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What is Latency...?

Latency is the time it takes for a Network Packet to get to a destination and back (Round Trip), this is as important as download speed because a network with high latency (slow) will take longer to pass information about and this can have a negative effect, web pages will take longer to load as each request for the next picture, script or text has a siginificant delay in between, online gaming experiences can be next to useless as you can not control in game action in real-time (or close to it), download speeds of files can be affected also in the same scenario as web-pages.

The following table illustrates the effect of latency (and packet loss) on TCP throughput. This data was generated by using a latency and packet loss generator between two PCs connected via 100Mbps Ethernet (full duplex). The packet loss rate was set to 2%, which means that 2% of packets were discarded by the test equipment. Note that the TCP throughput values are much lower in the presence of packet loss. (Credit: Smutz.us)

Round trip latency

TCP Throughput with no packet loss

TCP Throughput with 2% packet loss

0 ms

93.50 Mbps

3.72 Mbps

30 ms

16.20 Mbps

1.63 Mbps

60 ms

8.07 Mbps

1.33 Mbps

90 ms

5.32 Mbps

0.85 Mbps

(Credit: Smutz.us)

What Causes Latency?

End-to-end latency is a cumulative effect of the individual latencies along the end-to-end network path. Listed are some of the typical components of latency from a workstation to a servers:

  • workstation LAN / Wifi (response to in/out traffic)
  • Router (response to in/out traffic)
  • ISP link/Servers (response to in/out traffic)
  • ISP network (overloaded, faulty)
  • Path from ISP to Host (exchange, dslam, switches, patch points etc responding to traffic)
  • Host's internal network (overloaded, faulty)

Network routers are the devices that create the most latency of any device on the end-to-end path. Routers can be found in each of the above network segments. Packet queuing due to link congestion is most often the culprit for large amounts of latency through a router. Some types of network technology such as satellite communications add large amounts of latency because of the time it takes for a packet to travel across the link. Since latency is cumulative, the more links and router hops there are, the larger end-to-end latency will be. (cred: smutz.us)

There are many tests online that check latency but I personally feel its better to test it yourself using a CMD Prompt as you can choose what to ping and can test your home network as well as beyond it, if you wish to use an online test then Pingtest is probably the best one to use (never use results from a speedtester as they are nearly always much higher than what they actually are) it will also test for packet-loss.

A normal broadband line will have a latency of around 20-40ms (milliseconds), anything under 40ms is desired and considered as good, the higher the number the slower it is.

Testing Latency:

The first thing we do is ping your Network Card (NIC) on your computer to make sure its working ok, then we ping your Router/Modem to see how your network responds so we can see the latency on it, finally we ping websites out on the internet to test your ISP's Network Latency. Latency will be slightly higher using wifi than it will on LAN (Ethernet Cable) but only by small amount, if you use Wifi you may want to test both Wifi and LAN, especially if you get a high result on Wifi. Latency may also be slightly higher if you use a seperate modem and router rather than an all-in-one. Firstly you need to find out what your router/modem IP Address is:

hold down the 'Windows' key on your keyboard (usually left of the space bar) and press 'R' - this opens the RUN box, in that box type cmd and press enter, this will open a Command Prompt window that looks like the one below...

In the CMD Prompt type in ipconfig and press enter, scroll up and look for your 'Default Gateway' and make a note of this IP Address (this is the address of your modem/router).

***Before you run these tests be sure nobody else is using your network or broadband and that you have no applications running on your computer that may be downloading files in the background or using the internet in anyway, its essential that when testing your connection there should be no activity on the line***

TESTING INTERNAL NETWORK CARD:
In the CMD Prompt window type in ping 127.0.0.1 and press enter, this will ping your network card, typical results should be <1ms (less than 1 millisecond).

TESTING MODEM/ROUTER GATEWAY:
We are now going to ping your modem/router, in the CMD Prompt window type ping (enter default gateway IP address) , it should look something like this ping 192.168.0.1 (depending on what the IP address is) and press enter, typical results should be 1-2ms or less.

TESTING ISP/EXTERNAL NETWORK:
We are now going to ping a website out on the internet, your best using a website in your own country nearby, a popular one to use in UK is the BBC website, In the CMD Prompt windows type ping www.bbc.co.uk and press enter, typical results would be under 40ms for a healthy connection, if you get high results on BBC then try a few websites to ensure that its continous and not just on the BBC.

If your Latency is high then head over to our Speed Up Your Internet page to see if you can fix it.

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