10.2 Modem compatibility commands

27.0073GPPAT command set for User Equipment (UE)Release 18TS

Tools: ARFCN - Frequency Conversion for 5G NR/LTE/UMTS/GSM

10.2.0 General

This clause describes how existing AT commands, designed for use with a modem, may be used to control a Packet Domain MT. This is to provide backwards compatibility with existing communications software. For new applications it is recommended that the Packet Domain-specific commands, described in previous clauses, be used.

10.2.1 MT originated PDP context activation

10.2.1.0 General

In this mode of operation, the MT behaves like an originating modem and accepts the normal V.250 commands associated with placing and clearing a call. If Packet Domain-specific configuration commands are required, they may be sent to the MT as part of the modem initialization commands.

10.2.1.1 Request packet domain service ‘D’

Table 130: D command syntax

Command

Possible Response(s)

D*<GPRS_SC>[*[<called_address>][*[<L2P>][*[<cid>[,<cid>[,…]]]]]]#

CONNECT

ERROR

Description

This command causes the MT to perform whatever actions are necessary to establish communication between the TE and the external PDN.

The V.250 ‘D’ (Dial) command causes the MT to enter the V.250 online data state and, with the TE, to start the specified layer 2 protocol. The MT shall return CONNECT to confirm acceptance of the command prior to entering the V.250 online data state. No further commands may follow on the AT command line.

The detailed behaviour after the online data state has been entered is dependent on the PDP type. It is described briefly in clause 9 (for IP) of 3GPP TS 27.060 [34]. PS attachment and PDP context activation procedures may take place prior to or during the PDP startup if they have not already been performed using the +CGATT and +CGACT commands.

When the layer 2 protocol has terminated, either as a result of an orderly shut down of the PDP or an error, the MT shall enter V.250 command state and return the NO CARRIER final result code.

If <called address> is supported and provided, the MT shall automatically set up a virtual call to the specified address after the PDP context has been activated.

If <L2P> and <cid> are supported, their usage shall be the same as in the +CGDATA command. The +CGDCONT, +CGQREQ, etc. commands may be used in the modem initialization AT command string to set values for for PDP type, APN, QoS etc..

If <L2P> is not supported or is supported but omitted, the MT shall use a layer 2 protocol appropriate to the PDP type.

If <cid> is not supported or is supported but omitted, the MT shall attempt to activate the context using:

(a) any information provided by the TE during the PDP startup procedure, e.g. the TE may provide a PDP type and/or PDP address to the MT;

(b) a priori knowledge, e.g. the MT may implement only one PDP type; or

(c) using the ‘Empty PDP type’ (3GPP TS 24.008 [8]). (No PDP address or APN shall be sent in this case and only one PDP context subscription record shall be present in the HLR for this subscriber.)

This command may be used in both normal and modem compatibility modes.

NOTE: The dial string conforms to the syntax specified in 3GPP TS 22.030 [19].

Defined values

<GPRS_SC>: (GPRS Service Code) a string of digits (value 99) which identifies a request to use the Packet Domain service.

<called_address>: a string that identifies the called party in the address space applicable to the PDP. For communications software that does not support arbitrary characters in the dial string, a numeric equivalent may be used. Also, the character comma ‘,’ may be used as a substitute for the character period ‘.’.

<L2P>: a string which indicates the layer 2 protocol to be used (see +CGDATA command). For communications software that does not support arbitrary characters in the dial string, the following numeric equivalents shall be used:

0 NULL (Obsolete)

1 PPP

2 PAD (Obsolete)

3 X25 (Obsolete)

9yyyy M-xxxx

Other values are reserved and will result in an ERROR response

<cid>: a string of digits which specifies a particular PDP context definition (see the +CGDCONT and +CGDSCONT commands).

Implementation

Optional if the +CGDATA command is supported. If the D command is provided, then support for <called_address>, <L2P> and <cid> are optional. If they are not supported but values are provided by the TE, the values shall be ignored and this shall not constitute an error.

