Tuesday, August 24, 2010

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Zen X380 - Dual SIM GSM music mobile phone Low Price Mobile Phone Rs 1,399

Tuesday, May 18, 2010

Some basic terms to Know

3
3G:Third-generation mobile communication system. Generic name for mobile network/ service based on the IMT-2000 family of global standards. [ITU(1)]

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A

ADSL:Asynchronous Digital Subscriber Line. ADSL variant in which traffic is transmitted at different rates in different directions (upstream and downstream). [TMG]
Amplifier:A device used to increase the strength of electronic signals Telecommons
Analogue:Communications signal represented by the pitch and the volume of a voice. [ITU(1)]
Antena: The device that concentrates a beam of electromagnetic waves to a focal point so as to send /receive signals. [Telecommons]
Aperture: The effective cross sectional area of the antenna. The larger the aperture, the stronger the signal the antenna receives or transmits. [Telecommons]
ATM: "Asynchronous Transfer Mode. A very fast data transmission methods. It dramatically allocates bandwidth and uses a fix-ed size packet." [ITU(1)]

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B

Backbone: The main line that ties networks, phone systems or computers together. It's like the human skeleton, with many small connections (called nodes or terminals), Branching off from the backbone. [Telecommons]
Bandwidth: The range of frequencies available to be occupied by signals. In analogue systems it is measured in terms of Hertz (Hz) and in digital systems in bit/s per second (bit/s). The higher the bandwidth, the greater the amount of information that can be transmitted in a given time. High bandwidth channels are referred to as broadband which typically means 1.5/2.0 Mbit/s or higher. [ITU(2)]
Bit rate: The speed at which bits are transmitted usually expressed in bits per second (bps). [Telecommons]
Broadband: Transmission capacity with sufficient bandwidth to permit combined provision of voice, data and video. According to ITU report, it refers to DSL and cable modem services with band width greater than 128kbps in at least one direction. [ITU(1)]

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C

Cable: A cable is one or more insulated wires inside a common protective wrapper. [Telecommons]
Carrier: A company that owns a transmission medium and rents, leases or sells portions for a set tariff. [Telecommons]
CATV: The transmission, usually for a fee, of television signals, including signals that originate at over-the- air television stations, to consumers on a wired network. [Telecommons]
CDMA: Code Division Multiple Access. A technology for digital transmission of radio signals based on spread spectrum techniques where each voice or data call uses the whole radio band and is assigned a unique code. [ITU(3)]
Channel: An electrical transmission path between two or more stations. Channels may be furnished by wire, radio, fiber or a combination of all three. [Telecommons]
Circuit: A physical transmission path between two or more points. [Telecommons]
Communication satellite: A device sent up into space used to relay telecommunications signals between two or more points. The main advantage of satellites is the relatively low cost of the earth station equipment needed to link up with satellites compared to stringing wire or fiber optic cable over very long distances. [Telecommons]
Competition: Refers to a situation in a market in which firms or sellers independently strive for the patronage of buyers in order to achieve a particular business objective, e.g., profits, sales and/or market share. [OECD]
Convergence: Refers to two different trends: - convergence between the broadcasting and telecommunications sectors. Advances in technology make it possible to use different media (cable networks, terrestrial and satellite radio relay systems, computer terminals and television sets) to carry and process all kinds of information and services, including sound, images and data. This type of convergence is due to a revolution in technology (digitisation). It has economic and regulatory implications. - fixed/mobile convergence. Increasingly similar technologies are used and services provided by fixed telephone and mobile telephone systems. This type of convergence opens up prospects for operators to propose the same services to all users, regardless of the technology or networks they use. [Autorie de regulation des telecommunications]
Cost-based pricing: "The general principle of charging for services in relation to the cost of providing these services. [WTO]
Coverage: Refers to the area on earth capable of effectively receiving transmission of network. Often use for cellular or satellite network. [ITU(1)]

