1.
Point-to-multipoint communication
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Point-to-multipoint is often abbreviated as P2MP, PTMP, or PMP. Point-to-multipoint telecommunications is most typically used in wireless Internet and IP telephony via gigahertz radio frequencies, P2MP systems have been designed both as single and bi-directional systems. A central antenna or antenna array broadcasts to several receiving antennas, Point to Multipoint is the most popular approach for wireless communications that have a large number of nodes, end destinations or end users. Point to Multipoint generally assumes there is a central Base Station to which remote Subscriber Units or Customer Premises Equipment, connections between the Base Station and Subscriber Units can be either Line of Sight or for lower-frequency radio systems Non-Line-of-Sight where link budgets permit. Generally, lower frequencies can offer non-Line-of Sight connections, various software planning tools can be used to determine feasibility of potential connections using topographic data as well as link budget simulation. Often the point to multipoint links are installed to reduce the cost of infrastructure and increase the number of CPEs, Point to Multipoint wireless networks employing directional antennas are affected by the hidden node problem in case they employ a CSMA/CA medium access control protocol. The negative impact of the hidden node problem can be mitigated using a TDMA based protocol or a polling protocol rather than the CSMA/CA protocol, the telecommunications signal in a Point to Multipoint system is typically bi-directional, either time division multiple access or channelized. Systems using Frequency Division Duplexing offer full duplex connections between base station and remote sites, and Time Division Duplex systems offer half duplex connections, Point to Multipoint systems can be implemented in Licensed, Semi-licensed or Unlicensed frequency bands depending on the specific application. The Base Station may have a single Omnidirectional antenna or multiple Sector Antennas which is used to increase both range and capacity. All-to-all communication Multipoint microwave distribution system Point-to-point Wireless Communications Wireless Access Point List of emerging technologies Backhaul
2.
Unicast
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In computer networking, unicast transmission is the sending of messages to a single network destination identified by a unique address. The term unicast is contrasted with the term broadcast which means transmitting the data to all possible destinations. Another multi-destination distribution method, multicasting, sends data only to interested destinations by using special address assignments and this failure of Unicast to cast to a single device is called a Unicast flood. Unicast messaging is used for all processes in which a private or unique resource is requested. Such applications include streaming media of many forms, internet radio stations using unicast connections may have high bandwidth costs. These terms are used by streaming content providers services. Unicast-based media servers open and provide a stream for each unique user, multicast-based servers can support a larger audience by serving content simultaneously to multiple users. IP address Multicast Broadcasting Differences Between Multicast and Unicast
3.
Broadcasting (networking)
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In telecommunication and information theory, broadcasting is a method of transferring a message to all recipients simultaneously. All-to-all communication is a communication method in which each sender transmits messages to all receivers within a group. This contrasts with the point-to-point method in which each sender communicates with one receiver, in computer networking, broadcasting refers to transmitting a packet that will be received by every device on the network. In practice, the scope of the broadcast is limited to a broadcast domain, Broadcasting a message is in contrast to unicast addressing in which a host sends datagrams to another single host identified by a unique IP address. Broadcasting is the most general method, and is also the most intensive in the sense that a large number of messages are required. Broadcasting may be performed as all scatter in which each sender performs its own scatter in which the messages are distinct for each receiver, the MPI message passing method which is the de facto standard on large computer clusters includes the MPI_Alltoall method. Not all network technologies support broadcast addressing, for example, neither X.25 nor frame relay have broadcast capability, instead it relies on multicast addressing - a conceptually similar one-to-many routing methodology. However, multicasting limits the pool of receivers to those that join a specific multicast receiver group, both Ethernet and IPv4 use an all-ones broadcast address to indicate a broadcast packet. Token Ring uses a value in the IEEE802.2 control field. Broadcasting may be abused to perform a type of DoS-attack known as a Smurf attack, the attacker sends fake ping requests with the source IP-address of the victim computer. The victim computer is flooded by the replies from all computers in the domain, broadcast radiation Point-to-multipoint communication Unicast Encyclopædia Britannica entry broadcast network Network Broadcasting and Multicast
4.
Anycast
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Broadcast addressing uses a one-to-many association, datagrams are routed from a single sender to multiple endpoints simultaneously in a single transmission. The network automatically replicates datagrams as needed for all segments that contain an eligible receiver. Multicast addressing uses a one-to-unique many association, datagrams are routed from a sender to multiple selected endpoints simultaneously in a single transmission. Unicast addressing uses a one-to-one association between destination address and network endpoint, each destination address uniquely identifies a single receiver endpoint, geocast refers to the delivery of information to a group of destinations in a network identified by their geographical locations. It is a form of multicast addressing used by some routing protocols for mobile ad hoc networks. On the Internet, anycast is usually implemented by using Border Gateway Protocol to simultaneously announce the same destination IP address range from different places on the Internet. This results in packets addressed to destination addresses in this range being routed to the nearest point on the net announcing the given destination IP address, in the past, anycast was suited to connectionless protocols, rather than connection-oriented protocols such as TCP that keep their own state. However, assuming a deterministic destination selection for all packets within a session and these conditions are typically referred to as a pop switch. To correct this issue, there have been proprietary advancements within custom IP stacks which allow for healing of stateful protocols where it is required, with the growth of the Internet, network services increasingly have high-availability requirements. As a result, operation of anycast services has grown in popularity among network operators, nearly all Internet root nameservers are implemented as clusters of hosts using anycast addressing. 12 of the 13 root servers A-M exist in multiple locations, the 12 servers with multiple locations use anycast address announcements to provide a decentralized service. This has accelerated the deployment of physical root servers outside the United States, RFC3258 documents the use of anycast addressing to provide authoritative DNS services. Many commercial DNS providers have switched to an IP anycast environment to increase performance, redundancy. In IPv4 to IPv6 transitioning, anycast addressing may be deployed to provide IPv6 compatibility to IPv4 hosts and this method, 6to4, uses a default gateway with the IP address 192.88.99.1, as described in RFC3068. This allows multiple providers to implement 6to4 gateways without hosts having to know each individual providers gateway addresses, content delivery networks may use anycast for actual HTTP connections to their distribution centers, or for DNS. Because most HTTP connections to such networks request static content such as images and style sheets, they are generally short-lived, the general stability of routes and statelessness of connections makes anycast suitable for this application, even though it uses TCP. Anycast allows any operator whose routing information is accepted by a router to hijack any packets intended for the anycast address. While this at first sight appears insecure, it is no different from the routing of ordinary IP packets, as with conventional IP routing, careful filtering of who is and is not allowed to propagate route announcements is crucial to prevent man-in-the-middle or blackhole attacks
5.
Geocast
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Geocast refers to the delivery of information to a group of destinations in a network identified by their geographical locations. It is a form of multicast addressing used by some routing protocols for mobile ad hoc networks. A geographic destination address is expressed in three ways, point, circle, and polygon, a geographic router calculates its service area as the union of the geographic areas covered by the networks attached to it. This service area is approximated by a closed polygon. Geo Routers exchange service area polygons to build routing tables, the routers are organized in a hierarchy
6.
