请教：line up protocal down

最甜美微笑

两台路由器，通过传输在不同的地市。
故障是端口起来了但协议down
路由器一配置：
Serial0:4 is up, line protocol is down
  physical layer is E1, baudrate is 128000 bps
  Maximum Transmission Unit is 1500
     Encapsulation is PPP
     LCP reqsent, IPCP initial, IPXCP initial, CCP initial
  5 minutes input rate 0.00 bytes/sec, 0.00 packets/sec
  5 minutes output rate 1.67 bytes/sec, 0.09 packets/sec
  Input queue size/max/drops)
  0/50/0
  Queueing strategy: FIFO
  Output queue: (size/max/drops) 0/75/0
  192865308 packets input,  1542753389 bytes, 0 no buffers
  178266813 packets output, 2009049390 bytes, 0 no buffers
  132104 input errors, 21472 CRC, 83140 frame errors
  0 overrunners, 27492 aborted sequences, 0 input no buffers
  Timeslot(s) Used: 9-10
路由器二配置：
Serial0 is up, line protocol is down
  physical layer is synchronous
  interface is DTE, clock is DTECLK1, cable type is V35
  Internet address is 130.85.9.170  255.255.255.252
     Encapsulation is PPP
     LCP reqsent, IPCP initial, IPXCP initial, CCP initial, BRIDGECP initial
  5 minutes input rate 0.00 bytes/sec, 0.00 packets/sec
  5 minutes output rate 1.67 bytes/sec, 0.09 packets/sec
  Input queue size/max/drops)
  0/75/0
  Queueing strategy: FIFO
  Output Queue size/max/drops)
  0/75/0
  472 packets input,  8544 bytes, 0 no buffers
  37230 packets output, 669900 bytes, 0 no buffers
  1245263309 input errors, 1245248083 CRC, 14871 frame errors
  0 overrunners, 355 aborted sequences, 0 input no buffers
  DCD=UP  DTR=UP  DSR=UP  RTS=UP  CTS=UP

请教前辈要怎么一一查明原因呢？路由器间连接是本来好好的，不知怎么就断了
我的qq：25155405