Group_18:Awesum4sum-Stop and Wait ARQ

Efficiency

The stop and wait protocol is clearly not particularly efficient. Even in the ideal case of no loss, most of the time is spent with the link idle, waiting for the other end to reply. When packets require retransmission, efficiency lowers further.

Efficiency can be calculated fairly easily. Let the size of the data we want to send be D bits, and the header (used for addressing or error detection, for example) be H bits long. Also let the corresponding acknowledgement packet be A bits in size. We must also take into account the link parameters, propagation time Ts and bit rate B bits/s.

The time taken to complete the transaction is the sum of three terms: the time taken to send the packet, the time taken to send the ack, and the two propagation delays inbetween. This gives us t = (D + H)/B + A/B + 2T as the total time. Ideally, the time taken to send D bits of data across a link with bit rate B would be simply D/B. Rearranging these gives a no-retransmission efficiency of:

η = D/(D + H) × 1/(A + 2TB)

The retransmission timer used by the sender has an ideal value for efficiency. Clearly, it must wait at least the maximum time taken for an acknowledgement to be returned: this is the propagation delay for the data packet, plus the time taken to send the acknowledgement, plus the propagation delay for the acknowledgement. Therefore, the stop time must be S ≥ 2T + A/B.

Since header and ACK size are normally kept to a minimum anyway, the equation above shows that efficiency is governed by the 2TB term. This has the effect that increasing link bit rate actually decreases efficiency; more obviously, efficiency also decreases as the link latency increases. Therefore, a stop and wait protocol is very inefficient over long or high bandwidth links.

Implementations

While stop and wait is time-inefficient, its requirement that the transmitter needs to buffer only one packet makes it very easy to implement. It is ideal for lightweight protocols such as Trivial FTP (TFTP), used to load kernels over a network by diskless workstations. TFTP must often be implemented in only a few tens of bytes of assembler, since it must be kept on a small ROM in the network card or BIOS of the diskless machine.

Additionally, since TFTP most commonly operates over Ethernet, link latency is normally low enough that efficiency isn’t a problem. When link length becomes larger, more efficient protocols (such as go-back N or selective retransmission) are necessary for reasonable data transfer times.

Group_18:Awesum4sum-Presentation

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Group18_Awesome4some:Stop and Wait Protocol Operations

Protocol Operation

The protocol is very easy to understand, and just as simple to implement. A communication pair is made up of a transmitter and a receiver. The transmitter sends a packet across a communications link, then stops and waits for a reply. Positive acknowledgements are sent back along the link by the receiver; negative acknowledgements can be sent back too, but are often assumed after some time out period has expired.

A sample exchange is shown below.

——————————————> Time

(Packet lost) (Retransmission)

——             ——             ——

TX | Data |         | Data |      | Data |

——.          ——.      .——

.  —–         .      .          —–

RX .   | Ack | .      .| Ack |
. .—–         .      .          —–
. .              .      .
Link                      Timeout

propagation           value

delay

All data packets sent by the transmitter take a certain time to reach the receiver. This is related to the length and velocity of the communications link, and is known as the link propagation delay. The receiver replies to the packet once it has been received by sending an ACK; this is also subject to the propagation delay.

When a packet is lost, as the second packet is in this case, the transmitter’s acknowledgement timer expires. It then can assume that either the data or the acknowledgement didn’t arrive, and so retransmits the previous packet.

Stop&Wait ARQ Sender's end

Stop&Wait ARQ Receiver's side

Group18_Awesome4some: PartA project Q&A session

<Question answered by Prabha.>

1.Why is tunneling needed in case we can access different blocked sites using proxy server?
Tunneling is useful in unblocking or passing through the restrictions against one particular site. Proxy is used for more than one site.

<Question answered by Prabha. Asked by Bhaskar>

2.What is the significance of / in a http address?
It indicates the access of the required page from the sub directory present in the root directory mentioned in the http address.

<Question answered by Anita. Asked by Tanushree>

3. What is DNS server?
Its a server that is used to translate a hostname or a domain name to its corresponding binary identifier.

<Question answered by Lisha. Asked by Anil>

4. How the cache of proxy will accomodate new entries when it is full?
Cache of proxy is less than cache of internet. There are many algorithms to update Cache. (Rest of it has been answered by Ma’am).

