LAN Bridge

LAN Bridge

Post by Srandal awe » Tue, 17 Jun 2003 17:16:41



Looking at a project to connect a remote site (about 8miles) to the main
switched LAN. Currently using a leased E1 (2Mbit/s) but reliability and rising
rental costs making this option no longer viable.

Have two main options direct fibre link or microwave radio.

Fibre sounds nice and easy but would be very expensive to install or lease.

The microwave radio option appears to be the answer but I have no experience of
this type of equipment. We have clear line of sight to the remote site so that
is not an issue.

Equipment I am looking at will provide 8Mbit/s which is fine as performance on
the old E1 was not too much of an issue. It also has normal Layer 2 switch
capability including tagged VLAN support which means it just simply plugs into
the switches at both ends and "bridges" them.

Has anyone any experience good or bad of microwave radio links. I have "heard"
about not working when it rains etc but the supplier is quoting a 99.99%
availabilty which is far better than we ever got on the E1.

As a side question, why do optical line driver suppliers quote
bandwidth/throughput as pps (pulses per second?). e.g 10Mbit/s line driver
quoted as 14800 pps. Is this somthing to do with the line codes that they use.

Regards

Simon

 
 
 

LAN Bridge

Post by shop » Wed, 18 Jun 2003 04:08:36



Quote:

> Looking at a project to connect a remote site (about 8miles) to the main
> switched LAN. Currently using a leased E1 (2Mbit/s) but reliability and
rising
> rental costs making this option no longer viable.

> Have two main options direct fibre link or microwave radio.

> Fibre sounds nice and easy but would be very expensive to install or

lease.

Look at BT SHDS (LES circuit) - 10 Mbps LES if the geography is right is
cheaper than E1.

Quote:

> The microwave radio option appears to be the answer but I have no
experience of
> this type of equipment. We have clear line of sight to the remote site so
that
> is not an issue.

You might have to pay some licence fees.

Quote:

> Equipment I am looking at will provide 8Mbit/s which is fine as
performance on
> the old E1 was not too much of an issue. It also has normal Layer 2 switch
> capability including tagged VLAN support which means it just simply plugs
into
> the switches at both ends and "bridges" them.

> Has anyone any experience good or bad of microwave radio links. I have
"heard"
> about not working when it rains etc but the supplier is quoting a 99.99%
> availabilty which is far better than we ever got on the E1.

Microwave and the close cousin infra red tend to "fade" when the weather
goes. Supplier should be able to tell you how much margin there is across
the planned link, and how that translates into weather.

Remember the dish etc will be exposed to other issues - lightning for one -
you may want to have a maint contract.

Microwave can be very reliable, but some cheap systems dont seem to be - ask
for reliability info, and also if that is backed up by an SLA or other
guarantees.

Just remember you are not exactly comparing like with like - a bunch of kit
and some support vs a rented circuit.

a LES circuit will come with  guarantees - more to the point they tend to be
rock solid reliable once commissioned.

Quote:

> As a side question, why do optical line driver suppliers quote
> bandwidth/throughput as pps (pulses per second?). e.g 10Mbit/s line driver
> quoted as 14800 pps. Is this somthing to do with the line codes that they

use.

Packet / sec. 14880 is theoretical max with smallest packet size on an
Ethernet (in each direction on full duplex).

This is important because lots of kit traditionally had trouble keeping up
with worst case link load and small packets.

Quote:

> Regards

> Simon

--
Regards

Stephen Hope - remove xx from email to reply

 
 
 

LAN Bridge

Post by ch.. » Wed, 18 Jun 2003 13:40:42




Quote:

>Looking at a project to connect a remote site (about 8miles) to the main
>switched LAN. Currently using a leased E1 (2Mbit/s) but reliability and rising
>rental costs making this option no longer viable.

>Have two main options direct fibre link or microwave radio.

>Fibre sounds nice and easy but would be very expensive to install or lease.

>The microwave radio option appears to be the answer but I have no experience of
>this type of equipment. We have clear line of sight to the remote site so that
>is not an issue.

>Equipment I am looking at will provide 8Mbit/s which is fine as performance on
>the old E1 was not too much of an issue. It also has normal Layer 2 switch
>capability including tagged VLAN support which means it just simply plugs into
>the switches at both ends and "bridges" them.

>Has anyone any experience good or bad of microwave radio links. I have "heard"
>about not working when it rains etc but the supplier is quoting a 99.99%
>availabilty which is far better than we ever got on the E1.

>As a side question, why do optical line driver suppliers quote
>bandwidth/throughput as pps (pulses per second?). e.g 10Mbit/s line driver
>quoted as 14800 pps. Is this somthing to do with the line codes that they use.

>Regards

>Simon

Also consider that you will want some sort of vpn or encryption over a
radio link.  Otherwise you'll be broadcasting you companies data all
over.
 
 
 

LAN Bridge

Post by NICKT » Thu, 19 Jun 2003 01:10:02


Quote:

>Equipment I am looking at will provide 8Mbit/s which is fine as performance
>on

>Has anyone any experience good or bad of microwave radio links. I have
>"heard"
>about not working when it rains etc but the supplier is quoting a 99.99%
>availabilty which is far better than we ever got on the E1.

Take it you are UK based. All microwave radio links are subject to a RA (Radio
Authority) licence. The cost of this licence is dependant on bandwidth used and
EIRP, how much RF power you transmit. The availability quoted is typical for UK
based microwave radio links. If you want 99.999% you have to pay more!!

You have been quoted a 8Mbit/s link because all radios were designed to deliver

"X" E1s. So this equipment is a rehashed 4 x 2Mbit/s to give 8Mbit/s in the
same RF channel.

I have seen quoted that 8Mbit/s gives the same performance as "wire" 10Mbit/s
but not sure how that works.

Correctly installed microwave should give very good performance but check which
RF  band they are using 8 miles is too far for 38GHz and might be OK for
23/25GHz. Your next band would be 13/15GHz but there is a lot of use in this
area.

As for rain fade, this is frequency dependant. Higher the frequency the worse
the problem. Again good fade margin is what you need so ask what signal level
they are expecting and ask for 10 -3 error level. You need at least 30dB of
margin.

Regards

Nick