COM1204 Spring 2001 -- A call originating at a remote phone
Professor Futrelle -- College of Computer Science, Northeastern U., Boston, MA
The figure below is taken from Fig. 3.16 of Wireless Personal Communication Systems by
David J. Goodman (copyright 1977 by Addison Wesley Longman, Inc.)
It deals specifically with a call originated at a remote phone, directed to a cell phone.
Note that many of the operations shown deal with the fact that transmission and reception
may be so weak or noisy that they may fail. Our simulation does not deal with these RF
signal strength problems, real though they are in practice.
It has more complex signalling than we need to simulate in our class project.
For some of the basic nomenclature, refer to the
first of these pair of figures.
Some of the more important parts of the figure are:
- The MTSO is the Mobile Telephone Switching Office, a large system that interfaces
with the public phone network, including other cell systems and land (wired) systems.
- In this example the Base sends a PAGE message to the cell phone over the FOCC.
This message includes the number of the cell phone and only the phone with this number
will respond, if it is on, idle and within range so that the signal from the Base
is strong enough to be detected properly.
- The phone then sends a PAGE RESPONSE message over the RECC to the Base, indicating
that it is ready to accept the call.
- The Base Station selects one of the voice channels, if any is available, and
sends an INITIAL VOICE CHANNEL message over the FOCC with the identity of the voice
channel that the phone is to use. (There are two voice channels, one Forward Voice
Channel, FVC, from the Base and the Reverse Voice Channel, RVC, to the Base.)
- If the phone is successful in getting a basic signal over the voice channel the Base
will send it an ALERT message and only at this time does the phone activate the
ring, alerting the user. Note that this message is sent over the FVC.
(If no voice channel is available it will never be
assigned one and never ring.)
- If the user answers the ring a message to the Base states this and the Base
sends the phone a STOP ALERT signal over the FVC and the ring is stopped.
- When the remote caller hangs up a RELEASE is sent over the FVC
to the cell phone by the Base.
- The phone confirms this and shuts off its transmitter so the Base can reuse the voice
There are variations on the above sequence; this is only one example.
Go to COM1204 home page
Return to Prof. Futrelle's home page