Equipment Needed
The following equipment is needed to perform this lab exercise:
Two Cisco routers, one of which must have a BRI interface and the other must have a PRI interface
•
One ISDN PRI circuit and one ISDN BRI circuit
•
Cisco IOS 11.2 or higher
•
A PC running a terminal emulation program for console port connection on the routers
•
Configuration Overview
This configuration will demonstrate a BRI connected router calling into a PRI connected router. PRI connected routers are used for large−scale access servers. A typical topology is to have multiple spoke sites that are BRI connected dialing into a PRI−enabled hub router.
The two routers are connected as shown in Figure 3−17. RouterA and RouterB are connected to an Adtran Atlas 800 ISDN switch.
Figure 3−17: ISDN BRI to ISDN PRI
A PC running a terminal emulation program should be connected to the console port of one of the routers using a Cisco rolled cable.
Note A PRI is different from a BRI. A PRI is carried on a T1 circuit and consists of 23 B channels, each carrying 56K or 64K of user traffic. A PRI has a 64K D channel used for signaling between the user device and the ISDN switch. A BRI consists of two B channels, each carrying 56K or 64K of user traffic. A BRI has a 16K D channel used for signaling between the user device and the ISDN switch.
Note A PRI ISDN circuit does not have a SPID associated with each B channel.
ISDN Switch Setup
If you do not have access to actual ISDN circuits, you can use an ISDN desktop switch. Information on configuring an ISDN desktop switch can be found in the ISDN switch configuration section earlier in this chapter.
Router Configuration
The configurations for the two routers in this example are as follows. ISDN commands are highlighted in bold.
RouterA
RouterA#show run
Building configuration...
Current configuration:
!
version 11.2
no service udp−small−servers
no service tcp−small−servers
isdn switch−type basic−ni1 ← Set D channel call control
!
interface BRI0/0
ip address 196.1.1.1 255.255.255.0 encapsulation ppp
isdn spid1 8995101 5101 ← Set SPID value for both B channels isdn spid2 8995102 5102
dialer idle−timeout 30 ← Define how many seconds to disconnect after last interesting packet
dialer map ip 196.1.1.7 name RouterB broadcast 8991000 ← Associate next hop address with a dial string
dialer load−threshold 1 ← Define threshold to add additional B channels dialer−group 1 ← Associate interface with dialer−list 1
no fair−queue
ppp authentication chap
ppp multilink ← Request a PPP multilink session
!
no ip classless
dialer−list 1 protocol ip permit ← Define interesting traffic
!
isdn switch−type primary−5ess ← Set D channel call control for the PRI
!
controller T1 0
framing esf ← Set T1 Extended Superframe Framing linecode b8zs ← Set T1 line coding
pri−group timeslots 1−24 ← Define entire T1 to belong to the PRI
!
interface Serial0:23 ← D channel of the PRI ip address 196.1.1.7 255.255.255.0
encapsulation ppp no ip mroute−cache
isdn incoming−voice modem
dialer idle−timeout 900 ← Set the interesting traffic timeout dialer−group 1 ← Associate the interface with dialer−list 1 no fair−queue
no cdp enable
ppp authentication chap ppp multilink
!
interface Dialer1 no ip address encapsulation ppp dialer in−band
dialer idle−timeout 900 dialer−group 1
no fair−queue
ppp authentication chap
!
no ip classless
ip route 192.1.5.0 255.255.255.0 196.1.1.1
dialer−list 1 protocol ip permit ← Define interesting traffic
!
line con 0
exec−timeout 60 0 password cisco login
line aux 0 line vty 0 4 login
! end
Notice that the configuration for the PRI interface on RouterB is quite different from a BRI configuration.
When configuring a PRI, you must first define a T1 controller interface and specify the proper T1 framing and line coding. The PRI gets configured as a serial interface:23, specifying the D channel of the PRI interface.
Monitoring and Testing the Configuration
Let's start by connecting to RouterA and verifying that the BRI circuit is up and active. Type the show isdn status command to display the status of the ISDN interface. We see that a SPID has been sent for both B channels to the ISDN switch and has been validated. We also see under the layer 3 status that there are no active calls on the router at this time.
