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THE CLOUD NETWORK

A modem is a device used to send a signal called modulation by another signal called a carrier. Modems have been used since the 60's , mainly due to direct transmission of electronic signals intelligible over long distances is not efficient, for example, to transmit audio signals over the air, it would take large antennas (on the order of hundreds of meters) for proper reception. It is common in many switched network modems ease of response and automatic dialing, enabling them to connect when receiving a call from the PSTN (Public Switched Telephone Network Switched) and proceed to dial any number previously recorded by the user. These features can automatically perform all operations of establishment of the comunicación.El modulator emits a signal called carrier . Generally, it is a simple sinusoidal electrical signal of much higher frequency than the modulating signal. The modulating signal is the information that is prepared for transmission (modem prepares the information to be transmitted, but does not perform the transmission). The modulator adjust any property of the carrier (which is the action of modular), so you get a signal, which includes information from the modulator. Thus the demodulator can recover the original modulating signal, removing the carrier. The features that you can modify the carrier signal are amplitude
, leading to a modulation amplitude (AM / ASK). Frequency
, leading to a frequency modulation (FM / FSK). Phase
, leading to a phase modulation (PM / PSK)
also be a combination of complex modulations, or modulations as quadrature amplitude modulation .

how it works:

The modulator emits a signal called carrier . Generally, it is a simple sinusoidal electrical signal of much higher frequency than the modulating signal. The modulating signal is the information that is prepared for transmission (modem prepares the information to be transmitted, but does not perform transmission). The modulator adjust any property of the carrier (which is the action of modular), so you get a signal, which includes information from the modulator. Thus the demodulator can recover the original modulating signal, removing the carrier. The features that you can modify the carrier signal are amplitude
, leading to a modulation amplitude (AM / ASK). Frequency
, leading to a frequency modulation (FM / FSK). Phase
, leading to a phaser (PM / PSK)
also be a combination of complex modulations, or modulations as quadrature amplitude modulation .

MODEN PC: The main distinction is often made is between internal modems and external modems, but recently have appeared modems called "software modems , better known as" winmodems "or" linuxmódems ", which complicated the picture somewhat. There are also modems for XDSL, ISDN , etc. and used to connect via 75-ohm coaxial cable (cable modems ). Internal
: consist of a expansion card on which are arranged the various components that make up the modem. Exist for different types of connector:
ISA Bus: Due to the low speeds that are managed in these devices for many years was used exclusively this connector, now obsolete (outdated).
PCI Bus : the most common format today, still in use. AMR
: In some boards, cheap but not recommended for low performance. Today is an obsolete technology.
The main advantage of these modems is their greater integration with the computer, not occupying space on the table and receive electricity directly from the computer itself. They also tend to be more flights due to lack of housing and transformer, especially if they are PCI (in this case, are almost all like "software modem"). On the contrary, are more complex to install and status information can be obtained only by software. External
: similar to above, but external to the computer or PDA . The advantage of these modems is its easy portability between different computers (some of them more easily transportable and smaller than others), besides being able to tell the modem status (dialing, with or without online, broadcast ...) by the leds incorporating state. On the contrary, and obviously take more space than internal
TYPES OF CONNECTION:
Connecting phone modems external computer is usually done by a traditional serial port or COM (RS232), so use the UART computer, it must be able to provide sufficient communication speed . The UART must be 16550 or higher for the performance of a modem of 28,800 bps or more is adequate. These modems need an outlet for your transformer.
PC Modem Card : they are shaped card modems, which were used in laptops, before the advent of USB (PCMCIA ). Its size is similar to Credit card slightly thicker, but their abilities are the same as standard models.
There are models for USB port , connection and configuration even easier, not need power supply. There are models for both connection via landline to mobile telephony. Modems
software, HSP (Host Signal Processor) or Winmodems: modems are generally internal, in which various electronic parts have been removed (eg chips especializados), de manera que el microprocesador del ordenador debe suplir su función mediante un programa. Lo normal es que utilicen como conexión una ranura PCI (o una AMR ), aunque no todos los módems PCI son de este tipo. El uso de la CPU entorpece el funcionamiento del resto de aplicaciones del usuario. Además, la necesidad de disponer del programa puede imposibilitar su uso con sistemas operativos no soportados por el fabricante, de manera que, por ejemplo, si el fabricante desaparece, el módem quedaría eventualmente inutilizado to a future system update. Despite its low cost, little or nothing are recommended.
full Modems: Modems classics HSP, whether internal or external. In them, the performance depends almost entirely on the speed of the modem and the UART Modem phone
most common use is known and data transmissions via telephone .
The computers process data in a digital , but the phone lines core network only broadcast analog signals .
modulation methods and other features of the phone modems are standardized by the ITU- T (formerly CCITT ) in the series of Recommendations "V". These recommendations also determine the speed of transmission. Highlights:
V.21. Communication Full-Duplex between two analog modems by a variation in carrier frequency range from 300 baud , achieving a transfer of up to 300 bps (bits per second).
V.22. Communication Full-Duplex between two analog modems using PSK modulation of 600 baud to achieve a data transfer of up to 600 or 1200 bps.
V.32. Transmitted at 9,600 bps .
V.32bis. Transmission at 14,400 bps.
V.34. Modem standard that allows up to 28.8 Kbps bidirectional data transfer rates of modulation Depending on whether the digital modem or analog modulation is used the same nature. For digital modulation have, for example, the following types of modulation:
ASK (Amplitude Shift Keying, Modulation Amplitude): the amplitude of the carrier is modulated to levels corresponding to the input binary digits 1 or 0.
FSK (Frequency Shift Keying, Frequency Shift Keying) carrier frequency is modulated by adding or subtracting an offset frequency which represents the binary digits 1 or 0. Modulation is common in low-speed modems in which two states of the binary signal is transmitted as two different frequencies.
PSK (Phase Shift Keying, Phase Modulation) modulation where the transmitted carrier moves some number of degrees in response to configuration data. Biphasic modems for example, use displacement of 180 ° to represent the binary digit 0.
But there are also telephone channel interference must face the modem to transmit information. These disorders can be listed at: Distortions and echoes. Random and impulsive noise. Finally the interference.
For analog modulation are, for example, the following types of modulation: Amplitude Modulation
AM: amplitude of the carrier is varied by the amplitude modulator.
FM frequency modulation: the carrier frequency is varied by the amplitude modulator.
PM Phase Modulation. Phase Modulation: In this case the parameter that varies is the carrier phase signal, is mathematically almost identical to the frequency modulation. Also in AM and FM, is the amplitude modulation which is used to affect the carrier. Orders Orders

