6.2. - lans cabling topologies segments and bridges switches and routers
TRANSCRIPT
6.2. - LANs
CablingTopologiesSegments and bridgesSwitches and routers
At the end of this session you will be able to:Describe different types of cabling and other communication methodsDescribe the term topologyDescribe the operation of different types of networks such as Bus, Ring, Star, Switched Ethernet and hubsCompare advantages and disadvantages of eachDefine and explain the terms Segment and Bridge and why they are used in LANs.
Give another name for Network Adapter
A. ModemB. ASDLC. Network Interface CardD.Network Information Centre
Network adapter card
Why are NICs used?
A. Converts analogue signal into digitalB. Allows the PC to send and receive data
with other devices on the network.C. To connect to the Internet.D.To remotely access parts of an
internal network.
Identify the advantage of using a bus network
A. It is easy to locate a fault if a cable failsB. Easy to add more stations without disrupting the
networkC. If the main cable fails only one station is affectedD. The performance is not affected under a heavy
load
Give an advantage of star network
A. If one cable fails, only one station is affected
B. Is easy and inexpensive to install as it requires the least amount of cabling
C. The whole network goes down if a cable fails at any point
D.There is no central computer
Identify a common feature of Bus topology and Star with hub.
A. Easy to expand to a larger network.B. Cheap to install and maintain.C. Every node competes for a fraction of the
total bandwidth by broadcasting the packets to all nodes.
D.Uses intelligent routing of packets.
Describe the function of the hub at the centre of a star network.
A. Hub stores information temporarily then send it out to another destination on the network
B. Hardware device which will enable any printer to be connected to the network
C. It regenerates the incoming signals and sends them out to all nodes connected to hub.
Cables
Twisted pairBaseband Coaxial cable (digital transmission e.g .Bus Ethernet)Broadband coaxial Cable (analog transmission e.g .cable TV – is more expensive, larger geo area)Fibre Optics
Other Wireless Communication methods used in LANs
Radio Waves – WLAN Bluetooth (uses time division full duplex)
Microwaves –max 30 miles apart because of earth’s curvature. Mobile phones
Satellite – travel in Geosynchronous orbit about 22,000 miles above earth.
Cable versus Wireless LANs
Task – 5 minutes:Group 1:
Identify advantages/disadvantages of cabling over wireless
Group 2Identify advantages/disadvantages of wireless over cabling
Group 1 -disadvantages of cabling over wireless
Group 2 -disadvantages of wireless over cabling
Advantages/disadvantages of Wireless
Wireless +Convenience - locationMobilityProductivity due to increased mobility. Deployment – initial set up costs – less complexity because less cablingExpandability – easy to add devicesCost – initial cost but maintenance / expansion cost is low
Wireless -Security – more complex to secure than wired LAN, wireless packets can be intercepted, encryption neededRange is limited- repeaters are required – costlyReliability – radio frequency – interference from other devices such as printersSpeed –can be slow compared to slowest common wired LANs – low bandwidth
Advantages/disadvantages of Cabling
Cable +Reliable technologyHigher speed than wireless (100 Mbps Fast Ethernet )Security – more difficult to intercept packets
Cable –Static location – cost and expertise to move devicesCables and connection need to be set up -more complex and costlyExpandability – more costly as extra cables are required
Evolution of LAN Devices
NICs, Repeaters, & Hubs
Bridges
Switches
Routers
NIC Specifics
NICs provide hosts with access to media by using a MAC address.
MAC stands for Media Access Control
NICs operate at Layer 1 – Network Access layer of TCP/IP model
NICs, Repeaters, & Hubs
To connect two computers, you must...Install a NIC card in each.
The First LAN
NICNIC
NIC NIC
Attach computers using a crossover cable
NICs, Repeaters, & HubsRepeaters can be
used to increase the distance
What’s the maximum distance for Cat 5 cable?
100 meters or approx. 300 feetSo what can we use if this
distance is greater than 100 meters?
NIC NIC
Repeaters amplify and retime signals
NICs, Repeaters, & Hubs
NIC NIC
NIC NIC
Using repeaters was fine as long as a business only needed two computers
networked.What if a business
wanted a third computer attached?
