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translating bits from sending node into form that can be send via network
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representation of bits transmitted over the link, so they can be delivered to the end node
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media access control (MAC) Lernen beginnen
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how to share medium efficiently among nodes
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Wireless network, Last-mile links networks, Local Area Networks (LAN)
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hardware that connects a node to a link, it encodes bits into signals at the sending node and decodes signals into bits at the receiving node
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Non-return to zero, Non-return to zero inverted, Manchester, 4B5B
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Non-return to zero approach Lernen beginnen
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when bit is 0 then signal is low and vice versa, sequences of consecutive 0s/1s makes singnal stays low/hgih for long
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Non-return to zero inverted approach Lernen beginnen
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bit 1 change the signal frequency (low/high)
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0 being encoded as low-to-high transition and 1 being encoded as high-to-low transition
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insert extra bits into the bit stream so as to break up long sequences of 0s or 1s
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Byte oriented framing methods Lernen beginnen
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Usage of special characters (sentinel characters), Include number of bytes in the frame
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High Data Level Control Protocol- used for transmission of bit data, ensures reliable data transfer and can operate without a continuous connection
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when a specific sequence of bits appears in the data an extra bit is added to break the pattern, prevents the receiver from mistaking the data for control information
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Notify the sender, to get the message again. Reconstruct the correct message by recipient
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redundant information bits to help receiver determine if error occurs
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achived using acknowledgments and timeouts
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after transmitting one frame, the sender waits for an acknowledgment before transmitting the next frame. If ACK do not arrive retransmit message
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sender assigns a sequence number to each frame and the sender maintains three variables: send window size, last ACK received and last frame send
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device that forwards digital signal but do not understand it
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spread the signal over a wider frequency band to minimize the impact of interference from other devices
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spread spectrum techniques Lernen beginnen
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frequency hopping, direct sequence spread
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transmition of the signal over a random sequence of frequencies
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adds redundant bits for greater tolerance of interference
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Endpoints in wireless networks Lernen beginnen
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Base station, Mesh networks
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has no mobility but has a wired connection to the Internet or other networks
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nodes are peers, there is no base station nodes
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