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Microprocessor-based systems
Course 11 Computer networks
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The need for communication networks
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The need for communication (data and program
exchange) between computer systems
Shared use of computing resources (computers,
storage, peripheral devices)
First networks:
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DARPA-NET – network for military purposes
Academic networks (Americans)
CERN – inter-networks
Today:
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the network is a communication and cooperation
infrastructure for the development of distributed
applications
A set of small computers (PCs), plus a network is
more powerful than a computer and several
terminals
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Classification of networks
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Based on the way it is used:
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Point-to-point networks, dedicated connection
between two devices
Broadcasting networks: communication
medium for more equipment
Unicast - one recipient
 Multicast - multiple recipients
 Broadcast - all network nodes are addressed
 Anycast – at least one node is addressed
After stretching area:
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•
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•
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Personal Area Networks (PAN)
Local Area Networks (LAN)
Metropolitan Networks (MAN)
Wide Area Networks (WAN)
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Personal area networks (PANs)
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Have a stretch of 1-2m
Intended for interconnection of
equipment at an individual phone,
PDA, headphones, MP3 player, etc..
Examples: Bluetooth, ZigBee
Low speed
Wireless connectivity in the
frequency of public
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Local Area networks (LAN)
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Interconnect equipment in the same
building
Belong to some organizations
Distances: 10m-1km
Speed: 10-100Mbs, 1Gbs
Standard protocols:
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Ethernet (CSMA / CD),
Token Ring,
Token Bus
Low error rate
Communication medium: twisted pair or
coaxial electrical cable
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Metropolitan area networks
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Interconnected local networks in the territory of a
locality or region
Can be private or public
Example: the metropolitan network of universities
in Cluj
Distances: 1-10km
Speed: 100kbs-10Mbs-100Mbs
Standard protocols:
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DQDB (Double Queue Doubel bus),
ATM,
Frame Relay
Communication medium: fiber optics
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Wide Area Networks (WAN)
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allow transfer of information from very
large and diverse places
internet = network of networks
Distances: thousand miles
Protocol: TCP / IP
Speed: 100kbs-10Mbs – 100 Mbs
Example:
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Internet
AOL
Geant
RoEduNet
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Network communication models
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the need for a model: to ensure
compatibility between equipment
and networks, regardless of
manufacturer, type, location
ISO-OSI model - Open Systems
Interchange
Separating the functions of
communication on several layers of
abstraction:
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7 layers
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The OSI model
Equipment 1
equipment 2
High-level protocols
Application
Application
Presentation
Presentation
Session
Session
Transport
Transport
The communication sub-network
Network
Network
Network
Network
Data link
Data link
Data link
Data link
Physical
Physical
Physical
Physical
Low-level protocols (host-router)
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Packaging the message
Header
Useful content
Footer
…….
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Access to the communication services
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Each layer offers a set of communication services
There are layers with one type of service (in the
Internet the network layer is only IP), or layers
with different types of services (e.g. for transport
layer: TCP - connection-oriented service and UDP
– service with no connection)
Higher layers access lower layer services through
access points (service access points)
Two components of the same layer but from
different computers communicate as if they are
directly connected - logical connection
A communication travels through the entire
protocol stack
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The TCP/IP model compared with OSI
OSI model
Aplication
Presentation
Session
Transport
Network
Data Link Layer
Physical
TCP/IP model
Aplication
TCP/UDP
IP
Host-to-network
connection
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ATM model
Plane Administration
Layer admin.
Control
Utilizator
High layers
CS
SAR
ATM Adaptation
layer
ATM Layer
TC
PMD
Physical Layer
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Protocol layers
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Physical layer
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Physical layer deals with information transmission at the bit. A physical layer
protocol must specify:
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the nature of the signals used to encode binary data (eg voltage layers, currents, laser
beam, etc..), and acceptance layers
electrical characteristics, mechanical performance and transmission medium (electrical
cables, optical, radio)
methods to reduce noise and eliminate the influence of transmission errors
type of connectors used
Physical protocol must ensure efficient use of transmission medium, and a
transfer rate as large.
Depending on the nature of transmission medium can use different encryption
methods and compaction of binary information.
