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New Member

CTS is down

I have two LANS which I have connected using 2611 and 1601 cisco routers interfaced by codex modems on each end and a 14.4 k data line.My problem is when I ping my serial interfaces, the suceess rate ranges from 40 to 60 % which to me shows something is not ok. When I checked the interface i.e s1/3 statistics on the 2611 router which I am using to connect to the other router I have noted the following on the last line of the interface statistics:

DCD=up DSR=up DTR=up RTS=up CTS=down

I dont know if the loss of the packets is ralated to the CTS being down or I dont know what causes CTS to be down? The rest of the statistics of the interface is as shown dowm.

Serial1/3 is up, line protocol is up

Hardware is CD2430 in sync mode

Description: Connecting xxxxxxxx

Internet address is

MTU 1500 bytes, BW 128 Kbit, DLY 20000 usec, rely 245/255, load 9/255

Encapsulation HDLC, loopback not set, keepalive set (10 sec)

Last input 00:00:00, output 00:00:01, output hang 06:53:34

Last clearing of "show interface" counters never

Input queue: 0/75/0 (size/max/drops); Total output drops: 72

Queueing strategy: weighted fair

Output queue: 0/1000/64/70 (size/max total/threshold/drops)

Conversations 0/13/256 (active/max active/max total)

Reserved Conversations 0/0 (allocated/max allocated)

5 minute input rate 1000 bits/sec, 4 packets/sec

5 minute output rate 4000 bits/sec, 4 packets/sec

41641 packets input, 2363638 bytes, 0 no buffer

Received 14124 broadcasts, 0 runts, 0 giants, 0 throttles

864379 input errors, 535651 CRC, 0 frame, 0 overrun, 0 ignored, 328726 abort

81934 packets output, 20944585 bytes, 0 underruns

0 output errors, 0 collisions, 35651 interface resets

0 output buffer failures, 0 output buffers swapped out

32 carrier transitions

DCD=up DSR=up DTR=up RTS=up CTS=down


New Member

Re: CTS is down

CTS can be configured on the modem to be high, also you should clear the counters on the serial interface and monitor the interface, It does look like the link between the modems is poor. You should also be able to monitor the state of the circuits on the modems by looking at signal to noise ratios, db levels , impluse hits .


Cisco Employee

Re: CTS is down

CTS is the hardware flow control signal used by DCE. CTS will be low if the DCE (modem) buffer overfills. Low CTS is the indication to DTE (router) for not to send data. CTS will be high once modem buffer recovers. So CTS low may not be the problem here in your case.

Looking on the interface stats, i can see that we have many input errors along with CRC errors too. So i think something is wrong on the receiving side which creates those errors. Try changing the modems if possible.

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