EC-11.6 Wireless Links, Measurement and First Security
You can say what changes when the last hop is radio, describe how a cellular network hands a moving device between cells, measure a network's behaviour with capture and timing tools, and state what encryption on a link does and does not protect.
Almost every network a reader uses has a radio hop at one end, and almost every networking course treats radio as an afterthought. This topic closes that gap, and it ends with the measurement and security material because those are the two things a graduate is most often asked to do on a network they did not design.
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What radio changes about a link
The medium is shared with everyone in range, the error rate is orders of magnitude higher and varies with position, and capacity is not the same in both directions. Every one of those breaks an assumption made on a cable.
NPTEL: Introduction to Wireless and Cellular Communications (IIT Madras) · CourseLocal wireless networks, and avoiding rather than detecting clashes
A sender cannot listen while transmitting, so the scheme asks permission first and waits a random time before sending. Acknowledgement of every frame is needed because loss is normal rather than exceptional.
NPTEL: Introduction to Wireless and Cellular Communications (IIT Madras) · CourseCells, handover and a device that moves
Coverage is divided into cells with a base station each, and frequencies are reused between cells that are far enough apart. Handover is the process of moving a live connection from one cell to the next.
NPTEL: Introduction to Wireless and Cellular Communications (IIT Madras) · CourseMeasuring a network: capture, timing and loss
A packet capture shows what actually crossed the link rather than what should have. Round-trip timing and path tracing locate a problem, and loss statistics say whether it is capacity or configuration.
NPTEL: Computer Networks (IIT Indore) · CourseWhat encryption on a link protects
Encrypting a link hides the contents from anyone listening on that link. It does not hide who is talking to whom, does not protect the message beyond the far end, and does not prove who sent it.
NPTEL: Cryptography and Network Security (IIT Kharagpur) · CourseThe first three attacks worth understanding
Listening to an unencrypted medium, pretending to be another address, and flooding a service until it stops answering. All three are cheap on a network with no authentication, which is why one is added.
NPTEL: Cryptography and Network Security (IIT Kharagpur) · Course
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