The TEI (Terminal Endpoint Identifier) value
for this Terminal Endpoint. If isdnEndpointTeiType
is set to static(2), valid numbers are 0..63,
while otherwise the value is set internally.
The default value of this object is 0 for static
TEI assignment.
The default value for dynamic TEI assignment is also
0 as long as no TEI has been assigned. After TEI
assignment, the assigned TEI value is returned.