Networks & Networking
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Transcript of Networks & Networking
Networks & Networking
MSI Lecture on 15th February 2003
By Dr.I.Sarafis
Computer Networks Concepts
• Objectives– describe components of telecommunications
system– calculate capacity of telecommunications
channels & evaluate transmission media– compare types of networks & network services– compare alternative network services– identify applications for supporting electronic
commerce, business
Management challenges
– Telecommunications revolution
– Components, functions of telecommunications system
– Communications networks
– Electronic commerce & electronic business technologies
1. MANAGING LOCAL AREA NETWORKS: Must be carefully administered, monitored, vulnerable to interruption, data loss, viruses
2. MANAGING BANDWIDTH:
While costs per unit are dropping and capacity is growing, sudden demand can overwhelm system
Connection Types
• Need for communication
• Communication between 2 devices– Point-to-point
• Multi subscriber communication– 3 -> 6 devices , 3 lines– 4 -> 12 devices , 6 lines
The need for networks
• Ν subscribers– Ν-1 devices– (Ν-1)/2 lines
Communication Network
Communication Node
Terminal Node
Network Uses
Benefits of Networks
• Resource sharing
• Reliability
• Money savings
• Communication
An example
Convergence between I.T. & Telecommunications
– No significant difference between processing of data (computers) and of telecommunication signals (communication equipment)
– Unification between data, voice, video communications
– Hard to distinguish between uni-processor computers, multi-processor systems, local area networks, wide area networks
Network Services
• Voice Networks– Information Transfer– Signaling– Call waiting, Caller ID, call redirection etc.
• Data Networks– File, printer sharing– E-mail, ftp, chat, web– Videoconference, multimedia streaming
• Unification of Services
Communication Categories
• Synchronous
• AsynchronousBit Series
Packets
Network
Network
Bit Errors
Asynchronous communication categories
• Connection oriented
• Connectionless
Connection oriented: packets are transmitted with the right order
Connectionless: packets are transmitted with arbitrary order and without guarantied delivery
Network
Network
Switching
Multiplexing
Using multiplexing multiple sources are transmitted through the same physical medium
Multiplexer De-multiplexer
Circuit Switching
PBX Networks(Public Branch eXchange)
Public Telephone Networks are circuit switched
Switching Node
Public circuit-switching network
Packet Switching
In packet switching information is broken in packets.Each packet is routed independently
Switching techniques comparison
• Circuit switching– Continuous channel occupation– Compatibility of transfer rate– No information processing
• Packet switching – Better bandwidth allocation– Transfer rate conversion– Continuous operation under load– Packet priority techniques
Asynchronous Transfer Mode (ATM)
• New technology– Combines advantages of both techniques– Guarantied packet delivery (circuit switching)– Quality of Service (QoS) (circuit switching)– Effectiveness, flexibility (packet switching)
Autonomous Packets (datagram)
Digital & Analog sources
Digital Source
Digital Source
Analog Source
Analog Source
Digital & Analog signalsA
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Time Time
Time Time
Digital Signals
Analog Signals
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Advantages of Digital Technologies
• Use of cheap digital circuits• Application of Integrated Circuits techniques• High security with the use of data
cryptography• Integration of a variety of information (data,
voice, video, text)• Easy signal repetition over long distances
– Disadvantages• High bandwidth• Synchronization
Data Coding
Communication Protocols
• What is it?– Specific procedures between devices– Followed with specific order– The “language” of communicating
• Every day protocols example– Waiting for someone to finish talking before we
start talking– Expressing pleasure when seeing someone after
long time
Network Architecture
– Use of independent structural elements– Layered architecture– Layers / levels– Transparent communication– Differences between architectures
• Communication between incompatible devices– Is very complicated to handled by a single
protocol– Use of layered & structured architecture
Layered Architecture
Layers, protocols & interfaces
What Goes Wrong in the Network?
• Bit-level errors (electrical interference)
• Packet-level errors (congestion)
• Link and node failures
• Messages are delayed
• Messages are deliver out-of-order
• Third parties eavesdrop
Advantages of Layered Architecture
• Partitioning the problem– To small ones and– Easier to handle
• Easy upgrade / addition of services– Since the necessary changes concern one layer
only
• General advantages of using modules
The interface
• Defines – The basic operations and services– That a layer offers to the higher one
• Defines– The messages between neighbouring layers
• Should be– Clear & explicit
Architectures standards
• System Network Architecture (SNA), IBM
• Open Systems Interconnection (OSI), ISO
• TCP/IP– Transfer Control Protocol / Internet Protocol
• Architecture is– The collection of protocols, layers & interfaces
OSI Model
OSI LayersApplication LayerProvides access to network services for the users
Presentation LayerCares for the proper data representation
Session LayerControls the communication process. Starts, ends and manages sessions and connections
OSI LayersTransport LayerCares for the reliable data transfer, for data flow control and for error correction
Network LayerIsolates higher layers from transfer and switching technologies. Cares for data transfer through the proper route
Data link LayerEnsures reliable information transfer on the physical media. Transfers frames with synchronization, flow control & error correction
Physical LayerDeals with cabling issues and physical (electrical) bit transfer
Network Categories(geographical)
• Local Area Networks (LANs)
• Wide Area Networks (WANs)
Comparison LAN / WAN
• Different area size
• Different implementation techniques
• Different organizations
• Different transfer rates (speeds)
Standardization & Standards
• What is it?
