Metrodata and Backhaul

Metrodata specialise in designing hardware for integrating satellite and terrestrial networks. We understand the applications involved in Satcoms, and supply many features as standard that are specific to Satellite.

The main area where we are involved is in back-haul, reach-back or longhaul. Terminology differs between military and commercial industries, but the concept is the same. Where you have a requirement to take a connection from a satellite modem, and transport it over Fiber, Wide Area Network Circuits, Microwave Radio or Free Space Optics then we can help. This might be extending your Satellite Service from a Teleport to the Customers site, or integrating your Satellite Service from your Head-end Teleport into your Terrestrial Network Infrastructure.

Backhaul History

In the past, most ISP Backbone Links via Satellite were asymmetric in nature, such as:

• 8/2Mbps
• 34/8Mbps

The reason why these rates were chosen was because Satellite Modems existed to support these. Mainly for voice, SDH and PDH infrastructure these rates would equate to E1 (2Mbps), E2 (8.448Mbps) and E3 (34.368Mbps). Typically the Satellite Modem would have a G.703 interface.

As High Speed Serial (HSSI) Satellite Modems became more widely used, they also allowed operation of Satellite Links asymmetrically. However, HSSI Satellite Modems were not restrained by specific fixed data rates and could be configured in 1Bit increments.

For some time these HSSI Satellite Modems were utilised simply to give a more easy and neat solution to Asymmetric Data Rates. The potential to support any bitrate was never really utilised, and so speeds supported were much as before (8/2Mbps & 34/8Mbps).

More recently it has become possible to measure the amount of bandwidth required for a given application, it's possible to measure usage and therefore to predict to some extent what Satellite Capacity is required. This has meant an increase in "odd" data rates as End Users are purchasing only the bandwidth they need.

Typically this would be in 1Mbits increments, and so Metrodata introduced in 2000 a HSSI Module for our APSAT platform that supported fixed rate Asymmetric clocking in 1Mbit increments. This was possible by using a VCXO Clock Crystal for the Transmit Data Rate and a separate VCXO for the Receive Rate.

Using Satellite capacity in 1Mbit increments is not very efficient though, as given a certain Power, Modulation and FEC you can have all sorts of odd data rates. In 2001 Metrodata developed our current HSSI Module for the APSAT which supports 1Bit increments, to match exactly with the flexibility of Satellite Modems 1Hz scalability.

Where possible we have implemented 1Bit increments of clocking on Metrodata products.

Metrodata specialise in interfacing satellite modems to terrestrial infrastructure. We support the following satellite modem interfaces:

• HSSI - Up to 90Mbps
• G.703 - E1, T1, E2 E3 and DS-3
• ASI
• ECL
• EIA530 - Up to 20Mbps (To match EIA530 Crypto Equipment)
• V.35, X.21, RS442

We are the only manufacturer in the world who specialises in back-haul equipment for satellite networks and supports all the different common satellite modem interfaces. Metrodata are also the only company that can match the flexibility of data rate of satellite modems. We support the following operations:

• Asymmetric
• Simplex - With Alarm Masking
• Multicast
• Full Duplex

All data rates are configurable in 1Bit increments so we can match clocking to the satellite network.

Often our equipment is used to back-haul over Transatlantic DS-3 and OC-3 Circuits. However, this might just as easily be a local fiber optic link.

SATELLITE BACKHAUL PRODUCTS

The Metrodata Satellite product Portfolio includes around 25 different products which can be used for backhaul of satellite services. Dependent on your mode of operation (Asymmetric, Symmetric or Simplex), date rate and backhaul infrastructure there are 4 main Metrodata products that are most widely used. These are the:

• APSAT
• FM4000
• DC3200
  

APSAT BACKHAUL

The Metrodata APSAT Platform has been developed specifically for Satellite Backhaul. It is our flagship product in the Satellite sector and can be used for a variety of different applications. For an overview of the APSAT and its different modules, modes and Chassis please check out the Application Note APN047_APSAT.

Because the APSAT has a Modular Chassis, it can be used to backhaul single or multiple satellite services. There are 3 Chassis the AP3000 (3 Slot), AP4000 (4 or 5 Slot) and the AP8000 (8 or 9 Slot). The AP3000 forms the usual foundation of any Satellite backhaul for single satellite services.

The AP3000 is a Fully Functioning ATM Switch. It can support ATM in and out on any port, non-ATM in and ATM out, and even non-ATM in and non-ATM out (Only using ATM across the back-plane).

100-250V AC / 50-400Hz Version -48V DC Version

AP MODULES

Metrodata APSAT supports a wide range of Modules to allow integration of Satellite, Terrestrial, Wireless and Fiber based networks. Satellite Modem Interfaces supported include the following:

• HSSI - From 8k to 90Mbps
• EIA530 - From 8k to 20Mbps
• G.703 - Fractional E1, E1 (2.048Mbps), E2 (8.448Mbps), E3(34.368Mbps) and DS-3 (44.736Mbps)
• ECL - Up to 90Mbps
• ASI - Up to 51.84Mbps for Video
• ASI - Up to 155.52Mbps for ATM/Data
  

All Modules will work in any of the AP Chassis, which means you can start with an AP3000 and as your services grow upgrade to an AP4000 or AP8000 Chassis.

The APSAT Platform Overview should give you an idea of what kind of Chassis and Modules you need, but please contact us to make sure. There are many ways of using the Metrodata APSAT, and it is advisable for you to discuss your requirements with our Technical Staff to ensure the optimal and most cost effective solution.

