1. Troubleshooting ISDN
1174_04F8_c1

2. Thierry Martens

3. What You Should Know
BRI
T1 and E1 PRI
ISDN protocol architecture

4. Basic Rate Access (BRI)
2B + D
S0 interface
B-CHANNEL
BRI
2 B channels at 64 kbps each
1 D channel at 16 kbps
Framing and synchronization at 48 kbps
Total speed 192 kbps
Intended to be used at small concentration points
Referred to as S0 interface
B-CHANNEL
D-CHANNEL

5. T1 Primary Rate Interface (PRI)
T1 PRI or S1 interface
Used in North America and Japan
23 B + D
B-CHANNEL
T1-PRI
23 B channels at 64 kbit/s
1 D channel at 64 kbit/s
Framing and synchronization at 8 kbit/s
Total speed 1544 kbit/s
D-CHANNEL

6. E1 Primary Rate Interface (PRI)
E1 PRI or S2 interface
Used in Europe
30 B + D
B-CHANNEL
E1-PRI
30 B channels at 64 kbit/s
1 D channel at 64 kbit/s
Framing and synchronization at 64 kbit/s
Total speed 2048 kbit/s
D-CHANNEL

7. ISDN Protocol Architecture
B-Channel
D-Channel
IP, …
Q.931
Network
Network
PPP
LAPD–Q.921
Data Link
Data Link
I.430 (BRI)–I.431 (PRI)
Physical
Physical

8. Troubleshooting ISDN
“There are only two possible problems with ISDN: The first problem occurs when you try to install it The second problem occurs when you receive the first invoice”

9. Troubleshooting ISDN Be systematic Go step by step
Always troubleshoot both ends of the connection

10. Troubleshooting Menu Troubleshooting Ping remote int Debug dialer
Sh isdn stat
Layer 1
Layer 2
Layer 3
Debug PPP
LCP
Speed 56/64
Pap/chap
NCP
Ping remote net
Tune cost

11. Ping Remote ISDN Int
Troubleshooting
Ping remote int
Ping remote net
Tune cost
ping
ping
ISDN
Do not bother to look at routing or cost issues if that doesn’t work

12. Debug Dialer router# debug dialer events
Troubleshooting
Ping remote int
Debug dialer
Sh isdn stat
Debug PPP
Ping remote net
Tune cost
router# debug dialer events
Dialing cause: BRI0: ip (s= d )
router# debug dialer packets
BRI0: ip (s= , d= ),100 bytes, interesting (ip PERMIT)

13. SH ISDN Status router#sh isdn stat ISDN BRI0 interface Layer 1 Status:
Troubleshooting
Ping remote int
Debug dialer
Sh isdn stat
Layer 1
Layer 2
Layer 3
Debug PPP
Ping remote net
Tune cost
router#sh isdn stat
ISDN BRI0 interface
Layer 1 Status:
DEACTIVATED
Layer 2 Status:
Layer 2 NOT Activated
Layer 3 Status:
No Active Layer 3 Call(s)
Activated dsl 0 CCBs are 0, Allocated = 0
New command included around 10.2(3)

14. TDM Multiplexing Creates B1, B2, and D channels
Troubleshooting
Ping remote int
Debug dialer
Sh isdn stat
Layer 1
Layer 2
Layer 3
Debug PPP
Ping remote net
Tune cost
Creates B1, B2, and D channels
48-bit physical frame, frames/s, 192 kbps
2 x 8 B1 bits, 2 x 8 B2 bits, 4 x 1 D bit 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 B B B B B B B B F N B B B B B B B B B B B B B B B B B B B B B B B B F D D D D 1 1 1 1 1 1 1 1 A 2 2 2 2 2 2 2 2 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2
Frame from NT to TE 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 B B B B B B B B F B B B B B B B B B B B B B B B B B B B B B B B B F D D D D 1 1 1 1 1 1 1 1 A 2 2 2 2 2 2 2 2 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2
Frame from TE to NT

