Networking revision notes

Network topology

A physical star topology connects each host to a central networking device using a separate physical link. The central device provides the point through which the hosts' connections are arranged. A logical bus network topology describes how data behaves on the network: the hosts share the behaviour of a bus and use a bus protocol to control access to it.

These are different descriptions. Physical topology concerns the actual arrangement of cables and devices, whereas logical topology concerns how communication operates. A network can therefore be physically wired as a star but behave logically as a bus. This can be achieved by using a bus protocol together with appropriate physical switching. The physical arrangement and the logical operation must not be confused.

Types of networking between hosts

In peer-to-peer networking, every computer has equal status. Computers can provide services to one another rather than relying on a nominated central server. This is suitable when the computers need to share resources directly and no computer needs to have the special server role.

In client-server networking, most computers are nominated as clients and one or more computers are nominated as servers. A client requests a service and a server provides it. Examples of servers include a file server, which provides file services, and an email server, which provides email services. This model is suitable when services are intended to be provided centrally by dedicated server computers.

WiFi and its components

WiFi is a wireless local area network based on international standards. Its purpose is to enable devices to connect to a network wirelessly. A wireless network requires a wireless network adapter in a device and a wireless access point to provide the wireless connection to the network.

The SSID, or Service Set Identifier, identifies the wireless network. Disabling SSID broadcast is one security measure: the network name is not openly broadcast to devices. Other specified security measures include using strong encryption for transmitted data with WPA or WPA2, and using a MAC address allow list so that only permitted MAC addresses are allowed to connect.

CSMA/CA

Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) is a wireless protocol. A device senses whether the shared wireless medium is being used before attempting to transmit. It attempts to avoid a collision rather than detecting a collision after transmission. With RTS/CTS (Request to Send/Clear to Send), a device first requests permission to transmit and the access point can respond with permission, helping coordinate access to the wireless medium. Without RTS/CTS, the device uses carrier sensing and collision-avoidance behaviour without this request-and-clear exchange.

Common errors

• Describing a star as a logical topology without specifying that the description is physical.
• Saying that every peer-to-peer network has a server; equal-status computers are the defining feature.
• Treating the SSID as encryption; the SSID identifies the wireless network, while WPA/WPA2 provides strong encryption of transmitted data.
• Confusing CSMA/CA, which is required for wireless networking here, with CSMA/CD, which is not required for this topic.
• Listing a wireless access point without also recognising the need for a wireless network adapter in the connecting device.