E/Nc interface protocol

Description of the E/Nc Interface Protocol

• Scenario Description
• Protocol Stack
• Message List

Scenario Description

The MSC interworks with another MSC. In this networking, the MSC communicates with another MSC through MAP. Figure 1 shows the application of the E/Nc interface protocol.

Figure 1 Application of the E/Nc interface protocol 

Protocol Stack

Figure 2 through Figure 4 show the protocol stack of the E/Nc interface.

Figure 2 Protocol stack of the E/Nc interface (non-peer-to-peer M3UA networking)

Figure 3 Protocol stack of the E/Nc interface (peer-to-peer M3UA networking) 

Figure 4 Protocol stack of the E/Nc interface (M2UA networking)

The MAP messages are encoded in the ASN.1 format and encapsulated in the user data of TCAP messages. Figure 5 shows the message structure.

Figure 5 MAP message structure 

Message List

Table 1 List of common E/Nc interface messages
Message	Direction	Function
MAP_PREPARE_HANDOVER_REQ	MSC-A->MSC-B	This message is sent to hand over a call from the source MSC (MSC-A) to the target MSC (MSC-B).
MAP_PREPARE_HANDOVER_RSP	MSC-B->MSC-A	This message is sent by MSC-B to MSC A to acknowledge the MAP_PREPARE_HANDOVER_REQ message.
MAP_PROCESS_ACCESS_SIGNALLING	MSC-B->MSC-A	This message is sent by MSC-B to transparently transmit the received Relocation Detect IE (in the case of 2G network) to MSC-A, indicating that the MS has detected a new channel.
MAP_SEND_END_SIGNAL_REQ	MSC-A->MSC-B	This message is sent by MSC-A to transparently transmit the received Relocation Complete IE (in the case of 2G network) to MSC-B, indicating that the inter-MSC handover is complete.
MAP_SEND_END_SIGNAL_RSP	MSC-B->MSC-A	This message is sent by MSC-B to release inter-MSC MAP resources and release the call.
MAP_PREPARE_SUBSEQUENT_HANDOVER_REQ	MSC-B->MSC-A	This message is sent by MSC-B to inform MSC-A that a handover or relocation to either MSC-A or a third MSC is required.
MAP_PREPARE_SUBSEQUENT_HANDOVER_RSP	MSC-A->MSC-B	This message is sent by MSC-A to acknowledge the MAP_PREPARE_SUBSEQUENT_HANDOVER_REQ message and inform MSC-B of the information about subsequent handback and resource allocation.

Description of the Common Part of Messages

• Reference Standards

Table 1 IEs carried in the common part of messages
IE	Description
Dialogue ID	Identifies a MAP dialogue. The MAP_PREPARE_HANDOVER_REQ message is considered as an example here. In this example, ie-dialogue-id is 0x40a.
Operation code	Identifies the functions of messages. It corresponds to the operation code in the TCAP component. The MAP_PREPARE_HANDOVER_REQ message is considered as an example here. In this example, ie-map-operation-code is prepare-handover.

Reference Standards

For details, see 3GPP TS29002-870.