SRNS Relocation Problem - 2 GGSN involved

[ivanbrij]

Dear Experts,

I have a problem with SRNS Relocation. There are two different GGSN involved in the relocation. Target RNC doesn't have IPPath/IP Route to the GGSN where Serving RNC is connected.

Both RNC are connected to 2 SGSNs using IuFlex. Also 3G Direct Tunnel is enabled.

SGSNs has configured GGSN1 for Serving RNC and GGSN2 for Target RNC. During Relocation proccess, SGSN sends Iu Trans Address (IP Address) of GGSN1 to the Target RNC, but Target RNC only has IP Path/ IP Route to GGSN2. There is a relocation failure due to TNL (Iu Trans Address unreachable).

Someone of you had this problem before and can help me?. Operator doesn't want to add IP Path/IP Route to GGSN2. I think SGSN need update GGSN before send Iu Trans Address to Target RNC, but how to solve this issue?. Both RAN/CN are Huawei.

Thanks in advance for your ideas,

Ivan

[scorpion]

SRNS Relocation request can happen..because that is being attempted at RNC/SGSN Layer... I beleive you have pool also.
But it will fail eventually. What is the failure code you are getting ?

I feel this is not possible , until you connect both RNC to same GGSN and arrange the SGSN also in similar fashion to handle the flow with Pool in place.
The crux is that GGSN is the anchor...you cannot expect a anchor to do packet forwarding...if GGSN Receives GTP in one end then it will not put that particular payload again on GTP.

Anyway...nowadays vendors are surprising a lot. I am also interested to see any alternate solution.

[ivanbrij]

Hi Scorpion,

The faul code is: Iu Transport Connection Failed to Establish

There are 2 SGSN in pool because of the IuFlex. Both SGSN are connected to 6 GGSN, but Source RNC is connected only to GGSN1 and Target RNC is connected to GGSN2. Also 3G Direct Tunnel feature is enabled between RNCs - CN.

All cases describe in 3GPP TS 23.060 only have one single GGSN involved in SRNS Relocation. If we have 2 GGSN involved, how will be the procedure.

I think SGSN could keep IuPS with 2 GTP tunnels ( Target RNC - SGSN - GGSN1) then update the second GTP tunnel to the GGSN2 and then, create one tunnel Target RNC - GGSN2. But I'm no sure about 3GPP for this case.

Also I think if SGSN is in pool, then GGSN also must be a pool, and RNCs should have IP Path/ IP Route to all GGSNs (6). The client doesn't want this solution.

More ideas about the problem and how to solve it.

BR,

Ivan

[scorpion]

Can I know the reason why your customer don't want that any idea...? commercial ?

[ivanbrij]

Operator doesn't want than RNCs have a lot of IP Paths to GGSNs. Commercial Network. There are IP Paths only to one GGSN, In case of failure, there is a GGSN backup.

BR,

Ivan

[rfsupp]

Dear Ivanbrij,

Do you have sure that the pool are configured correctly?
Can ping the DEVIP (RNC`s Target)? If you can't, for sure there is something wrong in this route.

[ivanbrij]

Dear,

Yes, Source RNC can ping Target RNC (There is IPpath/IProute between then for Iur and for IuPS-UP).

The problem is. SGSN send SRNS Relocation required command to Target RNC, but in the message. SGSN send IP Address of GGSN1 as Iu Trans Address for user plane.

Target RNC answer with fail code: Iu Transport Connection Failed to Establish. It's because Target RNC only have IP Path/ IP Route to GGSN2.

BR,

Ivan