Tutorial 1

Question 1

(i) Hypertext Transfer Protocol (Http) and Hypertext Transfer Protocol Secure (Https) 

HTTP and HTTPS: What do they do, and how are they different? 

Hypertext Transfer Protocol (HTTP) is a protocol used in networking. When you type any web address in your web browser, your browser acts as a client, and the computer having the requested information acts as a server. When client requests for any information from the server, it uses HTTP protocol to do so. The server responds back to the client after the request completes. The response comes in the form of web page which you see just after typing the web address and press “Enter”.

Hypertext Transfer Protocol Secure (HTTPS) is a combination of two different protocols. It is more secure way to access the web. It is combination of Hypertext Transfer Protocol (HTTPS) and SSL/TLS protocol. It is more secure way to sending request to server from a client, also the communication is purely encrypted which means no one can know what you are looking for. This kind of communication is used for accessing those websites where security is required. Banking websites, payment gateway, emails, and corporate sector websites are some great examples where HTTPS protocols are used. 

For HTTPS connection, public key trusted and signed certificate is required for the server. These certificate comes either free or it costs few dollars depends on the signing authority. There is one other method for distributing certificates. Site admin creates certificates and loads in the browser of users. Now when user requests information to the web server, his identity can be verified easily.

Here are some major differences between HTTP and HTTPS:

HTTP	HTTPS
URL begins with “http://”	URL begins with “https://”
It uses port 80 for communication	It uses port 443 for communication
Unsecured	Secured
Operates at Application Layer	Operates at Transport Layer
No encryption	Encryption is present
No certificates required	Certificates required

(ii) The Operation of Packet-Switched Network 

Packet-switched describes the type of network in which relatively small units of data called packets are routed through a network based on the destination address contained within each packet. Breaking communication down into packets allows the same data path to be shared among many users in the network. This type of communication between sender and receiver is known as connectionless (rather than dedicated). Most traffic over the Internet uses packet switching and the Internet is basically a connectionless network. 

How does packet switching work?

Imagine that you have a data file, perhaps an email or a document which is 2 Megabytes in size. You want to send this file to someone in another country. 

When you send the file, it isn’t sent as one document (remember the telephone call), instead it is broken up into lots of small 'data packets'. Our 2MB file would be broken up into chunks of 512 bytes in size. 

Before each packet is sent, it is given a 'header' containing the network IP address that it needs to arrive at and also details of the IP address from which it was sent. The header also gives each packet a number and records how many packets the data was split up into.

How do the packets get through the network?

Now comes the clever bit. Try to imagine the Internet as billions of computers all connected together in a huge mesh. There isn’t just one way to get from one computer to another, there are literally millions of different routes which can be taken.

So, the packets leave your computer and are sent through the network, knowing where they need to get to. The packets start to head off in different directions taking the least busy path at that instant. A machine called a 'Router' works out which is the next fastest connection and sends each packet on its way. During the course of its journey, a packet will travel through many routers, possibly in many different countries.

This method works extremely well, because if one branch gets too busy or broken, then the packets are automatically routed through another path instead.

What happens when the packets arrive?

When the packets arrive at their destination, they are put back together again in the right order. Remember earlier on we told you that each packet was given a number? This makes it possible to correctly reorder them. The header also contained a record of the number of packets into which the file was split. So, if any packets fail to arrive within a certain length of time then a message is sent back to the original computer asking for a replacement packet.

What happens to lost packets?

Sometimes packets can get lost and keep bouncing around from router to router, never quite getting to their destination.

A system had to be developed to deal with this because eventually the network would choke with these 'lost' packets. So to solve this problem a 'hop' count is also added to the packet header. Each packet is allowed to 'hop' from one router to another a maximum of say 100 times. Each time the packet passes through a router the ‘hop number’ is decreased by one. If the packet hasn’t arrived at its destination within the number of ‘hops’ allowed then it is deleted by the next router.

Advantages of Packet Switching

• It makes very efficient use of the network - no tied-up lines.
• It can easily get around broken bits of the network.
• As customers increase, the network only has to expand slowly compared to circuit switching.

Disadvantages of Packet Switching

• The time it takes to put back the data package changes each time, which can be a problem for time-critical information such as an emergency signal. The fancy name is for this is 'latency'.
• Not very good for small data packages - for example if the data package itself is only 600 bytes long, then two packets of 512 bytes need to be used, plus the address information.

(iii) Differences of cellular transmission General Packet Radio Service (GPRS) and 4G

General Packet Radio Service (GPRS)

One step up from no data signal at all is GPRS, which stands for General Packet Radio Service. Wikipedia defines GPRS as a “best effort” service and “a packet oriented mobile data service on the 2G and 3G cellular communication system's global system for mobile communications (GSM).”

Depending on who you believe in 2G systems GPRS provides data rates of 35–171Kilobits per second (Kbps). 2G cellular technology combined with GPRS is sometimes described as 2.5G. It provides slow-speed data transfer, by using unused time division multiple access (TDMA) channels in, for example, the GSM system.

All you need to know is that GPRS means you might eventually get a webpage to load or an email or iMessage to send, but it will probably take longer than you have patience for.

4G (LTE)

4th generation network called LTE (Long Term Evolution), works in a very different manner than 2nd and 3rd generations. Shared access is done by OFDMA - the available channel is divided into subchannels (also called subcarriers) and each of them is treated separately; groups of those subcarriers are assigned to different mobile phones. Also LTE is designed as a data-only network so all of the traffic is IP-based and there are no more circuit-switched connections. In fact unless the operator has VoLTE service (Voice over LTE), your 4G connection will only handle sending data, and to make/receive a voice call your phone will have to fall back to a 2G or 3G network. Of course the data speeds will be quite higher, you can expect tens of Mbps.

The Main Difference Between General Packet Radio Service (GPRS) & 4G(LTE)

One limitation of GPRS

Speed - Most GPRS connections run slower than 56K connections on a computer because of the limitations of the GPRS technology. Although certain enhancements exist that help raise the bar, the speed does not compare to using a wired network connection or an alternative mobile Internet connection.

Question 2
Video- History of Internet