• Benefits :– Independence from companies– Independence from architectures– Competitiveness
Example:TCP/IP is a de facto standard and is documented with a large number of RFCs (Request for Comments). Despite the fact that it is not approved by any specific organization, TCP/IP is been used in the largest implemented network in the world, the Internet, instead of OSI which is official.
Standardization Organizations
– ISO (International Standards Organization)
– ITU (International Telecommunication Union )
– IETF (Internet Engineering Task Force)– IAB (Internet Architecture Board)– ETSI (European Telecommunications
Standards Institute)– ΕΛΟΤ (Greek Standards Organization)
Note:Official standards firstly are been developed and then companies are trying to comply. On the other hand, de-facto standards are not becoming standards until they are recognized for their usability and efficiency.
Integrated Services Networks
• Integrated Services Digital Network, ISDN
• narrowband ISDN• broadband ISDN ή B-ISDN• ΑΤΜ
Integrated Services Networks
Note:A Wide Area Integrated Network should provide high-speed integrated services (voice, data, video, images). It is expected that there will be a variety of applications that will take advantage of such networks. Applications like video-on-demand, video-conference and other bandwidth-intensive applications.To realize the consequences of high speed transfer rates, here is a simple example:a high resolution image (109 bits) would need over 4 hrs to be transferred through a 64 kbps line, 11 minutes through a 1.5 Mbps line and only 7 seconds through a 150 Mbps ATM line.
Data Rate Requirements
Network Topologies
• Linear Bus - Ethernet/IEEE 802.3 10Base2 and 10Base5
• Star Wired Ring - Token Ring/IEEE 802.5• Star Wired Bus - Ethernet/IEEE 802.3i 10BaseT• Dual Counter Rotating Ring - FDDI/ANSI
X3T9.5• Wireless - Product Specific
Star topology
Node Node
Node Node
Central Hub
Ring Topology
Node
NodeNode
Node
Data direction
ReceiverTransmitter
Repeater
Bus Topology
Node Node
Node
Star-wired Bus Topology
Node
Concentrator Hub
Node
Node
Node
Node
Node
Physical Media
• Physical media provide the connections between network devices that make internetworking possible.
• There are four main types of physical media in widespread use today:– Coaxial Cable
– Twisted Pair
– Fiber Optic Cable
– Wireless Media
Wired media
• Copper wires on posts– Too few cables
• Twisted pairs– Δέσμες καλωδίων– Twisted to avoid co-hearing– Inside tubes fro protection
• Coaxial cables– Used in long installations and underwater
Copper wires
• Twisted so that the pairs are marked
• Thousands of kilometers installed
• Low-pass filters– Difficulty for Data
Twisted Pair Characteristics
• Advantages– Ease of use and installation– Low cost– Wide available
• Disadvantages– Noise sensitive– Lower capacity than coaxial
Coaxial cable
Coaxial cable characteristics
• Advantages – Low noise sensitivity– Increased bandwidth & security– Longer distances
• Disadvantages – More expensive and bulky– Mechanical stiffness and difficult to connect
Fiber optics
Fiber optics characteristics
• Advantages – Very large bandwidth
• Up to 9.9 Gbps
– Long transmission distances– Insensitive to noise– More secure to eavesdropping
• Disadvantages – Expensive, especially in small scale
installations– Termination & connection difficulties (special
equipment and expert personnel needed )
Wireless transmission media
• Advantages – Independent of physical media
• Disadvantages – Noise sensitivity– Data security– High transmitter power– Limited available frequencies
Land microwave connections
• Directed transmission
• Very high frequencies (2-40 GHz)
• Parabolic antennas (dishes)
• Every 40-50 kms
• Up to 100s Mbps
• Example - > ΟΤΕ antennas
Satellite microwave connections
• Uplink– For sending data from earth stations
• & Downlink– For broadcasting (e.g. TV) but also for unicast
(satellite Internet)
Geostatic satellites
Earth curvature
Satellite coverage
Cellular telephony
• Spatial cells (1.5 – 13 kms)
• Low power transmitter
• Frequencies 900 & 1800 MHz
• Different for adjacent cells
• Data transmission capability (GPRS)