15. Synchronization 1st Line Code Violation 2nd Line Code Violation F
Troubleshooting
Ping remote int
Debug dialer
Sh isdn stat
Layer 1
Layer 2
Layer 3
Debug PPP
Ping remote net
Tune cost F
1st Line Code
Violation
2nd Line Code
Violation 1 2 3 4
Each frame starts with a double line code violation (binary 0 coded with same polarity as previous 0)
F bit (always 0) creates first violation
First data 0 or FA or N bit (one of them always 0) create second violation
The start of every physical frame is marked by a valid pair of line code violations.
F bit and first data 0
F bit and FA bit (bit 14 - TE to NT direction)
F bit and FA or N bit (bit 14 or 15 - NT to TE direction)
A pair of line code violations is called valid if both violations are separated by maximum :
13 bittimes in TE to NT direction
14 bittimes in NT to TE direction
As soon as 3 successive valid pairs of line code violations are detected, a device will assume that synchronization is achieved
As soon as no valid pair of line code violations is detected in two successive physical ISDN frames, synchronization is lost 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 B B B B B B B B F N B B B B B B B B B B B B B B B B B B B B B B B B F D D D D 1 1 1 1 1 1 1 1 A 2 2 2 2 2 2 2 2 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2
Frame from NT to TE 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 B B B B B B B B F B B B B B B B B B B B B B B B B B B B B B B B B F D D D D 1 1 1 1 1 1 1 1 A 2 2 2 2 2 2 2 2 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2
Frame from TE to NT

16. Activation (A Bit) A=0: Deactivated A=1: Activated Troubleshooting
Ping remote int
Debug dialer
Sh isdn stat
Layer 1
Layer 2
Layer 3
Debug PPP
Ping remote net
Tune cost
A=0: Deactivated
A=1: Activated 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 B B B B B B B B F N B B B B B B B B B B B B B B B B B B B B B B B B F D A D D D 1 1 1 1 1 1 1 1 A 2 2 2 2 2 2 2 2 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2
Frame from NT to TE 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 B B B B B B B B F B B B B B B B B B B B B B B B B B B B B B B B B F D D D D 1 1 1 1 1 1 1 1 A 2 2 2 2 2 2 2 2 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2
Frame from TE to NT

17. Activation Procedure: INFO 0TE NT
1– INFO 0–Not Active: No Signal
No Signal
No Signal
TE states
state F1 : inactive
state F2 : sensing (after power up)
state F3 : deactivated
state F4 : awaiting signal (waiting for info 2)
state F5 : identifying input (info 2 or info 4)
state F6 : synchronized (waiting for info 4)
state F7 : activated
state F8 : lost framing

18. Activation Procedure: INFO 1TE NT
1– INFO 0–Not Active: No Signal
No Signal
No Signal
2– INFO 1–TE becomes Active: " " Signal (= HDLC Flags)
TE states
state F1 : inactive
state F2 : sensing (after power up)
state F3 : deactivated
state F4 : awaiting signal (waiting for info 2)
state F5 : identifying input (info 2 or info 4)
state F6 : synchronism (waiting for info 4)
state F7 : activated
state F8 : lost framing

19. Activation Procedure: INFO 2TE NT
1– INFO 0–Not Active: No Signal
No Signal
No Signal
2– INFO 1–TE becomes Active: " " Signal (= HDLC Flags)
3– INFO 2–Network Sends Frames with A-bit = 0 F
A=0
TE states
state F1 : inactive
state F2 : sensing (after power up)
state F3 : deactivated
state F4 : awaiting signal (waiting for info 2)
state F5 : identifying input (info 2 or info 4)
state F6 : synchronized (waiting for info 4)
state F7 : activated
state F8 : lost framing

20. Activation Procedure: INFO 3TE NT
1– INFO 0–Not Active: No Signal
No Signal
No Signal
2– INFO 1–TE becomes Active: " " Signal (= HDLC Flags)
3– INFO 2–Network Sends Frames with A-bit = 0 F
A=0
TE states
state F1 : inactive
state F2 : sensing (after power up)
state F3 : deactivated
state F4 : awaiting signal (waiting for info 2)
state F5 : identifying input (info 2 or info 4)
state F6 : synchronized (waiting for info 4)
state F7 : activated
state F8 : lost framing
4– INFO 3–TE Synchronizes and Sends Physical Frames F

21. Activation Procedure: INFO 4TE NT
1– INFO 0–Not Active: No Signal
No Signal
No Signal
2– INFO 1–TE becomes Active: " " Signal (= HDLC Flags)
3– INFO 2–Network Sends Frames with A-bit = 0 F
A=0
TE states
state F1 : inactive
state F2 : sensing (after power up)
state F3 : deactivated
state F4 : awaiting signal (waiting for info 2)
state F5 : identifying input (info 2 or info 4)
state F6 : synchronized (waiting for info 4)
state F7 : activated
state F8 : lost framing
4– INFO 3–TE Synchronizes and Sends Physical Frames F
5–INFO 4–NT Synchronizes and Sends Frames with A-bit = 1 F
A=1

