Sierra Wireless DART 200 CDPD Modem - Manual (Page 61)

DART 200 CDPD Modem User’s Guide 5 DART Supported Protocols
PN1197-00 Revision 1.0 5-7
• Receive locking
• Backwards compatibility
The details of these options follow.
• Friends Only Mode - Restricts communication with the modem (for
security reasons) to a predefined group of addresses (friends)
This feature is controlled by S-Register 82 which enables and
disables the comparison of datagram source addresses against a list
stored in the DART 200’s destination dial directory. Refer to the
AT&Z command in Modem dial directory, p. 8-24, or Appendix F,
DART AT Command Set for details. Only the IP Address portion of
the addresses in the dial directory is used with this feature. Bit 0 of
S-Register 82 controls this mode. The default is to accept all
incoming datagrams (bit 0 = 0)
.
This bit is significant only when the UDP connection is established
passively (server mode). When the connection is established actively
(by an ATDP command), incoming datagrams are accepted from the
destination address specified in the dial command regardless of the
address being in the friends list; this is consistent with basic UDP
operation.
In both of the above cases, the source address (IP Address and port
number) of the last accepted datagram is saved in a temporary
variable for use as the current destination address for all datagrams
being sent by the MAS during the current session. This source
address information is also saved in S-Register 53 where it can be
obtained with an ATS53? command. However, if the application
design allows the M-ES to receive messages from multiple clients,
outbound datagrams can only be sent to the last source of input data.
If this is a potential problem due to timing considerations, refer to the
next bullet point on receive locking.
• Receive Locking - A UDP server feature that allows time for the
MAS to respond to a datagram without concern that another
datagram from a different source will overlay the current destination
address
This feature is controlled by bit 2 of S-Register 82. The default is
receive locking disabled (bit 2 = 0). The lock time out period is
specified in S-Register 83 in tenths of seconds (default is 3 seconds).
If receive locking is enabled, all datagrams arriving after the first
one, regardless of their source address, are held in a First-In-First-
Out (FIFO) queue until a data transmission occurs, or the time out
period expires, releasing the first datagram in the queue.
• Backward Compatibility - Permits the UDP server to operate in a
mode compatible with the basic UDP provided in earlier versions of
the software (prior to version 2.0)