AT ATA
communication: with this command the modem waits for a phone call, acting as a receiver (autoanswer).
Each modem uses a sequence of commands "AT" common and other specific. Therefore, it should make use of the manuals that came with the modem to configure it properly. Where each of the modems are applied records or records
S records are portions of memory where you can permanently store parameters defining the profile of the modem (profiles). In addition to the commands "AT", is available in this series of records that allow the user to modify other characteristics of its operation. As with the command "AT", records and other specific common modem. Listing the most common.
Register 0: number of calls that the modem waits before answering (Autoanswer). If set to 0, the modem never respond to calls.
Register 1: Posting of calls made / received.
Register 2: character code used to activate the escape sequence. Usually a +.
Register 3: code line ending character. Usually a 13 (enter). Register
4: code line feed character (line feed).
Register 5: character code reverse deleted (backspace).
Register 6: Waiting time before starting to dial ( s ).
Register 7: wait time for receiving carrier (s). Register
8: time allocated to the break Hayes (Comma in s). Register
9: Response time to detect carrier, to enable the DCD (in tenths of a second).
Record 10: maximum time of loss of carrier to cut the line. Increasing the value allows the remote to temporarily cut the modem connection without local start shutdown sequence. If 255, it is assumed that there is always a carrier. This time must be greater than that of register 9 (in tenths of a second). Register
12: determines the guard time, this is the minimum time that precedes and follows a code (+++), escape without any data transmitted or received. If 0, no time limit (S12 x 20 ms). Register
18: contains the duration of the tests. Register
25: time to consider that the modem signal DTR has changed. Register
26: response time signal RTS to CTS.
operation
's profile There are 3 types of modems for operation:
The factory (default).
Assets.
the user.
These profiles are stored in memory nonvolatile RAM and the profile of manufactures is stored in ROM .
There are two options, or memory places where you can save profiles
AT & Y0, (starting to load the profile = 0)
AT & Y1, (starting to load the profile = 1)
These orders are shipped before turning off the modem to load them into your next encendido.Cuando written orders "AT", depending on size modem buffer, concatenating can go without writing for each of them the prefix "AT". Thus, for example when a program calls a modem initialization string can be included together in a single line all the commands required to configure the modem.
then describes the processes carried out to establish a communication steps to establish communication.
1) dial tone detection. The modem has a dial tone detector. This is activated if the tone remains more than a second. Otherwise, either because it has been a second without detecting anything or not has remained active this time the tone, the computer sends the message "No dialtone".
2) Dial the number. If not given the call mode, first try to call tones, and if the tone detector is still active, it to call pulses. In the period between each digit of telephone number, the IDP (interdigit press), it continues to address the tone detector. If at any IDP detector is active, the call is terminated and returns a message BUSY. Once the dial, re-attend the tone detector to check for connection. In this case, several things can happen: Rings
out. Are detected and counted the rings to be received, and compared with S1 registration of the modem. If you go there content value returns the message "NO ANSWER".
If no response is activated voice detector / signal, detecting the response of the other modem is through high-band filter (must be active at least 2 seconds).
If the tone detector fluctuates over a period of 2 seconds returns the message "VOICE." "NO ANSWER" can be obtained if an interval of silence after of the call.
3) To establish the link. Involves a sequence of processes that depend on whether you are calling or if the call is received.
If you are calling is: Set
receiving data to 1. Select
low speed mode. On
0.6 seconds and wait for dial tone dial tone. Disable dial tone

