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Closed User Groups are encoded either as a class A facility followed
by the two-digit number encoded in one byte, or, in the case of Bilateral
groups, as a class B facility with the four-digit number encoded in two
bytes. The encoding is a simple one of each decimal digit being encoded
in four bits.

For example, a call within group 78 would have facilities encoded:

00000011 C. U. G. facility
01111000 to group 78

A call within bilateral group 7654 would have facilities encoded:

01000001 Bilateral C. U. G. facility
01110110
01010100 to group 7654

Reverse Charging This is a class A facility encoded in one of the
following two ways:

00000001 Reverse Charging facility
xx000000 Reverse Charging NOT requested
00000001 Reverse Charging facility
xx000001 Reverse Charging requested

The same facility code is used for requesting Fast Select, as shown below;
thus there has to be an encoding of the second byte for not requesting
use of the facility.

Fast Select This is a class A facility encoded with a facility code of
00000001 as for reverse charging. The first two bits of the second byte
are encoded as follows:

00xxxxxx Fast Select NOT requested
01xxxxxx Fast Select NOT requested
10xxxxxx Unrestricted response Fast Select requested
11xxxxxx Restricted response Fast Select requested

RPOA selection This is a class B facility encoded with a facility code of
01000100. The two parameter bytes contain the Data Network
Identification Code (DNIC) of the requested Recognized Private
Operating Agency. The DNIC is covered in Chapter 7.

Flow control negotiation The flow control parameters are packet size
and window size, which may be requested in Call Request packets if the
facility is subscribed to. The Call Accept also contains a facility field

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