Multiple Simultaneous Connections

By Raul Bernardino

Introduction:

The HyperText Transfer Protocol (HTTP) is the web application protocol”, Kurose J. and Ross K., (2010, P.126). With this HTTP as a fundamental for web applications protocol whereas we can browser web sites from anywhere to any single web server or multiple web servers. It is implementing in client and server programs. The HTTP can be defining what sites that client requested and on the web server site HTTP will be transferring the web sites according to the request. In other words the HTTP will be acting as messenger to bring the request from client to the web servers and to bring the responses from web servers to the clients.

Nowadays, web browser can be configuring in order to have concurrent links to the web site. In today web browser default it sets to five to ten concurrent links over Transmission Control Protocol (TCP). For example: The IE6 and EI7 on the HTTP 1.1 can be supporting two concurrent links while IE8 already have six concurrent links in the default setting. These all can be configured via regedit command to edit the windows register, give the value to the register. It depends on needs.

The TCP is end to end links or point to point links whereas it calls also virtual circuit. 

How TCP is working as follows:

1. The TCP is established link or connection: where to set up the two pairs of computers in order to exchange the data.
2. TCP operate in full duplex: where only one can connect to each one at the time.
3. Error checking: The TCP uses checksum techniques to verify packets; either it is valid packets or corrupted packets.
4. Sequencing: All packets are flagged with the numbers in order to identify the sequence order numbers in the destination and it also allows the operating system to define which packet is missing.
5. Acknowledgement:  when it is reached the destination the TCP will be sending acknowledgement (ack) that packets is received. If not the sender will be re-transmitting the missing packets.
6. Flow control:  in some case if the sender is transmitting very quick and receiver can’t receive it, the packet will drop and alert the sender to slow down.
7. Packet recovery services:  There are two way to do. First, sender can re-transmit the packets because the sender is not receiving the acknowledgement from the destination. Second, the destination can request to the sender to re-transmit such packet that need to be completed.

The advantages Transmission Control Protocol (TCP) links as follows:

•  The TCP will be assuring the communication that the data is reaching the destination within the time frame and no duplications in data transmission.
• The operating system will be handling the TCP processes and we just wait for the result.
• The data is transforming in to the packets by TCP before it send out to your end.
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The disadvantages Transmission Control Protocol links as follows:

1. While operating system will handle the processes therefore if  in the system has a bugs then will be having several problems on the browsing or searching and including downloads.
2. The TCP is not broadcast and multicast links.
3. Because it is checking error, making sequences of the packets, making acknowledgment, and etc. it will slowdown the speed.

Reference List:

1. Kurose J.F., Ross K.W., 2010: Computer Networking; A Top-Down Approach: 5^th Edition’; Boston, Addison-Wesley
2. Lecture notes, CPCOMM_week2_lecture
3. DVANTAGES AND DISADVANTAGES OF TCP AND UDP, [on-line]. Available from: http://smblog.iiitd.com/2010/09/advantages-and-disadvantages-of-tcp-and.html   (Accessed date: August 12, 2011)
4. TCP (Transmission Control Protocol), [on-line]. Available from:  http://www.linktionary.com/t/tcp.html (Accessed date: August 12, 2011)

Wireless Communication (802.11)

By Raul Bernardino

Introduction:

Nowadays, internet becomes resource or media for the information seeker, and also it is using the internet media to communicate with his or her relatives, at anytime and anywhere. The internet also becomes a place where the business players found themselves to operate on, such as e-commerce, e-businesses, way or media to communicate to the branch offices, and etc.

Almost every nation has the access of the internet and it is very simple connection to communicate with the destination host and browser the information from it over the networks. The internet is a collection of the hosts that connect through the larger networks in the world wide. The communication among hosts can be over dial up using the telephone infrastructure or use the satellite link in which is point to point communication.

The scope of the internet is to let users to interact each other as follows:

• Simple connection through Personal Computer (PC) and with local telecom infrastructure or Internet Service Provider (ISP)
• Email exchange with any that have email account on the internet
• Place where people are posting their information to the public in order to allow global user are able to access and view the information
• Place where people can accessing the multimedia such as video streaming, pictures, sounds, and some graphics
• Place where people can putting in their perspectives from the globe

All activities over internet are governed by protocols. “Protocols are running everywhere in the internet however with the common approach it is about computer networks protocols”, Kurose J.F. and Ross K.W., (2010). Protocols are defining as the way how to exchange the messages from one end to the other end.

The wireless communications are”based on the IEEE 802.11 technology” Kurose J.F. and Ross K.W., (2010).

The 802.11 technology is standard wireless that can be use as:

• Point to point or peer to peer communication and it can be integrated to the wired local area network (WLAN).
• The mobility of the devices that have a proper configuration, can be traveled in the range of the multiple wireless communication
• The wireless may has an overlapping signal from different access points
• The security of the wireless communication in which can use SSID and password or use MAC filtering

In Timor-Leste, we have no regulation yet to regulate wireless communication in the city. Therefore there is lots of overlapping wireless signals in the city.

How do we access the internet from home? I do have an access point in which is pointing back to the office. The access point are operating in 2.4 GHz. This access point is connecting to the wireless router Linksys (IEEE 802.11.g) with 54 Mbps. The cost of this wireless router is $95 USD. With this wireless router, I configured the SSID and password for users to connect mobiles, laptops and others PCs. There are also 3G from telecom operator; however the 3G modem is expensive including the data rate price.

Reference List:

1.     Kurose James, Ross Keith, 2010;’Computer Networking; A Top-Down Approach: 5^th Edition’; Boston, Addison-Wesley

2.     Lecture notes, CPCOMM_week1_lecture

3.     What is the Internet [on-line]. Available from: http://www.centerspan.org/tutorial/net.htm  (Accessed date: August 6, 2011)

4.      Sharma, Raju; Singh, Gurpal; Agnihotri, Rahul, 2010, Comparison of performance analysis of 802.11a, 802.11b and 802.11g standard: International Journal on Computer Science & Engineering, Vol. 2 Issue 6, [on-line]. Available from: http://ehis.ebscohost.com.ezproxy.liv.ac.uk/eds/pdfviewer/pdfviewer?sid=0ca1d7c2-1267-4045-ad74-e4abaf8e7559%40sessionmgr115&vid=1&hid=103  (Accessed date: August 6, 2011)