What is a Switched Network?

A switched network is a telecommunications network in which a series of nodes or switches route data packets between various devices connected to the network. The primary function of these switches is to establish a dedicated path for data transmission, allowing for efficient communication between different devices. In a switched network, the data traffic is intelligently managed as the switches direct packets towards their intended destinations based on the destination address contained within each packet. 

Dissecting Switched Network

Switched networks were introduced in the 1990s as a collaborative effort involving multiple companies and individuals in the networking industry, including key players such as Cisco Systems, 3Com, and Alcatel-Lucent (formerly known as Lucent Technologies). They were developed to address the limitations of traditional hub-based networks in several aspects:

1. Collision domains: Switched networks effectively isolate each device into its own collision domain, allowing multiple devices to transmit data simultaneously without collisions, resulting in improved network efficiency and performance.
2. Bandwidth utilization: Unlike hubs, which broadcast data to all connected devices, switches intelligently route data packets based on the destination address, forwarding them only to the intended recipient. This selective transmission significantly improves bandwidth utilization and reduces unnecessary network traffic.
3. Network scalability: Switched networks can handle a larger number of devices more efficiently due to their intelligent packet routing capabilities and isolation of collision domains, making them more suitable for larger network deployments and addressing the scalability issues that hub-based networks faced.

By addressing these limitations, switched networks provided a more efficient and scalable solution for growing networks, leading to improved performance and reduced bottlenecks compared to traditional hub-based networks.

Development of Switched Network

The development of Switched Networks involved a series of iterative improvements and innovations in networking technology, revolutionizing data transmission and connectivity. 

• Early Switching Concepts (1970s-1980s): In the 1970s, the concept of packet switching emerged, laying the foundation for modern switched networks. Packet switching involved breaking data into smaller packets and sending them across a network. The introduction of Ethernet in the 1980s provided a means to connect devices using a shared medium, but it relied on hubs, which caused network congestion and limited scalability.
• Introduction of Network Switches (1990s): In the early 1990s, network switches started gaining popularity as a solution to the limitations of hub-based networks. Switches were initially used in enterprise environments where high-performance networks were essential.
• Fast Ethernet and Gigabit Ethernet: In the mid-1990s, Fast Ethernet (100 Mbps) became a widely adopted standard, providing faster network speeds and enabling more efficient switched networks. Towards the late 1990s, Gigabit Ethernet (1 Gbps) emerged, offering even higher network speeds and enhancing the capabilities of switched networks.
• Layer 3 Switching: Layer 3 switching, introduced in the late 1990s, combined the functionality of switches and routers, enabling faster and more intelligent routing within a switched network. Layer 3 switches could make routing decisions based on IP addresses, enhancing network performance and scalability.
• Evolution of Switching Speeds: Over time, switching speeds continued to increase with the introduction of 10 Gigabit Ethernet (10 Gbps), 40 Gigabit Ethernet (40 Gbps), and 100 Gigabit Ethernet (100 Gbps) standards. Higher-speed switches enabled the support of bandwidth-intensive applications and facilitated the growth of data centers and high-performance networks.

How Switched Networks Work

A network switch functions at the data-link layer, also known as Layer 2, of the OSI model. Specifically, in a local area network (LAN) that utilizes Ethernet technology, the switch uses the media access control (MAC) address to determine the appropriate destination for incoming message frames. To accomplish this, switches maintain tables that associate each MAC address with the corresponding receiving port.

1. Device A sends data to Device B: Device A encapsulates the data into a data frame, including the source MAC address (Device A's MAC address) and the destination MAC address (Device B's MAC address).
2. Switch receives the data frame: The network switch receives the data frame on the switch port connected to Device A.
3. Switch learns the MAC address: The switch examines the source MAC address and updates its MAC address table, associating Device A's MAC address with the corresponding switch port.
4. Switch determines the destination: The switch inspects the destination MAC address to determine where to forward the data. It checks its MAC address table to find the switch port associated with the destination MAC address (Device B's MAC address).
5. Switch forwards the data frame: If the destination MAC address is found in the MAC address table, the switch forwards the data frame to the switch port associated with that MAC address (Device B's port). If the destination MAC address is not found, the switch floods the data frame to all ports except the incoming port.
6. Device B receives the data frame: Device B, connected to the switch port associated with its MAC address, receives the data frame. The switch forwards the data frame only to Device B's port.
7. Acknowledgment (if applicable): If the transmission requires an acknowledgment, Device B sends an acknowledgment frame back to Device A. The switch delivers the acknowledgment frame to Device A using the same process based on the MAC addresses.

OSI Model

The OSI model has multiple layers that work together to enable communication between devices in a network, ensuring that data is properly encapsulated, transmitted, and received. While switched networks primarily operate at the data link layer, they interact with and facilitate communication between the higher layers of the OSI model.

• Physical Layer: It defines the electrical, mechanical, and procedural aspects of network communication. It specifies details such as cables, connectors, voltage levels, and transmission rates. Examples of physical layer technologies include Ethernet cables (such as Cat5e or Cat6), fiber optics, and wireless transmission.
• Data Link Layer: It provides error-free transmission of data frames between adjacent network nodes (usually between two directly connected devices). It handles framing, error detection using techniques like checksums, and flow control to regulate data flow. Examples of data link layer protocols are Ethernet, Point-to-Point Protocol (PPP), and Wi-Fi.
• Network Layer: It controls logical addressing, routing, and packet forwarding across different networks. It assigns unique IP addresses to devices and uses routing protocols (e.g., OSPF or BGP) to determine optimal paths for packet delivery. Internet Protocol (IP) is a key network layer protocol.
• Transport Layer: It ensures reliable and transparent end-to-end data delivery between host systems. It breaks data into smaller segments and manages their reliable transmission and reassembly at the destination. Transmission Control Protocol (TCP) and User Datagram Protocol (UDP) are transport layer protocols.
• Session Layer: It establishes, manages, and terminates communication sessions between applications on different network devices. It provides synchronization points in data exchange and supports functions such as session establishment, maintenance, and termination. Session layer protocols include NetBIOS, Remote Procedure Call (RPC), and Secure Shell (SSH).
• Presentation Layer: It deals with data representation, encryption, compression, and formatting for the application layer. It ensures that data from the application layer is properly formatted and can be understood by the receiving application. Examples of presentation layer functions are data encryption using Secure Sockets Layer (SSL) or formatting data as XML.
• Application Layer: It provides a means for applications to access network services and exchange data with other applications. It includes protocols and interfaces used by applications for tasks such as email (SMTP), file transfer (FTP), web browsing (HTTP), and domain name resolution (DNS).