6 Interworking in the S4-SGSN

29.0103GPPInformation element mapping between Mobile Station - Base Station System (MS - BSS) and Base Station System - Mobile-services Switching Centre (BSS - MSC)Release 17Signalling Procedures and the Mobile Application Part (MAP)TS

6.1 General

This clause provides a detailed specification for the interworking performed by the S4-SGSN.

6.2 Interworking between RANAP protocol messages and S1AP protocol messages

This clause defines a mapping of RANAP and S1AP cause values used in connection with inter RAT Handover to avoid different mappings in different implementations.

Inter RAT Handover from UTRAN to LTE:

The table 6.2.1 defines a cause value mapping performed by the S4-SGSN when the S4-SGSN receives the Forward Relocation Response message from the MME. This mapping is only needed if the inter RAT Handover failed in LTE.

Table 6.2.1: Cause value mapping from S1AP Cause to RANAP Cause for failure case

36.413 [21]		25.413 [7]
HANDOVER FAILURE (S1AP Cause)		RELOCATION PREPARATION FAILURE (RANAP Cause)
Group	Value	Group	Value
Radio Network Layer Cause	No Radio Resources Available in Target Cell	Radio Network Layer Cause	No Radio Resources Available in Target Cell
Radio Network Layer Cause	Encryption and/or integrity protection algorithms not supported	Radio Network Layer Cause	Requested Ciphering and/or Integrity Protection algorithms not supported
Miscellaneous Cause	O&M Intervention	Miscellaneous Cause	O&M Intervention
Any other value		Radio Network Layer Cause	Relocation Failure in Target CN/RNC or Target System

Inter RAT Handover from LTE to UTRAN:

Table 6.2.2 defines a cause value mapping performed by the S4-SGSN when the S4-SGSN receives the Forward Relocation Request message from the MME.

Table 6.2.2: Cause value mapping from S1AP Cause to RANAP Cause

36.413 [21]		25.413 [7]
HANDOVER REQUIRED (S1AP Cause)		RELOCATION REQUEST (RANAP Cause)
Radio Network Layer Cause	Handover Desirable for Radio Reasons	Radio Network Layer Cause	Relocation Desirable for Radio Reasons
Radio Network Layer Cause	Time Critical Handover	Radio Network Layer Cause	Time critical Relocation
Radio Network Layer Cause	Reduce Load in Serving Cell	Radio Network Layer Cause	Reduce Load in Serving Cell
Radio Network Layer Cause	CS Fallback Triggered	Radio Network Layer Cause	CS Fallback triggered
Any other value		Radio Network Layer Cause	Resource Optimized Relocation

6.3 Interworking between BSSGP protocol messages and S1AP protocol messages

This clause defines a mapping of BSSGP and S1AP cause values used in connection with inter RAT Handover to avoid different mappings in different implementations.

Inter RAT Handover from GERAN to LTE:

Table 6.3.1 defines a cause value mapping performed by the S4-SGSN when the S4-SGSN receives the GTPv2 Forward Relocation Response message from the MME.

NOTE1: The mapping in Table 6.3.1 has been derived based on Table 6.2.1 in this specification and Table 15.2 in 3GPP TS 29.060 [23].

Table 6.3.1: Cause value mapping from S1AP Cause to BSSGP Cause for failure case

36.413 [21]		48.018 [24]
HANDOVER FAILURE (S1AP Cause)		PS HANDOVER REQUIRED NACK (BSSGP Cause)
Group	Value	Value
Radio Network Layer Cause	No Radio Resources Available in Target Cell	Cell traffic congestion
Radio Network Layer Cause	Encryption and/or integrity protection algorithms not supported	Requested ciphering and/or integrity protection algorithms not supported
Miscellaneous Cause	O&M Intervention	O&M Intervention
Any other value		Relocation failure in target system

Inter RAT Handover from LTE to GERAN:

Table 6.3.2 defines a cause value mapping performed by the S4-SGSN when the S4-SGSN receives the GTPv2 Forward Relocation Request message from the MME.

NOTE2: The mapping in Table 6.3.2 has been derived based on Table 6.2.2 in this specification and Table 15.3 in 3GPP TS 29.060 [23].

Table 6.3.2: Cause value mapping from S1AP Cause to BSSGP Cause

36.413 [21]		48.018 [24]
HANDOVER REQUIRED (S1AP Cause)		PS HANDOVER REQUEST (BSSGP Cause)
Group	Value	Value
Radio Network Layer Cause	Handover Desirable for Radio Reasons	Better cell
Radio Network Layer Cause	Time Critical Handover	Time critical relocation
Radio Network Layer Cause	Reduce Load in Serving Cell	Cell traffic congestion
Any other value		Traffic

6.4 Interworking between BSSGP protocol messages and RANAP protocol messages

For the mapping of BSSGP and RANAP cause values used in connection with inter RAT Handover between GERAN and UTRAN, the mapping tables in clause 15 in 3GPP TS 29.060 [23] applies. The mapping is performed by the target S4-SGSN.