Network Layers, Ethernet, and WAN Technologies

Posted on Mar 12, 2025 in Computer Engineering

Application and Presentation Layer

Application and Presentation Layer: Services, files, printers, applications, databases.

Transport and Network Layer

Transport and Network Layer: Network management, routing protocols, switch.

Data Link and Physical Layers

Data Link Layer and Physical: Ethernet communications management, UTP Cat 5, SONET, physical media, hardware.

  • The first Ethernet standard was an association between Digital Equipment Corp., Intel, and Xerox (DIX).
  • Ethernet was released as an open standard.
  • In 1985, the IEEE standardized LANs for the public.

Physical Layer Limitations

  1. Cannot communicate with superior layers.
  2. They can identify devices.
  3. Only recognizes streams in bits.
  4. Cannot determine the source of transmission when multiple devices are transmitting.

Data Link Layer Functions

  1. Connects to upper layers through LLC.
  2. Uses addressing schemes to identify devices.
  3. Uses patterns to organize data into groups.
  4. Uses the MAC to see who is transmitting.

802.2 = LLC, 802.3 = MAC

  • The LLC may be the NIC software; however, the physical and transmit bit by IAS could be the MAC.

LLC

LLC: Connection to upper layers, enters the packet network layer, identifies the network layer protocols, hardware-independent.

MAC Functions

MAC Functions: Data encapsulation, media access control.

Data Encapsulation

Data Encapsulation: Frame delimitation (header), addressing (MAC orig. and MAC dest.), error detection (CRC or FCS)

Ethernet’s Success

Ethernet Success: Simplicity and ease of maintenance, ability to incorporate new technologies, reliability, low cost, and ease of installation.

  • The first versions of Ethernet used coaxial cable.

Thicknet 10BASE5 = Thick coaxial, 500 meters max, 10 Mbps

ThinNet 10BASE2 = Thin coaxial, 185 meters max, 10 Mbps

Packages

Packages: We divide message data into small blocks (packets) and include the address, routing, CRC, and the data.

Frames

Frames: Organizes small packets of data into frames (similar to what a package does).

VPN

VPN = Private networks, managed by outside companies that provide application services and hardware maintenance, etc. (Outsourcing). Used in special connections, LAN to WAN.

  • WAN switched networks use two different technologies:
    1. Circuit switching
    2. Packet switching
  • These two technologies differ in how they route the information between nodes.

Circuit-Switching

Circuit-switching: Is a type of communication that creates a dedicated channel (or circuit) for the duration of the session (e.g., talking on the phone). After the close of the session, the channel is released and is available to be used again.

Circuit Switching Phases

Therefore, there are 3 phases in circuit switching: Connection phase, transmit phase, and disconnection phase.

Circuit Switching Problems

Two problems with circuit switching:

  1. The lines are busy most of the time.
  2. They offer connections at a constant speed from end to end, which makes the interconnection of different teams difficult.

Packet Switching

Packet switching: Emerged as a solution to the problems of circuit switching in the 1970s. Its explanation is very simple: the data to be sent is chopped, if necessary, into packets.

Packet Switching Advantages

Advantages:

  • Link sharing.
  • Each node can use a different speed.
Network Layer Functions

Network Layer Functions: Identifies each host exclusively by segmenting it to a part of the network to avoid mass broadcasting. Through its IP, it identifies the data link layer to the MAC. It chooses the optimal route for packets. It controls and avoids congestion. It checks that the user does not abuse the service. It is connectionless, and it does not establish a session before transmitting. It works independently of the media.