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INTERNET SERVICES INTERNET DEVELOPMENT The history of the Internet began with the ARPANET (Advanced Research Projects Agency Network) and connected mainframe computers on dedicated connections. The second stage involved adding desktop PCs which connected through telephone wires. The third stage was adding wireless connections to laptop computers. And currently the Internet is evolving to allow mobile phone Internet connectivity ubiquitously using cellular networks. An Internet service provider (ISP, also called Internet access provider or IAP) is a company that offers its customers access to the Internet. The ISP connects to its customers using a data transmission technology appropriate for delivering Internet Protocol datagrams, such as dial-up, DSL, cable modem or dedicated high- speed interconnects. ISPs may provide Internet e-mail accounts to users which allow them to communicate with one another by sending and receiving electronic messages through their ISPs' servers. (As part of their e- mail service, ISPs usually offer the user an e-mail client software package, developed either internally or through an outside contract arrangement.) ISPs may provide other services such as remotely storing data files on behalf of their customers, as well as other services unique to each particular ISP. THE DOMAIN NAME SYSTEM (DNS) is a hierarchical naming system for computers, services, or any resource participating in the Internet. It associates various information with domain names assigned to such participants. Most importantly, it translates domain names meaningful to humans into the numerical (binary) identifiers associated with networking equipment for the purpose of locating and addressing these devices world-wide. An often used analogy to explain the Domain Name System is that it serves as the "phone book" for the Internet by translating human-friendly computer hostnames into IP addresses. For example, http://en.wikipedia.org/wiki/Example.com translates to 126.96.36.199. The Domain Name System makes it possible to assign domain names to groups of Internet users in a meaningful way, independent of each user's physical location. Because of this, World-Wide Web (WWW) hyperlinks and Internet contact information can remain consistent and constant even if the current Internet routing arrangements change or the participant uses a mobile device. Internet domain names are easier to remember than IP addresses such as 188.8.131.52(IPv4) or 2001:db8:1f70::999:de8:7648:6e8 (IPv6). People take advantage of this when they recite meaningful URLs and e-mail addresses without having to know how the machine will actually locate them. The Domain Name System distributes the responsibility of assigning domain names and mapping those names to IP addresses by designating authoritative name servers for each domain. Authoritative name servers are assigned to be responsible for their particular domains, and in turn can assign other authoritative name servers for their sub-domains. This mechanism has made the DNS distributed, fault tolerant, and helped avoid the need for a single central register to be continually consulted and updated. In general, the Domain Name System also stores other types of information, such as the list of mail servers that accept email for a given Internet domain. By providing a world-wide, distributed keyword-based redirection service, the Domain Name System is an essential component of the functionality of the Internet. Other identifiers such as RFID tags, UPC codes, International characters in email addresses and host names, and a variety of other identifiers could all potentially utilize DNS . The Domain Name System also defines the technical underpinnings of the functionality of this database service. For this purpose it defines the DNS protocol, a detailed specification of the data structures and communication exchanges used in DNS, as part of the Internet Protocol Suite (TCP/IP). The context of the DNS within the Internet protocols may be seen in the following diagram. The DNS protocol was developed and defined in the early 1980s and published by the Internet Engineering Task Force (cf. History) LEVELS OF CONNECTIVITY There are several levels of Internet connectivity. For our purposes, I am just going to call these levels "Level One," through "Level Six." Before I talk about the six levels of connectivity, experience shows that I have to say the following to keep myself from being overrun with e-mail: the "six level approach" to Internet connectivity is a very simplified view of the different ways that you can access the Internet. This is just my way of describing the levels, you will not hear anyone else describing connectivity with these levels. This oversimplification is on purpose. Please recognize that I have taken some editorial liberties in this lesson to make the lesson easier to understand for the new users (a.k.a. "newbies"). Level One Internet access ("remote modem access") is access