Assignment 5 - ELECTRONIC MAIL

ELECTRONIC MAIL

1.What is the difference between Web-based and Client Email.

Web-based Email-

Web-based email is allow you to access email through a web browser.The interface of the email is depends on what the web site provided.For instance, organize , read and send the email.When you download the mail it does not save in your computer but it just save in your email.You can only read and write email when you are online logged on into your web mail account.The example of web mail system are Yahoo!,Hotmail MSN and so on.

Client Email-

Message are downloaded onto computer hard drive using an email client account.For instance, Eudora , Netscape ,Thunderbird and Outlook.The downloaded message are available whether you are online or not.When you write an email while you offline the mail will send when you are online next time.You can only check email email through your own computer.

2.Briefly explain all client email program that you know.

• Thunderbird - Thunderbird is an free and open source application to managing emails and news feed.Thunderbird is develop , tested , translated, and supported by the folks at Mozilla Corporation and by a group of dedicated volunteers.Mozilla corporation is a wholly-owned subsidiary of the non profit Mozilla Foundation.
• Opera Mail- Opera Mail is one of those clients that surprise a lot of  people.Most have heard of the Opera browser , few know about the mail client. That is the shame that Opera Mail has a nice list of features.
• Dreammail- is another lesser-known client that will POP3 and allow yo to set up and use multiple accounts and multiple user. Dreammail does offer some handy feature like templates and signature managment, anti-spam, message filtering , address book, search and so on.

3. What is the differences between POP3 and IMAP? Show how to configure these email client.

• POP3 -You can use only one computer to check your email.The mails are stored on the computer that you use .Sent mail is stored locally on your PC not on a mail server.
• IMAP - You can use multiple computers computers  to check your email.Your mails are stored on the server.Sent mail stays on the server so you cn see it from any device.

                       

 

                          

ASSIGNMENT 4

TASK 4

1.      What is a client-server?

Client server is a program relationship in which one program where client request a service or resource from another program where it is server. In the easy term, server will serve request from a client. Client will establish a connection to the server over local area network(LAN) or wide area network(WAN), such as the internet. Once the server has fulfilled the client’s request, the connection is terminated. Web browser is a client program that has requested service from a server in fact the service and resource that the server provide is the delivery of this Web page.

2.      How does it works?

The client–server model of computing is a distributed application structure that partitions tasks or workloads between the providers of a resource or service, called servers, and service requesters, called clients. Often clients and servers communicate over a computer network on separate hardware, but both client and server may reside in the same system. A server host runs one or more server programs which share their resources with clients. A client does not share any of its resources, but requests a server's content or service function. Clients therefore initiate communication sessions with servers which await incoming requests.

Examples of computer applications that use the client–server model are email ,network printing, and the World Wide Web.

3.      Why is a client server good?

The client–server characteristic describes the relationship of cooperating programs in an application. The server component provides a function or service to one or many clients, which initiate requests for such services. Whether a computer is a client, a server, or both, is determined by the nature of the application that requires the service functions. For example, a single computer can run web server and file server software at the same time to serve different data to clients making different kinds of requests. Client software can also communicate with server software within the same computer. Communication between servers, such as to synchronize data, is sometimes called inter-server or server-to-server communication

4.      What are the drawback to the client-server model.

The drawback of client server model are stated as below:

1)Congestion in Network: Too many requests from the clients may lead to congestion, which rarely takes place in P2P network. Overload can lead to breaking-down of servers. In peer-to-peer, the total bandwidth of the network increases as the number of peers increase. 
2) Client-Server architecture is not as robust as a P2P and if the server fails, the whole network goes down. Also, if you are downloading a file from server and it gets abandoned due to some error, download stops altogether. However, if there would have been peers, they would have provided the broken parts of file. 
3) Cost: It is very expensive to install and manage this type of computing.
4) You need professional IT people to maintain the servers and other technical details of network.

5.      What are the correlation the thin and thick client to this topic

Thin client-

                       

A thin client (sometimes also called a lean, zero or slim client) is a computeror a computer program that depends heavily on another computer (its server) to fulfill its computational roles. This is different from the traditional fat client, which is a computer designed to take on these roles by itself. The specific roles assumed by the server may vary, from providing data persistence (for example, for diskless nodes) to actual information processing on the client’s behalf.

