Long Distance Data Transmission

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Questions and Answers

What are the two primary methods for achieving full-duplex transmission in modems?

Frequency division multiplexing (FDM) and echo canceling (EC).

How do simplex modems differ from full-duplex modems in their operation?

Simplex modems can only transmit signals in one direction, while full-duplex modems can transmit and receive signals simultaneously.

What defines asynchronous modems and how do they operate?

Asynchronous modems operate at slow to moderate rates, typically up to 1800 bps, and use framing bits with no clock to manage data transmission.

What is the maximum data rate for synchronous modems operating in audio lines?

Synchronous modems can operate at rates up to 28800 bps in audio lines. Signup and view all the answers

What role do equalizers play in synchronous modems?

Equalizers help to offset the signal degradation due to the attenuation of telephone lines. Signup and view all the answers

How do PSTN signals differ from digital signals in terms of data transmission?

PSTN signals are analog in nature, focusing on voice transmission, while digital signals transmit data in discrete units or bits. Signup and view all the answers

What modulation methods are commonly used by synchronous modems?

Synchronous modems commonly use phase modulation and integrated phase and amplitude modulation. Signup and view all the answers

What is the significance of using seven-bit ASCII code with even parity in asynchronous data transmission?

It provides a method for error checking and ensures data integrity during transmission. Signup and view all the answers

What is the purpose of modulation in data transmission?

Modulation converts digital signals into analog signals for transmission over communication channels. Signup and view all the answers

Describe the difference between local ANALOG loop and remote DIGITAL loop in modem diagnostics.

The local ANALOG loop tests the integrity of the local modem and associated connectors, while the remote DIGITAL loop checks the entire path including the carrier connection and remote modem. Signup and view all the answers

What role does the V.54 protocol play in modem diagnostics?

The V.54 protocol provides a standard for loopback tests used in modems to check the integrity of telephone circuits. Signup and view all the answers

How does bit-error-rate testing assist in modem functionality?

Bit-error-rate testing identifies and resolves problems in communication links and assesses the quality of T1/E1 links. Signup and view all the answers

Explain how digital signals differ from PSTN signals in the context of modem functionality.

Digital signals are converted from their original format for transmission, whereas PSTN signals are typically analog and may require modulation for compatible transmission. Signup and view all the answers

What should be done with equalizers when the line is replaced and why?

Equalizers should be re-tuned when the line is replaced to ensure optimal operation due to changes in line parameters. Signup and view all the answers

How do automatic equalizers function in modems?

Automatic equalizers tune themselves when a connection is established and continually adjust to the line conditions approximately every 15ms to 25ms. Signup and view all the answers

What distinguishes synchronous modems from asynchronous modems?

Synchronous modems operate at higher rates and can split channels for multiple consumers, unlike asynchronous modems. Signup and view all the answers

Why is it important for digital information to be transmitted on communication channels?

It is essential to move digital information efficiently from one location to another through these channels. Signup and view all the answers

What is the bandwidth limitation of typical telephone lines for data transmission?

Typical telephone lines have a usable bandwidth frequency range of 300 Hz to 3300 Hz. Signup and view all the answers

What happens to digital signals transmitted over analog media, like telephone lines?

Digital signals can become distorted when transmitted over analog media due to bandwidth limitations. Signup and view all the answers

What is the role of the data source in synchronous data transmission?

The data source is responsible for assembling data blocks with framing codes and any required error detection bits. Signup and view all the answers

What does it mean for a modem to be 'transparent' to data types?

A transparent modem does not interfere with the formatting of the data being transmitted. Signup and view all the answers

What is the recommended frequency for tuning equalizers in low-quality lines?

Equalizers should be tuned frequently when the line quality is low and its parameters change often. Signup and view all the answers

How does the fitness process in modems operate in relation to line quality?

The fitness process can operate at rates of up to 2400 times a second, continuously adjusting based on the current line quality. Signup and view all the answers

What characteristic does a Split System Modem (SSM) have?

A Split System Modem can split channels for several consumers, allowing different speeds of data transmission. Signup and view all the answers

What is the significance of the clock signal in synchronous data?

