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Repeater & Access Point

Last response: in Wireless Networking
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March 4, 2011 12:12:44 AM

I saw an article talking about wireless repeater will loss of bandwidth. May I know will access point got the same problem?

More about : repeater access point

a b F Wireless
March 4, 2011 11:07:33 AM

It depends.

The reason a repeater losses bandwidth is because the user of the repeater must make two wireless hops to reach the wireless router.

[wireless router]<-- wireless -->[repeater]<-- wireless -->[wireless client]

All the wireless stations are using the same wireless frequency. But only two wireless stations can be transmitting at any given time. So whenever the wireless client is talking to the repeater, the repeater can’t be talking w/ the wireless router, and vice versa. In effect, all communications is serialized, it never happens in parallel (as would be the case w/ wire). As a result, the effective bandwidth is HALVED for the wireless client. Add more repeaters and it’s HALVED again and again.

The reason I said it depends is because this same problem *does* affect any wireless access point.

[wireless router]<-- wireless -->[wireless clients (two of them)]

In this case, whenever BOTH wireless clients are trying to communicate w/ the wireless router at the same time, one of them must wait for the other to complete its transmission before the other can begin. IOW, it’s the exact same issue as when using a repeater!

A repeater is just a specific example of a more general problem. The fact everyone is using the same frequency means everyone is in contention for that frequency. It’s like having everyone using walkie-talkies on the same frequency. It’s a party line and ppl have to take turns. And the more ppl you add, the more it slows communications throughput.

The only reason we speak of the problem more readily w/ repeaters is that a repeater is GUARANTEED to cause a bandwidth loss with even a single wireless client, whereas in the second case it would require at least two wireless clients, AND, only when attempting to access the wireless access point at the exact same time (e.g., two large, concurrent downloads). For many ppl, the latter is not something that either happens to them (they are the lone wireless client), or it does so only rarely, or when it does, they don’t notice the impact over short-lived transmissions. But it’s always there lurking as a potential problem.

Hopefully that explanation should stir some ideas about how to avoid the problem. One way is to create YOUR OWN repeater. Nothing says you can’t chain a wireless ethernet bridge to another wireless access point (that’s all a repeater is), each using DIFFERENT frequencies, and thus preserve your bandwidth.

[wireless router]<-- wireless -->[wireless ethernet bridge]<-- wire -->[wireless access point]<-- wireless -->[wireless client]

Yes, it adds more “bulk” to the solution, but it’s still a repeater, and now each side of the repeater can communicate at the same time.


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March 7, 2011 1:09:34 AM

Thank you very much for your help. I setup a wireless lan as:
[Wireless Router]<--wireless-->[wireless access point]<--wireless-->[2 wireless clients(IP Camera)]. I encount the 2 IP Cameras like you mention one of them must wait for the other to complete it transmission before the other can begin. That why I face this problem when 1 camera detect motion the other camera signal drop, sometime disconnected. Do you have any solution?
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a b F Wireless
March 7, 2011 2:16:28 AM

In the case of the two IP cameras, if you have clients (wired or wireless) actively accessing both the IP cameras at the same time, then yes, they must take turns communicating w/ the wireless access point. But of course, each IP camera it taking turns in quick succession, so it appears to be a constant stream to the client from each IP camera. But if you were to measure the actually throughput per camera over a given period of time, it would be less than a single IP camera over that same period of time.

So it's not as if having multiple IP cameras should cause these wireless connections to drop or otherwise be disconnected. The wireless access point just doesn't perform as well as more wireless devices contend for the same frequency. Of course, if you get enough wireless devices requiring the access point at the same time (or each IP camera is sucking a HUGE chunk of the available bandwidth, e.g., if it’s an HD stream over wireless G), throughput *might* be so low as to appear to be a dropped connection. But we're talking about a LOT of wireless contention in that case, far more than a couple wireless clients and wireless IP cameras.

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March 7, 2011 2:29:47 AM

Hi Veteran,
Thank for your infomation. In this case you know now the router or AP come with Qos feature. Will this feature help?
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March 17, 2011 12:22:35 AM

eibgrad said:
In the case of the two IP cameras, if you have clients (wired or wireless) actively accessing both the IP cameras at the same time, then yes, they must take turns communicating w/ the wireless access point. But of course, each IP camera it taking turns in quick succession, so it appears to be a constant stream to the client from each IP camera. But if you were to measure the actually throughput per camera over a given period of time, it would be less than a single IP camera over that same period of time.

So it's not as if having multiple IP cameras should cause these wireless connections to drop or otherwise be disconnected. The wireless access point just doesn't perform as well as more wireless devices contend for the same frequency. Of course, if you get enough wireless devices requiring the access point at the same time (or each IP camera is sucking a HUGE chunk of the available bandwidth, e.g., if it’s an HD stream over wireless G), throughput *might* be so low as to appear to be a dropped connection. But we're talking about a LOT of wireless contention in that case, far more than a couple wireless clients and wireless IP cameras.


Hi Eibgrad,

You know anything about "Qos" feature in the router?
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October 12, 2012 3:38:53 PM

Hi

I have a question regarding the similar issue.

With wireless access point, can you do the following:

<wireless router>-----wireless-----<wireless access point>----wireless----<wireless access point>---wireless---<wireless client>

or does this only works for repeater?

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