CIS 1140 Network FundamentalsChapter 5 – Topologies and Ethernet Standards

Collected and CompiledBy JD WillardMCSE, MCSA, Network+, Microsoft IT Academy AdministratorComputer Information Systems InstructorAlbany Technical College

Attention: Accessing Demos• This course presents many demos. • The Demos require that you be logged in to the Virtual

Technical College web site when you click on them to run. • To access and log in to the Virtual Technical College web site:

– To access the site type www.vtc.com in the url window– Log in using the username: CIS 1140 or ATCStudent1– Enter the password: student (case sensitive)

• If you should click on the demo link and you get an Access Denied it is because you have not logged in to vtc.com or you need to log out and log back in.

• If you should click on the demo link and you are taken to the VTC.com web site page you should do a search in the search box for the CompTIA Network+ (2009 Objectives) Course and run the video from within that page.

Objectives

• Describe the basic and hybrid LAN physical topologies, and their uses, advantages, and disadvantages

• Describe the backbone structures that form the foundation for most networks

• Compare the different types of switching used in data transmission

• Explain how nodes on Ethernet networks share a communications channel

• Identify the characteristics of several Ethernet standards

• Topology is the term used to describe how devices are connected and how messages flow from device to device

• There are two types of network topologies:– Physical topology is the physical layout of the network,

including cable and device configuration– Logical topology refers to the method used to

communicate between the devices It is important to understand the physical topology before

designing networks, because they can affect the logical topology chosen, how the building is cabled, and what kind of media is used

Network Topologies

Network Topology Basics Demo

Simple Physical Topologies

• Physical topology– Physical layout of nodes on a network

– Depicts broad scope

– Does not specify:• Device types• Connectivity methods• Addressing schemes

• Topology integral to type of network, cabling infrastructure, and transmission media used

• Fundamental shapes– Bus, ring, star

– Hybrid

Physical Topologies Demo

Topologies pt. 1 Demo Topologies pt. 2 Demo

Bus

• Bus topology– Single cable

• The single cable is called the bus and supports one channel, where each node shares total capacity

– Connects all network nodes– No intervening connectivity devices– One shared communication channel

• Physical medium– Coaxial cable

• Passive topology– Node listens for, accepts data– Uses broadcast to send

Bus Topology Demo

Basic Ethernet Bus

• An Ethernet network where all machines are daisy chained using coaxial cable (Thin Ethernet/Thin-net or Thick Ethernet/Thick-net).

• Machine 2 wants to send a message to machine 4.1. First it 'listens' to make sure no one else is using the network. 2. If it is all clear it starts to transmit its data on to the network (represented by the

yellow flashing screens). 3. Each packet of data contains the destination address, the senders address, and

of course the data to be transmitted. 4. The signal moves down the cable and is received by every machine on the

network but because it is only addressed to number 4, the other machines ignore it.

5. Machine 4 then sends a message back to number 2 acknowledging receipt of the data (represented by the purple flashing screens).

A terminated bus topology network

• Terminators– Bus requires a terminator

at each end of cable

– 50-ohm resistors

– Stop signal at end of wire • Prevents signal bounce

• Signal bounce– Signal travels endlessly

between two network ends

• One end grounded– Removes static electricity

Bus (cont’d.)• Bus topology advantage

– Easy to install and add devices– Relatively inexpensive

• Requires less cable

• Disadvantages– Requires 50 ohm terminators at each end of the cable– Requires grounding loop– Does not scale well– Difficult to troubleshoot– Not very fault tolerant

• Entire network shuts down if the cable breaks (signal bounce)

Ring• Ring topology

– Node connects to nearest two nodes– Circular network– Clockwise data transmission

• One direction (unidirectional) around ring• Token passing

– Token Ring and FDDI networks– Active topology

• Workstation participates in data delivery• Data stops at destination

– Physical medium• Twisted pair or fiber-optic cabling

Ring Topology Demo

Ring (cont’d.)• Ring advantages

– No network collisions

• Drawbacks– Malfunctioning workstation can disable network

– Not very flexible or scalable

A ring topology network

Star• Star topology

– Node connects through central device

• Hub, Router or switch

• Physical medium– Twisted pair or

fiber-optic cabling

• Single cable connects only two devices A star topology network

Star Topology Demo

Star• Most popular

fundamental layout– Modern Ethernet

networks based on star topology

• 1024 addressable logical network nodes maximum

How Ethenet accesses the cable and transmits using a hub.

Star (cont’d.)• Star advantages

– Fault tolerant– Easier to troubleshoot

• A break in the cable does not shut down the network

• Higher reliability

– Flexible– No terminators required

• Star disadvantages– Uses more cable than ring or bus networks– Connectivity devices more expensive than

terminators– Connectivity device failures take down

entire LAN segmentsAny single cable connects only two devices, Cabling problems affect two nodes at most

Hybrid Topologies

• Pure bus, ring, star topologies– Rarely exist because too restrictive

• Hybrid topology– More likely– Complex combination of pure topologies– Several options

Hybrid Topologies Demo

Hybrid Topology Demo

Star-Wired Ring

• Star-wired ring topology– Star physical

topology– Ring logical

topology• Token

passing data transmission method

• Benefit– Star fault tolerance– Reliability of token passing

• Network use– Token Ring networks

• IEEE 802.5

Star-Wired Ring (cont’d.)

• Token Ring MAUs can be connected together using straight-through patch cables to connect the Ring Out port of one MAU and the Ring In port of the next MAU until the network of MAUs forms a circle.