The clock signal ensures that synchronous data is timed correctly for consistent transmission and reception. Signup and view all the answers

What kind of distortion occurs to digital signals transmitted over analog media?

Digital signals, when transmitted over analog media, become distorted from their original square wave form. Signup and view all the answers

Why must data sources assemble blocks in synchronous data transmission?

Data sources must assemble blocks to include framing codes and error-detecting bits as per the protocol requirements. Signup and view all the answers

What happens to the quality of digital information when transmitted through low-bandwidth channels?

The quality of digital information can diminish due to distortion and loss of signal integrity in low-bandwidth channels. Signup and view all the answers

In modem operation, what is the role of equalizers when the connection is established?

Equalizers are tuned automatically during the connection establishment to adapt to line conditions. Signup and view all the answers

What is the primary benefit of using short haul modems in communication systems?

Short haul modems are cost-effective solutions for short distances, providing reliable communication without extensive error correction mechanisms. Signup and view all the answers

How does the ITU V.90 standard define modem speeds, specifically the 56K modem?

The ITU V.90 standard defines the 56K modem as capable of transmitting data at a maximum rate of 56,000 bits per second. Signup and view all the answers

Why are analog modems considered less sophisticated than digital modems?

Analog modems utilize simple modulation techniques without advanced error control or equalization devices, limiting their effectiveness at higher speeds. Signup and view all the answers

What causes signal attenuation in short haul modems, and how is it mitigated?

Signal attenuation in short haul modems occurs due to distance; it is mitigated by lowering the transmission rate to maintain consistent and error-free communication. Signup and view all the answers

Describe the significance of the seven-bit ASCII code in data representation.

The seven-bit ASCII code allows for the representation of up to 128 unique characters, including letters, numerals, and punctuation. Signup and view all the answers

What is the maximum data rate supported by basic analog modems highlighted in the content?

Basic analog modems typically operate at a maximum data rate of 9600 bps, with some capable of reaching up to 64,000 bps. Signup and view all the answers

How do short haul modems operate differently based on their distance limitations?

Short haul modems are optimized for distances up to 15 km, where their lower cost and reduced circuitry suffice for reliable communication. Signup and view all the answers

What distinguishes the ITU V.34 standard from the ITU V.90 standard regarding modem speeds?

The ITU V.34 standard defines an upper limit data speed of 33,600 bps, while the ITU V.90 standard allows speeds up to 56,000 bps. Signup and view all the answers

What is the main function of a DSLAM at the telephone company site?

The DSLAM packetizes the data to be sent to the Internet (ISP server). Signup and view all the answers

How does HDSL differ from T-1 lines in terms of encoding and operational distance?

HDSL uses 2B1Q encoding, allowing operation without repeaters up to 12,000 ft, compared to T-1's 3200 ft limit. Signup and view all the answers

What are the advantages of SDSL for businesses compared to ADSL?

SDSL offers symmetric communication, supporting equal upload and download speeds, while ADSL has a higher downstream than upstream rate. Signup and view all the answers

What type of cable types can VDSL operate on, and what does this imply for its use cases?

VDSL can use coaxial, fiber-optic, or twisted-pair cables, making it adaptable for high-speed connections in various installations. Signup and view all the answers

Explain the purpose of a splitter in an ADSL installation.

The splitter separates the voice line from the data line to prevent interference between telephone and internet signals. Signup and view all the answers

Why is ADSL considered expensive compared to its alternatives?

ADSL requires professional installation of separate data lines and the use of splitters, increasing overall installation costs. Signup and view all the answers

What modulation technique is used by ADSL and how does it affect data transmission?

ADSL uses DMT (Discrete Multitone Technique), allowing efficient utilization of available bandwidth for data transmission. Signup and view all the answers

What is the maximum achievable data rate of HDSL without the need for repeaters?

HDSL can achieve data rates of up to 2 Mbps without repeaters. Signup and view all the answers

How does ADSL technology address bandwidth variability due to the local loop cable conditions?

ADSL technology uses adaptive technology to test line conditions and adjust the data rate accordingly. Signup and view all the answers

What is the function of the discrete multi-tone technique (DMT) in ADSL?

