Measurement and Classification of OutofSequence Packets in a Tier1 IP Backbone

1
Measurement and Classification of
Out-of-SequencePackets in a Tier-1 IP Backbone

• Sharad Jaiswal,
• Gianluca Iannaccone, Member, IEEE, Christophe
  Diot, Jim Kurose, Fellow, IEEE,
• Don Towsley, Fellow, IEEE
• Paper Presented by Saroj Patil

2
Introduction

• Study of out-of-sequence packets in TCP
  connection over Sprint IP backbone.
• Measurements taken in the middle of end-to-end
  path.
• Analyze traces from OC-12 and OC-48 links in
  nearly 7600 unique ASes.
• Result shows relatively consistent rate of
  out-of-sequence packets of approximately 4

3
Related Work

• Benett sent bursts of ICMP probe packets through
  public exchange point, and reported packet
  reordering by specific switch.
• Paxson examined packet reordering and replication
  in TCP between pairs of measurement sites.
• Bellardo described technique that can estimate
  packet reordering in TCP data transfers from a
  remote host.

4
Methodology

• Retransmission Sender infers packet is lost and
  retransmits the packet.
• Network duplication A nonsender retransmitted
  copy of packet is observed.
• In-network reordering The network can invert the
  order of two packets.

5
Retransmissions

• R1.a W?W
• R1.b t-tgtRTO
• R1.c Duplicate acksgt3
• R2.a t-tgtRTO
• R2.b duplicate acksgt3 and timelaggtRTT
• R3.a flag infastRecovery set and xltsndHigh

6
Reordering and Duplicates

• R4 t-tltRTT
• R5 t-tltRTT

7
Unneeded Retransmissions

• R6 ACK is lost between measurement point and the
  sender, or sender timeouts prematurely.
• R7 Unknown

8
Estimating RTT

• RTT helps to compute RTO and to identify
  reordering and duplicates.
• Senders RTTd1d2
• Sources of Estimation Inaccuracy
• Variable delays along end-to-end path if d2gtd1
  overestimate or d2ltd1 underestimate observed RTT.
• End-host delays
• Estimation of cwnd

9
Experimental Validation

• Three sets of experiment with no packet drops, 3
  drop rate and 5 drop rate.
• Also another set with wireless hop.
• Relative Error of RTT Estimation
• pi is latest packet observed at measurement
  point.
• Spi and mpi are the most recent samples taken at
  sender.
• n is the total number of packets observed.

10
(No Transcript)
11
Measurements and Classification Research

• Measurement Data
• Out-of-sequence Packets
• Network Anomalies

12
Discussion of Results

• Representativeness of Sampled Flows
• Compare number of ASes.
• Examine the distribution of number of path
  length.
• Compare frequency.

13

• Measuring End-End Reordering/Duplication
  Frequency
• A duplicate ACK may be generated upon receipt of
  packet classified as out-of-sequence.
• A receiver sends duplicate ACKs upon receipt of
  the unneeded transmission
• Duplicate ACKs are also used to update the
  receiver advertised window
• If the receiver follows a delayed ACK policy,
  some of out-of-sequence-events will not trigger a
  duplicate ACK.

14
Conclusion

• About 4 of packets generated by TCP connections
  are out-of- sequence, most of which are due to
  retransmission in response to a packet loss.
• Packet reordering affects about 1-1.5 of all
  data packets, however, they have little impact on
  the quality of a TCP/IP protocol connection as
  perceived by the end users
• Other network anomalies such as duplication of
  packets represent a very marginal phenomenon in
  the Internet.

15
Future Directions

• Identify causes behind packet losses i.e.
  congestion, routing or link failure
• Study if a TCP connection experiences congestion
  in a single or multiple bottlenecks along the
  path
• Identify tools to detect ASes that are
  responsible for the out-of-sequence packets.

16
References

• 1 J. Bellardo and S. Savage, Measuring packet
  reordering, presented at the ACM SIGCOMM
  Internet Measurements Workshop San Francisco, CA,
  Nov. 2002.
• 2P. Benko and A. Veres, A passive method for
  estimating end-to-end TCP packet loss, presented
  at the IEEE Globecom Taipei, Taiwan, Nov. 2002.
• 3 J. Bennett, C. Partridge, and N. Shectman,
  Packet reordering is not pathologial network
  behavior, IEEE/ACM Trans. Networking, vol. 7,
  Dec. 1999.
• 4 R. Cáceres, N. Duffield, D. Towsley, and J.
  Horowitz, Multicast-based inference of
  network-internal loss characteristics, IEEE
  Trans. Inf. Theory, vol. 45, pp. 24622480, Nov.
  1999.
• 5 C. Fraleigh, S. Moon, B. Lyles, C. Cotton, M.
  Khan, D. Moll, R. Rockell, T. Seely, and C. Diot,
  Packet-level traffic measurements from the
  sprint IP backbone, IEEE Network, 2003.
• 6 S. Jaiswal, G. Iannaccone, C. Diot, J.
  Kurose, and D. Towsley, Measurement and
  classification of out-of-sequence packets in a
  Tier-1 IP backbone, presented at the IEEE
  INFOCOM, San Francisco, CA, 2003.
• 7 S. Jaiswal, G. Iannaccone, C. Diot, J.
  Kurose, and D. Towsley, Inferring TCP connection
  characteristics through passive measurements,
  presented at the IEEE INFOCOM, Hong Kong, 2004.
• 8 H. Jiang and C. Dovrolis, Passive estimation
  of TCP round-trip times, ACM Comput. Commun.
  Rev., vol. 32, no. 3, Jul. 2002.
• 9 V. N. Padmanabhan, L. Qiu, and H. J. Wang,
  Server based inference of internet link
  lossiness, presented at the IEEE INFOCOM, San
  Francisco, CA, 2003.
• 10 V. Paxson, End-to-end routing behavior in
  the internet, IEEE/ACM Trans. Networking, vol.
  5, pp. 601615, Oct. 1997.
• 11 , End-to-end internet packet dynamics,
  IEEE/ACM Trans. Networking, vol. 7, pp. 277292,
  Jun. 1999.
• 12 L. Rizzo, Dummynet A simple approach to
  the evaluation of network protocols, ACM Comput.
  Commun. Rev., vol. 27, no. 1, Jan. 1997.