The transmission media used in digital communication are:
a. twisted pair cable - is cheap, with the frequency dependent transmission distance, may
be shielded or unshielded (UTP - Unshielded Twisted Pair), twisting the two wires of the
cable increases noise immunity.
b. The coaxial cable - is high bandwidth and high noise immunity, transmission distance is
relatively large, there are two ways of using: the basic band (one channel / cable) or
broadband (multi-channel / cable )
c. optical fiber - is a transmission medium with high performance parameters (high
bandwidth, low delay) has full immunity to electromagnetic noise, on a single optical
wireless can transmit many channels
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Physical Layer
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Communication
media:
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Twisted pair cable
(UTP)
Coaxial cable
Fiber Optic
Radio
IR transmission
Topology:
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Star
Ring
Bus
Tree
graph
Star
Ring
Bus
Tree
Graph
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Data Link Layer
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Role:
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Structuring data within packages
Providing a secure communication channel
Detecting transmission errors
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Types of services:
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The parity bits, checksum, CRC
unconfirmed service without connection
confirmed service without connection
confirmed the connection-oriented service
Examples:
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HDLC protocol (High Data Link Control)
01111110
8 biţi
Adresă
8 biţi
Control
8 biţi
Date
>=0
SC
16biţi
01111110
8 biţi
Figura 12-5 Formatul unui cadru HDLC
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SLIP protocol (Serial Line Internet Protocol)
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Unaltered IP packets for transmission (Internet)
PPP (Point-to-Point Protocol)
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Access mechanisms to the communication
environment (MAC – sub-layer)
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Layer used for local area networks where the same
medium is shared by multiple nodes
Access control:
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Centralized
Distributed
Classification of access methods
Algorithm
Centralized
Distributed
Round-Robin
Polling
Token ring, Token bus
With reservation
Central reservation
Distributed reservation
With multiple access
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CSMA/CD (Ethernet)
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Network layer
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Role: routing messages
Solutions:
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Routing algorithms:
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A
B
C
D
E
The shortest path routing
Flooding algorithm (flooding)
Flow-based routing
Vector-distance routing
Hierarchical routing
Network layer on the Internet – IP (Internet protocol)
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Circuit switching - phone system
Packet Switched
The network is organized around three hierarchical levels:
high-speed network that makes up the backbone of the system (backbone)
regional networks (Europe, America, Asia, ..)
academic networks, government, companies, ISPs, etc..
The IP addresses: 4 bytes, 232 possible addresses – not enough
0 Net
Host
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Network
Host
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Reţea
Gazdă
1110
Multicast address
11110
Reserved for the future
1.0.0.0-127.255.255.255
128.0.0.0- 191.255.255.255
192.0.0.0- 223.255.255.255
224.0.0.0- 239.255.255.255
240.0.0.0-247.255.255.255
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Transport layer
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Role: creates a secure channel of communication on an uncertain
environment
It makes a logical connection between remote applications (like a
dedicated pipeline for the two applications)
Transport layer on the Internet:
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Operations performed:
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reordering messages in order to respect the initial order
re-transmits erroneous messages
eliminates duplicate messages
It uses the message confirmation technique
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TCP – connection-based transport protocol
UDP - connectionless transport protocol
Packets are numbered to keep track of their order
Connection is done through sockets (Socket)
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Socket = port + IP address
Ap1
Ap1
Ap2
Ap2
Ap n
Internet
Apn
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Other OSI layers
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Session Layer:
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Presentation Layer:
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responsible for controlling the sequence of dialogue
between the two applications that communicate with
each
handles authentication dialog between partners by
checking the access passwords
It deals with issues concerning coding-decoding for data
security
Application level:
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offers various models and communication interfaces for
user applications:
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Network virtual terminal (eg TELNET)
File transfer (eg FTP)
Email (eg SMTP)
Remote execution of procedures (RPT)
Network management (eg SNMP)
Web browsing, etc..
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Other Application layer protocols
DNS (Domain Name System) - is a service that allows addressing
messages based on symbolic names, the protocol allows transformation
of symbolic names for network addresses (IP addresses)
- NFS (Network File System) - is a mapping service that allows remote
file folders in your local directory, this service provides a uniform access
to files regardless of their location
- NIS (Network Information System) - is a service providing resource
information contained in the network, such applications can be
identified, gateway services, etc.., Resembles the "yellow pages"
published to identify firms and services they provide
- RPC (Remote Procedure Call) - is a protocol through which
applications can be launched remotely or procedures, the Protocol
provides the procedures and appeal mechanisms for transmitting call
parameters, many network applications are based on an RPC
mechanism
- WWW (World Wide Web) - is a distributed information service that
allows searching of information through various databases across the
network in Internet, information is organized in the form of pages, a
page can contain text, pictures, small applications ( applet's) and
especially links to other sites containing similar information, search
information is through programs of "navigation" (eg Netscape, Internet
Explorer, etc.). is writing pages using HTML and protocol HTTP
communication is used.
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