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D

Dark fiber: A bare capacity and does not involve any of the electronics necessary to transmit or receive signals over that capacity. [FCC]
Demodulation: Demodulation converts data back and forth between digital and analogue. [Telecommons]
Digital: Any type of information that can be output, transmitted and interpreted as individual bits of binary information (the use of the numbers 0 and 1), using electrical or electromagnetic signals that can be modulated to convey their specific content. A TV picture will be more like a rectangle and have up to 1,080 lines of resolution, producing a crisper picture. [FCC]
Digital divide: "Refers to the gap between individuals, households, businesses and geographic areas at different socio-economic levels with regard to both their opportunities to access information and communication technologies (ICTs) and to their use of the Internet for a wide variety of activities. The digital divide reflects various differences among and within countries. [OECD]
Digital switched network (DSN): A high-speed digital switched public network allows access to a wide range of services such as telecommuting, video conferencing, telemedicine, distance learning, etc. Telecommons
Download: To receive data from another computer into your computer. The opposite is called "Upload". [FCC]
DSL: "Digital Subscriber Line. A high-speed Internet connection using telephone lines." [ITU(1)]
Duplex Transmission : Simultaneous two-way(transmit and receive) independent transmission. [Telecommons]

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E

Earth station: The antenna, receivers, transmitters and other equipment needed on the ground to transmit and receive satellite communication signals. [Telecommons]
E-Commerce: "Electronic commerce. Refers to commercial transactions occurring over open networks, such as the Internet. Both business-to-business and business-to-consumer transactions are included." [OECD]
E-Government: Refers to the use of new information and communication technologies (ICTs) by governments as applied to the full range of government functions. In particular, the networking potential offered by the Internet and related technologies has the potential to transform the structures and operation of government. [OECD]
Electronic data interchange (EDI): "Electronic Data Interchange. Transmission of information between computers using standardized electronic versions of common business documents." [ITU(1)]
EMS: Enhanced Messaging Service. EMS is a text service allowing mobile users to send and receive short text messages from other mobile and PC users. Compared to SMS, EMS includes additional features such the transmission of simple melodies, graphics, sounds, animations and modified text as an integrated message. [ITU(2)]
E-strategies: The national information infrastructure strategies arise from the Internet and the convergence of telecommunications ,computing and broadcasting. [The World Bank]
Exchange: A basic unit for the administration of telephone service, which generally includes everyone in one town plus adjacent areas. There can be more than one exchange within a larger town or city. The territory served by an exchange, within which local rates apply, is known as the exchange area or local service area. [Telecommons]

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F

Fiber optics transmission system (FOTS): A system which uses glass fibers the size of human hairs through which light is transmitted. By changing the patterns of light sent through the lines, information is transmitted. These signals are read by light-sensitive devices. Fiber optics generally allow for a much greater speed and bandwidth than transmitting over regular wires, microwaves or satellite. [Telecommons]
Firewall: A hardware- and/or software-based system that is used as an interface between the internet and a computer system to monitor and filter incoming and outgoing communications. [OECD]
Frame Relay: A high-speed data service. Telecommons
Frequency: The rate at which an electrical current alternates, usually measured in Hertz. It is also used to refer to a location on the radio frequency spectrum, such as 800, 900 or 1800 Mhz. [ITU(1)]

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G

Gateway: An interface between some external source of information and a World Wide Web server. In this instance a gateway is a web enabled search mechanism which allows users to search a distributed network of directory nodes. [OECD]
Geographical Information Systems (GIS): A geographical information system (GIS) can be seen as a system of hardware, software and procedures designed to support the capture, management, manipulation, analysis, modeling and display of spatially referenced data. [OECD]
GSM: "Global Systems for Mobile communications. European-developed digital mobile cellular standard." [ITU(3)]

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H

High speed: Usually refers to data communications systems operating at speeds above 9,600 bps. [Telecommons]
Host: Internet access provider's computer. You may use one of its hard- wired terminals, if you are at an institution with a mainframe computer connected directly to the Internet, or you may dial up via modem to connect with the Internet access provider's host computer. [FCC]
Hub: Central point for the collection, sorting, transshipment and distribution of goods for a particular area. [FCC]
Hyper-Text Mark-Up Language(HTML): The programming language used to design and present computer sites on the Internet in a graphical user interface fashion. HTML is the language used by programmers on the Internet as part of the World Wide Web project. [OECD]
Hyper-Text Transport Protocol(HTTP): The method for moving "hypertext" files across the Internet. Requires an HTTP program at one end and a server at the other. [FCC]

