Globale linker
Inet+
Tester
Braindumps
Chapter 1 - Internet basics
- Describe the structure, function and purpose of URLs
- Identify issues affecting Web site functionality
- Describe the implementation and impact of caching on the Internet clients and servers
- Describe the structure and function of search engines on the Internet.
Prior to the introduction of HTTP (Hyper Text Transfer Protocol) some universities and agencies organized information in a directory tree format. This allowed users to find, view and access information in a textual format with protocols like FTP (File Transfer Protocol) and Gopher.
One key to using the Internet is the addressing system that enable every participant to find any resources on the Web. On the Internet, the resources are organized by IP addresses and URLs.
A computer that is physically connected to the Internet has an IP (Internet Protocol) address, which is understood by the TCP/IP protocol suite. This is the unique address of a particular machine connected somewhere on the Internet. The IP address is bound to a domain name. The IP address is assigned to each registered URL by InterNic, a governing body for those addresses.
The IP address(es) for a Web site can be listed using the Nslookup utility at the DOS command prompt.
Each IP host (web site or server) is assigned a domain name. E.g.:
www.domain_name.top_level_domain
www.microsoft.com
Each domain has a Top-Level Domain (TLD). The most familiar TLDs are .com, .edu, .gov, .org and .net.
Only accredit domain name registration service companies (registrars) are allowed to provide domain names in the .com, .net and .org domains. ICANN (Internet Corporation for Assigned Names and Numbers) oversees the registrars.
Think of a URL as a file path that can find and display the files located anywhere in the network of machines that make up the Internet.
http://www.2tp.no/inet/chapter1.htm:80
- http, https, ftp, shttp and Gopher are protocols that are used to access information through the Internet
- : (colon) separates the the protocol from the rest of the URL
- // (slashes) indicate that a host name will follow. If the slashes are not used, a folder and page may be accessed at the same site.
- host, server or domain name (e.g. 2tp.no) is the DNS domain name assigned to the site
- Folder (e.g. inet) is the foldername where the file to be accessed is stored
- File (e.g. chapter1.htm) is the name of the file to be accessed.
- Port (e.g. 80) Default port (80) is assumed by browsers automatically and therefor is invisible in the URL. If a different port is assigned, a port number will follow the hostname and a colon.
Ports
A port is a logical connection within the TCP/IP protocol. TCP/IP uses ports to allow a client program to specify a particular server program.
Ports are numbered from 0 to 65536
Ports 0 through 1024 are reserved, some are:
- port 21 = FTP (File transfer Protocol)
- port 23 = Telnet
- port 25 = SMTP (Simple transfer protocol) = e-mail
- port 70 = Gopher
- port 80 = HTTP (Hypertext Transfer Protocol)
- port 119 = NNTP (Network News Transfer Protocol) = newsgroups
- port 194 = IRC (Internet Relay Chat)
- port 443 = Secure Hypertext Transfer Protocol (HTTPS) = SSL
Using nonstandard port numbers can provide limited security since hackers would not know the assigned port. Attackers can use a program called a port scanner to test each port on a target machine and list the port numbers detected until a connection is discovered.
Protocols and URLs
- Mailto is a protocol that specifies an address where the
local mail server should send an e-mail message. When the
hyperlink is clicked the default mail application is launched.
<a href="mailto:test@2tp.no">test@2tp.no</a> = test@2tp.no - News is a protocol that provides the information necessary for the browser to read and display Usenet news.
- Localfile is a property of FTP and is used during a direct file transfer to indicate the name of a local file. The localfile must be a fully qualified filename; c:\documents\readme.txt.
- FTP was designed to transfer files without concern for the types of computers and operating systems involved. Allows sharing of files without requiring a personal username on the source computer. Users can share files without much security risk to their computers
- The File command determines the type of file and initializes
the corresponding application.
<a href="file://serverA/sounds/welcome.wav">Welcome sound</a> - Gopher is a protocol that preceded HTTP. File servers store files in a hierarchical menudriven fashion, and the Gopher application/protocol brings those files to a user's browser. Was used several years at the university level.
- HTTP. A Web server and Web client communicates via HTTP.
The client (browser) initiates the communication by sending
a request. The host (server) parses the request and sends
a response. The connection between the client and the host
is terminated as soon as the response is sent.
HTTP 1.1 allows persistent connection (HTTP Keep-Alives) until some action indicate that the conversation is over.- Every HTTP request or response has a header and a body. A header
and body can be sent together, or the header can be
sent independently.
Request headers contains important information that the server needs in order to locate the requested resource and fulfill the response. E.g. it contains the URI (Uniform Resource Identifier) for the resource being requested. It can also contain information about preferred languages, conditions where the content should be downloaded and information that identifies the type of browser (User Agent) sending the request.