Select high speed mode.
expect to receive some, then pass around and activate the transmission
analyze the data received to test a connection. If this is not achieved within the time limit set in register S7, it gives the message "NO CARRIER", otherwise, left to send some, is activated switching signal, releases the data reception and gives the message "CARRIER".
If you are getting is:
response mode selection.
Disable scrambler.
Select low-speed mode and activate the tone of response (eg. 2,400 Hz for 3'3 s).
Disable the transmitter. Wait
carrier, if there is no transmitter power, high-speed mode and tone of 1,800 Hz
Wait for time specified in S7, if no connection sends the message "NO CARRIER", if any, states " CONNECT, "it triggers the transmitter, the carrier detector and switching signal.
To summarize the steps for establishing a connection are
The terminal DTR line up.
is sent from the terminal the command ATDT 5551234 ("AT" -> attention, D -> mark, T -> tone, 5551234 -> number to call.)
up modem line and dials the number.
The modem performs hand shaking with the remote modem.
The communication program expects the result code.
result code "CONNECT". Hayes Modems Test

tests let you check the local modem, local terminal, remote modem communications line. With the S18 modem log indicates the duration of the tests. If your content is 0, no time limit and is due to end user testing with AT & T0 command. The modem at power makes a series of internal reviews. In the event of any error, it tells the DTE time.
tests may be performed: Local
analog loopback (local loop analog) & T1 runs. Check the connection between the modem and the local terminal. After entering AT & T1, after a few seconds, it goes into online mode. To perform the test must be turned on local echo. The successful execution of the test means that each character typed by the user appears doubled. To complete the test, Pressing the escape sequence and then AT & T0. If the test is started while already connected to a service, this connection is cut.
Local Digital Loopback (digital local loop) runs & T3. You can only take place at a remote modem connection. Check the connection between local and remote modem and the line circuit. Sent to remote modem strings received from him.
Remote Digital Loopback (remote digital loop) runs & T6. Check the local terminal, the local modem, remote modem and the line circuit. Should be for a connection, and the remote modem must accept the request of the test. To complete it is passed to command mode with the escape sequence and type AT & T0. The local terminal compares the received string with the previously provided by it. Strings are provided by the user. Remote Digital Loopback with
Selftest (remote digital loop self test) runs & T7. Check the local modem, remote, and the circuit line. Should be for a connection and to complete it you must specify the escape sequence and AT & T0. It generates a binary pattern, according to the CCITT V.54 recommendation to check the connection. At the end of the test shows the number of errors appeared (from 000 to 255). Local Analog Loopback
with Selftest (local analog loop with self test) runs & T8. Check the local modem. After starting the test, after a few seconds, it returns to command mode. It ends with & T0 or if it hits the time limit defined in S18. The test checks channels for transmitting and receiving modem. It uses a binary pattern, according to the CCITT Recommendation V.54. If connected to a service, the connection is cut. At the end of the test will return the number of errors (000 to 255). Protocols

error checking error control: There are several techniques by which checks the reliability of the data blocks or characters. Parity
: function where the transmitter adds another bit to a symbol encoding. Is even parity, when the symbol has a number of bits and odd otherwise. The receiver recalculates the number of bits with value one, and if the recalculated value agrees with the parity bit sent, accept the package. This will detect single bit errors in the transmitted symbols, but multiple errors.
CRC (Cyclic Redundancy Check, cyclic redundancy test). This error detection technique consists of a cyclic algorithm in which each block or frame of data is checked by the modem that sends and the receiver. The modem is sending inserts the result of calculation in each block as a CRC code. For its part, the modem is receiving compared the result with the received CRC code and responds with a positive acknowledgment or negative depending on the outcome.
MNP (Microcom Networking Protocol, Microcom Network Protocol). Error control is developed by Microcom, Inc. This protocol ensures error-free transmission by file transfer protocols Xmodem
: it is the most popular protocol, but is slowly being replaced by protocols more reliable and faster. Xmodem sends files in blocks 128 characters at a time. When the computer is receiving checks that the block has arrived intact, well said and hoped the next block. The check is a checksum error or a more sophisticated check cyclic redundancy. Some communications software and could support both automatically using the most appropriate for a given time. During a download, the software tends to use the CRC, but will switch to checksum if it detects that the host does not support the CRC. Xmodem protocol also needs to be declared in your configuration: no parity, eight data bits and one stop bit.
Xmodem-1K is a slight variation of the above, using blocks that pose a kilobyte (1,024 bytes) in size. This protocol is still so-called 'Ymodem' for some programs, but people gradually inclined to call it correctly.
Xmodem-1k-g: is a variant of the previous error-free channels such as hardware error correction or cable lines null-modem between two computers. Achieved faster by sending blocks one after another without having to wait for acknowledgment from the receiver. However, it can not retransmit the blocks in case of errors. If an error is detected at the receiver, the transfer will be aborted. As above, it is often wrongly called 'Ymodem-g'.
Zmodem: This protocol is very rapid progress as ensuring good reliability and offers several features. Zmodem uses packages of 1 kb in a clean line, but can reduce the size of the package as if the line quality will deteriorate. Once the quality of the line is retrieved the packet size increases again. Zmodem to transfer a group of files in a batch (batch) and keep the exact size and date of files. You can also quickly detect and recover errors, and interrupt transfers can be summarized in a later period. It is also very good for satellite links and packet switched networks.
ASCII in ASCII transfer is as if the sender was actually typing the characters and the receptor recording now. Not used any form of error detection. Usually, only ASCII files can be sent in this manner, ie as binary files that contain characters.
Ymodem: This protocol is a variant of Xmodem, which allows multiple files to be sent in a transfer. Throughout it saves the correct name, size, and file date. You can use 128 or (more commonly), 1,024 bytes for the blocks.
Ymodem-g: this protocol is a variant of the above, which reaches a very high transfer rate, sending blocks one after another without waiting for recognition. This, however, means that if an error is detected by the receiver, the transfer will be aborted.
TELink: This protocol is mainly found in Fido Bulletin Board Systems. It's basically the Xmodem protocol using CRC check and an extra block header of the file sent as saying the name, size and date. For its part, also allows more than one file is sent at the same time (Fido is a very popular BBS, which is used throughout the world.)
Kermit: This protocol was developed to make it easier for different types of computers to exchange files between them. Almost any computer using Kermit can be configured to send files to another computer that also use Kermit. Kermit uses small packets (usually 94 bytes) and although reliable, is slow because the data connection protocol to use is higher than in many other protoc

