Digitalization, Networks, and Telecommunications Technologies

Posted on Dec 8, 2024 in Technology

1.6 Digitalization of the Signal

Digitization is the process that transforms analog signals, such as sound and video, into digital signals.

1.6.1 Analog to Digital Conversion

There are several methods, the most extended being pulse code modulation. This system digitizes the signal and transmits it by telephone line with the rest of the signals.
The original 4 kHz signal is converted into a bit stream at a speed of 64 kbit/s, consisting of three stages: sampling, quantization, and encoding.

• Sampling, Quantization, and Coding

For the voice to be transmitted, it is required to convert pressure waves. This process is done by the phone’s microphone. The voice information is contained mostly between 300 and 3,400 Hz. A sample contains sufficient information to permit reconstruction.
The samples still have endless potential amplitude values. For the signal that has a finite number of values, the signal has to be discretized. Finally, the samples are to be converted into bits.

2.5 Wireless Local Networks (Wi-Fi)

The origin of the WLAN goes back to the publication in 1979 of the results of an experiment conducted by engineers from IBM, using infrared links to create a local network in a factory. The FCC allocated the 902-928 MHz ISM bands, 2,400-2,483.5 GHz, and 5,725-5,850 GHz for use in wireless radio networks.

2.5.1 WLAN Standardization

In 1989, the IEEE 802.11 committee was formed, which began to work to try to generate a standard for WLANs. In 1999, the rule was finalized.
In 1992, a consortium led by Apple was created to obtain frequency bands for PCS systems. In 1993, IrDA was also created to promote the development of WLANs.

• 802.11: Established in 1997, it reached a speed of 2 Mbit/s with modulation signal for direct sequence spread spectrum (DSSS). 802.11 is a wireless local network that is used for radio transmission in the 2.4 GHz band, or infrared regimes, with binary speeds from 1 to 2 Mbit/s.
  
• 802.11b: Created in 1999 for enterprise WLANs at a speed of 11 Mbit/s and a range of 100 meters, it uses the ISM band of 2.4 GHz. To indicate the compatibility between wireless devices, the Wi-Fi logo is incorporated, with teams supported by over 150 companies. Wireless networks are insecure; an essential element is WEP encryption.
  
• 802.11g: Created in 2003, compatible with 802.11b, it reaches a speed of 22 Mbit/s or even up to 54 Mbit/s. It can coexist, although the bands used are different.
  
• 802.11a: Created in 1999 with a QAM-64 modulation and OFDM encoding, it reaches speeds of 54 Mbit/s at 5 GHz but with a reach of 50 meters.

2.6 Token Ring Local Network

It is a logical network with ring topology, supported by IBM at the time, that meets the IEEE 802.5 standard. Each terminal communicates with others through the Token Passing protocol and supports speeds of 4 and 16 Mbit/s. It supports a total of 260 teams per ring. The ring is achieved with a star wiring in the center with a MAU.

3. Wide Area Networks

A WAN is a network that can cover a large geographic area. They can be voice, data, images, etc.

3.1 The Switching Techniques

Switching is the process by which a user is placed in communication with another user through an infrastructure. The three core services are telephone, telegraph, and data, so you can use one of three techniques: circuit, messages, and packets.

3.1.1 Circuit Switching

It may be time or space. It is the establishment of a physical circuit prior to the submission of information that is kept open for as long as it does the same.
This technique is appropriate when switching between computers is done in the same way, not requiring conversion of codes, protocols, or speeds.

3.1.2 Message Switching

It is a treatment method based on the information block provided with a source address and a destination that can be treated by switching centers of the network that store it and continue its retransmission.

3.1.3 Packet Switching

Similar to the previous one, but with shorter messages and fixed length, which allows sending them without receiving the entire message that, previously, has been cut.
The packets remain very little time in memory, allowing conversational-style applications.

3.2 The Transmission

Many telecommunications authorities decided to promote the use of digital technology, which would require the renewal of the installed plant. So begins the study for the development and deployment of ISDN and gives way to JDS to replace JDP.

3.2.1 JDP

The technique used in telephone networks to transform analog signals into digital is known as MIC, which allows multiple use of a line through multiplexing.
The operation of the JDP is conceptually very simple: at the lower level, the input signals are multiplexed for each channel at the byte level, while at higher levels, it is bitwise. Whenever the velocity is the same for all channels, there is no problem; if so, it becomes necessary to add padding bits.