through a dial-up terminal connection. Through the use of a modem, you access a "host" computer, usually a UNIX-based computer that displays text and operates with commands you type in on individual lines. Your your home computer acts like it is a terminal on a 'mainframe'. You may type the commands on your own computer, but it is the host that carries out your commands. Level One connectivity once was the most "popular" (in the sense that more people had Level One connectivity than any other level) and the most misunderstood level of connectivity. To begin with, Level One connectivity limits you to using the programs (also known as "clients") that are running on the host. If, for example, you hear of this hot new client called "Mosaic" and you want to try it out, if your host does not have a Mosaic client on it you are out of luck! Putting a copy of the Mosaic client software on your own computer won't do ANYTHING for you -- remember that the only programs that you can use when you have Level One connectivity are the programs that the host has! Also, with Level One connectivity you must always remember that everything you are doing is through the host, NOT through your own computer. If you download a file from somewhere (like we did last Friday with the GET command) that file will go to the host, NOT to your own personal computer. You'll need to download the file one more time -- this time from the host to your computer -- if you want the file to be on YOUR computer Level Two connectivity ("access through a gateway") is access to the Internet from a network that really isn't "on" the Internet. This is becoming less and less common as network providers are adopting the Internet standard. Services that used this model have been 'Compuserve', 'Prodigy', and 'AOL'. Picture two circles that touch each other at only one point. One of the circles is the Internet, the other circle is a non-Internet network, and the point where the two networks touch is called a gateway. The gateway allows the two networks to "talk" to each other, but users of the non-Internet network are limited in their ability to fully access all of the tools of the Internet. For example, AOL is, in effect, its own network. It has a great number of different programs that its subscribers can use, but ALL of these programs only run on the AOL network. Gradually, AOL has been shifting to adopt the Internet standard, and has essentially become an Internet Service Provider in addition to its own services, providing you with many of the features of the Internet. Both Level One and Two are older means of connecting. They are still in use, but the primary means of connecting for home and small business users is Level Three. Level Three connectivity can also be called "On-Demand Direct Connectivity." Since you probably aren't going to spend twenty-four hours a day on the Internet, there are many service providers that will let you connect to the Internet whenever you want using a high speed modem and something called "Point to Point Protocol (PPP)" or "Serial Line Internet Protocol (SLIP)" connection. Nearly all Internet service providers such as Sovernet or Togethernet, or I- 100, or ...... use this type of service, and I suspect most of you do too. There are two cool things about PPP and SLIP connections. First, because you aren't connected to the Internet all day long, (using up your phone line) it doesn't cost as much as regular Level Three connectivity (you can find sites that will only charge you about $15 or $20 US per month for a PPP or SLIP connection). The second cool thing about PPP and SLIP connections is that the client software is stored on YOUR computer. Want to play with Netscape or Explorer? Load it onto your computer and play with it. The majority of local Vermont Internet service providers provide PPP or SLIP Services. These providers include SoVerNet and Together Networks; I-100, Plainfield By Pass, Kingdom.Com and PowerShift. These companies allow users to dial into their systems and then provide access to the Internet network. The first three levels mentioned above all use conventional modems to access the network. We discussed how these worked in the last lesson. Modems have speeds up to 56K or kilobits per second, or 56 thousand bits (Os and 1s) passing through the line per second. But this is a big limitation for some users who need or want a lot of data transferred quickly. Another limitation - one usually doesn't receive full 56K access due to line 'noise' - static or other interruptions that limit the data through-put. This is particularly common in rural areas. Digital switches and fiber transmission improves line quality, but this requires the replacement of all the wire to your building, and that won't happen overnight. Better performance is possible through higher levels of service and digital transfers. Level Four connectivity is in a way a hybrid of Level Three and Level Four. Three major types of high speed connectivity have emerged in the last few years and