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Packet Pacing Benefits for Midgress Traffic

Akamai's Smooth Delivery Pacing (SDP) made an impression last year by increasing client network performance while simultaneously reducing retransmissions.  If you missed the details and want to learn more about SDP, please check out our past discussion.  In this article, we'll explore if SDP's benefits can be applied to Akamai's midgress network.

Akamai's midgress network serves as the communication medium between Akamai servers.  The network is mainly comprised of powerful servers physically hardwired to large capacity links and switches.  Compared to the potpourri of client devices and network mediums present at the edge, Akamai's midgress network is relatively homogenous and high performing with very few retransmissions. 

Smooth Delivery Pacing was enabled on Akamai's midgress network in Q3 of 2018.  We compared 30 days of traffic before and after SDP using Akamai's internal performance measurement framework.

Figure 1 illustrates the averaged retransmissions on the midgress network with and without pacing.  Even though Akamai's migress network retransmission rates were low to start with (low single digit), SDP was able to further reduce it by up to 50%.  Lowering network retransmissions is beneficial as it frees up network capacity for additional traffic.

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Figure 1: Akamai's Midgress Network Average Retransmissions

But does a lower network retransmission rate lead to higher performance as in the edge use case?  In Figure 2, we measure the average goodput of Akamai's midgress network.

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Figure 2: Akamai's Midgress Network Average Goodput

Reducing retransmissions from an already low percentage doesn't readily translate to higher average performance according to the data.  The SDP goodput metrics  show only a slight difference which could be attributed to noise from the billions of data samples or any number of factors.  Nonetheless, we discovered that lower bandwidth connections did show improvements by up to 10%.  We believe that packet pacing could help slower midgress connections where retransmissions are more detrimental to overall performance. 

Overall, Smooth Delivery Pacing's effect on Akamai's networks varies.  In the edge use case, SDP was able to improve network performance while simultaneously reducing retransmissions.  With the midgress traffic, packet pacing was also able to reduce network retransmissions but does not appear to have a tangible performance benefit except in lower bandwidth cases.  This area could be targeted for further study.

The Smooth Delivery story continues with Smooth Delivery Rate Limiting (SDRL)!  Stay tuned for our next update.

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