22. Debug BRI: Activation :24: BRI: write_sid: scp = 0, wrote = 1B
SID interrupt. status reg = C
23:57:24: BRI: Received activation indication…
23:57:26: BRI: write_sid: scp = 0, wrote = E

23. Debug BRI: T3 Timer Expires
BRI: Starting Power Up timer for unit = 2
BRI: write_sid: wrote 3 for subunit 2, slot 1
BRI: Starting T3 timer after expiry of Power Up timeout for unit = 2, current state is F4
(…)
BRI: write_sid: wrote 92 for subunit 2, slot 1
BRI: write_sid: wrote 93 for subunit 2, slot 1
BRI: T3 timer expired for unit = 2, current state is F2
BRI: write_sid: wrote 1 for subunit 2, slot 1
BRI: write_sid: wrote 0 for subunit 2, slot 1
BRI: Forced interrupt for subunit 2, slot 1 is F
BRI: write_sid: wrote FF for subunit 2, slot 1
BRI: Deactivation for unit = 2, current state is F2
Timer T3 maximum 30 s.

24. SH CONT BRI 0 router#sh cont bri BRI unit 0 D Chan Info:
Layer 1 is Activated
Idb 0x9F6E8, ds 0xA56F8, reset_mask 0x8
buffer size 1524
RX ring with 2 entries at 0x : Rxhead 0
00 pak=0x0AB0A4 ds=0x40CE70 status=D000 pak_size=0
(…)

25. PRI: SH CONT: No Alarms sh cont t1 T1 2/0 is up
Description: Primary Rate Interface to DMS-100
No alarms detected
Framing is ESF, Line Code is B8ZS, Clock Source is Line
Data in current interval (165 seconds elapsed):
0 Line Code Violations, 0 Path Code Violations
0 Slip Secs, 1 Fr Loss Secs, 0 Line Err Secs, 0 Degraded Mins
0 Errored Secs, 0 Bursty Err Secs, 0 Severely Err Secs, 12 Unavail Secs

26. PRI: SH CONT: Alarms sh cont t1 T1 2/1 is down
Transmitter is sending remote alarm
Receiver has loss of signal
Framing is ESF, Line Code is B8ZS, Clock Source is Line
Data in current interval (160 seconds elapsed):
0 Line Code Violations, 0 Path Code Violations
0 Slip Secs, 0 Fr Loss Secs, 0 Line Err Secs, 0 Errored Secs, 0 Bursty Err Secs, 0 Severely Err Secs, 160
Unavail Secs

27. SH ISDN Status router#sh isdn stat
Troubleshooting
Ping remote int
Debug dialer
Sh isdn stat
Layer 1
Layer 2
Layer 3
Debug PPP
Ping remote net
Tune cost
router#sh isdn stat
The current ISDN Switchtype = basic-net3
ISDN BRI0 interface
Layer 1 Status:
Activated
Layer 2 Status:
Layer 2 NOT Activated
Layer 3 Status:
No Active Layer 3 Call(s)
Activated dsl 0 CCBs are 0, Allocated = 0

28. ISDN Protocol Architecture
B-Channel
D-Channel
IP, …
Q.931
Network
Network
PPP
LAPD–Q.921
Data Link
Data Link
I.430 (BRI)–I.431 (PRI)
Physical
Physical

29. Q.921–LAPD TE ET The Data Link Layer
The ISDN network does not impose the use of any data link layer protocol for the B channels
On the D channel the use of Q.921 or LAPD is defined
LAPD: Link Access Procedure on the D channel
Specified in CCITT I.441 and Q.921
Q.921 protocol is used between the TE and the local ISDN switch (not end-to-end)
Q.921–LAPD TE ET
NT1 LT
1174_04F8_c1 29

30. TEI Assignment TE sends ID REQ, switch answers with ID ASSN
AI = 127 asks for any TEI
AI = 64 means TEI 64 is assigned
Reference Indicator (RI) is a random number
RI must match in request and response
ID Request (AI = 127 , RI = 23)
ID Assigned (AI = 64 , RI = 23) TE ET

31. Debug ISDN Q921: TEI Assigned
TEI 64 gets assigned by the switch
TX -> IDREQ ri = ai = 127
RX <- IDASSN ri = ai = 64

32. Debug ISDN Q921: No TEI IDREQ gets retransmitted
Timer T202 (default 2 seconds)
Every IDREQ has a different RI
TX -> IDREQ ri = ai = 127
TX -> IDREQ ri = ai = 127
TX -> IDREQ ri = ai = 127
Could point to the fact that the switch is expecting TEI = 0
In Europe ask point-to-multipoint
In US ask point-to-point

