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It's Time to Focus on One-Way Network Delays

Alan Breznick
5/15/2017
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In a world where most video traffic only flows downstream, it's high time for wireline and wireless service providers to reconsider how they tackle the critical problem of excessive network delays.

Why? Because high latency, or lengthy network delays, is an issue bedeviling video content and service providers of all stripes and sizes. Buffering delays of even just a few milliseconds can lead to a poorer customer quality-of-experience (QoE) and much higher rates of video abandonment by subscribers, according to research conducted by Akamai Technologies Inc. (Nasdaq: AKAM) and others. In turn, these higher rates of abandonment can lead to substantial amounts of lost revenue.

How substantial? Well, Amazon.com Inc. (Nasdaq: AMZN) figures that a page load slowdown of a just a single second could cost it $1.6 billion in sales each year. Google (Nasdaq: GOOG) has calculated that slowing its search results by merely four-tenths of a second could wipe out 8 million searches per day, costing it countless millions in ad revenues. And a research paper published last year concluded that a millisecond delay at a data center could cause $100 million in lost revenues.

Such latency issues will only become more paramount as video increasingly rules both the world and the Internet. In the latest edition of its Visual Networking Index (VNI), Cisco Systems Inc. (Nasdaq: CSCO) projects that IP video will account for a whopping 82% of all global IP traffic by 2020, up from 70% in 2015. Similarly, the Cisco VNI forecast predicts that consumer Internet video will make up 82% of all consumer Internet traffic by the decade's end, up from 68% in 2015. Plus, the VNI report projects that mobile video will account for 78% of the world's mobile data traffic by 2021, up from 60% last year.

With more and more video traffic pulsing over their lines, service providers know they need to find ways to target latency issues and cut down on network delays or risk losing customers in droves. But what they may not know, and need to know, is that viewer QoE will likely become more and more of a crucial differentiator when consumers are choosing between video providers in the future, as the research is beginning to indicate.

Many service providers are trying to address the latency issue by measuring and monitoring video traffic delays in both directions on their networks, using such legacy methods as packet timing and Global Positioning System (GPS). They then take the two-way latency results and simply divide them in two to calculate the estimated delay in each direction. But this approach is faulty and can lead to big problems for network operators.

The obvious shortcoming with these rough estimates is that they don't offer any visibility into what might actually be happening on either network path. As a result, the estimates for one-way delays could be way off because of the asymmetrical nature of most video traffic. Worse yet, these estimates could wind up producing "false positives," incorrectly indicating no latency problems overall when in fact there may be huge traffic delays occurring in one direction or the other.

It seems clear, then, that service providers must measure and monitor one-way network latency directly and accurately. Unfortunately, though, the traditional methods to track one-way delays accurately are complex and expensive.

Take GPS, for instance. While this type of approach usually delivers the most accurate delay measurements, it's quite costly because it requires investment at all measurement sites. It can also be challenging to carry out in urban settings due to intermittent signals, as well as in indoor settings where GPS deployment is tricky. Plus, there's the extra opex cost of rolling a truck to repair or replace faulty equipment.

So, a better type of one-way latency testing is sorely needed. Without a better approach, video providers will not be able to do much better than guess about the scale of the latency issues they are struggling to master. Consider this question: How much is your inability to measure one-way latency costing your company?

This blog is sponsored by EXFO.

— Alan Breznick, Cable/Video Practice Leader, Light Reading

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Sr.Embed22197
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Sr.Embed22197,
User Rank: Light Beer
5/15/2017 | 2:18:37 PM
Re: Ummm
It's actually a bit of both, yes.

I guess my original point is that One Way measurments have some clock sync requirements that are far more strict than Two Way.  Y.1731 DMM, TWAMP, the test can compensate to a certain degree because you can factor out the time differences at each end.  One Way testing, the clocks have to be sync'd a lot tighter.

It's a price upgrade for hardware and infrastructure to do that and customers hate spending the extra money.  Most switches currently installed that I have to support, still rely on NTP.

The point of the article is that One Way testing is needed, and I'm seeing requests to add it, as well as defects reports about it's accuracy on older devices.  I agree that it's useful, but making it report valid numbers isn't just a slight tweak of the software. :)
brooks7
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brooks7,
User Rank: Light Sabre
5/15/2017 | 1:33:46 PM
Ummm
I think about 1/2 your commentary is actually about Jitter and not latency.  Absolute Latency is important at the start of a stream (which includes channel switching).  But once a stream has started it is packet jitter that is the problem (i.e. the variance in delay between receipt of packets).

seven

 
Sr.Embed22197
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Sr.Embed22197,
User Rank: Light Beer
5/15/2017 | 12:50:48 PM
Re: When the devices clocks are accurate enough ...
I'm working with 100G Ethernet. :)  PtP is the protocol they should be using, to have a chance of being accurate, so I agree with you there.  It's not available on low end switches though and customers want cheap switches.

Over multiple hops, from the customers testing center to the NTE, the end to end clocks have be be in sync if you're going to use something like Y.1731 1DM.  Sure, there are games you can play, run 100 frame tests, throw out the outliers, take the average.  You're still going to get odd results at times because someplace in the middle of the test, NTP updated the clock and slewed it someplace.

Customers hate running repeating tests and noticing occasional results that wandered out into the weeds because of a clock update.  Everytime a leap second hits, we get a couple of calls and we explain it all over again.
Duh!
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Duh!,
User Rank: Blogger
5/15/2017 | 12:29:14 PM
Re: When the devices clocks are accurate enough ...
Off by a couple of orders of magnitude. Prop delay through fiber is 4.9 microseconds (μs) per kilometer. Serialization delay at 1 Gbps for an MTU-sized packet is 12.3 μs.

IEEE 1588 - Precision Time Protocol can provide commensurate accuracy.
Sr.Embed22197
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Sr.Embed22197,
User Rank: Light Beer
5/15/2017 | 12:07:11 PM
When the devices clocks are accurate enough ...
When most vendors/customers use NTP to keep their clock accurate, I'd love to hear somebody explain how a clock that is +/- 128ms accuracy is going to get used to time the one way flight of a packet that takes nanoseconds to travel.

Yeah, there are better time protocols and sync Ethernet, but nobody wants to pay for it.

 
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