C:\WINWORD\CCITTREC.DOT ANNEX A (to Recommendation X.25) Range of logical channels used for virtual calls and permanent virtual circuits In the case of a single logical channel DTE, logical channel 1 will be used. For each multiple logical channel DTE/DCE interface, a range of log- ical channels will be agreed upon with the Administration according to Figure A–1/X.25. Figure A–1/X.25 - CCITT 34901 ANNEX B (to Recommendation X.25) Packet layer DTE/DCE interface state diagrams B.1 Symbol definition of the state diagrams Figure CCITT 19172 B.2 Order definition of the state diagrams For the sake of clarity, the normal procedure at the interface is described in a number of small state diagrams. In order to describe the nor- mal procedure fully, it is necessary to allocate a priority to the different fig- ures and to relate a higher order diagram with a lower one. This has been done by the following means: – The figures are arranged in order of priority with Figure B–1/X.25 (restart) having the highest priority and subsequent figures having lower priority. Priority means that when a packet belonging to a higher order diagram is transferred, that diagram is applicable and the lower order one is not. – The relation with a state in a lower order diagram is given by includ- ing that state inside an ellipse in the higher order diagram. FIGURE B–1/X.25 - CCITT 34910 FIGURE B–2/X.25 - CCITT 18551 FIGURE B–3/X.25 - CCITT 18561 ANNEX C (to Recommendation X.25) Actions taken by the DCE on receipt of packets in a given state of the packet layer DTE/DCE interface as perceived by the DCE Introduction This annex specifies the actions taken by the DCE on receipt of pack- ets in a given state of the packet layer DTE/DCE interface as per- ceived by the DCE. It is presented as a succession of chained tables. The following rules are valid for all these tables: 1) there may be more than one error associated with a packet. The net- work will stop normal processing of a packet when an error is encountered. Thus only one diagnostic code is associated with an error indication by the DCE. The order of packet decoding and checking on networks is not standardized; 2) for those networks which are octet aligned, the detection of a non– integral number of octets may be made at the data link or packet layer. In this annex, only those networks which are octet aligned and detect the non–integral number of octets at the packet layer are concerned with the considerations about octet alignment; 3) in each table, the actions taken by the DCE are indicated in the fol- lowing way: – DISCARD: the DCE discards the received packet and takes no subsequent action as a direct result of receiving that packet; the DCE remains in the same state; – DIAG ## x: the DCE discards the received packet and, for net- works which implement the diagnostic packet, transmits to the DTE a diagnostic packet containing the diagnostic ## x. The state of the interface is not changed; – NORMAL or ERROR: the corresponding action is specified after each table. 4) Annex E gives a list of the diagnostic codes which may be used. TABLE C–1/X.25 Special cases Packet from DTE Any state Any packet with packet length shorter than 2 octets, including data link layer valid I–frame containing no packet DIAG ## 38 Any packet with invalid general format identifier (GFI) DIAG ## 40 Any packet with unassigned logical channel DIAG ## 36 Any packet with correct GFI and assigned logical channel, or with correct GFI and bits 1 to 4 of octet 1 and bits 1 to 8 of octet 2 equal to 0 (see Table C–2/X.25) TABLE C–2/X.25 Action taken by the DCE on receipt of packets in a given state of the packet layer DTE/DCE interface as perceived by the DCE: restart and registration procedure State of the interface as perceived by the DCE Packet from the DTE Packet layer ready r1 DTE restart request r2 DCE restart indication r3 Restart request with bits 1 to 4 of octet 1 and bits 1 to 8 of octet 2 equal to zero NOR- MAL (r2) DIS- CARD NOR- MAL (r1) DTE restart confirmation with bits 1 to 4 of octet 1 and bits 1 to 8 of octet 2 equal to zero ERROR (r3) ## 17 ERROR (r3) ## 18 NOR- MAL (r1) Registration request (when sup- ported by the DCE) with bits 1 to 4 of octet 1 and bits 1 to 8 of octet 2 equal to zero NOR- MAL (r1) NOR- MAL (r2) NOR- MAL (r3) Packet supported by the DCE other than restart request, DTE restart confirmation and registration request (when supported by the DCE) with bits 1 to 4 of octet 1 and bits 1 to 8 of octet 2 equal to zero DIAG ## 36 DIAG ## 36 DIAG ## 36 Packet having a packet type identi- fier which is shorter than 1 octet, with bits 1 to 4 of octet 1 and bits 1 to 8 of octet 2 equal to zero DIAG ## 38 ERROR (r3) ## 38 DIS- CARD Packet having a packet type identi- fier which is undefined or not sup- ported by the DCE (i.e., reject or registration packets), with bits 1 to 4 of octet 1 and bits 1 to 8 of octet 2 equal to zero DIAG ## 33 ERROR (r3) ## 33 DIS- CARD Data, interrupt, call set–up and clearing, flow control or reset, with assigned logical channel See Table C–3/X.25 or C–4/X.25 (see Note) ERROR (r3) ## 18 DIS- CARD Restart request, DTE restart confir- mation or registration request (when supported by the network) with bits 1 to 4 of octet 1 or bits 1 to 8 of octet 2 unequal to zero See Table C–3/X.25 or C–4/X.25 (see Note) ERROR (r3) ## 41 DIS- CARD Packet having a packet type identi- fier which is shorter than 1 octet, with assigned logical channel See Table C–3/X.25 or C–4/X.25 (see Note) ERROR (r3) DIS- CARD ## 38 Packet having a packet type identi- fier which is undefined or not sup- ported by the DCE (i.e., reject or registration packets), with assigned logical channel See Table C–3/X.25 or C–4/X.25 (see Note) ERROR (r3) ## 33 DIS- CARD Note – Table C–3/X.25 for logical channels assigned to virtual calls, Table C–4/X.25 for logical channels assigned to permanent virtual circuits. ERROR (r3): ## x The DCE discards the received packet, indicates a restarting by transmitting to the DTE a restart indication packet, with the cause “Local procedure