1.
Network Time Protocol
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Network Time Protocol is a networking protocol for clock synchronization between computer systems over packet-switched, variable-latency data networks. In operation since before 1985, NTP is one of the oldest Internet protocols in current use, NTP was designed by David L. Mills of the University of Delaware. NTP is intended to synchronize all participating computers to within a few milliseconds of Coordinated Universal Time and it uses a modified version of Marzullos algorithm to select accurate time servers and is designed to mitigate the effects of variable network latency. NTP can usually maintain time to within tens of milliseconds over the public Internet, asymmetric routes and network congestion can cause errors of 100 ms or more. The protocol is described in terms of a client-server model. Implementations send and receive timestamps using the User Datagram Protocol on port number 123 and they can also use broadcasting or multicasting, where clients passively listen to time updates after an initial round-trip calibrating exchange. NTP supplies a warning of any impending leap second adjustment, the current protocol is version 4, which is a proposed standard as documented in RFC5905. It is backward compatible with version 3, specified in RFC1305, the technology was later described in the 1981 Internet Engineering Note 173 and a public protocol was developed from it that was documented in RFC778. Other related network tools were available both then and now and they include the Daytime and Time protocols for recording the time of events, as well as the ICMP Timestamp and IP Timestamp option. In 1985, NTPv0 was implemented in both Fuzzball and Unix, and the NTP packet header and round-trip delay and offset calculations, in 1988, a much more complete specification of the NTPv1 protocol, with associated algorithms, was published in RFC1059. It drew on the results and clock filter algorithm documented in RFC956 and was the first version to describe the client-server and peer-to-peer modes. In 1989, RFC1119 was published defining NTPv2 by means of a state machine and it introduced a management protocol and cryptographic authentication scheme which have both survived into NTPv4. The design of NTP was criticized for lacking formal correctness principles by the DTSS community and their alternative design included Marzullos algorithm, a modified version of which was promptly added to NTP. The bulk of the algorithms from this era have also survived into NTPv4. In 1992, RFC1305 defined NTPv3, in subsequent years, as new features were added and algorithm improvements were made, it became apparent that a new protocol version was required. In 2010, RFC5905 was published containing a proposed specification for NTPv4, but the protocol has significantly moved on since then, and as of 2014, an updated RFC has yet to be published. Following the retirement of Mills from the University of Delaware, the implementation is currently maintained as an open source project led by Harlan Stenn. NTP uses a hierarchical, semi-layered system of time sources, each level of this hierarchy is termed a stratum and is assigned a number starting with zero at the top
2.
AppleTalk
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AppleTalk was a proprietary suite of networking protocols developed by Apple Inc. for their Macintosh computers. AppleTalk includes a number of features that allow local area networks to be connected with no setup or the need for a centralized router or server of any sort. Connected AppleTalk-equipped systems automatically assign addresses, update the distributed namespace, AppleTalk was released in 1985, and was the primary protocol used by Apple devices through the 1980s and 1990s. Versions were also released for the IBM PC and compatibles and the Apple IIGS, AppleTalk support was also available in most networked printers, some file servers, and a number of routers. The rise of TCP/IP during the 1990s led to a reimplementation of most of these types of support on that protocol, many of AppleTalks more advanced autoconfiguration features have since been introduced in Bonjour, while Universal Plug and Play serves similar needs. After the release of the Apple Lisa computer in January 1983, known as AppleNet, it was based on the seminal Xerox XNS protocol stack but running on a custom 1 Mbit/s coaxial cable system rather than Xeroxs 2.94 Mbit/s Ethernet. AppleNet was announced early in 1983 with an introduction at the target price of $500 for plug-in AppleNet cards for the Lisa. At that time, early LAN systems were just coming to market, including Ethernet, Token Ring and this was a topic of major commercial effort at the time, dominating shows like the National Computer Conference in Anaheim in May 1983. All of the systems were jockeying for position in the market and it was at this show that Steve Jobs asked Gursharan Sidhu a seemingly innocuous question, Why has networking not caught on. Four months later, in October, AppleNet was cancelled, at the time, they announced that Apple realized that its not in the business to create a networking system. We built and used AppleNet in-house, but we realized if we had shipped it. In January, Jobs announced that they would instead be supporting IBMs Token Ring, through this period, Apple was deep in development of the Macintosh computer. During development, engineers had made the decision to use the Zilog 8530 serial controller chip instead of the lower cost and more common UART to provide serial port connections. The SCC cost about $5 more than a UART, but offered much higher speeds up to 250 kilobits per second, the SCC was chosen because it would allow multiple devices to be attached to the port. Peripherals equipped with similar SCCs could communicate using the built-in protocols and this would eliminate the need for more ports on the back of the machine, and allowed for the elimination of expansion slots for supporting more complex devices. The initial concept was known as AppleBus, envisioning a system controlled by the host Macintosh polling dumb devices in a similar to the modern Universal Serial Bus. The Macintosh team had begun work on what would become the LaserWriter. A series of memos from Bob Belleville clarified these concepts, outlining the Mac, LaserWriter, by late 1983 it was clear that IBMs Token Ring would not be ready in time for the launch of the Mac, and might miss the launch of these other products as well
3.