Computer network
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A computer network or data network is a telecommunications network which allows nodes to share resources. In computer networks, networked computing devices exchange data with other using a data link. The connections between nodes are established using either cable media or wireless media, the best-known computer network is the Internet. Network computer devices that originate, route and terminate the data are called network nodes, nodes can include hosts such as personal computers, phones, servers as well as networking hardware. Two such devices can be said to be networked together when one device is able to exchange information with the other device, Computer networks differ in the transmission medium used to carry their signals, communications protocols to organize network traffic, the networks size, topology and organizational intent. In most cases, application-specific communications protocols are layered over other more general communications protocols and this formidable collection of information technology requires skilled network management to keep it all running reliably. The chronology of significant computer-network developments includes, In the late 1950s, in 1960, the commercial airline reservation system semi-automatic business research environment went online with two connected mainframes. Licklider developed a group he called the Intergalactic Computer Network. In 1964, researchers at Dartmouth College developed the Dartmouth Time Sharing System for distributed users of computer systems. The same year, at Massachusetts Institute of Technology, a group supported by General Electric and Bell Labs used a computer to route. Throughout the 1960s, Leonard Kleinrock, Paul Baran, and Donald Davies independently developed network systems that used packets to transfer information between computers over a network, in 1965, Thomas Marill and Lawrence G. Roberts created the first wide area network. This was an precursor to the ARPANET, of which Roberts became program manager. Also in 1965, Western Electric introduced the first widely used telephone switch that implemented true computer control, in 1972, commercial services using X.25 were deployed, and later used as an underlying infrastructure for expanding TCP/IP networks. In July 1976, Robert Metcalfe and David Boggs published their paper Ethernet, Distributed Packet Switching for Local Computer Networks, in 1979, Robert Metcalfe pursued making Ethernet an open standard. In 1976, John Murphy of Datapoint Corporation created ARCNET, a network first used to share storage devices. In 1995, the transmission speed capacity for Ethernet increased from 10 Mbit/s to 100 Mbit/s, by 1998, Ethernet supported transmission speeds of a Gigabit. Subsequently, higher speeds of up to 100 Gbit/s were added, the ability of Ethernet to scale easily is a contributing factor to its continued use. Providing access to information on shared storage devices is an important feature of many networks, a network allows sharing of files, data, and other types of information giving authorized users the ability to access information stored on other computers on the network
7.
Router (computing)
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A router is a networking device that forwards data packets between computer networks. Routers perform the traffic directing functions on the Internet, a data packet is typically forwarded from one router to another router through the networks that constitute the internetwork until it reaches its destination node. A router is connected to two or more lines from different networks. When a data packet comes in on one of the lines, then, using information in its routing table or routing policy, it directs the packet to the next network on its journey. The most familiar type of routers are home and small office routers that simply pass IP packets between the computers and the Internet. An example of a router would be the cable or DSL router. Though routers are typically dedicated hardware devices, software-based routers also exist, when multiple routers are used in interconnected networks, the routers can exchange information about destination addresses using a dynamic routing protocol. Each router builds up a table listing the preferred routes between any two systems on the interconnected networks. A router may have interfaces for different physical types of connections, such as copper cables, fibre optic. Its firmware can also support different networking communications protocol standards, each network interface is used by this specialized computer software to enable data packets to be forwarded from one protocol transmission system to another. Routers may also be used to two or more logical groups of computer devices known as subnets, each with a different network prefix. The network prefixes recorded in the table do not necessarily map directly to the physical interface connections. It does this using internal pre-configured directives, called static routes, static and dynamic routes are stored in the Routing Information Base. The control-plane logic then strips non-essential directives from the RIB and builds a Forwarding Information Base to be used by the forwarding-plane, Forwarding plane, The router forwards data packets between incoming and outgoing interface connections. It routes them to the network type using information that the packet header contains. It uses data recorded in the routing control plane. Routers may provide connectivity within enterprises, between enterprises and the Internet, or between internet service providers networks, the largest routers interconnect the various ISPs, or may be used in large enterprise networks. Smaller routers usually provide connectivity for typical home and office networks, other networking solutions may be provided by a backbone Wireless Distribution System, which avoids the costs of introducing networking cables into buildings
8.
Network switch
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A network switch is a computer networking device that connects devices together on a computer network by using packet switching to receive, process, and forward data to the destination device. Unlike less advanced network hubs, a network switch forwards data only to one or multiple devices that need to receive it, a network switch is a multiport network bridge that uses hardware addresses to process and forward data at the data link layer of the OSI model. Switches for Ethernet are the most common form and the first Ethernet switch was introduced by Kalpana in 1990, Switches also exist for other types of networks including Fibre Channel, Asynchronous Transfer Mode, and InfiniBand. A switch is a device in a network that electrically and logically connects together other devices. Multiple data cables are plugged into a switch to enable communication between different networked devices, Switches manage the flow of data across a network by transmitting a received network packet only to the one or more devices for which the packet is intended. Each networked device connected to a switch can be identified by its network address and this maximizes the security and efficiency of the network. Because broadcasts are still being forwarded to all connected devices, the newly formed network segment continues to be a broadcast domain, an Ethernet switch operates at the data link layer of the OSI model to create a separate collision domain for each switch port. In full duplex mode, each switch port can simultaneously transmit and receive, in the case of using a repeater hub, only a single transmission could take place at a time for all ports combined, so they would all share the bandwidth and run in half duplex. Necessary arbitration would result in collisions, requiring retransmissions. The network switch plays an role in most modern Ethernet local area networks. Mid-to-large sized LANs contain a number of linked managed switches, in most of these cases, the end-user device contains a router and components that interface to the particular physical broadband technology. User devices may include a telephone interface for Voice over IP protocol. Segmentation involves the use of a bridge or a switch to split a larger collision domain into smaller ones in order to reduce collision probability, in the extreme case, each device is located on a dedicated switch port. In contrast to an Ethernet hub, there is a separate collision domain on each of the switch ports and this allows computers to have dedicated bandwidth on point-to-point connections to the network and also to run in full-duplex without collisions. Full-duplex mode has one transmitter and one receiver per collision domain. Switches may operate at one or more layers of the OSI model, including the data link, a device that operates simultaneously at more than one of these layers is known as a multilayer switch. In switches intended for use, built-in or modular interfaces make it possible to connect different types of networks, including Ethernet, Fibre Channel, RapidIO, ATM. This connectivity can be at any of the layers mentioned, while the layer-2 functionality is adequate for bandwidth-shifting within one technology, interconnecting technologies such as Ethernet and token ring is performed easier at layer 3 or via routing
9.
Base station subsystem
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Typically a BTS for anything other than a picocell will have several transceivers which allow it to serve several different frequencies and different sectors of the cell. A BTS is controlled by a parent BSC via the station control function. The BCF is implemented as a unit or even incorporated in a TRX in compact base stations. The BCF provides an operations and maintenance connection to the management system. The functions of a BTS vary depending on the technology used. There are vendors which build their BTSs so the information is preprocessed, target cell lists are generated, the advantage in this case is less load on the expensive Abis interface. This modulation is a kind of continuous-phase frequency shift keying, antenna combiners are implemented to use the same antenna for several TRXs, the more TRXs are combined the greater the combiner loss will be. Up to 8,1 combiners are found in micro and pico cells only, frequency hopping is often used to increase overall BTS performance, this involves the rapid switching of voice traffic between TRXs in a sector. A hopping sequence is followed by the TRXs and handsets using the sector, several hopping sequences are available, and the sequence in use for a particular cell is continually broadcast by that cell so that it is known to the handsets. A TRX transmits and receives according to the GSM standards, which specify eight TDMA timeslots per radio frequency, a TRX may lose some of this capacity as some information is required to be broadcast to handsets in the area that the BTS serves. This information allows the handsets to identify the network and gain access to it and this signalling makes use of a channel known as the Broadcast Control Channel. By using directional antennas on a station, each pointing in different directions. Typically these directional antennas have a beamwidth of 65 to 85 degrees and this increases the traffic capacity of the base station whilst not greatly increasing the interference caused to neighboring cells. Typically two antennas are used per sector, at spacing of ten or more wavelengths apart and this allows the operator to overcome the effects of fading due to physical phenomena such as multipath reception. Some amplification of the signal as it leaves the antenna is often used to preserve the balance between uplink and downlink signal. The base station controller provides, classically, the intelligence behind the BTSs, typically a BSC has tens or even hundreds of BTSs under its control. The BSC handles allocation of channels, receives measurements from the mobile phones. A key function of the BSC is to act as a concentrator where many different low capacity connections to BTSs become reduced to a number of connections towards the mobile switching center
10.
