N O V A T E L W I R E L E S S T E C H N O L O G I E S L T D .
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A T C o m m a n d S p e c i f i c a t i o n - E x p e d i t e a n d M e r l i n
W i r e l e s s I P M o d e m s
Data Transmission Mode
Packet Assembly
The NRM provides a local Packet Assembly and Disassembly (PAD) function. For transmission,
the character stream from the Host is assembled into packets for RF transmission under the
following conditions:
-Idle time-out: If the time between successive characters exceeds the time interval specified in
register S50, any pending data is assembled for transmission.
Buffering and Flow Control
The NRM has an input data buffer which is intended to be set larger than the longest transmit
message used by existing protocols in the Host. The size of this buffer is 578 characters.
If hardware flow control is disabled and, the NRM is formatting and transmitting data blocks
associated with a packet, the Host should not send additional data as this may cause input buffer
overflow. Buffer overflow will result in a loss of data with no indication to the Host. In order to
avoid data loss, it is recommended (and anticipated) that the Host application protocol operates
using a half-duplex ACK/NAK protocol. It should be expected that the Host acknowledgment
time-out should be set greater than that required for circuit-switched modem configurations. This
is to account for propagation delays through the NRM, CDPD base station and CDPD and Internet
networks.