Thin clients occur as components of a broader computer infrastructure, where many clients share their computations with the same server. As such, thin client infrastructures can be viewed as providing some computing service via several user interfaces. This is desirable in contexts where individual fat clients have much more functionality or power than the infrastructure requires.

Thick client-

In contrast, a thick client (also called a fat client) is one that will perform the bulk of the processing  in client/server applications. With thick clients, there is no need for continuous server communications as it is mainly communicating archival storage information to the server. As in the case of a thin client, the term is often used to refer to software, but again is also used to describe the networked computer itself. If your applications require multimedia components or that are bandwidth intensive, you'll also want to consider going with thick clients. One of the biggest advantages of thick clients rests in the nature of some operating systems and software being unable to run on thin clients. Thick clients can handle these as it has its own resources.

                       

TASK 3:Difference between TCP nd UDP

1.      TCP or Transmission Control Protocol 

-          TCP is connection oriented – once a connection is established, data can be sent bidirectional.

2.      UDP or User Datagram Protocol.

-          UDP is a simpler, connectionless Internet protocol. Multiple messages are sent as packets in chunks using UDP.

	TCP	UDP
Connection	TCP is a connection-oriented protocol	UDP is a connectionless protocol.
Function	As a message makes its way across the internet from one computer. This is connection based.	UDP is also a protocol used in message transport or transfer. This is not connection based which means that one program can send a load of packets to another and that would be the end of the relationship.
Usage	TCP is suited for applications that require high reliability, and transmission time is relatively less critical.	UDP is suitable for applications that need fast, efficient transmission, such as games. UDP's stateless nature is also useful for servers that answer small queries from huge numbers of clients.
Use By Other Protocols	HTTP, HTTPs, FTP, SMTP, Telnet	DNS, DHCP, TFTP, SNMP, RIP, VOIP.
Ordering Of Data Packets	TCP rearranges data packets in the order specified.	UDP has no inherent order as all packets are independent of each other. If ordering is required, it has to be managed by the application layer.
Speed Of Transfer	The speed for TCP is slower than UDP	UDP is faster because there is no error-checking for packets.
Reliability	There is absolute guarantee that the data transferred remains intact and arrives in the same order in which it was sent.	There is no guarantee that the messages or packets sent would reach at all.
Header Size	TCP header size is 20 bytes	UDP Header size is 8 bytes.
Common Header Fields	Source port, Destination port, Check Sum	Source port, Destination port, Check Sum
Streaming Of Data	Data is read as a byte stream, no distinguishing indications are transmitted to signal message (segment) boundaries.	Packets are sent individually and are checked for integrity only if they arrive. Packets have definite boundaries which are honored upon receipt, meaning a read operation at the receiver socket will yield an entire message as it was originally sent.
Weight	TCP is heavy-weight. TCP requires three packets to set up a socket connection, before any user data can be sent. TCP handles reliability and congestion control.	UDP is lightweight. There is no ordering of messages, no tracking connections, etc. It is a small transport layer designed on top of IP.
Data Flow Control	TCP does Flow Control. TCP requires three packets to set up a socket connection, before any user data can be sent. TCP handles reliability and congestion control.	UDP does not have an option for flow control
Error Checking	TCP does error checking	UDP does error checking, but no recovery options.
Fields	1. Sequence Number, 2. AcK number, 3. Data offset, 4. Reserved, 5. Control bit, 6. Window, 7. Urgent Pointer 8. Options, 9. Padding, 10. Check Sum, 11. Source port, 12. Destination port	1. Length, 2. Source port, 3. Destination port, 4. Check Sum
Acknowledgement	Acknowledgement segments	No Acknowledgment
Handshake	SYN, SYN-ACK, ACK	No handshake (connectionless protocol)
Checksum	checksum	to detect errors

TASK 2:Briefly describe the process of sendin packet from host A to host D.

The transmission would go like this:

Host A wants to send a packet to Host D. Host A must knows Host D's IP address. However, if it does not know, then it will send something called an ARP request (Address Resolution Protocol) to the network, with the destination IP. 

