traffic via best path
Components
IP switches
Replacing routers
Less expensive
Faster
Gateway
Connects LANs with dissimilar protocols
Performs protocol conversion
• PCs
• Network
cable
• NIC
WAN- Wide Area Network
Link computers in geographically distant locations
Network Topology
Bus topology
Ring topology
Star topology
Tree topology
Mesh topology
Check the
textbook
OSI Model
Textbook P 445
OSI Model …
Layer 1 - Physical
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Defines the cable or physical medium itself
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e.g., thinnet, thicknet, unshielded twisted pairs (UTP).
All media are functionally equivalent.
Layer 2 - Data Link
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Defines the format of data on the network
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A network data frame, aka packet, includes
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checksum,
source and destination address, and
data.
The largest packet that can be sent through a data link layer
defines the Maximum Transmission Unit (MTU). net interface to
handle connections to the outside world, and a loopback interface
to send packets to itself.
OSI Model …
Layer 3 - Network
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NFS uses Internetwork Protocol (IP) which is responsible
for routing, directing datagrams from one network to
another.
The layer may have to break large datagrams, larger
than MTU, into smaller packets and host receiving the
packet will have to reassemble the fragmented datagram.
Layer 4 - Transport
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Subdivides user-buffer into network-buffer sized
datagrams
Reliability and
enforces desired transmission control.
speed are the
primary
Two transport protocols sits at this layer
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Transmission Control Protocol (TCP)
User Datagram Protocol (UDP)
difference
between these
two protocols.
OSI Model …
Layer 5 - Session
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Defines the format of the data sent over the connections
The NFS uses the Remote Procedure Call (RPC) for its
session protocol
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RPC may be built on either TCP or UDP
Layer 6 - Presentation
• External Data Representation (XDR) sits at this level.
• Converts local representation of data to its canonical form
and vice versa.
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The canonical uses a standard byte ordering and structure
packing convention, independent of the host.
Layer 7 - Application
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Provides network services to the end-users. Mail, ftp,
telnet, DNS, NIS, NFS … network applications.
Network Devices
NIC
Repeater
Hub
Bridge
Switch
Router
Gateway
P449