ADSL Packagers in Sri Lanka TELECOM

ADSL Entrée package – This package is mainly design on home internet browsing with low cost. Specially people who are satisfied only with wed browsing and used it infrequently, because in this package ISP (Internet Service Provider) provides low free usage of 1024 Mb and charge 50cent for every additional 1Mb.User can download and upload very few files (low capacity) and he is not able to do streaming, video conferencing, etc.

ADSL Home package – This package is mainly design on home internet browsing and downloads files with low cost. Especially people who are not satisfied with ADSL Entrée package they can go this solution. When consider uplink and downlink, we can see download capacity is higher than upload capacity, because home users, they really download more than upload. We can have unlimited download capacity in this package, they fore user can download more. And ISP provides this service with reasonable monthly charge.

ADSL Xcite package – This package is mainly design for small office and home users. If they have more than one computer at house or really interesting in downloading, he can buy this package download files with reasonable cost. And small business people can buy this package because ISP supplies more uplink and downlink compare to others above packagers.

ADSL Office package - This package is mainly design for middle scale business purposes that have a LAN. They want more uplink and downlink for their needs. We can see download capacity is more than upload capacity, therefore if they want to download bulky files, can purchase this package. When we consider monthly rental, it is high. Home and small business users are not able to purchase this package due to high cost. This also unlimited package therefore users can upload and download files at any time unlimitedly. We know offices need there E-mail addresses, DNS hosting, Virtual mail service, and web hosting. Therefore SLT gives those services through package.

ADSL Office 1IP package – This package is specially design for middle scale business purposes people who are having servers. In this package ISP (SLT) gives static IP for users. Other services are same as above ADSL Office package.

ADSL Xcel package - This package is really focused on large businesses that are having number of PCs. ISP provides 4Mb download capacity therefore if users  want to download bulky files, can purchase this package. This also unlimited package therefore users can upload and download files at any time unlimitedly. We know offices need there E-mail addresses, DNS hosting, Virtual mail service, and web hosting. Therefore SLT gives those services through package. They give 5 Mb for web hosting to the users.

PAP and CHAP ; Authentication Protocols That Used in ADSL

PAP and CHAP is the two main authentication protocols that used in ADSL.

Advantages and disadvantages of PAP and CHAP

•  CHAP has a more secure procedure for connecting to a system than PAP.

Because after sending the challenge message to user, the user responds with a value that calculates with the use of a one-way hash function and send sends respond packet. The RADIUS checks the response against its own calculation of the expected hash value. CHAP uses encrypted massage that includes user name and password. But PAP uses password in clear text and is a one way step process. That can be unsecured, half way communication.

Another feature of CHAP is that it doesn't only require the client to authenticate itself at startup time, but sends challenges at regular intervals to make sure the client hasn't been replaced by an intruder, for instance by just switching phone lines.

CHAP requires that the secret be available in plain text form. Irreversibly encrypted password databases commonly available cannot be used. It is not as useful for large installations, since every possible secret is maintained at both ends of the link.

•   CHAP provide access to the server in every time

It sends challenge massages frequently to the user, Because of that the user is always connected to RADIUS. Therefore we can prevent the rick of another client replacement to the server using same line.   

Throughout this article I hope you may get some thing. This provides very basic explanation and future will cover more. Comments are well come. Thank you

Synchronization Technique Used in Analog FDM

 Frequency division multiplexing (FDM) is an analog modulation technique that combines analog signals. In FDM several frequencies bandwidths are carried through a single line. Then it is transmitted to the receiver. In this case, in FDM we use guard bands within two bandwidths. Using guard band is a technique that use in FDM for synchronization. We can see it in this figure.

 

When we transmit these 10 kHz bandwidths (signals) to receiver without guard (5 kHz) bands, the receiver cant identity what is the 1^st, 2^nd, 3^rd signal. It hasn’t any understand about the bandwidth of the signal.

               We can see in this figure, if we use a guard band between them the receiver can identify the signals. It can know the bandwidth of the signal.

               That’s how synchronization technique used in analog FDM.

Throughout this article I hope you may get some thing. This provides very basic explanation and future will cover more. Comments are well come. Thank you.

