INSY 3303 Exam 1

Application Layer Functions

1. Data Storage - data storage and retrieval 2. Data Access Logic - the processing required to access the data (database queries) 3. Application Logic -simple or complex depending on the application 4. Presentation Logic - the presentation of information to the user and acceptance of the users commands.

Parts of a SMTP Packet

1. Header - lists the source and destination email addresses. 2. Body - The word DATA followed by the message itself.

Five Fundamental Application Architectures

1. Host-Based 2. Client-Based 3. Client-Server 4. Cloud Based 5. Peer-toPeer

Internet Model Layers

1. Physical Layer 2. Data Link Layer 3. Network Layer 4. Transport Layer 5. Application Layer

OSI Model Layers

1. Physical layer 2.Data Link Layer 3.Network Layer 4.Transport Layer 5.Session Layer 6.Presentation Layer 7.Application Layer

Pros of digital transmission

1. Produces fewer errors 2. Higher maximum transmission rates 3.More efficient 4. More secure 5. Integrating voice, video, and data is much simpler with digital

Parts of an HTTP Response

1. Response Status - Contains the HTTP version of the server, a status code (I.e Error:404 "not found or 200 "ok") and a reason phrase / reason for status code 2. Response Header - contains optional information like the web server being used, the date, and the URL of the web page 3. Response Body - Is the webpage itself.

Parts of an HTTP request

1. The request line - starts with a command, provides webpage, HTTP Version Number 2. Request Header - Contains optional information such as web browser used & date. **Still required 3. Request Body - Contains information sent by the user (Form info) **Not Required / Optional

Client-Server Pros

1. allows for scalability 2. The most reliable 3. Usually the cheapest to deploy 4. Enable cloud computing.

Layer PDUs

1. application layer - HTTP packet 2. transport layer - TCP segment 3. network layer - IP packet 4. datalink layer - Ethernet frame

Pros and Cons of layers

1. easy to develop new software 2.ensuring the software used at different layers is the same 3. It is somewhat inefficient because of encapsulation.

Three basic components of a network:

A server, client, and a circuit.

Software as a service

AKA Hardware as a service Only the hardware is outsourced to provider. (infrastructure) Organization manages all the application and software(operating system database software), and data.

Scalability

Ability to increase or decrease the capacity of the servers to meet changing needs.

Synchronous Transmission

All letters or data in one group of data are transmitted at one time as a block of data called a frame. start and stop bits are placed around the entire frame. point-to-point and multipoint circuits

Full-Duplex

Allow simultaneous communication both ways

Half-Duplex

Allows for two way communication but you can only transmit one way at a time. con is turnaround time or retrain time. which is the time it takes to switch between sending and receiving.

Host-Based Architecture

Application software and all data is stored on the one server. utilizes terminals one point of control Problems: Server Overload Not scaleable, upgrades are large and expensive.

Client Server Architectures

Balance processing between client and server Client is responsible for the presentation logic server is responsible for data access logic and data storage. application logic can either reside on the client or the server, or be split between the two. Enable software and hardware from different vendors to used together. requires use of middleware to make the software/hardware from different vendors work together. ***Two-Tier, Three-Tier, & n-Tier Architecture.

Bipolar Vs Unipolar

Bipolar signaling experiences fewer errors than unipolar.

Data Rate

Calculated by multiplying the number on each symbol by the maximum symbol rate

White Noise

Caused by thermal agitation of electrons and is therefore inescapable (TV & Radio)

Client Based Architectures

Client is responsible for presentation, application and data access logic. Server simply store the data. usually client and server are on the same network (LAN) Problem Overloads the network circuit All data must be transmitted from server to client.

Access Request

Clients send request to the device controlling the circuit to ask for permission to transmit

POP (Post Office Protocol)

Commonly used standard for communication between client and email server Email must be copied to clients hard disk and deleted from the email server before it cam be read.

Contention

Computers wait until the circuit is free and transmit when ever they have data to send Usually used in Ethernet LANs

Controlled Access

Controls the circuit and determines which clients can transmit at what time

Media Access Control

Controls the physical hardware Controls how and when the physical layer converts and transmits bits into the physical symbols that are transmitted

Time Division Multiplexing

Divides the circuit vertically Shares the circuit among two or more computers by having them take turns.

