7 X.21 interface procedures to 04.08 mapping

07.033GPPTerminal Adaptation Functions (TAF) for services using synchronous bearer capabilitiesTS

7.1 X.21 procedures mapping

The X.21 procedures mapping is shown in figures 10 and 11. The Bearer Capability Elements required on Dm channel are shown in GSM 07.01 [8] Annex 2.

NOTE: DTE corresponds to TE2 and DCE corresponds to MT2 in the signal names of X.21 interface.

7.1.1 Mobile originated call (see figure 10)

Call Request of TE2 to Dm channel SET‑UP:

At R interface: In Ready state both TE2 and MT transmit (1,OFF). When the calling TE2 indicates Call Request (0,ON), the MT transmits Proceed to Select (+,OFF). Then the TE2 sends the Selection signals (IA5,ON) and End of Selection (+,ON) and enters the state DTE Waiting (1,ON). The MT shall transmit DCE Waiting (SYN,OFF).

At MS‑MSC interface: By receiving Call Request at R‑interface, the MT shall start mobile originated call establishment (CHANNEL REQUEST message etc.). When the MT has received Selection signals and End of Selection from TE2, it shall send SET‑UP, when possible.

CALL PROCEED:

After the traffic channel assignment is complete, the MT shall start sending (1,OFF) within the 40 bit frames (see sections 4.1.3 and 4.2.2) via the Bm (Lm) channel.

Dm channel ALERT to Call Progress to TE2:

This is applicable only to manually answered calls.

When the MT receives ALERT from Dm channel, it shall transmit Call Progress signals (IA5,OFF) to TE2 and then enter the state DCE Waiting (SYN,OFF).

Dm channel CONN to Ready For Data to TE2:

When the MT receives CONN from Dm channel, it shall respond with CONN ACK message and it may send DCE Provided Information to the calling TE2. The MT transmits then Connection in Progress (1,OFF) to TE2.

When the MT receives a frame with all data bits set to ONE, it performs the switch‑through of data and control lines to TE2.

7.1.2 Mobile terminated call (see figure 10)

Dm channel SET‑UP to Incoming Call to TE2:

When the TE2 is in Ready state and the MT receives SET‑UP via Dm channel, the MT shall respond with ALERT in case of manual answering. Via R interface the MT transmits Incoming Call (Bell,OFF) to TE2.

Call Accepted of TE2 to Dm channel CONN:

When the MT receives Call Accepted via R interface (1,ON), it shall send CONN message via Dm channel.

Dm channel CONN ACK to Ready For Data to TE2:

When the MT receives CONN ACK from Dm channel, it shall start sending (1,OFF) within the 40 bit frames via the Bm (Lm) channel. Via R interface the MT transmits Connection in Progress (1,OFF) to TE2 after delivering DCE Provided Information if any.

When the MT receives a frame with all data bits set to ONE, it performs the switch‑through of data and control lines to TE2.

7.1.3 Mobile termination clearing (see figure 11)

DTE Clear Request (0,OFF) is transmitted via Bm (Lm) channel to the cleared terminal. The MT at the clearing TE2 recognizes the Clear Request, transmits DCE Clear Confirmation (0,OFF) to TE2 and sends DISCONNECT message via Dm channel. When the radio channel is released, the MT shall transmit DCE Ready (1,OFF) and TE2 shall then enter the state DTE Ready (1,OFF).

7.1.4 Distant end terminal clearing

When the MT receives DCE Clear Request via Bm (Lm) channel, it shall transmit DCE Clear Indication (0,OFF) to its TE2 via R interface. After the MT has received DTE Clear Confirmation (0,OFF), it sends DISCONNECT message via Dm channel. When the radio channel is released, the MT shall transmit DCE Ready (1,OFF) and TE2 shall then enter the state DTE Ready (1,OFF).