33. Connection Establishment
The TE or the switch send an SABME to establish the data link connection
SABME needs to be acknowledged by an UA
SABME (SAPI=0 , TEI=64) TE ET
UA (SAPI=0 , TEI=64)

34. Debug ISDN Q921: Connection
You need a TEI before you can send an SABME
SAPI=0 means this data link will be used for signaling
TX -> IDREQ ri = ai = 127
RX <- IDASSN ri = ai = 64
TX -> SABMEp sapi = 0 tei = 64
RX <- UAf sapi = 0 tei = 64

35. Information Transfer
Once the data link connection is established, INFO frames can be exchanged
INFO frames get acknowledged by other INFO frames or by RR frames
INFO (SAPI=0 , TEI=64 , N(S)=0 , N(R)=0) TE ET
INFO (SAPI=0 , TEI=64 , N(S)=0 , N(R)=1)
RR (SAPI=0 , TEI=64 , N(R)=1)

36. Debug ISDN Q921: INFO 2656.612 TX -> IDREQ ri = 14613 ai = 127
RX <- IDASSN ri = ai = 64
TX -> SABMEp sapi = 0 tei = 64
RX <- UAf sapi = 0 tei = 64
RX <- INFOc sapi = 0 tei = 64 ns = 0 nr = 0
TX -> RRr sapi = 0 tei = 64 nr = 1
TX -> INFOc sapi = 0 tei = 64 ns = 0 nr = 1

37. Data Link Monitor
If no INFO frames are exchanged, the status of the data link can be checked by the periodic exchange of RR frames
This procedure is optional
RR (SAPI=0 , TEI=64 , N(R)=3) TE ET
RR (SAPI=0 , TEI=64 , N(R)=7)

38. Debug ISDN Q921: RR 180484 RX <- RRp sapi = 0 tei = 80 nr = 5
TX -> RRf sapi = 0 tei = 80 nr = 4
RX <- RRp sapi = 0 tei = 80 nr = 5
TX -> RRf sapi = 0 tei = 80 nr = 4
RX <- RRp sapi = 0 tei = 80 nr = 5
TX -> RRf sapi = 0 tei = 80 nr = 4
RX <- RRp sapi = 0 tei = 80 nr = 5
TX -> RRf sapi = 0 tei = 80 nr = 4

39. Sh ISDN Stat Layer 1 Status: ACTIVE Layer 2 Status:
Troubleshooting
Ping remote int
Debug dialer
Sh isdn stat
Layer 1
Layer 2
Layer 3
Debug PPP
Ping remote net
Tune cost
Layer 1 Status:
ACTIVE
Layer 2 Status:
TEI = 0, State = MULTIPLE_FRAME_ESTABLISHED
Layer 3 Status:
0 Active Layer 3 Call(s)
Activated dsl 0 CCBs = 0

40. ISDN Protocol Architecture
B-Channel
D-Channel
IP, …
Q.931
Network
Network
PPP
LAPD–Q.921
Data Link
Data Link
I.430 (BRI)–I.431 (PRI)
Physical
Physical

41. Q.931 TE ET The Network Layer
The ISDN network does not impose the use of any network link layer protocol for the B channels
On the D channel the use of Q.931 is defined
Q.931 protocol is used between the TE and the local ISDN switch (not end-to-end!)
Inside the ISDN network SS#7 ISUP is used
Q.931 TE ET
NT1 LT
1174_04F8_c1 41

42. ISDN Switch Type Q.931 comes in many local flavors
Use the ISDN switch-type command to specify the correct version of the protocol
basic 1tr6 - ntt
basic-5ess - primary-4ess
basic-dms primary-5ess
basic-net3 - primary-dms100
basic-ni1 - primary-net5
basic-nwnet3 - vn2
basic-nznet3 - vn3
basic-ts013

43. Call Setup
En-bloc sending: the initial set-up message contains all necessary addressing information
Setup
Setup TE ET ET TE
Call Proceeding
Connect
Connect
Connect ACK

44. Debug ISDN Q931: Outgoing Call
TX -> INFOc sapi = 0 tei = 80 ns = 6 nr = 6
SETUP pd = 8 callref = 0x02
Bearer Capability i = 0x8890
Channel ID i = 0x83
Called Party Number i = 0x80, '372756'
RX <- INFOc sapi = 0 tei = 80 ns = 6 nr = 7
CALL_PROC pd = 8 callref = 0x82
Channel ID i = 0x89
RX <- INFOc sapi = 0 tei = 80 ns = 7 nr = 7
CONNECT pd = 8 callref = 0x82

