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