Chapter 2: Application Layer -- N&DP

Middleware is the software that sits between the application software on the client and the application software on the server.

True

All three parts (request line, request header, request body) of an HTTP request from a web browser to a web server are required when a request is made.

False

A "thin client" approach places most of the application logic on the client.

False

A "thin client" architecture approach:

places all or almost all of the application logic on the server

In a client-server network, ___ gets software from different vendors to work together

middleware

With the two-tier client-server architecture, the client is responsible for the logic.

Presentation

1. When adopting a cloud-based architecture, what are the main differences between the private, public, and community cloud deployment models?

   1. The programming languages and frameworks supported by the cloud provider

   2. The level of control, security, and investment required for the organization

   3. The number of users and the volume of data to be processed

   4. The physical location of the cloud infrastructure and data centers

The level of control, security, and investment required for the organization

In a client-server architecture, what is the main reason for separating the presentation logic on the client and the data access/storage logic on the server?

To improve the scalability and reliability of the system

What is the key difference between a thin client and a thick client architecture in a client-server system?

Thin clients perform most processing on the server, while thick clients perform most processing on the client

How does the number of tiers in a client-server architecture affect the distribution of processing and logic?

A two-tier architecture has a client and a server, while a three-tier architecture adds a separate application server

Network applications are software packages that run in the application layer and the only real reason for having a network is to enable these applications

true

Application architecture

The way functions of the application layer software are distributed among clients and servers.

The work done by any application program is divided into what five general functions?

1) Data storage

2) Data access logic

3) Application logic

4) Presentation logic

5) Services logic

What is the data storage function?

Application programs require data to be stored and retrieved

What is the data access logic function?

Processing required to access data

What is the application logic function?

Referred to as business logic

What is the presentation logic function?

How infomration is presented to the user and the acceptance of the user’s commands

What is the services logic function?

like the user interface but rather than users making requests, other application software can make requests.

What are the four fundamental application architectures used today?

1) host-based

2) client-based

3) client-server

4) cloud-based

Host-based architecture

A very simple architecture where the server (host computer) performs all the work

Client-based architecture

A very simple architecture where the client computer performs most of the work and the server usually only has a data storage function.

Clients and servers are usually personal computers on the same network (LAN)

Client-server architecture

The work is shared between clients and servers. Complicated and expensive to deploy

Cloud-based architecture

The cloud provides services to the client

What are the three types of cloud computing deployment models?

1) Private cloud

2) Public cloud

3) Community cloud

Private cloud

Created and exclusively used for a single private organization

Public cloud

Used by multiple organizations that share the same cloud resources

Community cloud

A subset of public cloud; used by organizations that have a common purpose

What are the two fundamental problems with host-based architectures?

1)Server must process all messages (slower)

2) Higher cost to upgrade

What is the fundamental problem in client-based networks?

All data on the server must travel to the client for processing (slow)

What is the greatest strength of client-server networks?

They enable software and hardware from different vendors to be used together which is rather difficult without middleware

Middleware and what it does

Software that sits between the application software for the client and the application software for the server.

1) Provides a standard way of communication between softwares

2) Manages the message transfer so clients don’t need to know what server has the application data

What are the most important standards for middleware our of the dozens there are?

1) Distributed Computing Environment (DCE)

2) Common Object Request Broken Architecture (CORBA)

3) Open Database Connectivity (ODBC) which provides standards for data access logic

Two-Tier Architecture

Most common architecture that uses only two computers

Client: Presentation logic, Application logic, Data access logic

Server: Data storage

Three-tier architectures

Uses three computers

Client: Presentation logic

Server: Services logic, Application logic

Database server: Data access logic, data storage

n-tier architectures

3+ computers

Client: Presentation logic

Web server: Application logic

Application server: Services logic, Application logic

Database server: Data access logic, Data storage

What are the advantages and disadvantages of n-Tier architectures?

Advantages: It’s more scalable because it separates the processing so much to better balance it.

Disadvantages: 1) A greater load on the network

. 2) Much more difficult to program and test software

Thin-client architecture

places little or no application logic on the client and are easier to manage

Enables cloud-based architecture

Thick-client architecture

places all or almost all of the application logic on the client

There is a direct relationship between think and thick clients and two-, three-, and n-tire architectures

False

What are the three common cloud-based architecture models that an organization can choose from:

1) Infrastructure as a service

2) Platform as a service

3) Software as a service

Software as a service (SaaS)

organization outsources the entire application to the cloud provider and then uses it through a browser (thin client)

Ex: email or customer relationship management (CRM)

SaaS is built on…

multitenancy: there is only one application everyone shares but they can customize it to their individual needs

Platform as a service (PaaS)

The organization manages the application and its own data but uses the database software (data access logic) and OS provided from the cloud provider.

For PaaS, the needed hardware and software infrastructure that is rented from the cloud provider is called the platform

True

Infrastructure as a Service (IaaS)

The cloud provider manages the hardware (servers, storage, and networking components)

The organization manages its software (OS, Database software, and its applications and data)

You don’t have to spend as much on hardware and maintenance.

IaaS is sometimes referred to as…

Hardware as a Service (Haas)

Peer-to-Peer Architectures

All computers act as both a client and a server therefore they perform all five functions.

What are the advantages and disadvantages of P2P networks

Advantages: the data can be installed anywhere on the network

Disadvantages: Poor security because of lack of authority or authentication

Almost all new applications today are ____ applications

Client-server; Most reliable, usually cheapest and enable cloud computing.

With hypertext, any document can contain a link to any other document

True

The web is a two-tier client-server architecture

True

What are the 3 parts of an HTTP request (2 required, 1 optional)

1) request line

2) request header

3) request body (optional)

What does a request line consist of in an HTTP request?

Starts with command (e.g GET), provides web page, HTTP version number the browser understands

What does a request header consist of in an HTTP request?

Random info such as the web browser being used and the date

What does a request body consist of in an HTTP request?

The optional part of HTTP request. Just information that the user has typed into form.

What are the 3 parts of an HTTP response (1 required, 2 optional)

1) response status

2) Response header

3) response body

What is in response status for HTTP response?

HTTP version the server used, status code, and reason phrase

What is in response header for HTTP response?

Server being used, the date, exact URL of the page

What is in response body for HTTP response?

The web page itself

The most commonly used standard of email is SMTP (Simple Main Transfer Protocol)

True

How is SMTP email usually implemented?

As a two-tier thick client-server architecture

Mail user agent

For SMTP email, each client computer runs an application layer software package called a mail user agent

Mail transfer agent

For SMTP email, the user agent sends the SMTP packet to a mail server that runs a application software package called a mail transfer agent.

Two most common standards for mail servers and the difference between them:

1) Post Office Protocol (POP)

2) Internet Message Access Protocol (IMAP)

Pop deletes email from server when copied to client’s computer but IMAP does not.

An email with three-tier thin client-server architecture is often called a…

Web-based email allowing you to use your browser.

An SMTP packet has two parts which consist of…

1) header: source and dest. email add. and the address of itself

2) body: the word DATA, and the message

SMTP is a simple standard that permits only the transfer of text messages and works together with MIME software

True

Telnet

lets users log in to servers; PuTTY

Videoconferencing

provides real-time transmission of video and audio to allow two people to have a meeting (desktop videoconferencing)

Webcasting

One-directional non-interactive videoconferencing sent from server to user.

One of the most commonly used business applications is an…

SQL server

One of the top three security risks on the Internet is…

SQL injection and another one is email spoofing