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Packetloss / Packetdiscard / unidentifiable Packets by MCU & endpoints

Bernd Aulibauer
Level 1
Level 1

Hello,

i want to discover how many packets are discarded by our MCU due to "out of order" or similar state of the packets, there is only a statistic for packetloss effected to one particular participant in a conference in the detail statistic. I havent found a way to find out how many packets are discarded by the MCU due to too late receiving them or something similar.

We have problems with downspeeding the receiving video bitrate of an endpoint, down to 64kbit/s sended by Flow Control messages, and we think it has to do with packetloss or packet discards caused by our loadbalancing routers.


EDIT:

After several sniffs on some accessports we have discovered that our MCU and different endpoints with different firmwares are sending sporadic unidentifiable UDP-Packets threw the Media Session. 

This Packets aren´t RTP or RTCP also the sequencenumber isn´t correct. Therefore they have "out-of-order-state" and i think MCU drops them, also the Sequencenumbers of the following RTP or RTCP-Packets are false, cause by this packets. From my point of view, threw Mediasession (Transmit <-> Receive) only RTP or RTCP packets should be send/transmit. 

Has anybody a idea what these packets are or why they are sended from MCU and endpoints in sporadic intervals?

Best Regards,

Bernd

2 Replies 2

Elias Sevilla Duarte
Cisco Employee
Cisco Employee

From the endpoints perspective, the UDP packets generated are only media traffic or H323 RAS messages for GateKeeper registration, though if you do not see the UDP port 1719 in those "Unknown" packets, then I would assume that those are media packets (RTP/RTCP). (Have you tried decoring those packets?)

The issue you describe sounds like "jitter" in the network, tipically caused by load balancers present in the network, causing the packets to get to its destination in more than 100ms of delay. Cisco video endpoints drop packets that come with more than 100ms of delay, (subsequently causing packet loss) and those packets are flagged as "out of order".

Like I said, this is only from the endpoints perspective, but I would assume that MCUs use the same mechanism when "jitter" is present.

Hi,

thank you for help, im sorry for my delayed answer, i was on holiday last week.

I have understand what you mean, but we have already locked out:
- jitter (not above 50ms over all)

- loadbalancing, theres no loadbalancing per packet -> one session always goes the same way

-DSCP(express forward) configured correct and also handled belong the whole transportdistance

I have found another interessting behavior, i will desribe you now:

Between Sessions from our MSE8510 and endpoints there are about ~0,6 percent of sended and received packets in this session which payload type (22) isn´t described in RFC3551. These packets also have an different upgoing sequencenumber which isn´t compatible with the other ones in RTP Stream. Those packets appear in both directions MCU -> endpoint and endpoint -> MCU in not cyclical intervals. 

Further we found about ~0,3 percent of packets which have the right payload type for RTP described in RFC between 96-127 but they are already in state "Malformed Packet".

I think that those packets are dropped by both, mcu and endpoints, and that they are causing our problems.

About the testscenario:

-pcaps directly on mirrored accessport of our mcu (latest firmware 4.5 (1.89))

-pcaps directly on mirrored accessport of different endpoints (firmware between TC7.3.6 and TC7.3.8)

-RTCP ports filtered out (so only RTP session in one direction was analysed at a time)

Just for understanding: those packets (~0,9 percent) are  already "leaving" mcu or endpoint in the states "malformed" and "wrong payloadtype" 

Does anyone has an idea, where these packets come from?

Best regards,

Bernd

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