Asynchronous Transfer Mode
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ATM was developed to meet the needs of the Broadband Integrated Services Digital Network, as defined in the late 1980s, and designed to unify telecommunication and computer networks. It was designed for a network that must handle both traditional high-throughput data traffic, and real-time, low-latency content such as voice and video. The reference model for ATM approximately maps to the three lowest layers of the ISO-OSI reference model, network layer, data link layer, and physical layer. ATM is a protocol used over the SONET/SDH backbone of the public switched telephone network and Integrated Services Digital Network. This differs from approaches such as the Internet Protocol or Ethernet that use variable sized packets, ATM uses a connection-oriented model in which a virtual circuit must be established between two endpoints before the actual data exchange begins. ATM eventually became dominated by Internet Protocol only technology, in the ISO-OSI reference model data link layer, the basic transfer units are generically called frames. In ATM these frames are of a length and specifically called cells. Under normal queuing conditions the cells might experience maximum queuing delays, to avoid this issue, all ATM packets, or cells, are the same small size. In addition, the cell structure means that ATM can be readily switched by hardware without the inherent delays introduced by software switched and routed frames. Thus, the designers of ATM utilized small data cells to reduce jitter in the multiplexing of data streams.544 to 45 Mbit/s in the USA, at this rate, a typical full-length 1500 byte data packet would take 77.42 µs to transmit. In a lower-speed link, such as a 1.544 Mbit/s T1 line, a queuing delay induced by several such data packets might exceed the figure of 7.8 ms several times over, in addition to any packet generation delay in the shorter speech packet. This was clearly unacceptable for speech traffic, which needs to have low jitter in the stream being fed into the codec if it is to produce good-quality sound. This allows smoothing out the jitter, but the delay introduced by passage through the buffer would require echo cancellers even in local networks, also, it would have increased the delay across the channel, and conversation is difficult over high-delay channels. Build a system that can provide low jitter to traffic that needs it. Operate on a 1,1 user basis, the design of ATM aimed for a low-jitter network interface. However, cells were introduced into the design to provide short queuing delays while continuing to support datagram traffic, ATM broke up all packets, data, and voice streams into 48-byte chunks, adding a 5-byte routing header to each one so that they could be reassembled later. The choice of 48 bytes was political rather than technical, most of the European parties eventually came around to the arguments made by the Americans, but France and a few others held out for a shorter cell length. With 32 bytes, France would have been able to implement an ATM-based voice network with calls from one end of France to the other requiring no echo cancellation,48 bytes was chosen as a compromise between the two sides
11.
InfiniBand
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InfiniBand is a computer-networking communications standard used in high-performance computing that features very high throughput and very low latency. It is used for data interconnect both among and within computers, InfiniBand is also utilized as either a direct, or switched interconnect between servers and storage systems, as well as an interconnect between storage systems. As of 2014 it was the most commonly used interconnect in supercomputers, Mellanox IB cards are available for Solaris, RHEL, SLES, Windows, HP-UX, VMware ESX, AIX. It is designed to be scalable and uses a switched fabric network topology, as an interconnect, IB competes with Ethernet, Fibre Channel, and proprietary technologies such as Intel Omni-Path. The technology is promoted by the InfiniBand Trade Association, links can be aggregated, most systems use a 4X aggregate. 12X links are used for cluster and supercomputer interconnects and for inter-switch connections. InfiniBand also provides RDMA capabilities for low CPU overhead, InfiniBand uses a switched fabric topology, as opposed to early shared medium Ethernet. All transmissions begin or end at a channel adapter, each processor contains a host channel adapter and each peripheral has a target channel adapter. These adapters can also exchange information for security or quality of service, InfiniBand transmits data in packets of up to 4 KB that are taken together to form a message. A message can be, a memory access read from or, write to. A channel send or receive a transaction-based operation a multicast transmission, an atomic operation In addition to a board form factor connection, it supports both active and passive copper and optical fiber cable. The Infiniband Association also specified the CXP copper connector system for speeds up to 120 Gbit/s over copper, the standard only lists a set of verbs like ibv_open_device or ibv_post_send, which are abstract representations of functions or methods that must exist. The syntax of these functions is left to the vendors, the de facto standard software stack is that developed by OpenFabrics Alliance. It is released under two licenses GPL2 or BSD license for GNU/Linux and FreeBSD, and as WinOF under a choice of BSD license for Windows and it has been adopted by most of the InfiniBand vendors, for GNU/Linux, FreeBSD, and Windows. InfiniBand originated in 1999 from the merger of two competing designs, Future I/O and Next Generation I/O and this led to the formation of the InfiniBand Trade Association, which included Compaq, Dell, Hewlett-Packard, IBM, Intel, Microsoft, and Sun. At the time it was some of the more powerful computers were approaching the interconnect bottleneck of the PCI bus. Version 1.0 of the InfiniBand Architecture Specification was released in 2000, initially the IBTA vision for IB was simultaneously a replacement for PCI in I/O, Ethernet in the machine room, cluster interconnect and Fibre Channel. IBTA also envisaged decomposing server hardware on an IB fabric, following the burst of the dot-com bubble there was hesitation in the industry to invest in such a far-reaching technology jump
12.
Internet Protocol
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The Internet Protocol is the principal communications protocol in the Internet protocol suite for relaying datagrams across network boundaries. Its routing function enables internetworking, and essentially establishes the Internet, IP has the task of delivering packets from the source host to the destination host solely based on the IP addresses in the packet headers. For this purpose, IP defines packet structures that encapsulate the data to be delivered and it also defines addressing methods that are used to label the datagram with source and destination information. The Internet protocol suite is often referred to as TCP/IP. The first major version of IP, Internet Protocol Version 4, is the dominant protocol of the Internet and its successor is Internet Protocol Version 6. The Internet Protocol is responsible for addressing hosts and for routing datagrams from a source host to a destination host across one or more IP networks. For this purpose, the Internet Protocol defines the format of packets, each datagram has two components, a header and a payload. The IP header is tagged with the source IP address, the destination IP address, the payload is the data that is transported. This method of nesting the data payload in a packet with a header is called encapsulation, IP addressing entails the assignment of IP addresses and associated parameters to host interfaces. The address space is divided into networks and subnetworks, involving the designation of network or routing prefixes, IP routing is performed by all hosts, as well as routers, whose main function is to transport packets across network boundaries. Routers communicate with one another via specially designed routing protocols, either interior gateway protocols or exterior gateway protocols, IP routing is also common in local networks. For example, many Ethernet switches support IP multicast operations and these switches use IP addresses and Internet Group Management Protocol to control multicast routing but use MAC addresses for the actual routing. The versions currently relevant are IPv4 and IPv6, in May 1974, the Institute of Electrical and Electronic Engineers published a paper entitled A Protocol for Packet Network Intercommunication. The papers authors, Vint Cerf and Bob Kahn, described a protocol for sharing resources using packet switching among network nodes. A central control component of this model was the Transmission Control Program that incorporated both connection-oriented links and datagram services between hosts, the model became known as the Department of Defense Internet Model and Internet protocol suite, and informally as TCP/IP. IP versions 0 to 3 were experimental versions, used between 1977 and 1979, IEN26, dated February 1978 describes a version of the IP header that uses a 1-bit version field. IEN28, dated February 1978 describes IPv2, IEN41, dated June 1978 describes the first protocol to be called IPv4. The IP header is different from the modern IPv4 header, IEN44, dated June 1978 describes another version of IPv4, also with a header different from the modern IPv4 header
13.
