This Application Note concentrates on the different options available to interface ATM Switches and Satellite Modems. It does not cover the benefits
of ATM, or the concept of ATM Over Satellite. We are more concerned with the real problems that might exist when integrating Satellite into an
ATM network, or extending an ATM network over Satellite.

Within the United States, there are a number of ATM Vendors that have validated interoperability with Metrodata Products. The majority of
products are ATM Switches [Fore ASX-200, Cisco Lightstream 1010, Cisco Stratacom BPX], though we have also undertaken testing with Routers
that have ATM Modules [such as the Cisco 3600 and 7500 Series Routers].

As ATM is mainly used as a means of multiplexing multiple lower data rates, into a single larger "trunk" link, interfaces tend to correspond to fixed rates such as DS-3 [44.736Mbps] and OC-3 [155.52Mbps]. This is fine, when the rates your are using are Nx64k, T1, E1, E2, E3, DS-3 and OC-3.

However, in Military networks bandwidth tends to be controlled and allocated carefully - especially for satellite and wireless capacity. Applications
that require an exact data rate such as 9.123Mbps, might use a DS-3 interface on an ATM Switch, but they wouldn't use a DS-3 across the Satellite Link. Rather, the satellite link would be run as closely as possible to the application data rate.

This would require a serial interface such as EIA530 or HSSI on the Satellite Modulator. This conversion of DS-3 ATM to EIA530 or HSSI, would be simple with Metrodata.

NATO NC3A ATM Over Satellite Tests - Metrodata's Involvement

NATO Consultation, Command and Control Agency [NC3A] conducted a series of interoperability tests, experiments and demonstrations of asynchronous transfer mode [ATM] over Satellite Communications [SATCOMS] links, using Commercial Off The Shelf [COTS] equipment.

Bilateral testing with the United States Communications Electronics Command [CECOM] was conducted from late 1995 through mid 1996.

The Satcom Link was implemented using a standard E1 2.048Mbps Carrier. The Comtech EFDATA SLM 8650 Modem was employed at NC3A, and provided a standard 2.048Mbps G.703/G.704.

This E1 G.703/G.704 interface was connected to the Metrodata ATM Switching DSU, which converted the E1 ATM cell rate on the Satellite Modem
to an OC-3 ATM cell rate on the Fore Systems ASX200 ATM Switch.

This was one of the first highly successful instances of Metrodata's involvement in ATM Over Satellite.

Interfacing ATM Switches to HSSI, EAI530 or ASI Satellite Modems

The main product used throughput this Application Note is the Metrodata Access Processor. This is a modular ATM Switch, which comes in 3 Port,
4/5 Port and 8/9 Port Versions. As we are primarily concerned with converting between 2 different pieces of equipment we have mostly used the
3 Port AP3000.

When considering connecting an ATM Switch to a Satellite Modem there are 2 elements that need to be considered:

• Is the ATM Switch connecting to another ATM Switch at the far end of the satellite link?
• Is the ATM Switch connecting to a non-ATM Network at the far end of the satellite link?

In the first instance, the Satellite Link would have to carry ATM point-to-point between the ATM Switches. This requires that the Serial Module on
the AP3000 can support ATM cells. This Serial ATM Module would then connect to the Serial Satellite Modem to enable a seamless connection
end-to-end. At the far end of the Satellite link a second AP3000 would be required to reconvert Serial back to ATM. This Can be seen in the
diagram below.

In the second instance, it is more than likely that the ATM Switch is providing back-haul across an ATM network. As such, the Serial Module on the AP3000 does not need to support ATM cells, as the data it is receiving is not ATM. It might be encrypted though, but as the Serial Module transports
a bit-stream of data it doesn't matter to Metrodata if the data is encrypted or not. This can be seen in the diagram below.

This Application Note is concerned with ATM Over Satellite. If you have a requirement to back-haul NON-ATM traffic from a Satellite Modem over
an ATM Network then please contact us for our Application Note on "Back-hauling Satellite Over ATM Networks".