Benefits of Modulation in Telecommunication

Modulation for efficient transmission

                                                         

                      Signal transmitting over appreciable distance always involves a traveling electromagnetic wave. The efficiency of any particular transmission method depends upon the frequency of the signal being transmitted. By exploit in the frequency translation property of modulation the message can be inserted into carrier which has the frequency selected for the desired transmission method.

Modulation to overcome hardware limitation

                                             

                      The design of the communication may be constrict by the cost availability of the hardware, performance of the hardware often depends on the frequencies involved. Modulation permits that designer to place a signal in some frequency range that avoids the hardware limitation.

Modulation to reduce noise and interferences

                      A method for overcoming noise and interferences is to increase signal power until it overcomes the contamination. But increasing power is costly and may damage the equipments. Fortunately FM and certain other types of modulations have a valuable property of suppressing both noise and interferences.

Modulation for frequency assignment

                      When we tune a radio or television, particular station we are selecting one of the many signals being received at that time. Since each station has a different assigned carried frequency that desired signal can be separated from the others by filtering.

    Throughout this article I hope you may get some thing. This provides very basic explanation and future will cover more. Comments are well come. Thank you.

ATM technology in SDH

By using ATM technology, variable bit traffic is transport over SDH Network. In hybrid ATM, payload of SDH frame are filled with ATM cells by using ATM cells. The bit rates are depends on the number of ATM cells. In this system SDH traffic and ATM traffic are combined in to same SDH bearer, Nodes have the visibility of ATM cells. Therefore they separate the SDH traffic from ATMJ. And they route each one to their respective switching fabric. After they have been swathed, they may recombine in a hybrid payload, network element requires both SDH & ATM traffic management. ATM cells are mapped in conceded STS-N payload. 

SDH frames with ATM cells

Voice traffic ATM over SDH

ATM is a core protocol used over the sonnet/SDH backbone of the ISDN. All the data packets in the link always encounter full size under normal quinine conditions so that experience maximum quinine delays, so that we need some technique to avoid this. It is ATM. Reduction of this end to end delay is very much important when carrying voice traffic, because the conversion of digitized voice in to an analog audio signal is a hesitantly real time process. When there is a stream of data and in they stream there is a space and patently they data is not available. If it is valid able delayed due to quinine then we face a problem to overcome that we uses ATM over SDH.

    Throughout this article I hope you may get some thing. This provides basic explanation and future will cover more. Comments are well come. Thank you.

What are the Collected Infomation Before Impliment a Computer Network

Geographical state of the Company.

How computers are arranged in the Network.

Ex- There can be several sections in a one department, according to that information we should set up a LAN for a department.

Details about the building which we going to setup a network.

How those departments are located.

Ex-   In a same building or in different buildings. If Departments are in different buildings & the distance of two buildings are more than 100m we can’t use UTP CAT 5, for over come that should use Fiber optics cables.

Old or new building.

Ex- If the building has a historical value we should setup a Wireless Network.

Details about departments.

When we plan a structured cable design need that information.

Ex- We can use UTP CAT 5 cables for IT, Finance & HR departments but we should install STO CAT 5 cables for Production and Transport departments.

Cost of set up

What are the technologies that used for connect with each branch.

EX- Lease line, Private Lease line or over PSTN.

What are the appropriate equipments that we needed to implement the network.

EX- The type, technology, ports of Switch and Router & how these characteristics are suitable for our implementation.

When we design structure cables we can use Patch panels & Wall sockets.

What are the internet access technologies that used?

Ex- Internet Lease Line, ADSL, SDSL, IDSL

Future network expansions.

What are the additional devices that commonly used?

Ex- Printers, Scanners & other equipments.

The development of the company.

Ex- The production and Sales rates. According to these parameters we can have clear image of the future network expansions.

Security and Reliability of the system.

Redundant connection of the network.

Redundant Internet access technologies.

Administrator privilege of the PCs.

Maintain cost

The equipments must have low maintain cost.

Ex-cost of the implementation is high in Fiber optics but maintain cost is low compare to CAT 5 cables.

    Throughout this article I hope you may get some thing. This provides  basic explanation and future will cover more. Comments are well come. Thank you.

