[cisco-bba] High TCP packet loss over ATM

Mark mac at telvia.it
Mon Nov 6 09:17:10 EST 2006

After a bit of research i found that rx_cell_loss are increasing quickly.
What this means?

James Wakefield ha scritto:
> Mark wrote:
>> Hi ,
>> i'm getting crazy about the problem below.
>> We aggregate xDSL customers using PPP (PPPoA or PPPoE) over PA-A3 ATM 
>> adapters.
>> Now, some customers are experiencing very high tcp packet loss but when 
>> we test ATM (with ATM OAM pings) we don't see any packet loss. It is 
>> possible that it is a problem on the router? Only some customers are 
>> experiencing the problem. We tried anything on the router (delete pcv, 
>> change PPP type etc) but problem persist.
>> I'm pretty sure that problems are on ATM provider, but on ATM side what 
>> i need do check? ATM Buffers? ATM Errors? My ATM provider say that ATM 
>> ping are enough to check that ATM network is working well but I'm sure 
>> that problems are atm related. Maybe a IOS Bug?
> G'day Mark,
> Check the QoS parameters (Sustained Cell Rate, Peak Cell Rate, Maximum 
> Burst Size) that your PVC is configured for against your ATM provider's 
> SLA/technical spec.  If you're bursting faster/for longer than what your 
> provider is configured for, it'll start dropping cells.  This will 
> likely only be noticed with larger packets than your typical 64 byte 
> ICMP echo, such as your typical ~1000 byte TCP packet.  Try pinging the 
> IP interface on your ATM provider's end of the PVC with various packet 
> sizes up to the MTU.
> Cheers,

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