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I

ICT Applications: Hardware and software solutions that utilize ICT to meet business, public administration, social and other goals; there are also sometimes referred to as informatics. [The World Bank]
IMT 2000: Worldwide standards for third generation mobile systems which enable mobility services to be improved. [Autorie de regulation des telecommunications]
IMT 2001: International Mobile Telecommunications-2000. The International Telecommunications Union (ITU) recommendation for 3G networks. [TMG]
Informatics: It deals with ICT as a theme, a way of doing things (e.g. ICT in Education, e-government). [The World Bank]
Information and Communication Infrastructure (ICI): Refers to physical telecommunications systems and networks (cellar, broadcast, cable, satellite, postal) and the services that utilize them (Internet, voice, mail, radio, and television). [The World Bank]
Information and Communication Technologies (ICT): Consists of the hardware, software, networks, and media for the collection, storage, processing, transmission and presentation of information (voice, data, text, images), as well as related services. ICT can be split into ICI and IT. [The World Bank]
Information Technology (IT): Refers to the hardware and software of information collection, storage, processing, and presentation. [The World Bank]
Interconnection: The physical connection of telecommunication networks owned by two different operators. [ITU(1)]
Interconnection charge: A charge levied by network operators on other service providers to recover the costs of the interconnection facilities (including the hardware and software for routing, signaling, and other basic service functions) provided by the network operators. [WTO]
Interface: The point at which two systems or pieces of equipment are connected.[Telecommons]
IP: Internet Protocol.[ ITU(1)]
IP address: Address identifying a terminal connected to the Internet network. [Autorie de regulation des telecommunications]
IP telephony: The use of IP technology to transfer voice and data. [Autorie de regulation des telecommunications]
ISDN: Integrated Services Digital Network. A digital switched network supporting transmission of voice, data and images over conventional telephone lines. [ITU(1)]
ISP: Internet Service Provider. [ITU(1)]

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K

Knowledge economy: Refers to the use of knowledge to produce economic benefits. The phrase came to prominence in New Zealand in the mid-to late-1990s as a way of referring to the manner in which various high-technology businesses, especially computer software, telecommunications and virtual services, as well as educational and research institutions, can contribute to a country's economy. [The World Bank]
Knowledge management: A concept in which an enterprise gathers, organizes, shares, and analyzes its knowledge in terms of resources, documents, and people skills. Knowledge management involves data mining and some method of operation to push information to users. [The World Bank]

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L

Leased line: A telecommunications channel leased between two or more points at a flat monthly rate. Also called dedicated or private line. [Telecommons]
Local Area Network (LAN): The electronic linking, by cable or infrared beams, of several or all computer workstations within a specific physical area to a file server or storage and processing device. It allows all users connected to the network to access the server's software and data files and to exchange electronic messages via an electronic mail system. Frequently includes printers, scanners, and other related equipment. [OECD]
Local loop: The connection that runs from the subscriber's telephone exchange equipment. This term is synonymous with the term fixed line. [ITU(1)]

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M

Microwave transmission system: A high-capacity transmission system that sends information using high-frequency radio signals called microwaves. Originally, microwaves systems offered only analogue transmission, but today they are commonly digital. [Telecommons]
Modem: Computers generate data in digital form. To send this, this digital stuff over an analogue phone line, the data has not be converted. [Telecommons]
Multiplexing: Techniques that allow a number of simultaneous transmissions over a single circuit so as to accommodate multiple users or uses. [Telecommons]
Multipoint: A line or channel connecting more than two specific service points. [Telecommons]

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N

Network: Combination of telecommunications resources, for example, exchanges, wire links (copper cable, optical fiber) and terrestrial or satellite radio transmission links. [Autorie de regulation des telecommunications]
Number portability: Possibility for subscribers to retain their telephone number when changing local loop operator or when changing geographic location or local loop operator, or both. [Autorie de regulation des telecommunications]