X.25
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X.25 is an ITU-T standard protocol suite for packet switched wide area network communication. An X.25 WAN consists of packet-switching exchange nodes as the networking hardware, X.25 is a family of protocols that was popular during the 1980s with telecommunications companies and in financial transaction systems such as automated teller machines. X.25 was originally defined by the International Telegraph and Telephone Consultative Committee in a series of drafts and finalized in a publication known as The Orange Book in 1976. While X.25 has, to an extent, been replaced by less complex protocols, especially the Internet protocol. X.25 is one of the oldest packet-switched services available and it was developed before the OSI Reference Model. The protocol suite is designed as three conceptual layers, which correspond closely to the three layers of the seven-layer OSI model. It also supports functionality not found in the OSI network layer, X.25 was developed in the ITU-T Study Group VII based upon a number of emerging data network projects. Various updates and additions were worked into the standard, eventually recorded in the ITU series of books describing the telecommunication systems. These books were published every year with different-colored covers. The X.25 specification is only part of the set of X-Series specifications on public data networks. The public data network was the name given to the international collection of X.25 providers. Their combined network had large global coverage during the 1980s and into the 1990s, publicly accessible X.25 networks were set up in most countries during the 1970s and 1980s, to lower the cost of accessing various online services. Beginning in the early 1990s, in North America, use of X.25 networks started to be replaced by Frame Relay, most systems that required X.25 now use TCP/IP, however it is possible to transport X.25 over TCP/IP when necessary. X.25 networks are still in use throughout the world, a variant called AX.25 is also used widely by amateur packet radio. Racal Paknet, now known as Widanet, is still in operation in many regions of the world, running on an X.25 protocol base. Additionally X.25 is still under heavy use in the business even though a transition to modern protocols like X.400 is without option as X.25 hardware becomes increasingly rare. As recently as March 2006, the United States National Airspace Data Interchange Network has used X.25 to interconnect remote airfields with Air Route Traffic Control Centers, france was one of the last remaining countries where commercial end-user service based on X.25 operated. Known as Minitel it was based on Videotex, itself running on X.25, as planned, service was terminated 30 June 2012
4.
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
5.
