5.2.1.3. Philosophy of loop avoidance in public/ OpenScape 4000/HiPath
4000 network 
If the administered alternate routing number leads to an external
destination within the OpenScape 4000/HiPath 4000 network, special classmark
information will be transported in the call_setup message, that takes
care of loop avoidance in the target OpenScape 4000 switch. No additional
administration is necessary for that case.
If the administered alternate routing number leads to an external
destination within the OpenScape 4000/HiPath 4000 network but using a
partly routing via public network, this classmarks cannot be transported.
In this case, the loop avoidance only can be done with use of an enlarged
alternate routing destination number. For this purpose, 2 DARs "ALTRTOOS,
ALTRTAPE" are newly created.
Example_1:
In case of AP Emergency, the calling device out of AP_x wants to
reach the called subscriber in AP_y via public network.
Called subscribers extension number = 4711, outgoing public trunk
access = 004989, incoming trunk access = 722, digit string, that leads
to DAR "ALTRTAPE" in the switch = 99.
The individual alternate routing number could be = 004989-722-99-4711.
The source-group related alternate routing number could be = 004989-722-99.
Example_2:
In case of OOS, for the called device (NOT_READY) in switch_1, the
alternate routing number will be designed in that way to reach an alternate
subscriber in OpenScape 4000 (switch_2) via public network.
Extension number of alternate subscriber in switch_2 = 4812, outgoing
public trunk access = 004989, incoming trunk access (switch_2) = 723,
digit_string, that leads to DAR ' ALTRTOOS" in switch_2 = 98.
The individual alternate routing number could be = 004989-723-98-4812
A source-group related alternate routing number is not allowed in
this case.
Warning:
The use of the 2 new DARs "ALTRTAPE" , "ALTRTOOS" for designing the
alternate routing number is only an option for loop avoidance in public
network. The necessity to use this option is much higher in case of alternate
routing for APE than for OOS. Nevertheless, the option in general should
be used only in following cases:
- An alternate destination should be reached in a OpenScape 4000 switch partly routed via public network.
- The used new DARs "ALTRTAPE" or "ALTRTOOS" have to be administered in the target OpenScape 4000 switch.
If the DARs are unknown, the digit translation in the target switch surely
will not find a valid result.
If this option is used in case of a routing only in OpenScape 4000/HiPath
4000 network, it does not create a problem at all, but it is not necessary.