Download 02. Components of Network. Communication Subnetwork

Lecture #2: Components of Network.
Communication Subnetwork
Contents
 Network Architecture: 2
– Terminal Network
– Computer Network

Data Transmission Modes
– Circuit Switching
– Message switching
– Packet Switching
4
• virtual channels 5
• datagram switching


Communication Subnetwork
Network Components 9
6
1
Network Architecture:
Terminal Network


From Terminal Complex to Terminal
Network
Terminal Network Structure:
– host,
– communication processor,
– concentrator,
– terminal processor
2
Network Architecture:
Computer Network

From Terminal Network to Computer Network:
– distributed control
– distributed resources
– remote access

Network Range:
– LAN (local area)
– MAN (metropolitan area)
– WAN (wide area)
– Global Network

Network Topology: star, ring, tree, complete,
irregular.
3
Data Transmission Modes Circuit Switching




Messages: information transmitted
between source and receiver
Circuit switching: set of connected
channels for monopoly use during
whole transmission (e.g. phone lines)
Message switching: dynamical routing
of the messages; intermediate buffering
(drawback: long buffers)
Packet switching: messages divided in
fixed size short packets (e.g 1Kb -10
4
Kb)
Packet Switching Transmission Modes



Transmission Modes
Virtual Channel: sequenced packets’ order
provided by the communication subnetwork
Datagram Switching: packets (called
datagrams) are provided with destination
address and ordering number fields. Routing is
random for any datagram. The message is
completed only in the end station. Advantages:
speed and traffic balancing; Drawbacks:
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communication overload.
Communication Subnetwork

Specialized equipment for data tranmission-
– separates data processing and communication
tasks: hosts perform user data processing
– communication devoted resources:transmission
channels; buffers; error control processing; fault
tolerant algorithms

Network Components: hosts, routers, hubs,
terminals, concentrators, terminal processors, synchronous
and asynchronous adapters, modems, interfaces,
synchronous and asynchronous multiplexor, intersystem
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adapter (host-host).
Communication
Subnetwork

Interface standards:
– DTE (Data Terminal Equipment): host,
terminal or any end processing device
– DCE (Data Circuit-Termination
Equipment): modem i.e. data
transmission unit
– Standard Interface RS 232
(evolved in RS 422 / EIA-422)
7
DTE/DCE Interfaces



Interface - hardware or software
components for interconnection
between different type devices
Serial Interfaces: bit slice
transmission
Parallel Interfaces: byte slice
transmission
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Serial Interfaces


Main Serial Interfaces
RS 232:
– voltage levels: [-15,-3] [+3,+15]
– busses
• Information busses- TxD(2) , RxD (3): bit-slice (serial)
data transmit from-DTE-to-DCE/receive from-DCE-to-DTE
depending on control busses
• Control busses: RTS(4), DTR(20), CTS (5), DSR (6): “1”
allow transmit/receive or denote “ready” device; “0”
forbid transmit/recive, or device “not ready”
• Timing busses: TC_1(15), TC_2(24), RC(17)
• Ground lines
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• Reserved
Information Transmission
Protocols
– Byte Oriented Protocols - for symbol
transmission (e.g. using ASCII) synchronization
symbols (bytes) in the beginning and the end of
each block
– Bit Oriented Protocols - for symbol and data
transmission - binary coding of text and data
(universal use). Special sequence called TAG
(usually 01111110) marks the start and the end of
the information block. “Zero bit insertion”
procedure for differing the info data from the TAG.
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