Point-to-point line : A physical connection in which a single network termination supports exactly one terminal equipment device. This is supported by both BRI and PRI. Here, the NT (NT1 or NT2) and TE (TE1 or TA) can be upto 1 km apart.
Point-to-multipoint line :
A physical connection in which a single network termination supports
multiple terminal equipment devices. A point-to-multipoint connection is
a connection established between one user-network interface and more than
one user-network interfaces.
There are two types of point-to-multipoint configurations, both employing
a passive bus. It is called passive because this configuration does not
contain any active components, such as amplifiers or repeaters and therefore
devices can passively monitor the activity on the physical line without
affecting that activity.
In the short passive bus configuration, upto eight TEs can be connected
to a single NT on a bus upto 200m in length. The TEs and the NT may be
anywhere on the bus with respect to each other. In the extended passive
configuration, upto eight TEs may be grouped together at one end of a bus,
upto 1 km from the NT.
Note that in a point-to-multipoint configuration multiple TEs share access
to a single D channel and both B channels. As far as the B channels are
concerned, only one TE can use it at any instant of time. The user network
signalling procedures ensure that no more than one TE seizes a B channel
at any given point of time. This in turn means that, in BRI, even
though eight TE's can be there on the S/T bus, at any point of time, only
two TEs can access B channels because BRI has only two B channels. As far
as access to the D channel is concerned, all TEs have access to it at all
points of time and they share the D channel simultaneously to exchange
signalling and call control messages.
