Muxing over a single satellite

Using the APSAT it is possible to multiplex several terrestrial services across a single satellite link. This is most often multiple E1’s over HSSI or EIA530 Satellite Modems.

The APSAT is a modular switch, based on an ATM backplane. It’s possible to mux ATM and NON-ATM traffic together into a single ATM cellstream. This makes it ideal for doing “odd” data rates over satellite, that do not fit into the PDH/SDH Hierarchy. For example, its easy to transport 4 x E1 using an E3 PDH Mux. You would use 8.448Mbps and a G.703 Satellite Modem. If you wanted to Mux 2,3,5+ x E1 its pretty difficult unless you use the APSAT.

Terrestrial Interfaces Supported

With our Quad E1 Module its possible for us to Mux up to 32 x E1 per AP8000L Chassis, and we can daisy chain further Chassis up to 61 x E1.

Using the Metrodata APSAT also gives you the added benefit of being able to transport other services across the satellite link, for example HSSI Data, E1 Voice, 10/100BaseT Data/IP and also ASI based Video.

The interfaces we support on the Terrestrial side are:

E1, T1, E2, E3, DS-3, OC-3/STM-1

Ethernet 10/100BaseT

Serial EIA530

ASI Video

HSSI (High Speed Serial Interface)

Satellite Modem Interfaces Supported

Metrodata have developed a portfolio of products for interfacing satellite and terrestrial networks. On the APSAT, we have the following interfaces for Satellite:

G.703 – Fixed Telco rates on the Modem are T1, E1, E2, E3, DS-3

HSSI – Up to 90Mbps

ASI – Up to 155.52Mbps

EIA530 – Up to 20Mbps

ATM Over Satellite

The APSAT uses ATM to Multiplex and therefore transport the traffic over the satellite link. With E1 transport, this uses ATM AAL.1 Circuit Emulation over a HSSI/ASI or EIA530 interface.

AAL.1 uses a payload of 47 bytes, and adds 1 byte of Sequence Number and 5 bytes of ATM Cell Header.

An E1 is 2,048,000bytes or 2.048Mbps

2,048,000 divided by 8 = 256,000

256,000 divided by 47 = 5,447

5,447 is the number of ATM Cells per second

In order to get the overhead calculation for using ATM, you need to add on the ATM Cell Header.

5,447 x 53 = 288,681

288,681 x 8 = 2,309,447 or 2.309Mbps

The APSAT HSSI and EIA530 ATM Interfaces use G.832 framing to give link integrity and performance monitoring, which adds additional overhead. A G.832 frame comprises 4296 bits, of which only 4240 bits are payload.

Therefore to transport an E1 AAL.1 payload (2.309Mbps) using HSSI or EIA530 will require the G.832 framing to be added. (If you use ASI then you do not have this G.832 framing).

2,309,447 x 296 divided by 4240 = 2,339,949

Then we suggest allowing a 1% overhead margin, to allow for miscalculations:

2,339,949 x 1.01 = 2,363,348 or 2.363Mbps per E1

This is shown in the following table: