Additional delay than expecetd in P2P network (Delay within the p2p device)

[Krishna Bharadwaj Pisupati]

Hi there,

I'm having a P2P network with four nodes (1, 2, 3 and 4). 1-2, 3-4 are 1 Gbps link with 0 ms delay and 2-3 is a bottleneck link with 10 Mbps and 100 us delay. UDP Client-Server application with 15 Mbps datarate (Inter arrival time - 0.000778667 seconds) from 1 to 4

Also, I'm connecting trace sources from p2p net device (MacTx and MacRx). When I tried to calculate end-to-end delay (1 to 4), I'm seeing an average delay of around 800 ms than expected (100 packet (1490 bytes) buffer and 10 Mbps bottleneck link => around 120 ms).

When I saw the output from trace sources, here's what I've observed.

Device 2,9.6554,ns3::PppHeader (Point-to-Point Protocol: IP (0x0021)) ns3::Ipv4Header (tos 0x0 DSCP Default ECN Not-ECT ttl 64 id 12400 protocol 17 offset (bytes) 0 flags [none] length: 1488 10.1.1.1 > 10.1.1.6) ns3::UdpHeader (length: 1468 49153 > 4000) ns3::SeqTsHeader ((seq=12400 time=+9.65538s)) Payload (size=1448)
Device 2,11.0987,ns3::PppHeader (Point-to-Point Protocol: IP (0x0021)) ns3::Ipv4Header (tos 0x0 DSCP Default ECN Not-ECT ttl 63 id 12400 protocol 17 offset (bytes) 0 flags [none] length: 1488 10.1.1.1 > 10.1.1.6) ns3::UdpHeader (length: 1468 49153 > 4000) ns3::SeqTsHeader ((seq=12400 time=+9.65538s)) Payload (size=1448)

At device 2 (node 2), a packet with seq no: 12400 is being received at 9.6554 seconds from the source node 1 --- (MacRx). The same packet is put into the TxQueue of other interface (node 3) at 11.0987 seconds --- (MacTx), which is larger delay > 1 second within the device.

Am I missing to configure something ? Or is it some kind of bug ? Kindly clarify. The code is also attached for the reference.

Kind Regards,

Krishna.