Streaming media
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Streaming media is multimedia that is constantly received by and presented to an end-user while being delivered by a provider. A client end-user can use their player to begin to play the data file before the entire file has been transmitted. For example, in the 1930s, elevator music was among the earliest popularly available streaming media, the term streaming media can apply to media other than video and audio such as live closed captioning, ticker tape, and real-time text, which are all considered streaming text. As of 2017, streaming is generally taken to refer to cases where a user watches digital video content or listens to audio content on a computer screen. With streaming content, the user does not have to download the digital video or digital audio file before they start to watch/listen to it. There are challenges with streaming content on the Internet, as of 2016, two popular streaming services are the video sharing website YouTube, which contains video and audio files on a huge range of topics and Netflix, which streams movies and TV shows. Live streaming refers to Internet content delivered in real-time, as events happen, Live internet streaming requires a form of source media, an encoder to digitize the content, a media publisher, and a content delivery network to distribute and deliver the content. Live streaming does not need to be recorded at the origination point, in the early 1920s, George O. Attempts to display media on computers date back to the earliest days of computing in the mid-20th century, however, little progress was made for several decades, primarily due to the high cost and limited capabilities of computer hardware. From the late 1980s through the 1990s, consumer-grade personal computers became powerful enough to various media. These technological improvement facilitated the streaming of audio and video content to users in their homes and workplaces. The band Severe Tire Damage was the first group to live on the Internet. On June 24,1993, the band was playing a gig at Xerox PARC while elsewhere in the building, as proof of PARCs technology, the bands performance was broadcast and could be seen live in Australia and elsewhere. Microsoft Research developed a Microsoft TV application which was compiled under MS Windows Studio Suite, realNetworks was also a pioneer in the streaming media markets, when it broadcast a baseball game between the New York Yankees and the Seattle Mariners over the Internet in 1995. The first symphonic concert on the Internet took place at the Paramount Theater in Seattle, the concert was a collaboration between The Seattle Symphony and various guest musicians such as Slash, Matt Cameron, and Barrett Martin. When Word Magazine launched in 1995, they featured the first-ever streaming soundtracks on the Internet.4 in 1999, in June 1999 Apple also introduced a streaming media format in its QuickTime 4 application. It was later widely adopted on websites along with RealPlayer. In 2000 Industryview. com launched its worlds largest streaming video archive website to help promote themselves
14.
IPTV
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Unlike downloaded media, IPTV offers the ability to stream the source media continuously. As a result, a client media player can begin playing the data almost immediately and this is known as streaming media. Although IPTV uses the Internet protocol it is not limited to television media streamed from the Internet, IPTV in the telecommunications arena is notable for its ongoing standardisation process. Historically, many different definitions of IPTV have appeared, including elementary streams over IP networks, transport streams over IP networks and these services may include, for example, Live TV, Video On Demand and Interactive TV. These services are delivered across an access agnostic, packet switched network that employs the IP protocol to transport the audio, video, the term IPTV first appeared in 1995 with the founding of Precept Software by Judith Estrin and Bill Carrico. Precept developed an Internet video product named IP/TV, the software was written primarily by Steve Casner, Karl Auerbach, and Cha Chee Kuan. Precept was acquired by Cisco Systems in 1998, Internet radio company AudioNet started the first continuous live webcasts with content from WFAA-TV in January 1998 and KCTU-LP on January 10,1998. The operator added additional VoD service in October 2001 with Yes TV, kingston was one of the first companies in the world to introduce IPTV and IP VoD over ADSL as a commercial service. The service became the reference for various changes to UK Government regulations, in 2006, the KIT service was discontinued, subscribers having declined from a peak of 10,000 to 4,000. In 1999, NBTel was the first to commercially deploy Internet protocol television over DSL in Canada using the Alcatel 7350 DSLAM, the service was marketed under the brand VibeVision in New Brunswick, and later expanded into Nova Scotia in early 2000 after the formation of Aliant. IMagic TV was later sold to Alcatel, in 2002, Sasktel was the second in Canada to commercially deploy Internet Protocol video over DSL, using the Lucent Stinger DSL platform. In 2005, SureWest Communications was the first North American company to offer high-definition television channels over an IPTV service, in 2005, Bredbandsbolaget launched its IPTV service as the first service provider in Sweden. As of January 2009, they are not the biggest supplier any longer, TeliaSonera, in 2007, TPG became the first internet service provider in Australia to launch IPTV. Complementary to its ADSL2+ package this was, and still is, free of charge to customers on eligible plans and now offers over 45 local free to air channels, by 2010, iiNet and Telstra launched IPTV services in conjunction to internet plans but with extra fees. In 2008, PTCL launched IPTV under the name of PTCL Smart TV in Pakistan. S. Markets with an IPTV service called Prism and this was after successful test marketing in Florida. During the 2014 Winter Olympics Shortest path bridging was used to deliver 36 IPTV HD Olympic channels, in 2016, KCTV introduced the Set-top box called Manbang, claiming to provide video-on-demand services in North Korea via quasi-internet protocol television. According to KCTV, viewers can use the service not only in Pyongyang, stating that the demands for the equipment are particularly high in Sinuiju, with several hundred users in the region
15.
Videotelephony
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Videotelephony comprises the technologies for the reception and transmission of audio-video signals by users at different locations, for communication between people in real-time. A videophone is a telephone with a display, capable of simultaneous video. Videoconferencing implies the use of technology for a group or organizational meeting rather than for individuals. Telepresence may refer either to a high-quality videotelephony system or to meetup technology which goes beyond video into robotics, Videoconferencing has also been called visual collaboration and is a type of groupware. It is also used in commercial and corporate settings to facilitate meetings and conferences, Simple analog videophone communication could be established as early as the invention of the television. Such an antecedent usually consisted of two closed-circuit television systems connected via cable or radio. An example of that was the German Reich Postzentralamt video telephone network serving Berlin, the development of the crucial video technology first started in the latter half of the 1920s in the United Kingdom and the United States, spurred notably by John Logie Baird and AT&Ts Bell Labs. This occurred in part, at least with AT&T, to serve as an adjunct supplementing the use of the telephone, a number of organizations believed that videotelephony would be superior to plain voice communications. However video technology was to be deployed in analog television broadcasting long before it could become practical—or popular—for videophones, during the first manned space flights, NASA used two radio-frequency video links, one in each direction. TV channels routinely use this type of videotelephony when reporting from distant locations, the news media were to become regular users of mobile links to satellites using specially equipped trucks, and much later via special satellite videophones in a briefcase. This technique was very expensive, though, and could not be used for such as telemedicine, distance education. Videotelephony developed in parallel with conventional voice telephone systems from the mid-to-late 20th century, Only in the late 20th century with the advent of powerful video codecs combined with high-speed Internet broadband and ISDN service did videotelephony become a practical technology for regular use. In the 1980s, digital telephony transmission networks became possible, such as with ISDN networks, assuring a bit rate for compressed video. During this time, there was research into other forms of digital video. Many of these technologies, such as the Media space, are not as used today as videoconferencing but were still an important area of research. The first dedicated systems started to appear in the market as ISDN networks were expanding throughout the world, one of the first commercial videoconferencing systems sold to companies came from PictureTel Corp. which had an Initial Public Offering in November,1984. The company also secured a patent for a codec for full-motion videoconferencing, in 1992 CU-SeeMe was developed at Cornell by Tim Dorcey et al. In 1995 the first public videoconference between North America and Africa took place, linking a technofair in San Francisco with a techno-rave and cyberdeli in Cape Town
16.
