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Comms & Networking (OSI Layers (1 Physical:
Bits, 3 Network
Packets
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Comms & Networking
Transmission Modes
Half-Duplex: Data goes both ways, NOT at the same time
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Topologies
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Ring: Each node is connected to it's two neighbors (back & front) by PtoP link to form a loop (circle).
Messages go from one host to the other until reach destination
Mesh: Dedicated PtoP link between each node and all other devices. The most expensive and more reliable topology.
(n-1) (N = No of Nodes) is the number of cables on EACH device
Tree: Evolution of the Star Topology. Necessarily has more than one network device (Hubs, Switches).
Connects multiple network devices together to form a big tree
Bus: The only Multipoint Topology. All nodes are connected to a single link that comes from the Transmitter.
Hybrid: Mix of Topologies. Ex. Star & Bus: Multiple links connected to a hub, with multiple nodes connected to each link
Protocols
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De-encapsulation: The reverse, the removal of headers from the message as it goes UP in the OSI model
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OSI Layers
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3 Network
Packets
Packets provides path selection, routing, and addressing.
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Cables:
Types:
Coaxial:
inner copper core and a secondary conducting outer core
Mainly isolated because of outer conductor
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Thicknet vs Thinnet:
Maximum Segment Lenghts, 500m vs 200m
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Bandwidth Utilisation
Multiplexing:
Shared use of communication capacity. Commonly used in high-capacity fiber and WANs in general
Many simultaneous transmission over one single cable
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Demultiplexer: accepts multiplexed data stream, separates the data according to channel, and delivers them to the appropriate output lines.
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Spreading:
Spread spectrum was designed to be used in wireless applications
The goal is to prevent eavesdropping and jamming
Switching
Layer 2
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Circuit Switching:
Better suited for older types of Analog connection like landlines
It locks the channel for use until all data has been sent
Not suitable for digital as it needs to be dynamic.
Time-Division:
Slots divided by time
Uses Time Division Multiplexing (TDM)
Advantage: No crosspoint necessary
Disadvantage: Creates Delay, Each time-slot must be stored in RAM, then retrieved.
Space-Division:
Slots divided by Space (Transistors)
Crossbar Switch
Necessary crosspoint = n x m
Advantage: Instanteneous
Disadvantage: Number of Crosspoint necessary