network whole sem!!

Data Communications

refers to the transmission of digital data between two or more computers.

example: cable, radio waves, and fiber optics

Data

refers to information presented in whatever form is agreed upon by the parties creating and using the data.

Telecommunication

means communication at a distance.

1. Delivery

2. Accuracy

3. Timeliness

4. Jitter

Fundamental Characteristics of a data communication system

- these are the qualities that determine how effective and reliable communication is.

Delivery

The system must deliver data to the correct destination. Data must be received by the intended device or user and only by that device or user.

Accuracy

The system must deliver the data accurately. Data that have been altered in transmission and left uncorrected are unusable.

Timeliness

The system must deliver data in a timely manner. Data delivered late are useless.

(overall arrival time ng data)

Jitter

Refers to the variation in the packet arrival time. It is the uneven delay in the delivery of audio or video packets.

(consistency of arrival)

1. Message

2. Sender

3. Receiver

4. Transmission medium

5. Protocol

Five Components of Data Communication

Message

It is the information (data) to be communicated. It can be text, numbers, pictures, audio, video, etc.

Sender

It is the device that sends the data message. It can be a computer, workstation, telephone handset, video camera, etc.

Receiver

It is the device that receives the message. It can be a computer, workstation, telephone handset, television, etc.

Transmission medium

It is the physical path by which a message travels from sender to receiver. Examples are twisted-pair wire (land cable), coaxial cable, fiver-optic cable, radio waves, etc.

Protocol

It is a set of rules that govern data communications. It represents an agreement between the communicating devices.

Data Flow

Refers to the direction in which data is transmitted between two devices in communication systems

- Simplex

- Half-duplex

- Full-duplex

three Data Flow:

Simplex

The communication is unidirectional. Only one of the two devices on a link can transmit; other can only receive.

Examples are Keyboard in which can only introduce input; and monitor can only accept output. The simplex mode can use the entire capacity of the channel to send data in one direction.

Half-duplex

Each station can both transmit and receive, but not at the same time. When one device is sending, the other can only receive, and vice versa.

Example: Walkie-talkies and CB (citizens band) radios are both half-duplex systems.

Full-duplex

Both stations can transmit and receive simultaneously.

Example: modern internet connection, we can upload and download data at the same time through internet. Another example is Discord na software, pede kang magsalita/give information at the same time pede mo rin silang marinig.

Networks

A set of devices connected by communication links. A node can be a computer, printer, or any other device capable of sending and/or receiving data generated by other nodes on the network.

Distributed Processing

Where task is divided among multiple computers.

Example: Online games, multiple servers handle different regions or player group, online games have million of players if only one server handle everyone it would be overloaded and slow cause high lag, delay, or crash. So, game companies use many servers to share the workload.

1. Performance

2. Reliability

3. Security

Network Criteria

Performance

can be measured in many ways:

- Transit time

- Response time

Transit time

is the amount of time required for a message to travel from one device to another.

simply, it is just sending the data out.

Response time

is the elapsed time between an inquiry and a response.

it is a full route trip delay until you see the result.

Reliability

can be measured by:

- The frequency of failure

- The time to recover from failure

- The network's robustness in a catastrophe. (This is about how will the network continues to function during major problems such as power outage, natural disasters, or cyber attacks.)

Security

issues include:

- Protecting data from unauthorized access, damage, and change

- Implementing policies and procedures for recovery from breaches and data losses.

Protocol

A set of rules that govern data communications. It defines what is communicated, how it is communicated, and when it is communicated. The key elements of this are syntax, semantics, and timing.

Syntax

The structure or format of the data, meaning the order in which they are presented.

Semantics

Meaning of each section of bits.

Example: traffic lights, the colors are like the bits in the data communication and the semantics is the agreed meaning of each color.

Timing

Refers to two characteristics; when data should be sent and how fast they can be sent.

In data communication, timing ensures the sender and receiver are synchronized and data is sent at a rate the receiver can handle.

Standards

Are essential in creating and maintaining an open and competitive market for equipment manufacturers and guaranteeing national and international interoperability of data and telecommunications technology and processes.

