networks are about communication!
DESCRIPTION
Networks are about Communication!. What is a good model of communication?. A COMMUNICATION MODEL. DATA COMMUNICATION NETWORK. comm.net. comm net node. net station i.e computer terminal or telephone. DATA COMMUNICATION NETWORKS. Communication networks. switched unswitched. - PowerPoint PPT PresentationTRANSCRIPT
Networks are about Communication!
What is a good model of communication?
A COMMUNICATION MODEL
Source Channel
noise
Destination
xmitted signal rcvd signal
DATA COMMUNICATION NETWORK
comm.net
comm net node
net station i.ecomputer terminal or telephone
DATA COMMUNICATION NETWORKS
Communication networks
switched unswitched
Switched
Circuit Switched Packet Switched
DATA COMMUNICATION NETWORKS
Unswitched(broadcast nets)
DATA COMMUNICATION NETWORKS
packet radio satellite local
Packet switched nets are store and forward nets.
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
DATA COMMUNICATION NETWORKS
Dish
LAN EXAMPLES:
DATA COMMUNICATION NETWORKS
Ethernet with a bus topology:
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
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.
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.
Computer Communications Architecture
Applications Applications
Transport layer 1 2 3
Transport layer 1 2 3
network access
network accessCom net
Protocol Data Units
TPDU1 = transport protocol data unit := transport hdr, chunk1
TPDU2 = transport hdr, chunk2
NPDU = network protocol data unit network hdr, TPDU
Protocol Data Units
Application data = chunk1 + chunk2 + ...
Destination SAP (service access points)
TPDU has destination SAP so that appropriate application obtains data
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)
Transmission Terminology
point-to-point :- guided transmission is unshared
I.e. O(N**2) connectivity (completely connected)
L12
(N 2 N ) = number of links
Transmission Terminology
Multipoint guided transmission allows shared medium
Transmission Terminology
ANSI Defs:–simplex - one direction only–half-duplex - two-way but not at the same time.
– full-duplex - simultaneous two way transmission
Transmission Terminology
CCITT– CCITT vs ANSI– simplex = half-duplex– duplex = full-duplex
CCITT = international telegraph and telephone consultive committee
Analog and Digital Data Transmission
data - entities which convey meaning
signals - encoding of data
signaling - act of sending a signal
transmission - communication of data by propagation and processing
of signals
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?
Analog and Digital Data Transmission
lim s(t) s(a)
t a
s(t) is continuous (i.e. analog) iff
for all a
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
ISO-OSI ModelISO= International Standards Organization
OSI = Open Systems Interconnection
OSI Model = a 7 layer model used to describe most networks today
1. Physical Layer
This is a physical connection between machines. BITS
2. Data Link Layer
Provides reliable transfer of information across the physical links. FRAMES/Packets or DLPDU
3. Network Layer
Routing
4. Transport Layer
error recovery and flow control
5. Session Layer
Control for communication, close and open connections
6. Presentation LayerData formatting and character code conversion
7. Application Layer
file transfer, virtual terminals, electronic mail
etc..