Sdc Negotiation - Paradyne COMSPHERE 3920Plus Technical Reference Manual

SDC Negotiation

The use of the synchronous data compression function and the value of the associated parameters
is negotiated at link establishment via a protocol. The three associated parameters have the same
meaning as those used for asynchronous data compression:
• Dictionary size parameter
• Maximum string length parameter
• Data compression request parameter
The SDC Negotiation configuration option determines how two modems connect when one or both
modems have SDC installed. Two settings are available in the SDC Negotiation configuration
option: LAPM_Buffer and LAPM_Discon.
Table H-1 shows the six possible SDC Negotiation configuration scenarios.
Originating Modem
SDC enabled with LAPM_Buffer
negotiation.
SDC enabled with LAPM_Buffer
negotiation.
SDC enabled with LAPM_Discon
negotiation.
SDC enabled with LAPM_Discon
negotiation.
SDC enabled with LAPM_Buffer
negotiation.
SDC enabled with LAPM_Discon
negotiation.
SDC disabled.
SDC disabled.
* If during the negotiation phase, the modem with SDC enabled receives data from the remote modem indicating that it
has SDC disabled, the link will not be established between the two modems. For example, the remote is configured
for Async and Error Control Mode is V42/MNP/Bfr, or V42/MNP/Dsc, or LAPM/Bfr, or LAPM/Dsc.
* * On a leased line, the originating modem sends endless EC negotiation sequence. Data cannot be successfully
transmitted.
*** On a leased line, the answering modem waits indefinitely for error negotiation sequence. Data cannot be
successfully transmitted.
3920-A2-GH30-40
Table H-1
SDC Negotiation Configuration Scenarios
Answering Modem
SDC enabled with LAPM_Buffer negotiation.
SDC enabled with LAPM_Discon
negotiation.
SDC enabled with LAPM_Buffer negotiation.
SDC enabled with LAPM_Discon
negotiation.
SDC disabled.
SDC disabled.
SDC enabled with LAPM_Buffer negotiation.
SDC enabled with LAPM_Discon
negotiation.
October 1998
Synchronous Data Compression
Negotiation Results
Dial: SDC connection.
Leased: BufferMode connection
with no Error Control.
SDC connection.
SDC connection.
SDC connection.
BufferMode connection with no
Error Control.*
Disconnect.**
BufferMode connection with no
Error Control.*
Disconnect.***
H-7