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MODEN

Cloud computing:

computing in the cloud, the English cloud computing is a paradigm that can offer services computer through Internet . The "cloud" is a metaphor Internet. Introduction:
In this kind of computing can offer everything that a computer system is provided as a service , [1] so that users can access services available "in the Internet cloud" [2] without knowledge (or at least not experts) in the management of the resources they use. [3] According to the IEEE Computer Society , is a paradigm in which information is permanently stored in servers on the Internet and sent to temporary caches client, including desktop computers, entertainment centers, notebooks, etc. This is because, although the PC's capabilities have improved substantially, much of its power is wasted, being general purpose machines. [Citation needed ]
Cloud computing is a new model provision of business services and technology, which allows the user to access a catalog of standardized services and respond to the needs of your business a flexible and adaptive, if demands are not predictable or peaks of work, paying only for the use made.
The paradigm shift offered is that cloud computing will increase the number of web-based services. This generates profits for suppliers that can offer more rapid and efficient, a greater number of services to users who are able to access them, enjoying the 'transparency' and immediacy of the system and a pay per use. Cloud computing gets
provide these benefits, based on a dynamic IT infrastructure that is characterized, among other factors, a high degree of automation, rapid mobilization of resources, a high adaptability to meet variable demand, and advanced virtualization and a flexible price made according to consumption.
Cloud computing is a concept that incorporates software as service, as in Web 2.0 and other recent concepts, also known as technology trends, which have in common that they rely Internet to meet the computing needs of users.

Beginnings:
The concept of computing in the cloud began to Internet service providers to large scale as Google, Amazon AWS and others who built their own infrastructure. From among them emerged architecture: a system of horizontally distributed resources, introduced as virtual services and massively scalable IT resources configured and managed as a continuous joint. This architecture model was immortalized by George Gilder in his October 2006 article in Wired magazine titled The Information Factories. The farm on which he wrote Gilder, were similar in architecture to the processing grid (network, grid), but while the grids are used technical processing applications slightly coupled (loosely coupled a system composed of subsystems with some autonomy of action, which maintains a continuous interaction between them), this new cloud model was applied to Internet services.

Benefits: Proven
* Web services integration. By their nature, Cloud Computing technology can be integrated with greater ease and speed with the rest of their business applications (both traditional and Cloud Computing software infrastructure-based), whether developed internally or externally. [5]
* Provision of services worldwide. Cloud Computing infrastructure provides greater resilience, complete disaster recovery and minimizing downtime.
* A 100% infrastructure Cloud Computing need not install any hardware. The beauty of Cloud Computing technology is its simplicity ... and the fact that it requires far less investment to start working.
* Implementation faster and with less risk. You can start to work very quickly thanks to a cloud computing infrastructure. There you will have to wait months or years and invest large amounts of money before a user log into your new solution. Its applications in cloud computing technology will be available within weeks or months, even with a considerable level of customization or integration.
* Automatic updates do not adversely affect IT resources. If we update to the latest version of the application, we will have to devote time and resources (not have) to re-create our customizations and integrations. * The Cloud Computing technology does not require him to decide whether to upgrade and keep their jobs, because these customizations and integrations are automatically preserved during the upgrade.
* Contribute to the efficient use energy. In this case, the energy required to operate the infrastructure. In traditional data centers, servers consume much more energy than actually required. In contrast, in the clouds, the energy consumed is only necessary, significantly reducing waste.

Layers:
Software as a Service (SaaS, its acronym in English)
SaaS is on the higher layer and characterized a complete application offered as a service, on-demand, via multitenencia-meaning a single instance of software that runs on the provider's infrastructure and serves multiple customer organizations. The example of more widely known SaaS is Salesforce.com, but now there are many more, including Google Apps that provide basic business services such as e-mail. Of course, the implementation of Salesforce.com multitenencia has been the best example of cloud computing for a few years. On the other hand, like many other players in the business of cloud computing, Salesforce.com now operates in more than one cloud layer with its Force.com, which is already in service, and that is a development environment companion application ("companion application") or as a service platform.

* Platform as a Service (PaaS their siglas en inglés)

La capa del medio, o PaaS, es la encapsulación de una abstración de un ambiente de desarrollo y el empaquetamiento de un carga de servicios. La carga arquetipo es una imagen Xen (parte de Servicios Web Amazon) conteniendo una pila básica Web (por ejemplo, un distro Linux, un servidor Web, y un ambiente de programación como Perl o Ruby). Las ofertas de PaaS pueden dar servicio a todas las fases del ciclo de de desarrollo y pruebas del software, o pueden estar especializadas en cualquier área en particular, tal como la administración del contenido.
Los ejemplos comerciales incluyen Google App Engine, que sirve aplicaciones de la infraestructura Google. Servicios PaaS such as these can provide a great deal of flexibility, but may be restricted by the capabilities that are available through the provider.

