unreasonable latency in a lossy network

[realdream]

Bug report

Required Info:

• Operating System:
  • Ubuntu 16.04
• Installation type:
  • from source
• Version or commit hash:
  • release bouncy
• DDS implementation:
  • Fast-RTPS
• Client library (if applicable):
  • rclcpp

QoS Setting

• PUB:
  • history: KEEP_LAST
  • depth:300
  • reliability: RELIABLE
• SUB:
  • history: KEEP_LAST
  • depth:300
  • reliability: RELIABLE

Steps to reproduce issue

1.run a minimal pub and sub node together in a single launch(the QoS setting is listed above)
2.the publisher will pub a std:string message every 500ms
3.then simulate some package lost in local loopback

sudo tc qdisc add dev lo root netem loss 30%

Expected behavior

with almost infinite bandwidth and low latency in local loop-back
the RELIABLE QoS setting should ensure the message to transmit on schedule

Abnormal behavior

1. the sub node will not receive any message for about 5 seconds then suddenly get all the overdue message in a split second
   ``
   [INFO] [my_test]: Publishing: 'Hello, world! 600'
   [INFO] [my_test]: Publishing: 'Hello, world! 601'
   [INFO] [my_test]: Publishing: 'Hello, world! 602'
   [INFO] [my_test]: Publishing: 'Hello, world! 603'
   [INFO] [my_test]: Publishing: 'Hello, world! 604'
   [INFO] [my_test]: Publishing: 'Hello, world! 605'
   [INFO] [my_test]: Publishing: 'Hello, world! 606'
   [INFO] [my_test]: Publishing: 'Hello, world! 607'
   [INFO] [my_test]: Publishing: 'Hello, world! 608'
   [INFO] [my_test]: Publishing: 'Hello, world! 609'
   [INFO] [my_test]: Publishing: 'Hello, world! 610'
   [INFO] [my_test]: Publishing: 'Hello, world! 611'
   [INFO] [my_test]: I heard: 'Hello, world! 600'
   [INFO] [my_test]: I heard: 'Hello, world! 601'
   [INFO] [my_test]: I heard: 'Hello, world! 602'
   [INFO] [my_test]: I heard: 'Hello, world! 603'
   [INFO] [my_test]: I heard: 'Hello, world! 604'
   [INFO] [my_test]: I heard: 'Hello, world! 605'
   [INFO] [my_test]: I heard: 'Hello, world! 606'
   [INFO] [my_test]: I heard: 'Hello, world! 607'
   [INFO] [my_test]: I heard: 'Hello, world! 608'
   [INFO] [my_test]: I heard: 'Hello, world! 609'
   [INFO] [my_test]: I heard: 'Hello, world! 610'
   [INFO] [my_test]: I heard: 'Hello, world! 611'
   [INFO] [my_test]: Publishing: 'Hello, world! 612'
   [INFO] [my_test]: Publishing: 'Hello, world! 613'
   [INFO] [my_test]: Publishing: 'Hello, world! 614'
   [INFO] [my_test]: Publishing: 'Hello, world! 615'
   [INFO] [my_test]: Publishing: 'Hello, world! 616'
   [INFO] [my_test]: Publishing: 'Hello, world! 617'
   [INFO] [my_test]: Publishing: 'Hello, world! 618'
   [INFO] [my_test]: Publishing: 'Hello, world! 619'
   [INFO] [my_test]: Publishing: 'Hello, world! 620'
   [INFO] [my_test]: Publishing: 'Hello, world! 621'
   [INFO] [my_test]: Publishing: 'Hello, world! 622'
   [INFO] [my_test]: Publishing: 'Hello, world! 623'
   [INFO] [my_test]: Publishing: 'Hello, world! 624'
   [INFO] [my_test]: Publishing: 'Hello, world! 625'
   [INFO] [my_test]: Publishing: 'Hello, world! 626'
   [INFO] [my_test]: Publishing: 'Hello, world! 627'
   [INFO] [my_test]: Publishing: 'Hello, world! 628'
   [INFO] [my_test]: Publishing: 'Hello, world! 629'
   [INFO] [my_test]: I heard: 'Hello, world! 612'
   [INFO] [my_test]: I heard: 'Hello, world! 613'
   [INFO] [my_test]: I heard: 'Hello, world! 614'
   [INFO] [my_test]: I heard: 'Hello, world! 615'
   [INFO] [my_test]: I heard: 'Hello, world! 616'
   [INFO] [my_test]: I heard: 'Hello, world! 617'
   [INFO] [my_test]: I heard: 'Hello, world! 618'
   [INFO] [my_test]: I heard: 'Hello, world! 619'
   [INFO] [my_test]: I heard: 'Hello, world! 620'
   [INFO] [my_test]: I heard: 'Hello, world! 621'
   [INFO] [my_test]: I heard: 'Hello, world! 622'
   [INFO] [my_test]: I heard: 'Hello, world! 623'
   [INFO] [my_test]: I heard: 'Hello, world! 624'
   [INFO] [my_test]: I heard: 'Hello, world! 625'
   [INFO] [my_test]: I heard: 'Hello, world! 626'
   [INFO] [my_test]: I heard: 'Hello, world! 627'
   [INFO] [my_test]: I heard: 'Hello, world! 628'
   [INFO] [my_test]: I heard: 'Hello, world! 629'
   [INFO] [my_test]: Publishing: 'Hello, world! 630'
   [INFO] [my_test]: Publishing: 'Hello, world! 631'