Hypertext Transfer Protocol
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The Hypertext Transfer Protocol is an application protocol for distributed, collaborative, and hypermedia information systems. HTTP is the foundation of data communication for the World Wide Web, Hypertext is structured text that uses logical links between nodes containing text. HTTP is the protocol to exchange or transfer hypertext, development of HTTP was initiated by Tim Berners-Lee at CERN in 1989. Standards development of HTTP was coordinated by the Internet Engineering Task Force and the World Wide Web Consortium, culminating in the publication of a series of Requests for Comments. The first definition of HTTP/1.1, the version of HTTP in common use, occurred in RFC2068 in 1997, although this was obsoleted by RFC2616 in 1999 and then again by RFC7230 and family in 2014. A later version, the successor HTTP/2, was standardized in 2015, HTTP functions as a request–response protocol in the client–server computing model. A web browser, for example, may be the client, the client submits an HTTP request message to the server. The server, which provides resources such as HTML files and other content, or performs other functions on behalf of the client, the response contains completion status information about the request and may also contain requested content in its message body. A web browser is an example of a user agent, other types of user agent include the indexing software used by search providers, voice browsers, mobile apps, and other software that accesses, consumes, or displays web content. HTTP is designed to permit intermediate network elements to improve or enable communications between clients and servers, high-traffic websites often benefit from web cache servers that deliver content on behalf of upstream servers to improve response time. Web browsers cache previously accessed web resources and reuse them when possible to network traffic. HTTP proxy servers at private network boundaries can facilitate communication for clients without a globally routable address, HTTP is an application layer protocol designed within the framework of the Internet protocol suite. Its definition presumes an underlying and reliable transport layer protocol, however HTTP can be adapted to use unreliable protocols such as the User Datagram Protocol, for example in HTTPU and Simple Service Discovery Protocol. HTTP resources are identified and located on the network by Uniform Resource Locators, using the Uniform Resource Identifiers schemes http, uRIs and hyperlinks in HTML documents form inter-linked hypertext documents. HTTP/1.1 is a revision of the original HTTP, in HTTP/1.0 a separate connection to the same server is made for every resource request. HTTP/1.1 can reuse a connection multiple times to download images, scripts, stylesheets, HTTP/1.1 communications therefore experience less latency as the establishment of TCP connections presents considerable overhead. Tim Berners-Lee and his team at CERN are credited with inventing the original HTTP along with HTML and the technology for a web server. Berners-Lee first proposed the WorldWideWeb project in 1989—now known as the World Wide Web, the first version of the protocol had only one method, namely GET, which would request a page from a server
6.
Frame Relay
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Frame Relay is a standardized wide area network technology that specifies the physical and data link layers of digital telecommunications channels using a packet switching methodology. Originally designed for transport across Integrated Services Digital Network infrastructure, it may be used today in the context of other network interfaces. Network providers commonly implement Frame Relay for voice and data as a technique used between local area networks over a wide area network. Each end-user gets a line to a Frame Relay node. The Frame Relay network handles the transmission over a frequently changing path transparent to all end-user extensively used WAN protocols and it is less expensive than leased lines and that is one reason for its popularity. The extreme simplicity of configuring user equipment in a Frame Relay network offers another reason for Frame Relays popularity. With the advent of Ethernet over fiber optics, MPLS, VPN and dedicated broadband services such as cable modem and DSL, however many rural areas remain lacking DSL and cable modem services. In such cases, the least expensive type of non-dial-up connection remains a 64-kbit/s Frame Relay line, thus a retail chain, for instance, may use Frame Relay for connecting rural stores into their corporate WAN. Frame Relay puts data in units called frames and leaves any necessary error-correction up to the end-points. This speeds up overall data transmission, an enterprise can select a level of service quality, prioritizing some frames and making others less important. Frame Relay can run on fractional T-1 or full T-carrier system carriers.520 Mbit/s to 622.080 Mbit/s, Frame Relay has its technical base in the older X.25 packet-switching technology, designed for transmitting data on analog voice lines. When a Frame Relay network detects an error in a frame, the end points have the responsibility for detecting and retransmitting dropped frames. Frame Relay often serves to connect local area networks with major backbones, as well as on public wide-area networks and it requires a dedicated connection during the transmission period. Frame Relay does not provide a path for voice or video transmission. However, under circumstances, voice and video transmission do use Frame Relay. Frame Relay originated as an extension of integrated services digital network and its designers aimed to enable a packet-switched network to transport over circuit-switched technology. The technology has become a stand-alone and cost-effective means of creating a WAN, Frame Relay switches create virtual circuits to connect remote LANs to a WAN. The Frame Relay network exists between a LAN border device, usually a router, and the carrier switch, the technology used by the carrier to transport data between the switches is variable and may differ among carriers
