We are sending a 20 Mbit MP3 file from a source host Sto a destination host D. All links in the path between source and destination have a transmission rate of 10 Mbps, unless otherwise noted. Assume that the propagation speed is 2x108 meters/sec, and the distance between source and destination is 100,000 km. The following questions (1-3) refer to this setup (A). Now suppose there are two links between source and destination, with one router connecting the two links. Each link is 50,000 km long. Again suppose the MP3 file is sent as one packet. Suppose there is no congestion, so that the packet is transmitted onto the second link as soon as the router receives the entire packet. The following questions (d-f) refer to this setup (B).
A. The end-to-end delay (defined again as from the time S starts transmitting the first bit, until D receives the last bit of the MP3 file) is:
B. Assume again two links with the previous parameters (Problem B), but now suppose that the MP3 file is broken into 2 packets, each of 10 Mbits. Ignore headers that may be added to these packets. Also ignore router processing delays. Assume store and forward packet switching at the router. The total delay is:
C. Consider again two links between S and D and the rest of the setup of Problem B. Also assume negligible packet headers (i. e., H=0 bits is added to every packet). What is the optimal number of packets to breakdown the MP3 file so as to minimize the end-to-end delay?

Infrared sensor is most used sensor in wireless technology where remote controlling functions and detection of surrounding objects/ obstacles are involved. this post will discuss about what is infrared sensor, its working principle, how it works, types, applications, advantages and disadvantages. what is infrared sensor

ir sensor is a simple electronic device which emits and detects ir radiation in order to find out certain objects/obstacles in its range. some of its features are heat and motion sensing.

ir sensors use infrared radiation of wavelength between 0.75 to 1000µm which falls between visible and microwave regions of electromagnetic spectrum. ir region is not visible to human eyes. infrared spectrum is categorized into three regions based on its wavelength i.e. near infrared, mid infrared, far infrared.

wavelength regions of infrared spectrum

near ir – 0.75µm to 3 µm
mid ir – 3 µm to 6 µm
far ir – > 6 µm
1 introduction to infrared sensor

fig. 1 – introduction to infrared sensor

working principle of infrared sensor

infrared sensors works on three fundamental physics laws:

planck’s radiation law: any object whose temperature is not equal to absolute zero (0 kelvin) emits radiation.
stephan boltzmann law: the total energy emitted at all wavelengths by a black body is related to the absolute temperature.
wein’s displacement law: objects of different temperature emit spectra that peak at different wavelengths that is inversely proportional to temperature.
key elements of infrared detection system

the key elements of infrared detection system are:

ir transmitter

ir transmitter acts as source for ir radiation. according to plank’s radiation law, every object is a source of ir radiation at temp t above 0 kelvin. in most cases black body radiators, tungsten lamps, silicon carbide, infrared lasers, leds of infrared wavelength are used as sources.

transmission medium

as the name suggests, transmission medium provides passage for the radiation to reach from ir transmitter to ir receiver. vacuum, atmosphere and optical fibers are used as medium.

ir receiver

generally ir receivers are photo diode and photo transistors. they are capable of detecting infrared radiation. hence ir receiver is also called as ir detector. variety of receivers are available based on wavelength, voltage and package.

ir transmitter and receivers are selected with matching parameters. some of deciding specifications of receivers are photosensitivity or responsivity, noise equivalent power and detectivity.