Electromechanical Switch

Devices which carry out electrical operations by using moving parts are known as electromechanical.

The basic operation of electromechanical switches is based on the simple theory of electromagnetic induction. They rely on mechanical contacts as their switching mechanism. eg. Relay

Solid State Switch

A solid state switch is an electronic switching device based on semiconductor technology (e.g. MOSFET, PIN diode). Function wise, it is similar to an electromechanical switch except that it has no moving parts.

Broadband Integrated Services Digital Network

In the 1980s the telecommunications industry expected that digital services would follow much the same pattern as voice services did on the public switched telephone network, and conceived an end-to-end circuit switched services, known as Broadband Integrated Services Digital Network (B-ISDN).

BISDN is both a concept and a set of services and developing standards for integrating digital transmission services in a broadband network of fiber optic and radio media. BISDN will encompass frame relay service for high-speed data that can be sent in large bursts, the Fiber Distributed-Data Interface (Fiber Distributed-Data Interface), and the Synchronous Optical Network (Synchronous Optical Network). BISDN will support transmission from 2 Mbps up to much higher, but as yet unspecified, rates.

BISDN is the broadband counterpart to Integrated Services Digital Network, which provides digital transmission over ordinary telephone company copper wires on the narrowband local loop.

ATM

Asynchronous Transfer Mode (ATM) is, according to the ATMForum, "a telecommunications concept defined by ANSI and ITU (formerly CCITT) standards for carriage of a complete range of user traffic, including voice, data, and video signals". ATM was developed to meet the needs of the Broadband Integrated Services Digital Network, as defined in the late 1980s,[2] and designed to unify telecommunication and computer networks. It was designed for a network that must handle both traditional high-throughput data traffic (e.g., file transfers), and real-time, low-latency content such as voice and video.

ATM provides functionality that is similar to both circuit switching and packet switching networks: ATM uses asynchronous time-division multiplexing,[4][5] and encodes data into small, fixed-sized packets (ISO-OSI frames) called cells.

PDH/SDH

PDH stands for Plesiochronous Digital Hierarchy and SDH stands for Synchronous Digital Hierarchy.

Both PDH and SDH are terminologies associated with digital multiplexers used in exchanges. The different hierarchies having different bit rates are combined. These hierarchies will comprised of many such bit streams/channels (either 24, 30 or multiples) often called as tributaries.

PDH

In PDH, digital multiplexer's inputs (bit streams) are of same bit rate and are derived from different clocks from different oscillators. Each will differ within tolerance of few clock periods. Hence it is called plesiochronous.

Bit Interleaving is used in PDH to combine digital signals.

In PDH there are two main standards i.e. 30 channel one used in Europe and 24 channel one used in North America/Japan. Basic rate is 64 Kbps in North America(designated as DS0) and in Europe (designated as E0). Rates derived from 2.048 Mbps basic rate including bit stuffing in 30 channel case are mentioned below.

2.048 x 4 gives 8.448 Mbps (120 channels)

8.448 x 4 gives 34.368 Mbps (480 channels) 

34.368 x 4 gives 139.264 Mbps (1920 channels)

139.264 x 4 gives 564.992 Mbps (7680 channels) 

The figure-1 depicts PDH level hierarchy used in North America while figure-2 depicts PDH levels used in Europe. Rates derived from 1.544 Mbps basic rate including bit stuffing in 24 channel case are mentioned below.

 1.544 x 4 gives 6.312 Mbps (96 channels) 

6.312 x 7 gives 44.736 Mbps (672 channels)

 44.736 x 6 gives 274.16 Mbps (4032 channels) 

44.736 x 3 gives 139.264 Mbps

44.736 x 12 gives 564.992 Mbps 

The table below mentions PDH rates used in Japan.

Level

data rate in Japan

0

0.064 Mbps

1

1.544 Mbps

2

6.312 Mbps

3

32.064 Mbps

4

97.928 Mbps

Following are the limitations of PDH:

•  In PDH, different frame is used for transmission and in data laye. Hence multiplexing and de-multiplexing is very complex. 

• Accessing lower tributary requires the whole system to be de-multiplexed. 

• The maximum capacity for PDH is 566 Mbps, which is limited in bandwidth

• Tolerance is allowed in bit rates. 

• PDH allows only Point-to-Point configuration. 

• PDH does not support Hub. 

• Every manufacturer has its own standards; PDH also has different multiplexing hierarchies making it difficult to integrate interconnecting networks together.

SDH

As PDH was not scalable to support high capacity bandwidth and hence was not suitable to accomodate growing traffic need. SONET was developed as American Standard while SDH as European Standard.

SDH supports various topologies such as point to point, ring, star, linear bus etc. It uses TDM and octet multiplexing. It uses extremely precise timings. It employs both electrical and optical specifications.

