Specifications

Multiport for TNPP and TAP Outdial
136 025-9035AA
Types of Packets
A TNPP packet may contain capcode pages, subscriber ID pages, and various types of
network related information. Capcode pages include a description of the target pager, such
as GSC type II-A pager, channel and zone information, and message class such as beep-
only, numeric, or alpha. Because capcode pages fully describe the pager to activate, they
do not access the subscriber database. ID pages just send a subscriber ID code, and depend
on the receiving terminal to obtain the pager description for its local database. Both
capcode pages and ID pages may include a display message, and both carry a function
code and a flag indicating whether the page has low or high priority.
The TNPP card connects to the outside world through ports. There is one special port,
referred to as port zero, which actually is the connection between the Network card and
the paging terminal. This port needs no special interface, as it is part of the Multiport card
hardware. Besides that, there is some number of external ports, the exact number
depending on the particular configuration of your terminal. Each active port is one end of
a link.
Types of Links
A TNPP network port may be considered an RS-232 serial interface. The data is sent in
asynchronous format, with eight data bits and no parity. Any method of getting the serial
data from one system to another is fine; all that is required is a transmission link that can
carry 8-bit digital data. Each active port on the network card is programmed to select its
baud rate, network mode, network timing requirements, and other parameters.
With normal TNPP, the link is bi-directional, so when a packet is sent from one node to
another the sending node expects a reply code from receiver. Pages may be passed in both
directions. There must be a link for each active port on the card; that is, a pair of directly
connected nodes must have a dedicated link between them connecting a pair of ports.
The majority of TNPP networks use a UDS 202T modem on a leased 4-wire audio
telephone line to communicate between the paging terminals. The 202T modem is widely
used in transmitter control links, allowing the same modem type to be kept for spares for
both TNPP and transmitter control. The 202T modem is slightly easier to set up than the
212-style modem, but does require the 4-wire telephone lines or equivalent. A microwave
link has been used in place of actual telephone lines.
Some systems use 212-type modems instead of 202. This has the advantage that 2-wire
telephone lines are used, instead of 4-wire. However, the 212 modem is a bit more
sensitive to noise and slightly harder to set up. The 212 modem is not a “Hayes” style
modem, but rather a “dumb” modem similar to the original Bell 212 modems.
Other systems use packet radio modems, with pairs of modems programmed to be
“permanently” connected to each other. The packet modems provide error detection and
data retransmission independent of the error handling of TNPP. While this would seem to
allow using TNPP in simplex mode, normally, full duplex TNPP should be used even if
the paging traffic is all in one direction. By retaining duplex mode, various problems will
be posted in the 2000 Series log files. Poor connection conditions and loss of the link