MAC address
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A media access control address of a computer is a unique identifier assigned to network interfaces for communications at the data link layer of a network segment. MAC addresses are used as an address for most IEEE802 network technologies, including Ethernet. Logically, MAC addresses are used in the access control protocol sublayer of the OSI reference model. MAC addresses are most often assigned by the manufacturer of a network interface controller and are stored in its hardware, if assigned by the manufacturer, a MAC address usually encodes the manufacturers registered identification number and may be referred to as the burned-in address. It may also be known as an Ethernet hardware address, hardware address or physical address and this can be contrasted to a programmed address, where the host device issues commands to the NIC to use an arbitrary address. A network node may have multiple NICs and each NIC must have a unique MAC address, sophisticated network equipment such as a multilayer switch or router may require one or more permanently assigned MAC addresses. MAC addresses are formed according to the rules of one of three numbering name spaces managed by the Institute of Electrical and Electronics Engineers, MAC-48, EUI-48, the IEEE claims trademarks on the names EUI-48 and EUI-64, in which EUI is an abbreviation for Extended Unique Identifier. The original IEEE802 MAC address comes from the original Xerox Ethernet addressing scheme and this 48-bit address space contains potentially 248 or 281,474,976,710,656 possible MAC addresses. The distinction between EUI-48 and MAC-48 identifiers is purely nominal, MAC-48 is used for hardware, EUI-48 is used to identify other devices. Instead, the proprietary term EUI-48 should be used for this purpose, in addition, the EUI-64 numbering system encompasses both MAC-48 and EUI-48 identifiers by a simple translation mechanism. To convert a MAC-48 into an EUI-64, copy the OUI, to convert an EUI-48 into an EUI-64, the same process is used, but the sequence inserted is FF-FE. In both cases, the process can be reversed when necessary. Organizations issuing EUI-64s are cautioned against issuing identifiers that could be confused with these forms, the IEEE has a target lifetime of 100 years for applications using MAC-48 space, but encourages adoption of EUI-64s instead. IPv6 — one of the most prominent standards that uses a Modified EUI-64 — treats MAC-48 as EUI-48 instead and this results in extending MAC addresses to Modified EUI-64 using only FF-FE and with the U/L bit inverted. An Individual Address Block was a 24-bit OUI managed by the IEEE Registration Authority, followed by 12 IEEE-provided bits, an IAB is ideal for organizations requiring fewer than 4097 unique 48-bit numbers. IABs have been replaced with 12-bit MA-S address blocks, addresses can either be universally administered addresses or locally administered addresses. A universally administered address is assigned to a device by its manufacturer. The first three octets identify the organization issued the identifier and are known as the Organizationally Unique Identifier
17.
Internet Group Management Protocol
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The Internet Group Management Protocol is a communications protocol used by hosts and adjacent routers on IPv4 networks to establish multicast group memberships. IGMP is an part of IP multicast. IGMP can be used for one-to-many networking applications such as streaming video and gaming. IGMP is used on IPv4 networks, Multicast management on IPv6 networks is handled by Multicast Listener Discovery which uses ICMPv6 messaging in contrast to IGMPs bare IP encapsulation. A network designed to deliver a multicast service using IGMP might use this basic architecture, switches featuring IGMP snooping derive useful information by observing these IGMP transactions. Protocol Independent Multicast is then used between the local and remote multicast routers, to direct multicast traffic from the multicast server to many multicast clients, IGMP operates on the network layer, just the same as other network management protocols like ICMP. The IGMP protocol is implemented on a particular host and within a router, a host requests membership to a group through its local router while a router listens for these requests and periodically sends out subscription queries. A single router per subnet is elected to perform this querying function, some multilayer switches include an IGMP querier capability to allow their IGMP snooping features to work in the absence of an IP multicast capability in the larger network. IGMP is vulnerable to attacks, and firewalls commonly allow the user to disable it if not needed. There are three versions of IGMP, as defined by Request for Comments documents of the Internet Engineering Task Force. IGMPv1 is defined by RFC1112, IGMPv2 is defined by RFC2236, IGMPv2 improves over IGMPv1 by adding the ability for a host to signal desire to leave a multicast group. IGMPv3 improves over IGMPv2 mainly by supporting source-specific multicast and Membership Report aggregation, IGMP messages are carried in bare IP packets with IP protocol number 2. There is no transport layer used with IGMP messaging, similar to the Internet Control Message Protocol, there are several types of IGMP messages, Membership Queries, Membership Reports, and Leave Group messages. Membership Queries are sent by multicast routers to determine which multicast addresses are of interest to systems attached to its network, routers periodically send General Queries to refresh the group membership state for all systems on its network. Group-Specific Queries are used for determining the state for a particular multicast address. Group-and-Source-Specific Queries allow the router to determine if any systems desire reception of messages sent to a multicast group from a source address specified in a list of unicast addresses. Where, Type Indicates the message type as follows, Membership Query, Membership Report, the field has a resolution of 100 milliseconds, the value is taken directly. This field is only in Membership Query, in other messages it is set to 0
18.
Middleware
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Middleware is computer software that provides services to software applications beyond those available from the operating system. It can be described as software glue, middleware makes it easier for software developers to implement communication and input/output, so they can focus on the specific purpose of their application. The term is most commonly used for software that enables communication, an IETF workshop in 2000 defined middleware as those services found above the transport layer set of services but below the application environment. In this more specific sense middleware can be described as the dash in client-server, middleware includes web servers, application servers, content management systems, and similar tools that support application development and delivery. ObjectWeb defines middleware as, The software layer that lies between the system and applications on each side of a distributed computing system in a network. Services that can be regarded as middleware include enterprise application integration, data integration, message oriented middleware, object request brokers, database access services are often characterised as middleware. Some of them are language specific implementations and support heterogeneous features, examples of database-oriented middleware include ODBC, JDBC and transaction processing monitors. Distributed computing system middleware can loosely be divided into two categories—those that provide services and those that perform in machine-time. This latter middleware is somewhat standardized through the Service Availability Forum and is used in complex, embedded systems within telecom, defense. The term middleware is used in contexts as well. Middleware is sometimes used in a sense to a software driver. The mer software distribution is a middleware, it lacks the Linux kernel, mer is targeted at hardware vendors mobile-oriented operating systems. The Android operating system uses the Linux kernel at its core, in addition, Android provides a middleware layer including libraries that provide services such as data storage, screen display, multimedia, and web browsing. Because the middleware libraries are compiled to machine language, services execute quickly, middleware libraries also implement device-specific functions, so applications and the application framework need not concern themselves with variations between various Android devices. Androids middleware layer also contains the Dalvik virtual machine and its core Java application libraries, game engine software such as Gamebryo and Renderware are sometimes described as middleware, because they provide many services to simplify game development. In simulation technology, middleware is used in the context of the high level architecture that applies to many distributed simulations. It is a layer of software that lies between the code and the run-time infrastructure. Wireless networking developers can use middleware to meet the associated with a wireless sensor network
19.