Interestingly enough, there are only a finite number of ways of connecting an ATM Switch to a Serial Satellite Modem. Which Satellite
Modem interface is used, tends to depend upon the intended data rate of the link.

Standard operations are:

• EIA530/TTL would be used at speeds up to 10Mbits
• HSSI would be used at speeds up to 52Mbits
• ASI would be used above 52Mbits

But, EIA530 on a Satellite Modem can go to 20Mbits, HSSI to 90Mbits and ASI over 155.5Mbits.

Metrodata support the following standard ATM interfaces:

• E1 - 2.048Mbits
• E2 - 8.448Mbits
• E3 - 34.368Mbits
• DS-3 - 44.736Mbits
• OC-3 - 155.52Mbits

We also have the following Access Processor Modules available that support ATM cells. These can be used to connect ATM Switches together over
a satellite link:

• HSSI ATM UNI Module
• ASI ATM UNI Module

If you have a requirement to use EIA530 Satellite Modems to connect ATM Switches together, please let us know. Metrodata have an EIA530 ATM
UNI Module designed. External Converters are available to convert HSSI to EIA530 and HSSI to V.35

Our ATM Products have been tested with a variety of different Satellite Modem Vendors Equipment including Newtec, Comtech EFDATA and
Radyne Comstream.

As the previous page establishes, there are 2 types of conversion:

• Fixed Rate ATM Switch to Variable/Scalable Rate ATM Satellite Modem
• Fixed Rate ATM Switch to Fixed Rate ATM Satellite Modem

Applications are categorised by the Interface of the ATM Switch:

• E3 - 34.368Mbps [pages 4-6]
• DS-3 - 44.736Mbps [pages 7 - 9]
• OC-3 - 155.52Mbps [pages 10 - 15]

For each of the above ATM Interfaces, we look at connecting to:

• EIA530 Satellite Modems
• HSSI Satellite Modems
• G.703/G.704 Satellite Modems
• ASI Satellite Modems

Connecting E3 ATM Switches to Satcoms

Connecting E3 ATM Switches to Satcoms

Whilst ATM Switches widely support DS-3, more typical outside of the United States is the E3 Speed, which is 34.368Mbps. If you are installing
ATM equipment in Europe it is likely that you will be using E3 Leased Lines in some areas. This does not mean that you will have to have an E3
ATM interface, and it is possible to connect a DS-3 or OC-3 ATM Switch to an E3 Leased Line by using the Metrodata ATM Switching DSU.

• Connecting E3 ATM Switches Over EIA530 Satellite Modems
• Connecting E3 ATM Switches Over HSSI/ECL Satellite Modems
• Connecting E3 ATM Switches Over Fixed Rate G.703/704 Satellite Modems
• Connecting E3 ATM Switches Over ASI Satellite Modems
• Connecting E3 ATM Switches to EIA530 Satellite Modems

The Metrodata Access Processor can provide Single E3 ATM to EIA530 Conversion, where only a single Full Duplex Satellite Connection exists.
Also, aggregation of multiple EIA530 is possible onto a single E3 ATM interface.

The only product we have that can convert E3 to EIA530 to support ATM cells is the Metrodata AP3000. The Metrodata AP EIA530 Module currently supports a single EIA530 interface. This interface can operate at Simplex, Full-Duplex and Asymmetric speeds. It can support exact clock rates
down to 1Hz. As its maximum speed is currently 20Mbps, this gives it 20 Million different clock rates.

Connecting E3 ATM Switches to HSSI Satellite Modems

How you connect an E3 ATM Switch to a HSSI Satellite Modem depends on 3 factors:

• Is the data rate fixed at 34.368Mbps
• Is the data rate an "odd" or non telco standard rate
• Is the data rate going to have to be changeable or scalable

If the data rate is fixed at 34.368Mbps, we can provide an E3 34.368Mbps G.703 to HSSI Converter, of which Metrodata have 2
products - DC3445 [also supports DS-3] and the FM4900 [only supports E3]. Typically these devices are used to connect HSSI Routers with E3 or
DS-3 Leased Lines. However, because they operate in an unframed mode, they can transparently pass ATM cells.

