Paging Networks
By Marlar Wain
00042301
The work contained in this
assignment, other than that specifically attributed to another source, is that
of the author. It is recognised that,
should this declaration be found to be false, disciplinary action could be
taken and the assignments of all students involved will be given zero
marks. No collaboration occurred.
Disclaimer: This web page was produced by a student of 48740
Communication Networks, spring 2002. While all the information presented was
thoroughly researched and cross checked, no responsibility can be taken if any
information is found to be untrue.
Acknowledgements
Thankyou Graeme and Skye for your advice and help.
1.1.
What is a paging network?
1.2.
When and how did
paging networks evolve?
2.
Components and System Architecture
2.1.
What components
are involved in a paging network?
3.1.
Are there
different types of paging networks? How do they differ?
4.
How do paging systems work?
4.2.
How does a paging network work?
4.3.
What protocols
are there for paging networks?
5.1.
What standards
currently exist for paging networks?
5.2.
How do the
applications of these standards affect the way in which a paging network operates?
6.1. What is the main
application of paging networks in society?
7.1.
What is the main
technology competing with paging networks?
7.2.
What are the
differences between a paging network and its competitor?
7.2.1.
How do cellular networks and phones work?
8.1.
Are paging
networks readily available in
9.
Companies producing paging technology
10.
Future trends for paging networks
1.
INTRODUCTION
1.1.
What is a
Paging Network?
Paging networks
are used as communication systems for sending a page to a subscriber of that
system. A page is a message that is
simulcast over the entire paging service area to all base stations at a
time. The messages sent are either
numeric, such as a telephone number, alphanumeric or even voice. Originally the messages were only used to
alert the user that someone was trying to get in touch with them, but now
pagers can be used to receive stock quotes or sports scores or even retrieve
your email. [1]
1.2.
When and
how did paging networks evolve?
The development
of the pager emerged from the work of a man named Al Gross.
Gross had worked
during the Second World War developing a two-way ground to air communication
system. After the war, in 1949 the pager
was patented. In 1950, the first one-way
paging system was developed for use in hospitals on the 460-470 MHz band. It wasn’t until 1952 that Gross received
certification for the system by the U.S. Federal Communication Commission
(FCC). The FCC set a larger spectrum for
use by paging networks improving reliability and popularity. A service provider called Aircall Inc. was
based in
Originally the
pagers were analogue and used as an alert only device that informed the person
that they had messages that were waiting to e retrieved. The person then had to use a telephone to
dial in to retrieve those messages. The
late 1970s brought digital paging so now numeric paging and alphanumeric aging
services were available. This was for
transmitting either a return telephone number, or a short text message.
When the mobile
phone industry started to grow, it was thought that paging would soon become
obsolete. What actually happened was
surprising because the paging industry experienced its biggest market
growth. This was mainly because mobile
phone users needed to pay for incoming and outgoing phone calls so pagers were
used to check if a call was worth answering or not on the spot or wait until a
landline phone was available. Also, when
mobile phones were first introduced, they were very big and bulky whereas
pagers were quite small and light. This
meant that many users preferred to have mobile phones in their cars only, and
carry pagers when they were out of the car. [4]
The paging
networks were continually improved upon, leading to great network
coverage. As most pagers are only one
way, the page has to be received on the first try. This was done through “simulcasting” where each
transmitter has a large area of coverage but the coverage overlaps with other
transmitters. This means that the
problem of penetrating building is reduced because cover is coming from many
different places. Unfortunately this
leads to “multipath interference” which makes paging networks operate at low
speeds. [2]
2. Components and System Architecture
2.1.
What
components are involved in a paging network?
A paging network consists of a number of elements. These include telephone, paging
service, paging centre, base stations and transmitters, and a pager. The telephone is
used to make a message. The paging service takes the message and sends it onto the paging centre. The paging centre transmits the message to the base stations and transmitters. The pager actually receives the message. [5]
The network structure for a paging network is quite
simple. These elements work together
sending and receiving signals to get the page from the sender to its
destination. The most basic network
model is shown to the right consisting of the person leaving a message, the
paging service, the paging centre, the transmission towers and finally the
pager. [4]
3.1. Are there
different types of paging networks? How do they differ?