<Question answered by Lisha. Asked by Amit>

5. In case of dynamic pages what is the role of proxy server?
Principally, the working of the Proxy server in case of dynamic web pages is to check the cached page. If it has expired the update time of the dynamic web page then the request is sent to the server.

(Rest of this answered by Ma’am) But in actual sense, either of the push or pull method is used  in this case.

<Question answered by Anita. Asked by Dhanusha>

6. What is the use of cache when buffer is there?
Buffer and cahe are two different entities. Buffer is used to temporarily hold data while it is been moved from one place to another where as cache is temporary storage area where frequently accessed data can be stored for rapid access.

<Question answered by Anita. Asked by Pavan S>

7. What does HTTPS do? What does S stand for?

S stands for Secure. It is a non-cacheable object site which has no cache storage header in it. Hence it makes this secure.

Group18_Awesome4some: Part A Project Report

Introduction
A proxy server is a server (a computer system or an application program) that acts as an intermediary for requests from clients seeking resources from other servers. A client connects to the proxy server, requesting some service, such as a file, connection, web page, or other resource, available from a different server. The proxy server evaluates the request according to its filtering rules. A proxy is a web page that provides Internet users with the ability to browse web sites that may be blocked by a content filter, such as WebSense or SmartFilter. By making use of the proxy as the portal to the blocked site, it is possible to circumvent the work of whatever content filter is in place. At the same time, the proxy site also helps to mask the visit to the site, so that there is less evidence that the content filter was not successful in preventing the visit.

How does a proxy server work?
A proxy server shares one internet connection with all the computers on your local network or it is a computer that offers a computer network service to allow clients to make indirect network connections to other network services. So basically a proxy (proxy server) is a server that acts as mediator between the client (the computer of a user) and server (the computer on the other ends of network connection on which the information requested by the user appears for example web server site.) When clients request data from an Internet resource, traffic goes from your web browser/application first through the proxy before it reaches the requested sources and back through the proxy then the proxy will transmit the data to you.

A proxy server sits between a client application, such as a Web browser, and a real server. It intercepts all requests to the real server to see if it can fulfill the requests itself. If not, it forwards the request to the real server.

Literature survey
The different types of Proxy Servers
There are many different types of Proxy Servers out there. Depending on the purpose you can get Proxy Servers to route any of these common protocols, and many more:

1) FTP Proxy Server:
Relays and caches FTP Traffic.

2) HTTP Proxy Server:
A one way request to retrieve Web Pages.

3) Socks Proxy Server:
A newer protocol to allow relaying of far more different types of data, whether TCP or UDP.

4) NAT Proxy Server:
This one works a little different; it allows the redirection of all packets without a Program having to support a Proxy Server.

5) SSL Proxy Server:
An extension was created to the HTTP Proxy Server which allows relaying of TCP data similar to a Socks Proxy Server. This one done mainly to allow encryption of Web Page requests.

Here we consider only the first two proxy servers – HTTP proxy server and FTP proxy server.

HTTP Proxy Server:
Hypertext is words/ phrases/ images which upon a click or stroke from the keyboard redirects to the related page. Thus hypertext (hyperlinks) forms a sort of network of related data.

An HTTP proxy server is a server that handles HTTP requests from clients. If the clients are of a common organization or domain, or exhibit a similarity in browsing behavior, the proxy can effectively cache requested documents. Caching, which migrates documents across the network closer to the users, reduces network traffic, reduces the load on popular Web servers and reduces the time that end users wait for documents to load.

A proxy server accepts requests from clients. When possible and desired, it generates replies based upon documents stored in its local cache; otherwise, it forewords the requests, transfers the replies to the clients and caches them when possible.

The proxy thus acts both as a server and as a client. It is a server when accepting HTTP requests from its clients, but a client to the remote servers it connects to when it is unable to fulfill requests by the means of its local cache.

FTP proxy server
FTP proxy is an application level gateway for FTP. It sits between a client and a server forwarding command and data streams supporting a subset of the file transfer protocol.

File Transfer Protocol.
FTP stands for the File transfer protocol and is used to transfer files between an FTP server  and another computer. In the past, FTP was much more common than it is today and was the dominant file transfer mechanism on the Internet. If you needed to transfer files between two computers, you would use FTP to do so. FTP is still very popular today when a service requires that a lot of files be hosted for other to people to download. FTP also tends to be faster than other contemporary methods of transferring files because it was designed to do so.