10.2.1.2 Request packet domain IP service ‘D’

Table 131: D command syntax

Command

Possible Response(s)

D*<GPRS_SC_IP>[*<cid>[,<cid>[,…]]]#

CONNECT

ERROR

Description

This command causes the MT to perform whatever actions are necessary to establish communication between the TE and the external PDN.

The detailed behaviour after the online data state has been entered is described briefly in clause 9, for IP, of 3GPP TS 27.060 [34]. GPRS attachment and PDP context activation procedures may take place prior to or during the PDP startup if they have not already been performed using the +CGATT and +CGACT commands.

When the layer 2 protocol has terminated, either as a result of an orderly shut down of the PDP or an error, the MT shall enter V.250 command state and return the NO CARRIER final result code.

If <cid> is supported, its usage shall be the same as in the +CGDATA command. The +CGDCONT, +CGQREQ, etc. commands may be used in the modem initialization AT command string to set values for for PDP type, APN, QoS etc.

If <cid> is not supported or is supported but omitted, the MT shall attempt to activate the context using:

(a) any information provided by the TE during the PDP startup procedure, e.g. the TE may provide a PDP type and/or PDP address to the MT;

(b) a priori knowledge, e.g. the MT may implement only one PDP type; or

This command may be used in both normal and modem compatibility modes.

NOTE. The dial string conforms to the syntax specified in 3GPP TS 22.030 [19].

Defined values

<GPRS_SC_IP>: (GPRS Service Code for IP) a string of digits (value 98) which identifies a request to use the GPRS with IP (PDP types IP and PPP).

<cid>: a string of digits which specifies a particular PDP context definition (see +CGDCONT command).

Implementation

Optional if the +CGDATA command is supported. If the D command is provided, then support for <cid> is optional. If it is not supported but a value is provided by the TE, the value shall be ignored and this shall not constitute an error.

10.2.2 Network requested PDP context activation

10.2.2.0 General

In this mode of operation, the MT behaves like an answering modem and accepts the normal V.250 commands associated with answering a call. If Packet Domain-specific configuration commands are required, they may be sent to the MT as part of the modem initialization commands.

The +CGAUTO command is used to select modem compatibility mode.

10.2.2.1 Automatic response to a network request for PDP context activation ‘S0’

The V.250 ‘S0=n’ (Automatic answer) command may be used to turn off (n=0) and on (n>0) the automatic response to a network request for a PDP context activation.

When the ‘S0=n’ (n>0) command is received, the MT shall attempt to perform a PS attach if it is not already attached. Failure will result in ERROR being returned to the TE. Subsequently, the MT will announce a network request for PDP context activation by issuing the unsolicited result code RING to the TE, followed by the intermediate result code CONNECT. The MT then enters V.250 online data state and follows the same procedure as it would after having received a +CGANS=1 with no <L2P> or <cid> values specified.

NOTE: The ‘S0=n’ (n=0) command does not perform an automatic PS detach.

Implementation

Optional.

10.2.2.2 Manual acceptance of a network request for PDP context activation ‘A’

The V.250 ‘A’ (Answer) command may be used to accept a network request for a PDP context activation announced by the unsolicited result code RING. The MT responds with CONNECT, enters V.250 online data state and follows the same procedure as it would after having received a +CGANS=1 with no <L2P> or <cid> values specified. It is an error to issue the ‘A’ command when there is no outstanding network request.

Implementation

Optional.

10.2.2.3 Manual rejection of a network request for PDP context activation ‘H’

The V.250 ‘H’ or ‘H0’ (On-hook) command may be used to reject a network request for PDP context activation announced by the unsolicited result code RING. The MT responds with OK. It is an error to issue the ‘H’ command when there is no outstanding network request.

NOTE: This is an extension to the usage of the ‘H’ command that is described in ITU-T Recommendation V.250 [14].

Implementation

Optional.