Data Distribution Service
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DDS addresses the needs of applications like financial trading, air-traffic control, smart grid management, and other big data applications. The standard is used in such as smartphone operating systems, transportation systems and vehicles, software-defined radio. DDS was promoted for use in the Internet of things, a few proprietary DDS systems had been available for several years.0 in published in December 2004. Version 1.1 was published in December 2005,1.2 in January 2007, DDS is covered by several US patents, among others. An optional higher data local reconstruction layer, which allows for an integration of DDS into the application layer. Other related standards followed the core document. Although the specification is targeted at the DDS community, its use is not limited, versions 2.0 was published in April 2008, version 2.1 in November 2010, and 2.2 in September 2014. DDS for Lightweight CCM offers an architectural pattern that separates the logic from the non-functional properties. A2012 extension added support for streams, a Java 5 Language PSM for DDS defined a Java 5 language binding, referred to as a Platform Specific Model for DDS. It specified only the Data-Centric Publish-Subscribe portion of the DDS specification, Additionally, it encompasses the DDS APIs introduced by DDS-XTypes, dDS-PSM-Cxx defines the ISO/IEC C++ PSM language binding, referred to as a Platform Specific Model for DDS. It provides a new C++ API for programming DDS that is natural to a C++ programmer. The specification provides mappings for the programming interface specified in DDS-XTypes. Extensible and Dynamic Topic Types for DDS provided support for data-centric publish-subscribe communication where topics are defined with data structures. To be extensible, DDS topics use data types defined before compile time and this model is desirable when static type checking is useful. A Unified Modeling Language profile specified DDS domains and topics to be part of analysis and this specification also defined how to publish and subscribe objects without first describing the types in another language, such as XML or OMG IDL. An interface definition language was specified in 2014 independently from the Common Object Request Broker Architecture specification chapter 3 and this IDL3.5 was compatible with the CORBA3 specification, but extracted as its own specification so that it can evolve independently from CORBA. Starting with DDS version 1.4 in 2015, the optional DLRL layer was moved to a separate specification, DDS is networking middleware that simplifies complex network programming. It implements a publish–subscribe pattern for sending and receiving data, events, nodes that produce information create topics and publish samples
20.
Object Management Group
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The Object Management Group is an international, open membership, not-for-profit technology standards consortium. OMG Task Forces develop enterprise integration standards for a range of technologies and industries. OMG modeling standards enable visual design, execution and maintenance of software, originally aimed at standardizing distributed object-oriented systems, the company now focuses on modeling and model-based standards. OMG provides only specifications, and does not provide implementations, but before a specification can be accepted as a standard by OMG, the members of the submitter team must guarantee that they will bring a conforming product to market within a year. This is an attempt to prevent unimplemented standards, other private companies or open source groups are encouraged to produce conforming products and OMG is attempting to develop mechanisms to enforce true interoperability. OMG hosts four technical meetings for its members and interested nonmembers, founded in 1989 by eleven companies, OMGs initial focus was to create a heterogeneous distributed object standard. The founding executive team included Christopher Stone and John Slitz, as of November,2012, the leadership includes Chairman and CEO Richard Soley, President and COO Bill Hoffman and Vice President and Technical Director Andrew Watson. Since 2000, OMG international headquarters has been located in Needham, in November,2012, the headquarters was moved from 140 Kendrick St to 109 Highland Ave. The goal was a portable and interoperable object model with methods. In 1997, the Unified Modeling Language was added to the list of OMG adopted technologies, UML is a standardized general-purpose modeling language in the field of object-oriented software engineering. In 2006 the Business Process Model and Notation was adopted as a standard by OMG, in 2007 the Business Motivation Model was adopted as a standard by the OMG. In 2009 OMG, together with the Software Engineering Institute at Carnegie Mellon, in 2011 OMG formed the Cloud Standards Customer Council. Founding sponsors included CA, IBM, Kaavo, Rackspace and Software AG, CSCC is open to all end-user organizations. In September,2011, the OMG Board of Directors unanimously voted to adopt the Vector Signal, VSIPL and VSIPL++ contain hundreds of functions used for common signal processing kernel and other computations. These functions include basic arithmetic, trigonometric, transcendental, signal processing, linear algebra, the VSIPL family of libraries has been implemented by multiple vendors for a range of processor architectures, including x86, PowerPC, Cell, and NVIDIA GPUs. VSIPL and VSIPL++ are designed to high performance, increase programmer productivity. Additionally, VSIPL++ was designed from the start to support for parallelism. Late 2012 early 2013, The Object Management Group Board of Directors adopted the Automated Function Point specification, the push for adoption was led by the Consortium for IT Software Quality
21.
Internet Relay Chat
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Internet Relay Chat is an application layer protocol that facilitates communication in the form of text. The chat process works on a client/server networking model, IRC clients are computer programs that a user can install on their system. These clients communicate with chat servers to transfer messages to other clients, client software is available for every major operating system that supports Internet access. IRC usage has been declining steadily since 2003, losing 60% of its users, Jarkko intended to extend the BBS software he administered, to allow news in the Usenet style, real time discussions and similar BBS features. The first part he implemented was the part, which he did with borrowed parts written by his friends Jyrki Kuoppala. The first IRC network was running on a server named tolsun. oulu. fi. Oikarinen found inspiration in a system known as Bitnet Relay. This was the first irc network, Jarkko got some friends at the Helsinki University and Tampere University to start running IRC servers when his number of users increased and other universities soon followed. At this time Jarkko realized that the rest of the BBS features probably wouldnt fit in his program, Jarkko got in touch with people at the University of Denver and Oregon State University. They had their own IRC network running and wanted to connect to the Finnish network and they had gotten the program from one of Jarkkos friends, Vijay Subramaniam—the first non-Finnish person to use IRC. IRC then grew larger and got used on the entire Finnish national network—Funet—and then connected to Nordunet, in November 1988, IRC had spread across the Internet and in the middle of 1989, there were some 40 servers worldwide. In August 1990 the first major disagreement took place in the IRC world, the A-net included a server named eris. berkeley. edu. It was all open, required no passwords and had no limit on the number of connects, as Greg wumpus Lindahl explains, it had a wildcard server line, so people were hooking up servers and nick-colliding everyone. The Eris Free Network, EFnet, made the machine the first to be Q-lined from IRC. In wumpus words again, Eris refused to remove that line and it wasnt much of a fight, I got all the hubs to join, and almost everyone else got carried along. A-net was formed with the servers, EFnet was formed with the non-eris servers. History showed most servers and users went with EFnet, once ANet disbanded, the name EFnet became meaningless, and once again it was the one and only IRC network. It is around that time that IRC was used to report on the 1991 Soviet coup détat attempt throughout a media blackout and it was previously used in a similar fashion during the Gulf War
22.
Spanning tree
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In the mathematical field of graph theory, a spanning tree T of an undirected graph G is a subgraph that is a tree which includes all of the vertices of G, with minimum possible number of edges. In general, a graph may have several spanning trees, but a graph that is not connected will not contain a spanning tree. If all of the edges of G are also edges of a spanning tree T of G, several pathfinding algorithms, including Dijkstras algorithm and the A* search algorithm, internally build a spanning tree as an intermediate step in solving the problem. The Internet and many other networks have transmission links that connect nodes together in a mesh topology that includes some loops. -- require each router to remember a spanning tree, a tree is a connected undirected graph with no cycles. It is a tree of a graph G if it spans G and is a subgraph of G. A spanning tree of a connected graph G can also be defined as a set of edges of G that contains no cycle. Adding just one edge to a tree will create a cycle. There is a fundamental cycle for each edge, thus. For a connected graph with V vertices, any spanning tree will have V −1 edges, and thus, for any given spanning tree the set of all E − V +1 fundamental cycles forms a cycle basis, a basis for the cycle space. Dual to the notion of a cycle is the notion of a fundamental cutset. By deleting just one edge of the tree, the vertices are partitioned into two disjoint sets. The fundamental cutset is defined as the set of edges that must be removed from the graph G to accomplish the same partition, thus, each spanning tree defines a set of V −1 fundamental cutsets, one for each edge of the spanning tree. In graphs that are not connected, there can be no spanning tree, for other authors, a spanning forest is a forest that spans all of the vertices, meaning only that each vertex of the graph is a vertex in the forest. For this definition, even a connected graph may have a disconnected spanning forest, the number t of spanning trees of a connected graph is a well-studied invariant. In some cases, it is easy to calculate t directly, If G is itself a tree, when G is the cycle graph Cn with n vertices, then t = n. For a complete graph with n vertices, Cayleys formula gives the number of spanning trees as nn −2, If G is the complete bipartite graph K p, q, then t = p q −1 q p −1. For the n-dimensional hypercube graph Q n, the number of spanning trees is t =22 n − n −1 ∏ k =2 n k
23.
