1.综合数字业务网（ISDN）
综合数字业务网（ISDN）由数字电话和数据传输服务两部分组成，一般由电话局提供这种服务。ISDN的基本速率接口（BRI）服务提供2个B信道和1个D信道（2B+D）。BRI的B信道速率为64Kbps,用于传输用户数据。D信道的速率为16Kbps，主要传输控制信号。在北美和日本，ISDN的主速率接口（PRI）提供23个B信道和1个D信道，总速率可达1.544Mbps，其中D信道速率为64Kbps。而在欧洲、澳大利亚等国家，ISDN的PRI提供30个B信道和1个64Kbps D信道，总速率可达2.048Mbps。我国电话局所提供ISDN PRI为30B+D。
2.基本命令
注：1.交换机类型如下表,国内交换机一般为basic-net3。
3.ISDN实现DDR（dial-on-demand routing）实例:
设置如下：
Router1:
hostname router1
user router2 passWord cisco
!
isdn switch-type basic-net3
!
interface bri 0
ip address 192.200.10.1 255.255.255.0
encapsulation ppp
dialer map ip 192.200.10.2 name router2 572
dialer load-threshold 80
ppp multilink
dialer-group 1
ppp authentication chap
！
dialer-list 1 protocol ip permit
!
Router2:
hostname router2
user router1 password cisco
!
isdn switch-type basic-net3
!
interface bri 0
ip address 192.200.10.2 255.255.255.0
encapsulation ppp
dialer map ip 192.200.10.1 name router1 571
dialer load-threshold 80
ppp multilink
dialer-group 1
ppp authentication chap
！
dialer-list 1 protocol ip permit
!
Cisco路由器同时支持回拨功能，我们将路由器Router1作为Callback Server,Router2作为Callback Client。
与回拨相关命令:
设置如下：
Router1:
hostname router1
user router2 password cisco
!
isdn switch-type basic-net3
!
interface bri 0
ip address 192.200.10.1 255.255.255.0
encapsulation ppp
dialer map ip 192.200.10.2 name router2 class s3 572
dialer load-threshold 80
ppp callback accept
ppp multilink
dialer-group 1
ppp authentication chap
！
map-class dialer s3
dialer callback-server username
dialer-list 1 protocol ip permit
!
Router2:
hostname router2
user router1 password cisco
!
isdn switch-type basic-net3
!
interface bri 0
ip address 192.200.10.2 255.255.255.0
encapsulation ppp
dialer map ip 192.200.10.1 name router1 571
dialer load-threshold 80
ppp callback request
ppp multilink
dialer-group 1
ppp authentication chap
！
dialer-list 1 protocol ip permit
!
相关调试命令：
debug dialer
debug isdn event
debug isdn q921
debug isdn q931
debug ppp authentication
debug ppp error
debug ppp negotiation
debug ppp packet
show dialer
show isdn status
举例:执行debug dialer命令观察router2呼叫router1,router1回拨router2的过程.
router1#debug dialer
router2#ping 192.200.10.1
router1#
00:03:50: %LINK-3-UPDOWN: Interface BRI0:1, changed state to up
00:03:50: BRI0:1:PPP callback Callback server starting to router2 572
00:03:50: BRI0:1: disconnecting call
00:03:50: %LINK-3-UPDOWN: Interface BRI0:1, changed state to down
00:03:50: BRI0:1: disconnecting call
00:03:50: BRI0:1: disconnecting call
00:03:51: %LINK-3-UPDOWN: Interface BRI0:2, changed state to up
00:03:52: callback to router2 already started
00:03:52: BRI0:2: disconnecting call
00:03:52: %LINK-3-UPDOWN: Interface BRI0:2, changed state to down
00:03:52: BRI0:2: disconnecting call
00:03:52: BRI0:2: disconnecting call
00:04:05: : Callback timer eXPired
00:04:05: BRI0:beginning callback to router2 572
00:04:05: BRI0: Attempting to dial 572
00:04:05: Freeing callback to router2 572
00:04:05: %LINK-3-UPDOWN: Interface BRI0:1, changed state to up
00:04:05: BRI0:1: No callback negotiated
00:04:05: %LINK-3-UPDOWN: Interface Virtual-access1, changed state to up
00:04:05: dialer Protocol up for Vi1
00:04:06: %LINEPROTO-5-UPDOWN: Line protocol on Interface BRI0:1, changed state
to up
00:04:06: %LINEPROTO-5-UPDOWN: Line protocol on Interface Virtual-Access1, chang
ed state to up
00:04:11: %ISDN-6-CONNECT: Interface BRI0:1 is now connected to 572
#router1
4.ISDN访问首都在线263网实例:
本地局部网地址为10.0.0.0/24,属于保留地址，通过NAT地址翻译功能，局域网用户可以通过ISDN上263网访问Internet。263的ISDN电话号码为2633，用户为263，口令为263，所涉及的命令如下表：
具体配置如下：
hostname Cisco2503
!
isdn switch-type basic-net3
!
ip subnet-zero
no ip domain-lookup
ip routing
!
interface Ethernet 0
ip address 10.0.0.1 255.255.255.0
ip nat inside
no shutdown
!
interface Serial 0
shutdown
no description
no ip address
!
interface Serial 1
shutdown
no description
no ip address
!
interface bri 0
ip address negotiated
ip nat outside
encapsulation ppp
ppp authentication pap callin
ppp multilink
dialer-group 1
dialer hold-queue 10
dialer string 2633
dialer idle-timeout 120
ppp pap sent-username 263 password 263
no cdp enable
no ip split-horizon
no shutdown
!
ip classless
!
! Static Routes
!
ip route 0.0.0.0 0.0.0.0 bri 0
!
! Access Control List 2
!
access-list 2 permit any
!
dialer-list 1 protocol ip permit
!
! Dynamic NAT
!
ip nat inside source list 2 interface bri 0 overload
snmp-server community public ro
!
line console 0
exec-timeout 0 0
!
line vty 0 4
!
end
5.Cisco765M通过ISDN拨号上263
由于Cisco765的设置命令与我们常用的Cisco路由器的命令不同，所以以下列举了通过Cisco765上263访问Internet的具体命令行设置步骤。
set system c765
c765 set multidestination on
c765 set switch net3
c765 set ppp multilink on
c765 cd lan
c765:LAN set ip routing on
c765:LAN set ip address 10.0.0.1
c765:LAN set ip netmask 255.0.0.0
c765:LAN set briding off
c765:LANcd
c765 set user remotenet
New user remotenet being created
c765:remotenet set ip routing on
c765:remotenet set bridging off
c765:remotenet set ip framing none
c765:remotenet set ppp clientname 263
c765:remotenet set ppp password client
Enter new Password: 263
Re-Type new Password: 263
c765:remotenet set ppp authentication out none
c765:remotenet set ip address 0.0.0.0
c765:remotenet set ip netmask 0.0.0.0
c765:remotenet set ppp address negotiation local on
c765:remotenet set ip pat on
c765:remotenet set ip route destination 0.0.0.0/0 gateway 0.0.0.0
c765:remotenet set number 2633
c765:remotenet set active
命令描述如下：