Frequency Division Multiplexing (FDM)

Dividing the circuit horizontally many signals can travel the communication circuit simultaneously because they are different frequencies. Don't interfere with each other.

Telnet

Enables users to log into servers or other clients. Requires app layer on both the client and the server.

Statistical Time Division Multiplexing

Exception to the rule that the capacity of a multiplexed circuit must be equal to the sum of the circuits it combines. allows for more computers to be connected to a circuit than FDM or TDM. the transmission speed of the multiplexed circuit is based on a statistical analysis of the usage requirements of the circuits to be multiplexed.

What is a client?

Is the inout-output device at the user end. (I.E. clients computer)

Impulse noise

Is the primary source of errors in data communications aka spikes voltage changes, lightning, poor connections

What is a circuit?

It is the pathway through which a message (data) travels. Think everything in-between the server and client, connects them together.

Application Layer

It is the users access to the network. user defines what messages are sent over the network.

Types of networks:

LAN(local area network) - is a group of computers located in the same general area. Backbone Networks - larger, central networks connecting several LANs, other BNs, and WANs. Typically span 100's of feet to several miles. WAN(wide area networks)- connect BNs and MANs (metropolitan area networks). typically span hundreds or thousands of miles. Intranets- Is a LAN that uses the same technology as the internet but is only available to those inside the organization Extranets- Use the same technology as the internet, but provided to invited users

Data Link Layer Sublayers

Logical link control Media access control

Internet Model

Most commonly used model of the two. Its the network model that dominates current hardware and software. Simple five layer Collapses the top three layers of the OSI model into one layer. ( application layer, presentation layer, and session layer collapses down into the application layer.)

Cyclic Redundancy Check

Most popular error-checking scheme It adds 8,16,24, or 32 bits to the message

Two most important network models:

OSI (open systems interconnection reference) Internet model

Parity Checking

One additional bit is added to each byte in the message called a parity bit goal to make the number of 1s in a message odd or even

Simplex Transmission

One way transmission (Radio, TV)

Circuit Data

Only two kinds can flow through a circuit Digital and Analog

Error Detection Methods

Parity Checksum Cyclic Redundancy Check

Cloud Computing Architecture

Part or all of the infrastructure is outsourced Infrastructure as a service Platform as a service Software as a service ** Compared to traditional client-server arch. Where all of the infrastructure is managed internally.

Network Layer

Performs routing, selects the next computer to which the message should be sent. finds the address of the computer (receiver) if it is unknown

Thick-Client

Places all or almost all of application logic on client computer Not easy to manage, all clients need to be updated

Logical Circuit

Refers to the transmission characteristics of the connection. Such as how fast data can be sent through the connection.

Transport Layer

Responsible for linking the application layer software to the network and establishing end to end connection between the sender and receiver. responsible for breaking long messages into several smaller ones, and then reassembling them into the original one at receiving end.

Continuous ARQ

Sender does not wait for a response from the receiver before sending the next packet. Important for providing flow control Full Duplex Tech

Stop-Wait ARQ

Sender stops and waits for a response from the receiver after each data packet Acknowledgment ACK - no error Negative Acknowledgement NAK - Error Half-Duplex tech

Physical Circuit

The actual wire used to connect two devices

Amplitude Modulation (Amp Shift Keying)

The amplitude or height of the wave is changed

Circuit Configuration

The basic physical layout of the circuit Two fundamental configs are point-to-point and multipoint

Platform as a service

The needed hardware and software is outsourced to the cloud provider. (data access logic and software/operating system) Create your own application and manage the data.

Codec

Translates analog voice data into digital data

Line Noise

Twisted Pair and Coaxial cable noise manifests itself as extra bits, missing bits or bits that have been flipped

What is a server?

Typically servers provide some service for the clients. (data access, application logic, etc)

Overhead Bits

Used for purposes of error checking and marking the start and end of characters and packets.