Even more important, FTP support Automatic Resume. This means that if you are downloading the latest new game demo that is over 600 mega, and for some reason the download stops in the middle of the transfer, the ftp client will attempt to on the next download of the same file, to continue from where you left off. This feature can save you a huge amount of time but is generally only found in specialized FTP client software and not in your browser software.

Available applications for both HTTP and FTP Proxy servers
•    Web browsers
•     Proxy Chains
•     Download managers
•     Operating system (with lots of configuration)

Functions of proxy servers
Proxy servers implement one or more of the following functions:
•    Caching proxy server
•    Web proxy
•    Content-filtering web proxy
•     Anonymizing proxy server
•     Hostile proxy
•    Intercepting proxy server
•    Transparent and non-transparent proxy server
•     Forced proxy
•     Suffix proxy
•    Open proxy server
•    Reverse proxy server
•    Tunneling proxy server

Anonymizing proxy server
Anonymous browsing is simply browsing the World Wide Web with most of your identity hidden. This is primarily done through what is known as an anonymous browser based proxy. These are the websites that you can use to input the address of the web page that you wish to visit, and the service will take you to that website with information such as the location of your computer and the IP address hidden from the web page. For example, when the user tries to access something on a certain part of the web, the proxy will talk to that file as an ambassador of the user, maintaining the privacy of the user. The practice of anonymous browsing can also maintain the privacy of the user from potential loggers spying on the user’s connection.

Risks with Anonymous Browsing
Although anonymous browsing seems to be the solution to complete anonymity, it can potentially be harmful. This is because by the user anonymously browsing, they are using an anonymous proxy, which does not encrypt data when it is sent to the proxy server. Thus, important information such as logins, passwords, and credit card numbers could potentially be recorded and leaked by a proxy server administrator who has malicious plans. Users that are constantly looking to anonymously browse could also fall into Internet traps where web pages display a wrong security measure, which the user might believe and give out too much information. This could lead to an even greater disaster than non-anonymous browsing, as the proxy server itself and any proxy chains attached to that proxy server can see all of that user’s information.

Anonymous web proxy services tend to be somewhat unstable, the list of current anonymous web proxy services changes constantly. In addition, some anonymous web proxy services are free services and others are not. Most of the current proxy services offer some version of limited free service, and then try to up sell you to a monthly subscription.
Anonymous browsing is a very easy way to browse without needing to worry too much about information such as the IP address being released publicly. Nonetheless, it is critical to double check whether a certain anonymous browsing service is honorable or not to prevent any, potentially even worse, disasters from occurring.

Anonymous proxy
An anonymous proxy is a piece of software designed to protect the privacy and anonymity of web browsers from web site operators, Internet snoops, and even unfriendly governments. The anonymous proxy software resides on a proxy server. The web browser connects to the proxy server and the proxy server connects to the web server. The web server does not know who you are, it only knows who the proxy server is. The proxy server does know who you are — so you had better choose a proxy server that you trust.

In addition to hiding your IP address, an anonymous proxy server will typically remove traffic such as:
•    Cookies
•    Pop-ups
•    Banners
•    Scripts
•    Referrer information

These options should be configurable by the end-user to enable to proxy server to work with web sites which require cookies or pop-ups.

Anonymous surfing proxy sites will allow to
•    They allow you to enter the address (URL) of the site you wish to go to at the anonymous surfing proxy site.
•    The site will retrieve the page for you and present it to you.
•    The site you visit will not receive any particulars about your system.

Caching proxy server
Caching Overview
Increasing demand for information on the Internet causes congestion and long delays in retrieving information. Because much of the same information is retrieved over and over again, saving and storing this information can satisfy subsequent requests with more efficiency and less bandwidth.

Saving and storing information locally is known as caching. With Web caching, copies of recently requested content are stored temporarily on a cache server in locations that are topologically closer to the client. The content is then readily available to be reused for subsequent client requests for the same content.

By storing content locally, we:
• Optimize network resources
• Conserve network bandwidth
• Reduce Internet congestion
• Improve network response time and overall service quality

Using Proxy Caching
With proxy caching, each client is configured with the IP address of the proxy cache to which clients send content requests. You may also configure an URL for browsers to identify the location of the proxy configuration file for automatic proxy configuration. Each client’s content request is sent directly to the proxy cache IP address. The cache either returns the requested content if it has a local copy or sends a new request to the origin server for the information.

If all cache servers are unavailable in a proxy cache configuration, the client request does not pass to the origin server because clients are configured with the proxy cache VIP.