45. Debug ISDN Q93: Incoming Call
RX <- UI sapi = 0 tei = 127
SETUP pd = 8 callref = 0x45
Bearer Capability i = 0x8890
Channel ID i = 0x8A
Calling Party Number i = 0x0083, '372500'
Calling Party SubAddr i = 0x80, 'P2902'
Called Party Number i = 0x
TX -> INFOc sapi = 0 tei = 80 ns = 8 nr = 8
CONNECT pd = 8 callref = 0xC5
RX <- INFOc sapi = 0 tei = 80 ns = 8 nr = 9
CONNECT_ACK pd = 8 callref = 0x45

46. SPIDS Service Profile Identifier
Used to bind a specific terminal to a specific service profile (only on BRI)
SPIDS are assigned by the service provider
SPID is 10 digit telephone number + extra digits
DMS-100 and NI-1 require SPIDS
Do not use SPIDS unless you have to
SPIDS are only used in North America

47. SPIDS: Configuration Isdn spid1 spid-number (ldn)
Assigned by service provider
Usually ten digit telephone number + some extra digits
ldn: local directory number
Optional
Required to receive incoming calls on the second B Channel

48. SPIDS: Configuration Examples
Isdn spid
Isdn spid
Spid-number:
415: area code
555: exchange
8362 and 8370: station ID
01 and 02: terminal identifier
ldn: local directory number

49. SPID Validation SPIDS are validated by the switch
Handshake between TE and local ISDN switch
Valid SPID is acknowledged with Endpoint ID
INFO (SPID = SPID1) TE ET
INFO (ENDPOINT IDENT)
INFO (SPID = SPID2)
INFO (ENDPOINT IDENT)

50. Debug ISDN Q931: Valid SPIDS
TX -> INFORMATION pd = 8 callref = (null)
SPID Information i = 0x
RX <- INFORMATION pd = 8 callref = (null)
ENDPOINT IDent i = 0xF180
TX -> INFORMATION pd = 8 callref = (null)
SPID Information i = 0x
RX <- INFORMATION pd = 8 callref = (null)
ENDPOINT IDent i = 0xF080

51. INFO (Invalid IE Contents) INFO (Invalid IE Contents)
Invalid SPIDS
Rejected by the network
INFO (SPID = SPID1) TE ET
INFO (Invalid IE Contents)
INFO (SPID = SPID2)
INFO (Invalid IE Contents)

52. Debug ISDN Q931: Incorrect SPID
TX -> INFORMATION pd = 8 callref = (null)
SPID Information i = 0x
RX <- INFORMATION pd = 8 callref = (null)
Cause i = 0x82E43A–Invalid IE contents

53. SH ISDN Stat Layer 1 Status: Layer 2 Status: Spid Status:
ACTIVE
Layer 2 Status:
TEI = 88, State = MULTIPLE_FRAME_ESTABLISHED
Spid Status:
TEI 88, ces = 1, state = 6(not initialized)
spid1 configured, no LDN, spid1 sent, spid1 NOT valid
TEI Not Assigned, ces = 2, state = 1(terminal down)
spid2 configured, no LDN, spid2 NOT sent, spid2 NOT valid
Layer 3 Status:
0 Active Layer 3 Call(s)
Activated dsl 1 CCBs = 0

54. Call Refused Call can be refused for various reasons Setup SetupTE ET ET TE
Release
Complete
Release
Complete

55. Debug ISDN Q93: Call Refused
0:03:10: TX -> SETUP pd = 8 callref = 0x01
0:03:10: Bearer Capability i = 0x8890
0:03:10: Channel ID i = 0x83
0:03:10: Called Party Number i = 0x80, ' '
0:03:10: RX <- RELEASE_COMP pd = 8 callref = 0x81
0:03:10: Cause i = 0x Call rejected

56. Call Clearing Any side can clear the call Disconnect DisconnectTE ET ET TE
Release
Release
Release
Complete
Release
Complete

57. Debug ISDN Q931: Call Cleared
RX <- INFOc sapi = 0 tei = 96 ns = 1 nr = 2
DISCONNECT pd = 8 callref = 0x81
Cause i = 0x82D8
Signal i = 0x03
TX -> RRr sapi = 0 tei = 96 nr = 2
received HOST_DISCONNECT_ACK
TX -> INFOc sapi = 0 tei = 96 ns = 2 nr = 2
RELEASE pd = 8 callref = 0x01
Cause i = 0x8090
RX <- RRr sapi = 0 tei = 96 nr = 3
RX <- INFOc sapi = 0 tei = 96 ns = 2 nr = 3
RELEASE_COMP pd = 8 callref = 0x81