Point-to-point Protocol

Used in WANs very similar to SDLC or HDLC designed for point-to-point but can be used on multipoint

Repeaters/Amplifiers

Used to avoid attenuation in telephone circuits

Three Tier Thin Client-Server Email Architecture

Uses a web server and a web browser to provide access to your email. you do not need an email client with this architecture. Uses HTTP, SMTP, and POP. STMP & POP for communication between the web server and the mail server. HTTP for communication between the web server and the client.

n-Tier

Uses more than three sets of computers Client - presentation App Server - Application Logic (split between two or more Application Servers) Database - Data access and storage

Two-Tier

Uses one client and one server Client - presentation and application logic Server - data

Three-Tier

Uses one client and two servers. Client - presentation App Server - Application Logic Database - Data access and storage

Ethernet

Very popular LAN protocol IEEE 802.3ac uses contention media access protocol

MIME (Multipurpose Internet Mail Extension)

Works with SMTP to allow for email to transfer non-text files. (Ex. Graphics)

Automatic Repeat reQuest (ARQ)

a receiver that detects an error asks the sender to retransmit the message until it is received without error. Stop-Wait Continuous

Checksum

added to the end of a message calculated by adding the decimal value of each character in the message and dividing by 255. The remainder is used as the checksum value

Point-To-Point

aka dedicated circuit Connects one computer to another. used when both computer generate enough data to fill the line.

Multipoint

aka shared circuits Allows many computers to share the same circuit Only one computer can use the circuit at a time.

Data compression

can increase the throughput of a circuit by compressing the data

IMAP (Internet Message Access Protocol)

commonly used standard for communication between client and email server All emails are stored on the email server until the user deletes them. Allows them to be viewed on many different devices.

Logical Link Control

data link layers connection to the network layer. responsible for communicating with the network layer and placing the IP packet into a ethernet frame.

Bandwidth

difference between the highest and the lowest frequencies in the set of frequencies.

Frequency Modulation(Freq Shift Keying)

each 0 and 1 is represented by a certain number of waves per second.

attenuation

is the loss of power a signal suffers as it travels.

SMTP (Simple Mail Transfer Protocol)

is the most commonly used email standard simply because it is the email standard used on the internet.

Physical Layer

is the physical connection between the sender and receiver. Includes all hardware devices specifies the type of connection and the signals/radio waves/or light waves that pass through it. Role is to transfer series of signals through the circuit.

Throughput

is the total number of information bits received per second, after taking into account overhead bits and the need for retransmission. smaller frames provide better throughput for circuits with more errors Larger frames provide better throughput for networks less prone to errors.

Multiplexing

means to break one high-speed physical communication circuit into several lower-speed logical circuits. Often done in multiples of 4.

Cross-talk

occurs when one circuit picks up signals in another.

High-level Data Link Control (HDLC)

often used in WANs An Information frame is used to transmit information An Supervisory frame is used to transmit ACKs and NAKs Address and control fields can be longer than those in SDLC

Software as a service

organization outsources the entire application to the cloud provider. based on multi-tenancy: there is one application that everyone shares, but can customize to fit their need.

Thin-Client

places little or no application logic on the client computer easier to manage, only server with app logic needs updating enables cloud-based architecture

Data Link Layer

responsible for moving a message from one computer to the other in the network path (sender to receiver). Controls physical layer by deciding when the physical layer will transmit messages. formats messages by indicating where they start and end. detects and may correct errors that occurred during transmission.

echoes

result of poor connection resulting in the signal being reflected back to transmitting equipment.

protocol stack

set of software used to understand the different protocols

intermodulation noise

signal from two circuits combines to form a new signal that falls in the frequency band of another signal.

Asynchronous Transmission

start-stop transmission because the transmitting computer can transmit a character whenever it wants and the receiving computer will accept it used on point-to-point full duplex circuits each character is transmitted independently start and stop bits are placed for each character

Phase Modulation

the direction in which the wave begins

OSI Model

the framework of standards for computer to computer communications. replaced by internet model, never caught on.

Transmission Efficiency

the total number of information bits divided by the total number of bits in transmission

Application Architecture

the way in which the functions of the application layer software are spread among clients and servers in the network (Client-Server Arch, P2P, etc)

Information bits

those used to convey the message

Modem

translates digital data into analog data to be transmitted through voice communication circuits and translates the analog data back into digital data.

Forward Error Correction

uses codes containing sufficient redundancy to prevent errors by detecting and correcting them at the receiving end without retransmission.