 A few things will happen here:

1. If the IP is local. The host with that IP will reply back to the sender with its MAC address.
2. If the IP is non-local. The gateway router will detect this and send its MAC address.
3. If the IP is non-local and Host A's default gateway and subnet mask are set. Using this information Host A can determine the non-locality of the IP address and send it to the router's MAC address (ARPing if not known yet).

If Host A found this out earlier, it will be in the ARP cache and Host A will just use that. Now that the MAC address is sent, the packet can be transferred. The next stop will be the switch. The switch knows which outbound port the MAC address listed as the destination is on, because it tracks every MAC address it's seen a packet come from and which port it came on, If it does not know, then it will flood it out every single port, guaranteeing it'll arrive.

As such, the packet arrives at the router. The IP model is that it divides every single IP address in the network/world into a hierarchy which is subnet. The packet is then sent out that port.

TASK 1: List all the dial-up modem speed (connection vs bitrate)

Note that the values given are maximum values, and actual values may be slower under certain conditions (for example, noisy phone lines)

Connection	Bitrate
110 baud (Bell 101)	0.1 kbit/s	(110 bits per second)
300 baud (Bell 103 or V.21)	0.3 kbit/s
1200 baud (Bell 212A or V.22)	1.2 kbit/s
2400 baud (V.22bis)	2.4 kbit/s
2400 baud (V.26bis)	2.4 kbit/s
4800 baud (V.27ter)	4.8 kbit/s
9600 baud (V.32)	9.6 kbit/s
14.4 kbit/s (V.32bis)	14.4 kbit/s
28.8 kbit/s (V.34)	28.8 kbit/s
33.6 kbit/s (V.34)	33.6 kbit/s
56k kbps (V.90)	56.0/33.6 kbit/s
56k kbps (V.92)	56.0/48.0 kbit/s
Hardware compression (V.92/V.44)	56.0 to 320.0 kbit/s	(variable)
Server-side web compression	200.0 to 1000.0 kbit/s	(variable)

The figure above shows that the connection with its modulation , bitrate and year released.

ASSIGNMENT 1

1.        How many visitors who have visited my website?

376

2.       With reference to Chapter 2, answer the following questions

i.         Briefly describe the function of the equipment at layers 1, 2 and 3.

       

        Layer 1:

·         Transmit and receive data to communication medium

·         Does not care about content

·         Media,  voltage , levels ,speed ,connector

                      Layer 2:

·         Detect and corrects error

·         Organizes data into frames before passing it down. Sequence packet(if necessary)

·         Accept acknowledgement from immediate receiver.

Layer 3:

·         Relay and route information to destination

·         Manage journey of datagram and figure out intermediate hops(if needed)

ii.       Specify 7 criteria to consider when selecting a NOS.

·         Reliability – stably perform in any condition

·         Performance-serve the clients in a seamless way

·         Adaptability-adapt request of different platform.

·         Affordability-ability to pay cost

·         Scalability-continue function well when size expand

·         Ease-ease installation

·         Security-ability to eliminate and repel threats

       

       

       

iii.      Explain the differences between Logical address and Physical address.

       

Physical Address	Logical Address
Address seen by the memory unit and it allow the data bus to access a particular memory cell in the memory	Generated by the CPU when executing a program are mapped in to physical address using the MMU.

iv.     Explain the differences between OS and NOS.

OS	NOS
Peer to peer model :Several computer using different operating systems in a small business or home can be connected to form a small LAN	User account: collection of all  of the information that pertains to a user on a computer
Client/server model :control which resource on the LAN are  shared, and who can access these resource	Authentication ,validation ,log in: The process of entering a correct user ID  and password  to gain access to a computer.

3.      In your opinion why IPv6 is still not fully implemented.

There is no specific date when everything must be upgraded to IPv6 (although some organizations, including governments, have already identified target dates for their own IPv6 implementation. IPv6 and its transition mechanisms have been designed for a long period of co-existence with IPv4 and it is expected that IPv4-only systems and applications will survive for many years. However, IPv6-only systems are expected to arise and many of these users are likely to be in emerging business markets and developing countries.