If you are going to change data rate or have an "odd" or non standard rate, then you will need to use the Metrodata AP3000. This would be configured with an E3 ATM UNI Module to connect to the E3 ATM Switch, and a HSSI ATM UNI Module to connect to the HSSI
Satellite Modem. This configuration would support any rate from 8Kbps to the maximum E3 rate of 34.368Mbps.

Connecting E3 ATM Switches to G.703/G.704 Satellite Modems

G.703/G.704 Satellite Modems support fixed Telecoms rates such E1, T1, E2, T2/J2, E3 and DS-3. Here it is the lower speeds that interest us, as
if you had an E3 ATM Switch, chances are you wouldn't be running a Satellite link any faster than 34.368Mbps. If you were running the link at 34.368Mbps then you could simply cable the Satellite Modem straight into the E3 ATM Switch. Because G.703/G.704 Satellite Modems only run
at fixed rates, they can be converted to E3 ATM by using the Metrodata Switching DSU. Currently this device supports the following ATM Rates
when converting to an E3 ATM Switch:

• E1 or 2.048Mbps - Using the Metrodata E3 to E1 Switching DSU
• E2 or 8.448Mbps - Using the Metrodata E3 to E2 Switching DSU

Rates which could be supported, given a customer requirement are T1 1.544Mbps and T2/J2 6.321Mbps.

Connecting E3 ATM Switches to ASI Satellite Modems

ASI Satellite Modems support rates up to 240Mbps [though this tends to be the Modulator, with lower speeds on the Demodulator]. This scalability exists because ASI is mainly used in the Broadcast Sector as a means of Distributing/Broadcasting Video Channels. As such a Video channel might take up around 4Mbps. You can Broadcast on one output multiple Video Channels and so would have multiple 4Mbps. All of this would be on a
single ASI Satellite Modem, so it has to support various different rates.

Because of the ability of ASI to operate at High Data rates [HDR], it is beginning to be used as a means of transporting data over satellite. But
typical data equipment such as Routers and ATM Switches do not have an ASI interface. Using the AP3000, you could easily convert between E3
and ASI using the E3 ATM UNI Module and the ASI ATM UNI Module.

Also, using ASI allows you to Multicast at High Data Rates. You could have an outbound channel of 110Mbps in a 36Mhz transponder and several receive sites.

Connecting DS-3 ATM Switches to Satcoms

DS-3 is widely used as an interface when multiple serial connections at lower speeds have been multiplexed together. These are then aggregated
up into an OC-3 or OC-12 ATM Trunk. DS-3 is also valid as a means of connecting ATM Switches together over Satellite. The reason for this is that satellite capacity is expensive, and as such must be used effectively. Satellite Links under 44.736Mbps are probably greater in number than satellite links over 44.736Mbps, within Government Networks.

Perhaps this is because until Metrodata it was difficult to interface Satellite Networks into ATM networks. In the DS-3 Section, we have the same
4 Satellite Modem Types as in the E3 section:

• Connecting DS-3 ATM Switches Over EIA530 Satellite Modems
• Connecting DS-3 ATM Switches Over HSSI/ECL Satellite Modems
• Connecting DS-3 ATM Switches Over Fixed Rate G.703/704 Satellite Modems
• Connecting DS-3 ATM Switches Over ASI Satellite Modems
• Connecting DS-3 ATM Switches to EIA530 Satellite Modems

The Metrodata Access Processor can provide Single DS-3 ATM to EIA530 Conversion, where only a single Full Duplex Satellite Connection exists.
Also, aggregation of multiple EIA530 is possible onto a single DS-3 ATM interface.

The most effective product Metrodata have to convert DS-3 to EIA530 to support ATM cells is the Metrodata AP3000. The Metrodata AP EIA530 ATM UNI Module currently supports a single EIA530 interface. This interface can operate at Simplex, Full-Duplex and Asymmetric speeds. It can support exact clock rates down to 1Hz. As its maximum speed is currently 20Mbps, this gives it 20 Million different clock rates.