error” and the diagnostic ## x, and enters stater3. If connected through a virtual call, the dis- tant DTE is also informed of the restarting by a clear indication packet, with the cause “Remote procedure error” (same diag- nostic). In the case of a permanent virtual circuit, the distant DTE will be informed by a reset indication packet, with the cause “Remote procedure error” (same diagnostic). NORMAL (ri): Provided none of the following error conditions has occurred, the action taken by the DCE follows the procedure as defined in §§ 3 and 6.1 and DTE/DCE interface enters state ri: a) If a restart request packet or DTE restart confirmation packet received in state r3, or a registration request packet received in state r2 or r3, exceeds the maximum permitted length, is too short or is not octet aligned (see rule 2 in the introduction of this annex), the DCE will invoke the ERROR ## 39, ## 38 or ## 82 procedure, respectively. Note – In the case of a registration request packet received in state r2 or r3 with the error(s) as noted above, alternative behavior by the DCE is for further study. Some networks may invoke the ERROR ## 81 procedure if the restarting cause field is not “DTE originated” in the restart request packet received in state r3. b) If a restart request or a registration request packet received in state r1 exceeds the maximum permitted length, is too short or is not octet aligned (see rule 2 in the introduction of this annex), the DCE shall invoke the DIAG ## 39, ## 38 or ## 82 procedure, respectively. Some networks may invoke the DIAG ## 81 procedure if the restarting cause field is not “DTE originated” in the restart request packet received in state r1. c) If a registration request packet is received from the DTE when the on–line facility registration facility is supported by the DCE but not subscribed by the DTE, the DCE shall transmit to the DTE a registration confirmation packet with the cause “Local procedure error”, the diagnostic ## 42, and no registration field. If a registration request packet modify- ing one or more of the facilities which can take effect only when all logical channels used for virtual calls are in state p1 (see Annex F), is received when it is possible to make the modification, the DCE shall transmit a restart indication packet with the cause “Registration/cancellation confirmed” and diagnostic ## 0 and enter state r3, if there is one or more logical channels assigned to permanent virtual circuits. This action ensures that the permanent virtual circuits are reset so that all of the negotiated facilities can properly take effect. TABLE C–3/X.25 Action taken by the DCE on receipt of packets in a given state of the packet layer DTE/DCE interface as perceived by the DCE: call set–up and clearing on logical channel assigned to virtual call (see Note 1) State of the inter- face as perceived by the DCE Packet layer ready r1 Read y DTE waitin g DCE waitin g Data transf er Call colli- sion DTE clear reque st DCE clear indi- cation Packet from the DTE with logical channel assigned to virtual call p1 p2 (see Note 3) p3 (see Note 2) p4 p5 (see Notes 2 and 3) p6 p7 Call request NOR MAL (p2) ERR OR (p7) ## 21 NOR MAL (p5) ERR OR (p7) ## 23 ERR OR (p7) ## 24 ERR OR (p7) ## 25 DISC ARD Call accepted ERR OR (p7) ## 20 ERR OR (p7) ## 21 NOR MAL (p4) ERR OR (p7) ## 23 ERR OR (p7) ## 24 ERR OR (p7) ## 25 DISC ARD Call request NOR MAL (p6) NOR MAL (p6) NOR MAL (p6) NOR MAL (p6) NOR MAL (p6) DISC ARD NOR MAL (p1) DTE clear confir- mation ERR OR (p7) ## 20 ERR OR (p7) ## 21 ERR OR (p7) ## 22 ERR OR (p7) ## 23 ERR OR (p7) ## 24 ERR OR (p7) ## 25 NOR MAL (p1) Data, interrupt, reset or flow con- trol ERR OR (p7) ## 20 ERR OR (p7) ## 21 ERR OR (p7) ## 22 See Table C–4/ X.25 ERR OR (p7) ## 24 ERR OR (p7) ## 25 DISC ARD Restart request, DTE restart con- firmation or regis- tration request with bits 1 to 4 of octet 1 or bits 1 to 8 of octet 2 unequal to zero ERR OR (p7) ## 41 ERR OR (p7) ## 41 ERR OR (p7) ## 41 See Table C–4/ X.25 ERR OR (p7) ## 41 ERR OR (p7) ## 41 DISC ARD Packets having a packet type iden- tifier which is shorter than one octet ERR OR (p7) ## 38 ERR OR (p7) ## 38 ERR OR (p7) ## 38 See Table C–4/ X.25 ERR OR (p7) ## 38 ERR OR (p7) ## 38 DISC ARD Packet having a packet type iden- tifier which is undefined or not supported by the DCE (i.e., reject or registration packet) ERR OR (p7) ## 33 ERR OR (p7) ## 33 ERR OR (p7) ## 33 See Table C–4/ X.25 ERR OR (p7) ## 33 ERR OR (p7) ## 33 DISC ARD Note 1 – On permanent virtual circuit, only state p4 exists and the DCE takes no action except those specified in Table C–4/X.25. Note 2 – This state does nos exist in the case of an outgoing one–way logi- cal channel (as perceived by the DTE). Note 3 – This state does not exist in the case of an incoming one–way logi- cal channel (as perceived by the DTE). ERROR (p7): ## x The DCE discards the received packet, indicates a clear- ing by transmitting to the DTE a clear indication packet, with the cause “Local procedure error” and the diagnostic ## x, and enters state p7. If connected through a virtual call, the distant DTE is also informed of the clearing by a clear indication packet, with the cause “Remote procedure error” (same diag- nostic). NORMAL (pi): Provide none of the following error conditions has occurred, the action taken by the DCE follows the procedures as defined in § 4 and the DTE/DCE interface enters state pi. In all the cases specified hereunder, the DCE will transmit to the DTE a clear indication with the appropriate cause and diagnostic, and enter state p7. If connected through a virtual call, the distant DTE is also informed of the clearing by a clear indication packet with the cause “Remote procedure error” (same diagnos- tic). a) Call request packet Error condition Cause Specific diag- nostics (see Note 3 of Annex E) 1. Packet not octet aligned (see rule 2 in the introduction of this annex) Local proce- dure error ## 82 2. Packet too short Local proce- dure error ## 38 3. Incoming one–way logical channel (as perceived by the