Computer network Learning Note _2

1_5

Traceroute, a command tool, you can see the network internal information, ISP internal information.

1_6

Understand the modular package of the network. Learning protocols and layers, this construction computer the key mechanism of networks. The package is the lower the protocol the more encapsulated outside, forming a protocol stack. Each layer is in the message plus its own header. When browser and server transmit information, they are encapsulated from Brower down, through the physical layer, and then from bottom to top demultiplexing. IP plays a large role in transmitting between different network technology, such as transmission between 802.11 and Ethernet, and the role of IP in intermediate translation.

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Keynote speaker Internet Reference Model.

Now the simplified model is this, just guidelines:

Functions of each part

Introduce some layer-based Names:

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Lectures on internet history. From Arpanet to NSFNet to modern Internet:

Ixp:internet EXchange Point.

2_1

Start layering bottom-up to explain the network, first of all the physical layer.

The first point of knowledge is the message latency:latency are the delay to send a message over a link = transmission delay+propagation delay. Latency calculation, l=m/r+d,m (bits), R (rate:bits/sec), D (propagation delay).

The second knowledge point is a common unit: Kilo Mega Giga Milli Micro Nano.

The third point of knowledge bandwidth-delay product:bd=r*d, calculated.

2_2

Introduces three kinds of types of media,media propagate signals that carry bits of information:wires,fiber (fiber optic), wireless (802.11).

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　　Keynote signals.

The first point of knowledge is bandwidth. Signals (high and low level) transmission will produce distortion, signal attenuation, noise, bandwidth limitation issues. The bandwidth in the EE field means the width of frequency band,measured in Hz. The bandwidth in the CS field means information carring capacity,in bits/sec. Bandwidth throttling will turn the signal round. Light transmission signal attenuation is small, need high-frequency carrier (many GHz.). The wireless signal also requires a carrier generator.

The second knowledge point signals over wireless some problems. Spatial reuse (of same freq), using signal attenuation 1/dis squared. Wireless Multipath make the signal received by the terminal chaotic, there is a phase difference, so the example can not be too far.

Computer network Learning Note _2