EE450_Discussion2_Fall08

EE450_Discussion2_Fall08 - EE:450 Computer Networks...

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Shirin Ebrahimi 1 EE:450 – Computer Networks Discussion Session #2 September 3rd, Fall 2008
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Shirin Ebrahimi 2 SIGNALS ± The electrical signals can be ANALOG or DIGITAL ± ANALOG – the amplitude can take infinite number of values ± Ex: TV/Radio transmission ± DIGITAL – the amplitude can take finite number of values only ± Ex: Computer Communications (uses two logic values 0 and 1) We will be dealing with DIGITAL transmissions We will be dealing with DIGITAL transmissions
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Shirin Ebrahimi 3 Some Terminology ± Bit (b) ± Basic unit of information in computers ± Binary : 0 or 1 ± Byte (B) ± 8 bits in one byte ± Bit Rate ± Number of bits transmitted in a time unit ± Typical unit is bits-per-second (bps) ± Used to measure transmission speed in digital transmissions
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Shirin Ebrahimi 4 Terminology continued… ± 1K Bytes = 2 10 Bytes = 1024 Bytes = 8192 bits ± Similarly, 1M Bytes = 2 20 Bytes However , ± 1 Kbps 2 10 bps 1 Kbps = 1000 bps ± Similarly, 1 Mbps = 10 6 bps In this course, the approximation 1KB ~ 1000 Bytes is always allowed
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Shirin Ebrahimi 5 Terminology ± Delay/Latency : Time it takes a message to travel from one end of a link to another ± It is a very important performance parameter ± End to End delay consists of several components ± Transmission time ± Propagation delay ± Nodal Processing time ± Queuing delay
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Shirin Ebrahimi 6 Transmission time ± How long does it take to transmit a message (usually in KB) over a link with bit rate (usually in Mbps)? ± Steps: ± 1. Convert message size to bits ± 1KB = 1024 bytes ± 1MB = 2 20 bytes ± 1 Byte = 8 bits ± Key is the difference between “ B ” and “ b
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Shirin Ebrahimi 7 Examples
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Shirin Ebrahimi 8 Transmission time ctd. ± 2. To obtain the transmission time, divide the message size (in bits) by the bit rate a.k.a. bandwidth (in bps) Transmission time = Message size/Bit rate
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Shirin Ebrahimi 9 Transmission time example Ex : How long does it take to transmit a 4KB file over a link with 1Mbps bandwidth? Solution
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EE450_Discussion2_Fall08 - EE:450 Computer Networks...

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