DTE) Local proce- dure error ## 34 4. Address length larger than remainder of packet Local proce- dure error ## 38 5. Address contains a non– BCD digit Local proce- dure error ## 67, ## 68 6. Invalid calling DTE address (see Note) Local proce- dure error ## 68 7. Invalid called DTE address (see Note) Local proce- dure error or not obtainable ## 67 Note – Possible reasons for invalid address are: – Prefix digit not supported; – Invalid type of address/numbering plan identification informations (A bit set to 1); – National address smaller than permitted by the national address for- mat; – National address larger than permitted by the national address for- mat; – DNIC less than four digits, etc. Error condition Cause Specific diag- nostics (see Note 3 of Annex E) 8. Value of the facility length field geater than 109 Local proce- dure error ## 69 9. No combination of facilities could equal facility length Local proce- dure error ## 69 1 0. Facility length larger than remainder of packet Local proce- dure error ## 38 1 1. Facility code not allowed Invalid facility request ## 65 1 2. Facility value not allowed or invalid Invalid facility request ## 66 1 3. Class coding of the facility corresponding to a length of parameter larger than remainder of packet Local proce- dure error ## 69 1 4. Facility code repeated Local proce- dure error ## 73 1 5. Invalid network user identi- fier Invalid facility request ## 84 1 6. NUI selection facility expected by the DCE and not provided by the DTE Local proce- dure error ## 84 1 7. Invalid/unsupported NUI value or missing NUI detected at inter–network interface Access barred ## 84 1 8. RPOA selection required RPOA out of order ## 76 1 9. Facility values conflicts (e.g., a particular combination not supported) Invalid facility request ## 66 2 0. CCITT–specified DTE facil- ity code or parameter not allowed or invalid Invalid facility request ## 77 2 1. Call user data larger than 16, or 128 in case of fast select facility Local proce- dure error ## 39 If the virtual call cannot be established by the network, the DCE should use a call progress signal and diagnostic code among the following: Error condition Cause Specific diag- nostics (see Note 3 of Annex E) 2 2. Requested RPOA out of order RPOA out of order ## 0 2 3. Requested RPOA invalid or not supported RPOA out of order ## 119 2 4. Unknown number Not obtainable ## 67 2 5. Incoming call barred Access barred ## 70 2 6. Closed user group protection Access barred ## 65 2 7. Ship absent Ship absent ## 0 2 8. Reverse charging rejected Reverse charg- ing acceptance not subscribed ## 0 2 9. Fast select rejected Fast select acceptance not subscribed ## 0 3 0. Called DTE out of order Out of order ## 0 ## greater than 127 3 1. No logical channel available Number busy ## 71 3 2. Call collision Number busy ## 71, ## 72 3 3. The remote DTE/DCE inter- face or the transit network does not support a function or a facility requested Incompatible destination ## 0 Note – Precise definition of error condition 30 necessitates further study, and should take into account the possible non–support of the virtual call service (only permanent virtual circuit) by the destination DTE. Error condition Cause Specific diag- nostics (see Note 3 of Annex E) 3 4. Procedure error at the remote DTE/DCE interface Remote proce- dure error [see b) and c) below and Annex D] 3 5. Temporary network conges- tion or fault condition within the network Network con- gestion ## 0, ## 122 or ## greater than 127 b) Call accepted packet Error condition Cause Specific diag- nostics (see Note 3 of Annex E) 1. Packet not octet aligned (see rule 2 in the introduction of this annex) Local proce- dure error ## 82 2. Address length larger than remainder of packet Local proce- dure error ## 38 3. Address contains a non– BCD digit Local proce- dure error ## 67, ## 68 4. Invalid calling DTE address [see Note under a)] Local proce- dure error ## 68 5. Invalid called DTE address [see Note under a)] Local proce- dure error ## 67 6. Value of the facility length greater than 109 Local proce- dure error ## 69 7. No combination of facilities could equal facility length Local proce- dure error ## 69 8. Facility length larger than remainder of packet Local proce- dure error ## 38 9. Facility code not allowed Invalid facility request ## 65 1 0. Facility value not allowed or invalid Invalid facility request ## 66 1 1. Class coding of the facility corresponding to a length of parameter field larger than remainder of packet Local proce- dure error ## 69 1 2. Facility code repeated Local proce- dure error ## 73 1 3. Invalid network user identi- fier Invalid facility request ## 84 1 4. NUI selection facility expected by the DCE and not provided by the DTE Local proce- dure error ## 84 1 5. Invalid/unsupported NUI value or missing NUI detected at inter–network interface Access barred ## 84 1 6. Facility value conflict (e.g., a particular combination not supported) Invalid facility request ## 66 1 7. CCITT–specified DTE facil- ity code or parameter not allowed or invalid Invalid facility request ## 77 1 8. Call user data larger than 128 (if fast select facility requested) Local proce- dure error ## 39 1 9. Call user data present (if fast select facility not requested) Local proce- dure error ## 39 2 0. The incoming call packet indicated fast select with restriction on response Local proce- dure error ## 42 Some networks may invoke the ERROR ## 74 procedure if the calling and/ or called DTE address length fields are not equal to 0 in the call accepted packet, except when the called line address modified notification facility is present in the facility field. c) Clear request packet Error condition Cause Specific diag- nostics (see Note 3 of Annex E) 1. Packet not octet aligned (see rule 2 in the introduction of this annex) Local proce- dure error ## 82 2. Packet too short Local proce- dure error ## 38 3. Packet length incorrectly larger than 5 octets Local proce- dure error ## 39 4. Calling DTE address length field not set to zero (at any time); called DTE address