Week 10 (LAN Topologies)

Lecture 7 Lecture 7 LAN TopologiesLAN Topologies

Data Communications and Networks

LAN TopologiesLAN Topologies

Data Communications and Networks

Semester 1

P d bPresented by:

Vajira De Silva B.Sc. (moratuwa), M.Sc. (melbourne)

LAN Transmission CategoriesLAN Transmission Categories

y LAN transmissions fit into one of three categories:y Unicasty Multicasty Broadcast

24/12/2009Data Communications & Networks - Lecture 72

UnicastUnicasty A single packet is sent from the source to a destination on a network.gy The source node addresses the packet by using the network address

of the destination node. y The packet is then forwarded to the destination network and the

network passes the packet to its final destination


MulticastMulticasty A single data packet is copied and forwarded to a specific subset of g

nodes on the network.

y The source node addresses the packet by using a multicast address.p y g


BroadcastBroadcasty Frame is addressed to the broadcast address (a broadcast frame) and

is copied and forwarded across the network to all the devices.

y Broadcasts are commonly found in LAN environments. yy Broadcasts do not traverse a WAN unless the Layer 3 edge-routing

device is configured to direct these broadcasts to a specified network address.

y An example of a data broadcast on a LAN could be a host searching for server resources.

y But, have to be cautious when used for multimedia broadcast traffic.y High bandwidth consumption


LAN AddressingLAN Addressingy LAN addresses identify individual or groups of devices. gy Addressing schemes vary depending on the protocol family and OSI

layer.yy MAC (Media Access Control) addressesy Network layer addresses


MAC AddressesMAC Addressesy MAC addresses identify network devices in LANs.y MAC addresses are unique for each LAN interface on a device.y 48 bits in length and are expressed as 12 hexadecimal digits:g p gy First six hexadecimal digits, which are administered by the IEEE,

identify the manufacturer or vendor organizational unique identifier y g qy Last six hexadecimal digits comprise the interface serial number a

value administered by the specific vendor

y MAC addresses are referred to as burned-in addresses (BIAs) because they are burned into read-only memory (ROM).

y MAC is defined at the data link layer (Layer 2) of the OSI model.


Network Layer AddressesNetwork Layer Addressesy Network layer addresses identify a device at the OSI network layer

(Layer 3).

y Network layer addresses have two parts: the network of which the y pdevice is a part and the device, or host, number of that device on that network.y Devices on the same logical network must have addresses with the

same network part; however, they will have unique device parts.

y The subnet mask determines where the network boundary ends and the host boundary begins.


The Network Topology Not in the lecture note ! The Network Topology

y The network topology defines the p gylayout of the network.

y It shows how devices on the network are interconnected.

y Devices on the network are termed nodes.

y A network has both a physical and a logical topology.


Physical vs Logical TopologyNot in the lecture note !

Physical vs. Logical Topologyy Physical topology shows the physical plan of a network, which g

refers to the actual physical layout of the devices and media.

y Logical topology refers to the paths that signals travel from one g p gy p gpoint on the network to another.


LAN TopologiesLAN Topologiesy Four LAN topologies exist:gy Star (Hub-and-Spoke)y Ringy Busy Tree


Star (Hub-and-Spoke) Topology (1)Star (Hub and Spoke) Topology (1)y All stations are attached by physical links to a central point, usually a

wiring hub or other device operating in a similar function.

y Shielded twisted-pair (STP), unshielded twisted-pair (UTP), fiber-p poptic cabling and wireless media can be used as physical links.

y The star topology is the most commonly used architecture in p gy yEthernet LANs and resembles spokes in a bicycle wheel.


Star (Hub-and-Spoke) Topology (2)Star (Hub and Spoke) Topology (2)


Star (Hub-and-Spoke) Topology (3)Star (Hub and Spoke) Topology (3)y Advantages:y N bl t i i l i t f f ily No cable segment is a single point of failure.y It is upgradeable, flexible, and reliable y It is easy to design and installIt is easy to design and instally This topology makes diagnosing problems relatively easy since the

problem is localized to one computer or devicey This topology allows for more throughput than any other topology

y Disadvantagesy Central hub is a single point-of-failure in that if it fails, every attached

station is out of service.y It requires a lot of cable to connect computers since a cable is required

between each device and the central location.y It is more expensive to build because of the additional cost of cables and devices y It is more expensive to build because of the additional cost of cables and devices