* Infrastructure as a Service (IAAS its acronym in English)
IaaS is in the bottom layer and is a means of delivering basic storage and computing capabilities and service standards in the network. Servers, storage systems, connections, routers and other systems concentrate (eg through virtualization technology) to handle specific types of workloads, from batch processing (batch) to increase server / storage during peak loads. The best known commercial example is Amazon Web Services, EC2 and S3 services which offer computing and storage services essential (respectively). Another example is Joyent whose main product is a line of virtualized servers, providing on-demand infrastructure for managing highly scalable Web sites, including complex Web applications written in Ruby on Rails, PHP, Python, and Java.

types of clouds:

* Public clouds are handled by third parties, and the work of many different clients can be mixed in servers, storage systems and other infrastructure in the cloud. End users do not know what works for other clients may be running on the same server, network drives as their own.

* Private clouds are a good option for companies that need high data protection and service level issues. Private clouds are on-demand infrastructure managed by a single client that controls which applications should run and where. They own the server, network, disk and can decide which users are allowed to use the infrastructure.

* Clouds hybrid models combine public and private clouds. You own shares of parts and others, but in a controlled manner. Hybrid clouds offer the promise of scaling externally provisioned, on-demand, but add the complexity of determining how to distribute the applications across these different environments. Companies may feel some attraction to the promise of a hybrid tag, but this option, at least initially, will probably be reserved for simple applications without constraints, which do not require any synchronization or require complex databases.

Comparisons

Cloud computing is often confused with grid computing (network) (a form of distributed computing why a "virtual supercomputer" is composed of a cluster bound loosely coupled computers, acting in concert to accomplish tasks too big).

Controversy:

Since computing Cloud does not allow users to physically possess the storage devices your information (with the exception of the ability to copy data to an external storage device like a USB flash drive or hard drive) leaves the responsibility for storage of data and its control in the hands of provider.
Cloud computing has been criticized for limiting freedom of users and make them dependent on the service provider. [9] Some critics claim that you can only use the applications and services that the provider is willing to offer. Thus, the London Times compares cloud computing to centralized systems of the 50 and 60, in which users connected through terminal "gregarious" with mainframes. Generally, users were free to install new applications, and needed the approval of administrators to perform certain tasks. In short, both freedom and limited creativity. The Times argued that cloud computing is a return to that era.

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100BASE-FX is a version fast Ethernet over fiber optic . Use two strands of multi-mode optical fiber for reception and transmission. Also known as fiber-optic version of 100BASE-TX . The maximum length is 400 meters to connections half-duplex (to ensure that collisions are detected) or 2 miles to full-duplex . 100BASE-FX supports 10BASE-FL , version 10-Mbit / s over fiber. Uses a wavelength of near infrared light at 1.3 microns
.100 BASE-TX standard is most common in this type is 100BaseTX Ethernet, and is supported by the majority of Ethernet hardware that occurs today. Uses 2
twisted copper pairs of category 5 or higher (a Category 5 cable contains 4 pairs, so it can support 2 100BASE-TX links). In a typical configuration
100Base-TX uses a twisted pair cables each direction ( full-duplex ). (See IEEE 802.3 for more details)
The configuration of a 100Base-TX is very similar to a 10Base-T type. When we use this standard to create a local area network, the network components (computers, printers, etc.) are usually connected to a switch or hub, creating a network with star topology. Alternatively, you can connect two components directly using crossover cable.
[ edit] 100BASE-T4
was one of the first implementations Fast Ethernet. It requires four twisted pairs of cable, but must be of category 3 rather than category 5 which is required by TX. Of the four pairs, one pair is reserved for transmitting, one for receive, and the remaining two are control data.

100BASE-T2 standard
This data is traveling over two copper pairs, 4 bits per symbol. First, a symbol of 4 bits is extended in two 3-bit symbols each using a complicated procedure coding based on a linear feedback register (see standard for details). This is necessary to flatten the bandwidth and spectrum signal. The original bitmap representing the code is not constant in time and have a long period (one might say that more often appears random). Fiber Optic Standards

The version on fiber these estandars get a higher speed and cover more surface without repeaters. 100BASE-FX

is a version of Fast Ethernet over fiber. Uses a type of light 1300 (NIR; nm near-infrared) that is transmitted via two fiber optic lines, one for receive (RX) and one for transmit (TX).
For these cases, the maximum length is 400 meters covered for half-duplex connections (to ensure collision detection) or 2 kilometers for full-duplex over multimode fiber (compared to 100 meters over copper cable).
As for the type of encoding used, 100BASE-FX uses the same 4B5B encoding and NRZI wearing 100BASE-TX
.100 BASE-SX uses two multimode fiber optic lines to receive and transmit. This is a lower cost alternative 100BASE-FX , since it uses a shorter wavelength, which is much less expensive than long wavelength used in 100BASE-FX. 100BASE-SX can operate at distances up to 300 meters.
100BASE-SX uses the same wavelength fiber-optic version 10BASE-FL. Due to the short wavelength used (850 nm), optical components are needed less expensive (LEDs instead of lasers), which makes it an attractive option for those upgrading from 10BASE-FL and which do not require long distances. 100BASE-BX

works through a single optical fiber line (as opposed to 100BASE-FX, which uses a fiber pair.) Because we have a single line, using a multiplexer that divides the signal into two different lengths wave, one for transmit and one for receiving

