Networks are about Communication! What is a good model of communication?
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Transcript of Networks are about Communication! What is a good model of communication?
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Networks are about Communication!
What is a good model of communication?
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A COMMUNICATION MODEL
Source Channel
noise
Destination
xmitted signal rcvd signal
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DATA COMMUNICATION NETWORK
comm.net
comm net node
net station i.ecomputer terminal or telephone
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DATA COMMUNICATION NETWORKS
Communication networks
switched unswitched
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Switched
Circuit Switched Packet Switched
DATA COMMUNICATION NETWORKS
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Unswitched(broadcast nets)
DATA COMMUNICATION NETWORKS
packet radio satellite local
Packet switched nets are store and forward nets.
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ckt switched nets have dedicated communication paths (i.e. telephone)
For example:
DATA COMMUNICATION NETWORKS
net station
node
A Broadcast Comm. Net can be WAN, the media is unshared
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DATA COMMUNICATION NETWORKS
Dish
LAN EXAMPLES:
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DATA COMMUNICATION NETWORKS
Ethernet with a bus topology:
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DATA COMMUNICATION NETWORKS
Ring topology net:
Note: No switching nodes ,media is shared in LAN For packet radio,every station can hear every other,the media is shared so this is a LAN technology
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DATA COMMUNICATION NETWORKS
Agent input device transmitter channel
channel receiver output device
This course addresses the communication systems parts between the input and output devices.
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Computer Communications Architecture
The Three Layer ModelApplication run on computer which use
networks network layer - xchange of data between computer and network transport layer - error detection and correction application layer - file xfer etc.
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Computer Communications Architecture
Applications Applications
Transport layer 1 2 3
Transport layer 1 2 3
network access
network accessCom net
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Protocol Data Units
TPDU1 = transport protocol data unit := transport hdr, chunk1
TPDU2 = transport hdr, chunk2
NPDU = network protocol data unit network hdr, TPDU
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Protocol Data Units
Application data = chunk1 + chunk2 + ...
Destination SAP (service access points)
TPDU has destination SAP so that appropriate application obtains data
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Protocol Data Units
Sequence # TPDU’s may be sent in any
order,and by different routes and
may arrive at different times.TPDU may have error detection or correction codes built-in
NPDU destination address (i.e. IP address) facilities requires (i.e. priority)
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Transmission Terminology
point-to-point :- guided transmission is unshared
I.e. O(N**2) connectivity (completely connected)
L12
(N 2 N ) = number of links
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Transmission Terminology
Multipoint guided transmission allows shared medium
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Transmission Terminology
ANSI Defs:–simplex - one direction only–half-duplex - two-way but not at the same time.
– full-duplex - simultaneous two way transmission
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Transmission Terminology
CCITT– CCITT vs ANSI– simplex = half-duplex– duplex = full-duplex
CCITT = international telegraph and telephone consultive committee
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Analog and Digital Data Transmission
data - entities which convey meaningsignals - encoding of datasignaling - act of sending a signaltransmission
- communication of data by propagation and processing
of signals
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Analog and Digital Data Transmission
digital data - takes on discrete values, i.e. text
integers.analog data - takes on continuously varying patterns
of intensity, i.e.. sound
But what is digital? What is Analog? How do we defines these things?
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Analog and Digital Data Transmission
lim s(t) s(a)t a
s(t) is continuous (i.e. analog) iff
for all a
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DATA and SIGNALS Modem (modulator/demodulator) modulation involves two waveforms:
The modulating signal (the message) and the carrier wave which is altered by the modulating signal
The complementary process is called demodulation
Bits <-> modem <-> analog signal <-> modem <-> bits
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ISO-OSI ModelISO= International Standards Organization
OSI = Open Systems Interconnection
OSI Model = a 7 layer model used to describe most networks today
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1. Physical Layer
This is a physical connection between machines. BITS
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2. Data Link Layer
Provides reliable transfer of information across the physical links. FRAMES/Packets or DLPDU
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3. Network Layer
Routing
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4. Transport Layer
error recovery and flow control
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5. Session Layer
Control for communication, close and open connections
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6. Presentation LayerData formatting and character code conversion
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7. Application Layer
file transfer, virtual terminals, electronic mail
etc..