De facto (by fact)

De jure (by law)

Data communication standards fall into two categories:

De facto (by fact)

Standards that have not been approved by an organized body but have been adopted as standards through widespread use.

De jure (by law)

Those standards that have been legislated by an officially recognized body.

Point-to-point

Multipoint

two Physical Structures

Point-to-point

Provides a dedicated link between two devices.

Example: Telephone call between two people, only the caller and receiver are connected.

Multipoint

Connection is one in which more than two specific devices shares a single link.

Example: Wifi network, sa bahay kung meron tayong router, pede nating i-connect yung tv, laptop, or smartphones natin.

Network Topology

The physical and logical relationship of nodes (any device that can send, receive, or forward data in a network). It is the schematic description of a network arrangement, connecting various nodes through lines of connection.

Network Topology - Physical

Means placement of various nodes.

Network Topology - Logical

Means it deals with the data flow in the network.

1. Mesh

2. Star

3. Bus

4. Ring

5. Hybrid

Types of Topologies

Mesh Topology

Every device has a dedicated point-to-point link to every other device.

- has n(n - 1)/2 physical channels to link n devices. (Kung ilan yung physical channels or cable na gagamitin mo, this is the formula.)

1. Partial Mesh

2. Full Mesh

Types of Mesh Topology

Partial Mesh Topology

Some of the nodes are connected but only with fewer connections for the same number of nodes.

Full Mesh Topology

Every node connects to every other node.

Star Topology

Each device has a dedicated point-to-point link only to a central controller, usually called a hub or a switch.

Bus Topology

Every node is attached to one shared bus cable.

- Transmits data only in one direction

- Every device is connected to a single cable.

(Disadvantage is kapag nag-fail yung backbone, the whole network goes down)

Ring Topology

Each device has a dedicated point-to-point connection with only the two devices on either side of it.

- Data is transferred in a sequential manner that is bit by bit. Data transmitted has to pass through each nodes of the network, till the destination node.

(Advantage is data moves in one direction, nire-reduce nito yung collisions and merong equal access--every device has equal opportunity to transmit avoiding network domination. Disadvantage is single point of failure, if one device or isang cable ay nag-fail the whole network may go down.)

Hybrid Topology

Is a mixture of two different types of topologies.

- Inherits the advantages and disadvantages of the topologies included

- Combination of two or more topologies

(Combines the best features of different topologies. Ginagawa nitong flexible, scalable, and reliable yung network flow.)

Local Area Networks (LANs)

A group of computers connected to each other in a small area.

- Less costly as it is built with inexpensive hardware such as hubs, network adaptors, internet cables, etc.

- Faster data transfer.

- High security.

(Can cover small areas like room, building, computer shop, or office. It connects computers and devices for resource sharing like files, printers, and internet. Examples: computer shop, school laboratory, or home wifi.)

Wide Area Networks (WANs)

A network that extends over a large geographical area such as states or countries.

- Spans over a large geographical area through telephone line, Fiber optic cable, or satellite links.

(Examples: internet, global banking networks, company offices worldwide)

Metropolitan Area Networks (MANs)

A network with a size between LAN and WAN.

- Normally covers the area inside a town or a city.

- Government agencies use MAN to connect the citizens and private industries.

(Example: cable ng tv networks sa city or yung city wide wifi)

OSI MODEL (Open Systems Interconnection)

a conceptual framework used to describe functions of a networking system.

OSI MODEL

uses layers to give visual description of what is going on with a particular networking system.

1. Physical

2. Data Link

3. Network

4. Transport

5. Session

6. Presentation

7. Application

OSI Model 7 layers

International Standards Organization (ISO)

was established in 1947, dedicated to worldwide agreement on international standards.

Open Systems Interconnection Model (OSI)

an ISO standard that covers all aspects of network communication

It was first introduced in late 1970s.

7) Application Layer

• used by network applications.

• enables user to access network. It provides user interfaces and support for services.

Network Services

1. File Transfer - FTP (File Transfer Protocol)

2. Web Surfing - HTTP/S (Hypertext Transfer Protocol)

3. Emails - SMTP (Simple Mail Transfer Protocol)

4. Virtual Terminals - TELNET

6) Presentation Layer

receives data from applications layer. These data are in form of numbers or characters.