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P

Packet: A group of digital bits put together in a bundle or packet to make transmission faster. One little packet includes not only your data but also control information such as a source and destination address and an identification number. [Telecommons]
Packet Switching: Technique where bit grouped packets are specifically routed to their destinations based on the availability of transmission paths. [Telecommons]
Penetration: A measurement of access to telecommunications. It is usually calculated by dividing the number of subscribers by the population, and multiplying by 100. Also referred to as density. [TMG]
Portals: A portal is the term given to that part of a Website which acts as a gateway, or launch point, through which users navigate the World Wide Web. [OECD]
Private Branch Exchanger (PBX): A private telephone switch that establishes voice-grade circuits over tie-lines between individual users and the switched network. [Telecommons]
Private Line Service: Dedicated telecommunications channels provided between two points or switched among multiple points. Privately leased for high-volume voice, data, audio, or video transmissions. [FCC]
Private Networks: Any network used to communicate within an organization (as distinct from providing service to the public) or to supply such communications to organizations, based on a configuration of own or leased facilities. The term includes networks used by private companies, state enterprises, or government entities. [OECD]
Protocol: A formal set of conventions governing how communication systems can talk to each other. [Telecommons]
Publicly Switched Telephone Network (PSTN): The world-wide dial-up telephone network or portion of that network. Whatever system you own should be linked somehow to the PSTN so you can make long distance phone calls, or go on the Internet. [ITU(3)]

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R

Reach: Refers to the availability of a service in the community. It is the number of homes to which the services is available regardless of whether or not residents choose to subscribe. [FCC]
Router: A special switching system in space that receives radio communication signs, from earth stations on earth and then retransmits them to earth location. [Telecommons]

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S

Server: A computer that has been set up to provide certain services to other computers (clients), for instance, a Web server is a central repository of data, software or client for the World Wide Web. [OECD]
Signal: The combination of waves that travel along a transmission channel and act on the receiving unit. [Telecommons]
SMS: Short message Service. A service available on digital networks, typically enabling messages with up to 160 characters to be sent or received via the message center of a network operator to a subscriber's mobile phone. [ITU(2)]
Spectrum Management: The spectrum or range of radio frequencies available for communication, industrial, and other uses. Frequency bands or segments are assigned to various categories of users for specific purposes, such as commercial radio and television, terrestrial microwave links, satellites, and police. At the international level this is done by the International Frequency Registration Board (IFRB) of the International Telecommunication Union (ITU). Individual national regulatory agencies monitor the occupancy of the radio spectrum and allocate frequencies to individual users or a groups of users so as to enable a large number of services to operate within specified limits of interference. [WTO]
Spectrum(Radio): The radio frequency spectrum of hertzian waves used as a transmission medium for cellular radio, radiopaging, satellite communication, over-the-air broadcasting and other services. [ITU(1)]
SSL: Secure Socket Layer. A programmed layer created by Netscape for managing the security of message transmissions in a network. SSL uses a public-and -private key encryption system, which also includes the use of a digital certificate. [ITU(2])
Subscription: A licensing agreement in which the licensee makes a payment to the service provider for access to ICTs. [TMG]

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T

Tariff / Unbundled tariff: Tariffs are the schedule of rates and regulations governing the provision of telecommunications services. Unbundling of tariffs is where each component of a communications service or product is priced separately, so that customers may select only those components needed and be charged accordingly." [WTO]
TCP/IP: Transmission control protocol/ Internet protocol. [ITU(1)]
Transmission system Local exchange carrier: A system to transfer information from one location to another. It could be copper wire, fiber optic lines, or radio waves.[Telecommons]
Transponder: An electronic device on a satellite used to boost or amplify signals before sending them back to earth. It can receives an uplinks signal at one frequency, convert its frequency, amplifies it, and transmits it to the ground. Satellites generally have 10-40 transponders. [Telecommons]

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U

Universal Access: Refers to reasonable access to ICTs for all. Includes universal service for those that can afford individual ICT service and widespread provision of ICTs within a reasonable distance for others. Stastically measured as the percentage of the population covered by information and communication technologies. [ITU(1)]
Universal Service: Refers to availability and widespread affordability of ICTs. The level of universal services is statistically measured as the percentage of households with ICTs. [ITU(1)]
Uplink: The transmission of signals from an earth station to a satellite. [Telecommons]

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V

Very Small Aperture Terminal: An earth station with a small antenna of usually 0.9-1.8 meter (3-6 foot) diameter. Typically used in point-to-multipoint data networks.[Telecommons]

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W

Wide Area Network (WAN): A computer network that connects computers over large distances by means of high-speed communications links or satellites. [OECD]
Wireless communication: Sending signals without a physical connection using technologies such as cordless telephones, cellular telephones or microwaves. [Telecommons]
WWW: World Wide Web. The World Wide Web is a part of the Internet designed to allow easier navigation of the network through the use of graphical user interfaces and hypertext links between different addresses. [OECD]

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X

XML: extensible markup language. [OECD]

What is SDH

SDH (Synchronous Digital Hierarchy) is an international standard for high speed
telecommunication over optical/electical networks which can transport digital signals
in variable capacities. It is a synchronous system which intend to provide a more flexible , yet simple
network infrastructure.

