Information Technology Reference
In-Depth Information
H.264 is a great improvement over H.263; it is also known as MPEG-4 Part 10 and Advanced Video Coding (AVC). H.264 allows the
compression of video much more effectively, and therefore has the capability to provide good quality video at much lower rates than
would have been required with previous standards. Furthermore, H.264 can be used in a wider range of applications than previous
standards.
Fax and Modem
In addition to voice traffic, fax and modem traffic can be transported over an IP network.
Fax Transmission over IP Networks
There are a number of fax standards, including the following:
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T.30:
Describes the handshaking between sending and receiving devices during fax transmission
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T.4:
Defines the encoding of the printed information send during fax transmission
There are a number of phases in a T.30 fax call, including the following:
Phase A:
The call setup phase.
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During this phase, the sending device sends a Calling Tone (CNG) to the receiving device. This identifies the sending device
as a fax machine. The receiving device responds with a Called Station Identifier (CED) tone that identifies the receiving
device as a fax machine.
Phase B:
The premessage procedure used to identify and select facilities.
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The receiving device sends a Digital Information Signal (DIS) that informs the sending device of its reception facilities
including maximum page length, image resolution, and so on.
The sending device then responds with a Digital Command Signal (DCS) that informs the receiving device of which facilities
to use for fax reception.
