1. Unit 28 Website Production
Assignment “2”

2. Understanding Web Servers
Needs protocols to ensure each computer can exchange data.
Most important protocols are:
Transmission Control Protocol
Allows for the delivery of data
Internet Protocol
Establishes consistent address format to allow machines to contact each other
Both of these date back to 1960s
Understanding Web Servers

3. Any device connecting to internet must have unique IP address (currently version 4)
Four octets of numbers (range ) separated by dots
Gives ~4 billion unique addresses
Now running out so moving to version 6 this will yield 3.4 * 10 38 IP

4. The TCP/IP Reference Model
Frame of reference used to develop the Internet's protocols.
Consists of layers that perform functions necessary to prepare data for transmission over a network.
Description
Protocols
Application
Provides network services to user applications
HTTP, HTML, Telnet, FTP, SMTP, DNS
Transport
Provides end-to-end management of data and divides data into segments
TCP, UDP
Internet
Provides connectivity between hosts in the network
IP, ICMP, RIP, ARP
Network Access
Describes the standards that hosts use to access the physical media
8.8.1 Define the TCP/IP model
The TCP/IP reference model
Frame of reference used to develop the Internet's protocols
Consists of layers that perform functions necessary to prepare data for transmission over a network
A message moves from the top (Application) layer down the TCP/IP layers to the bottom Network Access Layer. Header information is added to the message as it moves down through each layer and is then transmitted. After reaching the destination, the message travels back up through each layer of the TCP/IP model. The header information that was added to the message is stripped away as the message moves up through the layers toward its destination.
Application Layer protocols provide network services to user applications such as web browsers and programs
Transport Layer protocols provide end-to-end management of the data and divides the data into manageable segments for easier transport across the network
Internet Layer protocols provide connectivity between hosts in the network
Network Access Layer protocols describe the standards that hosts use to access the physical media. The IEEE Ethernet standards and technologies, such as CSMA/CD and 10BASE-T are defined in this layer.

5. The OSI Model
The OSI model is an industry standard framework that is used to divide network communications into seven layers.
Although other models exist, most network vendors today build their products using this framework.
A protocol stack is a system that implements protocol behavior using a series of layers.
Protocol stacks can be implemented either in hardware or software, or in a combination of both.
Typically, only the lower layers are implemented in hardware, and the higher layers are implemented in software.
8.8.2 Define the OSI model
The OSI model is an industry standard framework that is used to divide network communications into seven distinct layers. Although other models exist, most network vendors today build their products using this framework.
A system that implements protocol behavior consisting of a series of these layers is known as a protocol stack. Protocol stacks can be implemented either in hardware or software, or a combination of both. Typically, only the lower layers are implemented in hardware, and the higher layers are implemented in software.

6. The OSI Model "Please Do Not Throw Sausage Pizza Away" Layer
Description
Application 7
Responsible for network services to applications
Presentation 6
Transforms data formats to provide a standard interface for the Application layer
Session 5
Establishes, manages and terminates the connections between the local and remote application
Transport 4
Provides reliable transport and flow control across a network
Network 3
Responsible for logical addressing and the domain of routing
Data Link 2
Provides physical addressing and media access procedures
Physical 1
Defines all the electrical and physical specifications for devices
8.8.2 Define the OSI model
Each layer is responsible for part of the processing to prepare data for transmission on the network. The chart shows what each layer of the OSI model does.
NOTE: Mnemonics can help you remember the seven layers of the OSI. Some examples include: "All People Seem To Need Data Processing" and "Please Do Not Throw Sausage Pizza Away".
Remember the OSI layers with this mnemonic:
"Please Do Not Throw Sausage Pizza Away"

7. Compare OSI and TCP/IP Models
The OSI model and the TCP/IP model are both reference models used to describe the data communication process. The TCP/IP model is used specifically for the TCP/IP suite of protocols and the OSI model is used for development of standard communication for equipment and applications from different vendors.
The TCP/IP model performs the same process as the OSI model, but uses four layers instead of seven.
Student Activity: The student course content includes a matching activity, OSI Model. To complete this activity, students will match the OSI layers to the TCP/IP layers.

8. TCP/IP Application layer
Application Layer protocols provide network services to user applications such as web browsers and programs
They include:
HTTP,
HTML,
Telnet,
FTP,
SMTP,
DNS
Find definitions for each of these, explain what they do.
TCP/IP Application layer

9. P1 outline the web architecture and components which enable internet and web functionality
P2 explain the user side and server side factors that influence the performance of a website
M1 explain the role of web architecture in website communications
D1 explain the role of the TCP/IP protocol and how it links to application layer protocols
Assignment “2”

10. The Application layer, Layer seven, is the top layer of both the OSI and TCP/IP models.
It provides the interface between the applications we use to communicate and the underlying network over which our messages are transmitted.
Application layer protocols are used to exchange data between programs running on the source and destination hosts.
There are many Application layer protocols and new protocols are always being developed
Application Layer

11. The functionality of the TCP/IP application layer protocols fit roughly into the framework of the top three layers of the OSI model: Application, Presentation and Session layers

12. Application Layer Functions
In order for the communications to be successful, the application layer protocols implemented on the source and destination host must match.
Protocols establish consistent rules for exchanging data between applications and services loaded on the participating devices
Many different types of applications communicate across data networks. Therefore, Application layer services must implement multiple protocols to provide the desired range of communication experiences
Applications and services may also use multiple protocols in the course of a single conversation.
Application Layer Functions

