Transcript Chapter 4
Chapter 4 After completion of this chapter, you should be able to: Explain “what is the Internet? And how we connect to the Internet using an ISP. Explain how information is sent across the Internet through an ISP Internet???? The Internet is a worldwide collection of computer networks, cooperating with each other to exchange information using common standards. Through telephone wires, fiber optic cables, wireless transmissions and satellite links, Internet users can exchange information in a variety of forms. The Internet is a network of networks that connects users in every country in the world. There are currently over one billion Internet users worldwide. Internet Service Providers (ISPs) An ISP is a company that provides the connections and support to access the Internet. It also provide additional services such as Email and web hosting. No one gets on the Internet without a host computer, and no one gets on the Internet without going through an ISP. ISPs range in size from small to very large and differ in terms of the area they service. ISPs also differ in the types of connection technologies and speeds they offer. Examples of well known ISPs include AOL, EarthLink, and Roadrunner. The ISPs Relationship with the internet Individual computers and local networks connect to the ISP at a Point of Presence (POP). A POP is the connection point between the ISP's network and the particular geographical region that the POP is servicing. Note: POP-Point of interconnection between the communication facilities provided by the telephone company and the main distribution facility of the building An ISP may have many POPs depending on its size & the area it services. Within an ISP, a network of high-speed routers and switches move data between the various POPs. Multiple links interconnect the POPs to provide alternate routes for the data should one link fail or become overloaded with traffic and congested. ISPs connect to other ISPs in order to send information beyond the boundaries of their own network. The Internet is made up of very high-speed data links that interconnect ISP POPs and ISPs to each other. These interconnections are part of the very large, high capacity network known as the Internet Backbone. Connecting to the ISP at the POP provides users with access to the ISP's services and the Internet. Options for connecting to the ISP ISP provide a variety of ways to connect to the internet, depending on location & desired connection speed. More choices for ISPs in city rather than in rural area. For example cable internet access only available at metropolitan area while remote area may only have access via satellite or mobile broadband. Internet access require a network access device. Type of connection ISP LEVELs of service Various services available depending on the ISP and the connection technology such as Virus Scanning-Scan for malicious code both on files that have been uploaded from end user and those arriving. Content Filtering-Used to block objectionable and/or offensive web sites. Video on demand-Real-time downloading also known as streaming video. Connection speed-Download speed vary from 56kbps to 1.5Mbps or higher depend on technologies such as DSL & cable modem. Email accounts-ISPs generally provide multiple user emails on one account. Email addresses can be distributed among individuals or used to separate business mail from personal mail. Personal Homepage-Usually both the size of the web space & the traffic generated are limited. Design & maintain by individual author. Web Hosting-Offered by ISP to the organization. Always come with design & maintenance services. File Storage-Online storage with 24/7 access. Size range from a few megabytes to terabytes & include password protected. DATA TRANSFER Data transfer process refer to downloaded and uploaded. Downloading refers to information coming from the Internet to your computer. Uploading indicates the reverse path, from your computer to the Internet. When the download transfer rate is different from the upload transfer rate, it is called asymmetric. When the transfer rate is the same in both directions, it is called symmetric Asymmetric: Most commonly used for the home. Download speeds are faster than upload speeds. Necessary for users that download significantly more than upload. Most Internet users, especially those who use graphics or multimedia intensive web data, need lots of download bandwidth Symmetric: Most commonly used for business or individuals hosting servers on the Internet. Used when necessary to upload large amounts of traffic such as intensive graphics, multimedia, or video. It can carry large amounts of data in both directions at equal rates. Importance of the internet protocol(IP) The IP is one of a group of protocols that are collectively referred to as TCP/IP (Transmission Control Protocol / Internet Protocol). The Internet Protocol (IP) uses packets to carry data. Each IP packet must contain a valid source and destination IP address. IP defines the structure of the source and destination IP addresses. All protocols that operate on the Internet, including IP, are defined in numbered standards documents called RFCs (Request for Comments). An IP packet has a header at the beginning which contains the source and destination IP addresses. It also contains control information that describes the packet to network devices, such as routers, it passes through and also helps to control its behaviour on the network. IP addresses must be unique on the Internet. ISPs obtain blocks of IP addresses from a local, national or regional Internet registry (RIR). It is the responsibly of the ISPs to manage these addresses and assign them to end users. Computers in homes, small businesses and other organizations obtain their IP configuration from their ISP. Typically, this configuration is obtained automatically when the user connects to the ISP for Internet access. HOW ISPs HANDLE PACKETS Before being sent on the Internet, messages are divided into packets. IP packet size is between 64 to 1500 bytes for Ethernet networks, and contains mostly user data. Downloading a single 1 MB song would require over 600 packets of 1500 bytes. Each individual packet must have a source and destination IP address. When a packet is sent across the Internet, the ISP determines whether the packet is destined for a local service located on the ISP network, or a remote service located on a different network. Every ISP has a control facility for their network, known as the Network Operations Center (NOC). The NOC usually controls traffic flow and houses services such as email and web hosting. The NOC may be located at one of the POPs or at a completely separate facility within the ISP network. Packets looking for local services are usually forwarded to the NOC and never leave the ISP network. Routers in each of the ISP POPs use the destination address of the IP packets to choose the best path through the Internet. The packets you send to the ISP POP are forwarded by routers through the ISP's network and then through the networks of other ISPs. They pass from router to router until they reach their final destination. FORWARDING PACKETS ACROSS THE INTERNET The ping utility tests end-to-end connectivity between source and destination. It measures the time that it takes test packets to make a round trip from the source to the destination and whether the transmission is successful. However, if the packet does not reach the destination, or if delays are encountered along the way, there is no way to determine where the problem is located. The traceroute utility traces the route from source to destination. Each router through which the packets travel is referred to as a hop. Traceroute displays each hop along the way and the time it takes for each one If a problem occurs, the display of the time and the route that the packet travelled can help to determine where the packet was lost or delayed. The traceroute utility is called tracert in the Windows environment.