length field not set to zero except when the called line address modified notifica- tion facility is present in clearing a call in state p3 Local proce- dure error ## 74 5. Invalid called DTE address when the called line address modified notification facility is present in clearing a call in state p3 [see Note under a)] Local proce- dure error ## 67 6. Value of the facility length field greater than 109 Local proce- dure error ## 69 7. No combination of facilities could equal facility length Local proce- dure error ## 69 8. Facility length larger than remainder of packet Local proce- dure error ## 38 9. Facility code not allowed Invalid facility request ## 65 1 0. Facility value not allowed or invalid Invalid facility request ## 66 1 1. Class coding of the facility corresponding to a parameter field length larger than remainder of packet Local proce- dure error ## 69 1 2. Facility code repeated Local proce- dure error ## 73 1 3. Call deflection selection facility requested when the maximum number of call redirections and call deflec- tions is reached Invalid facility request ## 78 1 4. Call deflection selection facility requested after timer expiration Invalid facility request ## 53 1 5. Clear user data larger than 128 (if fast select facility requested) Local proce- dure error ## 39 1 6. Clear user data present (if fast select facility and call deflection selection facility not requested) Local proce- dure error ## 39 1 7. Clear user data larger than 16 (if fast select facility not requested and call deflection selection facility requested) Local proce- dure error ## 39 Some networks may invoke the ERROR ## 81 procedure if the clearing cause field is not “DTE originated” in the clear request packet. d) DTE clear confirmation packet Error condition Cause Specific diag- nostics (see Note 3 of annex E) 1. Packet not octet aligned (see rule 2 in the introduction of this annex) Local proce- dure error ## 82 2. Packet length greater than 3 octets Local proce- dure error ## 39 TABLE C–4/X.25 Action taken by the DCE on receipt of packets in a given state of the packet layer DTE/DCE interface as perceived by the DCE: data transfer (flow con- trol and reset) on assigned logical channels Data transfer (p4) State of the interface as per- ceived by the DCE Flow control ready DTE reset request DCE reset indicatio n Packet from the DTE with assigned logical channel (d1) (d2) (d3) Reset request NOR- MAL (d2) DIS- CARD NOR- MAL (d1) DTE reset confirmation ERROR (d3) ## 27 ERROR (d3) ## 28 NOR- MAL (d1) Data, interrupt or flow control NOR- MAL (d1) ERROR (d3) ## 28 DIS- CARD Restart request, DTE restart con- firmation or registration request with bits 1 to 4 of octet 1 or bits 1 to 8 of octet 2 unequal to zero ERROR (d3) ## 41 ERROR (d3) ## 41 DIS- CARD Packet having a packet type iden- tifier which is shorter than 1 octet ERROR (d3) ## 38 ERROR (d3) ## 38 DIS- CARD Packet having a packet type iden- tifier which is undefined or not supported by the DCE (i.e., reject or registration packet) ERROR (d3) ## 33 ERROR (d3) ## 33 DIS- CARD Invalid packet type on a perma- nent virtual circuit ERROR (d3) ## 35 ERROR (d3) ## 35 DIS- CARD Reject packet not subscribed ERROR (d3) ## 37 ERROR (d3) ## 37 DIS- CARD ERROR (d3): ## x The DCE discards the received packet, indicates a reset by transmitting to the DTE a reset indica- tion packet, with the cause “Local procedure error” and the diagnostic ## x, and enter state d3. The distant DTE is also informed of the reset by a reset indication packet, with the cause “Remote procedure error” (same diagnostic). NORMAL (di): Provided none of the following error conditions or spe- cial situations has occurred, the actions taken by the DCE follows the procedure as defined in § 4: a) if the packet exceeds the maximum permitted length, is too short, is not octet aligned (see rule 2 in the introduction of this annex), the DCE will invoke the ERROR ## 39, ## 38 or ## 82 procedure, respectively; b) some networks may invoke the ERROR ## 81 procedure if the resetting cause field in a reset request packet does not have the value “DTE originated”; c) some networks may invoke the ERROR ## 83 procedure if the Q bit is not set to the same value within a complete packet sequence; d) if the P(S) or the P(R) received is not valid, the DCE will invoke the ERROR ## 1 or ## 2 procedure respectively; e) the DCE will consider the receipt of a DTE interrupt confir- mation packet which does not correspond to a yet uncon- firmed DCE interrupt packet as an error and will invoke the ERROR ## 43 procedure. The DCE will consider a DTE interrupt packet received before a previous DTE interrupt packet has been confirmed as an error, and will invoke the ERROR ## 44 procedure; f) if the network has a temporary inability to handle data traf- fic for a permanent virtual circuit (see § 4.2), and if the packet is a data, interrupt, flow control or reset request packet received in state d1, the DCE shall transmit to the DTE a reset indication packet with the cause “Network out of order” and enter state d3 (data, interrupt or flow control packet) or d1 (reset request packet). ANNEX D (to Recommendation X.25) Packet layer DCE time–outs and DTE time–limits D.1 DCE time–outs Under certain circumstances this Recommendation requires the DTE to respond to a packet issued from the DCE within a stated maximum time. Table D–1/X.25 covers these circumstances and the actions that the DCE will initiate upon the expiration of that time. The time–out values used by the DCE will never be less than those indicated in Table D–1/X.25. D.2 DTE time–limits Under certain circumstances, this Recommendation requires the DCE to respond to a packet from the DTE within a stated maximum time. Table D–2/X.25 gives these maximum times. The actual DCE response times should be well within the specified time–limits. The rare situation where a time–limit is exceeded should only occur when there is a fault condition. To facilitate recovery from such fault conditions, the DTE may incor- porate timers. The time–limits given