In SDH, digital multiplexer's inputs are of same bit rate and are derived from common clock, hence are in phase. Hence it is synchronous.

Word(group of bits) Interleaving is used in SDH to combine digital signals.

SDH uses basic rate of 155.52 Mbps and four times multiples of this i.e. 622.08 Mbps and 2488.32Mbps. Basic SDH rate of 155.52 is also known as STM-1. STM stands for Synchronous Transport Module. SDH is referred as SONET (Synchronous Optical Network) in USA due to optical interfaces used. Figure-3 depicts table mentioning SONET and SDH levels with their respective data rates.

As per CCITT, any of PDH rates upto 140 Mbps can be integrated with SDH rates up to 155.52 Mbps.

Following are the merits or advantages of SDH: 

• A more simplified multiplexing and DE multiplexing technique.

• Synchronous networking and SDH supports multipoint networking.

• Capability of transporting existing PDH signals.

• Easy growth to higher bit rates which enhances the administration and maintenance process. 

• It is capable of transporting broadband signals.

• It is multivendor and supports different operators.

• It provides network transport services on LAN such as video conferencing, and interactive multimedia.

• Optical fibre bandwidth can be increased without limit in SDH.

• Switching protection to traffic is offered by rings.

• SDH allows quick recovery from failure.

DSL

Digital subscriber line (DSL; originally digital subscriber loop) is a family of technologies that are used to transmit digital data over telephone lines. In telecommunications marketing, the term DSL is widely understood to mean asymmetric digital subscriber line (ADSL), the most commonly installed DSL technology, for Internet access. DSL service can be delivered simultaneously with wired telephone service on the same telephone line. This is possible because DSL uses higher frequency bands for data. 

The bit rate of consumer DSL services typically ranges from 256 kbit/s to over 100 Mbit/s in the direction to the customer (downstream), depending on DSL technology, line conditions, and service-level implementation.

HDSL

HDSL (High bit-rate Digital Subscriber Line), one of the earliest forms of DSL, is used for wideband digital transmission within a corporate site and between the telephone company and a customer. The main characteristic of HDSL is that it is symmetrical: an equal amount of bandwidth is available in both directions. HDSL can carry as much on a single wire of twisted-pair cable as can be carried on a T1 line (up to 1.544 Mbps) in North America or an E1 line (up to 2.048 Mbps) in Europe over a somewhat longer range and is considered an alternative to a T1 or E1 connection.

ADSL

Asymmetric digital subscriber line (ADSL) is a type of digital subscriber line (DSL) technology, a data communications technology that enables faster data transmission over copper telephone lines than a conventional voiceband modem can provide. ADSL differs from the less common symmetric digital subscriber line (SDSL). Bandwidth (and bit rate) is greater toward the customer premises (known asdownstream) than the reverse (known as upstream). This is why it is called asymmetric. Providers usually market ADSL as a service for consumers to receive Internet access in a relatively passive mode: able to use the higher speed direction for the download from the Internet but not needing to run servers that would require high speed in the other direction.

Universal Mobile Telecommunications System (UMTS)

The Universal Mobile Telecommunications System (UMTS) is a third generation mobile cellular system for networks based on the GSM standard. Developed and maintained by the 3GPP (3rd Generation Partnership Project), UMTS is a component of the International Telecommunications Union IMT-2000 standard set and compares with the CDMA2000 standard set for networks based on the competing cdmaOne technology. UMTS uses wideband code division multiple access (W-CDMA) radio access technology to offer greater spectral efficiency and bandwidth to mobile network operators.

UMTS specifies a complete network system, which includes the radio access network (UMTS Terrestrial Radio Access Network, or UTRAN), the core network (Mobile Application Part, or MAP) and the authentication of users via SIM (subscriber identity module) cards.

UMTS (Universal Mobile Telecommunications System) is a so-called "third-generation (3G)," broadband , packet -based transmission of text, digitized voice, video, and multimedia at data rates up to and possibly higher than 2 megabits per second ( Mbps ), offering a consistent set of services to mobile computer ...

IMT-2000 

International Mobile Telecommunications for the year 2000 (IMT-2000) is a worldwide set of requirements for a family of standards for the 3rd generation of mobile communications. TheIMT-2000 "umbrella specifications" are developed by the International Telecommunications Union (ITU).