Response headers contain information the client needs in order to determine whether to accept the response and to properly display the content.
- Every HTTP request or response has a header and a body. A header
and body can be sent together, or the header can be
sent independently.
- HTTPS (Secure HTTP) provides secure Web-access to resources
using the Secure Sockets Layer (SSL) protocol.
The SSL protocol uses an initial client/server handshake process to hand the public key to the browser. Once the public key is handed off to the browser, all subsequent communications between the server and the client are encrypted and it is possible to to send encrypted messages across the Internet without fear of interception.
In order to implement SSL on a web site, a verification certificate must be obtained from a Certified Authority (CA) such as VeriSign or Cardservice.
Site function and performance
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Backbone and Internet Backbone Connectivity |
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|
Technology |
Bandwidth |
Type |
|
OC-256 |
13.271 Gbps |
Optical fiber |
|
OC-192/STM-64 |
10 Gbps |
Optical fiber |
|
OC-48/STM-16 |
2.488 Gbps |
Optical fiber |
|
Gigabit Ethernet |
1 Gbps |
Ethernet |
|
OC-12/STM-4 |
622.08 Mbps |
Optical fiber |
|
E5 |
565.148 Mbps |
E-class carriers |
|
OC-3/STM-1 |
155.52 Mbps |
Optical fiber |
|
|
|
|
|
ISP to Internet, Smaller Internet Links, and Large Company LANs |
||
|
Technology |
Bandwidth |
Type |
|
FDDI/2 Token Rings |
200 Mbps |
Token Ring |
|
E4 |
139.264 Mbps |
E-class carriers |
|
T3D |
135 Mbps |
T-class carriers |
|
100BaseFX |
100 Mbps |
Optical fiber |
|
100BaseT4, 100BaseTX |
100 Mbps |
Twisted pair |
|
FDDI/1 Token Ring |
100 Mbps |
Token Ring |
|
OC-1 |
51.84 Mbps |
Optical fiber |
|
E3 |
34.368 Mbps |
E-class carriers |
|
T3 |
44.736 Mbps |
T-class carriers |
|
E2 |
8.448 Mbps |
E-class carriers |
|
T2 |
6.312 Mbps |
T-class carriers |
|
E1 |
2.048 Mbps |
E-class carriers |
|
T1 |
1.544 Mbps |
T-class carriers |
|
|
|
|
|
The following chart displays the types of connectivity available for homes, schools, and small businesses.Business LANs |
||
|
Technology |
Bandwidth |
Type |
|
ISDN PRI |
1.544 Mbps |
T-Class |
|
10BaseT, 10Base2, 10Base5, 10BaseF |
10 Mbps |
Twisted pair |
|
Homes, Schools, Small Businesses |
||
|
Technology |
Bandwidth |
Type |
|
Cable modem |
52 Mbps (from 512 Kbps) |
Coaxial cable |
|
DSL |
8 Mbps (from 512 Kbps) |
Twisted pair |
|
Satellite |
400 Kbps |
Air |
|
ADSL |
1.5 Mbps (from 384 Kbps) |
Twisted pair |
|
ISDN BRI |
128 Kbps |
Twisted pair |
|
Frame Relay with dedicated 56 Kbps |
56 Kbps |
Various |
|
Plain Old Telephone Service (POTS) |
56 Kbps |
Twisted pair |
|
|
|
|
|
Technology |
Speed |
Use |
|
STM-64 |
10 Gbps |
Backbone |
|
STM-16 |
2.488 Gpbs |
Internet backbone |
|
STM-4 |
622.08 Mbps |
Internet backbone |
|
STM-1 |
155.52 Mbps |
Large company backbone and Internet backbone |
|
|
|
|
|
Technology |
Speed |
Use |
|
OC-256 |
13.271 Gbps |
Backbone |
|
OC-192 |
10 Gbps |
Backbone |
|
OC-48 |
2.488 Gbps |
Internet backbone |
|
OC-24 |
1.244 Gbps |
Internet backbone |
|
OC-12 |
622.08 Mbps |
Internet backbone |
|
OC-3 |
155.52 Mbps |
Large company backbone and Internet backbone |
|
OC-1 |
51.84 Mbps |
ISP to Internet; smaller Internet links |
- Bandwith
Bandwith is analogous to a highway. A highway with a higher speed limit and more lanes can carry a greater number of cars to their destination. The more Bandwidth a network is allotted, the greater the amount of data that can be transported. Bandwidth is measured in bps (bits per second)
Connectivity bandwidths for home and office include:- modems (9.600 - 56Kbps)
- ISDN (64Kbps - 128Kbps)
- cable (512Kbps - 52Mbps)
- DSL (512Kbps - 8Mbps)
- Satellite (400Kbps)
- ADSL (384Kbps - 1.5Mpbs)
- 10BaseT (10Mbps)
- Internet Backbone
A backbone is a larger data pipe that services other smaller networks, and normally contains much higher bandwidth than typical Internet connection.
The Internet is a collaboration of different types of computers and operating systems that are all connected via the TCP/IP protocol and run over public telecommunication networks worldwide. All of these Internet connections are tied together with the Internet backbone. The Internet backbone is the dozen or so Network Access Points (NAPs) in US that are connected to each other at 45Mbps.
Connectivity bandwidth range from OC3/STM-1 (155.52Mbps) to OC-256 (13.271Gbps).
Backbones include:- Savvis Communications
- UUNET Technologies
- Cable and USA
- GTE Internetworking
- AT&T CERFnet
- CompuServe
- Network Access Points (Naps)
The NAPs provide access to the Internet backbone. The NAPs create peer agreements with regional ISPs. It is the ISP that further distribute access to the Internet to businesses and end users.
- Internet Service Providers (ISPs)
ISPs sell bandwidth to large companies, small businesses, schools and home computer users, - File Problems
Files are stores on w Web server the same way as they are stored locally, in a file hierarchy that has a root directory, then subdirectories branching from the root. Do not store all files in the root directory, but structure your site, so that retrieval of files is easy for you and for others.
There are a few reasons why a Web site may take too long to load on your browser, including Cache size is not big enough. - Graphic Problems
Since graphic files contain more bytes that textfiles, they generally display more slowly.
GIF and JPG are natively supported by browsers
TIF, PNG, BMP and WMF requires a plug-in to be viewed.
The resolution of graphics can also affect website performance. You can reduce the size and resolution to decrease the file size of the graphic and speed up the delivery of the graphics to the clients. - Good Web Site Administration Practices
- Test on may browsers
- Check every link
- Keep the site under regular review
- Measure the response time
Caching
A cache is a place to store something temporarily. Cache eliminate repeated traffic and improve client performance. Web page caching can occur in a browser, Internet site server or intermediary nodes.
Types of cache include:
- Memory caches
Small areas of RAM that are faster than the main system memory. - File caching
Storing information on a hard-disk for faster retrieval. May happen on a local hard-disk, or on a server (proxy server). The purpose of file caching is to improve overall response time at the client and to reduce the amount of time that a client waits for a request for a file ti be fulfilled. - File Server cache
A file server cache is an area of main memory (RAM) on the server that is dedicated to reducing client access time by storing commonly used files temporarily in main memory.
Increasing the amount of RAM available to a file server will improve server performance. - Client-side browser cache
You can designate the file size limitation on the cache file in IE by selecting Tools > Internet Options > Temporary Internet Files > Settings. You can improve browser performance by setting a larger cache size. - Proxy server caching
Proxy caching saves valuable network bandwidth.
Instead of using a workstation's hard-drive to store cache information, space is served locally because it is stores on the proxy server.
Passive caching: updates occur upon request from a client browser
Active caching: updates cache objects automatically after a predetermined time interval.
Cache servers are servers designed to act as a buffer between the parent web site and the client.
Cache breakers are site implements that make sites difficult to cache:
- Rapidly changing content (Dynamic server pages, scripting)
- Misuses of tags
- Time and expiration information
- Unnecessarily large documents.
Searches and indexing
Search engines and indexing are two ways to aid users in quickly and easily finding the information they need.
Search engines
- Yahoo
- Lycos
- MSN
- Netscape
- Altavista
- Excite
A search engine has three major parts:
- Spider
An automated process, that crawls to a web page, looks at it and then proceeds to other pages by following links. - Catalog
Known as the index, the catalog where the spider puts the information it brings back. - Search engine software
Software reads the user's query and looks throughout the catalog to find matches.
Boolean operators
You can limit your searches by using Boolean logic operators, such as AND, OR and NOT.
- AND (&) - result must include both words
- OR (|) - Result must include at least of of the words
- + - Result must include particular word
- AND NOT (!) - Results must exclude particular word
- "" - Combine words into phrases
- () - Group Boolean operators
Site indexing
Site search is performed on a search egnine, whereas content search is done on the individual sites.
Internal search engine. As the number of documents stored on your site grows, it becomes increasingly difficult for users to locate desired content.
Site indexing is an important value-added feature of IIS 4.0. It offers the ability to provide indexed searches for information contained on your IIS.
A keyword index creates a searchable database of the keywords for pages on your site. A full text index indexes every word on your site allowing you to search everything.
You can also create a site map which shows the structure of the pages
in your site.