SDH (and its American variant- SONET) emerged from standard bodies somewhere around 1990.
these two standards create a revolution in the communication networks based on optical fibers ,
in their cost and performance.


before SDH

The development of digital transmission systems started In the early 70s , and was based on
the Pulse Code Modulation (PCM) method.

In the early 80's digital systems became more and more complex , yet there was huge
demand for some features that were not supported by the existing systems.
The demand was mainly to high order multiplexing through a hierarchy of increasing bit
rates up to 140 Mbps or 565 Mbps in Europe.
The problem was the high cost of bandwidth and digital devices. The solution that was
created then , was a multiplexing technique , allowed for the combining of slightly
non synchronous rates, referred to as plesiochronous*, which lead to the term plesiochronous digital hierarchy (PDH).

*plesiochronous - "almost synchronous , because bits are stuffed into the frames as padding and the
calls location varies slightly - jitters - from frame to frame".

multiplexing with PDH


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why using SDH ?

Although PDH was A breakthrough in the digital transmission systems , it has a lot of
weaknesses :

  • No world standard on digital format (three incompatible regional standards - European, North american and Japanese).
  • No world standard for optical interfaces. Networking is impossible at the optical level.
  • Rigid asynchronous multiplexing structure.
  • Limited management capability.
Because of PDH disadvantages, It was obvious That a new multiplexing method is needed.
The new method was called SDH.


multiplexing with SDH








SDH has a lot of advantages:

  • First world standard in digital format.
  • First optical Interfaces.
  • Transversal compatibility reduces networking cost. Multivendor environment drives price down
  • Flexible synchronous multiplexing structure .
  • Easy and cost-efficient traffic add-and-drop and cross connect capability.
  • Reduced number of back-to-back interfaces improve network reliability and serviceability.
  • Powerful management capability.
  • New network architecture. Highly flexible and survivable self healing rings available.
  • Backward and forward compatibility: Backward compatibility to existing PDH
    Forward compatibility to future B-ISDN, etc.
The following Graph Shows the differences between PDH and SDH Prices:








SDH is based on byte interleaving and not bit interleaving , as PDH was based on.
The bit rate increased from 64 Kbps in PDH to 1.5 - 2 Mbps in SDH.

SDH/SONET Vs. PDH rates


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when do we use SDH ?

  • When networks need to increase capacity , SDH simply acts as a means of increasing transmission capacity.
  • When networks need to improve flexibility , to provide services quickly or to respond to new change more rapidly.
  • when networks need to improve survivability for important user services.
  • when networks need to reduce operation costs , which are becoming a heavy burden .


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layers model of SDH

the following scheme describes the different layers of SDH , according to the OSI model :




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standards

  • SDH has been standardized by ITU-T in 1988.
  • In November 1988 the first SDH standards were approved.
  • In 1989 , the CCITT (International Consultative Committee on Telephony & Telegraphy) had published in its "Blue book" recommendations G.707 , G.708 & G.709 covering the SDH standards.
G.702 - Digital Hierarchy Bit Rates
G.703 - Physical/Electrical Characteristics of Hierarchical Digital
Interfaces
G.707 - SDH Bit Rates
G.708 - Network Node Interface for the SDH
G.709 - Synchronous Multiplexing Structure
G.773 - Protocol Suites for Q Interfaces for Management of
Transmission Systems
G.781 - (Formerly G.smux-1) Structure of Recommendations on
Multiplexing Equipment for the SDH
G.782 - (Formerly G.smux-2) Types and General Characteristics
of SDH Multiplexing Equipment
G.783 - (Formerly G.smux-3) Characteristics of SDH Multiplexing
Equipment Functional Blocks
G.784 - (Formerly Gsmux-4) SDH Management

SDH Elements

The most common SDH elements are :


The terminal multiplexer is used to multiplex local tributaries (low rate)
to the stm-N (high rate) aggregate. The terminal is used in the chain
topology as an end element.


