Subject: Some Developments - Internet Over Satellite Above 34/8Mbits

From: "Mike Holdsworth" <[email-masked]>
Date: Fri, 3 Nov 2000 17:34:39 -0000

Hi Everyone,

If anyone is currently looking at Internet Over Satellite (Or Broadcast or
any satellite network) at speeds in excess of the old 34/8Mbits "standard"
then this might prove interesting.

Also if you are attending COMDEX in Las Vegas drop me a mail as I am there
all week, and would prefer talking about Satellite Networking than whatever
the rest of the people are talking about. Sorry the rest of you ;-)!!

Mainly we are involved in interfacing between Satellite & Terrestrial Wide
Area Networks. There are a couple of issues here that are worth noting.

HSSI - High Speed Serial Interface

Commonly found on Satellite Modems and Cisco Routers (Also Lucent) this
interface can run at significantly higher speeds than the Cisco max of
51.84Mbits (STS-1/OC-1).

A lot of the HSSI/G.703 DSUs for 8Mbits, 34Mbits and 45Mbits are not
designed to work with Satellite Networks. In particular this is true of the
45Mbits/DS3 HSSI DSUs which often operate in Fractional T3 Mode, therefore
generating spurious errors. As opposed to a Clear Channel DS3 DSU.

Recently we supplied some 51.84Mbits HSSI to OC-3 Fiber Converters into a
Broadcast Network. This seemed to be the fastest possible on HSSI. A few
hours in the lab proved this completely wrong.

Using short HSSI Cables we have currently tested 70Mbits using our own ATM
Switches into EFDATA SDM2020 Satellite Modems. One Application we tested was
70/17Mbits as an Asymmetric Internet Backbone and this worked fine.

Satellite Modem Manufacturers

It seems that the main 3 Manufacturers COMTECH EFDATA, NEWTEC and RADYNE
COMSTREAM are offering Standard HSSI Modules to 51.84Mbits, and offering
Software Upgrade Keys to support up to 70Mbits.

I'm not sure why this is the "supported" rate, though I imagine this is
because to go faster you would need maybe a ASI or LVDS interface.

This presents a potential problem. There aren't many IP Routers out there
with ASI or LVDS modules. Also if you ramp the HSSI Module to 70Mbits what
are you going to plug it into. Cisco won't support this speed.

We've got a fix for this problem basically. I am just after some feedback to
see which way I should take this. Currently we can easily do 70Mbits HSSI
into our small 3-Port ATM Switch. We currently output this as OC-3/STM-1 ATM
to an ATM interface on a Router. Most Clients are fine with ATM on a router.

Would this be better if the Metrodata equipment supported Packet Over Sonet
(POS)?

We can go higher than 70Mbits on the HSSI Module. Clocking EFDATA SDM2020s
we got to 90Mbits on the Satmod HSSI Modules in testing though this was
using some proprietary HSSI Modules on the Metrodata Equipment.

We are currenlty developing an ASI Module for our equipment which is
expected to work at up to 130Mbits. This could then easily be interfaced
into an OC-3/STM-1 ATM Port on a router.

Currently the highest speed Asymmetric Application we have tested has been
with the Newtec SDH 155Mbits Satellite Modems. This was 155/70Mbits using 2
Bi-Direcitonal ATM PVCS between the 2 Earth Stations. We used Single Mode
Fiber Optic Modems in the 155Mbits path and HSSI Modems in the 70Mbits path.

The HSSI Modules in the Metrodata equipment are actually passing ATM cells,
and the Interface to the Routers was OC-3 ATM.

Also, one point I would like to mention is that when we can use ATM between
the 2 Metrodata boxes they require no clocking configuration. They simply
operate from the Satellite Modem Clock. This may be useful in a boradcast
network as you simply plug them in and forget about them, only needing to
change the Modem Clocks when the client wants more speed.

I've made some updates to our website at www.metrodata.co.uk which covers
most of the points here. fee; free to visit and please give me feedback.

Its not completely finished though and I apologise for this. I like playing
with the kit too much I guess!!

Regards and Have a great weekend

Mike

[email-masked]
Satellite Product Manager
====================
www.metrodata.co.uk/satellite