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100 BASE-T 10BASE-T BRIDGE

Network Bridge allows the connection of LAN segments cheaply and easily. A LAN segment is a section of network media that connects different teams. It is usual that a network has multiple LAN segments. Prior to Windows XP, Windows Server 2003, Standard Edition, and Windows Server 2003, Enterprise Edition, if you wanted to have a network with multiple LAN segments, had two options: IP routing and bridging hardware. IP routing required the acquisition of hardware routers or configuration of computers that act as routers, configuring IP addresses for each computer each segment of the network and the configuration of each network segment as a separate subnet. The jumper settings of hardware was not difficult, but required the acquisition of them. Also, if you used different types of network media, it was necessary to create a separate subnet for each type of medium.
Instead, the network bridge feature that is available in Windows XP, Windows Server 2003, Standard Edition and Windows Server 2003, Enterprise Edition connects LAN segments by simply clicking the menu command Bridge Connections. No configuration required and no need to purchase additional hardware such as routers or bridges. Network Bridge automates the settings required to route traffic between multiple network segments with a single type of media or mixed media.

layer 2 ( data link layer ) of the OSI model . This connects two network segments (or divides a network into segments) by the passage of data from one network to another, based on the physical address of destination of each packet.
A bridge connects two network segments as a single network using the same protocol for establishment of network.
operates through a table of MAC addresses detected in each segment is connected. When it detects that a node one of the segments is trying to transmit data to another node, the bridge copies the frame for another subnet. To use the machine learning mechanism, the bridges do not require manual configuration.
The main difference between a bridge and a hub is that the second pass any plot to any destination for all other connected nodes, whereas the former only passes the frames belonging to each segment. This feature improves performance networks to reduce unnecessary traffic.
To make the bridging or networking of more than 2 networks are used switch.
There are two types of bridge:
Local: used to directly link two networks physically close. Remote
or wide area, are connected in pairs, linking two or more local networks, forming a wide area network through telephone lines

A bridge is a hardware device used to connect two networks that work with the same protocol . Unlike a repeater , which runs on the physical level , the bridge runs in logical level (on layer 2 of the OSI model). This means you can filter frames to allow only the passage of those whose destination addresses correspond to a computer located across the bridge.
The bridge, thus, is used to segment a network, which retains the packets destined to the local area network and transmits those destined for other networks. This reduces the traffic (and especially the collisions) in each of the networks and increases the level of privacy because the information to a network can not escucharse en el otro extremo.
Sin embargo, el filtrado que lleva a cabo el puente puede provocar una leve demora al ir de una red a otra, razón por la cual los puentes deben ubicarse con buen criterio dentro de una red.

La función normal de un puente es enviar paquetes entre dos redes del mismo tipo:

Concepto: Un puente cuenta con dos conexiones a dos redes distintas. Cuando el puente recibe una trama en una de sus interfaces, analiza la dirección MAC del emisor y del destinatario. If a bridge does not recognize the sender, the address stored in a table to "remember" which side of the network is the issuer. Thus, the bridge can see if the sender and recipient are the same side or opposite sides of the bridge. If you are on the same side, the bridge ignores the message, if they are on opposite sides, the bridge sends the frame to the other network.

How a bridge
A bridge works at the data link layer of the OSI model , ie it works with the physical addresses of the computers. In fact, bridge is connected to several local area networks, called segments. The bridge creates a table of correspondence between the addresses of the computers and the segments to which they belong, and "listens" to data flowing through the segments.
At the time of data transmission, the bridge controls on the table set the segment to which computers belong senders and recipients (using your physical address, called the MAC address, not your IP address ) . If they belong to the same segment, the bridge does nothing, otherwise, it switches the data to the destination computer segment.

Why use a bridge?
A bridge is used to segment a network, ie (in the case presented above) for communication between the three top teams do not block grid lines passing through the three teams bottom. The information is transmitted when a team from one side of the bridge sends data to a computer on the opposite side. In addition, these bridges can be connected to a modem so they can operate with a remote local area network.
Below the diagram of a bridge:

A bridge is a device interconnect computer networks that operates at Layer 2 ( data link layer ) of the OSI model . This connects two network segments (or divides a network into segments) by the passage of data from one network to another, based on the physical address of destination of each packet.
A bridge connects two network segments as a single network using the same protocol for establishment of network.
operates through a table of MAC addresses detected in each segment that is connected. When it detects that a node one of the segments is trying to transmit data to another node, the bridge copies the frame for another subnet. To use the machine learning mechanism, the bridges do not require manual configuration.
The main difference between a bridge and a hub is that the second pass any plot to any destination for all other connected nodes, whereas the former only passes the frames belonging to each segment. This feature improves network performance by reducing unnecessary traffic.
To make the bridging or networking of more than 2 networks are used switch.
There are two types of bridge:
Local: used to directly link two networks physically close. Remote
or wide area, are connected in pairs, linking two or more local networks, forming a wide area network through telephone lines.

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10BASE-T
is a variety of network protocol Ethernet collected in the review IEEE 802.3i in 1990 that defines the connection using twisted pair cable. Used for short distances due to its low cost. Each twisted-pair cable contains 4 pairs of cables. In each pair are twisted together a colored wire and a white wire marked with the same color. The commonly used colors are orange, green, blue and brown. This cable is capable of transmitting at 10Mbps .


