On the Trail of Network Latency Over a Satellite Link

By Art Reisman – CTO – www.netequalizer.com

Art Reisman CTO www.netequalizer.com

This morning, just for fun, I decided to isolate the latency on a route from my home office, to a computer located at a remote hunting lodge. The hunting lodge is serviced by a Wild Blue satellite link.

What causes latency?

The factors that influence network latency are:

1) Wire transport speed.

Not to be confused with the amount of data a wire carry in a second, I am referring to the raw speed at which data travels on a wire. Once on the wire, the traversal time from end to end. For the most part, we can assume data travels at the speed of light: 186,000 miles per second.

2) Distance.

How far is the data traveling. Even though data travels at the speed of light, a hop across the United States will cost you about 4 milliseconds, and a hop up to a stationary satellite  ( round trip about 44,000 miles) adds a minimum of 300 milliseconds. I have worked through an example of how you can  trace latency across a satellite link below.

3) Number of hops.

How many switching points are there between source and destination? Each hop requires the data to move from one wire to another, and this requires a small amount of waiting to get on the next wire. Each hop can be an additional 2 or  3 milliseconds.

4) Overhead processing on a hop.

This can also add up, sometimes at the end points points, people like to look at the data, usually for security reasons, on their firewall. Depending on the number of features and processing power of the firewall this can also add a wide range of latency. Normal is from 1 or 2 milliseconds, but that can blow up to 50 milliseconds or in some cases even more when you turn on too many features on your firewall.

How much latency is too much?

It really depends on what you are doing. If it is a one way conversation, like you are watching a Netflix movie, you are probably not going to care if the data is arriving a half second after it was sent, but if you are talking interactively on a Skype call, you will find your self talking over the other person quite often – especially at the beginning of a call.

Tracing Latency across a satellite link.

Note: I am doing this all from the command line on my Mac.

Step one: I have the IP address of a computer that I know is only accessible by Satellite. So first I run a command called trace route to find all the hops along the route.

localhost:~ root# traceroute 75.104.xxx.xxx

When I run this command I get a list of every hop along the route, I also get some millisecond times for each hop from trace route but I am not sure if I trust them, so I am not showing them.

From my Mac command line I do:

traceroute to 75.104.xxx.xxx (75.104.xxx.xxx)
1 ( This is my local router or gateway the first hop
2 ( – This is the Comcast Router , the first router upstream from my house at the local Comcast NOC most likely.
3  te-8-1-ur01.boulder.co.denver.comcast.net ( – We then go through a bunch of Comcast links
4  te-7-4-ur02.boulder.co.denver.comcast.net (
5  te-0-10-0-10-ar02.aurora.co.denver.comcast.net (
6  he-3-10-0-0-cr01.denver.co.ibone.comcast.net (
7  xe-5-0-2-0-pe01.910fifteenth.co.ibone.comcast.net (
8 ( – and then we leave the Comcast network of routers here
9  if-1-1-2-0.tcore1.pdi-paloalto.as6453.net ( – and finally to some other back bone router
10 (
11  * * *
13 75.104.xxx.xxx ( This IP is on the other side of a Satellite link)

Now here is the cool part, I am going to ping the last IP address before the route goes up to the satellite, and then the hop after that to see what the latency over the satellite hop is.

Note the physical satellite does not have an IP, there is a router here on Earth that transmits data up and over the satellite link.

localhost:~ root# ping
PING ( 56 data bytes
64 bytes from icmp_seq=0 ttl=56 time=42.476 ms
64 bytes from icmp_seq=1 ttl=56 time=55.878 ms
64 bytes from icmp_seq=2 ttl=56 time=42.382 ms

About 50 milliseconds.

