Difference between pages "TDMA" and "Proxy server"

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'''TDMA - Time Division Multiple Access'''
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'''Proxy server''' is a server which services the requests of its clients by forwarding requests to other servers.
  
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== Overview ==
  
== Why use TDMA?==
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Proxy servers are widely used by organizations and individuals for different purposes:
TDMA (Time Division Multiple Access), has the largest network in the US.  It is a digital wireless communication method allowing many users to access a single radio frequency without interference.  Every individual user is given a unique time slot within each channel.  It increases the efficiency of transmission and offers a number of other advantages.  A major pro is it can be easily adapted to transmission of data as well as voice communication.  It offers the ability to carry date rates of 64 kbps to 120 mbps, which enables options of communication such as fax, voiceband data, sms, as well as bandwidth intensive apps.  TDMA allows the user to have extended battery life since the mobile is only transmitting a portion of the time during conversations.  Furthermore, it is the most cost effective technology for upgrading a current analog system to digital.
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==How it works==
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* Internet sharing (like [[NAT]]);
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* Traffic compression;
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* Accelerating service requests by retrieving content from cache;
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* and many others.
  
It’s necessary for TDMA to rely upon that fact that the audio signal has been digitized.  These signals are divided into a number of milliseconds.  TDMA is also the access technique used in the European digital standard, GSM, and the Japanese digital standard, personal digital cellular (PDC). The reason for choosing TDMA for all these standards was that it enables some vital features for system operation in an advanced cellular or PCS environment. Today, TDMA is an available, well-proven technique in commercial operation in many systems.
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Proxy servers are often used for malicious purposes (such as fraud).
A single channel can carry all four conversations if each conversation is divided into relatively short fragments, is assigned a time slot, and is transmitted in synchronized timed.
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==Pros & Downfaults==
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== HTTP proxies ==
  
TDMA can be wasteful of bandwidth because time slots are allocated to specific conversations whether or not anyone was speaking at the given moment.  There is an enhanced version however, EDTMA, which attempts to correct this problem.  Unlike TDMA which waits to determine whether a subscriber is transmitting, ETDMA assigns subscribers using a dynamic method.  The data is sent through pauses which normal speech contains.  If the subscriber has something they would like to transmit, it is placed as one bit in the buffer queue.  The system then scans the buffer and notices the user has something to transmit, allocating the bandwidth accordingly.  However, if there is nothing to transmit, it goes to the next subscriber.  This technique can be 10 times more efficient as analog transmission of TDMA.
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''These proxy servers are using HTTP.''
  
==Cell Phone Providers==
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Example request (direct; with relative URI):
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<pre>
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GET / HTTP/1.1
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Host: cryptome.org
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User-Agent: Mozilla/5.0 (X11; U; Linux i686; en; rv:1.9.0.3) Gecko/20080528 Epiphany/2.22 Firefox/3.0
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Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
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Accept-Encoding: gzip,deflate
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Accept-Charset: ISO-8859-1,utf-8;q=0.7,*;q=0.7
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Keep-Alive: 300
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Connection: keep-alive
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If-Modified-Since: Tue, 14 Oct 2008 13:59:19 GMT
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If-None-Match: "e01922-62e9-45937059ec2de"
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Cache-Control: max-age=0
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</pre>
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Example request (using proxy; with absolute URI):
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<pre>
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GET http://cryptome.org/ HTTP/1.1
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Host: cryptome.org
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User-Agent: Mozilla/5.0 (X11; U; Linux i686; en; rv:1.9.0.3) Gecko/20080528 Epiphany/2.22 Firefox/3.0
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Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
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Accept-Encoding: gzip,deflate
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Accept-Charset: ISO-8859-1,utf-8;q=0.7,*;q=0.7
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Keep-Alive: 300
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Proxy-Connection: keep-alive
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If-Modified-Since: Tue, 14 Oct 2008 13:59:19 GMT
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If-None-Match: "e01922-62e9-45937059ec2de"
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Cache-Control: max-age=0
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</pre>
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''Note:'' this HTTP request was intercepted on the way to proxy server.
  
There are several cell phone companies competing to sell their phones and advertise their network coverage area. They will primarily be competing within two categories:  TDMA and [[CDMA]]. The pros and cons of TDMA have been mentioned, and the companies that offer TDMA are the following: AT&T, Cingular, Nextel, T-Mobile.  The companies that support [[CDMA]] are:  ALLTEL, Amp'd Mobile, Cricket Wireless, ESPN, Quest, Sprint, Verizon, Virgin Mobile.  As we can see, more companies are supporting [[CDMA]].  The question that arises is, what makes the two so different? 
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According to RFC 2068 (section 5.1.2):
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<pre>
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The absoluteURI form is required when the request is being made to a proxy.
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</pre>
  
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== HTTPS proxies ==
  
==TDMA Vs. [[CDMA]]==
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''The same as above, but using HTTPS (HTTP over SSL/TLS).''
  
TDMA is better for international plans and debately has better battery life.  [[CDMA]] claims it has better battery life and coverage, however, Cingular is supposed to have the best coverage area and that is TDMA.  All of this started however ever since [[CDMA]] was introduced in 1989, and the wireless world has been in debate over merits of TDMA and [[CDMA]].  Those who are for [[CDMA]] have claimed that its technology has bandwidth efficiency of up to 13 times that of TDMA and between 20 to 40 times that of analog transmission. Furthermore, [[CDMA]] lovers say its spread spectrum technology is more secure and offers higher transmission quality than TDMA because of TDMA's increased resistance to multipath distortion.  
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Sometimes HTTP proxies that support CONNECT method are called ''"HTTPS proxies"''. These HTTP proxies can tunnel almost every TCP-based protocol.
  
Those who favor TDMA point out that there has been no successful major trial of [[CDMA]] technology that supports the capacities it claims. Not to mention, theoretical improvements in bandwidth efficiency claimed [[CDMA]] is now being approached by enhancements to TDMA technology. TDMA's evolution allows capacity increases of 20 to 40 fold over analog in the near future. [[CDMA]] is a very expensive technology that needs $300,000 per base station, compared to $80,000 for TDMA.  Lastly, TDMA is the proven leader as the most economical digital migration path for existing AMPS networks.  No one has the final word in this debate, however, it is evident that TDMA will remain the dominant technology in the wireless market.
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Example request:
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<pre>
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CONNECT home.netscape.com:443 HTTP/1.0
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User-agent: Mozilla/1.1N
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</pre>
  
== External Links ==
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== SOCKS proxies ==
  
http://en.wikipedia.org/wiki/Time_division_multiple_access <br>
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SOCKS is an Internet protocol that allows client-server applications to transparently use the services of a network firewall.
http://www.iec.org/online/tutorials/tdma/topic04.html <br>
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http://www.cellphoneinfo.com/index.html
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== Web proxies (CGI proxies) ==
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These are web sites that allow a user to access a site through them. They generally use PHP or CGI to implement the proxy functionality.
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== Proxy detection ==
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[[Category:Anti-Forensics]]
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[[Category:Network Forensics]]

Revision as of 14:06, 15 October 2008

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Please help to improve this article by expanding it.
Further information might be found on the discussion page.

Proxy server is a server which services the requests of its clients by forwarding requests to other servers.

Contents

Overview

Proxy servers are widely used by organizations and individuals for different purposes:

  • Internet sharing (like NAT);
  • Traffic compression;
  • Accelerating service requests by retrieving content from cache;
  • and many others.

Proxy servers are often used for malicious purposes (such as fraud).

HTTP proxies

These proxy servers are using HTTP.

Example request (direct; with relative URI):

GET / HTTP/1.1
Host: cryptome.org
User-Agent: Mozilla/5.0 (X11; U; Linux i686; en; rv:1.9.0.3) Gecko/20080528 Epiphany/2.22 Firefox/3.0
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
Accept-Encoding: gzip,deflate
Accept-Charset: ISO-8859-1,utf-8;q=0.7,*;q=0.7
Keep-Alive: 300
Connection: keep-alive
If-Modified-Since: Tue, 14 Oct 2008 13:59:19 GMT
If-None-Match: "e01922-62e9-45937059ec2de"
Cache-Control: max-age=0

Example request (using proxy; with absolute URI):

GET http://cryptome.org/ HTTP/1.1
Host: cryptome.org
User-Agent: Mozilla/5.0 (X11; U; Linux i686; en; rv:1.9.0.3) Gecko/20080528 Epiphany/2.22 Firefox/3.0
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
Accept-Encoding: gzip,deflate
Accept-Charset: ISO-8859-1,utf-8;q=0.7,*;q=0.7
Keep-Alive: 300
Proxy-Connection: keep-alive
If-Modified-Since: Tue, 14 Oct 2008 13:59:19 GMT
If-None-Match: "e01922-62e9-45937059ec2de"
Cache-Control: max-age=0

Note: this HTTP request was intercepted on the way to proxy server.

According to RFC 2068 (section 5.1.2):

The absoluteURI form is required when the request is being made to a proxy.

HTTPS proxies

The same as above, but using HTTPS (HTTP over SSL/TLS).

Sometimes HTTP proxies that support CONNECT method are called "HTTPS proxies". These HTTP proxies can tunnel almost every TCP-based protocol.

Example request:

CONNECT home.netscape.com:443 HTTP/1.0
User-agent: Mozilla/1.1N 

SOCKS proxies

SOCKS is an Internet protocol that allows client-server applications to transparently use the services of a network firewall.

Web proxies (CGI proxies)

These are web sites that allow a user to access a site through them. They generally use PHP or CGI to implement the proxy functionality.

Proxy detection