The regenerator is used to regenerate the (high rate) stm-N in case that the
distance between two sites is longer than the transmitter can carry.

The Add And Drop Multiplexer (ADM) passes the (high rate) stm-N through
from his one side to the other and has the ability to drop or add any (low rate)
tributary. The ADM used in all topologies.


The synchronous digital cross connect receives several (high rate) stm-N and switches
any of their (low rate) tributaries between them. It is used to connect between
several topologies.

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SDH Topologies


The linear bus (chain) topology used when there is no need for protection
and the demography of the sites is linear.


The ring topology is the most common and known of the sdh topologies
it allows great network flexibility and protection.


The mesh topology allows even the most paranoid network manager
to sleep well at nights because of the flexibility and redundancy that it
gives.


The Star topology is used for connecting far and less important sites
to the network.

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Usage of SDH elements in SDH Topologies


The Terminal multiplexer can be used to connect two sites in a high rate
connection .


The Add And Drop Multiplexer (ADM) is used to build the chain topologies in the above picture.
At the ends of the chain usually a Terminal Multiplexer is connected.


The Add And Drop Multiplexer (ADM) is used to build the ring topology.
At each site we have the ability to add & drop certain tributaries.

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SDH Protection

The SDH gives the ability to create topologies with protection for the data transferred.
Following are some examples for protected ring topologies.


At this picture we can see Dual Unidirectional Ring . The normal data flow is
according to ring A (red). Ring B (blue) carries unprotected data which is lost in
case of breakdown or it carries no data at all.


In case of breakdown rings A & B become one ring without the broken segment.


The Bi-directional Ring allows data flow in both directions. For example if data from one
of the sites has to reach a site which is next to the left of the origin site it will flow to the left
instead of doing a whole cycle to the right.


In case of breakdown some of the data is lost and the important data is
switched. For example if data from a site should flow to its destination through
the broken segment, it will be switched to the other side instead.

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SDH Management

SDH has enhanced management capabilities :

  • Alarm/Event Management
  • Configuration Management
  • Performance Management
  • Access and Security Management

Depicted above is a Management Station connected to a SDH ring through site 1 which contains the
gateway element. The Gateway elements receives the status of all the other elements in the net through
the special fields that exists in the SDH protocol (in band).

SDH vs. PDH

Few years ago the common way to build a backbone network that supplies broadband communication
to the suppliers (BT, Bezeq etc.) was a PDH network. The topology of a PDH network is the Mesh
topology where every multiplexer in each site worked with its own clock. In order to synchronize between two multiplexers that works together, usually the transmission was made according to the local clock and the reception was made according to the recovered clock that was recovered from the received data.
The PDH contains 4 basic bit rates:

  • E1 - 2.048 Mbit/Sec
  • E2 - 8.448 Mbit/Sec
  • E3 - 34.368 Mbit/Sec
  • E4 - 139.264 Mbit/Sec
The En is the result of multiplextion of 4 En-1.

The fact that each of the multiplexers transmits according to its own clock creates a problem when we need to multiplex several transmitted data streams, the problem is that we can't decide which clock to choose for the multiplexing. If we will choose a fast clock we will not have enough data to put in the frame from a slower incoming data stream (we will get empty spaces in the frame), from the other hand if we will choose a slow clock the data at the faster incoming stream will be lost.

This problem was solved with a stuffing algorithm, which is implemented by using a fast clock, that allows transmission of indication bits and stuff bits. In case that the data is slower then "expected", the indication bits indicate that the following stuff bits are "garbage" and if the data is faster then "expected" the indication bits indicate that the following stuff bits are data. This is the reason why 4 * En-1 <>

There are two common ways to connect between two PDH sites. The first is by Radio Frequency (RF)
and the other is by Electrical Signal over copper cable. since we cant afford to many cables or frequencies
usually E3 or E4 is used.
In order to transmit E1 (a very common data rate) we need 2 or 3 levels of multiplexing, this means that
in a full E4 constellation 1+4+16=25 multiplexers are needed.
Further more there is no inband management in the PDH protocol if we need to know the status of 1 of the multiplexers, or if we need to change the route of 1 of the trails we have to go to the site or build an
outside network that allows us to manage the PDH network.