in Table D–2/X.25 are the lower limits of the times a DTE should allow for proper operation. A time–limit longer than the values shown may be used. Suggestions on possible DTE actions upon expiration of the time–limits are given in Table D–2/X.25. Note – A DTE may use a time shorter than the value given for T21 in Table D–2/X.25. This may be appropriate when the DTE knows the normal response time of the called DTE to an incoming call. In this case, the timer should account for the normal maximum response time of the called DTE and the estimated maximum call set–up time. TABLE D–1/X.25 DCE time–outs Time –out num ber Time –out value Started when State of the logic al chan nel Normally termi- nated when Actions to be taken the first time the time–out expires Actions to be taken the second time the time–out expires Local side Remote side Local side Remote side T10 60 s DCE issues a restart indicat ion r3 DCE leaves the r3 state (i.e., the restart confirmat ion or restart request is received) DCE remains in r3, sig- nals a restart indi-cat- ion (local procedure error ## 52) again, and restarts time–out T10 For per- manent virtual circuits, DCE may enter the d3 state signalling a reset indication (remote proce- dure error ## 52) DCE enters the r1 state and may issue a diagnosti c packet (## 52) For per- manent virtual circuits, DCE may enter the d3 state signalling a reset indication (remote proce- dure error ## 52) T11 180 s DCE issues an incomi ng call p3 DCE leaves the p3 state (e.g., the call accepted, clear request or call request is received) DCE enters the p7 state sig- nal-ling a clear indi-cat- ion (local procedure error ## 49) DCE enters the p7 state sig- nal-ling a clear indication (remote proce- dure error ## 49) T12 60 s DCE issues a reset indicat ion d3 DCE leaves the d3 state (e.g., the reset con- fir-mat- ion or reset request is received) DCE remains in d3, sig- nals a reset indi- cation (local procedure error ## 51) again, and restarts time–out T12 DCE may enter the d3 state signalling a reset indication (remote proce- dure error ## 51) For vir- tual calls, DCE enters the p7 state sig- nal-ling a clear indication (local procedure error ## 51). For per- manent virtual circuits, DCE enters the d1 state and may issue a diag-nos- tic packet (## 51) For vir- tual calls, DCE enters the p7 state sig- nal-ling a clear indi-cat- ion (remote procedure error ## 51). For per- manent virtual circuits, DCE may enter the d3 state signalling a reset indication (remote proce- dure error ## 51) T13 60 s DCE issues a clear indicat ion p7 DCE leaves the p7 state (e.g., the clear con- firmation or clear request is received) DCE remains in p7, sig- nals a clear indication (local procedure error ## 50) again, and restarts the time– out T13 DCE enters the p1 state and may issue a diagnosti c packet (## 50) TABLE D–2/X.25 DTE Time–limits Time– out numbe r Time – limit value Started when State of the logica l chann el Normally termi- nated when Preferred action to be taken when time–limit expires T20 180 s DTE issues a restart request r2 DTE leaves the r2 state (i.e., the restart confirma- tion or restart indication is received) To retransmit the restart request (see Note 1) T21 200 s DTE issues a call request p2 DTE leaves the p2 state (e.g., the call connected, clear indication or incoming call is received) To transmit a clear request T22 180 s DTE issues a reset request d2 DTE leaves the d2 state (e.g., the reset confirma- tion or reset indi- cation is received) For virtual calls, to retransmit the reset request or to transmit a clear request. For virtual per- manent call cir- cuits, to retransmit the reset request (see Note 2) T23 180 s DTE issues a clear request p6 DTE leaves the p6 state (e.g., the clear confirma- tion or clear indi- cation is received) To retransmit the clear request (see Note 2) T28 (see Note 3) 300 s DTE issues a registratio n request any DTE receives the registration con- firmation or a diagnostic packet May retransmit the registration request, but should at some point recognize that the on–line facility registra- tion facility is not offered Note 1 – After unsuccessful retries, recovery decisions should be taken at higher layers. Note 2 – After unsuccessful retries, the logical channel should be considered out of order. The restart procedure should be invoked for recovery if reini- tialization of all logical channels is acceptable. Note 3 – The DTE timers T24 through T27 have been assigned by ISO in the specification of the packet layer for X.25 DTEs. To avoid ambiguity and confusion, the time–out number has therefore been assigned T28. ANNEX E (to Recommendation X.25) Coding of X.25 network generated diagnostic fields in clear, reset and restart indication, registration confirmation and diagnostic packets TABLE E–1/X.25 (see Notes 1, 2 and 3) Diagnostics Bits 8 7 6 5 4 3 2 1 Deci- mal No additional information 0 0 0 0 0 0 0 0 0 Invalid P(S) 0 0 0 0 0 0 0 1 1 Invalid P(R) 0 0 0 0 0 0 1 0 2 0 0 0 0 1 1 1 1 15 Packet type invalid 0 0 0 1 0 0 0 0 16 For state r1 0 0 0 1 0 0 0 1 17 For state r2 0 0 0 1 0 0 1 0 18 For state r3 0 0 0 1 0 0 1 1 19 For state p1 0 0 0 1 0 1 0 0 20 For state p2 0 0 0 1 0 1 0 1 21 For state p3 0 0 0 1 0 1 1 0 22 For state p4 0 0 0 1 0 1 1 1 23 For state p5 0 0 0 1 1 0 0 0 24 For state p6 0 0 0 1 1 0 0 1 25 For state p7 0 0 0 1 1 0 1 0 26 For state d1 0 0 0 1 1 0 1 1 27 For state d2 0 0 0 1 1 1 0 0 28 For state d3 0 0 0 1 1 1 0 1 29 0 0 0 1 1 1 1 1 31 Packet not allowed 0 0 1 0 0 0 0 0 32 Unidentifiable packet 0 0 1 0 0 0 0 1 33 Call on one–way logical channel 0 0 1 0 0 0 1 0 34 Invalid packet type on a per- manent virtual circuit 0 0 1 0 0 0 1 1 35 Packet on unassigned logical channel 0 0 1 0 0 1 0 0 36 Reject not subscribed to 0 0 1 0 0 1 0 1 37 Packet too short 0 0 1 0 0 1 1 0 38 Packet too long 0 0 1 0 0 1 1 1 39 Invalid general format identi- fier 0 0 1 0 1 0 0 0 40 Restart or registration packet with nonzero in bits 1 to 4 of octet 1, or bits 1 to 8 of octet 2 0 0 1 0 1 0 0 1 41 Packet type not compatible with facility 0 0 