There are
different types of paging networks. The
two main types are one-way and two-way paging networks. As the names imply, a one-way paging network
can only receive incoming pages, while a two-way paging network can send pages
as well as receive them. The main
difference between these two systems is the pager involved. This will be explored when we find out how
pagers work.
For both the
one-way and two-way paging networks, there are different kinds of paging
services. The first is known as a manual
paging system. The manual system works
much like a call centre where the person wanting to send the page talks to an
operator who types the message and pager number into an encoding system before
the message is sent onto the paging centre. [4]
The second type
of paging service is an automated system.
For the automated service there is no operator. The person wanting to send the message types
it into a telephone keypad along with the pager number. Software does the work of what a normal
operator would do. The message is then
sent over the internet to the paging centre.
4. HOW DO PAGING SYSTEMS WORK?
Pagers, like
other radio devices receive a radio frequency (RF) signal through an
antenna. The received signal is then
converted into letters or numbers and displayed on a liquid crystal display
(LCD). The conversion is done through a
series of applied electrical devices inside the pager.
Each pager has
its own unique code used for identification.
The RF signal is sent out to the pager using the unique code. The signal is picked up by an antenna on the
pager. This signal is quite weak when it
is picked up and there is a significant amount of background noise. A low-noise amplifier is used to strengthen
the paging signal. [4]
Once the signal
is strengthened it goes through a down conversion. The paging signal is at a fairly high
frequency at the moment, and high frequency signals are more difficult to
amplify than lower frequency signals.
The signal is down-converted to a lower frequency to make the
amplification process easier. The down
conversion is done with the use of an oscillator which produces the wave to be
used for the conversion of the paging signal.
Now the signal
can be amplified. The signal is
amplified by over 100 times the original strength. This makes the processing by electronics
easier to do. The amplified signal is
now sent to an analogue to digital converter, which changes the paging signal
into digital information for processing and display. The digital signal is sent to the arithmetic
logic unit (ALU) of the pager, where the message is decoded, error checking is
carried out ad messages are stored. It
also sends a tone and/or vibrating alert that a message has been received and
sends the message to the display driver so it can be displayed. The display driver takes the information it
receives and puts it out to display, usually on a LCD. [4,5]
4.2. How does a paging network work?
When someone
wants to send a page they ring up the call system, be it either manual or
automated. The cal system takes the
message and pager number from the sender.
The pager number is matched to a special system code that corresponds to
that pager. The code is converted to a
transmittable form and the page is sent with the code to the paging
centre.
The paging centre
sends the page to every base station and transmitter on the network. Each station covers a wide area range from 15
to 30 miles. The page is transmitted
over RF by the transmitter. Different
frequencies are used by different paging companies so that there is no
interference between the different pages getting transmitted.
The frequency on
the pager is the same as the frequency on the base station’s transmitters. The pager “listens” for a signal on that
frequency. Any other pages are ignored
except for on that signal. When a
message with that unique paging code is picked up the pager receives the page. The message is received, decoded and
displayed through the internal electronics of the pager. [4]
The following is
an animation showing how a one-way paging network works.
A two-way pager
allows you to both send and receive messages.
A two-way pager also needs to have a transmitter to be able to send
pages.
The page is sent
in the same way through the manual or automated system and then through the
paging centre. A two-way pager
constantly sends a signal to the paging centre so that the system knows where
the pager is at all times. As the
location is always known, only one transmitter is needed to send out the page
to the pager. This way, the network is
less busy and network traffic is minimized.
The page is received in the same way as the one-way pager does. [4]
When a message
has been received a page can be sent back out to respond to it. The two-way pager has a keypad, and rather
than just a receiver, it has a transreceiver which enables that pager to send
and receive RF signals. A message can be
typed and sent to another pager.
The signal from
the pager is relatively weak and is usually less than 1 W. So, there is a need for more receiving towers
than transmitting towers so that the signal can be picked up and sent on. When the signal is picked up from the
receiver, it is transmitter back to the paging centre and then transmitted in
the same way as previously mentioned. [4]
Two-way pagers
can also send and receive email. For
this to happen, the paging network needs to be connected to the internet, and
then be able to access the email account in question so that any email can be
retrieved. To send an email, a
connection to the internet and mail server known as a simple mail transfer
protocol (SMTP). [5]
4.3. What
protocols are there for paging networks?
The paging industry has mostly
boomed in the
The PCIA acts as the “voice for
the wireless communications industry” [7] and through knowledge and leadership,
the group has been able to address and make some real changes to problematic
areas of wireless communications along with the FCC.
Some paging protocols that have
resulted from PCIA are the telocator alphanumeric protocol (TAP), telocator
network paging protocol (TNPP), telocator data protocol (TDP) and the wireless
communications transfer protocol (WCTP).
The telocator alphanumeric
protocol is the standard digital communications protocol used for “sending page
requests from automated equipment… to radio paging systems” like the automated
paging service mentioned earlier. With
this protocol, alphanumeric messages are forwarded over a telephone connection
through the use of dial up modems. [7]
The telocator network paging
protocol is used to transport pages from one base station to another regardless
of whom them manufacturer is. The TNPP
has a point to point connection between base stations. This ensures that pages will be delivered
between the stations where TNPP is.
Routing and other non-paging information can also be carried through
TNPP. It is only used between carriers
that are under agreement is not available for public access.
The telocator data protocol is
the next generation TAP. TDP supports
the use of “priority paging, time-of-day paging and periodic paging”
[7] which was not supported by TAP. TDP also allows binary data to be received
from application such as databases, spreadsheets and other computer
applications with the intention displaying the information on a laptop or palm
pilot. With TDP, messages that are
significantly larger in size than normal pages can be received and delivered,
and it can be done in a TCP/IP environment.
The wireless communications transfer protocol is
specifically designed for open communication between one and two way wireless
devices. WCTP is an operated over the
internet, and data can be both sent and received to and from computers, other
wireless devices and applications.
The standards that will be investigated involve the paging channel (PCH). The paging channel is one type of logical
channel. A hierarchy of logical channels
can be seen in figure 2. Logical
channels consist of the traffic channel, control channel and cell broadcast
channel. The control channel consists of
the broadcast channel, common control channel and dedicated control
channel. The paging channel falls under
the common control channel, along with the access grant channel and random
access channel. The paging channel “represents a logical sub-channel of the
short message service, paging, and access channel (SPACH). It is used for
delivering paging messages, message-waiting messages, and user alerting
messages.” [8,9]
Figure
2: The Logical Channel Hierarchy [10]
5.1. What
standards currently exist for paging networks?
According to Park [10], the standard for the paging channel is as
follows:
·
Transmission rate is at 9.6 or 4.8 kbps
·
Frame duration is 20 ms
·
Frame length is 192 bits for 9.6 kbps channel
·
Frame length is 96 bits for 4.8 kbps channel
Figure 3: The paging channel slot [10]
Figure 3 shows the format for a paging channel slot. A paging channel is divided into slots that
are 80 ms long each. A slot has four
paging channel frames. These frames are
then divided into two half frames. Each
half frame is composed of two subfields. These are the synchronised capsule
indicator (SCI) and the half frame body subfield. A capsule is a fixed sized frame that holds the message. [10]
5.2. How do
the applications of these standards affect the way in which a paging network
operates?
The format of the
paging channel effects how data is sent and transmitted. The paging channel slot is, as mentioned
previously, 80 ms long. This 80 ms slot
is repeated during the cycle of 2048 slots which is known as the “maximum slot cycle”
[11]. A message that is to be
transmitted is put into a capsule.
Capsules can either be synchronised or unsynchronised. In the case of an unsynchronised capsule, the
message can just go into the capsule without padding. Padding is used for synchronised capsules
when the message size is less than the capsule size. The padding fills up the rest of the capsule
to ensure that the next message will start at the beginning of the next capsule
and hence, stay synchronised. In order
to fill a paging channel slot, eight half frames are used with each having a
duration of 10 ms, from a paging channel message. So, each paging channel message capsule is
split into eight segments. These are
known as a paging channel half frame body and each one is attached to a SCI
subfield to form the paging channel half frame.
The paging channel half frames are put into the paging slot so that it
can be transmitted.
The actual paging
channel messages take to format of the message length field, the message body
field, and the cyclic redundancy check (CRC) field, with lengths of 8 bits,
variable and 30 bits long respectively.