DMT combines QAM and FDM to modulate data over multiple channels simultaneously, improving data transfer efficiency. Signup and view all the answers

What is the maximum achievable upstream bandwidth in ADSL, and why is the actual data rate typically lower?

The maximum achievable upstream bandwidth is 1.44 Mbps, but actual data rates are typically below 500 kbps due to deleted carriers in noisy frequencies. Signup and view all the answers

Explain the bandwidth allocation for downstream data transfer in ADSL.

Downstream data transfer utilizes channels 31 to 255, achieving potential rates of up to 13.4 Mbps but typically below 8 Mbps due to noise-related channel deletions. Signup and view all the answers

What types of channels are reserved for voice communication in the ADSL bandwidth allocation?

Channel 0 is reserved for voice communication, while channels 1 to 5 are idle and provide gaps between voice and data. Signup and view all the answers

What role does the splitter play in an ADSL modem installation at a customer's site?

The splitter separates voice and data communications, allowing simultaneous use of the telephone and internet services. Signup and view all the answers

How many channels are typically available for data transfer upstream in an ADSL system, and what modulation technique is used?

There are typically 24 channels available for upstream data transfer, using QAM modulation. Signup and view all the answers

Describe how the total available bandwidth of 1.104 MHz is divided in ADSL technology.

The bandwidth is divided into 256 channels, each using approximately 4.312 KHz, with specific channels reserved for voice and control. Signup and view all the answers

What are the upstream bit rates provided by XDSL technologies, and at what distances?

The upstream bit rates range from 25 to 55 Mbps at distances of 3000 to 10,000 ft. Signup and view all the answers

What differentiates asymmetric configurations from symmetric configurations in XDSL?

Asymmetric configurations have higher bandwidth in one direction, suitable for web browsing, while symmetric configurations have the same bandwidth in both directions, suitable for video conferencing. Signup and view all the answers

What is the maximum transmission rate for HDSL technology in the XDSL variations?

HDSL technology supports a maximum rate of 2.048 Mbps over two pairs at distances up to 4.2 km. Signup and view all the answers

Describe the data rates supported by RADSL technology.

RADSL technology supports a variety of data rates that adapt based on the quality of the local loop, reaching up to 6 Mbps in one direction. Signup and view all the answers

What is the purpose of a LAN extender, and what distance limitation does it address?

A LAN extender is used to extend Ethernet beyond the standard distance limitation of approximately 100 meters (330 ft). Signup and view all the answers

How does the VDSL technology differ from ADSL in terms of data rates?

VDSL technology can reach up to 52 Mbps in one direction, whereas ADSL typically supports lower speeds up to 6 Mbps in one direction. Signup and view all the answers

What is the significance of the single pair configuration in S-HDSL/SDSL?

S-HDSL/SDSL transmits data over a single pair at a rate of 768 Kbps, providing symmetric bandwidth which is efficient for both upstream and downstream traffic. Signup and view all the answers

Identify one application suitable for symmetric configurations in XDSL technology.

Symmetric configurations are suitable for video conferencing applications. Signup and view all the answers

What is the main advantage of using a LAN extender over standard Ethernet connections?

A LAN extender allows for traffic forwarding between LANs over much greater distances than standard Ethernet. Signup and view all the answers

Describe the data transmission capabilities of 2BASE-TL technology.

2BASE-TL can deliver a minimum of 2 Mbit/s and a maximum of 5.69 Mbit/s over distances up to 2700 m using a single copper pair. Signup and view all the answers

How do media converters improve network performance?

Media converters enable the use of fiber optic cable, extending links over greater distances and protecting data from noise and interference. Signup and view all the answers

What is the maximum distance that 10PASS-TS technology can transmit data?

10PASS-TS technology can transmit data over distances of up to 750 m. Signup and view all the answers

What is a specific application of an Ethernet to Fiber Media Converter?

An Ethernet to Fiber Media Converter is used to interconnect copper-Ethernet devices over fiber in EMI-prone environments. Signup and view all the answers

What encoding methods can LAN extenders use for transmitting information?

