Central Site Remote Access Switch 391
C
ONFIGURING
O
THER
A
DVANCED
O
PTIONS
The Digital Modem
The Digital Modem software identifies, directs, and converts the data stream appropriately. For
example, if an incoming call to the system is identified as coming from an analog modem, the
associated ISDN B-channel is routed to the Digital Modem adapter. Software assigns it to one of the
digital modem modules, and all of the operations of a V.34+ or K56Flex modem are performed just
as if the call had gone to an analog modem through an analog phone line. The data is demodulated,
and then sent to an internal Asynchronous Usage Discriminator (AUD), which monitors the data
stream. This AUD determines if the caller wishes to use PPP protocol, or whether it is requesting
remote analog console access. This determination is made within a configurable time frame:
•
if the AUD detects four carriage returns from the caller, it will provide the caller with remote an-
alog console access by presenting the caller with a CyberSWITCH login prompt.
•
if the AUD detects PPP LCP frames, it connects the caller to a PPP stack. An Async-PPP-to-Sync-
PPP conversion is performed, and then the system sends the data to the LAN as appropriate.
•
if the AUD does NOT detect the PPP LCP frames nor the carriage returns, it will still attempt to
send the data to the PPP stack.
The Digital Modem feature supports the following features:
•
auto speed detection and negotiation
•
auto step down and step up during session if line is noisy
•
up to 56 Kbps modem speed (backwards compatible down to 300 baud)
•
data compression which is automatically negotiated (with maximum 4:1 compression, up to
115.2 Kbps DTE speed)
•
error control
These features are also dependent upon the analog modem you are using, since the features must
be supported by both devices in order to be operable.
Refer to the following chapters for more information:
Hardware Overview
,
Hardware Installation
and
System Adapters Appendix
. Refer to the
Digital Modem Commands
section for methods to display
active connections, display or erase digital modem statistics, add or delete individual modems, and
upgrade modem firmware when necessary.
S
UPPORTED
M
ODES
OF
C
ONNECTION
The Digital Modem supports either a PPP mode or terminal mode type of connection.
In PPP mode, the Digital Modem uses Asynchronous Point-to-Point Protocol (Async-PPP) as its
link protocol. Therefore, the system with Digital Modem will support remote devices attached by
modem that provide Async-PPP dial-in. This protocol is very popular for analog modem
networking, and is built into many leading remote application programs. Modem connectivity is
not provided for RFC 1294 devices or HDLC Bridge devices.
For authentication, the remote device must support either PAP and/or CHAP.
In addition to Async-PPP, the CyberSWITCH supports a terminal-mode type of connection. This
mode provides the opportunity for remote user-level authentication before Async-PPP data
transfer, or it provides the opportunity for remote analog console access. For more information,
refer to
Terminal Mode
in the Default Async Protocol section.