How to Uncrease the Bandwidth in Same Fiber

To increase the bandwidth in same fiber we can use several modulation techniques which can offer high spectral efficiency and high receiver sensitivity. In Oder to increase the bandwidth in we can go for different multiplexing techniques. Wavelength division multiplexing (WDM), has proven more cost effective in many instances. It allows using current electronics and current fibers, but simply shares fibers by transmitting different channels at different wavelengths of light. Systems that already use fiber optic amplifiers as repeaters also do not require upgrading for most WDM systems. But nowadays people use Dense Wavelength Division Multiplexing, using that we can increase the bandwidth,

Dense Wavelength Division Multiplexing

For submarine cables, DWDM enhances the capacity without adding fibers, which create larger cables and bulkier and more complicated repeaters. DWDM is designed for long-haul transmission where wavelengths are packed tightly together. Vendors have found various techniques for cramming 32, 64, or 128 wavelengths into a fiber. In this each wave length, we can store different data types (STM4 or STM 5) and can transmit it. This compression exposes to carry more bandwidth at the transmitting end when multiplexing. Since each channel is demultiplexed at the end of the transmission back into the original source, different data formats being transmitted at different data rates can be transmitted together.

    Throughout this article I hope you may get some thing. This provides very basic explanation and future will cover more. Comments are well come. Thank you.

Important Factors of designing a Optical Fiber submarine cable

Type of optical fiber – when we are designing a cable for submarine cable, we have to select proper fiber type for the network. Most suitable fiber optic type for this network is” standard single mode fibers (G654) “which are having almost zero dispersion at 1300 nm is suitable for long distance fiber optical links.

Dispersion - We know submarine cable has very high length; therefore the main interference to the system is dispersion. To avoid that, we can use DCF fibers at regular places.

Reliability - The reliability of submarine cables is so important and it needs to be high strength. Especially in the point of splicing. It is in the see, thus we can’t maintain the cable day by day.

Transmitting power – Transmitting power is also very important In a SEA-WE-ME 4 cable, we need to supply better and sufficient transmitting power to the source. Because of the attenuation of the signal is high when it is travelling high distance through under the see. And also we need to maintain sufficient power for repeaters through the cable.

Source type - For high-data-rate applications as like this, we can use semi conductor laser diode (SLD). Because it gives narrow spectral width, directivity, higher transmitting power etc makes it most suitable for long distance transmission.

Receiver sensitivity - We know in a long haul communication the transmitting signal is attenuated. Then the receiver gets weak signal. Therefore it should have the high receiver sensitivity for grab the receiving signal.

Detector type - Through SEA-WE-ME 4 cable, signals are traveling more distance. Therefore we need detector with higher sensitivity. Therefore we can use Avalanche photo diode (APD).

Bit Error rate - When the signal travels through SEA-WE-ME 4 cable there are many inter symbol interferences. It confuses the receiving data. Therefore bit error happens. In order to avoid bit errors we need to reduce the base band data rate. But it is difficult to reduce the data rate because we nee high data rate.

Number of connectors - When we have number of amplifiers and repeaters we also introduce loss to the system by increasing number of connectors. And also SEA-WE-ME 4 cable is connected to 14 countries. Here also we need to setup connector. These losses will reduce the length of the high bit rate long haul fiber optical links. Therefore it is better keep the connecters in a low number.

Number of splicing points - In this SEA-WE-ME 4 cable it has length of 20,000 km. therefore it may need 10,000 splices if we use 2km cable. And we know each splicing point introduce a loss to the system. But we can’t control when the link is rising.

    Throughout this article I hope you may get some thing. This provides very basic explanation and future will cover more. Comments are well come. Thank you.

Telephone Switching Concept

Manual Switch – In the telephone exchange all subscribers are connected to a central switch and it is manually operated by an operator. If a person want to call another person first he or she should call to telephone exchange. There is a person who can connect the two subscribers together by plugging in the exchange.

Strowger Switch - Every subscriber line ended at the Strowger switch with a relay, referred to as line relay. This switch had stepping relays that worked according to the dial pulses. Upon completing one digit, the first stepping relay would activate another stepping relay. Complete connection was achieved by serial activation of several stepping relays. The line relays were connected to an electromechanical device called line finder.