1 0 1 0 1 0 42 Unauthorized interrupt con- firmation 0 0 1 0 1 0 1 1 43 Unauthorized interrupt 0 0 1 0 1 1 0 0 44 Unauthorized reject 0 0 1 0 1 1 0 1 45 0 0 1 0 1 1 1 1 47 Time expired 0 0 1 1 0 0 0 0 48 For incoming call 0 0 1 1 0 0 0 1 49 For clear indication 0 0 1 1 0 0 1 0 50 For reset indication 0 0 1 1 0 0 1 1 51 For restart indication 0 0 1 1 0 1 0 0 52 For call deflection 0 0 1 1 0 1 0 1 53 0 0 1 1 1 1 1 1 63 TABLE E–1/X.25 (cont.) Diagnostics Bits 8 7 6 5 4 3 2 1 Deci- mal Call set–up, call clearing or registration problem 0 1 0 0 0 0 0 0 64 Facility/registration code not allowed 0 1 0 0 0 0 0 1 65 Facility parameter not allowed 0 1 0 0 0 0 1 0 66 Invalid called DTE address 0 1 0 0 0 0 1 1 67 Invalid calling DTE address 0 1 0 0 0 1 0 0 68 Invalid facility/registration length 0 1 0 0 0 1 0 1 69 Incoming call barred 0 1 0 0 0 1 1 0 70 No logical channel available 0 1 0 0 0 1 1 1 71 Call collision 0 1 0 0 1 0 0 0 72 Duplicate facility requested 0 1 0 0 1 0 0 1 73 Non zero address length 0 1 0 0 1 0 1 0 74 Non zero facility length 0 1 0 0 1 0 1 1 75 Facility not provided when expected 0 1 0 0 1 1 0 0 76 Invalid CCITT–specified DTE facility 0 1 0 0 1 1 0 1 77 Maximum number of call redirections or call deflec- tions exceeded 0 1 0 0 1 1 1 0 78 0 1 0 0 1 1 1 1 79 Miscellaneous 0 1 0 1 0 0 0 0 80 Improper cause code from DTE 0 1 0 1 0 0 0 1 81 Not aligned octet 0 1 0 1 0 0 1 0 82 Inconsistent Q bit setting 0 1 0 1 0 0 1 1 83 NUI problem 0 1 0 1 0 1 0 0 84 0 1 0 1 1 1 1 1 95 Not assigned 0 1 1 0 0 0 0 0 96 0 1 1 0 1 1 1 1 111 International problem 0 1 1 1 0 0 0 0 112 Remote network problem 0 1 1 1 0 0 0 1 113 International protocol prob- lem 0 1 1 1 0 0 1 0 114 International link out of order 0 1 1 1 0 0 1 1 115 International link busy 0 1 1 1 0 1 0 0 116 Transit network facility prob- lem 0 1 1 1 0 1 0 1 117 Remote network facility problem 0 1 1 1 0 1 1 0 118 International routing prob- lem 0 1 1 1 0 1 1 1 119 Temporary routing problem 0 1 1 1 1 0 0 0 120 Unknown called DNIC 0 1 1 1 1 0 0 1 121 Maintenance action (see Note 4) 0 1 1 1 1 0 1 0 122 0 1 1 1 1 1 1 1 127 Reserved for network spe- cific diagnostic information 1 0 0 0 0 0 0 0 128 1 1 1 1 1 1 1 1 255 Note 1 – Not all diagnostic codes need apply to a specific network, but those used are as coded in the table. Note 2 – A given diagnostic need not apply to all packet types (i.e., reset indication, clear indication, restart indication, registration confirmation and diagnostic packets). Note 3 – The first diagnostic in each grouping is a generic diagnostic and can be used in place of the more specific diagnostics within the grouping. The decimal 0 diagnostic code can be used in situations where no additional information is available. Note 4 – This diagnostic may also apply to a maintenance action within a national network. ANNEX F (to Recommendation X.25) Applicability of the on–line facility registration facility to other facilities Name of facility or inter- face parameter Refer- ence to definiti on (§) Negotia- ble in reg- istration request and regis- tration confirmat ion pack- ets Indica- tion in registratio n confir- mation packets whether the facil- ity is sup- ported by the DCE Negotia- ble only when every log- ical chan- nel used for vir- tual calls is in state p1 Extended packet sequence numbering 6.2 Yes (see Note 1) Yes (see Note 1) Yes D bit modification 6.3 Yes Yes Yes Packet retransmission 6.4 Yes Yes Yes Incoming calls barred 6.5 Yes No No Outgoing calls barred 6.6 Yes No No One–way logical channel outgoing 6.7 (see Note 2) One–way logical channel incoming 6.8 (see Note 2) Non–standard default packet sizes 6.9 Yes Yes No Non–standard default win- dow sizes 6.10 Yes Yes No Default throughput classes assignment 6.11 Yes Yes No Flow control parameter negotiation 6.12 Yes No No Throughput class negotia- tion 6.13 Yes No No Closed user group related facilities 6.14 No No – Bilateral closed user group related facilities 6.15 No No – Fast select 6.16 No No – Fast select acceptance 6.17 Yes No No Reverse charging 6.18 No Yes – Reverse charging accep- tance 6.19 Yes Yes No Local charging prevention 6.20 No Yes – NUI related facilities 6.21 No No – Charging information 6.22 (per interface basis) Yes Yes No (per call basis) No Yes – RPOA related facilities RPOA subscription 6.23.1 (see Note 1) (see Note 1) (see Note 1) RPOA selection 6.23.2 No Yes – Hunt group 6.24 No No – Call redirection 6.25.1 (see Note 1) (see Note 1) (see Note 1) Call deflection related facil- ities 6.25.2 (see Note 1) (see Note 1) (see Note 1) Call redirection or call deflection notification 6.25.3 No No – Called line address modi- fied notification 6.26 No No – Transit delay selection and indication 6.27 No Yes – Allocation of logical chan- nel type range Annex A Yes Yes Yes Note 1 – Further study is needed. Note 2 – Negotiation of one–way logical channel ranges is accomplished by allocation of logical channel type ranges negotiation. ANNEX G (to Recommendation X.25) CCITT–specified DTE facilities to support the OSI Network service G.1 Introduction The facilities described in this annex are intended to support end–to– end signalling required by the OSI Network service OSI Network service. They follow the CCITT–specified DTE facility marker defined in § 7.1. These facilities are passed unchanged between the two packet mode DTEs involved. Procedures for use of these facilities by DTEs are specified in ISO 8208. Subsequent provision of X.25 facilities to be acted on by public data networks is for further study. Coding of the facilities in this annex is defined here in order to facilitate a consistent facility coding scheme in such future evolution. G.2 Coding of the facility code fields Table G–1/X.25 gives the coding of the facility code field for each CCITT–specified DTE facility and the packet types in which they may be present. These facilities are conveyed after the CCITT–specified DTE facil- ity marker. TABLE G–1/X.25 Coding of the facility code field Facility Packet types in which the facility may be used Facility code Call