Outbound ISDN calls fail due to NAI value

Symptom

An E1 ISDN line on a Dialogic IMG Integrated Media Gateway connected to British Telecom (BT) is able to receive inbound calls but attempting to make an outbound call can fail with a cause code relating to the number being invalid or incorrect.
 

Analysis

The following traces were obtained from a telnet session with the IMG 1010. By entering ‘Advanced Debug’ mode (d) from the main menu, then ‘ISDN Diags’ (I) and ‘2->06->ff’ we enabled a raw Q.931 trace on all E1s. The trace is disabled with ‘2->00’. The same commands can be used on the IMG 1004 and IMG 2020. 

A successful inbound call:

08:43:25.927 ISDN(I) 7bf8 01 R 00 00 1 55 40 0 021 SETUP 0001

08:43:25.927 ISDN(I) 020180aa0802000105a104039090a31803a983811e028583700781353831323139

02 000000-- Sapi = 0

------1- C/R: Command

-------0 Extension Bit = with extension

01 0000000- TEI = 0

-------1 Extension Bit = no extension

80 1000000- N(S) = 64

-------0 I-Frame

AA 1010101- N(R) = 85

-------0 P/F = 0

08 00001000 ProtocolDiscriminator DSS1

02 00000010 Length of CallReference = 2

00 0------- CallRef-Flag: Origination Side

-0000000 CallReference = 1

01 00000001 (CallReference)