RouterA#show isdn status
The current ISDN Switchtype = basic−ni1 ISDN BRI0/0 interface
Layer 1 Status:
ACTIVE
Layer 2 Status:
TEI = 64, State = MULTIPLE_FRAME_ESTABLISHED TEI = 65, State = MULTIPLE_FRAME_ESTABLISHED Spid Status:
TEI 64, ces = 1, state = 5(init)
spid1 configured, spid1 sent, spid1 valid ← B channel #1 Endpoint ID Info: epsf = 0, usid = B, tid = 1
TEI 65, ces = 2, state = 5(init)
spid2 configured, spid2 sent, spid2 valid ← B channel #2 Endpoint ID Info: epsf = 0, usid = C, tid = 1
Layer 3 Status:
0 Active Layer 3 Call(s) ← No active calls Activated dsl 0 CCBs = 2
CCB:callid=0, sapi=0, ces=1, B−chan=0 CCB:callid=0, sapi=0, ces=1, B−chan=0 Total Allocated ISDN CCBs = 2
The status of the D channel of the BRI circuit can be displayed by typing show interface bri 0/0. We see that the interface is in an up/up (spoofing) state, which indicates that the D channel is active.
RouterA#show interface bri 0/0
BRI0/0 is up, line protocol is up (spoofing) ← D channel of BRI
Hardware is QUICC BRI with U interface Internet address is 196.1.1.1/24
MTU 1500 bytes, BW 64 Kbit, DLY 20000 usec, rely 255/255, load 1/255 Encapsulation PPP, loopback not set
. .
We see from the show dialer command that the BRI interface will dial 8991000 to place its calls. The idle timer is set to 30 seconds. This value is set by the dialer idle−timeout 30 statement in the configuration for RouterA. It tells the router to disconnect a call 30 seconds after the last interesting packet has been received.
RouterA#show dialer
BRI0/0 − dialer type = ISDN
Dial String Successes Failures Last called Last status 8991000 5 0 00:07:48 successful 0 incoming call(s) have been screened.
BRI0/0:1 − dialer type = ISDN
Idle timer (30 secs), Fast idle timer (20 secs) Wait for carrier (30 secs), Re−enable (15 secs) Dialer state is idle
BRI0/0:2 − dialer type = ISDN
Idle timer (30 secs), Fast idle timer (20 secs) Wait for carrier (30 secs), Re−enable (15 secs) Dialer state is idle
Now let's connect to RouterB and view some PRI statistics. We will see that monitoring a PRI ISDN circuit is slightly different than monitoring a BRI circuit. Type the show isdn status command. We see that although there are 23 B channels, we will only get one Multiple_Frame_Established message. We also see that there are no indications of valid SPIDs being sent. This is because an ISDN PRI circuit does not have any SPIDs associated with it.
RouterB#show isdn status
The current ISDN Switchtype = primary−5ess ISDN Serial0:23 interface
Layer 1 Status:
ACTIVE Layer 2 Status:
TEI = 0, State = MULTIPLE_FRAME_ESTABLISHED Layer 3 Status:
0 Active Layer 3 Call(s) ← No active calls at this time Activated dsl 0 CCBs = 0
Total Allocated ISDN CCBs = 0
A PRI ISDN interface has an additional monitoring command. Type the show isdn service command. This command displays the B channel status of the entire PRI circuit. The state line shows which channels are currently connected, while the channel line shows which channels can accept or make a call. Possible states are:
• Idle
• Busy Reserved
• Restart
• Maint
•
We see that each B channel is in an idle state (State=0). The last eight channels are in a state of 3, which is reserved. These channels are used for an E1 PRI, which is the European counterpart to a T1. An E1 PRI has 31 B channels as opposed to the T1, which only has 23.
RouterB#show isdn service PRI Channel Statistics:
ISDN Se0:23, Channel (1−31) Activated dsl 0
State (0=Idle 1=Propose 2=Busy 3=Reserved 4=Restart 5=Maint) 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 3 3 3 3 3 3 3 3 Channel (1−31) Service (0=Inservice 1=Maint 2=Outofservice) 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
To display the status of the D channel of the PRI, use the show interfaces 0:23 command. The s 0 corresponds to the controller T1 0 command in the configuration for RouterB.