Or a fourth? What device would they
need?
NICs, Repeaters, & Hubs
NIC NIC
NIC NIC
A multi-port repeater! Also called a...
Hub
A Dilemma!
NIC NIC
NIC NIC
As businesses expanded their networks, they began to cascade hubs.
What’s The Problem?
1) Hubs share bandwidth between all attached devices.
2) Hubs are stupid, Layer 1 devices. They cannot filter traffic.
3) Most LANs use a “broadcast topology,” so every device sees every packet sent down the media.
BroadcastsIn this picture, all hubs forward all traffic to all devices.
So, if Host 1 wants contact Host 2, all hosts see the packets. This is what we mean by a broadcast topology
Broadcasts
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The red arrows show that all hosts receive the contact request. Only Host 2 will respond.
What’s The Solution?
We need a smarter hub!
What’s a “smarter hub” called?
A Bridge!
Bridges filter network traffic based on MAC addresses.
Let’s take a look at how this works.
SegmentDefinition: A run of cable to which are attached a
number of workstations
The portion of a computer network in which computers can access each other using a Network Access layer protocol (e.g., in Ethernet, this would be the ability to send an Ethernet packet to others using their MAC addresses). In this case, it is synonymous with broadcast domain. In Ethernet a segment is also known as the collision domain
This area should be kept small or heavy traffic can slow down network considerable
Bridge
Definition: Connects two segments at MAC (Media Access Control) address level.
Amplifies signal that passes throughBridge ‘learns’ address connected to ports.Examines data frame and extracts source and destination (MAC) addresses.If not on same segment as source – bridge will broadcast the frame on the other segment.
BridgePort 1
Port 2
segment
segment
BridgeTo lessen the amount of LAN traffic, businesses began to uses bridges to filter frames based on MAC addresses.
BridgeNow, if Host 1 contacts Host 2, only the hosts on that LAN segment see the packets. The bridges stop the packets.
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SwitchA switch (also know as a multi-port bridge), can effectively replace these four bridges.
SwitchAnother benefit of a switch is that each LAN segment gets dedicated bandwidth.
The Cloud
10 Mbps10 Mbps
10 Mbps
10 Mbps
10 Mbps
Ethernet Switch
Each node can transmit to switch at same time. No collisions occur as switches can receive and send data at same time to all connections.Two wire pairs providing full duplex operation.
Since a switch is a multi-port bridge, we know it will stop local pings from traveling to other network segments.
Switch
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But a switch cannot stop a ping destined for a different LAN segment from traveling to all other LAN segments as it uses Mac Addresses.
Switch
16
1
For example, Host 1 pings Host 16. Since Host 16 is on another LAN segment, the switch will flood the ping request out all ports.
What device will solve this problem?
Router
1
16
1
Routers filter traffic based on IP addresses. The IP address tells the router which LAN segment the ping belongs to.
Devices Function At Layers
Know These!
Devices Function At Layers
Also know that each device not only works at its layer, but all layers below it.
Devices Function At Layers
For example, a router is a layer 2 device but also uses MAC addresses (layer 1) and repeats the signal (layer 1)
Why are LANs based on a bus topology segmented?
A. Is cheaper as less wiring is requiredB. It reduces traffic in the LAN as the bridge
will block frames by looking at destination IP address and operates at internet layer or network layer.
C. It reduces traffic in the LAN as the bridge will block frames destined for an address on the same segment from being passed to the other segment and operates at Network Access layer or data link layer (physical layer).
Give an advantage of a Switched Star network (Ethernet)
A. Collisions cannot occurB. Is easy and inexpensive to install as it
requires the least amount of cablingC. Supports portable devicesD.Difficult to find cable failure between
node and switch.
What is a MAC address
A. A flat 48 bit number on the network card representing the manufacturer and vendor of card.
B. A dynamically assigned address representing the PC in a LAN
C. A flat 32 bit number that can be used to identify a computer in WAN
Which of the following elements does a peer-to-peer network require?
A. WorkstationsB. FileserverC. Network Interface Cards