3.2.2 JDS

Homogeneous transmission worldwide, easy to manage, and cost is the reason for the development of BOT with the idea of replacing the existing JDP.
The JDS is a transmission system that solves several limitations of the current network. Features:
– It is a global transmission standard
– JDS frames can be transmitted by single-mode fiber optics, multimode, and twisted copper pairs
– The frames can be extracted by a simple technique.
– Each plot is identified by a pointer to its location
– It presents efficient network management.
The JDS was standardized by ITU-T, largely adopting the ANSI T1.105 standard. This, in turn, was taken as a standard SONET system.

• Characteristics of the JDS

The objective of the ITU standardization for BOT intends to integrate the velocities of the two plesiochronous hierarchies at speeds in common worldwide use.
For this reason, the first level of hierarchy, SDH, the MTS-1, is normalized in order that it may be carrying transmission speeds of the JDP.
Currently, the last hierarchical level standard for JDS is the MTS-64, which corresponds to the speed of 9.9 Mbit/s.

• Guidelines for JDS

They are reflected in the number of recommendations of the ITU-T and ETSI.

4. The Conditions of Access

Users of telecommunications services can be found at home with the means employed to provide varies with this circumstance. In general, one can consider four types of access depending on the means of connection: twisted-pair cable, optical fiber, radio, etc.
Each mode has different characteristics; depending on them, the user must decide which is appropriate.

4.1 Access by Pair Cable

It is the most used to provide basic telephone service; it is the most important to consider when studying access networks. Its data transmission capacity has been conditioned by the limits imposed on telephone networks, 4 KHz. Users of the phone connect to its local central, which usually lies around 1.5-2 km with a pair of copper wires, which is the so-called local loop. As seen, the evolution and digitalization of the telephone network is integrated services digital network for voice and validated data, with a speed of 64 Kb/s, but it has serious limitations.

4.1.1 ADSL

The operating principle of xDSL technologies is based on the bandwidth of copper wire, which is, in practice, much higher than that imposed by the telephone network to a voice channel. One user at home and another at the termination of the loop can have a link with a capacity of several Mbit/s.
The implementation of ADSL subscriber loops requires not very long and good quality in terms of isolation and resistivity, as often it cannot be used, in which case a variant known as DSL Lite would have to be applied.
The advantages for the operator using this technology are many: a portion will be freed up stations and the switched network, and the data flow is separated at source, rerouting the phone and a data network, which can be offered individual service only for those who require it.

• HDSL: 1.5-2 Mb/s
• SDSL: 1.5-2 Mb/s
• ADSL: 1.5-9 Mb/s and 16-640 Kb/s
• ADSL Lite: 0.5-1.5 Mb/s to 384 kbit/s
• VDSL: 25 to 52 Mbit/s and 1.5 to 2.3 Mbit/s

• ADSL Features

Provides access and high-speed asymmetric through copper pair that users now have in their home or office for connection to the telephone network. Its main applications are communicating high-speed data and video on demand.
Faced with cable modems, ADSL has the advantage of being a dedicated service for each user.
These modems cannot connect as normal; you need, for each line, one at the user’s home and another at the local exchange.
A lower-cost version of ADSL is ADSL Lite, which avoids the need to install a filter. Using ADSL technology and the capacity rental method, different operators can offer their customers Internet access service, with or without a flat rate.

4.1.2 ICT

Each operator offers telecommunications services through its own infrastructure created for this purpose, so cable operators put their chests on sidewalks and wired by facades. The one that offers satellite TV services usually do so by installing a satellite dish and distributing by cable. The solution to the tangle of cables, networks, etc. records is to provide quality service and innovation for future-proof maintenance difficult.
Thus, ICTs are the infrastructure of access to telecommunications services in the interior of the buildings that are made pursuant to a project under the technical regulations in force.

4.1.3 PLC. Power Line Communications

Allows transmission of voice and data network cables for electric high-voltage transmission, basically for the purpose of teleoperation and remote control, as analog and low bit rate.
The electrical energy produced in a plant and from there through the network of high and medium voltage substations reaches the processing centers of the lines that are out in low voltage to provide electric service to subscribers. It is in these processing centers where they are placed, generally connected to the Internet gateway through optical fiber and using the low voltage network, have access to residential and business users.

4.2 Access by Coaxial Cable

An alternative to consider over access to the telephone network through the various telecommunications services is to make use of networks and hybrid fiber coaxial, which are deploying new cable operators.
These networks have already solved the problem of the return signal, making them valid for a real alternative to have many channels of TV, Internet access, or other data networks.
The infrastructure created on these networks is mixed, fiber optic and coaxial cable, while the engagement between the portion of the two means used in a study of cost/bandwidth/number of users.
Different FTTx modes are available:

• FTTF: single optical fiber is present in the backbone
• FTTSA: the distribution network is Fiber Optic and necessitates the use of amplifiers in the coaxial network
• FTTLA: in this case, amplifiers are not needed in the coaxial network.
• FTTC: Fiber reaches the block.
• FTTB: Fiber to the building comes from users and provides services to a very small number of subscribers.

