1KM link with 100MB bandwidth

RouterOS General
1

Can some some give me a spect on 802.11a to achieve 100MB on a 1KM link. can i achieve this with a routerbord 220 or must i use another board.

2

Routerboards and similar H/W with 266MHz CPU will give you 25Mbps half duplex max.
You need 1GHz CPUs to do the maximum 72Mbps TCP and 83Mbps UDP, again half duplex.
If you actually need 100Mbps full duplex you need either a licensed microwave link or a laser link (ideal at that distance).

Regards

Stephen

3

Or a kind of load balancing between links:)

4

Thanks Stephen, if i decide to use an indoor unit with the 1GHz board with LMR 400 120ft from ur experience would i still be able to achieve the maximum bandwidth for a 1KM link with the 30Dbi antennas i have.

Regards

Ndukwe

5

Hi amsco,

at 5GHz (802.11a) you have high losses on the RF cables, 120ft is a long way …
30dBi antennas sound great, that might counter the losses.
Personally I would use 1GHz CPU+radio in outdoor boxes, you have to have low-power-consumption ones, not Pentium4 power-guzzlers.
We have even newer ones now, just today we are testing a new Pentium M 600MHz board which has excellent features/performance, clocking 67Mbps traffic through it as I write. Very compact, even has a mini-PCI for the radio directly on the motherboard, and inbuilt power supply.

Regards

PS Eugene - have you (or anyone) actually tried load balancing on parallel RF links and got it to work?
Very interested to see the setup or an explanation if so.
We would be interested in documenting this and putting it up on our site as a sample configuration too.

6

Stephan thanks, i think i would go the way of outdoor radio, what make is the motherboord with minipci slot?

Ndukwe

7

It is important to keep in mind the delay involved in the link, since TCP is limited by delay, independently of the speed of the link.

For example, and this is just for example, I have no idea what type of delays you can acheive on the gear your looking at:

If you take the receive window of TCP as 65536, and figure a 100ms delay, then your looking at approx. 5Mbps thruput.

With 10ms delays you could get around 50Mbps and with 5ms delays around 100Mbps.

8

Hi Ndukwe,

There are high quality boards on the market using Intel chipsets. The cheaper VIA ones we have had problems with, they “lock up” at full speed - though many users might never see that, we’re an equipment supplier and our customers wouldn’t put up with that.
V10000’s suffer throughput problems, and M10000’s and M6000’s lock up.

The problem is that if you use the boards “as is” they still generate 10’s of watts of power - and then the heat stays in the box, so you either have to vent it with fans, which allows moisture ingress, or change the cooling system - which starts becoming much harder to implement - though there are some interesting solutions which are not exactly DIY.

Give me a mail off-forum and tell me about what you are trying to do, and I’ll give you some pointers.
stephen.patrick@cablefree.co.uk

Regards

Stephen


PS signal, you are right about delay, but at 1km there isn’t a huge “free space” delay, the major improvement is using Nstreme (which needs a fast CPU) to combat the collisions inherent in normal WiFi at such distances. There are people on the forum who have tens of megabits throughput at >30km, for example.

9

Hello stephenpatrick. Can You tell me where to find such motherboards/routerboards? Have you any description, manual, web page, anything… Thanx…

10

Hello Blue,

Can you send me a mail off-list, once I incurred the wrath of another user for “advertising” when I was trying to be helpful.
stephen.patrick@cablefree.co.uk

Regards