Minimizing Wide Area Network Latency
What causes wide area network latency and how to minimize it for critical applications.
By: John Shepler
Many companies have added low latency to their list of requirements for WAN (Wide Area Network) connections. Why has latency suddenly gained such importance and how do you get low latency?
What is Latency?
Latency is the time it takes for packets to get from one place to another. The latency on your LAN probably isn’t a worry. The latency on your long haul WAN connections may well cause you big problems. For some specific applications, minimizing latency is the holy grail of networking.
Bandwidth Differs From Latency
Latency and bandwidth aren’t directly related. You can have low speed connections with very minor latency. You can also have screaming Gbps connections with horrible latency. What drives latency is distance, network architecture, and equipment design.
A High Latency Example
Here’s an example of a network setup where you can’t do much about latency. Consider television remote broadcasts. These are the ones where a van with a satellite dish on top parks at the scene of a news event. It really doesn’t matter where in the world the van and the studio are located. The TV signal is going to have a considerable latency or time delay. You see the effect all the time. If the anchor and the field reporter don’t wait a second before they respond to the conversation, they’ll talk right over the top of each other.
The Trouble With Satellites
Why is this? It’s because the signal is being sent from the truck dish to a satellite in geosynchronous orbit at 22,236 miles above the Earth (mean sea level) and back down to another dish at the studio or network headquarters. That means the electromagnetic waves have to travel a minimum of 44,472 miles up and then back down. In practice, the distance is longer because the signal isn’t going straight up and down. Now, consider that the speed of all signals in space is 186,000 miles per second and you have at least a quarter second delay one way or a half second round trip. Any equipment in the path or additional landline connections only makes it worse.
One Way Is OK For Latency
This is why satellite broadband works great for one way TV broadcasts but terrible for VoIP conversations. One way streaming is unaffected by latency. Two way anything is definitely affected. Data file transfers aren’t terribly bothered by going through a satellite because the latency is often small compared to the transfer time. But video conferences can be awkward and real time gaming is an exercise in frustration.
The Minimum Latency To Expect
The point is that if you worry about latency, stay off geosynchronous satellite connections. Even your landline and undersea connections are affected to the tune of at least a millisecond per 186 miles simply due to the speed of light. Actually, you’d never even get that minimum latency value because light slows down in copper wires and fiber optic cores. The electronics that switch and route your path will also each add a small amount of latency to the total.
Low vs High Latency Connections
So, what differentiates a low latency connection from one that doesn’t concern itself much with latency? What you want is short paths between locations and a minimum of equipment in between. That suggests private networks, not the Internet. The Internet is designed for universal access and self-healing in the event of problems. Latency is an afterthought at best.
MPLS Networks Offer Low Latency Options
Many of today’s top MPLS networks are engineered to minimize latency. There are relatively few label switches to route the traffic and the networks have sufficient bandwidth to prevent congestion that backs up data flow and makes latency worse. You’ll want a network that has fiber runs as direct to your locations as possible to minimize path length. If MPLS will do the job, it has definite cost advantages and can give you mesh network connections so that all sites can easily communicate.
Private Lines Optimized For Latency
If latency is your number one priority, you’ll do even better with direct private line connections especially designed to minimize latency. These fiber paths are as close to a straight line as you can get and there is little in the way of electronics to slow things down. The one hitch is that these connections are primarily found between major international destinations, especially those like London, Frankfurt, New York and Chicago that are financial trading centers. High speed financial trading is the number one application driving the deployment of ultra low latency fiber optic services.
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