58. Show ISDN Status Layer 1 Status: ACTIVE Layer 2 Status:
Troubleshooting
Ping remote int
Debug dialer
Sh isdn stat
Layer 1
Layer 2
Layer 3
Debug PPP
Ping remote net
Tune cost
Layer 1 Status:
ACTIVE
Layer 2 Status:
TEI = 0, State = MULTIPLE_FRAME_ESTABLISHED
Layer 3 Status:
6 Active Layer 3 Call(s)
Activated dsl 0 CCBs = 6
CCB:callid=8020, sapi=0, ces=0, B-chan=22
CCB:callid=8026, sapi=0, ces=0, B-chan=20
CCB:callid=8027, sapi=0, ces=0, B-chan=18
CCB:callid=8029, sapi=0, ces=0, B-chan=23
CCB:callid=A02D, sapi=0, ces=0, B-chan=21
CCB:callid=A030, sapi=0, ces=0, B-chan=19
Total Allocated ISDN CCBs = 6

59. ISDN Protocol Architecture
B-Channel
D-Channel
IP, …
Q.931
Network
Network
PPP
LAPD–Q.921
Data Link
Data Link
I.430 (BRI)–I.431 (PRI)
Physical
Physical

60. Point-to-Point Protocol
Troubleshooting
Ping remote int
Debug dialer
Sh isdn stat
Layer 1
Layer 2
Layer 3
Debug PPP
Ping remote net
Tune cost
PPP: RFC others
Three main components of PPP
Multiprotocol encapsulation
Link Control Protocol (LCP)
Establishing and maintaining the data link
Option negotiation (e.g. use CHAP)
Several Network Control Protocols (NCP)
Establishing and configuring network layer protocols
Protocol specific option negotiation (addresses, …)
IPCP, IPXCP ATCP, …

61. LCP Negotiation Configure-Req proposes certain options
Troubleshooting
Ping remote int
Debug dialer
Sh isdn stat
Debug PPP
LCP
Speed 56/64
Pap/chap
NCP
Ping remote net
Tune cost
Configure-Req proposes certain options
If all options are acceptable, the remote station returns a Configure-ACK
Configure-Req
Configure-ACK

62. LCP Negotiation
In reality all PPP negotiations are double negotiations
Configure-Req
Configure-ACK
Configure-Req
Configure-ACK

63. Debug PPP Packet: LCP ACK
PPP BRI: B-Channel 1: I LCP CONFREQ(1) id 2 (4)
PPP BRI: B-Channel 1: O LCP CONFACK(2) id 2 (4)

64. Debug PPP Negotiation
ppp: sending CONFREQ, type = 3 (CI_AUTHTYPE), value = C023/0
ppp: sending CONFREQ, type = 5 (CI_MAGICNUMBER), value = 8C01B4
ppp: config ACK received, type = 3 (CI_AUTHTYPE), value = C023
ppp: config ACK received, type = 5 (CI_MAGICNUMBER), value = 8C01B4
1174_04F8_c1 64

65. SH INT BRI 0 1 BRI0: B-Channel 1 is up, line protocol is up
Hardware is BRI
MTU 1500 bytes, BW 64 Kbit, DLY usec,
rely 255/255, load 1/255
Encapsulation PPP, loopback not set, keepalive set (10 sec)
lcp state = OPEN
ncp ipcp state = REQSENT ncp osicp state = NOT NEGOTIATED
ncp ipxcp state = NOT NEGOTIATED ncp xnscp state = NOT NEGOTIATED
ncp vinescp state = NOT NEGOTIATED ncp deccp state = NOT NEGOTIATED
ncp bridgecp state = NOT NEGOTIATED ncp atalkcp state = NOT NEGOTIATED
Last input 0:00:00, output 0:00:00, output hang never
Last clearing of "show interface" counters never
Output queue 0/40, 0 drops; input queue 0/75, 0 drops
Five minute input rate 0 bits/sec, 0 packets/sec
Five minute output rate 0 bits/sec, 1 packets/sec
9099 packets input, bytes, 0 no buffer
(…)
Troubleshooting
Ping remote int
Debug dialer
Sh isdn stat
Debug PPP
LCP
Speed 56/64
Pap/chap
NCP
Ping remote net
Tune cost

