Section 3

Switches allow us to connect different devices via Ethernet in the same Local Area Network or LAN. Also, this switch can connect to a Router, which connects directly to the internet, allowing us connect our LAN to internet. Also, you can put a firewall between the router and the exterior to protect the connections. In the case that we also need to connect to another LAN, you can create a Wide Area Network or WAN.

• Topology.
• Speed.
• Cost.
• Security.
• Availability.
• Scalability.
• Reliability.

The OSI reference model is a standard from ISO standardises how computers communicate with one another over a network. It has seven layers for data transmission, dividing the operations into specific related group of actions at each layer. A layer serves the layer above it and is served by the one below it.

This is, when a senders sends a packet it needs to format it. This means:

1. Application.
2. Presentation.
3. Session.
4. Transport: TCP/UPD and port.
5. Network: source and destination IP address. (important for routers)
6. Data-link: it includes the MAC address. (Important for switches)
7. Physical.

When the receiver gets the packet, it checks for these layers in the inverse order.

The benefit of this model is that allows engineers to focus on just on one layer instead of having to design a end to end, top to bottom model.

The most classic one is:

• Please Do Not Throw Sausage Pizza Away.

This is a protocol stack which consists in two protocols including the Transmission Control Protocol (TCP) and the Internet Protocol (IP). The difference between this and the OSI model is conceptual, this stack is actually used in production networks.

This model also simplifies the layers of the OSI model, reducing the first three in the same one and the last to in the another one, living us with:

4. Application: represents data users, encodes and controls the dialog.
5. Transport: supports communication between end devices across a diverse network
6. Internet: provides a logical addressing and determines the best path through the network.
7. Network access: control the hardware devices and media that make up the network.

When two hosts are communicating, the exchange PDUs, and depending which layer we are talking, they’ll have different names, being: data, segment, packet and frames.

• We start with the Layer 7, which provides network services to the applications or the user.
• The main difference is that it doesn’t provide services to any other OSI layer.
• The application establishes availability of intended communication between partners.
• It then synchronizes and establishes agreement on procedures for error recovery and control of data integrity.

• This layer ensures that the information that is sent at the application layer of one system is readable by the application layer of another system.
• The presentation layer can translate among multiple data formats using a common format.

• This layer establishes, manages and terminates sessions between two communicating hosts.
• The sessions also syncs dialog between the presentation of two hosts and manages their data exchange.

• It defines whether TCP or UDP transport is used, and the port number.

• Definition:

  • The transport layer defines services to segment, transfer, and reassemble the data for individual communications between the end devices.
  • It breaks down large files into smaller segments that are less likely to incur transmission problems.

• It defines whether TCP or UDP transport is used, and the port number.

• Definition:

  • The transport layer defines services to segment, transfer, and reassemble the data for individual communications between the end devices.
  • It breaks down large files into smaller segments that are less likely to incur transmission problems.

• It provides the source and destination IP address. Routers operates in this layer.
• Definition:
  • The network layer provides connectivity and path selection between two host system that may be located on geographically separated networks.
  • The network layer is the layer that manages the connectivity of hosts by providing logical addressing.

• It provides the source and destination layer 2 address, like the MAC address. Switches operate at layer 2.
• Definition:
  • The data link layer defines how data is formatted for transmission and how to access physical media is controlled.
  • It also includes error detection and correction to ensure a reliable delivery of the data.

• This layer concerns literally the physical components like the cables.
• Definition:
  • The physical link enables bit transmission between end devices.
  • It defines specifications needed for activating, maintaining and deactivating the physical link between end devices.