like hubs and switches. 24/12/2009Data Communications & Networks - Lecture 7

14

Ring Topology (1)Ring Topology (1)y All stations in a ring topology are considered repeaters and are

l d i l d i tenclosed in a loop no end points.y The repeater in this case is LAN-attached stations NIC.B h NIC h LAN ll y Because each NIC is a repeater, each LAN station will repeat any signal that is on the network, regardless of whether it is destined for th t ti l t tithat particular station.y Failure of a single NIC could bring the entire network down. y Some NIC controllers are capable of recognizing and handling the y Some NIC controllers are capable of recognizing and handling the

defect and pulling itself off the ring, allowing the ring to stabilize and continue operating.p g

y Token Ring (IEEE 802.5) best represents a ring topology:y Physical topology (cabling) is considered to be a star topology.Physical topology (cabling) is considered to be a star topology.y But, it is a ring in logical topology.


Ring Topology (2)Ring Topology (2)y Although physical topology is a physical layer attribute, the media g g

access method used at the data link layer determines the logical topology. y Token Ring (IEEE 802.5) defines a logical ring and contention!

y A frame, called a token, travels around the ring and stops at each d node.

y If a node wants to transmit data, it adds that data and the addressing i f ti t th f information to the frame. y The frame continues around the ring until it finds the destination

node which takes the data out of the frame node, which takes the data out of the frame. y The advantage of using this method is that there are no collisions of

data packets.p


Ring Topology (3)Ring Topology (3)


Ring Topology (4) Not in the lecture note ! Ring Topology (4)y With single ring all the devices on the network share a single g g g

cable, and the data travels in one direction only.

y With dual ring two rings allow data to be sent in both g gdirections.

y This creates redundancy (fault tolerance) meaning that in the y This creates redundancy (fault tolerance), meaning that in the event of a failure of one ring, data will still be transmitted on the other ringthe other ring.

y Fiber Data Distributed Interface (FDDI) uses light instead of l t i it t t it d t d l ielectricity to transmit data over a dual ring.y But, FDDI rings are physically cabled in a star topology


Ring Topology (5) Not in the lecture note ! Ring Topology (5)


Bus Topology (1)Bus Topology (1)y Commonly referred to as a linear bus, all the devices on a bus y

topology are connected by one single shared cable segment.

y Every station on this segment sees transmissions from every y g yother station on the cable segment; this is known as a broadcast medium.

y The LAN attachment stations are definite endpoints to the cable segment and are known as bus network termination pointscable segment and are known as bus network termination points.y Ethernet (IEEE 802.3) best represents this topology. Ethernet has

the ability to utilize many different cable schemesthe ability to utilize many different cable schemes.


Bus Topology (2) Not in the lecture note ! Bus Topology (2)


Bus Topology (3)Bus Topology (3)y Advantages of a bus topology:y The thinnet cabling it uses is quite inexpensive. y It uses less cable compared to other physical topologies like star or

t d d textended stary It works well for small networksy It does not need a central device, such as a hub, switch, or routerIt does not need a central device, such as a hub, switch, or router

y Disadvantages of a bus topology:y It results in slower access to the network and less bandwidth due to the

sharing of the same cable by all devicesy It is challenging to identify and isolate problemsy A break at any point in the bus cable can disable the entire bus network y It needs terminators


Tree Topology (1)Tree Topology (1)y The tree topology is a logical extension of the bus topology and g g g

could be described as multiple interconnected bus networks.

y The physical (cable) plant is known as a branching tree with all p y p gstations attached to it.

y The tree begins at the root and expands to the network endpoints. g p py This topology allows a network to expand dynamically with only one

active data path between any two network endpoints.

y A tree topology network does not employ loops in its topology.y Example: a bridged or switched network running the spanning tree p g g p g

algorithm, usually found with Ethernet (IEEE 802.3) networks.


Tree Topology (1)Tree Topology (1)


Not in the lecture note !

Other Types of Topologies


Mesh TopologyMesh Topologyy The mesh topology connects all devices (nodes) to each other

for redundancy and fault tolerance. y It is used in wide-area networks (WANs) to interconnect LANs

and for critical networks. y The mesh topology is expensive and difficult to implement.


Hybrid TopologyHybrid Topologyy The hybrid topology combines more than one type of topology. y p gy yp p gyy When a bus line joins two hubs of different topologies, the

configuration is called a star bus.g .

y The bus line is used to transfer the data between the star topologies topologies.


Week 10 (LAN Topologies)

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