[nsp] Real IP troughput over ATM

[Michael Loftis]

CCing because I'm not sure if they're subbed...

Realistically you're getting pretty close to the max....  There is IP, TCP 
overhead too.  The packets/sec number is not IP.  That's down at the 
interface level already so it's really ATM frames methinks.  i never pay 
much attention to those numbers because they have been known to be wrong 
and are most certainly rounded off.

Your throughput will also depend on TCP window sizes and various other 
things.  A single stream has a hard time maxing out the link for a lot of 
reasons.

--On Thursday, November 06, 2003 17:47 -0300 "Noriega, Alejandro" 
<ANoriega at prima.com.ar> wrote:

>> Hello folks,
>> 	I have been reading all sorts of documents about real IP
>> troughput over ATM link but I didn't find anything useful.
>> The last week my company bought 130Mbps IP over an OC3 link.
>> I was testing the link, only with downstream traffic, and the link
>> never reaches more than 125Mbps (that was the info that the 'input
>> rate' of "show int ATM2/0" showed me. I'm not sure if that rate is IP
>> or ATM.)
>>
>> OC3 = 155.520Mbps
>> ATM AAL5 = 1 cell = 53bytes (48 payload + 5 header)
>>
>> I am not considering the bytes cosumed by the AAL5 cell trailer:
>> Should the real IP troughput over an ATM link be ~
>> 155.520/(53*8)*(48*8)=140.850 ?.
>> Well, if my calculation is right my link SHOULD have ~143.542 of
>> downstream to get 130Mbps IP, right? (143.54/(53*8)*(48*8)=130)
>>
>> My questions are:
>> lima10#sh int atm2/0
>> ATM2/0 is up, line protocol is up
>>   Hardware is ENHANCED ATM PA
>>   Description: Conexion: TeCo Fibra oscura - ID: 5601631
>>   MTU 4470 bytes, sub MTU 4470, BW 155000 Kbit, DLY 80 usec,
>>      reliability 255/255, txload 88/255, rxload 187/255
>>   Encapsulation ATM, loopback not set
>>   Encapsulation(s): AAL5
>>   4095 maximum active VCs, 1 current VCCs
>>   VC Auto Creation Disabled.
>>   VC idle disconnect time: 300 seconds
>>   0 carrier transitions
>>   Last input 00:00:01, output 00:00:00, output hang never
>>   Last clearing of "show interface" counters 02:19:19
>>   Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops:
>> 0
>>   Queueing strategy: Per VC Queueing
>>   5 minute input rate 113886000 bits/sec, 27138 packets/sec <--- This
>> info talks about packets so I assume it's IP traffic, right?
>>   5 minute output rate 53787000 bits/sec, 17195 packets/sec
>>      224971412 packets input, 2850386068 bytes, 0 no buffer
>>      Received 0 broadcasts, 0 runts, 0 giants, 0 throttles
>>      0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort
>>      138570460 packets output, 2615814337 bytes, 0 underruns
>>      0 output errors, 0 collisions, 0 interface resets
>>      0 output buffer failures, 0 output buffers swapped out
>>
>> If the input bits/sec referrs to IP traffic, in order to get my real
>> throughput over the link I should sum the ATM overhead.
>> So if the 'show int' shows me a peak of 125Mbps, my "real" traffic
>> SHOULD be 125/(48*8)*(53*8)=138.
>> Anyone has a PA-A3-OC3SMI handling more traffic?
>>
>> Thanks in advance.
>>
>> Regards,
>> Alejandro.
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