05 00000101 MSG-Type: SETUP

A1 10100001 I-Element: Sending Complete

04 00000100 I-Element: Bearer

03 00000011 Length = 3

90 1------- Extension Bit = no extension

-00----- Coding Standard: CCITT

---10000 Information Transfer Capability: 3.1 kHz Audio

90 1------- Extension Bit = no extension

-00----- Transfer Mode: circuit mode

---10000 Information Transfer Rate: 64 kbit/s

A3 1------- Extension Bit = no extension

-01----- Layer 1 Identifier

---00011 User Info Layer 1 Protocol: G.711 A-Law

18 00011000 I-Element: Channel Identification

03 00000011 Length = 3

A9 1------- Extension Bit = no extension

-0------ Interface Identifier present: interface implicitly identified

--1----- Interface Type: other interface

---0---- Spare

----1--- Preferred/Exclusive: exclusiv, only indicated channel is acceptable

-----0-- D-channel indicator: is not the D-channel

------01 Information Channel Selection = as indicated in following octets

83 1------- Extension Bit = no extension

-00----- Coding Standard: CCITT

---0---- Number/Map: Channel by Number

----0011 Channel Type/Map Element Typ: B-Channel Units

81 1------- Extension Bit = no extension

-0000001 Channel number: 1

1E 00011110 I-Element: Progress Indicator

02 00000010 Length = 2

85 1------- Extension Bit = no extension

-00----- Coding Standard: CCITT

---0---- Spare

----0101 Location: private network serving remote user

83 1------- Extension Bit = no extension

-0000011 Progress Description: origination address is non-ISDN

70 01110000 I-Element: Called Party Number

07 00000111 Length = 7

81 1------- Extension Bit = no extension

-000---- Type of Number: unknown

----0001 Numbering Plan: ISDN/Telephony

35 0------- Spare

-0110101 Number digit: 5

38 0------- Spare

-0111000 Number digit: 8

31 0------- Spare

-0110001 Number digit: 1

32 0------- Spare

-0110010 Number digit: 2

31 0------- Spare

-0110001 Number digit: 1

39 0------- Spare

-0111001 Number digit: 9

08:43:25.927 ISDN(I) 7bf8 01 T 00 00 0 41 55 0 00e CALL PROCEEDING 8001

08:43:25.927 ISDN(I) 0001aa8208028001021803a98381

08:43:26.157 ISDN(I) 7c0f 01 T 00 00 0 41 56 0 009 ALERTING 8001

08:43:26.157 ISDN(I) 0001ac820802800101

08:43:28.857 ISDN(I) 7d1d 01 T 00 00 0 41 57 0 009 CONNECT 8001

08:43:28.857 ISDN(I) 0001ae820802800107

08:43:28.917 ISDN(I) 7d23 01 R 00 00 1 58 41 0 009 CONNECT ACK 0001

08:43:28.917 ISDN(I) 020182b0080200010f

08:43:31.697 ISDN(I) 7e39 01 R 00 00 1 58 42 0 011 DISCONNECT 0001

08:43:31.697 ISDN(I) 020184b00802000145080285901e028288

08:43:31.757 ISDN(I) 7e3f 01 T 00 00 0 43 58 0 009 RELEASE 8001

08:43:31.757 ISDN(I) 0001b086080280014d

08:43:31.817 ISDN(I) 7e45 01 R 00 00 1 59 43 0 009 REL COMP 0001

08:43:31.817 ISDN(I) 020186b2080200015a

A failing outbound call:

08:45:34.256 ISDN(I) ae19 01 T 00 00 0 44 59 0 02a SETUP 0023

08:45:34.256 ISDN(I) 0001b288080200230504038090a31803a983816c06218032303031700ca13037373131333130353538a1

00 000000-- Sapi = 0

------0- C/R: Response

-------0 Extension Bit = with extension

01 0000000- TEI = 0

-------1 Extension Bit = no extension

B2 1011001- N(S) = 89

-------0 I-Frame

88 1000100- N(R) = 68

-------0 P/F = 0

08 00001000 ProtocolDiscriminator DSS1

02 00000010 Length of CallReference = 2

00 0------- CallRef-Flag: Origination Side

-0000000 CallReference = 35

23 00100011 (CallReference)

