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3.1 | |
Serial Point-to-Point Links | |
| 3.1.1 | |
Introduction to serial communication |
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WAN technologies are based on serial
transmission at the physical layer. This means that the bits of a
frame are transmitted one at a time over the physical medium.
The bits
that make up the Layer 2 frame are signaled one at a time by physical
layer processes onto the physical medium.
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The signaling methods
include Nonreturn to Zero Level (NRZ-L), High Density Binary 3,
(HDB3), and Alternative Mark Inversion (AMI). These are examples of
physical layer encoding standards, similar to Manchester encoding for
Ethernet. Among other things, these
signaling methods differentiate between one serial communication
method and another. Some of the many different serial communications
standards are the following: