How Users Interface with an Earth Station

Slide Number 1Rev -, July 2001

Technical Introduction to Geostationary Satellite Communication Systems Original Prepared by Telesat Canada

Section 4.4Section 4.4



4.4: How users interface with an Earth Station

4.4.1 Backhauls

4.4.2 Typical Interfaces

4.4.3 Demarcation Points

4.4.4 Customer Rooms at Teleports

4.4.5 Studio Facilities at Teleports

Vol 4: Earth Stations

Introduction



4.4.1: Backhauls

Backhauls

DefinitionA backhaul is a communication link between a customer’s premise and an Earth Station for the purpose of conveying the customer’s traffic between locations.

The link may be as simple as a wire pair running 100 meters between buildings, or it may be as complicated as a multiple-carrier, multiple media leased line.

The backhaul can carry analog or digital, video or audio or data, and usually terminates at baseband.

Sec 4: How Users Interface with an Earth Station




4.4.1: Backhauls

Backhauls

CopperTwisted pair lines coming into a Earth Station could be digital T1 data lines or individual analog voice circuits, which could also carry low speed data. These lines are typically rented from the local telephone company.

At termination, analog lines would normally employ echo cancellation and amplification equipment to condition the signal for its intended use.

Lines carrying low speed data would probably terminate at a modem and be converted to the desired data standard before being cabled out to the Earth Station equipment.





4.4.1: Backhauls

Backhauls

FiberWhere bandwidth demands warrant, fiber links may be used. Fiber links could carry high bitrate traffic—for digital video, for instance—or could terminate at channel bank equipment for further demultiplexing into component channels for voice communications or data requirements.

MicrowaveTerrestrial radio, line-of-sight links can also be used as backhauls. The radio signal is converted back to baseband for interface with Earth Station equipment.

CoaxialCoaxial cables can be used to deliver video and internet services.





Backhauls

DemarcationWhatever the backhaul type, it must always be contractually clear whether the customer or the Earth Station operator has ultimate responsibility for the backhaul. When the customer has responsibility for backhaul provision, the demarcation point between backhaul and Earth Station must be clearly specified.

Two-wire services, and fiber which has been terminated at channel banks and broken out, are typically wired out to a telco-style punch block (a BIX block) mounted on the wall near where the wires come into the building. This punch block is the demarcation point.

Data services might have demarcation points at the baseband output of a modem. Any agreed upon location can serve as a responsibility demarcation point.


4.4.1: Backhauls




Backhauls

DistributionAll services should be wired or cabled from their demarcation points out to a patch panel collocated with the satellite equipment. The lines should cross the patch panel before terminating at satellite baseband equipment. This work will be the responsibility of the Earth Station operator.

The use of a patch panel prior to feeding into satellite baseband equipment is an often overlooked design feature. A patch panel at this point, however, is an invaluable troubleshooting tool. It provides a break-in location for two-way circuit testing and, if the proper type of patch panel is chosen, can even provide a non-interrupting monitor point so that signal quality can be observed without disruption to service.


4.4.1: Backhauls




The X and V series recommendations both originate with the ITU. They are intended to facilitate hassle-free interconnection of communication services worldwide.

The V recommendations were developed for equipment working over the public telephone network (PSTN).

The X series recommendations were developed for equipment making use of the public data network (PDN).

The common telephone circuit only uses analogue signaling schemes that are suitable for voice transmission.

With the advent of computing, the ITU-V recommendations were developed specifically to assist in the interconnection of Data Communication Equipment (DCE) with the voice-optimized PSTN, since that was the only network available at the time.

Part 2: Typical Interfaces

Difference Between X & V Recommendations

4.4.2.1: Difference Between X & V Recommendations

Vol 4: Earth Stations, Sec 4: How Users Interface With an Earth Station



As time progressed, exchanges were developed that were capable of routing and switching data digitally, such as the X.25 exchange.

The X recommendations were developed to assist in the switching, routing and transmission of the binary information within all-digital networks.

Difference Between X & V Recommendations


4.4.2.1: Difference Between X & V Recommendations




ITU Modem Standards

V.21: The standard for full-duplex communication at 300 baud in Japan and Europe. In the United States, Bell 103 is used in place of V.21.

V.22: The standard for half-duplex communication at 1,200 bps in Japan and Europe. In the United States, the protocol defined by Bell 212A is more common.

V.22bis: The worldwide standard for full-duplex modems sending and receiving data across telephone lines at 1,200 or 2,400 bps.


4.4.2.2: ITU Modem Standards


If digital data is to be transmitted through the PSTN, it must be converted to analog. This is the function of the ModModulator/ DemDemodulator, or MODEM. A number of ITU-V recommendations apply to modems. Common ones are:



ITU Modem Standards

V.29: The standard for half-duplex modems sending and receiving data across telephone lines at 1,200, 2,400, 4,800, or 9,600 bps. This is the protocol used by fax modems.

V.32 : The standard for full-duplex modems sending and receiving data across phone lines at 4,800 or 9,600 bps. V.32 modems automatically adjust their transmission speeds based on the quality of the lines.

V.32bis: The V.32 protocol extended to speeds of 7,200, 12,000, and 14,400 bps.

V.34: The standard for full-duplex modems sending and receiving data across phone lines at up to 28,800 bps. V.34 modems automatically adjust their transmission speeds based on the quality of the lines.






ITU Modem Standards

V.42: An error-detection standard for high-speed modems. V.42 can be used with digital telephone networks as well.

V.90: Is a modem standard for 56 kbps transmission rate. It offers asymmetrical links: receive is 56 kbps but transmit is 33.6 kbps.






Typical Interfaces at Teleports

RS-232 / V.24

V.35

RS-449

RS-449 - RS422

RS-449 - RS423

RS530

RS485

X.21

G.703

ISDN

DS0

T1/DS1 North America

E1/DS1 Europe

Fiber Optic Digital Hierarchy


4.4.2.3: Typical Interfaces at Teleports




4.4.2.4.1: RS-232 / V.24RS232 is an EIA/TIA standard and is identical to ITU V.24/V.28, X.20bis/X.21bis, and ISO IS2110. The only difference is that RS232 specifies all aspects under one roof, whereas the ITU has split the interface into its electrical description (V.28) and a mechanical part (V.24), or Asynchronous (X.20 bis) and Synchronous (X.21 bis).

Functionally and electrically the RS-232 interface is compatible with the V.24 interface.

Mechanically V.24 specifies a DB-25 connector while RS-232C uses both the DB-25 and the DB-9 connector.


4.4.2.4: Data Interface and Bandwidth




The DB-25 connector is not specified in the standard but because of the universal acceptance of the connector for communications peripherals it was accepted into the RS-232C standard.

IBM has added a Sub-D 9 version which is found on almost all Personal Computers and is described in TIA 457.

RS-232C uses the same pin assignments as V.24 for its signaling, although there is a difference in pin assignment between the DB-25 and the DB-9 as is illustrated in the manual.

RS-232D specifies the use of the DB-25 connector.

4.4.2.4.1: RS-232 / V.24






RS-232D is the replacement of RS-232 revision C. It addresses additional issues like:

• Explicitly specify the use of the DB-25 connector.

• Provides loopback capabilities with pins 18, 21 and 25.

• Data Terminal Ready becomes DTE Ready.

• Data Set Ready becomes DCE Ready.

• Permits the use of shielded cable.

All pinning specifications are written for the DTE side.

All DTE-DCE cables are straight through, meaning the pins are connected one on one. DTE-DTE and DCE-DCE cables are cross cables.

4.4.2.4.1: RS-232 / V.24






To make a distinction between all different types of cables we have to use a naming convention.

• DTE - DCE: Straight Cable

• DTE - DTE: Null-Modem Cable

• DCE - DCE: Tail Circuit Cable

Electrical CharacteristicsAll signals are measured in reference to a common ground, which is called the signal ground (AB). A positive voltage between 3 and 15 Vdc represents a logical 0 and a negative voltage between 3 and 15 Vdc represents a logical 1.This switching between positive and negative is called bipolar. The zero state is not defined in RS232 and is considered a fault condition (this happens when a device is turned off).

4.4.2.4.1: RS-232 / V.24






Maximum Distance50 feet (15 meters) depending on wire gauge.

According to the official specifications, a maximum distance of 50 feet or 15 meters can be reached at a maximum speed of 20 kbps. This distance can be exceeded with the use of Line Drivers and low capacitance cables.

Connector TypesDB25, DB9, RJ11, RJ45.

SpeedUp to 20 kbps (faster speeds are possible, but 20 kbps is the official specification limit). Normally RS232 is not used higher than 64 kbps.

Figure 4.4.2.4.1 RS232 Connector Types

4.4.2.4.1: RS-232 / V.24






Recognizable by its blocky, 34-pin connector, V.35 combines the bandwidth of several telephone circuits to provide the high-speed interface between a DTE or DCE and a CSU/DSU (Channel Service Unit/Data Service Unit).

V.35 was originally designed for a 48 kbps modem. However, it has been shown that if a V.35 circuit is implemented correctly, 2.048MHz and faster is possible. It is commonly used by telcos to support speeds ranging anywhere from 48 to 64 kbps.

Maximum V.35 cable distances can theoretically range up to 4000 feet (1200 m) at speeds up to 100 kbps. Actual distances will depend on equipment and cable used.

To achieve such high speeds and great distances, V.35 combines both balanced and unbalanced voltage signals on the same interface.

4.4.2.4.2: V.35






For signaling, V.35 employs the RS232, unbalanced electrical specification, where signals are referenced to ground.

Data and clock are carried on balanced wire pairs that are referenced to each other only, and not to ground. V.35 receivers look for the difference between these two wires rather than an absolute signal level with respect to ground. For this reason, this part of the V.35 interface is referred to as differential.

The differential signals must be carried on a twisted wire pair. By twisting two wires together, any stray noise picked up on one wire will be picked up on the other as well. Because both wires pick up the same noise, they do not change with respect to each other. In this way, the effect of noise is negated at the receiver.

Most vendors are using the specifications from V.11 for this part of the V.35 interface, as recommended by the CCITT.

4.4.2.4.2: V.35






Note that for best results it is important to build V.35 cables properly. Cables must employ twisted pairs of wires for RDA & RDB, SDA & SDB, TCA & TCB, RCA & RCB, XTCA & XTCB.

The differential signals for V.35 are labeled as either "A and B" or "+ and -". Wire A, or +, does not connect to B, or -. Wire A always connects to A and B connects to B. If these wires are reversed, polarity is crossed and the data or clock signal becomes inverted.

The 1989 CCITT BLUE BOOK (CCITT is now ITU) recommended that the V.35 interface be allowed to become obsolete; however, it still exists today.

4.4.2.4.2: V.35






Electrical CharacteristicsTransmitter output voltage from a balanced transmitter indicating a MARK is +0.35Vdc for the B line, -0.2Vdc for the A line. Indication of a SPACE condition is +0.35Vdc for the A line, -0.2Vdc for the B line. Output voltage difference is 0.55Vdc.

To be recognized by the receiver, there must be at least 0.01Vdc difference between the A line and B line.

Vdc B>A –0.55V ±20% A>B +0.55V±20% -3 to -25 +3 to +25binary 1 0 1 0signal MARK SPACE Mark Space

function off on off On

DATA LEADS CONTROL LEADS

4.4.2.4.2: V.35






SpeedUp to 48 kbps (faster speeds are possible, but 48 kbps is the official limit in the specification).


V.35 supports synchronous applications only; asynchronous V.35 does not exist.

Connector Types34 pin M-block.

Figure 4.4.2.4.2 V.35 Connector Types

4.4.2.4.2: V.35






Cable Design The design of the cable depends on what equipment is being connected and the interface involved.

There are two standard interface types: "Data Terminal Equipment" (DTE) and "Data Communication Equipment" (DCE).

Assuming that both interfaces are V.35, the table in your manual illustrates a typical DTE to DCE connection.

Not all DTE equipment manufactured has a clocking source, in which case a modem eliminator with clock will be needed. If only one device has a clock it may be possible to use one clock to drive TX and RX in both devices.

Older type interfaces do not allow this, as the interface impedance becomes double-terminated and thus causes problems.

4.4.2.4.2: V.35






4.4.2.4.3: RS449

The Electronic Industries Association (EIA) is responsible for developing the RS-449 standard.

RS-449 utilizes both balanced and unbalanced circuit types.

RS-422-A specifies the electrical operation for the balanced circuits and RS-423-A specifies the unbalanced circuits.

RS-423 is equivalent to V.10 while RS-422 is equivalent to V.11.

There are two types of connectors that are used with this interface:

• DB-37 and a DB-9.

RS-449 itself does not define an electrical specification but it does provide a means of selecting a standard cable interface.






Electrical Characteristics

Speed Up to 2 Mbps


ConnectorDB37 or DB9

DC Voltage -4 to 10 +4 to +10Binary State 1 0

Signal Condition Mark SpaceFunction Off On


4.4.2.4.3: RS449






RS422 is a subset of RS449 and is compatible with V.11 and X.27.

RS422 is a balanced serial interface ideal for industrial applications where there are high levels of EMI/RFI noise and a need for long distance connections.

RS422 has no specific physical connectors.

Electrical CharacteristicsThe data is coded as a differential voltage between the wires. The wires are named A (negative) and B (positive). When B > A then the output is a mark (1 or off) and when A > B then it is counted as a space (0 or on).

4.4.2.4.4: RS422






In general, a mark is +1 Vdc for the A line and +4 Vdc for the B line. A space is +1 Vdc for the B line and +4Vdc for the A line.

At the transmitter end, the voltage difference should be between 2 and 6 Vdc.

At the receiver end the voltage must be at least 0.2 Vdc and neither of the lines can exceed -7 Vdc or +7 Vdc.

SpeedFrom 20 kbps to 10 Mbps.


ConnectorNo specific connector.

4.4.2.4.4: RS422






RS423 is an unbalanced serial interface that connects to an RS422-type balanced line receiver.

RS423 is compatible with V.10 and X.26.

The RS423 electrical characteristics make it clear that it is intended to supercede RS232, since its speeds are defined from 20 kbps (where RS232 stops) to 100 kbps.

All signals are defined with A and B lines, where all the B lines are tied to a common ground.

4.4.2.4.5: RS423






Electrical CharacteristicsThe output voltage from a driver is usually ±4 to ±6 volts. The receiver gets a valid signal if the voltage is at least + or – 0.2 volts.

SpeedFrom 20 kbps to 10 Mbps.


ConnectorDB25, DB37, DB9, DB15, MMJ, or RJ connectors.



4.4.2.4.5: RS423






RS530 is basically the same as the RS449 (V.11) interface standard put on a DB25 connector.

The RS530 interface is a generic, rather than actual, connector specification.

The connector pinning can be used to support RS422, RS423, V.35 and X.21, to name the most popular ones.

The purpose of RS530 is to replace the large RS449 Sub-D37 connector or the expensive M-block V.35 connector with the lower cost, smaller DB25 connector, as real-estate can be limited on communication equipment interfaces.

4.4.2.4.6: RS530






Electrical CharacteristicsThe Table below identifies the electrical conditions for a RS449 interface on a DB37 connector.

SpeedUp to 2 Mbps


ConnectorDB25




4.4.2.4.6: RS530






RS485 is a balanced serial interface.

The difference between RS422 and RS485 is that with RS485 it is possible to set-up a multi-point application with one master and several slaves.

The drivers of RS485 are tri-state: Mark, Space and Off. Only one driver may be in the on state at any one time.

Daisychaining a network is preferred above a star topology.

EIA specifies a maximum of 32 Unit Loads on one cable segment.

4.4.2.4.7: RS485






A Unit Load is defined as a passive transmitter (in OFF-state) plus a receiver.

This means that when RS485 is used in a 4-wire application (Full Duplex) and the transmit and receive circuits are thus separated, up to 64 devices can be added on a segment. In Half Duplex mode only 32 would be allowed.

A slave device may only speak when it is spoken to. This means that the master has to grant the slave permission to send. The transmit circuitry is enabled by raising RTS.

All slaves are connected to one another through a daisy chain. Below is a cabling example for one master and two slaves in a full-duplex and a half-duplex situation

4.4.2.4.7: RS485






Figure 4.4.2.4.7 RS-485 Full Duplex and Half Duplex Setup

4.4.2.4.7: RS485






Electrical CharacteristicsThe data is coded as a differential voltage between the wires.

• When B > A then the output is a mark (1 or off).

• When A > B then it is counted as a space (0 or on).

In general, a mark is +1 Vdc for the A line and +4 Vdc for the B line. A space is +1 Vdc for the B line and +4Vdc for the A line.

At the transmitter end, the voltage difference should not be less than 1.5 Vdc and not exceed 5 Vdc. This means the output differential voltage is about 3 volts.

At the receiver end the voltage difference must be at least 0.2 Vdc between the A and B lines. The minimum voltage level is -7 Vdc and maximum +12 Vdc.

4.4.2.4.7: RS485






SpeedFrom 1.2 kbps to 10 Mbps


ConnectorNo specific connector but DB 9 is commonly used as is a 4 wire screw block.

PinoutTX + Transmit +TX - Transmit -RX + Receive +RX - Receive -

DC Voltage “B” > ”A” “A” > ”B”Binary State 1 0


4.4.2.4.7: RS485






The X.21 interface was recommended by the CCITT in 1976. It is defined as a digital signaling interface between customer’s (DTE) equipment and a carrier's (DCE) equipment. Thus it is used primarily for telecom equipment.All signals are balanced, meaning there is always a pair (+/-) for each signal, as is the case in RS422. The Signal Element Timing (clock) is provided by the DCE. This means that the provider (local Telco office) is responsible for the correct clocking and that X.21 is a synchronous interface. Hardware handshaking is done by the Control and Indication lines. The Control line is used by the DTE and the Indication line is used by the DCE.

4.4.2.4.8: X.21






Electrical CharacteristicsElectrically, the X.21 signals are the same as RS422, so please refer to RS422 for the details.

SpeedMax. to 100 kbps (X.26).

Max. to 10 Mbps (X.27).


ConnectorDB15

Figure 4.4.2.4.8 X.21 Connector Types

4.4.2.4.8: X.21






G.703 is a standard that originally described voice over digital networks but is also used for data. It is a CCITT recommendation that is associated with the Pulse Coded Modulation (PCM) standard.

G.703 is an electrical and functional description. Electrical characteristics are different for 64 kbps, T1 and E1 speeds.

G.703 can be transported over balanced (120 ohm TP-twisted pair) and unbalanced (dual 75 ohm coax) wires. The balanced version with a speed of 64 kbps, is split into three different modes of transmission: co-directional (4-wire), central-directional (6/8 wire) and contra-directional (8-wire).

4.4.2.4.9: G.703






Signal RJ45 Description DTE RJ45 BNC Description DTE BNC

RxA Receive Input Negative 1 Receive Input TipRxB Receive Input Positive 2 Receive Ground RingTxA Transmit Output Negative 4 Transmit Output TipTxB Transmit Output Positive 5 Transmit Ground RingS1 Transmit Ground 3 S2 Receive Ground 6

4.4.2.4.9: G.703






The Integrated Services Digital Network (ISDN) is a system of digital phone connections that has been available for over a decade.

ISDN allows data to be transmitted simultaneously across the world using end-to-end digital connectivity.

Voice and data are carried by bearer channels (B channels) occupying a bandwidth of 64 kbps.

Some switches limit B channels to a capacity of 56 kbps.

A data channel (D channel) handles signaling at 16 kbps or 64 kbps, depending on the service type.

4.4.2.4.10: ISDN






There are two basic types of ISDN service: 1) Basic Rate Interface (BRI).

2) Primary Rate Interface (PRI).

BRI consists of two 64 kbps B channels and one 16 kbps D channel for a total of 144 kbps. This basic service is intended to meet the needs of most individual users.

PRI is intended for users with greater capacity requirements. Typically the channel structure is 23 B channels plus one 64 kbps D channel for a total of 1536 kbps.

4.4.2.4.10: ISDN






In Europe, PRI consists of 30 B channels plus one 64 kbps D channel for a total of 1984 kbps.

It is also possible to support multiple PRI lines with one 64kbps D channel using Non-Facility Associated Signaling (NFAS)

H channels provide a way to aggregate B channels. They are implemented as follows:

• H0=384 kbps (6 B channels)



• H12=1920 kbps (30 B channels) - International (E1) only

4.4.2.4.10: ISDN






Distance & LimitationsTo access a BRI service the customer must be within 18000 feet (about 3.4 miles or 5.5 km) of the telephone company central office.

Beyond that, expensive repeater devices are required, or ISDN service may not be available at all.

Customers will also need Terminal Adapters (sometimes called, incorrectly, "ISDN Modems") and or ISDN Routers to connect to a ISDN switch or telecommunications network.

4.4.2.4.10: ISDN






DS0 stands for Digital Signal 0.

Digital Signal X is a term for the series of standard digital transmission rates or levels based on DS0.

DS0 is a digital transmission rate of 64 kbps, the bandwidth normally used for one telephone voice channel. A standard telephone analog signal is converted by PCM to obtain a 64 kbps digital signal (DS0).

Both the North American T-carrier system and the European E-carrier systems of transmission operate using the DS series as a base multiple. The digital signal is what is carried inside the carrier system.

4.4.2.4.11: DS0, DS1, DS2, DS3






DS1, used as the signal in the T-1 carrier, is 24 DS0 (64 kbps) signals created using Pulse-Code Modulation (PCM) and time-division multiplexing (TDM).

DS2 is four DS1 signals multiplexed together to produce a rate of 6.312 Mbps.

DS3, the signal in the T-3 carrier, carries a multiple of 28 DS1 signals or 672 DS0s or 44.736 Mbps.

Digital Signal X is based on the ANSI T1.107 guidelines. The ITU-TS guidelines differ somewhat.

4.4.2.4.11: DS0, DS1, DS2, DS3






Digital Signal Designator

Data Rate DS0 Multiple T-Carrier E-Carrier

DS0 64 kbps 0 - -DS1 1.544 Mbps 24 T-1 -

- 2.048 Mbps 32 - E1DS1C 3.152 Mbps 48 - -DS2 6.312 Mbps 96 T-2 -

- 8.448 Mbps 128 - E2- 34.368 Mbps 512 - E3

DS3 44.736 Mbps 672 T-3 -- 139.264 Mbps 2048 - E4

DS4/NA 139.264 Mbps 2176 - -DS4 274.176 Mbps 4032 - -

- 565.148 Mbps 4 E4 channels - E5

4.4.2.4.11: DS0, DS1, DS2, DS3






Digital transmission, was first introduced in 1962 by Bell Labs scientists and engineers.

T1 is an electrical digital transmission system that transports, over a single twisted pair wire, 24 voice conversations—each conversation encoded at 64,000 bps—or a total of 1.544 million bits per second (Mbps).

The encoded signals of 24 conversations are multiplexed together on a T1 transmission circuit, creating a signal of 1.5 million bits per second, which is called a DS1 signal.

These DS1s are then multiplexed into higher digital rates and transmitted through the network.

4.4.2.4.12: T1/DS1 North America






How the T1 Carrier Got its Name:The term “carrier” is part of the communications industry's jargon for any medium used to carry communications signals.

There is a common misconception that the “T” in T1 “Transmission”, but actually it stands for Terrestrial. T was used to distinguish terrestrial, or land transmission from satellite transmission.

The 1 is an abbreviation of 1.5, which stands for the 1.544 Mb/s transmission rate.

4.4.2.4.12: T1/DS1 North America






E1 (or E-1) is a European digital transmission format devised by the ITU-TS and given its name by the Conference of European Postal and Telecommunication administration (CEPT).

It is the equivalent of the North American T-carrier system format.

E2 through E5 are carriers in increasing multiples of the E1 format.

The E1 signal format carries data at a rate of 2.048 Mbps and can carry 32 channels of 64 kbps each.

E1 carries at a somewhat higher data rate than T-1 (which carries 1.544 Mbps) because, unlike T-1, it does not do bit-robbing and all eight bits per channel are used to code the signal.

4.4.2.4.13: E1 Europe






E1 and T1 can be interconnected for international use.

E2 (E-2) is a line that carries four multiplexed E1 signals with a data rate of 8.448 Mbps.

E3 (E-3) carries 16 E1 signals with a data rate of 34.368 Mbps.

E4 (E-4) carries four E3 channels with a data rate of 139.264 Mbps.

E5 (E-5) carries four E4 channels with a data rate of 565.148 Mbps.

4.4.2.4.13: E1 Europe






As data rates increase, eventually they leave copper are carried on Optical Networks.

The Synchronous Optical Network (SONET) includes a set of signal rate multiples for transmitting digital signals on optical fiber.

•The base rate Optical Carrier 1(OC-1) is 51.84 Mbps.

•OC-2 runs at twice the base rate.

•OC-3 at three times the base rate, and so forth.

Planned rates include OC-1, OC-3 (155.52 Mbps), OC-12 (622.08 Mpbs), and OC-48 (2.488 Gbps).

4.4.2.4.14: Fiber Optic Network Digital Hierarchy






Signal Level Digital Bit Rate Voice Circuits Carrier SystemDS0 64 Kbps 1 (none)DS1 1.544 Mbps 24 T-1

DS1C 3.152 Mbps 48 T-1CDS2 6.312 Mbps 96 T-2DS3 44.736 Mbps 672 T-3OC1 51.84 Mbps 672 OC1

DS3D 135 Mbps 2016 T-3DOC3 155.52 Mbps 2016 OC3

OC12 622.08 Mbps 8064 OC12OC24 1.244 Gbps 16,128 OC24OC48 2.488 Gbps 32,256 OC48OC256 13.271 Gbps 172,032 OC256

4.4.2.4.14: Fiber Optic Network Digital Hierarchy






A telephone conversation requires transmission in both directions.

When both directions are carried on the same wire pair, we call it 2-wire transmission.

Most analog voice circuits are carried over twisted pair on 2 wires, such as the phones in our homes and offices.

All phone lines terminating at an Earth Station from a telco are 2 wire interface.

Carrier and radio systems require that oppositely directed portions of a single conversation occur over separate transmission paths or channels.

Two wires for the transmit path and 2 for the receive path together make a 4-wire, full duplex (two way) conversation.

4.4.2.5.1: 2-Wire or 4-Wire


4.4.2.5: Voice Interface




Nearly all long distance telephone conversations employ 4-wire links, with a “term set”—or termination set—converting back to 2-wire for the end user.

A term set also has an impedance or compromise balance network (CBN). This network allows impedance matching between the 2 wire and 4 wire circuits.

When the impedances of the 2-wire and 4-wire networks are not well matched, the hybrid circuit (see Figure 4.4.2.5.1) reflects power back along the line. This is called “echo” and can be heard by those using the telephone system, sometimes making it almost impossible to converse properly.

The idea of the CBN is to match the two impedances to minimize echo.

4.4.2.5.1: 2-Wire or 4-Wire






TermSet

TermSet

Direction ofTransm ission

Two-wireconnection

Two-wireconnection

Direction ofTransm ission

CBN CBN

Figure 4.4.2.5.1 Typical Long Distance Telephone Connection

4.4.2.5.1: 2-Wire or 4-Wire






This is an extension of a normal telephone line from the Central Office (CO) and is also known as an FX (foreign exchange) line.

The telco Foreign Exchange Office (FXO) end of the link connects to a Ground Start subscriber line at the CO, and the Foreign Exchange Station (FXS) connects to a telephone set(s).

The FXS end can be either Loop or Ground Start. In Loop Start systems, the off-hook condition (someone has just picked up the phone) is indicated by a contact closure and subsequent loop current. In a Ground Start system, off-hook is indicated by the application of ground potential.

FXO-FXO calling is not supported.




4.4.2.5.2: Loop Extension FXO/FXS Term Sets



Plug-in cards provide either an FXS or FXO signaling converter to convert a variety of signaling formats on the facility side to E&M signaling on the terminal side.

Formats are as follows:

• FXS to E&M - loop signaling used at the station end of a foreign exchange (remote satellite station would plug a telephone into the loop extension).

• FXO to E&M - loop signaling used at the office (switching equipment) end of a foreign exchange (satellite station would plug telephone line into satellite equipment) see example Figure 4.4.2.5.2.

• DX to E&M - extends E&M signaling over greater distances.

• E&M to E&M - converts E&M type signaling.







Voice CircuitFXSLoop

Extender

VoiceC ircuit

FXOLoop

Extender

PBX

Telephone

City

Telephone

Typ ica l R em oteEarth S tation

Typ ica l G atewayEarth S tation

VoiceC ircuit

FXOLoop

Extender Public Switch

Typical FXS/FXOSatellite Application

City

Satellite d ish Satell ite dish

Telephone

Term

inal

Sid

e

Faci

lity

Sid

e

Term inalS ide

FacilityS ide

Figure 4.4.2.5.2 Voice Interfaces - Loop Extension FXO/FXS Term Sets







APPLICATIONS: This service provides the means to extend a telephone line to any location where telephone service cannot be economically provided by the local telco.

Since the FXO end does not have to be at the nearest serving Central Office (CO), toll charges can be significantly reduced by placing the FXO in the local area of highest traffic.

As the remote hardware can be made highly portable, temporary service locations (i.e. mining, forestry, exploration, construction) are prime clients for this service.







A common method for trunk signaling between Central Offices or PBXs is 4 wire E&M. This allows for simultaneous two way or duplex signaling between offices.

These trunks can be extended over satellite. Typical interfaces for 4 wire E&M include Type 1, 2, 3, 4, and 5. Depending on variation of E&M type, either 6 wires or 8 wires are required per trunk.

A ccessN etwork CUC U P AB X

4WE &M

Telephone

V oiceCircuit

Vo iceCircuit

T elcoC entra lO ffice

4WE&M

4WE&M

Telephone

P AB X

VoiceCircuit

C UCUC U PA BX4W

E&M

Telephone

VoiceCircu it

Figure 4.4.2.5.3 Voice Interfaces - 4 Wire E & M




4.4.2.5.3: 4-Wire E&M



E&M signaling conveys supervisory information and dial address information to a switch using two control leads: Ear & Mouth.

Address information is sent via pulses on the Transmit and Receive pair wires. The E&M supervisory leads convey status information via the chart below.

Line Status Receive E-lead Transmit M-LeadIdle Open Ground

Busy Ground Battery

When the address information and the E&M signaling is complete, the same pair of wires are now open for voice communication.

Three or four pairs of wires are used for 4 wire E&M signaling. These are:

• Transmit pair, Receive pair, E&M pair and signal battery & signal ground.




4.4.2.5.3: 4-Wire E&M



Demarcation Points

As mentioned earlier, the customer’s demarcation point must be defined. This is essential in avoiding disputes about which parties are responsible for what parts of a link.

The demarcation point information should include the following:• Location – equipment rack, wall mount, etc.

• Interface type - T1, V.35, RS422, RS232, twisted pair, BIX, RJ11, RJ45 etc,

• Male or female connector

• Distance from demarcation point to the modem – are shorthaul modems required (distance limitations due to the physical interface)

• Power provisioning – AC, DC, not required or other

• Monitor and control provisioning required


4.4.3: Demarcation Points




Customer Equipment RoomsTeleports are often designed with customer equipment rooms.

A customer equipment room is physically separated from the Teleport by a wall, but close enough to connect to any Teleport equipment.

This room allows individual customers to install their own specialized equipment that must be installed close to the uplink equipment. These allow equipment options that otherwise may not be available.

The customer will pay for the lease of the room, and this figure should include a premium for power consumption if the customer’s equipment is fed from the Teleport’s power grid.

The customer’s rooms should be physically secure.


4.4.4: Customer Equipment Rooms




4.4.5: Studio Facilities at Teleports

Studio Facilities

Only an Earth Station the size of a Teleport can support a high-end, value-added service like studio facilities. Even at that, very few Teleports are so equipped.

Teleports with studio facilities: • Could include resident broadcasters such as movie channels,

sports channels, language channels, and weather channels, all of which are major users of satellite services.

• Other tenants could include the broadcast industry handling origination and transcoding services, studio and post-production services.

Most Teleports provide uplink services for off-premise broadcast clients such as major Broadcasting Corporations.



Date post:	09-Apr-2017
Category:	Engineering
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How Users Interface with an Earth Station

Engineering