1.
Internet protocol suite
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The Internet protocol suite is the conceptual model and set of communications protocols used on the Internet and similar computer networks. It is commonly known as TCP/IP because the protocols in the suite are the Transmission Control Protocol. It is occasionally known as the Department of Defense model, because the development of the model was funded by DARPA. The Internet protocol suite provides end-to-end data communication specifying how data should be packetized, addressed, transmitted, routed and received and this functionality is organized into four abstraction layers which are used to sort all related protocols according to the scope of networking involved. Technical standards specifying the Internet protocol suite and many of its constituent protocols are maintained by the Internet Engineering Task Force, the Internet protocol suite model is a simpler model developed prior to the OSI model. The Internet protocol suite resulted from research and development conducted by the Defense Advanced Research Projects Agency in the late 1960s, after initiating the pioneering ARPANET in 1969, DARPA started work on a number of other data transmission technologies. In 1972, Robert E. Cerf credits Hubert Zimmermann and Louis Pouzin, designer of the CYCLADES network, the protocol was implemented as the Transmission Control Program, first published in 1974. Initially, the TCP managed both datagram transmissions and routing, but as the protocol grew, other researchers recommended a division of functionality into protocol layers, postel stated, “we are screwing up in our design of Internet protocols by violating the principle of layering”. Encapsulation of different mechanisms was intended to create an environment where the layers could access only what was needed from the lower layers. A monolithic design would be inflexible and lead to scalability issues, the Transmission Control Program was split into two distinct protocols, the Transmission Control Protocol and the Internet Protocol. The new suite replaced all protocols used previously and this design is known as the end-to-end principle. Using this design, it possible to connect almost any network to the ARPANET, irrespective of the local characteristics. One popular expression is that TCP/IP, the product of Cerf and Kahns work. A computer called a router is provided with an interface to each network and it forwards packets back and forth between them. Originally a router was called gateway, but the term was changed to avoid confusion with other types of gateways, from 1973 to 1974, Cerfs networking research group at Stanford worked out details of the idea, resulting in the first TCP specification. A significant technical influence was the early networking work at Xerox PARC, DARPA then contracted with BBN Technologies, Stanford University, and the University College London to develop operational versions of the protocol on different hardware platforms. Four versions were developed, TCP v1, TCP v2, TCP v3 and IP v3, the last protocol is still in use today. In 1975, a two-network TCP/IP communications test was performed between Stanford and University College London, in November,1977, a three-network TCP/IP test was conducted between sites in the US, the UK, and Norway
2.
Border Gateway Protocol
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Border Gateway Protocol is a standardized exterior gateway protocol designed to exchange routing and reachability information among autonomous systems on the Internet. The protocol is often classified as a path vector protocol but is also classed as a distance-vector routing protocol. The Border Gateway Protocol makes routing decisions based on paths, network policies, BGP may be used for routing within an autonomous system. In this application it is referred to as Interior Border Gateway Protocol, Internal BGP, in contrast, the Internet application of the protocol may be referred to as Exterior Border Gateway Protocol, External BGP, or eBGP. The current version of BGP is version 4, which was published as RFC4271 in 2006, RFC4271 corrected errors, clarified ambiguities, and updated the specification with common industry practices. The major enhancement was the support for Classless Inter-Domain Routing and use of route aggregation to decrease the size of routing tables, bGP4 has been in use on the Internet since 1994. BGP4 is standard for Internet routing, required of most Internet service providers to establish routing between one another, very large private IP networks use BGP internally. An example is the joining of a number of large Open Shortest Path First networks, another reason to use BGP is multihoming a network for better redundancy, either to multiple access points of a single ISP or to multiple ISPs. BGP neighbors, called peers, are established by manual configuration between routers to create a TCP session on port 179, a BGP speaker sends 19-byte keep-alive messages every 60 seconds to maintain the connection. Among routing protocols, BGP is unique in using TCP as its transport protocol, when BGP runs between two peers in the same autonomous system, it is referred to as Internal BGP. When it runs between different autonomous systems, it is called External BGP, other deployment topologies are also possible, such as running eBGP peering inside a VPN tunnel, allowing two remote sites to exchange routing information in a secure and isolated manner. The main difference between iBGP and eBGP peering is in the way routes that were received from one peer are propagated to other peers, for instance, new routes learned from an eBGP peer are typically redistributed to all iBGP peers as well as all other eBGP peers. However, if new routes are learned on an iBGP peering and these route-propagation rules effectively require that all iBGP peers inside an AS are interconnected in a full mesh. How routes are propagated can be controlled in detail via the route-maps mechanism and this mechanism consists of a set of rules. Each rule describes, for routes matching some given criteria, what action should be taken, the action could be to drop the route, or it could be to modify some attributes of the route before inserting it in the routing table. During the peering handshake, when OPEN messages are exchanged, BGP speakers can negotiate optional capabilities of the session, including multiprotocol extensions and various recovery modes. If the multiprotocol extensions to BGP are negotiated at the time of creation and these families include the IPv4, IPv6, IPv4/IPv6 Virtual Private Networks and multicast BGP. Increasingly, BGP is used as a generalized signaling protocol to carry information about routes that may not be part of the global Internet, such as VPNs
3.