Next-generation network (NGN)

The next-generation network (NGN) is body of key architectural changes in telecommunication core and access networks. The general idea behind the NGN is that one network transports all information and services (voice, data, and all sorts of media such as video) by encapsulating these into packets, similar to those used on the Internet. NGNs are commonly built around the Internet Protocol, and therefore the term all IP is also sometimes used to describe the transformation of formerly telephone-centric networks toward NGN. The concept of future Internet refers instead to how the Internet itself might evolve

A next-generation network (NGN) is a packet-based network which can provide services including Telecommunication Services and is able to make use of multiple broadband, quality of Service-enabled transport technologies and in which service-related functions are independent from underlying transport-related technologies. It offers unrestricted access by users to different service providers. It supports generalized mobility which will allow consistent and ubiquitous provision of services to users.[

Real-time Transport Protocol (RTP)

The Real-time Transport Protocol (RTP) is a network protocol for delivering audio and video over IP networks. RTP is used extensively in communication and entertainment systems that involve streaming media, such as telephony, video teleconference applications, television services and web-based push-to-talk features.

RTP is used in conjunction with the RTP Control Protocol (RTCP). While RTP carries the media streams (e.g., audio and video), RTCP is used to monitor transmission statistics and quality of service (QoS) and aids synchronization of multiple streams. RTP is one of the technical foundations of Voice over IP and in this context is often used in conjunction with a signaling protocol such as the Session (SIP) which establishes connections across the network.

Voice over IP (VoIP)

 Voice over IP (VoIP) is a methodology and group of technologies for the delivery of voice communications and multimedia sessions over Internet Protocol (IP) networks, such as the Internet. Other terms commonly associated with VoIP are IP telephony, Internet telephony, broadband telephony, and broadband phone service.

Voice over Internet Protocol is a category of hardware and software that enables people to use the Internet as the transmission medium for telephone calls by sending voice data in packets using IP rather than by traditional circuit transmissions of the PSTN.

One advantage of VoIP is that the telephone calls over the Internet do not incur a surcharge beyond what the user is paying for Internet access, much in the same way that the user doesn't pay for sending individual emails over the Internet.

What is IP-PSTN?

    IP-PSTN is a gateway between a telephone and any SIP User Agent Client. It allows a person to call any (allowed) telephone number from any SIP-compliant client application.

Fig1. IP-PSTN Gateway

Intelligent Network (IN)

The Intelligent Network (IN) is the standard network architecture specified in the ITU-T Q.1200 series recommendations. It is intended for fixed as well as mobile telecom networks. It allows operators to differentiate themselves by providing value-added services in addition to the standard telecom services such as PSTN, ISDN and services on mobile phones..

Examples of IN services

Televising

Call screening

Telephone number portability

Toll free calls/Free phone

Prepaid calling

Account card calling

Virtual private networks (such as family group calling)

Centrex service (Virtual PBX)

Private-number plans (with numbers remaining unpublished in directories)

Universal Personal Telecommunications service (a universal personal telephone number)

Mass-calling service

Prefix free dialing from cellphones abroad

Seamless MMS message access from abroad.

Reverse charging

Home Area Discount

Premium Rate calls

Call distribution based on various criteria associated with the call

Location Based Routing

Time-based routing

Proportional call distribution (such as between two or more call centres or offices).

Call queueing

Call transfer

Intelligent Network (IN) is a telephone network architecture originated by Bell Communications Research (Bellcore) in which the service logic for a call is located separately from the switching facilities, allowing services to be added or changed without having to redesign switching equipment. According to Bell Atlantic, IN is a "service-specific" architecture. That is, a certain portion of a dialed phone number, such as 800 or 900, triggers a request for a specific service. A later version of IN called Advanced Intelligent Network (AIN) introduces the idea of a "service-independent" architecture in which a given part of a telephone number can interpreted differently by different services depending on factors such as time of day, caller identity, and type of call. AIN makes it easy to add new services without having to install new phone equipment.

GIS

A geographic information system or geographical information system (GIS) is a system designed to capture, store, manipulate, analyze, manage, and present all types of spatial or geographical data. 

In a general sense, the term describes any information system that integrates, stores, edits, analyzes, shares, and displays geographic information. GIS applications are tools that allow users to create interactive queries (user-created searches), analyze spatial information, edit data in maps, and present the results of all these operations.[2][3]Geographic information science is the science underlying geographic concepts, applications, and systems.[4]

GIS is a broad term that can refer to a number of different technologies, processes, and methods. It is attached to many operations and has many applications related to engineering, planning, management, transport/logistics, insurance, telecommunications, and business.[3] For that reason, GIS and location intelligence applications can be the foundation for many location-enabled services that rely on analysis and visualization.

GIS can relate unrelated information by using location as the key index variable. Locations or extents in the Earth space–time may be recorded as dates/times of occurrence, and x, y, and z coordinates representing, longitude, latitude, and elevation, respectively. All Earth-based spatial–temporal location and extent references should, ideally, be relatable to one another and ultimately to a "real" physical location or extent. This key characteristic of GIS has begun to open new avenues of scientific inquiry.