Overlay network
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An overlay network is a computer network that is built on top of another network. Nodes in the network can be thought of as being connected by virtual or logical links, each of which corresponds to a path, perhaps through many physical links. For example, distributed systems such as networks and client-server applications are overlay networks because their nodes run on top of the Internet. The Internet was originally built as an overlay upon the network, while today. Overlay networks are used in telecommunication because of the availability of digital switching equipment. Telecommunication transport networks and IP networks are all overlaid with at least an optical fiber layer, a transport layer, nowadays the Internet is the basis for more overlaid networks that can be constructed in order to permit routing of messages to destinations not specified by an IP address. For example, distributed hash tables can be used to route messages to a node having a logical address. Overlay networks have also proposed as a way to improve Internet routing. Previous proposals such as IntServ, DiffServ, and IP multicast have not seen wide acceptance largely because they require modification of all routers in the network. On the other hand, a network can be incrementally deployed on end-hosts running the overlay protocol software. For example, Akamai Technologies manages a network which provides reliable. Academic research includes End System Multicast and Overcast for multicast, RON for resilient routing, Resilient Overlay Networks are architectures that allow distributed Internet applications to detect and recover from disconnection or interference. Current wide area routing protocols that take at least several minutes to recover from are improved upon with this application layer overlay, the Resilient Overlay Network has a relatively simple conceptual design. RON nodes are deployed at various locations on the Internet and these nodes form an application layer overlay that cooperate in routing packets. Overlay multicast is also known as End System or Peer-to-Peer Multicast, throughout the last decade, a number of research projects have explored the use of multicast as an efficient and scalable mechanism to support such group communication applications. Multicast decouples the size of the set from the amount of state kept at any single node. In an overlay or end-system multicast approach participating peers organize themselves into an overlay topology for data delivery, each edge in this topology corresponds to a unicast path between two end-systems or peers in the underlying Internet. All multicast-related functionality is implemented at the peers instead of at routers, Overlay network protocols based on TCP/IP include, Distributed hash tables, such as KAD and other protocols based on the Kademlia algorithm, for example
24.
Peer-to-peer
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Peer-to-peer computing or networking is a distributed application architecture that partitions tasks or workloads between peers. Peers are equally privileged, equipotent participants in the application and they are said to form a peer-to-peer network of nodes. Peers are both suppliers and consumers of resources, in contrast to the traditional client-server model in which the consumption, while P2P systems had previously been used in many application domains, the architecture was popularized by the file sharing system Napster, originally released in 1999. The concept has inspired new structures and philosophies in many areas of human interaction, in such social contexts, peer-to-peer as a meme refers to the egalitarian social networking that has emerged throughout society, enabled by Internet technologies in general. While P2P systems had previously used in many application domains. The peer-to-peer movement allowed millions of Internet users to directly, forming groups and collaborating to become user-created search engines, virtual supercomputers. The basic concept of peer-to-peer computing was envisioned in earlier systems and networking discussions, reaching back to principles stated in the first Request for Comments. The early Internet was more open than present day, where two machines connected to the Internet could send packets to each other without firewalls and other security measures and this contrasts to the broadcasting-like structure of the web as it has developed over the years. As a precursor to the Internet, ARPANET was a successful client-server network where every participating node could request, however, ARPANET was not self-organized, and it lacked the ability to provide any means for context or content-based routing beyond simple address-based routing. Therefore, a messaging system that is often likened as an early peer-to-peer architecture was established. USENET was developed in 1979 and is a system that enforces a decentralized model of control, the basic model is a client-server model from the user or client perspective that offers a self-organizing approach to newsgroup servers. However, news servers communicate with one another as peers to propagate Usenet news articles over the group of network servers. In May 1999, with more people on the Internet, Shawn Fanning introduced the music. A peer-to-peer network is designed around the notion of equal peer nodes simultaneously functioning as both clients and servers to the nodes on the network. This model of network arrangement differs from the model where communication is usually to. Data is still exchanged directly over the underlying TCP/IP network, but at the application layer peers are able to communicate each other directly. Overlays are used for indexing and peer discovery, and make the P2P system independent from the network topology. Based on how the nodes are linked to each other within the overlay network, unstructured peer-to-peer networks do not impose a particular structure on the overlay network by design, but rather are formed by nodes that randomly form connections to each other
25.
Xcast
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The explicit multi-unicast is a variation of multicast that supports a great number of multicast sessions with a small number of recipients in each. It adds all the destination IP addresses in the IP header, the traditional multicast schemes over Internet Protocol scale to multicast groups with many members, but they have scalability problems for a great number of groups. Multicast schemes can be used to minimize the bandwidth consumption, Xcast minimizes bandwidth consumption for small groups, by eliminating the signaling protocols and state information for every session of the standard IP multicast scheme. In Xcast, the source node keeps all destinations of the multicast channel through which packets will be sent, the source encodes the destinations list in the Xcast header and sends the packet to a router. After that, the copies the packet with its correct Xcast header to every following jump. On the last hop, there is no need to make a new copy, the packet is treated just like a unicast packet, which is called Xcast to Unicast. The IP multicast standard was designed to scale to multicast groups with many members and it works well when doing a distribution similar to broadcasting, but it has scalability problems to a large number of groups. Multicast routing protocols keep routing tables that record multicast group addresses with members and these tables might become large, that prompted alternative schemes to reduce the quantity of state information. IP Multicast protocols announce a source or maintain routes between routers, the cost of these protocols can be significant even then the size of each group is reduced. Xcast follows philosophy that worked well to grow the Internet, keep the center of the network simple, an open source implementation was available from IBM starting in 2001. A MediaWiki-based web site indicates activity from 2004 through 2007, an informational specification was published by the Internet Engineering Task Force in November 2007 as RFC5058. Routers do not need to keep information for every session or channel and this makes Xcast very scalable about the number of sessions it can support. There is no need to make a direction assignment and they dont need protocols for multicast routing. They are routed correctly thanks to the common unicast protocols, Xcast minimizes the network latencies and maximizes efficiency. With traditional IP multicast routing protocols it is necessary to establish a communication between unicast and multicast routing protocols and that means a slow error recovery. Xcast reacts immediately to unicast routing changes, with Xcast all sources know the channel members and all routers are able to know the number of times each packet has been duplicated in its domain. The receptors can be heterogeneous since Xcast allows that every receptor is able to have its own requirements of service in each multicast channel, simplicity when implementing reliable protocols over Xcast. Flexibility, unicast, multicast and Xcast represent costs of bandwidth, signalization, depending on how the network is built or its load at certain moment, it may be better to use one system or another
26.