As most ATM Switches do not support ATM on their EIA530 Modules, this is quite a useful Module for connecting DS-3 ATM Switches to EIA530 Satellite Modems.

Connecting DS-3 ATM Switches to HSSI Satellite Modems

How you connect an DS-3 ATM Switch to a HSSI Satellite Modem depends on 3 factors:

• Is the data rate fixed at 44.736Mbps
• Is the data rate an "odd" or non telco standard rate
• Is the data rate going to have to be changeable or scalable

If the data rate is fixed at 44.736Mbps, we can provide a DS-3 44.736Mbps G.703 to HSSI Converter, of which Metrodata have 2 products -
DC3445 [also supports E3] and the FM4950 [only supports DS-3]. Typically these devices are used to connect HSSI Routers with DS-3 Leased Lines.
However, because they operate in an unframed mode, they can transparently pass ATM cells.

If you are going to change data rate or have an "odd" or non-standard rate, then you will need to use the Metrodata AP3000. This would be configured with an DS-3 ATM UNI Module to connect to the DS-3 ATM Switch, and a HSSI ATM UNI Module to connect to the HSSI Satellite Modem. This configuration would support any rate from 8Kbps to the maximum DS-3 rate of 44.736Mbps.
Connecting DS-3 ATM Switches to G.703/G.704 Satellite Modems

G.703/G.704 Satellite Modems support fixed Telecoms rates such E1, T1, E2, T2/J2, E3 and DS-3. If you've got a DS-3 ATM Switch, you wouldn't be running a Satellite link any faster than 44.736Mbps as you would have to discard any ATM cells that are over 44.736Mbps. If you were running the
link at exactly 44.736Mbps then you could simply cable the Satellite Modem straight into the DS-3 ATM Switch. Because G.703/G.704 Satellite
Modems only run at fixed rates, they can be converted to DS-3 ATM by using the Metrodata Switching DSU. Currently this device supports the following ATM Rates when converting to an DS-3 ATM Switch:

• E1 or 2.048Mbps - Using the Metrodata DS-3 to E1 Switching DSU
• E2 or 8.448Mbps - Using the Metrodata DS-3 to E2 Switching DSU
• E3 or 34.368Mb/s - Using the Metrodata DS-3 to E3 Switching DSU

Rates which could be supported, given a customer requirement are T1 1.544Mbps and T2/J2 6.321Mbps.

Connecting DS-3 ATM Switches to ASI Satellite Modems

ASI Satellite Modems support rates up to 240Mbps [though this tends to be the Modulator, with lower speeds on the Demodulator]. This scalability exists because ASI is mainly used in the Broadcast Sector as a means of Distributing/Broadcasting Video Channels. As such a Video channel
might take up around 4Mbps. You can Broadcast on one output multiple Video Channels and so would have multiple 4Mbps. All of this would be on
a single ASI Satellite Modem, so it has to support various different rates.

Because of the ability of ASI to operate at High Data rates [HDR], it is beginning to be used as a means of transporting data over satellite. But
typical data equipment such as Routers and ATM Switches do not have an ASI interface. Using the AP3000, you could easily convert between
DS-3 and
ASI using the DS-3 ATM UNI Module and the ASI ATM UNI Module.

Also, using ASI allows you to Multicast at High Data Rates. You could have an outbound channel of 110Mbps in a 36Mhz transponder and several receive sites.

Connecting OC-3 ATM Switches to Satcoms

OC-3 is used for Trunk Circuits. It might be aggregating multiple DS-3 connections from ATM Multiplexor's, or interfacing multiple connections
from other OC-3 ATM Switches.