4.3 Access by Radio Waves

It is imposed for ease of deployment, which is assumed to have no need to connect users one by one and meet the power demand with a highly flexible infrastructure that is shared and not dedicated.

4.3.1 Mobile

Mobile is using radio waves that connect to the user terminal with the radio base station that serves the area where it is located, and in turn, is linked to a switching center of mobile services that connects directly to the telephone network commuted.
• The TRAC: provides mobile phone service but can also be used to provide fixed telephone service.
• The evolution of GSM is the second generation, whose clearest examples are GSM in the EU and D-AMPS at the American level. It provides a new multimedia functionality that goes beyond the common applications of data at 9.6 kbit/s offered by existing networks.

4.3.2 Wireless

Wireless access using technologies such as DECT, adequate to cover areas with high densities of users. Services are aimed at providing access to public fixed networks to people on the move. We distinguish types of services:
– Residential use: wireless phones
– Telepoint: allows the use by the user of mobile phones.
– Wireless-PBX: allows connection to the switchboard of the company through terminals.

• The DECT Standard

It is the European telecommunications standard developed by ETSI for wireless communications of voice and data coverage radius between 25 and 50 meters indoors and up to 250 meters outdoors.
Interference-free DECT handles a large number of users and makes planning very simple cell.

4.3.3 Terrestrial Broadcast

By using microwaves, it is possible to provide access to any service. LMS is a technology for broadband wireless communications that falls within the media and is based on a concept-based wireless cells where each cell has a radius of 4 km approx. It uses frequencies in the band of 26-28 GHz.

4.3.4 Satellite Broadcast

To serve remote areas not easily accessible or widely dispersed users, this is one of the best alternatives, with broad coverage. The access speed is usually not very high; they often use a terrestrial environment to not raise the cost in excess of the terminal, LEO satellites.

4.3.5 Fiber Optic Access

It is the first network access for businesses and other entities that need large transfers of information; it is not in common use. Through the use of a unit called the UN, it provides video service through the STB connected to TV, and telephone or data transmission.

• Applications and Advantages of WDM

Systems using optical fiber based on injected at one end the electrical signal reaches the receiving end attenuated, which is received in a photodetector, is decoded and converted into electricity.
The type of modulation and/or encoding depends on a number of factors. Individual LEDs very well the modulation in the laser intensity as they produce a beam of coherent light.
The two traditional methods have been TDM and FDM. WDM provides each signal at a different laser frequency. You can multiply capacity by 4, by 8, by 16, 32, or even 1 Tbit/s. When the number exceeds 8, it is called DWDM. The use of DWDM allows owners of fiber infrastructures to provide more capacity installed.

6. Voice over IP Multiservice Networks

New quality standards allow services on IP networks; they have created an environment where it is possible to transmit voice over IP, as it did not mean in any way the disappearance of telephone networks. If the above is compounded by the Internet phenomenon, the conclusion is clear: VoIP is a topical issue.

6.1 The Standard VoIP

Solutions have emerged from different manufacturers using multiplexers that allow the use of WAN data transmission companies for voice traffic.
Undeniably, the definitive establishment of the IP protocol in the fields and domestic business. We can find three types of IP networks:

• Internet: the state of the network does not allow professional use for voice traffic
• Public IP-Network: Operators provide business connectivity to interconnect their local area networks in regards to the IP traffic.
• Intranet: The IP network implemented by the company itself. Usually consist of several LANs.

Voice over IP converts voice signals into standard data packets that are transported through data networks instead of traditional phone lines. The encapsulated signals may be carried by any network.

6.1.1 Characteristics of the Standard

The VoIP protocol is focused on ensuring interoperability between equipment from different manufacturers. These elements are basically concerned with directory services and the transmission of multi-tone signaling.
The VoIP/H.323 turn comprises a series of standards:
– Addressing, signaling, and voice compression
– Voice transmission.

Currently, a number of items are already available in the market. These are:
– Gatekeeper: optional element in the network. Its function is to manage and control network resources so that situations do not occur that cause saturation of it.
– Gateway: essential element in most networks because its mission is to connect the VoIP network with the analogue telephone network or ISDN.
– Conference-Multiple unit: used to establish a conference between multiple users and keep track of conversations.