The standard usually adopted for connectors RJ45 of these cables is BN-N-BV-A-BA-V-BM-M at both ends. This requires that there be a switch ( hub or switch ) between the machines involved in the connection. For a direct connection between two machines, you must use a crossover cable , instead of connecting wire to wire signals cross each other RX and TX changing greens and oranges.


is noteworthy that these cables are only used green and orange, so you can see there are cases where two lines pass through the same Ethernet cable with two connectors at each end, or line Ethernet and ISDN . Also, some people are using laptops to your network connection, a cable with a connector pair "direct" and another crusade. This would be done (for example) as follows:
End 1 Connector 1

BN-N-BV-2 connector
OoVoo
BM-M-BA-OOAOO

End 2 Connector 1
BN-N-BV- Connector 2

OoVoo BA-A-BM-OOMOO
marking the connectors 2 at each end with red tape or red marker to recognize as a crossover cable.


General Networks LAN are more common today. This system alleviates the defects known networks 10Base2 and 10Base5 , including incorrect detection of unwanted derivations of breaks and loose connectors. A major disadvantage is the facility connected by hubs which can be expensive and quite complicated for large networks. However, one of the big advantages is the possibility of connecting new components to the network as is used by other computers without having to restart. Physical environment


From your 10BASE-T name is extracted several characteristics of this medium, 10 indicates the transmission speed Megabits per second (Mb / s) , BASE is short for band base and T to use twisted pair cables . Specifically, the cable used, UTP Category 3 (25 MHz in lengths of 100 m), consists of four twisted pairs without screening, of which at least one pair is used for transmission and another for reception.
The maximum length of the collision domain (with repeaters) reaches up to 2500 m using a coaxial backbone and the maximum number of stations in the collision domain is 1024 accepted. The cable is connected via a connector RJ-45 to network card in the PC . Each station is connected to a hub or concentrator central topology following a star or extended star, but functions as a logical bus. There hubs with different configurations, with 4, 8, 12, 15 or 24 RJ-45 ports, and even the possibility of connecting cable Ethernet type 10Base2 or others.

Signage
simpler signal used is the NRZL (nonreturn to Zero Level), the signal returns to 0 and the voltage pulse has a duration of 1 bit. Usually a logical 1 voltage is a pulse while a logical 0 is the absence of the voltage pulse.
can not send data with a trigger signal. The receiver synchronizes through transitions of pulses received. But if you have a long sequence of zeros or ones, the signal remains constant over a long enough time line and the receiver can not identify the beginning and end of each bit, this problem is solved by encryption.
signal coding can be: unipolar in which the 1s can have positive or negative polarity and 0s none. Polar whose signal will be positive to negative values \u200b\u200b1 and 0 values, and bipolar, that alternating polarity digit and the other is always on.

cable morphology
A 10BASE-T node, such as a computer, communicate sending to pins 1 and 2, and will receive 3 to 6, as opposed to make the switch or hub that is connected, you will receive on pins 1 and 2, and output from the 3 and 6 . To connect two computers directly with each other will need to use a crossover cable .
The correct connection of these cables must be according to the following table:

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HUD

A hub or hub is a device that enables centralized wiring a network and to enlarge . This means that the device receives a signal and repeats the signal emitted by the different ports.

hub (hub) is the most basic connection device. It is used in local networks with a very limited number of machines. There is only one power strip that amplifies the signal RJ45 network (base 10/100). In this case, a request aimed at a particular PC on the network will be sent to all PCs on the network. This greatly reduces the bandwidth and causes problems of listening on the network. Network hub is a device in which we find many network ports, I think the smallest I've seen is 4 network ports. It takes a computer signal and redistributes all network ports that are under the next signal. There are many types depending on the technologies with which to design and shape but usually are classified as passive, active and intelligent. Liabilities that do not need power, take the signal and redistributes it simply and are recommended for cases that are networked computers that are relatively close. The active power is required, ie extra power needed, "up" signal received, ie make it a little harder, then distributed and are recommended when computers are not close.
The intelligent hub or hub has a processor that helps distribute the signal more quickly, it looks like a router or router but the signal is distributed equally on all ports so there is no router. The needs of people send in the use of them if you have a small network and located in a room should ideally be a passive hub, if the network is large and covers several rooms it is recommended as an intelligent hub. The Hub also respond to the needs of network configuration. For example they are ideal for star-shaped networks, ie where there is a distribution point (hence the name) where several computers communicate with a server or a router.
As for the usb hub which today are popular because they allow to connect multiple printers, scanners and up to several computers (usb networks are in their infancy but are extremely easy to set up), in theory to a USB port may branch up to 32 ports through a hub or more on but much weaker signal ends. What is often recommended in these cases is that ACADA USB port of the computer case at most, are placed eight ports, with the best four.