As mentioned above one of the first instances of Metrodata being involved in ATM Over Satellite was when NATO used the Metrodata
ATM Switching DSU to connect a Fore ASX200 OC-3 ATM Switch to an E1 G.703/G.704 Satellite Modem. In the OC-3 Section, we have the same 4 Satellite Modem Types as in the E3 and DS-3 section:

• Connecting OC-3 ATM Switches Over EIA530 Satellite Modems
• Connecting OC-3 ATM Switches Over HSSI/ECL Satellite Modems
• Connecting OC-3 ATM Switches Over Fixed Rate G.703/704 Satellite Modems
• Connecting OC-3 ATM Switches Over ASI Satellite Modems

Connecting OC-3 ATM Switches to EIA530 Satellite Modems

The Metrodata Access Processor can provide Single OC-3 ATM to EIA530 Conversion, where only a single Full Duplex Satellite Connection exists. Also, aggregation of multiple EIA530 is possible onto a single DS-3 ATM interface.

As the maximum speed of EIA530 is typically 20Mbps, OC-3 to EIA530 is not the most effective use of OC-3 ATM Ports. However, if you are aggregating multiple EIA530 connections into an OC-3 it might make more sense. The most effective product Metrodata have to convert OC-3 to EIA530 to support ATM cells is the Metrodata AP3000. The Metrodata AP EIA530 ATM UNI Module currentlysupports a single EIA530 interface. This interface can operate at Simplex, Full-Duplex and Asymmetric speeds. It can support exact clock rates down to 1Hz. As its maximum speed is currently 20Mbps, this gives it 20 Million different clock rates.

As most ATM Switches do not support ATM on their EIA530 Modules, this is quite a useful Module for connecting OC-3 ATM Switches to EIA530 Satellite Modems.

Connecting OC-3 ATM Switches to HSSI Satellite Modems

There is only one way of connecting an OC-3 ATM Switch to a Satellite Modem and that is the Metrodata AP3000. This would be configured with an OC-3 ATM UNI Module to connect to the DS-3 ATM Switch, and a HSSI ATM UNI Module to connect to the HSSI Satellite Modem. This configuration would support any rate from 8Kbps to about 90Mbps. We could push HSSI faster than this, but the line driving distance comes down dramatically once you get over about 45Mbps. For 90Mbps you would have to have HSSI cables no longer than about 50 centimetres.

If you already have HSSI Satellite Modems, and want to run them over the HSSI Router Max of 51.84Mbps, you could use an OC-3 ATM Port in your Router, or an ATM Switch. Then connecting this into the AP3000 would allow you to go nearly twice as fast.

Connecting OC-3 ATM Switches to G.703/G.704 Satellite Modems

G.703/G.704 Satellite Modems support fixed Telecoms rates such E1, T1, E2, T2/J2, E3 and DS-3. Because G.703/G.704 Satellite Modems only run at fixed rates, they can be converted to OC-3 ATM by using the Metrodata Switching DSU. Currently this device supports the following ATM Rates when converting to an OC-3 ATM Switch:

• E1 or 2.048Mbps - Using the Metrodata OC-3 to E1 Switching DSU
• E2 or 8.448Mbps - Using the Metrodata OC-3 to E2 Switching DSU
• E3 or 34.368Mb/s - Using the Metrodata OC-3 to E3 Switching DSU
• DS-3 or 44.736Mbps - Using the Metrodata OC-3 to DS-3 Switching DSU

Rates which could be supported, given a customer requirement are T1 1.544Mbps and T2/J2 6.321Mbps.

Connecting OC-3 ATM Switches to ASI Satellite Modems

ASI Satellite Modems support rates up to 240Mbps [though this tends to be the Modulator, with lower speeds on the Demodulator]. This scalability exists because ASI is mainly used in the Broadcast Sector as a means of Distributing/Broadcasting Video Channels. As such a Video channel might take up around 4Mbps. You can Broadcast on one output multiple Video Channels and so would have multiple 4Mbps. All of this would be on a
single ASI Satellite Modem, so it has to support various different rates.

Because of the ability of ASI to operate at High Data rates [HDR], it is beginning to be used as a means of transporting data over satellite. But typical data equipment such as Routers and ATM Switches do not have an ASI interface.

Also, using ASI allows you to Multicast at High Data Rates. You could have an outbound channel of 110Mbps in a 36Mhz transponder and several receive sites. This would require the AP8000 at the Hub Site to connect in all the separate ASI interfaces from the Satellite Modems, and AP3000's at the receive sites.