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Latency too high when using WLAN.

What is the problem when I ping all my server using Wireless Network, the latency is very high but when using Wired Netwok, latency <1ms.  Can someone help me?

When using WLAN, sometimes the times reach 1000ms and then request time out.  But when using the LAN. all the connection all in optimum condition.

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Wireless is an unregulated, often-unrestricted zone, into which you'll venture for the sake of convenience, and from which you (and your users) may experience much frustration.

Let's talk about why wireless can be slow:

  • It's half duplex.  Of COURSE it'll be slower than wireless.
  • It's using unrestricted and unregulated radio frequencies.  NATURALLY it's going to have inteferers (and they're invisible to you--maybe on the other side of the wall, maybe that WiFi / BlueTooth-enabled cell phone in everyone's pocket).
  • Throughput drops off with distance.  If you're right under a modern AP you could theoretically get 54 Mb/s (or better if you use MIMO) throughput--at half duplex.  Move further away from the AP and your throughput can drop down to 1 Mb/s.
  • There's a respectable percentage of overhead involved in wireless, including (but not limited to)
    • Encryption
    • SSID / VLAN frame information
    • Beacons.  There's one for every AP, one for every SSID.  If you have a LOT of AP's in an area, and/or a LOT of SSID's in the area, your poor wireless device has to pay attention to them ALL, then try to determine which one is "best" based on numerous factors.  It's enough to drive a notepad crazy.
  • Competing wireless (from your neighbor, the businesses upstairs, downstairs, across the street, behind your building) bleeds into your air space, meaning more overlapping AP's and Beacons.
  • Folks can actively try to insert themselves between two devices wirelessly, which is called a Man-in-the-middle attack - Wikipedia, the free encyclopedia.  That's not going to speed your traffic at all.  Worse, you could lose corporate or personal data that may have serious consequences.
  • If you think about CSMAC/D (What is Carrier Sense Multiple Access / Collision Detection CSMA/CD? Webopedia) and how it applies to hubs, there's a parallel to that half-duplex broadcast environment that we call a WLAN.  All those potential collisions mean a lot of potential retransmits--and that slows your traffic down further.
  • Oh, by the way, let's hide the fact from ourselves and our customers that we rely on a medium that can be affected by solar flares.  See Solar storm of 1859 - Wikipedia, the free encyclopedia and then imagine what will happen when this hits satellite feeds, and wired circuits around the world.  Or maybe you want to sleep at night . . .   Were you around in 1989?  Do you remember The Day the Sun Brought Darkness | NASA?  Or how about just thinking about the near miss we had only a few years ago that folks called "The solar storm of 2012 that almost sent us back to a post-apocalyptic Stone Age | ExtremeTech"?

Wireless was initially designed for a limited number of devices--particularly since it was 802.11b, and only worked best when you set your AP's to use just three of their radio channels (1, 6, and 11).

How about understanding why wired isn't slow when wireless IS slow?

  • Wired is full duplex--you effectively get twice the rated throughput
  • Throughput is limited to the speed of your switch and uplinks.  Today, that's going to be Gigabit or faster.  Hmmm . . . 11 Mb/s (or 54 Mb/s), minus overhead, plus collisions, plus interference---versus dedicated switched packet handling at wire speed, no collisions, no interference, no overhead.
  • Security is much improved--no man-in-the-middle attack
  • No collisions, no retransmits with full duplex switch wired connectivity.  Just fast, reliable data flow.

The problems with wireless grow worse as more devices join an already crowded air space.  In one of my environments, every time a person walks by on the sidewalk, or drives by in a car, or rides by in a bus, they bring their cell phone signals within range of some of my AP's.  That's a lot of interference, and if they have their phones set to automatically attach to any open network, they'll start searching and maybe try to join mine.  Depleting my DHCP scopes, consuming my AP's CPU and RAM resources, etc.

So without knowing the details of your environment and your device count and your configurations and setups, we can see that by its very nature wireless is at an extreme disadvantage to wired traffic.

Let's get practical--and worse:  What are lots of folks doing with wireless?  Streaming audio for personal entertainment.  Maybe if they're in a single environment, not driving or walking around, they might be streaming video.  Eating up your bandwidth and radio space and AP resources.

I won't dwell further on it.  Maybe you'll be able to use some of this information to help your team understand that the convenience of wireless does not come without a cost.  That cost is reliability, speed, security--AND capital funds for the wireless infrastructure to manage and try to secure it.  Hopefully you'll get some folks to begin to have an idea that wireless and wired connections are not equal in any way.

Much progress has been made towards improving wireless reliability.  But in a day when BYOD is becoming the norm, and users expect ubiquitous WLAN service while hackers sit out of sight using that same solution . . .

Well, I wish you good luck in improving your crew's thought process!

Swift (wired) Packets!

Rick S.

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I am going to shoot from the hip on this one, two of the key elements about wlan's that makes it different from conventional ethernet network is the collision avoidance mechanism  which means if there is access point is loaded with to many clients it will add latency to your connection the second thing interference you will need to ensure your access points is located in the best position through out your environment as to many access points at one place causes channel interference which will impact your wlan environment big time.

Hi Kevin,

Thanks for your feedback.  But how can you prove that? Actually i need to submit a report to my boss regarding this issue.  However, my Aruba AirWave is not functioning to provide the report.  Hope if u dont mind share with me any reference or article perhaps some open source software that can generate simple report for me.  Thanks again.

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I am not an expert on the Aruba wireless solutions, but to check if your access points is not overloaded with clients is the check the amount of clients connecting to the ap at any given check interference and to  get a good idea on the coverage of your wireless lan I would normally do an wlan survey this would tell me the coverage and interference levels.

is the response time from your wlan constant ?

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What/how did u do for the wlan survey? Are u using any software?  My response time surely not constant.  Thanks for your help.

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If you have a limited budget and can't purchase survey software or hire someone to do a survey, you might want to look at Ekahau.

I was able to do some surveying of a couple of our building with a wireless laptop with this at no cost.  It builds a heat map based on readings from the laptop wireless taken at various points.

John Handberg
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