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Available bandwidth on a Cisco 1841 Router

Posted on 2010-09-22
Medium Priority
Last Modified: 2012-06-27
How do I find out the actual bandwidth on a router's serial interface? When I look at the output of the sh int command, I see that the available bandwidth is 341 Kilobits\sec. Is my understanding correct that this doesn't mean that my connection provider is only giving that much bandwidth? If so, where do I find what the other reservations are that make my bandwidth to go from my expected 1500 Kilobits\sec to 341 Kilobits\\sec?

Thanks much!
Question by:NCLGS
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Expert Comment

ID: 33734421
What type of interface is this? There are multiple methods of doing this though, and chances are it's being done on the ISP side, not on your hardware. Otherwise it would be too easy for you to change it and get more than you're paying for.
LVL 50

Expert Comment

by:Don Johnston
ID: 33734593
>Is my understanding correct that this doesn't mean that my connection provider is only giving that much bandwidth?

Correct. On a serial interface, the "bandwidth" value is for reference by routing protocols, spanning-tree, etc.

>If so, where do I  find what the other reservations are that make my bandwidth to go from  my expected 1500 Kilobits\sec to 341 Kilobits\\sec?

On a serial interface, the speed is determined by the clocking signal. This signal is provided by the DCE device (CSU/DSU). If you have an integrated CSU in your router, you should be able to determine the speed of your link from the configuration.

Author Comment

ID: 33734886
Thank you for your response. Could you elaborate on how to determine the speed of the link from the config? It IS a serial interface that connects a remote location to the main office. I'm trying to determine if there is ,say, a QoS set for VoIP or anything else. Ultimately I'm trying to see if I can increase this bandwidth.

Another related question - how significant is this number? What I mean by that is: how does this number correspond to the actual speed that users will experience?

Thanks for your help!
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Expert Comment

ID: 33734998
T1 speed is determined by channel usage. Each channel is 64K of bandwidth.

It should say something like the following for a full T1: channel-group 1 timeslots 1-24

LVL 50

Accepted Solution

Don Johnston earned 1500 total points
ID: 33735009
>Could you elaborate on how to determine the speed of the link from the config?

If you have an integrated CSU, in the config for the T1 controller, you'll see a line "timeslots x-y". Each timeslot is 64k. So if the line is "timeslots 1-6" then 6x64=384. So you have a 384k service.

If you don't have an integrated CSU, then you will have to look at the config of the CSU to determine the number of timeslots.

>I'm trying to determine if there is ,say, a QoS set for VoIP or anything else.

QOS configs can get pretty involved but see if there are any "service-policy" statements on the interface configs. You can also review this white paper on QOS:


>What I mean by that is: how does this number correspond to the actual speed that users will experience?

This number has NO affect on the movement of traffic over the interface. You can set it to ANY value that you want and the speed of the link will not change. It is used by routing protocols and other services that need to know how fast the interface is. For example, if you have two links going to the same network and you use OSPF as your routing protocol. OSPF will use the bandwidth value to determine the best path to the destination.

Now this number SHOULD be set to the actual speed of the link. Otherwise the behavior of traffic will be... unexpected.

Author Comment

ID: 33737038
Thank you for all that explanation; it does throw a lot of light in the direct I'm looking at.

I think we have an integrated CSU. I'm trying to figure out how the channels were allocated (in terms of what we are doing with the rest of the timeslots). This link is extremely slow and I'm trying to understand/troubleshoot why it is that way.

From the output I don't see the timeslots assigned. Do you?

Here is the output from sh controllers of my serial interface:

Hardware is GT96K with Integrated FT1 CSU/DSU module
 TX and RX clocks detected.
idb at 0x62B07190, driver data structure at 0x62B0E954
wic_info 0x62A0FF50
Physical Port 0, SCC Num 0
MPSC Registers:
MMCR_L=0x000304C0, MMCR_H=0x00000000, MPCR=0x00000000
CHR1=0x00FE007E, CHR2=0x00000000, CHR3=0x000005F4, CHR4=0x00000000
CHR5=0x00000000, CHR6=0x00000000, CHR7=0x00000000, CHR8=0x00000000
CHR9=0x00000000, CHR10=0x00003008
SDMA Registers:
SDC=0x00002201, SDCM=0x00000080, SGC=0x0000C000
CRDP=0x073BD000, CTDP=0x073BD200, FTDB=0x073BD200
Main Routing Register=0x0003FFF8 BRG Conf Register=0x00480000
Rx Clk Routing Register=0x76543218 Tx Clk Routing Register=0x76543219
GPP Registers:
Conf=0x30002   , Io=0x64050   , Data=0x7F7BBFA9, Level=0x180000
Conf0=0x30002   , Io0=0x64050   , Data0=0x7F1BBFA9, Level0=0x180000
15240 input aborts on receiving flag sequence
0 throttles, 0 enables
3978 overruns
0 transmitter underruns
0 transmitter CTS losts
1101201328 rxintr, 1118546203 txintr, 0 rxerr, 0 txerr
1945419759 mpsc_rx, 0 mpsc_rxerr, 5486 mpsc_rlsc, 18044 mpsc_rhnt, 1945408795 mp
44 mpsc_rcsc, 0 mpsc_rovr, 0 mpsc_rcdl, 0 mpsc_rckg, 0 mpsc_bper
0 mpsc_txerr, 877041186 mpsc_teidl, 0 mpsc_tudr, 0 mpsc_tctsl, 0 mpsc_tckg
0 sdma_rx_sf, 26 sdma_rx_mfl, 3978 sdma_rx_or, 15240 sdma_rx_abr, 13969 sdma_rx_
0 sdma_rx_de, 0 sdma_rx_cdl, 44381 sdma_rx_ce, 0 sdma_tx_rl, 0 sdma_tx_ur, 0 sdm
0 sdma_rx_reserr, 0 sdma_tx_reserr
0 rx_bogus_pkts, rx_bogus_flag FALSE
0 sdma_tx_ur_processed