RouterB#show interface s 0:23
Serial0:23 is up, line protocol is up (spoofing) ← D channel of PRI Hardware is DSX1 ← T1 interface
Internet address is 196.1.1.7/24
MTU 1500 bytes, BW 64 Kbit, DLY 20000 usec, rely 255/255, load 1/255 Encapsulation PPP, loopback not set
Last input 00:00:08, output 00:00:08, output hang never Last clearing of "show interface" counters never
Queueing strategy: fifo
Output queue 0/40, 0 drops; input queue 0/75, 0 drops 5 minute input rate 0 bits/sec, 0 packets/sec
5 minute output rate 0 bits/sec, 0 packets/sec 1284 packets input, 5949 bytes, 0 no buffer
Received 0 broadcasts, 0 runts, 0 giants, 0 throttles
0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort 1285 packets output, 5541 bytes, 0 underruns
0 output errors, 0 collisions, 5 interface resets 0 output buffer failures, 0 output buffers swapped out 1 carrier transitions
Timeslot(s) Used:24, Transmitter delay is 0 flags
The show dialer command will display the status of the dialer on the router. We notice some differences from how this command looks when used on a BRI interface. When used on a PRI, the command will display the status of each of the 23 B channels.
RouterB#show dialer
Dialer1 − dialer type = IN−BAND SYNC NO−PARITY Idle timer (900 secs), Fast idle timer (20 secs) Wait for carrier (30 secs), Re−enable (15 secs)
Dial String Successes Failures Last called Last status
Serial0:0 − dialer type = ISDN
Idle timer (900 secs), Fast idle timer (20 secs) Wait for carrier (30 secs), Re−enable (15 secs) Dialer state is idle
Serial0:1 − dialer type = ISDN
Idle timer (900 secs), Fast idle timer (20 secs) Wait for carrier (30 secs), Re−enable (15 secs) Dialer state is idle
. . . . .
Serial0:22 − dialer type = ISDN
Idle timer (900 secs), Fast idle timer (20 secs) Wait for carrier (30 secs), Re−enable (15 secs) Dialer state is idle
Serial0:23 − dialer type = ISDN
Dial String Successes Failures Last called Last status 0 incoming call(s) have been screened.
Turn on PPP authentication and ISDN Q931 call control debugging with the debug ppp authen command and the debug isdn q931 command. The status of what debug commands are active can be displayed by typing the show debug command. Remember to use the term mon command to display the debug output if you are not connected to the console port of the router.
RouterA#show debug PPP:
PPP authentication debugging is on ISDN:
ISDN Q931 packets debugging is on
Now let's try to ping RouterB at IP address 196.1.1.7. We see that an ISDN call is made as soon as we start our ping.
RouterA#ping 196.1.1.7
Type escape sequence to abort.
Sending 5, 100−byte ICMP Echos to 196.1.1.7, timeout is 2 seconds:
ISDN BR0/0: TX −> SETUP pd = 8 callref = 0x06 ← B channel #1 Bearer Capability I = 0x8890
Channel ID I = 0x83
Keypad Facility I = '98991000'
ISDN BR0/0: RX <− SETUP_ACK pd = 8 callref = 0x86 Channel ID I = 0x89.
ISDN BR0/0: RX <− CALL_PROC pd = 8 callref = 0x86 ISDN BR0/0: RX <− CONNECT pd = 8 callref = 0x86 Signal I = 0x3F − Tones off
%LINK−3−UPDOWN: Interface BRI0/0:1, changed state to up PPP BRI0/0:1: treating connection as a callout
ISDN BR0/0: TX −> CONNECT_ACK pd = 8 callref = 0x06
PPP BRI0/0:1: Send CHAP Challenge id=5 ← Chap successful on B channel #1 PPP BRI0/0:1: CHAP Challenge id=6 received from RouterB
PPP BRI0/0:1: Send CHAP Response id=6
PPP BRI0/0:1: Passed CHAP authentication with remote PPP BRI0/0:1: CHAP response received from RouterB PPP BRI0/0:1: CHAP Response id=5 received from RouterB PPP BRI0/0:1: Send CHAP Success id=5
PPP BRI0/0:1: remote passed CHAP authentication.