LAN extenders can use various line encodings such as TC-PAM, 2B1Q, or DMT. Signup and view all the answers

What distinguishes copper-based Ethernet connections from those using fiber optic cabling in terms of distance limits?

Copper-based Ethernet connections are limited to a maximum distance of 100 meters, while fiber optic connections can extend much further. Signup and view all the answers

What type of wiring does 2BASE-TL require for its operations?

2BASE-TL requires unconditioned copper wiring without load coils for its operations. Signup and view all the answers

Study Notes

Long Distance Data Transmission

This chapter discusses modems, diagnostics, Digital Subscriber Loop (DSL), and extending networks using LAN extenders and media converters.

Modem

A modem is a telephone set for a computer, enabling digital devices (like computers) to communicate over analog telephone lines.

Modem Working

The Plain Old Telephone System (POTS), also known as PSTN (Public Switched Telephone Network), is over 100 years old.
It was designed for analog voice signals (300-4000 cycles per second) and not digital computer signals.
Modems convert digital data to analog signals for transmission over the PSTN (and vice versa).
Modems use modulation and demodulation.

Data Transmission Over Telephone Lines

Modems send analog data bits sequentially similar to telegraph systems (i.e., Morse Code).
They use a binary code called ASCII (American Standard Code for Information Interchange).
ASCII uses seven ones or zeros to represent alphabets, punctuation and numerals.
High-speed modems can transmit 300 to 56,000 bits per second.

Modem Classification by Range

Short Haul: Inexpensive modems for short distances (up to 15 km), often on private lines within the same central office area. These are distance sensitive (signal attenuation increases with distance).
Voice Grade (VG): Used for moderate to high data rates over leased or dial-up lines. Typically more expensive, offering consistent data rates, although tuning can be complex.
Wideband: Used for high data rates in large-volume applications and over long distances using dedicated lines. These enable high throughput for computer-to-computer communication.

Modem Classification by Operation Mode

Half Duplex: Signals can be sent in either direction, but not simultaneously.
Full Duplex: Signals can be sent in both directions simultaneously (e.g., using frequency division multiplexing or echo cancellation).
Simplex: Signals can only be sent in one direction.

Modem Classification by Synchronization

Asynchronous Modems: Used for slower data transfer rates (up to 1800 bps), with framing bits to synchronize.
Synchronous Modems: Used for higher data rates, operating in the audio domain using modulation methods to offset signal discrepancies. These modems use equalization for consistent performance despite changes in line quality.

Modem Classification by Modulation

Telephone lines have limited bandwidth (300 Hz to 3300 Hz).
Digital signals are converted into analog for transmission to avoid distortion.
Modulation techniques like QAM, QPSK, are used.

Modem Diagnostics

Local & Remote Loopbacks: (using V.54 Protocol) check the integrity of connections between modems and cables. Tools for checking the telephone circuits and isolating problems.
Bit-error-rate testing (BERT): measures data integrity for fault isolation where digital loops test connections and cables.

Digital Subscriber Line (DSL) and XDSL Modems

Provide high-speed internet access over existing telephone lines.
ADSL (Asymmetric DSL): Provides higher downstream (Internet to user) speeds than upstream (user to Internet) speeds.
HDSL (High Bit Rate DSL) and SDSL (Symmetric DSL): Offer symmetric upstream/downstream speeds but are often less efficient for residential customers.
VDSL (Very High Bit Rate DSL) and other variations: offer high-speed data transmission over short distances and often have a wider range of configurations.

LAN (Local Area Network) Extenders

Used to extend Ethernet networks (which are limited in distance).
Work transparently to higher network protocols.
Can use copper wire or fiber optics.

Media Converters

Connect UTP (twisted pair) copper-based Ethernet equipment to a fiber optic link.
Extend Ethernet links over greater distances.
Protect sensitive data from noise, EMI.
Enable transmission over longer distances within varied environments, such as industrial plants.

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Description

This quiz covers the essential concepts of long-distance data transmission, focusing on modems, DSL, and network extension methods. Explore how modems function within the Public Switched Telephone Network and learn about their role in transforming digital signals into analog for effective communication.