Packet Reordering in Todays Networks [623073]

Packet Reordering in Today’s Networks
Muhammad Bilal
Networks are imperfect. They introduce delays due to packets drop or out of order.
Networks with multiple paths or parallel processing paths are some of many reasons
for packet out of orders. Packets are out of order when the packets received over the
network are of different order than what was sent. These out of order packet can be
critical for seem less execution of services running on a particular application. The
quality of service can degrade if packets received are out of order more frequently.
The networks are expanding at more faster pace than ever before. To achieve the
ultimate goal of lower latency, the networks must overcome the obstacles like packet
drops and packets out of order.
1 Introduction
Higherdataratesandlowlatencyhasbecomethetrademarksforbusinessesaroundtheworld.The
circuit switch demands the highest priority while more and more traffic is shifting towards packet
switch. IP telephony and voice over IP are transforming the way of communication meanwhile
bringing the operational costs. The VOIP uses TCP-IP or UDP as connection protocols to transfer
packets over the internet. TCP is more reliable than UDP for data transmission as it guarantees
the transmission of data. The problem arises when the data is received in the wrong order. It
can be a difficult task to detect the packets that are out of order. It will also be required to tell
the sender that specific numbers of packets are out of order so that retransmission can happen
accordingly. In this Study, it will be discussed in detail that how the packet reordering is done is
TCP. This study also include how packet reordering impacts TCP. Then we discuss findings from
various research papers and collate different avoidance strategies for packet reordering in TCP.
2 Detection of Packets out of order
Packet out of order can be detected when the causes of the aforementioned phenomenon is known.
There are multiple causes of packet reordering [1]. In this section, the causes of packet reordering
will be discussed.
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2.1 Packet level multipath routing
2.2 Route fluttering
2.3 Inherent parallelism in routers
2.4 link layer retransmission
3 Impact of packet reordering on TCP
TCP waits for the acknowledgments(ACKs) from receiver that packet has been received correctly
and then sends another packet. If the momentum of receiving ACKs is accelerating, the source
can send the more packets in certain time interval. The introduction of packet reordering than
disrupts the packet flow, and retransmission starts happening [1][2]. In this section, the following
Impacts of packet reordering on TCP will be discussed.
3.1 Spurious Segment Retransmissions
3.2 Keeping Congestion Window Unnecessarily Small
3.3 Loss of ACK-Clocking
3.4 Understating Estimated RTT and RTO
4 Classification and comparison of reordering solutions for TCP
The reordering solutions can be classified in 2 categories, Ordinal approach and Temporal
approach. In this section, comparison between both of these approaches will be discussed. The
algorithm under both categories will also be compared and highlighted [1].
4.1 Avoidance technique in TCP-PR
The new version of TCP, TCP-PR, maintains high throughput despite of packet reordering
happening. TCP-PR uses timers instead of DUPACKs to observe that how long ago the packet
was sent [5].
5 Packet reordering in NIC’s
Intel Ethernet Flow Director is an advance network interface card technology(NIC). This study
also include how flow director can cause packet reordering and what are the impacts on NIC’s[4].
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5.1 Impact of packet reordering on NIC’s
5.2 Receive Side Scaling (RSS)
5.3 Impact of Flow Director on Packet reordering
6 Performance Evaluation
In this section, the performance of each algorithm mentioned above will be evaluated.
7 Conclusion
The main focus of this study is to manifest the effects of packet reordering on the network
performance and to look into feasible solutions given the circumstances. Real time applications
can get interrupted by the severity of packet reordering. The study suggests that frequency of
packet reordering can be reduced by avoiding parallelism or by using network nodes that uses
single path. This can be ensured by using some or any of the strategies discussed in this study.
Packet reordering happens silently and is difficult to be traced. As the requirement for bandwidth
by applications increases, it is expected that applications will rely more on parallel architecture
for processing of packets. So it is evident that some degree of packet reordering will always exist
in the network. We can try to minimize it by strategies available to us. Also, We can expect
more research on this topic as the technology advances[3].
Literatur
[1]Victor O.K. Li Ka-Cheong Leung und Daiqin Yang. An Overview of Packet Reordering in
Transmission Control Protocol (TCP): Problems, Solutions, and Challenges . Techn. Ber.
2007.
[2]Michael Laor und Inc. Lior Gendel Cisco Systems. „The Effect of Packet Reordering in a
Backbone Link on Application Throughput“. In: IEEE, 2002.
[3] Vern Paxson. End-to-End Internet Packet Dynamics . 1999.
[4]Wenji Wu Phil DeMar und Matt Crawford. Why Can Some Advanced Ethernet NICs Cause
Packet Reordering? 2011.
[5]Junsoo Stephan João und Katia. „A New TCP for Persistent Packet Reordering“. In: (2006).
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