3link - Link Layer: C3, C4 (4.1- 4.2) Overview of Functions...

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0 Link Layer: C3, C4 (4.1- 4.2) Overview of Functions Framing Media Access Logical Link Control error detection error correction ARQ congestion control Examples Network Layer Link Layer Logical Link Control Media Access Control Physical Layer
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1 Functions of the Data Link Layer Provide service interface to the network layer Media access Regulating data flow Slow receivers not swamped by fast senders Dealing with transmission errors error correcting codes automatic repeat request
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2 Framing Relationship between packets and frames.
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3 Services Provided to Network Layer (a) Virtual communication. (b) Actual communication.
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4 Services Provided to Network Layer (2) Placement of the data link protocol.
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5 Asynchronous and Synchronous Transmission Timing problems require a mechanism to synchronize the transmitter and receiver Two solutions Asynchronous Synchronous
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6 Asynchronous Data transmitted on character at a time 5 to 8 bits Timing only needs maintaining within each character Resync with each character In a steady stream, interval between characters is uniform (length of stop element) Good for data with large gaps (keyboard)
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7 Asynchronous (diagram)
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8 Character Count Framing A character stream. (a) Without errors. (b) With one error.
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9 Synchronous - Bit Level Block of data transmitted without start or stop bits Clocks must be synchronized Can use separate clock line Good over short distances Subject to impairments Embed clock signal in data Manchester encoding Carrier frequency (analog)
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10 Synchronous Framing (a) A frame delimited by flag bytes. (b) Four examples of byte sequences before and after stuffing.
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11 Bit Level Framing Bit stuffing (a) The original data. (b) The data as they appear on the line. (c) The data as they are stored in receiver’s memory after destuffing.
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Media Access Control Where Central Greater control Simple access logic at station Avoids problems of co-ordination Single point of failure Potential bottleneck
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This note was uploaded on 10/21/2011 for the course E E 362 at Pennsylvania State University, University Park.

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3link - Link Layer: C3, C4 (4.1- 4.2) Overview of Functions...

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