Directional antenna
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A directional antenna or beam antenna is an antenna which radiates or receives greater power in specific directions allowing for increased performance and reduced interference from unwanted sources. Directional antennas provide increased performance over dipole antennas – or omnidirectional antennas in general – when greater concentration of radiation in a direction is desired. A high-gain antenna is an antenna with a focused, narrow radiowave beam width. This narrow beam allows more precise targeting of the radio signals. Most commonly referred to during space missions, these antennas are also in use all over Earth, most successfully in flat, open areas where no mountains lie to disrupt radiowaves. Low gain antennas are used in spacecraft as a backup to the high-gain antenna. The most common types are the Yagi antenna, the antenna, and the corner reflector antenna. Cellular repeaters often make use of directional antennas to give a far greater signal than can be obtained on a standard cell phone. Satellite Television receivers usually use parabolic antennas, for long and medium wavelength frequencies, tower arrays are used in most cases as directional antennas. When transmitting, a high-gain antenna allows more of the power to be sent in the direction of the receiver. When receiving, a high gain antenna captures more of the signal, as a consequence of their directivity, directional antennas also send less signal from directions other than the main beam. This property may be used to reduce interference, there are many ways to make a high-gain antenna - the most common are parabolic antennas, helical antennas, yagi antennas, and phased arrays of smaller antennas of any kind. Horn antennas can also be constructed with high gain, but are commonly seen. Still other configurations are possible - the Arecibo Observatory uses a combination of a line feed with a spherical reflector. Antenna gain is often quoted with respect to an antenna that radiates equally in all directions. This gain, when measured in decibels, is called dBi, conservation of energy dictates that high gain antennas must have narrow beams. For example, if a high gain antenna makes a 1 watt transmitter look like a 100 watt transmitter, in turn this implies that high-gain antennas must be physically large, since according to the diffraction limit, the narrower the beam desired, the larger the antenna must be. Antenna gain can also be measured in dBd, which is gain in Decibels compared to the maximum intensity direction of a half wave dipole
27.
Broadcasting
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Broadcasting began with AM radio, which came into popular use around 1920 with the spread of vacuum tube radio transmitters and receivers. Before this, all forms of communication were one-to-one, with the message intended for a single recipient. Over the air broadcasting is usually associated with radio and television, the receiving parties may include the general public or a relatively small subset, the point is that anyone with the appropriate receiving technology and equipment can receive the signal. The field of broadcasting includes both government-managed services such as radio, community radio and public television, and private commercial radio. The U. S. Code of Federal Regulations, title 47, part 97 defines broadcasting as transmissions intended for reception by the general public, private or two-way telecommunications transmissions do not qualify under this definition. For example, amateur and citizens band radio operators are not allowed to broadcast, as defined, transmitting and broadcasting are not the same. Transmissions using a wire or cable, like television, are also considered broadcasts. In the 2000s, transmissions of television and radio programs via streaming digital technology have increasingly been referred to as broadcasting as well, the earliest broadcasting consisted of sending telegraph signals over the airwaves, using Morse code, a system developed in the 1830s by Samuel F. B. Morse, physicist Joseph Henry and Alfred Vail and they developed an electrical telegraph system which sent pulses of electric current along wires which controlled an electromagnet that was located at the receiving end of the telegraph system. A code was needed to transmit natural language using only these pulses, Morse therefore developed the forerunner to modern International Morse code. Audio broadcasting began experimentally in the first decade of the 20th century, by the early 1920s radio broadcasting became a household medium, at first on the AM band and later on FM. Television broadcasting started experimentally in the 1920s and became widespread after World War II, satellite broadcasting was initiated in the 1960s and moved into general industry usage in the 1970s, with DBS emerging in the 1980s. Originally all broadcasting was composed of signals using analog transmission techniques but in the 2000s. In general usage, broadcasting most frequently refers to the transmission of information, Analog audio vs. HD Radio Analog television vs.9 zettabytes. This is the equivalent of 55 newspapers per person per day in 1986. Historically, there have been several methods used for broadcasting electronic media audio and/or video to the public, Telephone broadcasting. Telephone broadcasting also grew to include telephone services for news and entertainment programming which were introduced in the 1890s. These telephone-based subscription services were the first examples of electrical/electronic broadcasting, Radio broadcasting, audio signals sent through the air as radio waves from a transmitter, picked up by an antenna and sent to a receiver
28.
Digital television
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Digital television is the transmission of audio and video by digitally processed and multiplexed signal, in contrast to the totally analog and channel separated signals used by analog television. Digital TV can support more than one program in the channel bandwidth. It is a service that represents the first significant evolution in television technology since color television in the 1950s. Several regions of the world are in different stages of adaptation and are implementing different broadcasting standards and this standard has been adopted in Europe, Singapore, Australia and New Zealand. Advanced Television System Committee uses eight-level vestigial sideband for terrestrial broadcasting and this standard has been adopted by six countries, United States, Canada, Mexico, South Korea, Dominican Republic and Honduras. Integrated Services Digital Broadcasting is a designed to provide good reception to fixed receivers. It utilizes OFDM and two-dimensional interleaving and it supports hierarchical transmission of up to three layers and uses MPEG-2 video and Advanced Audio Coding. This standard has adopted in Japan and the Philippines. ISDB-T International is an adaptation of this standard using H. 264/MPEG-4 AVC that been adopted in most of South America and is also being embraced by Portuguese-speaking African countries. Digital Terrestrial Multimedia Broadcasting adopts time-domain synchronous OFDM technology with a signal frame to serve as the guard interval of the OFDM block. The DTMB standard has adopted in the Peoples Republic of China, including Hong Kong. Digital TVs roots have been tied very closely to the availability of inexpensive and it wasnt until the 1990s that digital TV became a real possibility. S. Until June 1990, the Japanese MUSE standard—based on an analog system—was the front-runner among the more than 23 different technical concepts under consideration, then, an American company, General Instrument, demonstrated the feasibility of a digital television signal. This breakthrough was of significance that the FCC was persuaded to delay its decision on an ATV standard until a digitally based standard could be developed. In March 1990, when it became clear that a standard was feasible. The new ATV standard also allowed the new DTV signal to be based on new design principles. Although incompatible with the existing NTSC standard, the new DTV standard would be able to incorporate many improvements, the final standard adopted by the FCC did not require a single standard for scanning formats, aspect ratios, or lines of resolution. This outcome resulted from a dispute between the electronics industry and the computer industry over which of the two scanning processes—interlaced or progressive—is superior
29.
Interactive television
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Interactive television is a form of media convergence, adding data services to traditional television technology. Throughout its history, these have included delivery of content, as well as new uses such as online shopping, banking. Interactive TV is an example of how new information technology can be integrated vertically rather than laterally. Interactive television represents a continuum from low to moderate interactivity and high interactivity in which, for example, the most obvious example of this would be any kind of real-time voting on the screen, in which audience votes create decisions that are reflected in how the show continues. A return path to the provider is not necessary to have an interactive program experience. Once a movie is downloaded for example, controls may all be local, the link was needed to download the program, but texts and software which can be executed locally at the set-top box or IRD may occur automatically, once the viewer enters the channel. The first patent of interactive connected TV was registered in 1994 and it clearly expose this new interactive technology with content feeding and feedback through global networking. User identification allows interacting and purchasing, the viewer must be able to alter the viewing experience, or return information to the broadcaster. This return path, return channel or back channel can be by telephone, mobile SMS, radio, cable TV viewers receive their programs via a cable, and in the integrated cable return path enabled platforms, they use the same cable as a return path. Satellite viewers return information to the broadcaster via their regular telephone lines and they are charged for this service on their regular telephone bill. An Internet connection via ADSL, or other, data communications technology, is also being increasingly used, Interactive TV can also be delivered via a terrestrial aerial. In this case, there is no return path as such - so data cannot be sent back to the broadcaster. However, interactivity is still possible as there is still the opportunity to interact with an application which is broadcast, increasingly the return path is becoming a broadband IP connection, and some hybrid receivers are now capable of displaying video from either the IP connection or from traditional tuners. Some devices are now dedicated to displaying video only from the IP channel, the rise of the broadband return path has given new relevance to Interactive TV, as it opens up the need to interact with Video on Demand servers, advertisers, and web site operators. The term interactive television is used to refer to a variety of different kinds of interactivity. It does not change any content or its inherent linearity, only how users control the viewing of that content, dVRs allow users to time shift content in a way that is impractical with VHS. In the not too distant future, the questioning of what is real interaction with the TV will be difficult, Panasonic already has face recognition technology implemented its prototype Panasonic Life Wall. The Life Wall is literally a wall in house that doubles as a screen