In the latest years a new protocol was defined, this new protocol was aimed to provide all the PDH
capabilities and solve some of the PDH weaknesses that are mentioned above. This new protocol is the SDH.
The SDH network works with a single central clock that synchronizes all the elements in the network.
The SDH contains the following bit rates:

  • STM1 - 155 Mbit/Sec
  • STM4 - 622 Mbit/Sec
  • STM16 - 2.5 Gbit/Sec
  • STM64 - 10 Gbit/Sec
  • Etc.
In order to have the ability to connect a low rate PDH stream (E1, E3 etc.), an improved stuffing algorithm is used.
The SDH protocol enables transmitting any of the PDH bit rates directly by mapping it to the STM-n frame, that gives the user the flexibility to transmit any configuration of tributary rates using only one multiplexing element, depicted bellow the difference between the SDH network element and the PDH network elements that need to transmit different tributary rates.

PDH network elements.

The inband management functionality enables the SDH network manager to receive information about
the quality of service, the damaged elements (if there are any) and gives the manager the option to change the network configuration from a remote site. In order to be able to do the same things with the PDH network, one should build another separated network for the management and the remote control.

The ability to multiplex any of the standard bit rates into the STM-n frame is possible due to the complicated containers structure of the STM-n frame as depicted bellow.

In order to map an E1(2.048 Mbit/Sec) into the STM-n frame we have to create a TU-12 stream which is a low rate stream that is synchronized to the SDH network clock. The TU-12 is composed of the E1 data, indication bits, stuffing bits, management bits and a direct pointer to the E1 frame.
The TUG-2 is a structure that can be composed of 3 TU-12s (3 E1s), or 4 TU-11s (4 T1s), or 1 TU-2 (1 T2). This structure gives the STM frame its flexibility to multiplex different rates directly into the STM-n frame (impossible in the PDH protocol). The next stage is mapping 7 TUG-2s into 1 VC-3 or into 1 TUG-3 and so on according to the flow chart.

This method of multiplexing allow us to directly map the T1, T2, T3 (American standards) and the E1, E2, E3, E4 (European standards) into the STM-n frame.

Each time we map lower rate streams into a higher rate structure we add pointers to a fixed point in the lower rate streams, so we can directly extract the relevant information with out demultiplexing the all high rate stream.

When stuffing is needed the pointer to the fixed location is changed according to the direction of the stuffing, this is the improvement of stuffing algorithm used in the PDH .



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SDH Frame Structure

The STM-n frame structure is best represented as a rectangle of 9 x 270xN.
The 9xN first columns are the frame header and the rest of the frame is the inner structure data (including the data, indication bits, stuff bits, pointers and management).

The STM-n frame is usually transmitted over an optical fiber. The frame is transmitted row by row (first is transmitted the first row then the second and so on). At the beginning of each frame a synchronized bytes A1A2 are transmitted .


The multiplexing method of 4 STM-n streams into a STM-nx4 is an interleaving of the STM-n streams to produce the STM-nx4 stream. The method is shown in the next picture for producing STM-4 from 4 STM-1 streams.

After interleaving we get a higher order stream that in its rectangular form all the low order STM streams are placed as its columns which makes it easier to find each of them in the bigger frame.





SDH - In the future
The modern lifestyle requires high speed communication applications.
SDH provides large bandwidth that can meet the needs of this applications.
Here are some of the needs and there solutions.

Future of the private circuits

Demands:

  • In the future there will be an increasment in the demand for private circuits (leased line traffic) and the associated capacity increase in the trunk network.
  • Mega stream services will be available for end users.
SDH solution:
  • SDH networks have flexible routing ability for circuit protection thus allowing rapid circuit reallocation and high circuit availability.
Future of the Broadband ISDN

Demands:

  • Growing demand for non voice broadband services which require a variable bandwidth such as video signal transmission, video conferencing, remote data base access and high speed multimedia file transfer.
SDH solution:
  • ATM has been chosen by CCITT to be the target transfer mode for B-ISDN services, ATM cells can be easily transported in the SDH frame.
The Aothers :
  1. Galit Rozenboim
  2. Hay Shaul
  3. Shay Turel
  4. Arik Litinsky
  5. Jacob Rutstein
  6. Itsik Shalom