7.1.5 Network generated clearing (see figure 11)

When the MT has received DISCONNECT message via Dm channel, it shall transmit DCE Clear Indication (0,OFF) to its TE2 via R interface. After the MT has received DTE Clear Confirmation (0,OFF) and the radio channel is released, the MT shall transmit DCE Ready (1,OFF) and TE2 shall then enter the state DTE Ready (1,OFF).

NOTE: In the signal names of X.21 interface DTE corresponds with TE2 and DCE corresponds with MT2.

Figure 10: Example of a calling and a called TE2 (X.21)

NOTE: In the signal names of X.21 interface DTE corresponds with TE2 and DCE corresponds with MT2.

Figure 11: Example of a clearing and a cleared TE2 (X.21)

7.2 Dm Signalling causes mapping to X.21 call progress signals

The mapping of PLMN Dm channel signalling to X.21 call progress signals and DCE Provided Information is shown in table 7.

7.3. X.21 FACILITIES MAPPING

The X.21 facilities are shown in table 8. The mapping of these to PLMN supplementary services is for FS.

Table 7: Mapping of Dm cause fields to X.21 call progress signals

Item Dm signalling cause Code X.21 call progress signal sign. Code

01 Unassigned (unallocated) number 01 Not obtainable 43
02 No route to destination 03 Not obtainable 43
03 Channel unacceptable 06 Not obtainable 43
04 Normal call clearing 16 ‑‑‑‑ 05 User busy 17 Number busy 21
06 No user responding 18 No connection 20
07 User alerting, no answer 19 No connection 20
08 Call rejected 21 Controlled not ready 45
09 Number changed 22 Changed number 42
10 Destination out of order 27 Uncontrolled not ready 46
11 Invalid number format (incomplete) 28 Selection sign. procedure error 22
12 Facility rejected 29 Invalid facility request 48
13 Response to status enquiry 30 ‑‑‑‑ 14 Normal, unspecified 31 ‑‑‑‑ 15 No circuit/channel available 34 No connection 20
16 Network out of order 38 Out of order 44
17 Temporary failure 41 Out of order 44
18 Switching equipment congestion 42 Network congestion 61
19 Access information discarded 43 ‑‑‑‑ 20 Requested circuit/channel not available 44 No connection 20
21 Resources unavailable, unspecified 47 Network congestion 61
22 Quality of service unavailable 49 ‑‑‑‑ 23 Requested facility not subscribed 50 Invalid facility request 48
24 Bearer capability not authorized 57 Incompat. user class of service 52
25 Bearer capability not presently available 58 Network congestion 61
26 Service or option not available, unspecified 63 No connection 20
27 Bearer service not implemented 65 Invalid facility request 48
28 Only restricted digital information 70 Invalid facility request 48
bearer capability is available 29 Service or option not implemented, 79 Invalid facility request 48
unspecified 30 Invalid call reference value 81 Not obtainable 43
31 Incompatible destination 88 Not obtainable 43
32 Invalid transit network selection 91 Not obtainable 43
33 Invalid message, unspecified 95 Selection signal transmis. error 23
34 Mandatory info. element error 96 Selection signal procedure error 22
35 Message type non‑existent or 97 Selection signal procedure error 22
not implemented 36 Message not compatible with call state or 98 Selection signal procedure error 22
message type non‑existent or not implemented 37 Information element non‑existent 99 Selection signal procedure error 22
or not implemented 38 Invalid info. element contents 100 Selection signal transm. error 23
39 Message not compatible with call state 101 Selection signal procedure error 22
40 Recovery on timer expiry 102 Not obtainable 43
41 Protocol error, unspecified 111 Selection signal procedure error 22
42 Interworking, unspecified 127 RPOA out of order 72

Table 8: X.21 facilities

Facility request code Facility

1 Closed user group 45 DTE inactive registration
45 DTE inactive cancellation
60 Multiple address calling 61 Charging information 62 Called line identification 63 Redirection of callactivation
63 Redirection of callcancellation
63 Redirection of callstatus
64 Reverse status 65 Direct call registration 65 Direct call cancellation 66 Abbreviated address registration
66 Abbreviated address cancellation