The message length field and it indicates the total length of the
message. The message body field carries
the body of the message and the CRC field completes the error checking to
ensure that the message is received as it was sent. [10]
6.1. What is
the main application of paging networks in society?
It is not very
common now for many people not have some communication device be it a pager,
mobile phone or something else. Before
professionals like doctors only used pagers so they could be contacted in case
of an emergency. Pagers in particular
have become very popular, particularly in
These days, it
has become nearly necessity to be able to be contacted no matter the time or
place. The main applications for pagers
are for receiving alerts of different types and getting and keeping in touch
with each other. Messages such as stock
movements, sporting scores can be sent to your pager. You can be alerted when you have a new email
or voicemail message to get or that it is time to take your medication
[13]. You can just be a worried parent
trying to find out where your child is, or a friend wanting to let others know
that you are running late.
7.1. What is
the main technology competing with paging networks?
Pagers are
commonly used. They’re small,
unobtrusive, inexpensive and reliable, but with the development of cellular
phones, they are gradually getting replaced.
As mentioned earlier, pagers had their biggest boom when mobile phones
were first introduced as a means of screening calls because of how expensive
mobile phones were. Now with the more
developed technology and increasing popularity, mobile phones have become more
affordable, smaller and so convenient that it is hard to find someone that does
not own a mobile. The picture to the
left is an example of such a phone. [15]
Pagers were great when two-way pagers were introduced. Not only could you receive a message from
someone, but you could reply to it too.
Before all you could do with a mobile or cellular phone was call
someone, but with the introduction of short message service (SMS) you can now
message to and from mobiles similarly to a two-way pager, not to mention all
the additional features of mobiles such as games, calendar and calculator to
name a few. Competing against this
technology seems an enormous task for paging systems. [4]
7.2. What are
the differences between a paging network and its competitor?
7.2.1. How do cellular networks and phones work?
A cellular network consists of areas called cells. These cells each have a base station
sometimes known as a Base Transreceiver Station (BTS). Whenever a cellular phone or mobile system is
switched on or changes what cell it is in, it finds the closest base station
and makes a connection with it. This is
known as “registration” [4].
Communication between the mobile system and base stations continues over
a wireless network of antennas, receivers, transmitters and amplifiers as well
as other devices sending, receiving and converting signals as needs be. The base stations are also connected to the
Mobile Switching Centre (MSC) through an uplink, in order to transmit calls
back and forth from the cellular network.
MSCs are used to control a group or cluster of cells. The MSC routes all instructions and calls to
the relevant cell and base station, as well as having a link to relevant client
databases. One of these databases
contains the security information needed when authenticating a user, such as
checking pin numbers. Calls are routed
to the Gateway
Each cell phone has in its memory, a number assignment module (
When a phone is turned on, it is tuned into an overhead signal. This signal contains a SID as well as other
identification information. If the phone
cannot hear the signal, then it will have no network coverage. Different base stations transmit this signal,
and the phone will pick up whichever signal is strongest at the time in the
area. If the transmitted SID and the phone
SID match, then the phone is on the home network, otherwise the phone goes into
“roaming mode” and connects to a non-home network. Whether it is in roaming mode, or on the home
network, the phone sends out its ESN to identify itself. This information is sent to the MSC so that
the MSC knows generally where each subscriber is at in a given time, and which
base station to route a call to if there is one. [4]
For SMS, the message is entered by the keypad on a phone. This is sent to a mailbox as specified by the
user. The message is sent to the MSC,
then routes the message to the messaging centre to make a copy. The network then finds where the other phone
is, and the base station sends an alert over a control channel that there is a
message coming. In order to receive the
message the phone must tune into the control channel. Once the message is received, an
acknowledgement is sent to the messaging centre to inform that the message was
received. The copy will be deleted, but
if no acknowledgement is received, the centre will continue to try and send it
until an acknowledgement is received. [4]
8.1. Are
paging networks readily available in
Paging is
something that has never really taken off in
Another company Link Solutions
[16] is doing a project for the South Australian Government Radio Network (SA
GRN), which involves the construction of a state-wide radio network for
emergency services. The network will be
state of the art with the ability to “be accessed by operator, telephone, direct console
delivery, computer and alarm interface. Messages can be
delivered with a guaranteed delivery time for high priority messages” [17]. The network will improve the public safety of
South Australian (SA) organisations and Government
agencies which was previously was only partially covered by the
network.