A hub works by repeating each data packet in each one of the ports which account, except that it has received the package, so that all points have access to data. Also responsible for sending a signal shock to all ports if it detects a collision . They are the basis for networks of topology type star. Alternatively there are systems in which computers are connected in series, ie a line connecting some or all computers to one another, before reaching the central computer. also called multiport repeater, there 3 classes.
Liabilities: You do not need electricity. It is dedicated to networking.
Active: Needs food. In addition to concentrating the wiring, regenerates the signal, remove noise and amplify the signal
Smart: Also called smart hubs are active hubs including microprocessor.
Within the OSI model the hub operates at the physical layer , like repeaters, and can be implemented using only analog technology. Simply joins connections and does not alter the frames that arrive.
Considering the above we can draw the following conclusions:
The hub sends information to computers that are not interested. At this level there is only one recipient of the information, but to ensure that you receive the hub sends the information to all computers connected to it, and sure hits.
This generates added traffic collision more likely. A collision occurs when a computer wants to send information and issued simultaneously with another computer that does the same. By colliding the two messages are lost and need to relay. Moreover, as we add computers to the network will also increase the likelihood of collision. A hub works
at the speed of the slowest device on the network. If we observe how the hub is not capable of storing anything. So if a computer that emits at 100 Mb / s you convey to a 10-Mb / s something is lost in the message. In the case of ADSL the routers typically operate at 10 Mb / s, if we connect to our home network, the entire network will operate at 10 Mb / s, but our cards are 10 / 100 Mb / s.
A hub is a simple device, this affects both traits. The price is cheap. Add delays resulting from the transmission package to all computers on the network (including those who are not recipients of it).
Hubs were popular until the cheaper switch having a similar function but provide more security against programs like sniffer. The availability of ethernet switches low price has made them obsolete, but can still be found in older plants and in specialized applications.
Hubs also often come with a BNC and / or AUI connector to allow connection to 10Base5, 10Base2 or network segments. USES

Historically, the main reason for purchasing hubs rather than switches was the price. This has been largely eliminated by reductions in the price of switches, but hubs can still be useful in special circumstances:
A protocol analyzer connected to a switch not always receive all packets from that switch separates the ports into different segments. The protocol analyzer connected to a hub can see all traffic on the segment. (The expensive switches can be configured to allow a port to listen for traffic from another port. This is called port mirroring. However, these costs are much higher).
Some groups of computers or cluster require each team member to receive all traffic is going to the pool. A hub will do this, of course, use a switch in these cases requires the application of special tricks.
When a switch is accessible for end users to make connections, for example, in a conference room, an inexperienced user can reduce the network by connecting two ports together, causing a loop. This can be avoided by using a hub, where a loop is broken in the hub to other users. (It can also be prevented by purchasing switches that can detect and deal with loops, for example through the use of Spanning Tree Protocol.)
A cheap hub with a 10BASE2 port is probably the easiest and cheapest way to connect devices that only support 10BASE2 to a modern (not usually come with 10BASE2 ports switches flights

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FIRE (informatics)

Firewall (computing) A firewall (firewall in English ) is part of a system or network that is designed to block unauthorized access while allowing authorized communications . This is a device or group of devices configured to permit, restrict, encrypt, decrypt the traffic between different areas on the basis of a set of standards and other criteria.
Firewalls can be implemented in hardware or software, or a combination of both. Firewalls are frequently used to prevent unauthorized Internet users from accessing private networks connected to the Internet, especially intranets. All messages entering or leaving the intranet pass through the firewall, which examines each message and blocks those that do not meet specified security criteria. It is also common to connect the firewall to a third network, called Demilitarized Zone or DMZ , which houses the servers in your organization that should be accessible from the outside network. A properly configured firewall adds a necessary protection to the network, but in no case should be considered sufficient. The computer security covers more areas and more jobs and levels of protection.

types of firewalls:
Level
application gateway applies security mechanisms to specific applications such as FTP and Telnet servers. This is very effective, but can impose performance degradation.
Circuit-level gateway
Applies security mechanisms when a TCP connection or UDP is set. Once the connection has been made, packets can flow between the hosts without further control. Allows the establishment of a session that originates from an area of \u200b\u200bgreater security to a lower security area.
network layer firewall or packet filter
works at the network level (level 3) of the protocol stack (TCP / IP) and IP packet filter. At this level you can make filters for different IP packet fields: source IP address, destination IP address, etc. Often in this type of firewall to filter fields as transport layer (level 4) as the source and destination port, or data link layer (level 2) as the MAC address. This is one of the main types of firewalls. It is considered fairly effective and transparent but difficult to configure.
Application Layer Firewalls Work
the application level (level 7), so that the filter can be adapted to characteristics of the protocols at this level. For example, if traffic is HTTP can be performed according to filtered URL to which you are trying to access.
A firewall traffic at 7 HTTP is often referred proxy, and allows the computers of an organization come to the Internet in a controlled manner. A proxy effectively hides the true network addresses.

Personal Firewall is a special case of firewalls that are installed as software on a computer, filtering communications between that computer and the rest of the network. It is used for both a personal level.

advantages of portefuegos:

Intrusion Protect .- Access to certain segments of the network of an organization is only allowed from machines approved in other segments of the organization or the Internet.
protection of private information .- You can set different levels of access to information, so that an organization each defined user group has access only to services and information that are strictly necessary.
access Optimization .- Identifies internal network elements and optimizes the communication between them is more direct. This helps to reconfigure security parameters.

LIMITATIONS OF FIRE:

limitations arise from the very definition of firewall, traffic filtering. Any type of computer attack that uses traffic accepted by the firewall (for open TCP ports used specifically, for example) or simply not use the network, will remain a threat. The following list shows some of these risks
A firewall can not protect against those attacks that traffic does not pass through it.
The firewall can not protect against threats that are submitted by users or internal attacks negligent. The firewall can not prevent corporate spies copying sensitive data in physical storage media (disks, memories, etc..) And withdraw from the building.
The firewall can not protect against attacks social engineering.
The firewall can not protect against possible attacks to the internal network from viruses through files and software. The real solution is that the organization should be aware of installing antivirus software on each machine to protect against viruses that arrive via any storage medium or other source.
The firewall does not protect of the security flaws of the services and protocols which traffic is allowed. Must be configured properly and ensure the safety of the services that are published on the internet.