HSSI SATELLITE MODEM INTERFACE MODULES

This can be operated in 1Bit increments, Asymmetrically, Symmetrically or Simplex. In Simplex mode the APSAT can also Alarm Mask spurious errors generated by the link being in one direction only. This is the only products in the world to offer this in conjunction with such a flexible HSSI interface. Metrodata have 2 different HSSI Modules. The standard Flexi HSSI CE Module is used for the majority of Applications, but if you require ATM over your Satellite link (Mainly for Military) then we also have the HSSI UNI Module. Developed for BT Satellite originally for 90Mbps HSSI Operation, this Module has also been used more recently for Encrypted Military Networks (as ATM Crypto's have a lower overhead than IP Crypto's).

The HSSI CE Module can also be used at one end of the backhaul to interface to the Router, and ASI/EIA530 or G.703 can be used on the Satellite Modems (and vice versa).

EIA530 SATELLITE MODEM INTERFACE MODULES

When back-hauling Satellite Connections over Terrestrial Infrastructure, the APSAT platform uses ATM as a transport mechanism. However, we only use ATM where it suits the application. We make the use of ATM transparent to the network. If you consider that you are have a point-to-point link with Access Processors at either end, then the ATM UNI Modules are your line cards. Whether you are using a SONET/SDH DS-3, ATM OC-3 or E3 Microwave Radio it doesn't matter to the APSAT, you simply choose the module for your link rate. If you wish to transport 34/8Mbps over an E3 or 45/8Mbps over a DS-3 (Or similar rates) then the Zero Wastage feature will be useful for you. This is covered in more detail later on in this document.

ECL SATELLITE MODEM INTERFACE MODULES

ASI SATELLITE MODEM INTERFACE MODULES

The Metrodata APSAT supports ASI/Digital Video Backhaul up to 51.84Mbps. This is using the ASI CE Module. We also have a Data/ATM Module for the APSAT than can be used to transport up to 90Mbps over ASI Satellite Modems. This is the ASI UNI ATM Module.

As you can see there are a wide number of different interfaces on the APSAT that can be connected to the Satellite Modem. We also support a wide range of interfaces from the WAN/Backhaul element as well.

BACKHAUL INTERFACE MODULES

Primarily the APSAT is used to backhaul over E3, DS-3 and OC-3/Fiber. However, it can also be used to transport Satellite services over E1 and E2 links. These links can be Leased Line, Microwave Radio or Fiber Optics.

• Modules available include:
• E1 Backhaul
• E2 Backhaul
• E3 Backhaul
• DS-3 Backhaul
• OC-3/STM-1 Backhaul (Multimode SC Fiber)
• OC-3/STM-1 Backhaul (Single-mode Short Haul SC Fiber)
• OC-3/STM-1 Backhaul (Single-mode Long Haul SC Fiber)

The Metrodata APSAT can therefore offer data rates from 8k to 155.52Mbps, backhaul from E1 to Dark Fiber and supports many different interfaces.

However, in some Symmetric or E1 Applications the Metrodata APSAT is overkill.

FM4000

With Asymmetric Satellite services, clocking is the most important part of the network. Some Router interfaces cannot be clocked Asymmetrically and E1 G.703 is one of them. Also E1 G.703 on a Satellite Modem cannot support Asymmetric data rates on many of the Satellite Modems. With Asymmetric satellite services it makes sense to use Serial Router Interfaces and Serial Satellite Modems.

In the past Metrodata have effectively interfaced Asymmetric Satellite services to symmetric E1 lines by utilising 2 x DC3200 at either end of the link. For example, with a 1024k Receive and 512k Transmit Satellite Service, one DC3200 would be used for the transmit rate and one for the receive rate. The use of the DC3200 with its V.35 interface is simply because V.35 is a better interface for Asymmetric Clocking than X.21.

We've now added Asymmetric Clocking to the Metrodata FM4000, which gives us the ability to support Asymmetric or Symmetric Clock rates in one device. It also allows us to support a full 2.048Mbps Symmetric Service or an Nx64k Symmetric Service in the same device.

This allows you to offer a scalable Satellite Service which can start off Asymmetric at 1024k/512k for example and then be upgraded to a full 2.048Mbps Symmetric Satellite Service at a later date without changing the equipment out.

The ability to do Asymmetric Clocking is only available on the V.35 version of the FM4000. X.21 does not support Asymmetric Clocking. The Metrodata FM4000 is we believe the first E1 G.703 Converter/DSU to support Asymmetric Clocking for Satellite Network backhaul.

The DC3200 can be used to cost effectively transport a Serial Nx64k Satellite Service across a Terrestrial E1 Leased Line or E1 Microwave Radio System. The use of Dip Switches on the base of the DC3200 make it easy to configure the Nx64k timeslots and therefore quick to install, with minimum support required. The DC3200 has both an E1 G.703 interface and an E1 RJ45 interface to the E1 Backhaul link. The interface on the DC3200 to the Router or Satellite Modem is V.35. If you require EIA530 or X.21 this is available on the DC3000 directly (X.21) or via a converter cable (EIA530).

APSAT Application Notes

Please Note: This is simply a general Backhaul Product Overview. Metrodata have an extensive range of Application Notes covering Commercial and Military Satcoms. These notes are detailed Technical Documents, and are available on our Website or on CD. If you have any questions regarding the APSAT Platform, then please contact Metrodata, and we will be happy to discuss your application in more detail.