Network architecture serves as the blueprint that defines how all information technology (IT) and operational technology (OT) components communicate, including computers, software applications, and databases, creating an efficient and comprehensive interconnect of knowledge, tools, and information. In 1969, the first computer network, ARPANET, was officially brought online and became the structure for modern networks, from hardware components like switches, modems, routers, and firewalls to protocols such as IP/TCP, DHCP, and DNS, ensuring fast, secure, and accurate data transfers. Join me as I follow the journey of a single data packet through modern network architecture and discover the behind-the-scenes layers and technologies that create a network.
The email sending process across a network begins with a user's request made through an input device such as a keyboard or mouse. The computer's processor interprets these inputs and accesses the required software—in this case, Outlook—by retrieving it from long-term storage devices like a hard disk drive (HDD) or solid-state drive (SSD). This software is then loaded into short-term, faster memory (RAM) for quick access. The processor, acting as the system's brain, also locates and loads any files or media the user wants to attach to the email. I will follow my email packet starting at Layer 1 of the 5-layer model.
Physical Layer (Layer 1): Bit-Level Transmission
At the lowest level of the network model, the Physical Layer is responsible for transmitting raw bits over a physical medium. When a user clicks “Send” in their email software, the message is converted into a binary stream of 0s and 1s by the network interface card (NIC). Depending on the medium used, these bits are transmitted as electrical signals over Ethernet cables or radio waves over Wi-Fi.
Data Link Layer (Layer 2): Local Delivery with MAC Addresses
The Data Link Layer is responsible for framing the raw bits into a structured format known as a frame. Each frame contains a header with a Media Access Control (MAC) address, a unique hexadecimal identifier assigned to hardware during manufacturing to identify the source and destination devices on a local area network (LAN). At this point, a switch is utilized to pass data along the LAN to the default gateway (router). If the destination MAC address is unknown, the Address Resolution Protocol (ARP) maps IP addresses to MAC addresses.
3. Network Layer (Layer 3): Routing Across Networks
The Network Layer delivers packets from the source to the destination IP address across multiple networks. Internet protocol (IP) addresses are special codes assigned by software and can be changed by either a network administrator or an automated system called dynamic host configuration protocol (DHCP). IPv4 addresses are expressed in a decimal notation of 4 octets, each octet being 0-255, or an IPv6 address that consists of four hexadecimal numbers providing much larger variations. The data is encapsulated at this layer into IP packets, and the email client relies on the underlying operating system to append IP headers to each packet. These packets include both the source IP address (e.g., 192.168.1.10) and the destination IP address (e.g., the IP of the recipient's mail server, such as 74.125.206.26). Routers play a critical role in this layer by inspecting the destination IP address, consulting routing tables, and forwarding packets toward their destination.
4. Transport Layer (Layer 4): End-to-End Communication
The Transport Layer provides reliable, ordered data delivery between applications on the source and destination hosts. The most common protocol for email transmission is the Transmission Control Protocol (TCP), which offers reliability through mechanisms such as sequence numbers, acknowledgments, and retransmissions. TCP encapsulates the data into segments and reviews the source and destination port numbers to identify the correct processes. The Transport Layer ensures that the data arrives completely and in the proper order, despite being transmitted as multiple segments across an unreliable network. Typically, firewalls monitor network traffic at this layer and allow or block data through their assigned ports, but more advanced firewalls can operate at layer 2.
5. Application Layer (Layer 5): User Interaction and Protocol Services
At the top of the model is the Application Layer, where user-level programs interface directly with the network. This is the layer where the email message is composed, formatted, and sent using email-specific protocols like SMTP. Other protocols at this level are HTTP or HTTPS for web browsing, FTP for file transfer, or DNS for domain name resolution.
The transmission of an email across the internet is a multi-layered process governed by well-established protocols and supported by a diverse set of hardware. From the conversion of data into electrical signals at the Physical Layer to the application-specific formatting at the Application Layer, each stage plays a vital role in ensuring that the email is delivered accurately and efficiently. Understanding the roles of each layer not only illustrates this everyday process but also highlights the robust architecture that permits modern digital communication.
References
NetworkChuck. (July 3, 2020) FREE CCNA // What is a Network? // Day 0.
https://www.youtube.com/watch?v=S7MNX_UD7vY&list=PLIhvC56v63IJVXv0GJcl9vO5Z6znCVb1P
Kentik (December 9, 2024) Kentipedia Network. Architecture Explained: Understanding the Basics of Modern Networks.
https://www.kentik.com/kentipedia/network-architecture/
Physical Layer (Layer 1): Bit-Level Transmission
At the lowest level of the network model, the Physical Layer is responsible for transmitting raw bits over a physical medium. When a user clicks “Send” in their email software, the message is converted into a binary stream of 0s and 1s by the network interface card (NIC). Depending on the medium used, these bits are transmitted as electrical signals over Ethernet cables or radio waves over Wi-Fi.
Data Link Layer (Layer 2): Local Delivery with MAC Addresses
The Data Link Layer is responsible for framing the raw bits into a structured format known as a frame. Each frame contains a header with a Media Access Control (MAC) address, a unique hexadecimal identifier assigned to hardware during manufacturing to identify the source and destination devices on a local area network (LAN). At this point, a switch is utilized to pass data along the LAN to the default gateway (router). If the destination MAC address is unknown, the Address Resolution Protocol (ARP) maps IP addresses to MAC addresses.
3. Network Layer (Layer 3): Routing Across Networks
The Network Layer delivers packets from the source to the destination IP address across multiple networks. Internet protocol (IP) addresses are special codes assigned by software and can be changed by either a network administrator or an automated system called dynamic host configuration protocol (DHCP). IPv4 addresses are expressed in a decimal notation of 4 octets, each octet being 0-255, or an IPv6 address that consists of four hexadecimal numbers providing much larger variations. The data is encapsulated at this layer into IP packets, and the email client relies on the underlying operating system to append IP headers to each packet. These packets include both the source IP address (e.g., 192.168.1.10) and the destination IP address (e.g., the IP of the recipient's mail server, such as 74.125.206.26). Routers play a critical role in this layer by inspecting the destination IP address, consulting routing tables, and forwarding packets toward their destination.
4. Transport Layer (Layer 4): End-to-End Communication
The Transport Layer provides reliable, ordered data delivery between applications on the source and destination hosts. The most common protocol for email transmission is the Transmission Control Protocol (TCP), which offers reliability through mechanisms such as sequence numbers, acknowledgments, and retransmissions. TCP encapsulates the data into segments and reviews the source and destination port numbers to identify the correct processes. The Transport Layer ensures that the data arrives completely and in the proper order, despite being transmitted as multiple segments across an unreliable network. Typically, firewalls monitor network traffic at this layer and allow or block data through their assigned ports, but more advanced firewalls can operate at layer 2.
5. Application Layer (Layer 5): User Interaction and Protocol Services
At the top of the model is the Application Layer, where user-level programs interface directly with the network. This is the layer where the email message is composed, formatted, and sent using email-specific protocols like SMTP. Other protocols at this level are HTTP or HTTPS for web browsing, FTP for file transfer, or DNS for domain name resolution.
The transmission of an email across the internet is a multi-layered process governed by well-established protocols and supported by a diverse set of hardware. From the conversion of data into electrical signals at the Physical Layer to the application-specific formatting at the Application Layer, each stage plays a vital role in ensuring that the email is delivered accurately and efficiently. Understanding the roles of each layer not only illustrates this everyday process but also highlights the robust architecture that permits modern digital communication.
References
NetworkChuck. (July 3, 2020) FREE CCNA // What is a Network? // Day 0.
https://www.youtube.com/watch?v=S7MNX_UD7vY&list=PLIhvC56v63IJVXv0GJcl9vO5Z6znCVb1P
Kentik (December 9, 2024) Kentipedia Network. Architecture Explained: Understanding the Basics of Modern Networks.
https://www.kentik.com/kentipedia/network-architecture/
TestOut Corporation. (2024). CertMaster Learn Tech+
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