配置DCN-2655 路由器串口 PPP-PAP时，CTS=DOWN

这是我配置过的，加粗的是和教材上不一样的

RouteA#show int s0/2
Serial0/2 is up, line protocol is down
 Mode=Sync DCE Speed=64000
  DTR=UP,DSR=UP,RTS=UP,CTS=DOWN,DCD=UP
  MTU 1500 bytes, BW 2000 kbit, DLY 2000 usec
  Interface address is 192.168.1.1/24
  Encapsulation PPP, loopback not set
  Keepalive set(10 sec)
  LCP  Starting configuration exchange
  PAP  Closed,  Message: 'none'
  IPCP Listening -- waiting for remote host to attempt open
       local IP address: 192.168.1.1  remote IP address: 0.0.0.0
  60 second input rate 0 bits/sec, 0 packets/sec!
  60 second output rate 0 bits/sec, 0 packets/sec!
    0 packets input, 0 bytes, 8 unused_rx, 0 no buffer
    0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort
    8 packets output, 192 bytes, 0 unused_tx, 0 underruns
  error:
    0 clock, 0 grace
  PowerQUICC SCC specific errors:
    0 recv allocb mblk fail     0 recv no buffer
    0 transmitter queue full    0 transmitter hwqueue_full
    8 tx 31 bk 30 localfr

麻烦，有懂的大佬教一教