2.2. Services

The various features of the SDLI interface are defined in terms of the services provided by the SDL provider, and the individual primitives that may flow between the SDL user and the SDL provider.

The data link proivder interface supports only one mode of service: connection mode. The connection mode is circuit-oriented and enables data to be transfered over and established connection in a sequential manner. This specification also defines a set of local management functions that apply to this mode of service.

The services are tabulated below and described more fully in the remainder of this section.

Table 1. Cross-Reference of SDL Services and Primitives

Phase	Service	Primitives
Local Management	Information Reporting	LMI_INFO_REQ, LMI_INFO_ACK, LMI_ERROR_ACK
	Attach	LMI_ATTACH_REQ, LMI_DETACH_REQ, LMI_OK_ACK, LMI_ERROR_ACK
	Bind	LMI_BIND_REQ, LMI_BIND_ACK, LMI_SUBS_BIND_REQ, LMI_SUBS_BIND_ACK, LMI_UNBIND_REQ, LMI_OK_ACK, LMI_ERROR_ACK
Connection Establishment	Connection Establishment	SDL_CONNECT_REQ, SDL_CONNECT_IND, SDL_CONNECT_RES, SDL_CONNECT_CON, SDL_DISCONNECT_REQ, SDL_DISCONNECT_IND, SDL_OK_ACK, SDL_ERROR_ACK
Connection-mode Data Transfer	Data Transfer	SDL_DATA_REQ, SDL_DATA_IND
	Reset	SDL_RESET_REQ, SDL_RESET_IND, SDL_RESET_RES, SDL_RESET_CON, SDL_OK_ACK, SDL_ERROR_ACK
Connection Release	Connection Release	SDL_DISCONNECT_REQ, SDL_DISCONNECT_IND, SDL_OK_ACK, SDL_ERROR_ACK
Connectionless-mode Data Transfer	Data Transfer	SDL_UNITDATA_REQ, SDL_UNITDATA_IND
	Error Reporting	SDL_UDERROR_IND

Mapping of SDLI primitives onto CDI primitives:

Table 2. Mapping of SDLI to CDI primitives

SDL_INFO_REQ	CD_INFO_REQ
SDL_INFO_ACK	CD_INFO_ACK
SDL_ATTACH_REQ	CD_ATTACH_REQ
SDL_DETACH_REQ	CD_DETACH_REQ
SDL_ENABLE_REQ	CD_ENABLE_REQ
SDL_DISABLE_REQ	CD_DISABLE_REQ
SDL_OK_ACK	CD_OK_ACK
SDL_ERROR_ACK	CD_ERROR_ACK
SDL_ENABLE_CON	CD_ENABLE_CON
SDL_DISABLE_CON	CD_DISABEL_CON
SDL_ERROR_IND	CD_ERROR_IND

SDL_ALLOW_INPUT_REQ	CD_ALLOW_INPUT_REQ
SDL_READ_REQ	CD_READ_REQ
SDL_UNITDATA_REQ	CD_UNITDATA_REQ
SDL_WRITE_READ_REQ	CD_WRITE_READ_REQ
SDL_UNITDATA_ACK	CD_UNITDATA_ACK
SDL_UNITDATA_IND	CD_UNITDATA_IND
SDL_HALT_INTPUT_REQ	CD_HALT_INPUT_REQ
SDL_ABORT_OUTPUT_REQ	CD_ABORT_OUTPUT_REQ
SDL_MUX_NAME_REQ	CD_MUX_NAME_REQ
SDL_BAD_FRAME_IND	CD_BAD_FRAME_IND
SDL_MODEM_SIG_REQ	CD_MODEM_SIG_REQ
SDL_MODEM_SIG_IND	CD_MODEM_SIG_IND
SDL_MODEM_SIG_POLL	CD_MODEM_SIG_POLL

2.2.1. Local Management Services

The local management services apply to all modes of transmission. These services, which fall outside the scope of standards specifications, define the method for initializing a stream that is connected to an SDL provider. SDL provider information reporting services are also supported by the local management facilities.

2.2.1.1. Information Reporting Service

This service provides information about the SDLI stream to the SDL user. The message LMI_INFO_REQ requests the SDL provider to return operating information about the stream. The SDL provider returns the information in a LMI_INFO_ACK message.

Figure 12. SDLI Message Flow: Information Reporting

2.2.1.2. Attach Service

The attach service assigns a physical point of attachment (PPA) to a stream. This service is required for style 2 SDL providers (see section 2.1.3.1, Physical Attachment Identification) to specify the physical medium over which communication will occur. The SDL provider indicates success with a LMI_OK_ACK; failure with a LMI_ERROR_ACK. The normal message sequence is illustrated in Figure 13.

Figure 13. SDLI Message Flow: Attaching a Stream to a Physical Line

A PPA may be disassociated with a stream using the LMI_DETACH_REQ. The normal message sequence is illustrated in Figure 14.

Figure 14. SDLI Message Flow: Detaching a Stream from a Physical Line

2.2.1.3. Enable Service

The enable service activates the interface for data transfer. The SDL provider indicates success wiht a LMI_OK_ACK; failure with a LMI_ERROR_ACK. The normal message sequence is illustrated in Figure 15.

Figure 15. SDLI Message Flow: Attaching a Stream to a Physical Line

The interface can be deactivated using the LMI_DISABLE_REQ. The normal message sequence is illustrated in Figure 16.

Figure 16. SDLI Message Flow: Detaching a Stream from a Physical Line

2.2.2. Connection Services

The connection service enables a SDL user to establish a signalling data link connection, transfer data over that connection and release the connection when the conversation has terminated.

2.2.2.1. Connection Establishment Service

The connection establishment service establishes a signalling data link connection between a local SDL user and the physical medium associated with the SDL provider.

Data Transfer Service