66. 64 and 56 kbps Inter-switch connections may limit the speed to 56 kbps
Troubleshooting
Ping remote int
Debug dialer
Sh isdn stat
Debug PPP
LCP
Speed 56/64
Pap/chap
NCP
Ping remote net
Tune cost
Inter-switch connections may limit the speed to 56 kbps
The bearer capability can specify that the call is a 56 kbps call that uses V.110 rate adaptation
If the internal signalling protocol in the ISDN network is adapted to ISDN (SS#7 ISUP) this 56 kbps indication will carried up till the remote subscriber
Setup(56)
(56)
Setup(56) TE ET ET TE

67. 64 and 56 kbps
The dialer map allows you to specify the speed for the outgoing call
Dialer map ip speed 56
Default is 64 kbps
Setup(56)
(56)
Setup(56) TE ET ET TE

68. Call Not End-to-End ISDN
Many (international) ISDN connections do not yet use full ISDN signaling in the network
The consequence is that the 56 kbps indication is not passed to the remote switch
Setup(56)
(56)
Setup(64) TE ET ET TE
Not End-to-End ISDN
The receiving side thinks a 64 kbit/s call
The only indication is that the call is not end-to-end isdn. You can configure
isdn not-end-to-end 56

69. Debug ISDN Q931 17993.584 TX -> SETUP pd = 8 callref = 0x02
Troubleshooting
Ping remote int
Debug dialer
Sh isdn stat
Debug PPP
LCP
Speed 56/64
Pap/chap
NCP
Ping remote net
Tune cost
TX -> SETUP pd = 8 callref = 0x02
Bearer Capability i = 0x8890
Channel ID i = 0x83
Called Party Number i = 0x80, ' '
RX <- CALL_PROC pd = 8
callref = 0x82
Channel ID i = 0x89
Locking Shift to Codeset 5
Codeset 5 IE 0x2A i = 0x808E0C, 'OUTSIDE CALL'
RX <- PROGRESS pd = 8 callref = 0x82
Progress Ind i = 0x8A Call not end-to-end ISDN
RX <- CONNECT pd = 8 callref = 0x82
Progress Ind i = 0x Destination address is
non-ISDN

70. PAP and CHAP Authentication protocols
Troubleshooting
Ping remote int
Debug dialer
Sh isdn stat
Debug PPP
LCP
Speed 56/64
Pap/chap
NCP
Ping remote net
Tune cost
Authentication protocols
PAP: Password Authentication Protocol
CHAP: Challenge Handshake Authentication Protocol
CHAP is to be preferred over PAP

71. Configuration CHAP ISDN Router Left Router Right hostname left
username right password cisco
int bri 0
encapsulation ppp
ppp authentication chap
ip add
dialer map ip name right 12345
hostname right
username left password cisco
int bri 0
encapsulation ppp
ppp authentication chap
ip add
dialer map ip name left 54321
Passwords must be identical at both ends
Router name and password are case sensitive
ISDN
Router Left
Router Right
1174_04F8_c1 71

72. Debug PPP CHAP ISDN Event: Connected to 2823680 on B1 at 64 kbps
BRI0: B-Channel 1: PPP AUTH CHAP input code = 1 id = 10 len = 14
BRI0: B-Channel 1: PPP AUTH CHAP input code = 2 id = 16 len = 26
BRI0: B-Channel 1: remote passed CHAP authentication
BRI0: B-Channel 1: PPP AUTH CHAP input code = 3 id = 10 len = 4
BRI0: B-Channel 1: Passed CHAP authentication with remote…
CHAP code fields :
1 Challenge
2 Response
3 Success
4 Failure

73. SH DIALER brussels# sh dial BRI0 - dialer type = ISDN
Dial String Successes Failures Last called Last status
never
0 incoming call(s) have been screened
BRI0: B-Channel 1 - dialer type = ISDN
Rotary group 0, priority = 0
Idle timer (120 secs), Fast idle timer (20 secs)
Wait for carrier (30 secs), Re-enable (15 secs)
Time until disconnect 85 secs
Connected to (dallas)
If sh dialer displays the name of the remote router, it means we passed pap or chap authentication

74. The Prefix Issue Without PAP or CHAP With PAP or CHAP Router Right
54321 Not Yet Connected
Router Left
Router Right
54321
1st Call (from )
2nd Call (to 54321)
54321
12345
With PAP or CHAP
Left
Already Connected
Router Left
Router Right
54321
Call (from )
54321
12345

75. The Prefix Issue PAP/CHAP enable you to know which site is connected
Troubleshooting
Ping remote int
Debug dialer
Sh isdn stat
Debug PPP
LCP
Speed 56/64
Pap/chap
NCP
Ping remote net
Tune cost
PAP/CHAP enable you to know which site is connected
Without PAP or CHAP, this would be based on the ISDN calling number. This is often problematic
Calling number may not been presented
Calling number may be presented with/ without prefixes
The net result is that without PAP or CHAP you would open two half-duplex B channels (instead of one full duplex)