05 00000101 MSG-Type: SETUP

04 00000100 I-Element: Bearer

03 00000011 Length = 3

80 1------- Extension Bit = no extension

-00----- Coding Standard: CCITT

---00000 Information Transfer Capability: Speech

90 1------- Extension Bit = no extension

-00----- Transfer Mode: circuit mode

---10000 Information Transfer Rate: 64 kbit/s

A3 1------- Extension Bit = no extension

-01----- Layer 1 Identifier

---00011 User Info Layer 1 Protocol: G.711 A-Law

18 00011000 I-Element: Channel Identification

03 00000011 Length = 3

A9 1------- Extension Bit = no extension

-0------ Interface Identifier present: interface implicitly identified

--1----- Interface Type: other interface

---0---- Spare

----1--- Preferred/Exclusive: exclusiv, only indicated channel is acceptable

-----0-- D-channel indicator: is not the D-channel

------01 Information Channel Selection = as indicated in following octets

83 1------- Extension Bit = no extension

-00----- Coding Standard: CCITT

---0---- Number/Map: Channel by Number

----0011 Channel Type/Map Element Typ: B-Channel Units

81 1------- Extension Bit = no extension

-0000001 Channel number: 1

6C 01101100 I-Element: Calling Party Number

06 00000110 Length = 6

21 0------- Extension Bit = with extension

-010---- Type of Number: national

----0001 Numbering Plan: ISDN/Telephony

80 1------- Extension Bit = no extension

-00----- Presentation Indicator: presentation allowed

---000-- Spare

------00 Screening Indicator: user-provided, not screened

32 0------- Spare

-0110010 Number digit: 2

30 0------- Spare

-0110000 Number digit: 0

30 0------- Spare

-0110000 Number digit: 0

31 0------- Spare

-0110001 Number digit: 1

70 01110000 I-Element: Called Party Number

0C 00001100 Length = 12

A1 1------- Extension Bit = no extension

-010---- Type of Number: national

----0001 Numbering Plan: ISDN/Telephony

30 0------- Spare

-0110000 Number digit: 0

37 0------- Spare

-0110111 Number digit: 7

37 0------- Spare

-0110111 Number digit: 7

31 0------- Spare

-0110001 Number digit: 1

31 0------- Spare

-0110001 Number digit: 1

33 0------- Spare

-0110011 Number digit: 3

31 0------- Spare

-0110001 Number digit: 1

30 0------- Spare

-0110000 Number digit: 0

35 0------- Spare

-0110101 Number digit: 5

35 0------- Spare

-0110101 Number digit: 5

38 0------- Spare

-0111000 Number digit: 8

A1 10100001 I-Element: Sending Complete

08:45:34.446 ISDN(I) ae2c 01 R 00 00 1 5a 44 0 00e CALL PROCEEDING 8023

08:45:34.446 ISDN(I) 020188b408028023021803a98381

08:45:36.156 ISDN(I) aed7 01 R 00 00 1 5a 45 0 011 DISCONNECT 8023

08:45:36.156 ISDN(I) 02018ab40802802345080282811e028288

02 000000-- Sapi = 0

------1- C/R: Command

-------0 Extension Bit = with extension

01 0000000- TEI = 0

-------1 Extension Bit = no extension

8A 1000101- N(S) = 69

-------0 I-Frame

B4 1011010- N(R) = 90

-------0 P/F = 0

08 00001000 ProtocolDiscriminator DSS1

02 00000010 Length of CallReference = 2

80 1------- CallRef-Flag: Destination Side

-0000000 CallReference = 35

23 00100011 (CallReference)

45 01000101 MSG-Type: DISCONNECT

08 00001000 I-Element: Cause

02 00000010 Length = 2

82 1------- Extension Bit = no extension

-00----- Coding Standard: CCITT

---0---- Spare

----0010 Location: public network serving local user

81 1------- Extension Bit = no extension

-000---- Cause Class: normal event

----0001 Cause Value: Unallocated number;unassigned

1E 00011110 I-Element: Progress Indicator

02 00000010 Length = 2

82 1------- Extension Bit = no extension

-00----- Coding Standard: CCITT

---0---- Spare

----0010 Location: public network serving local user

88 1------- Extension Bit = no extension

-0001000 Progress Description: in-band information or appropriate pattern now available

08:45:36.256 ISDN(I) aee1 01 T 00 00 0 46 5a 0 009 RELEASE 0023

08:45:36.256 ISDN(I) 0001b48c080200234d

08:45:36.316 ISDN(I) aee7 01 R 00 00 1 5b 46 0 009 REL COMP 8023

08:45:36.316 ISDN(I) 02018cb6080280235a

From looking at the above, we can see that in the failure case the call is being rejected by the network because the number we dialled was unallocated or unassigned. Comparing the dialled number in the successful case against that of the failure case, we can see that the ‘type of number’ is set differently, i.e., ‘national’ in the failure call from the IMG and ‘000 - unknown’ in the successful call from BT.

By default, the IMG will pass whatever Nature of Address Indicator (NAI) it sees on the inbound call leg out to the outbound call leg. In the above case, the NAI is set to ‘national’ for the inbound leg and this will therefore be propagated to the outbound leg.

A solution is to change the behaviour on the IMG for this E1 by forcing the NAI for outbound calls over this E1 to ‘000 - unknown’.

Fix / Solution

Note: Screenshots in this article have been taken from an IMG 1010 but equally apply to the IMG 2020, though some features might look differently on the IMG 2020.
A new outgoing translation table to the routing configuration may need to be added if one does not already exist. Right-click on the ‘Routing Configuration’ node and select ‘New Outgoing Translation Tables’ to add the ‘Outgoing Translation Tables’ group. Then right-click on ‘Outgoing Translation Tables’ and select ‘New Translation Table’ to add a new table:

Open

To this table, we need to add a single dummy entry to apply to all dial strings. Right-click the table and select ‘New Translation Entry’. Set the ‘String’ and ‘Dialed # Translation’ as follows:

Open

This will allow any number dialled through unmodified. It will, however allow for applying an ‘Advanced Dialed Number Translation’ so that the NAI for this E1 can be modified.
On the IMG 1010 and IMG 1004 right-click the entry just added and add the advanced translation and modify the ‘Nature of Address’ parameter.
On the IMG 2020 create a translation profile and add an Advanced Dialed Number Parameters object to it, then modify the Nature of Address parameter. Then set this Translation Profile in the translation entry configured  above.

Finally, find the outbound channel group for this E1 and apply the outbound translation table to the channel group:

Once the above changes have been committed, it should be possible to route calls successfully to a British Telecom ISDN line.
 
Product List:
Dialogic IMG 1004 Integrated Media Gateway
Dialogic IMG 1010 Integrated Media Gateway
Dialogic IMG 2020 Integrated Media Gateway (IMG 2020), formerly referred to as Dialogic BorderNet™ 2020 Session Border Controller