Dynamic Host Configuration Protocol
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The Dynamic Host Configuration Protocol is a standardized network protocol used on Internet Protocol networks. The DHCP is controlled by a DHCP server that dynamically distributes network configuration parameters, such as IP addresses, a router or a residential gateway can be enabled to act as a DHCP server. A DHCP server enables computers to request IP addresses and networking parameters automatically, in the absence of a DHCP server, each computer or other device on the network needs to be statically assigned to an IP address. TCP/IP defines how devices on one network communicate with devices on another network, a DHCP server can manage TCP/IP settings for devices on a network, by automatically or dynamically assigning Internet Protocol addresses to the devices. As of 2011, networks ranging in size from home networks to large campus networks, most residential network routers receive a globally unique IP address within the provider network. Within a local network, a DHCP server assigns a local IP address to each device connected to the network, the DHCP operates based on the client–server model. When a computer or other device connects to a network, the DHCP client software sends a broadcast query requesting the necessary information, any DHCP server on the network may service the request. The DHCP server manages a pool of IP addresses and information about client configuration parameters such as default gateway, domain name, the name servers, a client typically queries for this information immediately after booting, and periodically thereafter before the expiration of the information. When a DHCP client refreshes an assignment, it requests the same parameter values. On large networks that consist of links, a single DHCP server may service the entire network when aided by DHCP relay agents located on the interconnecting routers. Such agents relay messages between DHCP clients and DHCP servers located on different subnets, the request-and-grant process uses a lease concept with a controllable time period, allowing the DHCP server to reclaim IP addresses that are not renewed. Automatic allocation The DHCP server permanently assigns an IP address to a client from the range defined by the administrator. This is like dynamic allocation, but the DHCP server keeps a table of past IP address assignments, manual allocation The DHCP server issues a private IP address dependent upon each clients MAC address, based on a predefined mapping by the administrator. If no match for the clients MAC address is found, the server may or may not optionally fall back to either Dynamic or Automatic allocation, DHCP is used for Internet Protocol version 4, as well as for IPv6. While both versions serve the purpose, the details of the protocol for IPv4 and IPv6 differ sufficiently that they may be considered separate protocols. For the IPv6 operation, devices may alternatively use stateless address autoconfiguration, IPv6 hosts may also use link-local addressing to achieve operations restricted to the local network link. In 1984, the Reverse Address Resolution Protocol, defined in RFC903, was introduced to allow simple devices such as diskless workstations to dynamically obtain a suitable IP address. However, because it acted at the link layer it made implementation difficult on many server platforms
4.
Domain Name System
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The Domain Name System is a hierarchical decentralized naming system for computers, services, or other resources connected to the Internet or a private network. It associates various information with domain names assigned to each of the participating entities, by providing a worldwide, distributed directory service, the Domain Name System is an essential component of the functionality of the Internet, that has been in use since 1985. The Domain Name System delegates the responsibility of assigning domain names, Network administrators may delegate authority over sub-domains of their allocated name space to other name servers. This mechanism provides distributed and fault tolerant service and was designed to avoid a large central database. The Domain Name System also specifies the technical functionality of the service that is at its core. It defines the DNS protocol, a specification of the data structures and data communication exchanges used in the DNS. Historically, other directory services preceding DNS were not scalable to large or global directories as they were based on text files. The Internet maintains two principal namespaces, the domain name hierarchy and the Internet Protocol address spaces, the Domain Name System maintains the domain name hierarchy and provides translation services between it and the address spaces. Internet name servers and a communication protocol implement the Domain Name System, a DNS name server is a server that stores the DNS records for a domain, a DNS name server responds with answers to queries against its database. The most common types of stored in the DNS database are for Start of Authority, IP addresses, SMTP mail exchangers, name servers, pointers for reverse DNS lookups. As a general purpose database, the DNS has also used in combating unsolicited email by storing a real-time blackhole list. The DNS database is stored in a structured zone file. An often-used analogy to explain the Domain Name System is that it serves as the book for the Internet by translating human-friendly computer hostnames into IP addresses. For example, the name www. example. com translates to the addresses 93.184.216.119 and 2606,2800,220, 6d, 26bf,1447,1097. Unlike a phone book, DNS can be updated, allowing a services location on the network to change without affecting the end users. Users take advantage of this when they use meaningful Uniform Resource Locators, an important and ubiquitous function of DNS is its central role in distributed Internet services such as cloud services and content delivery networks. When a user accesses a distributed Internet service using a URL and this process of using the DNS to assign proximal servers to users is key to providing faster and more reliable responses on the Internet and is widely used by most major Internet services. The DNS reflects the structure of administrative responsibility in the Internet, each subdomain is a zone of administrative autonomy delegated to a manager
5.
