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3.
DATA COMMUNICATION OVER A ROUTE
In the ISPBX a DTE can be connected via a modem/ALC or via a DLC/SOPHO-SET, SOPHO-
LAM or LAM as discussed in chapter 2. If the DTE requests a connection to an external DTE
(i.e. one connected to another PBX or to the PSTN) then a trunk or tie-line must be used. An
incoming data call, initiated by an external DTE, also uses a trunk or tie-line.
For an outgoing data call a connection to an external DTE can be established by dialling a trunk
access code to a specific destination followed by the external number of the DTE.
For an incoming call, dial information (DDI) is received over the trunk or tie-line. By analysing
this information in an analysis tree related to the route the connection set-up to an internal
DTE is possible. If the connection set-up is performed using a speech connection before
switching over to modems, both incoming and outgoing calls can be made with assistance of
the operator.
The trunk line involved can be assigned to an analogue or to a digital route. This distinction is
used in this chapter. Both a DTE connected via a modem to an ALC or a DTE connected via
the data port of a SOPHO-SET, SOPHO-LAM or LAM to a DLC/DTX can gain access to the
trunk line. For both types of parties the data communication aspects over an analogue route
and over a digital route are discussed.
A number of trunks or tie-lines can be grouped into bundles, a number of bundles can be
grouped into routes and a number of routes are related to a destination. The terms `line',
`bundle', `route' and `destination' are used in OM for the allocation of various parameters.
In this chapter only the V.24 interface is described. For all other types of interfaces a gateway
server has to be used. The connection between the DTE and the server is usually as for an
internal data call and is therefore discussed in chapter 2.
For more information about the routing aspects: see Facility Implementation Manual;
Networks and Routing.
3.1.
DATA COMMUNICATION OVER AN ANALOGUE ROUTE
Various types of Analogue Trunk Units (ATUs) are used to connect ISPBX to the public
network. There are many types to cater for the different transmission characteristics which
are used throughout the world. All ATUs are used in the same way, as far as data
communication is concerned.
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