13. The Transport layer uses an addressing scheme called a port number
The Transport layer uses an addressing scheme called a port number. Port numbers identify applications and Application layer services that are the source and destination of data
Domain Name System (DNS) - TCP/UDP Port 53
Hypertext Transfer Protocol (HTTP) - TCP Port 80
Simple Mail Transfer Protocol (SMTP) - TCP Port 25
Post Office Protocol (POP) - UDP Port 110
Telnet - TCP Port 23
Dynamic Host Configuration Protocol - UDP Port 67
File Transfer Protocol (FTP) - TCP Ports 20 and 21
Common Ports

14. Application Layer Software
Within the Application layer, there are two forms of software programs or processes that provide access to the network.
Network-Aware Applications: Some end-user applications are network-aware, meaning that they implement the application layer protocols and are able to communicate directly with the lower layers of the protocol stack. Ex: client, web browser
Application Layer Software

15. In a client/server network, the server runs a service, or process, sometimes called a server daemon.
Like most services, daemons typically run in the background and are not under an end user's direct control.
When a daemon "hears" a request from a client, it exchanges appropriate messages with the client, as required by its protocol, and proceeds to send the requested data to the client in the proper format
httpd, telnetd, ftpd and etc
Servers
KC KHOR, Multimedia Univ. Cyberjaya

16. Application Layer Protocol Functions
In order for the communications to be successful, the application layer protocols implemented on the source and destination host must match.
Protocols establish consistent rules for exchanging data between applications and services loaded on the participating devices
Many different types of applications communicate across data networks. Therefore, Application layer services must implement multiple protocols to provide the desired range of communication experiences
Applications and services may also use multiple protocols in the course of a single conversation.
Application Layer Protocol Functions

17. The Domain Name System (DNS) was created for domain name to address resolution for these networks.
DNS is a client/server service but a bit different from others
The DNS client runs as a service itself.
The DNS client, sometimes called the DNS resolver, supports name resolution for our other network applications and other services that need it
Try nslookup
DNS

18. A DNS server provides the name resolution using the name daemon, which is often called named, (pronounced name-dee).
When a client makes a query, the server's "named" process first looks at its own records to see if it can resolve the name. If it is unable to resolve the name using its stored records, it contacts other servers in order to resolve the name
Once a match is found and returned to the original requesting server, the server temporarily stores the numbered address that matches the name in cache.
ipconfig /displaydns command displays all of the cached DNS entries on a Windows XP or computer system.
DNS cont’d

19. DNS Heirarchy

20. When a web address (or URL) is typed into a web browser, the web browser establishes a connection to the web service running on the server using the HTTP protocol.
The browser interprets the 3 parts of the URL:
1. http (the protocol or scheme)
2. server name)
3. web-server.htm (the specific file name requested).
HTTP specifies a request/response protocol. When a client, typically a web browser, sends a request message to a server, the HTTP protocol defines the message types the client uses to request the web page and also the message types the server uses to respond. The three common message types are GET, POST, and PUT.
GET is a client request for data. A web browser sends the GET message to request pages from a web server.
POST and PUT are used to send messages that upload data to the web server
HTTPS?
HTTP

21. Post Office Protocol (POP) and Simple Mail Transfer Protocol (SMTP) are involved in email services.
Users use an application called a Mail User Agent (MUA), or client to allow messages to be sent and places received messages into the client's mailbox.
In order to receive messages from an server, the client can use POP.
Sending from either a client or a server uses message formats and command strings defined by the SMTP protocol.
protocols

22. schematic

23. FTP was developed to allow for file transfers between a client and a server. An FTP client is an application that runs on a computer that is used to push and pull files from a server running the FTP daemon (FTPd).
The client establishes the first connection to the server on TCP port 21. This connection is used for control traffic, consisting of client commands and server replies.
The client establishes the second connection to the server over TCP port 20. This connection is for the actual file transfer and is created every time there is a file transferred.
The file transfer can happen in either direction. The client can download (pull) a file from the server or, the client can upload (push) a file to the server.
FTP

24. DHCP
The Dynamic Host Confirmation Protocol (DHCP) service enables devices on a network to obtain IP addresses and other information from a DHCP server. This service automates the assignment of IP addresses, subnet masks, gateway and other IP networking parameters.
KC KHOR, Multimedia Univ. Cyberjaya

25. A DHCP server replies with a DHCP OFFER.
The DHCP server maintains a pool of IP addresses and leases an address to any DHCP-enabled client when the client is powered on.
DHCP DISCOVER packet to identify any available DHCP servers on the network
A DHCP server replies with a DHCP OFFER.
The client may receive multiple DHCP OFFER packets if there is more than one DHCP server on the local network, so it must choose between them, and broadcast a DHCP REQUEST packet that identifies the explicit server and lease offer that the client is accepting.
Assuming that the IP address requested by the client, or offered by the server, is still valid, the server would return a DHCP ACK message that acknowledges to the client the lease is finalized.
If the offer is no longer valid - perhaps due to a time-out or another client allocating the lease - then the selected server will respond with a DHCP NAK message (Negative Acknowledgement).
If receive DHCP NAK, begin again with a new DHCP DISCOVER.
KC KHOR, Multimedia Univ. Cyberjaya

26. Telnet
Telnet provides a standard method of emulating text- based terminal devices over the data network.
A connection using Telnet is called a Virtual Terminal (VTY) session, or connection.
Rather than using a physical device to connect to the server, Telnet uses software to create a virtual device that provides the same features of a terminal session with access to the server command line interface (CLI).
To support Telnet client connections, the server runs a service called the Telnet daemon. A virtual terminal connection is established from an end device using a Telnet client application.
If security is a concern, the Secure Shell (SSH) protocol offers an alternate and secure method for server access.
KC KHOR, Multimedia Univ. Cyberjaya