Computer Networks and The Internet
Tags: Fundamental Date: January 9, 2021
What Is the Internet
Nuts and Bolt Description
- The Internet is a computer network that interconnects hundreds of millions of computing devices throughout the world. (850 Million end system in 2012)
- In Internet jargon PC, Linux workstations, Web Pages, E-mail, Laptop, Smartphone, Tablets, TV. Webcams, automobiles, environmental sensing devices, home electrical and security systems, and other devices that connected to the internet are called hosts or end systems.
- End Systems are connected together by a network of communication links and packet switches. Different links can transmit data at different rates, with the transmission rate of a link measured in bits/second. The two most prominent packet switch types in today’s Internet are routers (used in network core) and link-layer switches (used in access networks).
- When one end system has data to send to another end system, the sending end system segments the data and adds header bytes to each segment, known as packets, then sent through the network to the destination end system, where they are reassembled into the original data.
- The sequence of communication links and packet switches traversed by a packet from the sending end system to the receiving end system is known as a route or path.
- Packet-switched networks are in many ways similar to logistic transportation in real life.
- End systems access the Internet through Internet Service Providers (ISP). ISP are interconnected through national and international ISP
- The Transmission Control Protocol (TCP) and the Internet Protocol (IP) are two of the most important protocols on the Internet. The IP protocol specifies the format of the packets that are sent and received among routers and end systems. The Internet’s principal protocols are collectively known as TCP/IP.
- IEFT develop Internet standards, the documents called Requests for Comments (RFCs) to resolve internet network problem. There are TCP, IP, HTTP (Web), SMTP (e-mail), and other 6000 RFC
A Services Description
- Internet is an infrastructure that provides services to applications.
- The applications are said to be distributed applications since they involve multiple end systems that exchange data with each other.
- Internet applications run on end systems, they do not run in the packet switches in the network core. Although packet switches facilitate the exchange of data among end systems, they are not concerned with the application that is the source or sink of data.
- End systems attached to the Internet provide an Application Programming Interface (API) that specifies how a program running on one end system asks the Internet infrastructure to deliver data to a specific destination program running on another end system.
What is Protocol
- A protocol defines the format and the order of messages exchanged between two or more communicating entities, as well as the actions taken on the trans- mission and/or receipt of a message or other event.
- Different protocols are used to accomplish different communication tasks
The Network Edge
- End systems are also referred to as hosts because they host (that is, run) application programs
- Hosts are sometimes further divided into two categories: clients and servers.
Access Network
- Today, the two most prevalent types of broadband residential access are digital subscriber line (DSL) and cable.
- Residence typically obtains DSL Internet access from the same local telephone company.
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While DSL makes use of the telco’s existing local telephone infrastructure, cable Internet access makes use of the cable television company’s existing cable television infrastructure.
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Cable internet access requires special modems, called cable modems.
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One important characteristic of cable Internet access is that it is a shared broadcast medium.
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In particular, every packet sent by the head end travels down- stream on every link to every home and every packet sent by a home travels on the upstream channel to the head end.
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For this reason, if several users are simultaneously downloading a video file on the downstream channel, the actual rate at which each user receives its video file will be significantly lower than the aggregate cable downstream rate.
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The modern home access network technology, fiber to the home, providing an optical fiber path from CO directly to the home.
- Each home has an optical network terminator (ONT), which is connected by dedicated optical fiber to a neighborhood splitter. The splitter combines a number of homes (typically less than 100) onto a single, shared optical fiber, which connects to an optical line terminator (OLT) in the telco’s CO.
- The OLT, providing conversion between optical and electrical signals, connects to the Internet via a telco router. In the home, users connect a home router (typically a wireless router) to the ONT and access the Inter- net via this home router. In the PON architecture, all packets sent from OLT to the splitter are replicated at the splitter (similar to a cable head end).
- In locations where DSL, cable, and FTTH are not available, a satellite link can be used to connect a residence to the Inter- net at speeds of more than 1 Mbps
- On corporate and university campuses, and increasingly in home settings, a local area network (LAN) is used to connect an end system to the edge router.
- Ethernet and wireless LAN (WiFi) are the access network technology mostly used for LAN
- Wide-Area Wireless Access ( currently 3G and 4G LTE) are the same wireless infrastructure used for cellular telephony to send/receive packets through a base station that is operated by the cellular network provider.
Physical Media
- When packet traveling from source to destination, passes through a series of transmitter-receiver pairs.
- For each transmitter-receiver pair, the bit is sent by propagating electromagnetic waves or optical pulses across a physical medium.
- Physical media fall into two categories: guided media and unguided media.
- Guided Meda: fiber-optic, copper wire, coaxial cable
- Unguided Media: Wireless LAN, digital satellite channel
- Twisted-Pair Copper Wire, the least expensive and most commonly used.
- Coaxial Cable, with its own construction can achieve high data transmission rate.
- Coaxial cable can be used as a guided shared medium. Specifically, a number of end systems can be connected directly to the cable, with each of the end systems receiving whatever is sent by the other end systems.
- Fiber Optics can support up to ten or even hundred gigabits per second.
- Immune to electromagnetic interference and low signal missing up to 100 km make fiver optics preferred for long- haul guided transmission media, particularly for overseas links.
- Has higher cost between three cable
- Terrestrial Radio Channels carry signals in the electromagnetic spectrum, they require no physical wire
- Environmental considerations determine path loss and shadow fading (which decrease the signal strength as the signal travels over a distance and around/through obstructing objects), multi- path fading (due to signal reflection off of interfering objects), and interference (due to other transmissions and electromagnetic signals).
- Can be classified into three group, short distance (1 - 2 meters), local area (10 - 100 meters), wide area (1 - 10 Km).
- Satellite Radio Channels link between ground station (Earth transmitter/receiver), by receives transmissions on one frequency band, regenerates the signal using a repeater (discussed below), and transmits the signal on another frequency.
- Two types of satellites are used in communications: geostationary satellites and low-earth orbiting (LEO) satellites.
- Geostationary satellites permanently remain above the same spot on Earth. This stationary presence is achieved by placing the satellite in orbit at 36,000 km above Earth’s surface.
- LEO satellites are placed much closer to Earth and do not remain permanently above one spot on Earth. They rotate around Earth (just as the Moon does) and may communicate with each other, as well as with ground stations.