Why bother?

Application Layer

Presentation Layer

Session Layer

Transport Layer

Network Layer

Data Link Layer

Physical Layer

Layer Overlap!

Exam Summary





Specifies electrical, mechanical, procedural, and functional requirements for activating, maintaining, and deactivating the physical link between end systems

Think of the physical layer as the road over which data is carried. Standards defined at this layer include things such as:

- cables and connectors (what shape is an RJ45 connector? Which of the pins is a transmit pin, which is a receive pin, etc),

- media type (copper, fibre, radio waves),

- signalling method,

- what kind of electrical voltage levels are used (for example, while you can use similar cabling for Ethernet and ISDN, the voltage level that crosses an ISDN link is a lot higher than for an Ethernet link. If you plug one end of a cable into an Ethernet interface and another into an ISDN interface you will fry the Ethernet interface and that’s a fact!)

- maximum transmission distances (these are specified because the longer a signal travels down a cable, the weaker it gets – specifies how long the cable can be before the signal is too weak to make sense at the other end).

There are no PDUs at the physical layer, just bits.


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