From Wikipedia:

VOICE OVER IP

Voice over Internet Protocol (VoIP) is a general term for a family of transmission technologies for delivery of voice communications over IP networks such as the Internet or other packet-switched networks. Other terms frequently encountered and synonymous with VoIP are IP telephony, Internet telephony, voice over broadband (VoBB), broadband telephony, and broadband phone.

Internet telephony refers to communications services — voice, facsimile, and/or voice-messaging applications — that are transported via the Internet, rather than the public switched telephone network (PSTN). The basic steps involved in originating an Internet telephone call are conversion of the analog voice signal to digital format and compression/translation of the signal into Internet protocol (IP) packets for transmission over the Internet; the process is reversed at the receiving end.

VoIP systems employ session control protocols to control the set-up and tear-down of calls as well as audio codecs which encode speech allowing transmission over an IP network as digital audio via an audio stream. Codec use is varied between different implementations of VoIP (and often a range of codecs are used); some implementations rely on narrowband and compressed speech, while others support high fidelity stereo codecs.

MULTICASTING

Multicast addressing is a network technology for the delivery of information to a group of destinations simultaneously using the most efficient strategy to deliver the messages over each link of the network only once, creating copies only when the links to the multiple destinations split.

The word "multicast" is typically used to refer to IP multicast which is often employed for streaming media and Internet television applications. In IP multicast the implementation of the multicast concept occurs at the IP routing level, where routers create optimal distribution paths for datagrams sent to a multicast destination address spanning tree in real-time. At the Data Link Layer, multicast describes one-to-many distribution such as Ethernet multicast addressing, Asynchronous Transfer Mode (ATM) point-to-multipoint virtual circuits or Infiniband multicast.

INTRANET SERVICES

An intranet is a private computer network that uses Internet Protocol technologies to securely share any part of an organization's information or operational systems within that organization. The term is used in contrast to internet, a network between organizations, and instead refers to a network within an organization. Sometimes the term refers only to the organization's internal website, but may be a more extensive part of the organization's information technology infrastructure. It may host multiple private websites and constitute an important component and focal point of internal communication and collaboration.

DVB S2

Digital Video Broadcasting - Satellite - Second Generation (DVB-S2) is an enhanced specification to replace the DVB-S standard, developed in 2003 and ratified by ETSI (EN 302307) in March 2005. The development of DVB-S2 coincided with the introduction of HDTV and H.264 (MPEG-4 AVC) video codecs.

The system allows transmission of one or more MPEG-2 or MPEG-4 audio–video streams, using QPSK or 8PSK or 16/32APSK (amplitude and phase shift keying) modulation with concatenated encoding.

DVB-S2 is based on the DVB-S standard which is used for satellite broadcasting, and the DVB-DSNG standard, which is used by mobile units for sending external footage back to television stations. Two new key features which were added to DVB-S are:

The authors of "DVB-S2-Ready for lift off" (see reference list below) claim that the DVB-S2 performance gain over DVB-S is around 30%[citation needed]. When the contribution of improvements in video compression is added, an (MPEG-4 AVC) HDTV service can now be delivered in the same capacity that supported an early DVB-S-MPEG-2 SDTV service only a decade before.

Main features

Performance can be configured to be within 0.7 dB of the Shannon limit.

TCP ACCELERATION

TCP acceleration is the name of a series of techniques for achieving better throughput on an Internet connection than standard TCP achieves, without modifying the end applications. It is an alternative or a supplement to TCP tuning.

Commonly used approaches include ACK pacing, TCP transparent proxies in two or more middleboxes, and TCP offload engines.

TCP transparent proxies

TCP transparent proxies involve breaking of long end-to-end control loops to several smaller control loops by intercepting and relaying TCP connections within the network. By adopting this procedure, they allow for the TCP flows to have a shorter reaction time to packet losses which may occur within the network and thus guarantees a higher throughput.

The idea of a TCP accelerator is to terminate TCP connections inside the network processor and then relay the data to a second connection toward the end system. The data packets that originate from the sender are buffered at the accelerator node, which is responsible for performing local retransmissions in the event of packet loss. Thus, in case of losses, the feedback loop between the sender and the receiver is shortened to the one between the acceleration node and the receiver which guarantees a faster delivery of data to the receiver.

Since TCP is a rate-adaptive protocol, the rate at which the TCP sender injects packets into the network is directly proportional to the prevailing load condition within the network as well as the processing capacity of the receiver. The prevalent conditions within the network are judged by the sender on the basis of the acknowlgedgments received by it. The acceleration node splits the feedback loop between the sender and the receiver and thus guarantees a shorter round trip time (RTT) per packet. A shorter RTT is beneficial as it ensures a quicker response time to any changes in the network and a faster adaptation by the sender to combat these changes.

Disadvantages of the method include the fact that the TCP session has to be directed through the accelerator; this means that if routing changes, so that the accelerator is no longer in the path, the connection will be broken. It also destroys the end-to-end property of the TCP ack mechanism; when the ACK is received by the sender, the packet has been stored by the accelerator, not delivered to the receiver.