This server accelerates service requests by retrieving content saved from a previous request made by the same client or even other clients. Caching proxies keep local copies of frequently requested resources, allowing large organizations to significantly reduce their upstream bandwidth usage and cost, while significantly increasing performance. Most ISPs and large businesses have a caching proxy. These machines are built to deliver superb file system performance (often with RAID and journaling) and also contain hot-rodded versions of TCP. Caching proxies were the first kind of proxy server.

Taking Squid as an example, we explain the page-fetch algorithm in the proxy server.
•    Check cache for existing copy of object
•    If it exists in cache
-Check object’s expire time; if expired, fall back to origin server
-Check object’s refresh rule; if expired, perform an If-Modified-Since against origin server
-If object still considered fresh, return cached object to requester
•    If object is not in cache, expired, or otherwise invalidated
- Fetch object from origin server
- If 500 error from origin server, and expired object available, returns expired object
-  Test object for cacheability; if cacheable, store local copy

Cacheable objects
•    HTTP
–    Must have a Last-Modified: tag
–    If origin server required HTTP authentication for request, must have Cache-Control: public tag
–    Ideally also has an Expires or Cache-Control: max-age tag
–    Content provider decides what header tags to include
•    Web servers can auto-generate some tags, such as Last-Modified and Content-Length, under certain conditions
•    FTP
–    Squid sets Expires time to fetch timestamp + 2 days

Non-cacheable objects
•    WAIS
•    HTTPS
–    No Last-Modified: tag
–    Authenticated objects
–    Cache-Control: private, no-cache, and no-store tags
–    URLs with cgi-bin or ? in them
–    POST method (form submission)

Content filtering Proxy server
A content-filtering web proxy server provides administrative control over the content that may be relayed through the proxy. It is commonly used in both commercial and non-commercial organizations (especially schools) to ensure that Internet usage conforms to acceptable use policy. In some cases users can circumvent the proxy, since there are services designed to proxy information from a filtered website through a non filtered site to allow it through the users proxy.

Some common methods used for content filtering include: URL or DNS blacklists, URL regex filtering, MIME filtering, or content keyword filtering. Some products have been known to employ content analysis techniques to look for traits commonly used by certain types of content providers.

A content filtering proxy will often support user authentication, to control web access. It also usually produces logs, either to give detailed information about the URLs accessed by specific users, or to monitor bandwidth usage statistics. It may also communicate to daemon-based and/or ICAP-based antivirus software to provide security against virus and other malware by scanning incoming content in real time before it enters the network.

This proxy server works based on ICAP

The Internet Content Adaptation Protocol (ICAP) is a lightweight HTTP based protocol specified in RFC 3507 designed to off-load specific content to dedicated servers, thereby freeing up resources and standardizing the way in which features are implemented. ICAP is generally used in proxy servers to integrate with third party products like antivirus software, malicious content scanners and URL filters.

ICAP in its most basic form is a “lightweight” HTTP based remote procedure call protocol. In other words, ICAP allows its clients to pass HTTP based (HTML) messages (Content) to ICAP servers for adaptation. Adaptation refers to performing the particular value added service (content manipulation) for the associated client request/response.

Reverse proxy server
A reverse proxy is a proxy server that is installed in the neighborhood of one or more web servers. All traffic coming from the Internet and with a destination of one of the web servers goes through the proxy server. There are several reasons for installing reverse proxy servers:
•    Encryption / SSL acceleration: when secure web sites are created, the SSL encryption is often not done by the web server itself, but by a reverse proxy that is equipped with SSL acceleration hardware. See Secure Sockets Layer. Furthermore, a host can provide a single “SSL proxy” to provide SSL encryption for an arbitrary number of hosts; removing the need for a separate SSL Server Certificate for each host, with the downside that all hosts behind the SSL proxy have to share a common DNS name or IP address for SSL connections.

•    Load balancing: the reverse proxy can distribute the load to several web servers, each web server serving its own application area. In such a case, the reverse proxy may need to rewrite the URLs in each web page (translation from externally known URLs to the internal locations).

•    Serve/cache static content: A reverse proxy can offload the web servers by caching static content like pictures and other static graphical content.

•    Compression: the proxy server can optimize and compress the content to speed up the load time.

•    Spoon feeding: reduces resource usage caused by slow clients on the web servers by caching the content the web server sent and slowly “spoon feeding” it to the client. This especially benefits dynamically generated pages.

