Internet Protocol
The Internet Protocol (IP) 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, as the primary protocol in the Internet layer of the Internet protocol suite, 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. It also defines addressing methods that are used to label the datagram with source and destination information.
Historically, IP was the connectionless datagram service in the original Transmission Control Program introduced by Vint Cerf and Bob Kahn in 1974; the other being the connection-oriented Transmission Control Protocol (TCP). The Internet protocol suite is therefore often referred to as TCP/IP.
The first major version of IP, Internet Protocol Version 4 (IPv4), is the dominant protocol of the Internet. Its successor is Internet Protocol Version 6 (IPv6).
Network packet
A network packet is a formatted unit of data carried by a packet-switched network. Computer communications links that do not support packets, such as traditional point-to-point telecommunications links, simply transmit data as a bit stream. When data is formatted into packets, the bandwidth of the communication medium can be better shared among users than if the network were circuit switched.
A packet consists of two kinds of data: control information and user data (also known as payload). The control information provides data the network needs to deliver the user data, for example: source and destination network addresses, error detection codes, and sequencing information. Typically, control information is found in packet headers and trailers, with payload data in between.
Routing
Routing is the process of selecting best paths in a network. In the past, the term routing was also used to mean forwarding network traffic among networks. However this latter function is much better described as simply forwarding. Routing is performed for many kinds of networks, including the telephone network (circuit switching), electronic data networks (such as the Internet), and transportation networks. This article is concerned primarily with routing in electronic data networks using packet switching technology.
In packet switching networks, routing directs packet forwarding (the transit of logically addressed network packets from their source toward their ultimate destination) through intermediate nodes. Intermediate nodes are typically network hardware devices such as routers, bridges, gateways, firewalls, or switches. General-purpose computers can also forward packets and perform routing, though they are not specialized hardware and may suffer from limited performance. The routing process usually directs forwarding on the basis of routing tables which maintain a record of the routes to various network destinations. Thus, constructing routing tables, which are held in the router's memory, is very important for efficient routing. Most routing algorithms use only one network path at a time. Multipath routing techniques enable the use of multiple alternative paths.
In case of overlapping/equal routes, the following elements are considered in order to decide which routes get installed into the routing table (sorted by priority):
Prefix-Length: where longer subnet masks are preferred (independent of whether it is within a routing protocol or over different routing protocol)
Metric: where a lower metric/cost is preferred (only valid within one and the same routing protocol)
Administrative distance: where a route learned from a more reliable routing protocol is preferred (only valid between different routing protocols)
Routing, in a more narrow sense of the term, is often contrasted with bridging in its assumption that network addresses are structured and that similar addresses imply proximity within the network. Structured addresses allow a single routing table entry to represent the route to a group of devices. In large networks, structured addressing (routing, in the narrow sense) outperforms unstructured addressing (bridging). Routing has become the dominant form of addressing on the Internet. Bridging is still widely used within localized environments.
Public switched telephone network
The public switched telephone network (PSTN) is the aggregate of the world's circuit-switched telephone networks that are operated by national, regional, or local telephony operators, providing infrastructure and services for public telecommunication. The PSTN consists of telephone lines, fiber optic cables, microwave transmission links, cellular networks, communications satellites, and undersea telephone cables, all interconnected by switching centers, thus allowing any telephone in the world to communicate with any other. Originally a network of fixed-line analog telephone systems, the PSTN is now almost entirely digital in its core network and includes mobile and other networks, as well as fixed telephones.
The technical operation of the PSTN adheres to the standards created by the ITU-T. These standards allow different networks in different countries to interconnect seamlessly. The E.163 and E.164 standards provide a single global address space for telephone numbers. The combination of the interconnected networks and the single numbering plan allow telephones around the world to dial each other.
Packet forwarding is the relaying of packets from one network segment to another by nodes in a computer network.
A unicast forwarding pattern, typical of many networking technologies including the overwhelming majority of Internet traffic
A multicast forwarding pattern, typical of PIM
A broadcast forwarding pattern, typical of bridged Ethernet
The Network Layer of the OSI Layer is responsible for Packet Forwarding. The simplest forwarding model—?unicasting—?involves a packet being relayed from link to link along a chain leading from the packet's source to its destination. However, other forwarding strategies are commonly used. Broadcasting requires a packet to be duplicated and copies sent on multiple links with the goal of delivering a copy to every device on the network. In practice, broadcast packets are not forwarded everywhere on a network, but only to devices within a broadcast domain, making broadcast a relative term. Less common than broadcasting, but perhaps of greater utility and theoretical significance, is multicasting, where a packet is selectively duplicated and copies delivered to each of a set of recipients.
