Procurve 2610 / 5406 TX packet drop issue in a IPTV network

[jfelber]

Hi ,

I have to configure a network consisting of a HP 5406 with only one 24 Port module as a core switch. 6 HP 2610-48 switches are connected to the HP5406 by gigabit interfaces. The HP 2610 work as boarder switches to TV sets (only one TV on each HP2610 port), here interface speed is only 100 MBit.

Multicasts (total ~ 500 MBit/s) are feed to the HP 5406 and are controlled by IGMP (5406 is the querrier).

Under certain but not quite clear dynamic conditions (i.e. number multicasts joined by IGMP on a single 2610, bandwidth of individual multicasts) I observe TX packet drop on the 2610s. This is no big surprise, as packet buffer on 2610 is rather small, so the GBit to 100MBit translation may cause overflow if multicasts arive in excessive bursts.

 To get rid of the TX drops or at least reduce the amount of packets dropped, I have switched on flow control on the interfaces of HP 5406 to HP 2610s. HP 5406 has a much larger packet buffer, so drop rate should be considerably less. In addition, in the next stage of optimization the HP5406 should relayflow control to the multicast server where sufficient buffering is no problem.

Now I observe that there is a small TX drop rate on the HP5406 interfaces towards the HP2610, but the much higher drop rate on the HP2610 still occurs.

I do not understand this behaviour as I would assume that with flow control switched on all packet drop (if any) should now occur on the HP5406 only. Why are the HP2610 still doing packet drops? Is the flow control mechanism not fast enough to prevent this?

Comments / explanations / proposals for optimzation kindly requested.

Regards, Josef