A method for determining a free connecting line in a switching center having a
number of subscriber access units is provided. The access units are controlled
by a switching center. At least one group of transmission lines of a subscriber
access unit and, possibly, a group of lines of the line trunk group form a logical
group of lines, which connects the switching center to another switching center.
When an incoming or outgoing call which is intended for another switching center
occurs at the subscriber access unit, a check is carried out to determine whether
a connecting line which leads away from this subscriber access unit in the group
of lines is free for a call, and, if one of these connecting lines is free, a connection
is set up to the other switching center via this connecting line.