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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 : Step 1: Convert the file size to bits 4 KB = 4 x 1024 Bytes = 4096 Bytes = 32768 bits 1Mbps = 10 6 bps Step 2: Transmission Time = file size / bandwidth t trans = 32768 bits / 10 6 bps = 32.8 ms
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Shirin Ebrahimi 10 Propagation delay Propagation delay
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