•    Security: the proxy server is an additional layer of defense and can protect against some OS and WebServer specific attacks. However, it does not provide any protection to attacks against the web application or service itself, which is generally considered the larger threat.

•    Extranet Publishing: a reverse proxy server facing the Internet can be used to communicate to a firewalled server internal to an organization, providing extranet access to some functions while keeping the servers behind the firewalls. If used in this way, security measures should be considered to protect the rest of your infrastructure in case this server is compromised, as its web application is exposed to attack from the Internet.

Tunneling proxy server
A tunneling proxy server is a method of defeating blocking policies implemented using proxy servers. Most tunneling proxy servers are also proxy servers, of varying degrees of sophistication, which effectively implement “bypass policies”.

A tunneling proxy server is a web-based page that takes a site that is blocked and “tunnels” it, allowing the user to view blocked pages. A famous example is elgooG, which allowed users in China to use Google after it had been blocked there. elgooG differs from most tunneling proxy servers in that it circumvents only one block.

Students are able to access blocked sites (games, chatrooms, messenger, offensive material, internet pornography, social networking, etc.) through a tunneling proxy server. As fast as the filtering software blocks tunneling proxy servers, others spring up. However, in some cases the filter may still intercept traffic to the tunneling proxy server, thus the person who manages the filter can still see the sites that are being visited.

Tunneling proxy servers are also used by people who have been blocked from a web site.

Another use of a tunneling proxy server is to allow access to country-specific services, so that Internet users from other countries may also make use of them. An example is country-restricted reproduction of media and webcasting.

The use of tunneling proxy servers is usually safe with the exception that tunneling proxy server sites run by an untrusted third party can be run with hidden intentions, such as collecting personal information, and as a result users are typically advised against running personal data such as credit card numbers or passwords through a tunneling proxy server.

In some network configurations, clients attempting to access the proxy server are given different levels of access privilege on the grounds of their computer location or even the MAC address of the network card. However, if one has access to a system with higher access rights, one could use that system as a proxy server for which the other clients use to access the original proxy server, consequently altering their access privileges.

Tools used and Description
Tool used: CC proxy

Description:  Proxy Server CCProxy is easy-to-use and powerful Internet connection sharing software. CCProxy can support broadband, DSL, dial-up, optical fiber, satellite, ISDN and DDN connections, it helps build your own proxy server and share Internet access within the LAN efficiently and easily. CC Proxy Server can act as an HTTP, mail, FTP, SOCKS, news and telnet proxy server. It features powerful account management functions, including Internet access control, bandwidth control, Internet web filtering, content filtering and time control. It also provides web caching, online access monitoring, access logging and bandwidth usage statistics functions. CC Proxy is compatible with Win98, WinME, WinNT, Win2000, WinXP, Win2003 and Vista.

The first version of Proxy Server CCProxy was developed in June 2000. It was initially designed to modem sharing within a LAN. Proxy Server CCProxy has now been expanded to support Internet connections of many other types, such as DSL sharing, cable modem sharing, wireless sharing, satellite sharing, parent proxy server connection sharing, and more. If there is a computer within a LAN that can access the Internet, all the other computers within the LAN can access the Internet via this proxy server software. This could make great savings for your business in terms of hardware and Internet connection fees.

CCProxy can act as web proxy software, which enables you to browse web pages, download files and send and receive e-mails via web browsers such as IE, Firefox, Netscape and etc. The web caching function can increase the Internet surfing speed.

CCProxy provides powerful management functions including several ways to control the Internet access on the LAN. They are IP address, IP range, MAC address, User Name/Password and group. It can also merge with Active Directory.
The web filtering and content filtering function can restrict clients’ access to particular sites. It will help you to ensure that employees concentrate on their work or that children are unable to visit unsuitable sites. The time schedule function is used to control the users’ online time.

Different proxy services can be allocated to different users. For example, some of them could be restricted to browsing web pages and others to sending and receiving e-mails.

CCProxy can allocate proxy client bandwidth as appropriate. That is to say, it can be used to control the users’ Internet surfing speed and balance the bandwidth to avoid the network traffic jams that can be caused by users who download big files or watch online media.

Access logging and online access monitoring will help you record the clients’ Internet access activities.

