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Telemedicine WS 09/10Computer Networks - 1
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computer networks
• Communication• Requirements for a network• Topologie of computer networks• ISO / OSI reference modell • Variety of cables
Carrier Sense Multiple Access with Collision Detect
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Token Ring
• Before starting to transmit, the sender has to wait for a permission (Token).
• All devices forward foreign packets.• When the data arrive at the receiver
it will remove the data and forwards the empty token.
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Token Ring
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Connection elementsRepeater
A Repeater works at the physical layer. It repeats and apmlifies signals into a second segment.
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Connection elements Hub
A hub works at the physical layer. It is the center of a star topology which builds a logical bus.Like a bus, all connected devices get all transmitted information. Hubs can be cascaded.
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Connection elements Bridge
A bridge works at the second level, the data link level. A bridge connects two segments. The bridge knows the addresses of both segments and forwards only those messages which are addressed to a device on the other side.
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Connection elements Router
A router is a device with connections to at least two networks. It works at the third level, the network layer. A router can connect networks with different technologies.
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ISO / OSI Schichten
Sicherung - Data Link
Physikalisch - Physical
Netzwerk - Network
Transport - Transport
Anwendung - Application
Darstellung - Presentation
Sitzung - Session
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TCP/IPObjectivs
• Independent of the network
technologie and the server
technologie
• All-purpose transmission
• End – to – end connection
• Standardised protocols
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ISO / OSI layers
Sicherung - Data Link
Physikalisch - Physical
Netzwerk - Network
Transport - Transport
Anwendung - Application
Darstellung - Presentation
Sitzung - Session
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TCP/IPIP-Protokoll
• Selection of the route• Converting the global address to a
local address• Buffer of messages• Assemble fragmented messages• Avoiding infinite loops
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ISO / OSI Schichten
Sicherung - Data Link
Physikalisch - Physical
Netzwerk - Network
Transport - Transport
Anwendung - Application
Darstellung - Presentation
Sitzung - Session
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TCP/IPTCP-Protokoll
Main objective: safe transportation of data through the network– full-duplex virtual connection– Transmission as a stream– Sequenznumbers– sliding-Window-function– Controlled connection termination