User`s guide

127
Since data is transferred across IP networks in synchronous format, the router supports
asynchronous to synchronous PPP conversion. This allows asynchronous terminals
connected to the units to communicate with remote synchronous PPP devices. Normally, this
is carried out using a single ISDN B-channel so that data can be transferred at speeds up to
64kbps. This is known as ASYNC to SYNC PPP operation and is supported as standard by
most terminal adaptors. To use ASYNC to SYNC PPP operation all that is necessary is to
ensure that the PPP protocol is bound to the ASY port to which the terminal or PC is
connected. (see Configuration – Network > Interfaces > Serial).
Note:
In order to use ASYNC to SYNC PPP the attached terminal must also support PPP (Windows
dial-up networking supports PPP).
In addition to ASYNC to SYNC operation (where the router only converts the PPP from one
form to another) the router can initiate its own PPP sessions. This is used for example
when:
The router is configured as a router to connect an Ethernet network to the Internet via ISDN
or W-WAN
The router is answering an incoming ISDN call with PPP either for remote management or
remote access to the Ethernet network to which the router is connected
The router is accessed locally through the serial port for configuration purposes by setting
up a Windows Dial-Up-Networking connection to the “phone number” 123
Note:
With the exception of MLPPP the parameters in this section are only relevant when the
router is generating the PPP, i.e. they are NOT relevant for ASYNC to SYNC PPP operation.
The unit also supports Multi-link PPP (MLPPP). MLPPP uses both ISDN B-channels
simultaneously (and two PPP instances), to provide data transfer speeds up to 128Kbps for
applications such as email or establishing a point-to-point connection between two units.
External Modems
Configuration – Network > Interfaces > Advanced> External Modems
The External Modems page contains external modem parameters. External modem support
added to GPRS builds. It is now possible to have a GPRS build that can also make outgoing
PPP connections via an external modem. It is also possible to answer incoming calls via an
external modem. The PPP 'use_modem' field has now been altered so that the value
indicates which modem type should be used. Value 1 indicates that GPRS modem should be
used, value 2 indicates that external modem should be used.It is now also possible (by
including enough modem call control instances) to do multilink PPP over multiple external
modems.