Understanding Networks II

Objectives Compare client and network operating systems Learn about local area network technologies, including Ethernet, Token Ring, FDDI, and wireless Use the OSI model to understand networking Learn how network computers and servers are addressed

Network Architecture Overview Network architecture is the overall design of a network, including how devices and components are connected, how devices and components communicate, and the network protocols needed to establish reliable communication among nodes on the network.

Network Architecture Overview A node is any device that can be accessed by a computer on a LAN, such as a computer, server, or printer. Physical topology is the physical arrangement or shape in which devices on a LAN are connected to each other.

How NICs Work Typically, an internal NIC plugs into a motherboard expansion slot. An individual NIC can be designed to support Ethernet, Token Ring, FDDI, or wireless architectures, but a single card will not support multiple architectures. The NIC must convert the data it is transmitting into a signal that is in a form that is appropriate for the network. The component on the card responsible for this signal conversion is called the transceiver.

How Ethernet Controls Data Traffic An Ethernet network is a passive network, meaning that the network just sits there and waits for a computer to use it. A computer that wants to send packets over Ethernet first listens on the network for silence. If it hears nothing, it begins to transmit. As it transmits, it also listens.

How Ethernet Controls Data Traffic (Continued) If it hears something other than its own data being transmitted, it stops transmitting and sends out a signal indicating that there has been a collision, which occurs when two computers attempt to send data at the same time. A collision can cause packets that were just sent to be corrupted. Each computer waits for a random amount of time and then tries to transmit again, first listening for silence.

How Ethernet Controls Data Traffic (Continued) This type of network technology is called a contention-based system because each computer must contend for an opportunity to transmit on the network. Computers using Ethernet gain access to the network using the CSMA/CD (Carrier Sense Multiple Access with Collision Detection) method. Another method that can be used by a network technology to control collisions is CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance).

Ethernet Hardware Three variations of Ethernet are available, primarily distinguished from one another by speed: 10-Mbps Ethernet, Fast Ethernet, and Gigabit Ethernet. A hub is a network device that can be used to connect devices that use a BNC or RJ-45 connector. A hub, like the one shown in Figure 5-20, is generally inexpensive and is best suited for a small, simple network. These devices can include computers, servers, or printers.

Ethernet Hardware (Continued) Hubs are easy to configure because they broadcast data packets to every device at once. A switch is used to connect computers on a LAN. A switch reads the destination address at the beginning of a data packet and sends the packet only to the destination computer. Attenuation occurs when signals are weakened due to being transmitted over long distances on a network.

Ethernet Hardware (Continued) A repeater is a device that amplifies signals on a network. There are two kinds of repeaters. An amplifier repeater simply amplifies all incoming signals. A signal-regenerating repeater reads the signal and then creates an exact duplicate of the original signal before sending it on.

Physical Topology A bus topology connects each node in a line and does not include a centralized point of connection; cables just stretch from one computer to the next one, and to the next, and so on. A star topology connects all nodes to a centralized hub or switch.

Physical Topology (Continued)

Wireless LAN Wireless LAN (WLAN) technology, as the name implies, uses radio waves or infrared light instead of cables or wires to connect computers or other devices. Connections are made using a wireless NIC, which includes an antenna to send and receive signals. Wireless devices can communicate directly, or they can connect to a LAN by way of a wireless access point (AP).

Wireless LAN (Continued) Access points are placed so that nodes can access at least on one access point from anywhere in the covered area. The first IEEE standard that outlined wireless LAN specifications was IEEE , published in Most current WLAN devices operate under the 1999 IEEE b standard. This standard is also called Wi-Fi (Wireless Fidelity).

Token Ring and FDDI Token Ring is an older LAN technology developed by IBM that transmits data at 4 Mbps or 16 Mbps. A Token Ring network is physically arranged using a star topology, because each node connects to a centralized device. The centralized device to which the network nodes connect is not a hub or switch, as used in Ethernet networks, but is called a Controlled Access Unit (CAU), a Multistation Access Unit (MSAU or sometimes just MAU), or a Smart Multistation Access Unit (SMAU).

Token Ring and FDDI (Continued) A token is a special series of bits used to control which device transmits data on the network. Because it has a physical star topology and a logical ring topology, a Token Ring network is sometimes said to have a star-wired ring topology. Token Ring can also use another type of connector that has no “male” or “female” version, known as a Universal Data Connector (UDC) or an IBM Data Connector (IDC).

Token Ring and FDDI (Continued) Fiber Distributed Data Interface (FDDI) is a type of network that also involves a token that travels in a ring. With FDDI, data frames travel on the ring without the token, and multiple nodes can have data on the ring at the same time.