Networking technologies tend to naturally support certain forwarding models. For example, fiber optics and copper cables run directly from one machine to another to form a natural unicast media – data transmitted at one end is received by only one machine at the other end. However, as illustrated in the diagrams, nodes can forward packets to create multicast or broadcast distributions from naturally unicast media. Likewise, traditional Ethernet (10BASE5 and 10BASE2, but not the more modern 10BASE-T) are natural broadcast media – all the nodes are attached to a single long cable and a packet transmitted by one device is seen by every other device attached to the cable. Ethernet nodes implement unicast by ignoring packets not directly addressed to them. A wireless network is naturally multicast – all devices within a reception radius of a transmitter can receive its packets. Wireless nodes ignore packets addressed to other devices, but require forwarding to reach nodes outside their reception radius.
At nodes where multiple outgoing links are available, the choice of which, all, or any to use for forwarding a given packet requires a decision making process that, while simple in concept, is sometimes bewilderingly complex. Since a forwarding decision must be made for every packet handled by a node, the total time required for this can become a major limiting factor in overall network performance. Much of the design effort of high-speed routers and switches has been focused on making rapid forwarding decisions for large numbers of packets.
The forwarding decision is generally made using one of two processes: routing, which uses information encoded in a device's address to infer its location on the network, or bridging, which makes no assumptions about where addresses are located and depends heavily on broadcasting to locate unknown addresses. The heavy overhead of broadcasting has led to the dominance of routing in large networks, particularly the Internet; bridging is largely relegated to small networks where the overhead of broadcasting is tolerable. However, since large networks are usually composed of many smaller networks linked together, it would be inaccurate to state that bridging has no use on the Internet; rather, its use is localized.
A network can use one of two different methods to forward packets: store-and-forward or cut through
Router (computing)
A router (/'ru?t?r/ or (chiefly North American and Australian) /'ra?-/ is a networking device that forwards data packets between computer networks. A router is connected to two or more data lines from different networks (as opposed to a network switch, which connects data lines from one single network). When a data packet comes in one of the lines, the router reads the address information in the packet to determine its ultimate destination. Then, using information in its routing table or routing policy, it directs the packet to the next network on its journey. This creates an overlay internetwork. Routers perform the "traffic directing" functions on the Internet. A data packet is typically forwarded from one router to another through the networks that constitute the internetwork until it reaches its destination node.
The most familiar type of routers are home and small office routers that simply pass data, such as web pages, email, IM, and videos between the home computers and the Internet. An example of a router would be the owner's cable or DSL router, which connects to the Internet through an ISP. More sophisticated routers, such as enterprise routers, connect large business or ISP networks up to the powerful core routers that forward data at high speed along the optical fiber lines of the Internet backbone. Though routers are typically dedicated hardware devices, use of software-based routers has grown increasingly common.
Bridging (networking)
Network bridging is the action taken by network equipment to create an aggregate network from either two or more communication networks, or two or more network segments.If one or more segments of the bridged network are wireless, it is known as wireless bridging. Bridging is distinct from routing, which allows multiple different networks to communicate independently while remaining separate.
A network bridge is a network device that connects multiple network segments. In the OSI model, bridging is performed in the first two layers, below the network layer.
There are four types of network bridging technologies: simple bridging, multiport bridging, learning or transparent bridging, and source route bridging
Network address
A network address is an identifier for a node or network interface of a telecommunications network.
Network addresses are often designed to be unique across the network, although some networks allow for relative or local addresses that may not be unique.
More than one type of network address may be used in any one network.
In some cases terminal nodes may have more than one network address, for example, each link interface may be uniquely identified. In addition, non terminal nodes are often assigned network addresses. Further, because protocols are frequently layered, more than one protocol's network address can occur in any particular network interface or node.
Internet protocol suite
Application layer
BGP,DHCP,DNS, FTP, HTTP ,IMAP, LDAP, MGCP, NNTP,NTP, POP, ONC/RPC, RTP, RTS,RIP, SIP,SMT, SNMP,SSH, Telnet, TLS/SSL XMPP
Transport layer
TCP ,UDP , DCCP, SCTP , RSVP
Internet layer
IP IPv4, IPv6, ICMPICMPv, OSPF, ECN , IGMP ,IPsec
Link layer
ARP NDP
Tunnels
L2TP, PPP, MAC , Ethernet , DSL, ISDN, FDDI
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