%LINK−3−UPDOWN: Interface Virtual−Access1, changed state to up PPP Virtual−Access1: treating connection as a callin
%LINEPROTO−5−UPDOWN: Line protocol on Interface BRI0/0:1, changed state to up
%LINEPROTO−5−UPDOWN: Line protocol on Interface Virtual−Access1, changed state to up ISDN BR0/0: TX −> SETUP pd = 8 callref = 0x07 ← B channel #2
Bearer Capability I = 0x8890 Channel ID I = 0x83
Keypad Facility I = '98991000'
ISDN BR0/0: RX <− SETUP_ACK pd = 8 callref = 0x87 Channel ID I = 0x8A
ISDN BR0/0: Event: incoming ces value = 2
%ISDN−6−CONNECT: Interface BRI0/0:1 is now connected to 98991000 RouterB ISDN BR0/0: RX <− CALL_PROC pd = 8 callref = 0x87
ISDN BR0/0: Event: incoming ces value = 2
ISDN BR0/0: RX <− CONNECT pd = 8 callref = 0x87 Signal I = 0x3F − Tones off
ISDN BR0/0: Event: incoming ces value = 2
%LINK−3−UPDOWN: Interface BRI0/0:2, changed state to up PPP BRI0/0:2: treating connection as a callout
ISDN BR0/0: TX −> CONNECT_ACK pd = 8 callref = 0x07 PPP BRI0/0:2: Send CHAP Challenge id=2
PPP BRI0/0:2: CHAP Challenge id=3 received from RouterB PPP BRI0/0:2: Send CHAP Response id=3
PPP BRI0/0:2: Passed CHAP authentication with remote PPP BRI0/0:2: CHAP response received from RouterB PPP BRI0/0:2: CHAP Response id=2 received from RouterB
PPP BRI0/0:2: Send CHAP Success id=2 ← Chap successful on B channel #1 PPP BRI0/0:2: remote passed CHAP authentication.
%LINEPROTO−5−UPDOWN: Line protocol on Interface BRI0/0:2, changed state to up
%ISDN−6−CONNECT: Interface BRI0/0:2 is now connected to 98991000 RouterB
..!!!
Success rate is 60 percent (3/5), round−trip min/avg/max = 32/32/32 ms RouterA#
Notice that the first two pings were not successful. This is because the router was still in the process of establishing the ISDN call. Another ping to 196.1.1.7 would be 100−percent successful.
Let's verify that we have an MLPPP bundle between RouterA and RouterB. Type the show ppp multilink command to view the status of the MLPPP Link. We see that there are two B channels in the MLPPP bundle.
These are the two B channels of the BRI.
RouterA#show ppp multi
Bundle RouterB, 2 members, Master link is Virtual−Access1 Dialer Interface is BRI0/0
0 lost fragments, 0 reordered, 0 unassigned, sequence 0xA/0xA rcvd/sent 0 discarded, 0 lost received, 1/255 load
Member Links: 2 ← B channel #1 and B channel #2 BRI0/0:1
BRI0/0:2
The show isdn status command can also be used to verify that we have two active calls on the router.
RouterA#show isdn status
The current ISDN Switchtype = basic−ni1 ISDN BRI0/0 interface
Layer 1 Status:
ACTIVE
Layer 2 Status:
TEI = 64, State = MULTIPLE_FRAME_ESTABLISHED TEI = 65, State = MULTIPLE_FRAME_ESTABLISHED Spid Status:
TEI 64, ces = 1, state = 5(init)
spid1 configured, spid1 sent, spid1 valid Endpoint ID Info: epsf = 0, usid = B, tid = 1 TEI 65, ces = 2, state = 5(init)
spid2 configured, spid2 sent, spid2 valid Endpoint ID Info: epsf = 0, usid = C, tid = 1 Layer 3 Status:
2 Active Layer 3 Call(s) ← Active call on both B channels Activated dsl 0 CCBs = 4
CCB:callid=0, sapi=0, ces=1, B−chan=0 CCB:callid=0, sapi=0, ces=1, B−chan=0 CCB:callid=8006, sapi=0, ces=1, B−chan=1 CCB:callid=8007, sapi=0, ces=2, B−chan=2 Total Allocated ISDN CCBs = 4
After the idle timeout period of 30 seconds, RouterA will disconnect the ISDN call. This period is defined by the dialer idle−timeout 30 statement on RouterA's configuration.
