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carrier transition

Regular Advisor

carrier transition

Hi All,
#sh int s0

Serial0 is up, line protocol is up
Hardware is MCI Serial
Internet address is, subnet mask is
MTU 1500 bytes, BW 1544 Kbit, DLY 20000 usec, rely 255/255, load 1/255
Encapsulation ATM-DXI, loopback not set, keepalive not set
Last input 0:00:02, output 0:00:01, output hang never
Last clearing of "show interface" counters never
Output queue 0/40, 0 drops; input queue 0/75, 0 drops
5 minute input rate 0 bits/sec, 0 packets/sec
5 minute output rate 1000 bits/sec, 0 packets/sec
15246 packets input, 14468957 bytes, 0 no buffer
Received 0 broadcasts, 0 runts, 0 giants
0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort
15313 packets output, 14445489 bytes, 0 underruns
0 output errors, 0 collisions, 4 interface resets, 0 restarts
1 carrier transitions RTS up, CTS down, DTR up, DSR down

question: what does cts down, rts up, dtr up, dsr down and dcd means?
2. 0 carrier transition vs 1 carrier transition vs 47 carrier transition-what is the difference between these?
Ron Kinner
Honored Contributor

Re: carrier transition

cts down, rts up, dtr up, dsr down and dcd?

CTS is Clear To Send
RTS is Ready To Send
DTR is Data Set Ready
DSR is Data Set Ready
DCD is Data Carrier Detected

All should be up in order to send and receive data. The two you have UP are the local indicators (your serial port is ready to work). The two that are Down are indicators that the link is down. Check your CSU/DSU to see if it has an error. It will drop the CTS and DSR lines if it loses the network connection. You probably need to call in a ticket to your circuit provider unless this is a local back to back connection that you are playing with.

You have turned off Keepalive (normally set to 10) which makes it look like the circuit is Up. Normally you would be seeing Serial0 is Down, line protocol is Down or on some routers Serial0 is up, line protocol is Down.

Keepalive should be On on both sides and set to the same value (usually 10 seconds) so that the card will know that the circuit is still alive. (The two ends of a serial circuit will normally send each other a message called a keepalive where one end says something like: this message is number 10 and I expect to see number 359 from you next time. The other end should reply with this message is 359 and I expect to see number 11 from you next time. If 3 times the keepalive period passes without a valid keepalive conversation the circuit is declared dead and an attempt to revive it by resetting is made. This is what usually causes a Carrier Transition to appear in the statistics. The other reason is that the actual network connection goes up and down.)

You might want to issue the
clear counters
command to reset the counters to zero. Then you will probably see that there are no packets coming in and only a few (keepalives)going out.

Regular Advisor

Re: carrier transition

is that means that we must set the keep alive?

57 carrier transition-what does 57 indicates?
Ron Kinner
Honored Contributor

Re: carrier transition

I would set the keepalive to 10 seconds on both ends. You can work without it if you have it off on both ends but then it is hard to see at a glance if the circuit is up or not.

The 57 transistions means that the circuit has gone up and down 57 times. Sometimes this is the result of the keepalive timing out and doing a reset on the circuit (it will reset the circuit every three keepalive periods or 30 seconds so you can say it has probably been down for 57/2 minutes if your counters were clear when it started.) and other times it is caused by the circuit actually going down and up. Sometimes a timing issue will cause this.

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