6) Presentation Layer

concerned with syntax and semantics of information exchanged between two systems.

1. Translation

2. Data Compression

3. Encryption

Functions of Presentation Layer

Translation

Converts data to binary format for machine to understand

Data Compression

Reduces number of bits that are used to represent original data.

Encryption

Enhances security of data.

Secure Sockets Layer (SSL)

is used in encryption and decryption of data.

Session Layer 5

helps in setting up and managing connections, enabling sending and receiving of data followed by termination of connections or sessions.

1. Synchronization

2. Dialog Control

3. Authentication

4. Authorization

Functions of the Session Layer

Synchronization

Allows a process to add checkpoints or synchronization points to a stream of data.

Dialog Control

Allows communication between two processes to take place in either half-duplex or full-duplex mode.

Authentication

process of verifying user.

• A session is established between server and computer once user is authenticated.

Authorization

Process used by server to determine if user has permission to access a file or a site.

4) Transport Layer

- Responsible for process-to-process delivery of entire message.

- provides enhancements to services of network layer.

- main task: ensure that data sent from one computer arrives reliably, in correct sequence, and without errors at receiving computer.

1. Segmentation

2. Flow Control

3. Error Control

Functions of the Transport Layer

Segmentation

Data received from session layer is divided into small data units called segments.

• Each segment contains a source and destination port and sequence number.

Flow Control

transport layer controls amount of data transmitted to a level that receiver can process.

• Example: A mobile phone connected to a server.

• The server can process data up to 100 Mbps, while mobile phone can only process 10 Mbps.

Error Control

If some data units never arrive at destination, transport layer uses

Automatic Repeat Request (ARQ)

schemes to retransmit lost or corrupted data.

Transmission Control Protocol (TCP)

• Connection-oriented transmission

• Gives feedback; data that is lost can be retransmitted

• Used for Internet surfing, Emails, FTP, etc.

User Datagram Protocol (UDP)

• Connectionless transmission

• No feedback whether data is really delivered or not

• Used for streaming, music, gaming, voice calls, DNS, etc.

3) Network Layer

Works for transmission of received data segments from one computer to another located in different networks.

1. Logical Addressing

2. Routing

3. Path Determination

Functions of the Network Layer

Logical Addressing

IP addressing (IPv4 or IPv6) is done at network layer.

• Every computer in a network has a unique IP address.

• It assigns sender and receiver IP addresses to each segment so that each data packet can reach correct destination.

Routing

Method of moving data packets from source to destination based on logical addressing.

Path Determination

Choosing best possible path for data delivery from source to destination.

• OSPF (Open Shortest Path First)

• BGP (Border Gateway Protocol)

• IS-IS (Intermediate System to Intermediate System)

2) Data Link Layer

Receives packets from network layer which contain IP addresses of sender and receiver.

1. Logical Addressing

2. Physical Addressing

Two kind of addressing:

Logical Addressing

Done at network layer where sender and receiver IP addresses are assigned to each data packet.

Physical Addressing

Done at data link layer where MAC addresses of both devices are assigned to receive data packet.

1. Framing

2. Flow Control

3. Error Control

4. Access Control

Functions of Data Link Layer

Framing

Divides stream of bits received from network layer into manageable data units called frames.

Flow Control

Imposes a flow control mechanism to avoid overwhelming receiver.

Error Control

Adds mechanisms to detect and retransmit damaged or lost frames.

Access Control

Determines which device has control over link at any given time.

1) Physical Layer

Converts binaries into signals (electrical, radio, or optical).

Functions of the Physical Layer

1. Physical Characteristics of Interfaces and Medium

2. Representation of Bits

3. Data Rate

4. Synchronization of Bits

5. Line Configuration

6. Physical Topology

7. Transmission Mode

Physical Characteristics of Interfaces and Medium

Defines interface between device and transmission medium, including type of transmission medium.

Representation of Bits

Defines how bits (binary data) are encoded into signals (electrical or optical).

Data Rate

Defines duration of a bit (how long it lasts).