%LINEPROTO−5−UPDOWN: Line protocol on Interface Virtual−Access1, changed state to down
%LINK−3−UPDOWN: Interface Virtual−Access1, changed state to down
%ISDN−6−DISCONNECT: Interface BRI0/0:1 disconnected from 98991000 RouterB, call lasted 55 seconds
%ISDN−6−DISCONNECT: Interface BRI0/0:2 disconnected from 98991000 RouterB, call lasted 51 seconds
ISDN BR0/0: TX −> DISCONNECT pd = 8 callref = 0x06 ← RouterA sends a
disconnect to the ISDN switch for B channel #1
Cause i = 0x8090 − Normal call clearing
ISDN BR0/0: TX −> DISCONNECT pd = 8 callref = 0x07 ← RouterA sends a
disconnect to the ISDN switch for B channel #2 Cause i = 0x8090 − Normal call clearing
ISDN BR0/0: RX <− RELEASE pd = 8 callref = 0x86
%LINK−3−UPDOWN: Interface BRI0/0:1, changed state to down ISDN BR0/0: TX −> RELEASE_COMP pd = 8 callref = 0x06 ISDN BR0/0: RX <− RELEASE pd = 8 callref = 0x87 ISDN BR0/0: Event: incoming ces value = 2
%LINK−3−UPDOWN: Interface BRI0/0:2, changed state to down ISDN BR0/0: TX −> RELEASE_COMP pd = 8 callref = 0x07
%LINEPROTO−5−UPDOWN: Line protocol on Interface BRI0/0:1, changed state to down
%LINEPROTO−5−UPDOWN: Line protocol on Interface BRI0/0:2, changed state to down
Now let's connect to RouterB and see what an incoming call looks like on the ISDN PRI interface. You can either attach a second terminal to RouterB so that you can place a call on RouterA with a ping and monitor RouterB at the same time or you can log the terminal output on RouterB to a log file.
Make sure that PPP authentication and ISDN Q931 call control debugging are enabled on RouterB by typing the debug ppp authen and debug isdn q931 commands. You can verify what debug commands are enabled on the router by typing the show debug command. Remember to use the term mon command to display the debug output if you are not connected to the console port of the router.
RouterB#show debug PPP:
PPP authentication debugging is on ISDN:
ISDN Q931 packets debugging is on
The following is a trace on RouterB while a call is coming in from RouterA.
The D channel of the PRI is referenced as Se0:23
↓<ΛΙΝΕ/>ISDN Se0:23: RX <− SETUP pd = 8 callref = 0x0C Bearer Capability i = 0x8890
Channel ID i = 0xA98393
Calling Party Number i = '!', 0x80, '8995201' ← Calling number Called Party Number i = 0xA1, '8991000' ← Called number
The first call that comes into the PRI connects to channel 18
↓
%LINK−3−UPDOWN: Interface Serial0:18, changed state to up Se0:18 PPP: Treating connection as a callin
ISDN Se0:23: TX −> CALL_PROC pd = 8 callref = 0x800C Channel ID i = 0xA98393
ISDN Se0:23: TX −> CONNECT pd = 8 callref = 0x800C Channel ID i = 0xA98393
ISDN Se0:23: RX <− CONNECT_ACK pd = 8 callref = 0x0C Se0:18 PPP: Phase is AUTHENTICATING, by both
Se0:18 CHAP: O CHALLENGE id 7 len 29 from "RouterB"
Se0:18 CHAP: I CHALLENGE id 6 len 28 from "RouterA"
Se0:18 CHAP: Waiting for peer to authenticate first Se0:18 CHAP: I RESPONSE id 7 len 28 from "RouterA"
Se0:18 CHAP: O SUCCESS id 7 len 4
Se0:18 CHAP: Processing saved Challenge, id 6
Se0:18 CHAP: O RESPONSE id 6 len 29 from "RouterB"
Se0:18 CHAP: I SUCCESS id 6 len 4
%LINK−3−UPDOWN: Interface Virtual−Access1, changed state to up Vi1 PPP: Treating connection as a callin
%LINEPROTO−5−UPDOWN: Line protocol on Interface Serial0:18, changed state to up
%LINEPROTO−5−UPDOWN: Line protocol on Interface Virtual−Access1, changed state to up
ISDN Se0:23: RX <− SETUP pd = 8 callref = 0x35 Bearer Capability i = 0x8890