And the last hop to the remote computer.

localhost:~ root# ping  75.104.xxx.xxx
PING (75.104.xxx.xxx): 56 data bytes
Request timeout for icmp_seq 0
64 bytes from 75.104.180.xxx: icmp_seq=0 ttl=109 time=1551.310 ms
64 bytes from 75.104.180.xxx: icmp_seq=1 ttl=109 time=1574.177 ms
64 bytes from 75.104.180.xxx: icmp_seq=2 ttl=109 time=1494.628 ms

Wow that hop up over the satellite link added about 1500 milliseconds to my ping time!

That is a little more latency than I would have expected, but in fairness to Wild Blue they do a good job at a reasonable price. The funny thing is streaming audio works fine over the Satellite link because it is not latency sensitive.  However a skype call might be a bit more painful , 300 milliseconds is about the tolerance level where users start to notice latency on a phone call, 500 is manageable, and up over 1000, starts to require a little planning and pausing before and after you speak.

References. A non technical guide to fixing TCP/IP problems

The Facts and Myths of Network Latency

There are many good references that explain how some applications such as VoIP are sensitive to network latency, but there is also some confusion as to what latency actually is as well as perhaps some misinformation about the causes. In the article below, we’ll separate the facts from the myths and also provide some practical analogies to help paint a clear picture of latency and what may be behind it.

Fact or Myth?

Network latency is caused by too many switches and routers in your network.

This is mostly a myth.

Yes, an underpowered router can introduce latency, but most local network switches add minimal latency — a few milliseconds at most. Anything under about 10 milliseconds is, for practical purposes, not humanly detectable. A router or switch (even a low-end one) may add about 1 millisecond of latency. To get to 10 milliseconds you would need eight or more hops, and even then you wouldn’t be near anything noticeable.

The faster your link (Internet) speed, the less latency you have.

This is a myth.

The speed of your network is measured by how fast IP packets arrive. Latency is the measure of how long they took to get there. So, it’s basically speed vs. time. An example of latency is when NASA sends commands to a Mars orbiter. The information travels at the speed of light, but it takes several minutes or longer for commands sent from earth to get to the orbiter. This is an example of data moving at high speed with extreme latency.

VoIP is very sensitive to network latency.

This is a fact.

Can you imagine talking in real time to somebody on the moon? Your voice would take about eight seconds to get there. For VoIP networks, it is generally accepted that anything over about 150 milliseconds of latency can be a problem. When latency gets higher than 150 milliseconds, issues will emerge — especially for fast talkers and rapid conversations.

Xbox games are sensitive to latency.

This is another fact.

For example, in may collaborative combat games, participants are required to battle players from other locations. Low latency on your network is everything when it comes to beating the opponent to the draw. If you and your opponent shoot your weapons at the exact same time, but your shot takes 200 milliseconds to register at the host server and your opponent’s shot gets there in 100 milliseconds, you die.

Does a bandwidth shaping device such as NetEqualizer increase latency on a network ?

This is true, but only for the “bad” traffic that’s slowing the rest of your network down anyway.

Ever hear of the firefighting technique where you light a back fire to slow the fire down? This is similar to the NetEqualizer approach. NetEqualizer deliberately adds latency to certain bandwidth intensive applications, such as large downloads and p2p traffic, so that chat, email, VoIP, and gaming get the bandwidth they need. The “back fire” (latency) is used to choke off the unwanted, or non-time sensitive, applications. (For more information on how the NetEqualizer works, click here.)

Video is sensitive to latency.

This is a myth.

Video is sensitive to the speed of the connection but not the latency. Let’s go back to our man on the moon example where data takes eight seconds to travel from the earth to the moon. Latency creates a problem with two-way voice communication because in normal conversion, an eight second delay in hearing what was said makes it difficult to carry a conversion. What generally happens with voice and long latency is that both parties start talking at the same time and then eight seconds later you experience two people talking over each other. You see this happening a lot with on television with interviews done via satellite. However most video is one way. For example, when watching a Netflix movie, you’re not communicating video back to Netflix. In fact, almost all video transmissions are on delay and nobody notices since it is usually a one way transmission.

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