有两个命令可以用来调试ISDN连接：debug isdn q921和debug isdn q931。每个命令都是用来调试OSI模型中特定层发生的事务的
Router#debug isdn q921
ISDN Q921 packets debugging is on
Router#
00:01:37: ISDN BR1/0: TX -> RRp sapi = 0 tei = 64 nr = 0
00:01:37: ISDN BR1/0: RX <- RRf sapi = 0 tei = 64 nr = 0
00:01:47: ISDN BR1/0: TX -> RRp sapi = 0 tei = 64 nr = 0
00:01:47: ISDN BR1/0: RX <- RRf sapi = 0 tei = 64 nr = 0
00:01:57: ISDN BR1/0: TX -> RRp sapi = 0 tei = 64 nr = 0
00:01:57: ISDN BR1/0: RX <- RRf sapi = 0 tei = 64 nr = 0
00:02:07: ISDN BR1/0: TX -> RRp sapi = 0 tei = 64 nr = 0
00:02:07: ISDN BR1/0: RX <- RRf sapi = 0 tei = 64 nr = 0
注意每1 0秒钟会进行一次Q.921信息的。这样就使得 器可以确定第2层连接的状态。记住，Q.921只在本地意义重大，它只用来确定 路由器和电话公司的ISDN机之间发生的动作。
Q.931是负责与另一台远程设备进行端对端通信的。
Dix5300#debug isdn q931
ISDN Q931 packets debugging is on
D i x 5 3 0 0 #
04:19:54: ISDN Se0:23: RX <- SETUP pd = 8 callref = 0x1624
0 4 : 1 9 : 5 4 : Bearer Capability i = 0x8090A2
0 4 : 1 9 : 5 4 : Channel ID i = 0xE980830D
0 4 : 1 9 : 5 4 : Calling Party Number i = ‘!’, 0x83,
‘ 9 1 9 3 0 3 3 3 0 4 ’
04:19:54: Called Party Number i = 0xA1, ‘9198390637’
04:19:54: ISDN Se0:23: TX -> CALL_PROC pd = 8 callref = 0x9624
0 4 : 1 9 : 5 4 : Channel ID i = 0xE980830D
04:19:54: ISDN Se0:23: TX -> ALERTING pd = 8 callref = 0x9624
04:19:54: ISDN Se0:23: TX -> CONNECT pd = 8 callref = 0x9624
04:19:54: ISDN Se0:23: RX <- CONNECT_ACK pd = 8 callref = 0x1624
总结
参加BCRAN考试时，要记住debug isdn q921是用来解决Cisco 路由器和电话公司交换机之间的连接故障的，而debug isdn q931是用来解决端对端连接的问题（一个Cisco 路由器到另一个Cisco 路由器），这是非常重要的。
【责编:admin】
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