Call divert from 3G to 2G

[aryan22in]

Dear Experts,

I have a requirement where if a Subscriber latched to 3G makes a voice call, his call should be automatically handed over to 2G network. This can be done from Radio end, but the Customer is asking if this can be done from MSC end. There is a parameter FORBRAT in MSC which has steer/restrict LU to 2G or 3G. But I could not find any parameter which can steer the calls from 3G to 2G.

If anyone has an idea about the same, kindly let me know. Many thanks for your support.

My MSC is E/// R14.1 Blade Cluster

BR<
Aryan

[s52d]

IMHO: Sorry, no.
User can do voice + data, and MSCS is not aware of data, so forced handover to GSM might be problematic.

Also, MSCS is not involved in early phases of call establishment, so it can not act. Especially when using MSCS in pool,
actual VLR to handle specific call is not known untill later phase of call setup.

On top of it: MSCS has no idea of UMTS cell load, and can not take appropriate actions.

So, back to RAN: it is RAN who can force handovers to GSM.

Restricting per location area is completely different story: it blocks data as well. Probably not what they want.
And you probably do use common LA over 2g and 3g like most networks.

Of course, by forcing additional handovers when not needed you force additional drops as well: KPI degradation is side effect.

Warning: maybe it can be done somehow, but I sincerely doubt in MSCS based approach.

BR
s52d

[kapil12]

It can be done by Service Handover options in CS and PS Core. below are some details.

Service Handover option allows CS and PS Core Networks to inform UTRAN that GSM is
preferred for this service, through the optional serviceHO Information Element (IE) which is
present in RANAP RAB Assignment Request message.
Based on the 3 different values that ServiceHo IE can have (if present), iMCTA algorithm may
dynamically change the GSM priority in the Priority table:
• IE = should: GSM priority is overwritten with P0, i.e. GSM becomes the most
preferred target Access
• IE = should not : GSM priority is overwritten with P8, i.e. GSM becomes the least
preferred target Access
• IE = shall not : GSM priority is overwritten with PNA, i.e. GSM is no more eligible for
target Access.
The processing of this optional IE is not systematic and can be enabled/disabled through
serviceHoRanapIeEnable parameter.

[kapil12]

The Service Handover option can be used for load distribution by preferring the GSM layer for
CS calls using the "should" option. GSM can provide similar service for CS calls as UMTS and
therefore it might be a good idea to handover CS call to a less loaded GSM system. If, however,
the UE has a simultaneous PS call then the UE should be kept in UMTS to allow for
simultaneous CS and PS calls, which is not supported in GSM by most GSM networks and UEs.