tx_limited = 1(2), errata19 count1 - 0, count2 - 0

Thanks again for all your help!
LVL 50

Expert Comment

by:Don Johnston
ID: 33738297
It will be at the bottom of the "show interface serial..." output.


Author Comment

ID: 33738380
Here is the output from the command:

Router1#sh int serial0/0/0
Serial0/0/0 is up, line protocol is up
  Hardware is GT96K with integrated T1 CSU/DSU
  Description: Point 2 Point
  Internet address is XXX.XXX.XXX.XXX
  MTU 1500 bytes, BW 1544 Kbit, DLY 20000 usec,
     reliability 255/255, txload 22/255, rxload 39/255
  Encapsulation PPP, LCP Open
  Open: CDPCP, IPCP, loopback not set
  Keepalive set (10 sec)
  Last input 00:00:00, output 00:00:00, output hang never
  Last clearing of "show interface" counters 1d06h
  Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 5
  Queueing strategy: Class-based queueing
  Output queue: 0/1000/64/5 (size/max total/threshold/drops)
     Conversations  0/12/256 (active/max active/max total)
     Reserved Conversations 4/4 (allocated/max allocated)
     Available Bandwidth 341 kilobits/sec
  5 minute input rate 240000 bits/sec, 87 packets/sec
  5 minute output rate 139000 bits/sec, 84 packets/sec
     2584018 packets input, 1532493227 bytes, 0 no buffer
     Received 0 broadcasts, 0 runts, 0 giants, 0 throttles
     19 input errors, 19 CRC, 8 frame, 6 overrun, 0 ignored, 9 abort
     2462227 packets output, 602199054 bytes, 0 underruns
     0 output errors, 0 collisions, 0 interface resets
     0 output buffer failures, 0 output buffers swapped out
     0 carrier transitions
     DCD=up  DSR=up  DTR=up  RTS=up  CTS=up
LVL 50

Expert Comment

by:Don Johnston
ID: 33738570
That's curious. Please post your config.

Author Comment

ID: 33738630
I think I'm closer to what we were looking for with the show service-module serial0/0/0. Also, I was under the impression that Path Code Violations are indicative of Layer 1 problems. Is that right? If so, when should I start getting concerned? Is 7 negligible or is that an issue?

Router1#sh service-module serial0/0/0
Module type is T1/fractional
    Hardware revision is 0.57, Software revision is 20051025,
    Image checksum is 0x3EFB7B, Protocol revision is 0.1
Receiver has no alarms.
Framing is ESF, Line Code is B8ZS, Current clock source is line,
Fraction has 24 timeslots (64 Kbits/sec each), Net bandwidth is 1536 Kbits/sec.
Last module self-test (done at startup): Passed
Last clearing of alarm counters 1d06h
    loss of signal        :    0,
    loss of frame         :    0,
    AIS alarm             :    0,
    Remote alarm          :    0,
    Module access errors  :    0,
Total Data (last 96 15 minute intervals):
    0 Line Code Violations, 7 Path Code Violations
    0 Slip Secs, 0 Fr Loss Secs, 0 Line Err Secs, 4 Degraded Mins
    4 Errored Secs, 2 Bursty Err Secs, 0 Severely Err Secs, 0 Unavail Secs
Data in current interval (430 seconds elapsed):
    0 Line Code Violations, 0 Path Code Violations
    0 Slip Secs, 0 Fr Loss Secs, 0 Line Err Secs, 0 Degraded Mins
    0 Errored Secs, 0 Bursty Err Secs, 0 Severely Err Secs, 0 Unavail Secs
LVL 50

Expert Comment

by:Don Johnston
ID: 33738697
Please post your config.
Here's Cisco's take on your output.

For the 'T1/fractional' interface:
INFO: With Extended Super Frame, the remote alarm condition is signaled out of band, in the Facility Data Link. Thus with ESF, it is recommended to enable remote alarms with the 'service-module t1 framing esf' command.

INFO: This interface has had Path Code Violations (i.e. framing errors); 7 in past intervals. A Path Coding Violation error event is a frame synchronization bit error in the D4 and E1-noCRC formats, or a CRC error in the ESF and E1-CRC formats.

NOTE: Although the output from the show service-module serial [number]command can be used to troubleshoot some problems, it cannot assist with all problems. It should be used in conjunction with other commands such as 'show interface serial', 'show isdn status' and 'show isdn service' (if ISDN is applicable). Submit the output from these commands to Output Interpreter for an expert analysis.

REFERENCE: For more information, see: Configuring Serial Interfaces for CSU/DSU Service Modules.


Author Comment

ID: 33746838
Thanks for your comments again. I will post the running config shortly. Something else came up at work today.

Author Closing Comment

ID: 34062517
The solution helped the situation but didn't completely answer the question

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