PRE FETCHING TECHNOLOGY

Link prefetching is a draft standards compliant mechanism used by some web browsers, which uses browser idle time to download or prefetch documents that the user might visit in the near future. A web page provides a set of prefetching hints to the browser, and after the browser is finished loading the page, and after an idle time has passed, it begins silently prefetching specified documents, storing them in its cache. When the user visits one of the prefetched documents, it can be served up quickly out of the browser's cache.

As prefetching is an Internet Draft standard, examples of prefetching can be divided into standard compliant and non-compliant:

ENCRYPTION

In cryptography, encryption is the process of transforming information (referred to as plaintext) using an algorithm (called cipher) to make it unreadable to anyone except those possessing special knowledge, usually referred to as a key. The result of the process is encrypted information (in cryptography, referred to as ciphertext). In many contexts, the word encryption also implicitly refers to the reverse process, decryption (e.g. “software for encryption” can typically also perform decryption), to make the encrypted information readable again (i.e. to make it unencrypted).

Encryption has long been used by militaries and governments to facilitate secret communication. Encryption is now commonly used in protecting information within many kinds of civilian systems. For example, in 2007 the U.S. government reported that 71% of companies surveyed utilized encryption for some of their data in transit.[1] Encryption can be used to protect data "at rest", such as files on computers and storage devices (e.g. USB flash drives). In recent years there have been numerous reports of confidential data such as customers' personal records being exposed through loss or theft of laptops or backup drives. Encrypting such files at rest helps protect them should physical security measures fail. Digital rights management systems which prevent unauthorized use or reproduction of copyrighted material and protect software against reverse engineering (see also copy protection) are another somewhat different example of using encryption on data at rest.

Encryption is also used to protect data in transit, for example data being transferred via networks (e.g. the Internet, e-commerce), mobile telephones, wireless microphones, wireless intercom systems, Bluetooth devices and bank automatic teller machines. There have been numerous reports of data in transit being intercepted in recent years.[2] Encrypting data in transit also helps to secure it as it is often difficult to physically secure all access to networks.

Encryption, by itself, can protect the confidentiality of messages, but other techniques are still needed to protect the integrity and authenticity of a message; for example, verification of a message authentication code (MAC) or a digital signature. Standards and cryptographic software and hardware to perform encryption are widely available, but successfully using encryption to ensure security may be a challenging problem. A single slip-up in system design or execution can allow successful attacks. Sometimes an adversary can obtain unencrypted information without directly undoing the encryption. See, e.g., traffic analysis, TEMPEST, or Trojan horse.

One of the earliest public key encryption applications was called Pretty Good Privacy (PGP), according to Paul Rubens. It was written in 1991 by Phil Zimmermann and was purchased by Network Associates (now PGP Corporation) in 1997.

There are a number of reasons why an encryption product may not be suitable in all cases. First, e-mail must be digitally signed at the point it was created to provide non-repudiation for some legal purposes, otherwise the sender could argue that it was tampered with after it left their computer but before it was encrypted at a gateway according to Paul. An encryption product may also not be practical when mobile users need to send e-mail from outside the corporate network.

Video Conference System

-A videoconference (also known as a videoteleconference) is a set of interactive telecommunication technologies which allow two or more locations to interact via two-way video and audio transmissions simultaneously. It has also been called visual collaboration and is a type of groupware. It differs from videophone in that it is designed to serve a conference rather than individuals.

SCPC

Single channel per carrier (SCPC) refers to using a single signal at a given frequency and bandwidth. Most often, this is used on broadcast satellites to indicate that radio stations are not multiplexed as subcarriers onto a single video carrier, but instead independently share a transponder. It may also be used on other communications satellites, or occasionally on non-satellite transmissions.

In an SCPC system, satellite bandwidth is dedicated to a single source. This makes sense if it is being used for something like satellite radio, which broadcasts continuously. Another very common application is voice, where a small amount of fixed bandwidth is required. However, it does not make sense for burst transmissions like satellite internet access or telemetry, since a customer would have to pay for the satellite bandwidth even when they were not using it.

Where multiple access is concerned, SCPC is essentially FDMA. Some applications use SCPC instead of TDMA, because they require guaranteed, unrestricted bandwidth. As satellite TDMA technology improves however, the applications for SCPC are becoming more limited.

Advantages

Disadvantages

MCPC

With multiple channels per carrier (MCPC), several subcarriers are combined into a single bitstream before being modulated onto a carrier transmitted from a single location to one or more remote sites. This uses time-division multiplexing (TDM). It is a retronym of sorts, as it was the only way radio networks were transmitted ("piggybacked" on television networks) until SCPC.

In digital radio and digital television, an ensemble or other multiplex or multichannel stations can be considered MCPC, though the term is generally only applied to satellites.

The major disadvantage of MCPC is that all of the signals must be sent to a single place first, then combined for retransmission — a major reason for using SCPC instead.

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