IB Computer Science - 3.1.2-3 Standards & Network Layers

3.1.2-3 Standards & Network Layers

Assessment Statements

3.1.2 Outline the importance of standards in the construction of networks.

3.1.3 Describe how communication over networks is broken down into different layers.

Transmission media in computer networks

Transmission medium is the means through which we send our data from one place to another. The first layer (physical layer) of Communication Networks OSI Seven layer model is dedicated to the transmission media. We will study the OSI Model later in this topic.

- Data is represented by computers and other telecommunication devices using signals.
- Signals are transmitted in the form of electromagnetic energy from one device to another.
- Electromagnetic signals travel through vacuum, air or other transmission mediums to move from one point to another(from sender to receiver).
- Electromagnetic energy (includes electrical and magnetic fields) consists of power, voice, visible light, radio waves, ultraviolet light, gamma rays etc.

Transmission Media

Transmission media of a computer network describes the material substances that carry energy waves, which include the data that’s being transmitted.

Wired/Guided = uses physical cables.

- - Twisted Pair Cables
    - - Copper wires twisted into pairs and wrapped in insulated material. Usually used for telephone services.
  - Coaxial Cables
    - - Consists of copper or aluminum wire wrapped inside an insulating layer
      - Used for TV companies
  - Fibre Optic Cables
    - - Central fibreglass core that is covered in several layers of protective material. An LED is used to create light pulses. Faster than most cables.

Unwired/Unguided/Wireless Connection = uses electromagnetic waves that travel through a vacuum or the air

- - Radio Waves, Microwaves and Infrared Waves
    - Don’t need cable but you will need other hardware for transmission of wireless signals.

Benefits of Fibre Optic over Copper

- - FIbre has better bandwidth
  - Low attenuation (reduction in signal strength occurring while transmitting analog or digital signal over long distances), Little signal loss and can move at higher speeds and greater distance (300 m to 40 km)
  - It doesn't radiate signals, is not easy to tap, and is much safer, and if it is tapped it is easy to detect.
  - Physically it is very durable, core is made of glass so no electric current can flow through, and thus is immune from electrical interference. It can be put nearly anywhere

image and info source: http://www.studytonight.com/computer-networks/transmission-mediums

Copper over Fiber Optics

- Copper is much CHEAPER
- Transmits data without loss at distances of two kilometers or less.

Factors that should be considered when selecting transmission media

1. Cost;
2. Speed;
3. Security;
4. Reliability;

Standards and Network Layers

Interoperability

- The ability of software and hardware on multiple machines and from multiple commercial vendors to communicate
- In a household or company, one's system may be set up by multiple different commercial devices (like Cisco etc.) and thus for these devices to communicate they must have interoperability, or a same set of protocols and standards.

Networking Standards

- Without standards, manufacturers of networking products have no common ground to build their systems around.
- Standards are needed so that heterogeneous networks can communicate with each other.

An Open System

A system that is based on a common model of network architecture and a suite of protocols

- Open systems maximize opportunity for interoperability
- Platform independent and vendor neutral
- Guarantee a high degree of flexibility and choice, prevent single vendor lock in by facilitating interoperability
- Benefits
  - - Flexibility
    - Choice
    - Efficiency

Standards Organizations

- Organizations are needed that will coordinate the creation and publishing of documents regarding the open standards and protocols. Usually non-profit organizations that specifically take a neutral stance regarding technologies and work for the betterment of the industry as a whole.
- Two standard organizations that you are likely to encounter
  - - Institute of Electrical and Electronics Engineers (IEEE)
      - Well-known professional organizations for electrical or electronics field, including computers and networking
        Best known for IEEE 802 Project, which encompasses things like Ethernet
    - International Organization for Standardization (ISO)
      - Biggest standards organization in the world.
        Federation of standards organizations from dozens of nations.
        Best known for OSI reference Model

Data Compression

Data compression is the process of modifying, encoding or converting the bits structure of data in such a way that it consumes less space on disk. Data compression is also known as source coding or bit-rate reduction. Data compression happens in the Presentation layer.

Use of data compression

- Data compression aids high-performance network communication.
- Enables reducing the storage size of one or more data instances or elements.
- Data compression enables sending a data object or file quickly over a network or the Internet and in optimizing physical storage resources.

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OSI Model

- One of the most common Open Network Standards is Open Systems Interconnection Reference Model (OSI). Developed by ISO.
- Used to develop network technologies.
- Defines a series of layers of network interaction.
- Each layer of the model is used to implement different protocols, each dealing with a particular aspect of network communication.
- For example, the highest layer deals with issues relating to specific application program, while the lowest layer deals with basic electrical and mechanical issues of the physical transmission medium (like wires).
- A key feature is encapsulation, since each layer does not have to have an understanding of how lower/other layers works.

How Networks Communicate

- Application layer, the only part users can see. Layer converts a message’s data into bits and attaches a header identifying the sender and receiving computers.
- Presentation Layer translates the message into a language that the receiving computer can understand. May compress and encrypt data. Adds another header specifying language and encryption schemes.
- Session Layer opens communication. It computer to a network server, or from a peer computer on a network to another peer computer. These virtual connections are referred to as sessions. They include negotiation between the client and host (or peer and peer) on matters of flow control, transaction processing, transfer of user information, and authentication to the network. They are called sessions because they set up connections that persist for some period of time.
- Transport Layer protects data being sent. It divides the data into segments and creates checksum tests to see if data is scrambled. Also can make backup copies of data.
- Network Layer selects routes for messages. Forms segments into packets, adds a header determining order and address.
- Data-Link supervises the transmission. Confirms checksums, address and duplicates packets. This layer keeps a copy of each packet until it receives confirmation from the next point along the route that the packet has arrived undamaged.
- Physical Layer encodes packets into the medium that will carry them, like an analog signal, and sends the packet along that medium.
  - - An intermediate node calculates and verifies the checksum for each packet. Might also reroute, message to avoid congestion.

Receiving node, the layered process is reversed.

- The physical layer reconverts the message into bits.
- Data-link recalculates checksum, confirms arrival and logs packets.
- Network layer recounts incoming packets for security.
- Transport layer recalculates checksum and reassembles the message segments.
- Session layer holds parts of message until it is complete and sends to next layer
- Presentation layer decrypts, expands and translates message
- Application layer identifies recipient converts bits to readable characters and directs data to correct application

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