Incom ing Call Call Clear Clear Bits reques t call accept ed conne cted reques t indica tion 8 7 6 5 4 3 2 1 Calling address extension X X X (see Note) 1 1 0 0 1 0 1 1 Called address extension X X X X X X 1 1 0 0 1 0 0 1 Quality of ser- vice negotiati on: Minimu m throughp ut class X X X (see Note) 0 0 0 0 1 0 1 0 End–to– end tran- sit delay X X X X X (see Note) 1 1 0 0 1 0 1 0 Priority X X X X X (see Note) 1 1 0 1 0 0 1 0 Protectio n X X X X X (see Note) 1 1 0 1 0 0 1 1 Expedite d data negotiati on X X X X X (see Note) 0 0 0 0 1 0 1 1 Note – Only when the call deflection selection facility is used (see § 6.25.2.2.). G.3 Coding of the facility parameter field G.3.1 Calling address extension facility The octet following the facility code field indicates the length of the facility parameter field in octets. It has a value of n + 1, where n is the num- ber of octets necessary to hold the calling address extension. The facility parameter field follows the length and contains the calling address exten- sion. The first octet of the facility parameter field indicates, in bits 8 and 7, the use of the calling address extension, as shown in Table G–2/X.25. TABLE G–2/X.25 Coding of bits 8 and 7 in the first octet of the calling extension facility parameter field Bits Use of calling address extension 8 7 0 0 To carry a calling address assigned according to Recommendation X.213/ISO 8348 AD2 0 1 Reserved 1 0 Other (to carry a calling address not assigned according to Recommendation X.213/ISO 8348 AD2) 1 1 Reserved Bits 6, 5, 4, 3, 2 and 1 of this octet indicates the number of semi– octets (up to a maximum of 40) in the calling address extension. This address length indicator is binary coded, where bit 1 is the low–order bit. The following octets contain the calling address extension. If bits 8 and 7 of the first octet of the facility parameter field are coded “00”, the following octets are encoded using the preferred binary encoding (PBE) defined in Recommendation X.213. Starting from the high–order digit of the Initial Domain Part Initial Domain Part (IDP), the address is coded in octet 2 and consecutive octets of the facility parameter field. Each digit, with padding digits applied as necessary, is coded in a semi–octet in binary coded decimal, where bit 5 or 1 is the low–order bit of the digit. In each octet, the higher–order bit is coded in bits 8, 7, 6 and 5. The Domain Spe- cific Part Domain Specific Part (DSP) of the calling OSI NSAP follows the IDP and is coded in decimal of binary, according to the PBE. For example, if the syntax of the DSP is decimal, each digit is coded in binary coded dec- imal (with the same rules applying to the DSP as to the IDP above). If the syntax of the DSP is binary, each octet of the calling address extension con- tains an octet of the DSP. If bits 8 and 7 of the first octet of the facility parameter field are coded “10”, each digit of the calling address extension is coded in a semi–octet in binary coded decimal, where bit 5 or 1 is the low–order bit of the digit. Starting from the high–order digit, the address is coded in octet 2 and consecutive octets of the facility parameter field with two digits per octet. In each octet, the higher order digit is coded in bits 8, 7, 6 and 5. When necessary, the facility parameter field shall be rounded up to an integral number of octets by inserting zeros in bits 4, 3, 2 and 1 of the last octet of the field. G.3.2 Called address extension facility The octet following the facility code field indicates the length of the facility parameter field in octets. It has a value of n + 1, where n is the num- ber of octets necessary to hold the called address extension. The facility parameter field follows the length and indicates the called address exten- sion. The first octet of the facility parameter field indicates, in bits 8 and 7, the use of the called address extension, as shown in Table G–3/X.25. TABLE G–3/X.25 Coding of bits 8 and 7 in the first octet of the called extension facility parameter field Bits Use of calling address extension 8 7 0 0 To carry a called address assigned according to Recommendation X.213/ISO 8348 AD2 0 1 Reserved 1 0 Other (to carry a called address not assigned according to Recommendation X.213/ISO 8348 AD2) 1 1 Reserved Bits 6, 5, 4, 3, 2 and 1 of this octet indicates the number of semi– octets (up to a maximum of 40) in the called address extension. This address length indicator is binary coded, where bit 1 is the low–order bit. The following octets contain the called address extension. If bits 8 and 7 of the first octet of the facility parameter field are coded “00”, the following octets are encoded using the preferred binary encoding (PBE) defined in Recommendation X.213. Starting from the high–order digit of the Initial Domain Part (IDP), the address is coded in octet 2 and consecu- tive octets of the facility parameter field. Each digit, with padding digits applied as necessary, is coded in a semi–octet in binary coded decimal, where bit 5 or 1 is the low–order bit of the digit. In each octet, the higher– order bit is coded in bits 8, 7, 6 and 5. The Domain Specific Part (DSP) of the called OSI NSAP follows the IDP and is coded in decimal of binary, according to the PBE. For example, if the syntax of the DSP is decimal, each digit is coded in binary coded decimal (with the same rules applying to the DSP as to the IDP above). If the syntax of the DSP is binary, each octet of the called address extension contains an octet of the DSP. If bits 8 and 7 of the first octet of the facility parameter field are coded “10”, each digit of the called address extension is coded in a semi–octet in binary coded decimal, where bit 5 or 1 is the low–order bit of the digit. Starting from the high–order digit, the address is coded in octet 2 and consecutive octets of the facility parameter field with two digits per octet. In each octet, the higher order digit is coded in bits 8, 7, 6 and 5. When necessary, the facility parameter field shall be rounded up to an integral number of octets by inserting