Impact Analysis
BICC establishes two formulas of Fast Forward and Forward Delay method that both
carry in a different way.
Fast Forward method: Before sending the IAM message of MSCs outgoing call, Fast Forward mode has
received the Tunnel Data from MGW and then sends the IAM message to backward
office that carry Tunnel Data consists of the IPBCP.
Pros:
Less Interaction of BICC messages.
Cons:
If the codec for two MSC’s are different, TC will be inserted in MGW. If improper TC is
defined in MGW, call maybe dropped.
Forward Delay’s method:
In MSC outgoing call, IAM and first APM message do not carry the Tunnel Data. The
carrier establishment will start after receiving the APM return message.
 Pros:
Codec negotiation can be carried out properly.
Cons:
More BICC messages than Fast forward which results in a slightly increase of call set up
time.
Since both uses different method but still Fast Forward mode cannot support the TrFO as
per protocol.
According to the protocol, ITU-T Q.1902.4 justify the rule of decode and mention that
edit the decode must be carried and completed before begin. Refer to section Q.1902.4
8.3, "when codec negotiation is required the negotiation has to be performed …
negotiation is needed before the bearers can be set up".
However in Fast Forward mode, the first IAM already make the IPBCP Request, it means
that in this period, codec has been selected already. So there is no chance to edit the
code.
Moreover if the duration of Fast Forward to backward office more than 10s, it can make
the call drop, because after UMG set up the bearer which will activate the 10s for
beginning, when backward office more than 10s, UMG UP initial will be overtime, UP
initial will be failed and then it will cause the call drop.
Subject to the peak hour of calling, UP initial cannot be successful rapidly, and then it will
make the UMGs IP usage resource increase which will cause the loosing of IP resources.
Suggestion:
Fast Forward clearly defines that this method cannot support TrFO.
Besides, subject to Fast Forward mode, for the long call setup time at backward office
may make the call drop or occupy long time resource.
So Forward Delay is prioritizing than Fast Forward method.
| 
Favorite (0)
Reply