76. NCP Network control protocols
Troubleshooting
Ping remote int
Debug dialer
Sh isdn stat
Debug PPP
LCP
Speed 56/64
Pap/chap
NCP
Ping remote net
Tune cost
Network control protocols
Negotiate and verify network level parameters (address)
Different NCP for the different network protocols (IPCP, IPXCP, …)
NCP Configure-req
NCP Configure-ACK

77. Debug PPP Negotiation
BRI0: B-Channel 1: O IPCP CONFREQ id D (10) Type3 (6)
BRI0: B-Channel 1: I IPCP CONFREQ id C (10) Type3 (6)
BRI0: B-Channel 1: O IPCP CONFACK id C (10) Type3 (6)
BRI0: B-Channel 1: I IPCP CONFACK id D (10) Type3 (6)

78. SH INT BRI 0 1 BRI0: B-Channel 1 is up, line protocol is up
Troubleshooting
Ping remote int
Debug dialer
Sh isdn stat
Debug PPP
LCP
Speed 56/64
Pap/chap
NCP
Ping remote net
Tune cost
BRI0: B-Channel 1 is up, line protocol is up
Hardware is BRI
MTU 1500 bytes, BW 64 Kbit, DLY usec, rely 255/255, load 1/255
Encapsulation PPP, loopback not set, keepalive set (10 sec)
lcp state = OPEN
ncp ipcp state = OPEN ncp osicp state = NOT NEGOTIATED ncp ipxcp state = REQSENT ncp xnscp state = NOT NEGOTIATED
(…)

79. SH INT BRI 0 1 BRI0: B-Channel 1 is up, line protocol is up
Troubleshooting
Ping remote int
Debug dialer
Sh isdn stat
Debug PPP
LCP
Speed 56/64
Pap/chap
NCP
Ping remote net
Tune cost
BRI0: B-Channel 1 is up, line protocol is up
Hardware is BRI
MTU 1500 bytes, BW 64 Kbit, DLY usec, rely 255/255, load 1/255
Encapsulation PPP, loopback not set, keepalive set (10 sec)
lcp state = OPEN
ncp ipcp state = OPEN
(…)

80. ISDN Protocol Architecture
B-Channel
D-Channel
IP, …
Q.931
Network
Network
PPP
LAPD–Q.921
Data Link
Data Link
I.430 (BRI)–I.431 (PRI)
Physical
Physical

81. Ping Remote Networks
Troubleshooting
Ping remote int
Debug dialer
Sh isdn stat
Debug PPP
Ping remote net
Tune cost
ping from
ping from
ISDN
Now that we can ping the remote ISDN interface, we can look at routing issues

82. Static or Dynamic Routes
Static routes are most often used
Dynamic routes risk to bring up the lines all the time
If you use dynamic routes, make sure broadcast updates are forwarded over ISDN
Snapshot routing is best suited dynamic solution
ip route

83. Don’t Wait for the First Bill
Troubleshooting
Ping remote int
Debug dialer
Sh isdn stat
Debug PPP
Ping remote net
Tune cost
ping from
ping from
ISDN

84. Interesting Traffic
Dialer filter triggers call if traffic is interesting
Use sh ISDN history, debug dialer, and the ISDN mib to debug issues
int bri 0
dialer-group 1
access-list 101 deny igrp
access-list 101 permit ip
dialer-list 1
list 101

85. Show ISDN History Router#sh isdn hist
ISDN CALL HISTORY
History Table MaxLength = 100 entries
History Retain Timer = 15 Minutes
Call Calling Called Duration Remote Time until
Type Number Number Seconds Name Disconnect
Out Paris
Out LA
Out Failed
In Orlando
In Active(57) Brussels

86. Debug Dialer router# debug dialer events router# debug dialer packets
Dialing cause: BRI0: ip (s= d= )
router# debug dialer packets
BRI0: ip (s= , d= ), 100 bytes, interesting (ip PERMIT)

87. Troubleshooting ISDN Be systematic Go step by step
Ping remote int
Debug dialer
Sh isdn stat
Layer 1
Layer 2
Layer 3
Debug PPP
LCP
Speed 56/64
Pap/chap
NCP
Ping remote net
Tune cost
Be systematic
Go step by step
Always troubleshoot both ends of the connection

88. 1174_04F8_c1 88