zeros in bits 4, 3, 2 and 1 of the last octet of the field. G.3.3 Quality of service negotiation facilities G.3.3.1 Minimum throughput class facility The minimum throughput class for the direction of data transmission from the calling DTE is indicated in bits 4, 3, 2 and 1. The minimum throughput class for the direction of data transmission from the called DTE is indicated in bits 8, 7, 6 and 5. The four bits indicating each throughput class are binary coded and correspond to throughput classes as indicated in Table 30/X.25. G.3.3.2 End–to–end transit delay facility The octet following the facility code field indicates the length in octets of the facility parameter field and has the value 2, 4 or 6. The first and second octets of the facility parameter field contain the cumulative transit delay. The third and fourth octets are optional and, when present, contain the requested end–to–end transit delay. If the third and fourth octets are present, then the fifth and sixth octets are also optional. The fifth and sixth octets, when present, contain the maximum acceptable end– to–end transit delay. The optional octets are not present in call accepted and call connected packets. Transit delay is expressed in milliseconds and is binary–coded, with bit 8 of the first of a pair of octets being the high–order bit and bit 1 of the second of a pair of octets being the low–order bit. The value of all ones for cumulative transit delay indicates that the cumulative transit delay is unknown or exceeds 65 534 milliseconds. G.3.3.3 Priority facility The octet following the facility code field indicates the length, in octets, of the facility parameter field. This may take the value 1, 2, 3, 4, 5 or 6. The first, second and third octets of the facility parameter field con- tain the target (call request packet), available (incoming call packet) or selected (call accepted and call connected packets) values for the priority of data on connection, priority to gain a connection and priority to keep a con- nection, respectively. The fourth, fifth and sixth octets of the facility param- eter field in call request and incoming call packets contain the lowest acceptable values for the priority of data on connection, priority to gain a connection and priority to keep a connection, respectively. When the facility is present in call request and incoming call packets, octet 2 through 6 of the facility parameter field are optional. For example, if the only values to be specified are the target and lowest acceptable values for priority to gain a connection, then the facility parameter field will contain at least 5 octets with octets 1, 3 and 4 containing the value “unspecified”, and octets 2 and 5 containing the specified values. When the facility is present in the call accepted and call connected packets, octets 2 and 3 are optional. The potential range of specified values for each sub–parameter is 0 (lowest priority) to 254 (highest priority). The value 255 (1111 1111) indi- cates “unspecified”. G.3.3.4 Protection facility The octet following the facility code indicates the length, in octets, of the facility parameter field. The two highest order bits of the first octet (i.e., bits 8 and 7) of the facility parameter field specify the protection format code as indicated in Table G–4/X.25. TABLE G–4/X.25 Coding of the two highest order bits in the first octet of the protection for- mat code Bits Use of calling address extension 8 7 0 0 Reserved 0 1 Source address specific 1 0 Destination address police 1 1 Globally unique The remaining six bits of the octet are reserved and must be set to zero. The second octet of the facility parameter field specifies the length “n”, in octets, of the target (call request packet), available (incoming call packet) or selected (call accepted and call connected packets) protection level. The actual value is placed in the following “n” octets. Optionally, the “n + 3” octet of the facility parameter field specifies the length “m”, in octets, of the lowest acceptable protection level in call request and incoming call packets. The actual value is placed in the following “m” octets. The optional octets are not present in call accepted and call connected packets. Note – The values of “n” and “m” are bounded firstly by the overall length of the facility (first octet), and secondly by each other. G.3.4 Expedited data negotiation facility The coding of the facility parameter field is: bit 1 = 0 for no use of expedited data bit 1 = 1 for use of expedited data Note – Bits 8, 7, 6, 5, 4, 3 and 2 may be assigned to other facilities in the future; presently, they are set to zero. ANNEX H (to Recommendation X.25) Subscription–time optional user facilities that may be associated with a network user identifier in conjunction with the NUI override facility (see § 6.21.2) Subscription–time optional user facility May be associated with an NUI On–line facility registration No Extended packet sequence numbering No D bit modification No Packet retransmission No Incoming calls barred No Outgoing calls barred No One–way logical channel outgoing No One–way logical channel incoming No Non–standard default packet sizes Yes Non–standard default window sizes Yes Default throughput classes assignment Yes Flow control parameter negotiation (subscrip- tion–time) Yes Throughput class negotiation (subscription– time) Yes Closed user group related facilities Closed user group Yes Closed user group with outgoing access Yes Closed user group with incoming access No Incoming calls barred within a closed user group No Outgoing calls barred within a closed user group No Bilateral closed user group related facilities Bilateral closed user group Yes Bilateral closed user group with outgoing access Yes Fast select acceptance No Reverse charging acceptance No Local charging prevention No Charging information (subscription–time) Yes RPOA subscription Yes Hunt group No Call redirection and call deflection related facili- ties Call redirection No Call deflection subscription No “TOA/NPI address” subscription No