File Transfer Protocol
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The File Transfer Protocol is a standard network protocol used for the transfer of computer files from a server to a client using the Client–server model on a computer network. FTP is built on a model architecture and uses separate control. FTP users may authenticate themselves with a clear-text sign-in protocol, normally in the form of a username and password, for secure transmission that protects the username and password, and encrypts the content, FTP is often secured with SSL/TLS. SSH File Transfer Protocol is sometimes used instead, but is technologically different. The original specification for the File Transfer Protocol was written by Abhay Bhushan, until 1980, FTP ran on NCP, the predecessor of TCP/IP. The protocol was replaced by a TCP/IP version, RFC765 and RFC959. FTP may run in active or passive mode, which determines how the connection is established. In both cases, the client creates a TCP control connection from a random, usually an unprivileged, in active mode, the client starts listening for incoming data connections from the server on port M. It sends the FTP command PORT M to inform the server on which port it is listening, the server then initiates a data channel to the client from its port 20, the FTP server data port. In situations where the client is behind a firewall and unable to accept incoming TCP connections, both modes were updated in September 1998 to support IPv6. Further changes were introduced to the mode at that time. The server responds over the connection with three-digit status codes in ASCII with an optional text message. For example,200 means that the last command was successful, the numbers represent the code for the response and the optional text represents a human-readable explanation or request. An ongoing transfer of data over the data connection can be aborted using an interrupt message sent over the control connection. While transferring data over the network, four data representations can be used, ASCII mode, Data is converted, if needed, from the sending hosts character representation to 8-bit ASCII before transmission, and to the receiving hosts character representation. As a consequence, this mode is inappropriate for files that contain other than plain text. Image mode, The sending machine sends each file byte by byte, EBCDIC mode, Used for plain text between hosts using the EBCDIC character set. Local mode, Allows two computers with identical setups to send data in a format without the need to convert it to ASCII
6.
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
7.
Media Gateway Control Protocol
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The Media Gateway Control Protocol is a signaling and call control communications protocol used in voice over IP telecommunication systems. It implements the media gateway control protocol architecture for controlling media gateways on Internet Protocol networks connected to the switched telephone network. The protocol is a successor to the Simple Gateway Control Protocol, which was developed by Bellcore and Cisco, the endpoints are low-intelligence devices, mostly executing control commands and providing result indications in response. The protocol represents a decomposition of other VoIP models, such as H.323, MGCP is a text-based protocol consisting of commands and responses. It uses the Session Description Protocol for specifying and negotiating the media streams to be transmitted in a call session, the media gateway control protocol architecture and its methodologies and programming interfaces are described in RFC2805. MGCP is a protocol that allows a call control device such as a Call Agent to take control of a specific port on a media gateway. In MGCP context media gateway controller is referred to as call agent and this has the advantage of centralized gateway administration and provides for largely scalable IP Telephony solutions. MGCP assumes a call control architecture where there is limited intelligence at the edge, the MGCP assumes that Call Agents, will synchronize with each other to send coherent commands and responses to the gateways under their control. The Call Agent uses MGCP to tell the media gateway which events should be reported to the Call Agent, how endpoints should be inter-connected, MGCP also allows the Call Agent to audit the current state of endpoints on a media gateway. The media gateway uses MGCP to report events, such as off-hook or dialed digits, while any signaling gateway is usually on the same physical switch as a media gateway, there is no such need. The Call Agent does not use MGCP to control the Signaling Gateway, rather, typically, a media gateway is configured with a list of Call Agents from which it may accept programming. In principle, event notifications may be sent to different Call Agents for each endpoint on the gateway, in the event of such a failure it is the backup Call Agents responsibility to reprogram the MG so that the gateway comes under the control of the backup Call Agent. Care is needed in cases, two Call Agents may know that they have lost contact with one another, but this does not guarantee that they are not both attempting to control the same gateway. The ability to audit the gateway to determine which Call Agent is currently controlling can be used to such conflicts. MGCP assumes that the multiple Call Agents will maintain knowledge of state among themselves or rebuild it if necessary. Its failover features take into account both planned and unplanned outages, MGCP recognizes three essential elements of communication, the media gateway controller, the media gateway endpoint, and connections between these entities. A media gateway may host multiple endpoints and each endpoint should be able to engage in multiple connections, multiple connections on the endpoints support calling features such as call waiting and three-way calling. MGCP is a text-based protocol using a command and response model, commands and responses are encoded in messages that are structured and formatted with the whitespace characters space, horizontal tab, carriage return, and linefeed, and the colon and the full stop
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