are increasingly available across the country. ISDN (Integrated Services Digital Network), DSL (Digital Subscriber Line) and Cable. ISDN is like a modem service that involves dial up, but it uses a high quality line capable of higher performance data transfer up to 256KB/second and higher. Generally this service is offered by the local phone company. It is falling out of favor due to cost and being replaced by digital services described below. Improvements in electronic hardware have allowed conventional phone lines to accept data transfers at high rates using new technology called "DSL" or Digital Subscriber Line. At 1.5 megabytes per second, the data transfer rates are almost fifty times faster than the fastest modems. All this for about $50.00 per month. Two 'flavors' of DSL are available, ADSL and SDSL. Of the two, SDSL is the more powerful performer and businesses generally choose it over ADSL. However, any DSL service is only available in larger metropolitan areas so far, as it requires that the phone company or other ISPs to have installed special hardware in their switch offices. Cable companies are offering high performance services through 'modems' that link through the conventional cable lines. These services require that you have cable service, and many parts of Vermont do not have this service. Data transfer rates and costs are similar to DSL services. Level Five connectivity ("Direct Internet Access") is the highest, and most expensive, level of connectivity there is. With Level Five connectivity, you are directly wired into the Internet using high- speed lines, and you are "on-line" twenty-four hours a day, seven days a week. Level Five connectivity is great if you are a mainframe, or a business with a number of users, but is not too advantageous if you are a sole user with a beat-up PC. Besides, Level Five Internet access is so incredibly expensive (1) (the University of Alabama pays $29,000.00 (US) each and every year as of 1995) just to connect to the Internet, and that doesn't include the software, hardware, facility, and staff expenses. Until recently, Level Five connectivity was limited to large corporations and Universities. Now, even small businesses are using Level Five services. Finally, there is another category of connectivity that uses satellites and wireless methods, and these provide the most promise for those in rural areas that need higher capacity. No land infrastructure is needed except the receiver. Wireless connections are like cell phones. You have to have a wireless modem and a laptop, or a hand-held computer that is wireless-capable, and you need a subscription to a service. This provides mobility, and for those folks really out of distance from a phone line, connection possibilities. Data transmission rates are not particularly high performance - the benefits are in the mobility. However, satellites offer high-speed data transmission. Today, services such as Web PC offer performance of up to 400kb/sec download via a dish like the small satellite TV dishes. The downside is that there has to be a land line or conventional phone line to send data requests to the Internet. So, there's some extra cost. Soon there will be full two way satellite service, which will really assist users in remote areas, with poor quality phone lines and no high speed services. This will initially be offered by Hughes Network Systems and Pegasus through the Direc PC service. LEVEL DESCRIPTION COMMENTS Commands executed by host All programs on host Can only run client software already on the host All files on host unless you download to your computer Remote modem One Example: Dial into a host computer access directly. (Dial in to UVM - Vermont Automated Libraries (VALS) has this kind of service) Speed: Access speed is determined by modem speed, quality of phone line.Up to 56K/second. Mix of Internet access and access to a private network. Access through Speed: Access speed is determined by Two a Gateway modem speed, quality of phone line. Up to 56K/second. Examples: AOL, Prodigy, CompuServe Most popular today. Connect when you want through a modem to an Internet Service Provider. Three PPP/SLIP (ISP) Client software runs on YOUR computer! Use Internet Explorer, Netscape Navigator, etc. Speed: Access speed is determined by modem speed, quality of phone line. Up to 56K/second. 24 hour connection. ISDN is like dial up services with better performance. DSL ISDN, DSL, and Cable are always available. Four Cable, Speed: High data transfer capablilities. Ranges from 56KB/second to 300KB/second depending. 24 hour connection. Speed: Very high data transfer Leased Line Five capablilities. Ranges from 56KB/second (56K to T-3) to 44 MB/second (T-3) Possible to buy fractions of a line. Wireless access through wireless modems Wireless and and cell phone-like towers. Six Satellite Satellite through 400kbps download and Services land line upload. Full two way satellite services will be offered soon.
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