Crossbar switch - Crossbar switch employed centralized common control equipment which encompassed a group of equipment engaged in establishing call set up. The equipment was released and was available for setting up other calls once setting up phase of a call was over. Crossbar switch replaced the line finder with line scanner, to check when a telephone line connected to a line link frame was off hook. 

SPC switch – after the evolution of electronics, especially the invention of the transistor, SPC switches came into use. The SPC switch entirely replaced the electromechanical common control equipment of the cross bar switch with electronic circuits, while retaining the same switching matrixes. These systems employ memories based on RAM (Random Access Memory) technology, tape and disk storage. SPC switching system was space division switching systems.

Fully Automated Water Supply System

              This is a project of fully automated water supply system designed with 16F887 Micro controller.

To build the process of the Washing machine we need several input& output devices. We use PIC 16f887 micro controller as central control device. First we should supply 5v dc to micro controller. We use a voltage stabilizer to do that. Weight sensor is used measure the weight of the cloths which we putted into washing machine. It gives analog input to the micro controller.

In this application we categorize the weight of the cloths. It as below,

0kg - 2kg = Low weight

2kg – 4kg = Medium weight

4kg – 6kg = High weight

According to these categorization put sufficient water into the washing machine. We use 3 Water level sensors to measure the water level. If we are high weight cloths have to wait for the three inputs from sensor 1, 2 and 3. After adding water to the washing machine we have to input time duration manually by rotating the timer knob. And also use LCD display (8 bit) to display timing process & massages. We use 8 bit LCD display because display time is very fast procedure, it changes rapidly.

8 bit and 32 bit ALU

                 In Micro controller system when we compare these ALUs both can do the same function. ALUs can add, subtract, multiply act, two numbers. But the difference is the speed and efficiency of these ALUs.

                 An 8 bit ALU would have to execute four instructions to add 32 bit number but 32 bit ALU can do it in one instruction. It is four times faster than 8 bit ALU.

8 bit and 32 bit ALU

 

8-bit ALU architectures are those that are based on registers, address buses, or data buses of that size. 8-bit is also a term given to a generation of computers in which 8-bit processors were the norm.

Eight-bit CPUs normally use an 8-bit data bus and a 16-bit address bus which means that their address space is limited to 64 Kb. This is not a "natural law", however, so there are exceptions.

The range of integer values that can be stored in 32 bits is 0 through 4,294,967,295 or −2,147,483,648 through 2,147,483,647 using two's complement encoding. Hence, a processor with 32-bit memory addresses can directly access 4 GB of byte-addressable memory.

The external address and data buses are often wider than 32 bits but both of these are stored and manipulated internally in the processor as 32-bit quantities

Proxy Server Operation

We use Proxy server for restrict the access of some web sides. The function of the Proxy server is blocking the web site. 

Proxy server operation

 

We type the address according to the OSI model before adding frame, we put destination IP address as 100.10.11.48, add frame and transmit frame to the destination (ABC   Server IP 100.10.11.48).This frame is going through the proxy server. Proxy server checks the destination IP address and if it restricts the web side by the network administrator, server blocks the Frame. That is the process of Proxy web server.

Wireless Broadband Solutions Available Today

WiFi (Wireless Fidelity) -. Wi-Fi is the short form for Wireless Fidelity. Wi-Fi is a simple, cost-effective way to connect to the Internet, to other Computers and to other Wi-Fi-enabled devices (such as high-end Mobile Phones), without the need to physically connect wires between the two Computers/ devices. WiFi is working on unlicensed spectrum at 2.4 GHz. In today's wired WiFi has a lot of advantages. Wireless networks are easy to set up and inexpensive. It do not need for long Network Cables, it also does not need a Network Socket for every Computer. There is less implementation cost. The disadvantages are cant go more distance with in wifi zone and three are lot security factors.

