2 cissp ® Official Study Guide Eighth Edition

Remember the OSI
To make the most of the OSI, you must fi rst be able to remember 
the names of the seven layers in their proper order. One common method of memorizing 
them is to create a mnemonic from the initial letters of the layer names so they are easier 
to remember. One of our favorites is Please Do Not Teach Surly People Acronyms. Do take 
note that this memorization mnemonic works from the Physical layer up to the Application 
layer. A mnemonic working from the Application layer down is All Presidents Since 
Truman Never Did Pot. There are many other OSI memorization schemes out there; just be 
sure you know whether they are top-down or bottom-up. 
Physical Layer 
The
Physical layer (layer 1)
accepts the frame from the Data Link layer and converts the 
frame into bits for transmission over the physical connection medium. The Physical layer 
is also responsible for receiving bits from the physical connection medium and converting 
them into a frame to be used by the Data Link layer. 

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OSI Model 
445
The Physical layer contains the device drivers that tell the protocol how to employ the 
hardware for the transmission and reception of bits. Located within the Physical layer are 
electrical specifications, protocols, and interface standards such as the following:
■
EIA/TIA-232 and EIA/TIA-449
■
X.21
■
High-Speed Serial Interface (HSSI)
■
Synchronous Optical Networking (SONET)
■
V.24 and V.35
Through the device drivers and these standards, the Physical layer controls throughput 
rates, handles synchronization, manages line noise and medium access, and determines 
whether to use digital or analog signals or light pulses to transmit or receive data over the 
physical hardware interface.
Network hardware devices that function at layer 1, the Physical layer, are network 
interface cards (NICs), hubs, repeaters, concentrators, and amplifiers. These devices perform 
hardware-based signal operations, such as sending a signal from one connection port out 
on all other ports (a hub) or amplifying the signal to support greater transmission distances 
(a repeater).