• Up to 255 stations can be connected to the network when using Shielded Twisted Pair cable and 72 when using Unshielded Twisted Pair cable.

MAU Showing Internal Ring

• A Token Ring hub (MAU) changes the topology from a physical ring to a star wired ring.

• MAU can automatically bypass any ports that are disconnected or have a cabling fault.

Star-Wired Bus

• Star-wired bus topology– Workstation groups

• Star-connected devices• Networked via single bus

• Advantage– Cover longer distances– Easily interconnect, isolate different segments

• Drawback– Cabling, connectivity device expense

• Basis for modern Ethernet networks

Star-Wired Bus (cont’d.)

A star-wired bus topology network

Logical Topologies

• Logical topology: how data is transmitted between nodes– May not match physical topology

• Bus logical topology: signals travel from one network device to all other devices on network– Required by bus, star, star-wired physical topologies

• Ring logical topology: signals follow circular path between sender and receiver– Required by ring, star-wired ring topologies

• Broadcast domain– All nodes connected to single repeating device or switch

Logical Topologies Demo

Logical Topology

Physical Topology

Description

Bus

Bus Messages are sent to all devices connected to the bus.Star

Ring

Ring Messages are sent from device-to-device in a predetermined order until they reach the destination device.

Star

Star StarMessages are sent directly to (and only to) the destination device.

Backbone Networks• Cabling connecting hubs, switches, routers• More throughput• Large organizations

– Fiber-optic backbone

– Cat 5 or better for hubs, switches

• Enterprise-wide network backbones – Complex, difficult to plan

• Enterprise– Entire organization

– Significant building block: backbone

Serial Backbone

• Simplest backbone– Two or more devices– Connect using single medium in daisy-chain fashion

• Daisy-chain– Linked series of devices

• Benefit– Logical growth solution

• Modular additions

– Low-cost LAN infrastructure expansion• Easily attach switches

Serial Backbone (cont’d.)

• Backbone components– Gateways,

routers, switches

• Serial connection of repeating devices– Limited distance

spanned between each

• Standards – Define number of repeating

devices allowed– Exceed standards

• Intermittent, unpredictable data transmission errors

• Not used in modern networks

Distributed Backbone

• Connectivity devices– Connected to

hierarchy of central connectivity devices

• Benefit– Simple expansion,

limited capital outlay

• More complicated distributed backbone– Connects multiple

LANs, LAN segments using routers

• Additional benefits– Workgroup segregation– May include daisy-chain linked

repeating devices• Consider length

• Drawback– Potential for single failure points

Collapsed Backbone

• Uses router or switch– Single central

connection point for multiple subnetworks

• Highest layer– Single router or

switch with multiprocessors

• Central router failure risk

• Routers may slow transmission• Advantages

• Interconnect different subnetwork types

• Central management

Parallel Backbone

• Most robust network backbone

• More than one central router, switch– Connects to each

network segment

• Requires duplicate connections between connectivity devices

• Advantage– Redundant links– Increased performance– Better fault tolerance

Switching

• Logical network topology component

• Determines connection creation between nodes

• Three methods– Circuit switching– Packet switching– Multiprotocol label switching

Circuit Switching and Packet Switching (3:30)

Circuit Switching

• Connection established between two network nodes– Before transmitting data

• Dedicated bandwidth• Data follows same initial path selected by switch• Monopolizes bandwidth while connected

– Resource wasted

• Uses– Live audio, videoconferencing– Traditional telephone calls– Most popular

Packet Switching

• Breaks data into packets before transporting• Packets

– Travel any network path to destination– Find fastest circuit available at any instant– Need not follow each other– Need not arrive in sequence– Reassembled at destination

• Requires speedy connections for live audio, video transmission

• Examples– Ethernet networks– Internet

MPLS (Multiprotocol Label Switching)• Introduced by IETF in 1999

• Enables multiple types of Layer 3 protocols:

– To travel over any one of several Layer 2 protocols

• Most often supports IP

• Common use

– Layer 2 WAN protocols

• Offers potentially faster transmission than packet- or circuit-switched networks

• Advantages

– Use packet-switched technologies over traditionally circuit switched networks

– Create end-to-end paths

– Addresses traditional packet switching limitations

– Better QoS (quality of service)

Ethernet• Most popular networking technology used

on modern LANs• Benefits

– Flexible– Can run on various network media– Excellent throughput– Reasonable cost

• All variations– Share common access method

• CSMA/CD

Ethernet Demo

What is Ethernet? Demo

CSMA/CD (Carrier Sense Multiple Access with Collision Detection)

• Network access method– Controls how nodes access communications channel– Necessary to share finite bandwidth

• Carrier sense– Ethernet NICs listen, wait until free channel detected

• Multiple access– Ethernet nodes simultaneously monitor traffic, access

media

CSMA/CD Access Method demo

CSMA / CD Demo

CSMA/CD (cont’d.)• Collision

– Two nodes simultaneously:• Check channel, determine it is free, begin transmission

• Collision detection– Manner nodes respond to collision– Requires collision detection routine

• Enacted if node detects collision– Jamming

• NIC issues

32-bit sequence• Indicates

previous

message faulty

CSMA/CD (cont’d.)

• Heavily trafficked network segments– Collisions common

• Segment growth– Performance suffers– “Critical mass” number

dependencies• Data type and volume

regularly transmitted

• Collisions corrupt data, truncate data frames– Network must detect and

compensate

CSMA/CD process

CSMA/CD and CSMA/CA (5:33)

CSMA/CD (cont’d.)• Collision domain

– