7A S121 Messages and Message Formats

29.2763GPP3GPP Evolved Packet System (EPS)Optimized handover procedures and protocols between E-UTRAN access and cdma2000 HRPD AccessRelease 17Stage 3TS

7A.1 Introduction

This section is divided into path management which defines the general messages for the pre-configured tunnel and a section for the specific messages used for information transfer over the control plane.

Table 7A.1 specifies GTPv2-C message types that are used across the S121 interface.

Table 7A.1: Message types for S121

Message Type value (Decimal)	Message	Reference
0	Reserved	3GPP TS 29.274 [6]
1	Echo Request	3GPP TS 29.274 [6]
2	Echo Response	3GPP TS 29.274 [6]
3	Version Not Supported Indication	3GPP TS 29.274 [6]
4-16	Reserved for S101 interface	7
17	RIM Information Transfer	7A.3.1
18-24	For future S121 interface use
25 to 31	Reserved for Sv interface	3GPP TS 29.280 [14]
32-239	Reserved for GTPv2-C spec	3GPP TS 29.274 [6]
240-247	Reserved for Sv interface	3GPP TS 29.280 [14]
248-255	Reserved for GTPv2-C spec	3GPP TS 29.274 [6]

7A.2 Path Management Messages

7A.2.1 Introduction

The path from the MME to the non-3GPP Access Network operationally requires management capabilities. The following GTPv2-C messages support path management for the S121 interface:

– Echo Request

– Echo Response

– Version Not Supported Indication

These messages are defined for GTPv2-C and the handling and definition shall also be as defined in GTPv2-C, see 3GPP TS 29.274 [6].

7A.2.2 Echo Request message

An MME or an HRPD access node may send an Echo Request to find out if the peer HRPD access node or MME is alive (see subclause 9.2). When and how often an Echo Request message may be sent is implementation specific but an Echo Request shall not be sent more often than every 60 s on each path.

An MME or an HRPD access node shall be prepared to receive an Echo Request at any time and it shall reply with an Echo Response. The optional Private Extension contains vendor or operator specific information.

3GPP TS 29.274 [6] specifies the information elements included in the Echo Request message.

7A.2.3 Echo Response message

The message shall be sent as a response to a received Echo Request.

3GPP TS 29.274 [6] specifies the information elements included in the Echo Response message.

The Recovery information element contains the local Restart Counter (see subclause 9.3) value for the node that sends the Echo Response message.

In this release of the specification, the MME and HRPD access node do not need to determine whether the peer node has restarted or not, i.e. they may ignore the Recovery information element.

The optional Private Extension contains vendor or operator specific information.

7A.2.4 Version Not Supported Indication message

This message contains only the S121 header and indicates the latest S121 version that the MME or HRPD access node entity on the identified UDP/IP address can support (see 3GPP TS 29.274 [6] subclause 7.1.3).

3GPP TS 29.274 [6] specifies the detailed handling and information elements included in the Version Not Supported Indication message.

7A.3 S121 Messages

7A.3.1 Introduction

The following message is used to support RIM information exchange between the MME and the HRPD Access Network:

– RIM Information Transfer

7A.3.2 RIM Information Transfer

The RIM Information Transfer message shall be sent on the S121 interface between MME and the HRPD Access Network to transfer RIM information between an eNodeB and the HRPD Access Network (see 3GPP TS 23.402 [2]).

For handling of protocol errors the RIM Information Transfer message is treated as a Response message.

Table 7A.3.2-1 specifies the information elements included in the RIM Information Transfer message.

Table 7A.3.2-1: Information Elements in a RIM Information Transfer

Information elements	Presence Requirement	Reference	Instance
S121 Transparent Container	Mandatory	7A.5.2	0
RIM Routing Address	Mandatory	7A.5.3	0
Private Extension	Optional	7A.5.4	VS

The S121 Transparent Container information element shall contain encapsulated RIM Information exchanged between the MME and the HRPD Access Network, i.e. all information elements from the BSSGP RIM PDU, starting from and including the BSSGP "PDU type" (see 3GPP TS 48.018 [15]).

The RIM Routing Address IE shall identify the destination RAN node where the RIM information needs to be sent to. It shall contain:

– an eNodeB ID when the message is sent from the HRPD Access Network to the MME;

– an HRPD Sector ID when the message is sent from the MME to the HRPD Access Network.

7A.4 Reliable Delivery of Signalling Messages

For the S121 interface protocol, the reliable delivery of signalling messages shall have the same handling as GTPv2-C. See 3GPP TS 29.274 [6] but with S121 node replacing GTPv2-C node as appropriate.

NOTE: In this release of the specification, the MME and HRPD access node do not need to and can not determine whether the peer node has received the RIM Information Transfer message.

7A.5 Information Elements

7A.5.1 Information Element Assignments

An S121 message may contain several information elements. The TLIV (Type, Length, Instance, Value) encoding format shall be used for all S121 information elements. See TS 29.274 [6] subclause 8.2 for the general encoding of the IEs.

Within information elements, certain fields may be described as spare. These bits shall be transmitted with the value defined for them. To allow for future features, the receiver shall not evaluate these bits.

Table 7A.5-1: Information Elements

IE Type Value	Information Element	Comment / Reference	Number of Fixed Octets
0	Reserved	3GPP TS 29.274 [3]	3GPP TS 29.274 [3]
1-3	Reserved for GTPv2-C.	3GPP TS 29.274 [3]	3GPP TS 29.274 [3]
4-34	Reserved for S101 interface
35	S121 Transparent Container	Variable Length / 7A.5.2	Not Applicaple
36	RIM Routing Address	Variable Length / 7A.5.3	Not Applicaple
37-50	For future use for the S121 interface.
51-70	Reserved for Sv interface.	3GPP TS 29.280 [14]	3GPP TS 29.280 [14]
71-254	Reserved for GTPv2-C.	3GPP TS 29.274 [6]	3GPP TS 29.274 [6]
255	Private Extension	7A.5.4	3GPP TS 29.274 [6]

7A.5.2 S121 Transparent Container

The S121 Transparent Container information element shall contain encapsulated RIM information, i.e. a transparent copy of the BSSGP RIM PDU as specified in 3GPP TS 48.018 [15].

It is variable in length and shall always be an integral number of octets. The highest numbered octet shall be filled, if necessary, with extra bits set to ‘0’ in the low order bit positions to create an integral number of octets.

Table 7A.5.2-1: S121 Transparent Container IE

		Bits
	Octets	8	7	6	5	4	3	2	1
	1	Type = 35
	2 to 3	Length = n
	4	Spare				Instance
	5 to (n+4)	S121 Transparent Container

7A.5.3 RIM Routing Address

The RIM Routing Address IE shall identify the destination RAN node to which the RIM Information needs to be sent to.

The RIM Routing Address information element is coded as depicted in Table 7A.5.3-1

Table 7A.5.3-1: RIM Routing Address IE

		Bits
	Octets	8	7	6	5	4	3	2	1
	1	Type = 36
	2 to 3	Length = n
	4	Spare				Instance
	5	Routing Address Type
	6 to (n+4)	Routing Address

Routing Address Type values are specified in Table 7A.5.3-2.

Table 7A.5.3-2: Routing Address Type values

Target Types	Values (Decimal)
Macro eNodeB ID	0
Home eNodeB ID	1
HRPD Sector Identifier	2
<spare>	3 to 255

The Routing Address Type is either a Macro eNodeB ID or a Home eNodeB ID for RIM Information Transfer towards E-UTRAN. In this case the Routing Address field includes Macro or Home eNodeB ID as defined in Figure 8.51-2 and 8.51-3 of 3GPP TS 29.274 [6].

The Routing Address Type is HRPD Sector Identifier for RIM Information Transfer towards HRPD Access Network. In this case the Routing Address field includes HRPD Sector Identifier which is defined in 3GPP2 C.S0024-B [7] section 13.9.

7A.5.4 Private Extension

The Private Extension information element shall contain vendor specific information. Refer to 3GPP TS 29.274 [6] for the encoding of this Information Element.