Steps to configure
1.    Setting the IP address of server and client
a.    Server: Connect the server system to the Internet.
Control Panel-> Network Settings-> IPv4-> Properties->
-    Set the IP to the allowed IP by the network.
-    Subnet Mask is obtained automatically.
-    Leave the Preferred Gateway settings empty.
-    Leave the Preferred and Alternate DNS settings empty.
b.    Client: Connect the client to the server via wired LAN (or wireless LAN).
-    Set the IP address to another IP which is allowed by the network.
-    Subnet Mask is obtained automatically.
-    Preferred Gateway should be set to the Server IP address settings.
-    Preferred DNS settings can be left empty or set to Server system’s IP address.

2.    Change Browser settings of the client
Once the IP configuration is done, the browser settings of the client are to be changed to access the Internet via the proxy server.
-    Tools -> Options -> Advanced-> Network-> (LAN) Settings-> Proxy Settings
-    Change the corresponding Proxy setting to the Server system’s IP address.
-    Set the Port to the defined port (Eg: HTTP – 8080).

3.    Now run the CC Proxy software.

4.    For every session of usage of CC Proxy software, registration is required.
-    Select Register
-    Copy the Machine Id
-    Paste it into the Key Maker
-    Copy and paste the serial number and Register Code from the Key Maker to the Registration tab
-    Register the session.

5.    To create users.
-    Select Account
-    New
-    Fill the form as required. It can be chosen to be password protected or not.
-    Select the required Web Filter.

6.    Setting the Web Filter.
-    Select Web Filter option
-    Type in the entire URL to be blocked (or unblocked).
-    Select the type of content to be blocked.
-    Save the settings and select Ok.

7.    Once all these settings are done for all the users which are connected to the Server via the proxy Server settings, the users can be allowed to access the required sites (or not access the required sites).

8.    Monitor option will provide the Recent Logs from the clients. Also the Account details and the IP address details.

Results
The CC Proxy Server setup on a local system serves exactly like a Proxy server according to our requirements. It is easy to setup and configure. The client (user) settings can be done according the server’s discretion. The corresponding websites or content are blocked to the respective users. The stimulation of a Proxy Server is done using the tool CC Proxy.

Group18_Awesome4some: Exploring “Squid”

Squid runs on most available operating systems, including Windows and is licensed under the GNU GPL. Squid is a caching proxy for the Web supporting HTTP, HTTPS, FTP, and more. It reduces bandwidth and improves response times by caching and reusing frequently-requested web pages. Squid has extensive access controls and makes a great server accelerator. A client sends a request to a particular web page, proxy servers like squid intercept these requests and reply back to the request as a real server will by sending the web page which was stored in the cache. This helps to reduce bandwidth and increases internet access speed. Clients can use this in either of the two ways. First is to specify the proxy being used to the ISP or as Transparent caching.

Another setup for proxies are reverse proxy. Here, after the first transfer of the requested web page is retrieved, it is stored in cache for the further requests. The real server does not get the actual IP address of the client system which requested the web page. But the real server can know the login of traffic or hits to their web page by the requests sent by the proxy server. A way to adapt the reporting on the source server is to use the X-Forwarded-For HTTP header reported by the reverse proxy, to get the real client’s IP address.

Proxy servers can act as both proxy and reverse proxy servers as per the requirement. The proxy can be used to increase the speed of access, whereas reverse proxy helps to log the traffic details. Squid software provides the choice of both the type of proxies.

Group18_Awesome4some: Introduction to the tools used for HTTP and FTP proxy server

We are planning to focus more on FTP proxy server, hence more emphasis and CuteFTP below.

Cute FTP is a file transfer Protocol used to transfer files between the PC and remote computers. it is a series of client applications developed by GlobalSCAPE since 1996 made for both home and professional use. Cute FTP gets your job of transferring the files really easier, let it be downloading a image or a music file, or publishing your website, in any case the job is best done using a FTP.

The most common uses of Cute FTP include

• Helps to Upload your web pages for viewing in web browser.
• Upload any of the work files to an FTP server.
• Upload your images to an FTP Server.
• Upload or download multimedia files such as music, images or video files.
• Download the latest game patches, programs or game demos from participating FTP servers.
• Download large files faster than when using your Web browser.
• Backup critical files to an FTP server in case your system crashes.

The tool we using is the cute FTP professional. It provides easy-to-use yet powerful tools for tackling the complex challenges of data management and helps achieve HIPAA, GLBA and Sarbanes-Oxley compliance.The features of this tool is as follows
Automation

• Schedule fast, fully-automated transfers.
• Safely backup or synchronize your sites.
• Easily monitor local folders for changes.
• Create labor and time saving scripts and macros.
• Create Podcast RSS feeds and manage audio files.

