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Chapter2 Networking Fundamentals
COMPUTER NETWORKS 4TH Edition
BY Andrew s. Tanenbaum
Topics Data Networks
1. Networking Devices including : Repeaters Hubs Bridges Routers Workgroup Switches2. Network Topologies types : 1. Physical Topologies BUS Ring Hierarchical Star Mesh2. Logical Topologies Broadcast Token Passing
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 DevicesRepeaters
• 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 DevicesHubs
• 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 DevicesBridges
• 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 DevicesWorkgroup 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 DevicesRouters
• 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 TopologiesBus 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 TopologiesRing 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 TopologiesStar 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 TopologiesExtended 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 TopologiesHierarchical
• 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 TopologiesMesh 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 TopologiesHybrid 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 TopologiesBroadcast
• 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 TopologiesToken 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– 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