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S3 interface in LTE?

+3 votes
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For LTE to UMTS network handover is it mandatory to configure S3 interface.

posted Sep 28, 2013 by Salil Agrawal

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2 Answers

+2 votes

Yes S3 and S4 both interfaces are necessary to support handover from LTE to UMTS. S3 interface exists between MME and SGSN and for data plane S4 interface between SGSN and SGW. One more thing I would like to add if there is no direct tunnel exist between SGW and RNC then only S4 between SGW and SGSN will be used.

answer Sep 28, 2013 by Vimal Kumar Mishra
+1 vote

S3 interface is not mandatory for handover from LTE to UMTS.

Rel 8 and latter SGSNs have support for S3/S4 interfaces. S3 between SGSN to MME for control plane and S4 is between SGSN and SGW for user plane. S3 is GTPv2 based and S4 is GTPv1 Based. SGW is the mobility anchor point. Direct tunneling while roaming can be achieved by using S12 interface between RNC and SGW.

We can also have Gn interface between SGSN to MME for control and Gn interface between SGSN to PGW for user plane. Both control and user part is GTPv1 based. This is the Pre-release 8 SGSN scenario and also have support in release 8 and latter SGSN to have support for connectivity with Pre-Rel 8 networks. PGW is the mobility anchoring point. Direct tunneling in roaming is not supported because while roaming in UMTS/GSM coverage traffic always needs to pass from SGSN.

answer Oct 7, 2013 by Luv Kumar
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