Channel ID i = 0xA98394
Calling Party Number i = '!', 0x80, '8995201' Called Party Number i = 0xA1, '8991000'
The second call that comes into the PRI connects to channel 19
↓
%LINK−3−UPDOWN: Interface Serial0:19, changed state to up Se0:19 PPP: Treating connection as a callin
ISDN Se0:23: TX −> CALL_PROC pd = 8 callref = 0x8035 Channel ID i = 0xA98394
ISDN Se0:23: TX −> CONNECT pd = 8 callref = 0x8035 Channel ID i = 0xA98394
ISDN Se0:23: RX <− CONNECT_ACK pd = 8 callref = 0x35 Se0:19 PPP: Phase is AUTHENTICATING, by both
Se0:19 CHAP: O CHALLENGE id 4 len 29 from "RouterB"
Se0:19 CHAP: I CHALLENGE id 3 len 28 from "RouterA"
Se0:19 CHAP: Waiting for peer to authenticate first Se0:19 CHAP: I RESPONSE id 4 len 28 from "RouterA"
Se0:19 CHAP: O SUCCESS id 4 len 4
Se0:19 CHAP: Processing saved Challenge, id 3 Se0:19 CHAP: O RESPONSE id 3 len 29 from "RouterB"
Se0:19 CHAP: I SUCCESS id 3 len 4
%LINEPROTO−5−UPDOWN: Line protocol on Interface Serial0:19, changed state to up
%ISDN−6−CONNECT: Interface Serial0:19 is now connected to 9148993601 RouterA
The show ppp multilink command on RouterB will reveal that two B channels are active in an MLPPP bundle.
RouterB#show ppp multi
Bundle RouterA, 2 members, Master link is Virtual−Access1 Dialer Interface is Serial0:23
0 lost fragments, 0 reordered, 0 unassigned, sequence 0x0/0x0 rcvd/sent 0 discarded, 0 lost received, 1/255 load
Member Links: 2 Serial0:18 Serial0:19
Type the show dialer maps command to view the dynamic dialer map that gets created when RouterA dials into RouterB.
RouterB#show dialer maps
Dynamic dialer map ip 196.1.1.1 name RouterA () on Serial0:23
The show isdn service command shows us that there are two active B channels on the PRI. The active channels are denoted by a 2 in the appropriate channel position of the PRI.
RouterB#show isdn service PRI Channel Statistics:
ISDN Se0:23, Channel (1−31) Activated dsl 0
State (0=Idle 1=Propose 2=Busy 3=Reserved 4=Restart 5=Maint) 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 2 2 0 0 0 3 3 3 3 3 3 3 3 Channel (1−31) Service (0=Inservice 1=Maint 2=Outofservice) 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
When the call disconnects on the PRI, we see that channels 18 and 19 receive a disconnect message from the ISDN switch. Remember that the far−end router (RouterA) is disconnecting the call so RouterB will receive a Disconnect message from the network.
%LINK−3−UPDOWN: Interface Virtual−Access1, changed state to down
ISDN Se0:23: RX <− DISCONNECT pd = 8 callref = 0x0C ← Disconnect for Channel 18
Cause i = 0x8090 − Normal call clearing
%ISDN−6−DISCONNECT: Interface Serial0:18 disconnected from 9148993601 RouterA, call lasted 32 seconds
%LINK−3−UPDOWN: Interface Serial0:18, changed state to down ISDN Se0:23: TX −> RELEASE pd = 8 callref = 0x800C
ISDN Se0:23: RX <− DISCONNECT pd = 8 callref = 0x35 ← Disconnect for Channel 19 Cause i = 0x8090 − Normal call clearing
%ISDN−6−DISCONNECT: Interface Serial0:19 disconnected from 9148993601 RouterA, call lasted 27 seconds
%LINK−3−UPDOWN: Interface Serial0:19, changed state to down ISDN Se0:23: TX −> RELEASE pd = 8 callref = 0x8035
ISDN Se0:23: RX <− RELEASE_COMP pd = 8 callref = 0x0C ISDN Se0:23: RX <− RELEASE_COMP pd = 8 callref = 0x35
%LINEPROTO−5−UPDOWN: Line protocol on Interface Serial0:18, changed state to down
%LINEPROTO−5−UPDOWN: Line protocol on Interface Serial0:18, changed state to down