Microwave Links - Microwave links are fixed-wireless broadband systems and were around long before the term wireless broadband was coined. It is the point-to-point LOS wireless transmission method for up to 155 Mbps with a range of up to 50 km. Basic advantages of microwave links are no cables needed, multiple channels available and can have wide bandwidth. And disadvantages are Line-of-sight will be disrupted if any barrier, such as new buildings, signal absorption by the atmosphere, microwaves suffer from attenuation due to atmospheric conditions and towers are expensive to build.

WiMAX – WiMAX is called as Worldwide Interoperability for Microwave Access. And it is the latest wireless broadband technology which is designed to deliver WiFi type connectivity over a much greater range and thereby compete as a point-to-multipoint last-mile broadband wireless access solution. It provides capacity up to 40 Mbit/s. The current WiMAX is based upon IEEE Std 802.16e-2005. advantages of Wimax is single station can serve hundreds of users, Much faster deployment of new users comparing to wired networks,  speed of 10Mbps at 10 kilometers with line-of-sight, and also  It is standardized and the same frequency equipment should work together. And disadvantages are Line of sight is needed for longer connections, Weather conditions like rain could interrupt the signal, other wireless equipment could cause interference and multiplied frequencies are used. WiMAX is very power intensive technology and requires strong electrical support and big installation and operational cost.

Direct Broadcast Satellite (DBS) – Direct Broadcast Satellite is a normal satellite system used for communication. The satellite s which is position in same space station related to the earth. Direct Broadcast Satellite (DBS) services also provide two-way high-speed data transmission services. Satellites are operating in the Ku band with a 12 GHz downlink and a 14 GHz uplink. Major drawback is that satellites being 22,300 km from the earth’s surface introduce a 250 ms delay into the network. In this method companies mainly supply satellite TV for users with more choice. And the advantages are rural availability, high capacity, and reliable service and can get digital picture & sound. 

FSO (Free Space Optics) - This is the technology uses the light propagating in free space to transmit data between two points. This system uses infra-red sources or lasers to support free-space data transmission rates of between 10Mbps and 1.25Gbps between a transmitter and a receiver over distances of up to 4km. The main advantages of FSO systems are the low installation costs and avoidance of radio spectrum licensing requirements as FSO systems use a light signal instead of a radio wave. The disadvantages are beam dispersion; atmospheric absorption of the signal, if there is a rain hard to transmit and opens the signal to environmental disturbances (Rain, Fog and Snow).

Wired Broadband Solutions Available Today

DSL technology - DSL technology uses the existing copper telephone infrastructure to facilitate high speed data connections.DSL equipment achieves this by dividing the voice and data signals on the telephone line. There a number of different DSL technologies, the key ones are ADSL, RADSL, HDSL, SDSL, and VDSL. The advantage of this technology is we can go for higher capacities with low implementation cost. And some types of DSL technologies give capacity according to requirement. The main advantage is the capacity will goes down when we increase the length of the line from the DSLAM to customer.

Hybrid Fiber Coax (HFC); Cable TV - Digital cable TV networks are able to offer bi-directional data transfer bandwidth in addition to voice and digital TV services. The advantage of this technology is that where the coaxial cable is in good condition and RF amplifiers exist (or can be installed) to extend the network reach, relatively high bandwidths can be provided to the end user without distance limitations. The disadvantage is this network is shared network. If the customers increase the bandwidth will be shared.

Broadband Power line (BPL) - Broadband Power line systems allow for high speed data transmission over existing power lines. BPL system, the data is transmitted over the existing power line as a low voltage, high frequency signal which is coupled to the high voltage low frequency power signal. The advantage of this solution is a cost-effective way to service a large number of subscribers with broadband. The disadvantage BPL is, it requires a high investment cost, to upgrade the power transmission network and bypass transformers, to support high speed and reliable broadband services.

And also we can’t use it with power transformers.

FTTx - FTTx is a generic term for those technologies which bring fiber, a step closer to the subscriber. It has many technologies related to ‘x’. They are FTTN - Fiber-to-the-node, FTTC - Fiber-to-the-cabinet, FTTB - Fiber-to-the-building, FTTH - Fiber-to-the-home ect. Using FTTx we can get fast Internet access with simultaneous delivery of high definition IPTV and voice over IP. But the disadvantage is high implementation cost of fiber.