In other countries however, especially the United
States of
With the deployment of two-way systems, the paging industry has gotten
its second wind. Certain regulatory
issues are hindering the growth of two-way paging in other parts of the world. The FCC was quick to license the regulations,
which included the need for paired spectrum.
As such, some European countries still have no pager uplink band
allocated. [19]
9. Companies producing paging technology
The main produces
of the paging technology are companies mainly based in
The
steps that the paging companies are now taking all lead to moving in on the
wireless data services currently being provided by cellular mobile networks.
These services would cost less to subscribe to through two-way paging as
opposed to cellular phones. For this
reason, it was predicted that in June 2001, that by 2002 the number of two-way
subscribers would increase by 1.6 million. [18]
10. Future trends for paging networks
The future of
paging networks hangs in the balance. It
is believed by some that the technology of two-way paging systems has been
developed too late. Subscribers are not
changing from the one-way to the two-way system as indicated by the number of
subscribers with Arch Wireless.
There are 11 million on the one-way system compared to only 200 000 on
the two-way system. These subscribers
are opting for mobile phones because of the voice enable but especially because
of the introduction of SMS. [18]
However, paging
systems are being picked up by businesses for their staff. Businesses such as law firms, advertising,
building and construction and for salespeople would benefit greatly from the
use of pagers. Pagers are cheaper to run
tan laptops or palm pilots. They can be
used to get the same information for clients such as quotes, meetings or
results as from mobiles or laptops or other devices. The ubiquity of paging networks allows great
network coverage and building penetration, but one concern is over
security. There is the problem of
whether the data to be sent can be kept safe especially if it relates to a
client’s personal information. Another
concern is whether the network will be able to handle so much data being
transferred. According to Carr [18], it
isn’t unheard of for high traffic customers to get their own transmitting tower
in their building to ensure strong, reliable network coverage.
A significant
factor when choosing a pager over a mobile for example is that the information
reached you straight away. Pagers are
always on and there is no fussing to get vital information. With a mobile however, there is a need to
open the alert, and then scroll through to the desired screen or ring to get
the information. Barry Shelton, a
consultant for Wireless Knowledge, says that “when event-driven information needs
to be propagated to mobile devices," says
A basic paging network consists of a telephone, paging service, paging centre, base stations and transmitters and a pager
There are two types of paging systems: one-way and two-way
One-way paging systems can only receive messages
Two-way systems can both send and receive messages as well check email
Pagers work with a radio frequency signal
Most pagers only have receivers (one-way); while others have a transreceiver (two-way)
To receive a page: someone calls the paging service and leaves a message and pager number. The number is matched with a coed number on the system and sent along with the message to the paging centre. The page is then sent to the base stations. The base stations transmit the page over network. The pager is tuned into the same frequency a the transmitters, and it "listens" for a page. When it "hears" the page, the signal goes through the internal electronics of the pager, which alerts the user of a message and decodes and displays the message.
Two-way paging: the pager sends a signal to the base station which gives a rough location of where the pager is. This way when there is a message the page need only be sent to the closest base station rather than transmitting over the entire network.
Messages can be sent from a pager by typing up the message and sending it. Receiver stations pick up the signal and send it back to the paging centre so that it can get transmitted to the person
Transmitters for the various companies operate off different frequencies so that there is no interference between networks
Transmitters can cover an area range of up to 30 miles
Many transmitters are needed for a one-way pager, whereas only one is needed at any time for a two-way pager
SMTP is used to connect a two-way pager to retrieve email
America's paging industry is most prominent in the world largely due to the FCC and other regulatory bodies
There are many different standards and protocols that exist for paging networks
A paging channel slot is 80 ms long
Pagers are very useful devices whether they are used to get in touch with people to screen incoming mobile calls or to get the latest news and stock movements.
Pagers are cheap, reliable, small and unobtrusive, which is why they are so popular
Unsure about the future especially with the introduction of SMS on mobile phone networks
Paging companies joining up with internet companies such as MSN and Yahoo, to secure their future