Chapter2 Networking Fundamentals COMPUTER NETWORKS 4TH Edition BY Andrew s. Tanenbaum Chapter2 Networking Fundamentals

Topics Data Networks Networking Devices including : Repeaters Hubs Bridges Routers Workgroup Switches 2. Network Topologies types : Physical Topologies BUS Ring Hierarchical Star Mesh 2. Logical Topologies Broadcast Token Passing In order to implement this algorithm we had to address these six issues.

Data Networks In the mid-1980s, the network technologies that had emerged had been created with a variety of different hardware and software implementations. Each company that created network hardware and software used its own company standards.

Data Networks One early solution was the creation of local-area network (LAN) standards. Because LAN standards provided an open set of guidelines for creating network hardware and software, the equipment from different companies could then become compatible.

Networking Devices Network devices include all the devices that connect the end-user devices together to allow them to communicate. End-user devices include computers, printers, scanners, and other devices that provide services directly to the user. End-user devices that provide users with a connection to the network are also referred to as hosts. The host devices can exist without a network, but without the network the host capabilities are greatly reduced. Host devices are physically connected to the network media using a network interface card (NIC).

Networking Devices Network devices provide transport for the data that needs to be transferred between end-user devices. Network devices provide extension of cable connections, concentration of connections, conversion of data formats, and management of data transfers. Examples of devices that perform these functions are repeaters, hubs, bridges, switches, and routers.

Networking Devices

Networking Devices Repeaters A repeater is a network device used to regenerate a signal. Repeaters regenerate analog or digital signals distorted by transmission loss due to attenuation. A repeater does not perform intelligent routing.

Networking Devices Hubs Hubs concentrate connections. In other words, they take a group of hosts and allow the network to see them as a single unit. This is done passively, without any other effect on the data transmission. Active hubs not only concentrate hosts, but they also regenerate signals.

Networking Devices Bridges Bridges convert network transmission data formats as well as perform basic data transmission management. Bridges provide connections between LANs. Bridges also perform a check on the data to determine whether it should cross the bridge or not.

Networking Devices Workgroup Switches Workgroup switches add more intelligence to data transfer management. Not only can they determine whether data should remain on a LAN or not, but they can transfer the data only to the connection that needs that data. Another difference between a bridge and switch is that a switch does not convert data transmission formats.

Networking Devices Routers Routers can regenerate signals, concentrate multiple connections, convert data transmission formats, and manage data transfers. They can also connect to a WAN, which allows them to connect LANs that are separated by great distances.

Network Topologies Network topology defines the structure of the network. One part of the topology definition is the physical topology, which is the actual layout of the wire or media. The other part is the logical topology, which defines how the media is accessed by the hosts for sending data.

Physical Topologies Commonly used physical topologies

Physical Topologies Bus Network Topology A bus topology uses a single backbone cable that is terminated at both ends. All the hosts connect directly to this backbone. All devices connected to a common central cable Inexpensive Easily expanded If cable fails, the entire network will shut down Bus is topology used most widely in businesses

Physical Topologies Ring Network Topology Each node connected to two other nodes in a ring Similar to the buss, but with the ends of the buss connected together More reliable than buss or star If one node fails, data rerouted around failed node Expensive and difficult to install Usually used by larger organizations who can afford the expense and to whom the reliability is very important

Physical Topologies Star Network Topology A star topology connects all cables to a central point of concentration. Star topology is centered around central routing device called a hub All network nodes connect to the hub Easy to install and update If hub fails, network fails

Physical Topologies Extended Star An extended star topology links individual stars together by connecting the hubs and/or switches. This topology can extend the scope and coverage of the network.

Physical Topologies Hierarchical A hierarchical topology is similar to an extended star. However, instead of linking the hubs and/or switches together, the system is linked to a computer that controls the traffic on the topology.

Physical Topologies Mesh Network Topology Every node connected to every other node Fast Reliable No hub or bus to fail If one device goes down, it is the only node affected Expensive Every node must be wired to every other node Difficult to add nodes If there are 32 nodes in a mesh network and you wish to add a new node, how many new cables must you add?

Physical Topologies Tree Network Topology Combination of bus and star Two or more star networks connected using a bus for the backbone

Physical Topologies Hybrid Topologies Combine two or more of the other topologies Bus used for LANs and ring used for campus backbone linking LANs together

Logical Topologies The logical topology of a network is how the hosts communicate across the medium. The two most common types of logical topologies are broadcast and token passing.

Logical Topologies Broadcast Broadcast topology simply means that each host sends its data to all other hosts on the network medium. There is no order that the stations must follow to use the network. It is first come, first serve. Ethernet works this way.

Broadcast Ethernet A set of rules for constructing message in a local network Most widely used protocol for transmitting data over LANs Listen before talk Simple Inexpensive Flexible Collisions High message volume greatly reduces transmission speed

Logical Topologies Token Passing Token passing controls network access by passing an electronic token sequentially to each host. When a host receives the token, that host can send data on the network. If the host has no data to send, it passes the token to the next host and the process repeats itself. Two examples of networks that use token passing are Token Ring and Fiber Distributed Data Interface (FDDI).

Token Passing Token Ring Also a set of rules for constructing message in a local network Only one node “talks” at a time Complex Expensive More fault tolerant than Ethernet No collisions Transmission speed unaffected by message volume

Network Software Network operating system Network management software Novell NetWare Microsoft Windows Server 2003 Network management software Helps ensure security of network Monitors performance Helps administrators reconfigure network Remote administration via push technology Network monitoring software Packet sniffers – see data as it moves over network Keystroke monitors – see what users are doing

Telecommunications Services Value Added Networks (VANs) Proprietary networks built using common carriers Provide enhanced services Video conferencing Electronic data interchange (EDI) Virtual Private Networks (VPNs) Use encryption to provide a secure end-to-end connection over common carriers or the Internet Remote access to internal networks w/o dialup Leased lines High speed, long distance data transfer