Simplicity

• Connect to new sites in a snap with step-by-step wizards.
• Painlessly edit remote documents with its built-in editor.
• Drag and drop files for easy transfers.
• View thumbnails of remote images.

Speed

Dramatically accelerate file transfers.

Securely work with multiple remote sites at one time.

Effortlessly perform up to 100 concurrent transfers.

Group18_Awesome4some: HTTP/FTP Proxy servers (introduction)

Proxy Servers:
A proxy server is a server (a machine or a program) which is present between the user (client side) and the Internet. When a person requests for a particular web page, the request is passed on directly to the server and the requested page is located, retrieved and sent back to the requested computer. This is done by locating the surfer’s IP address, and then transferring back to the same IP address which had requested the web page. But with the introduction of proxy servers the request is intercepted by it and the request does not reach the real server. The proxy server acts as a regular server by saving caches of all previously downloaded websites. When a request sent to server is intercepted by the proxy server, it checks in its cache. If the page is found then it is sent back to the IP which raised the request. If it is not found then, the proxy uses its own IP address and raises a request to the real server and then sends it to the requested terminal. This is useful in terms of retaining anonymity, to speed up the process of webpage retrieval and to filter requests. There are many types of Proxy servers like transparent proxy, anonymous proxy, distorting proxy, high anonymity proxy.

Http proxy server:
Hypertext Transfer Protocol (HTTP) is an application-level protocol used for retrieving inter-linked resources led to the establishment of the World Wide Web. HTTP is a request/response standard of a client (end user) and a server (web site). The client making an HTTP request—using a web browser, etc—is referred to as the user agent. The responding server—which stores or creates resources such as HTML files and images—is called the origin server.

HTTP proxy server is a proxy, allowing working on the Internet with HTTP and (not always) FTP protocols. It (as well as other proxy servers) can carry out caching of information downloaded from the Internet. HTTP proxy servers are the most prominently used.

Ftp Proxy server:
File Transfer Protocol (FTP) is a standard network protocol used to exchange and manipulate files over an Internet. FTP is also built on a client-server architecture and utilizes separate control and data connections between the client and server applications. FTP is also often used as an application component to automatically transfer files for program internal functions and can be used with user-based password authentication or with anonymous user access.

Ftp proxy is an application level gateway for FTP. It sits between a client and a server forwarding command and data streams supporting a subset of the file transfer protocol as described in RFC 959. Beside this basic function which makes the program useful on firewall or masqueraders it offers fixing the FTP server (e.g. for connections into a protected LAN) and proxy authentication.

Group18_awesum4sum: Undersatnding Computer Networks

Earlier a single computer served the whole organization’s computational needs. But now a large number of separate computers are capable of working individually and get the tasks done. But all these individual computers should be able to share and exchange the data and information in order to complete the organizational needs. This is possible by interconnecting the computers. These systems are called Computer Networks. There are two ways to communicate in a network. It can be a broadcast network, where a single communication channel is shared by all networks. The data is sent by any one of the system and any other system receives it. The system checks if the packets are intended for itself, if yes, it accepts the packets or it ignores. The data can also be sent to all the systems in the network. We can also have point to point networks, where there exists many computers between the source and the destination.

group18_awesum4sum: Stop and wait ARQ

Reliable transfer of communication is a critical requirement in communications between computers.One of them involves the ARQ ie Automatic Repeat re-Quest involves both identification of errors and retransmission to make sure that the data is received accurately by the user in spite of the various errors that occur during the transmission.

Stop and wait also known as bit banging protocol is one of the most simplest Automatic Repeat re-Quest method. In this method the sender sends one frame at a time and waits for an acknowledgement (ACK) from the receiver. If the receiver receives an uncorrupted frame an ACK is immediately sent. The errors in the frame are checked by the receiver using the redundancy bits added by the sender. Detection of an error is understood when the receiver does not send any ACK. In cases of errors the frame has to be resent to the receiver, but if the receiver does not respond when the error occurs the sender would not know if the frame has to be resent. In order to solve this the sender keeps a copy of the frame sent and starts of a timer once the frame is sent, if the sender does not receive the ACK within a specific duration of time (also known as time out) the sender sends the copy again.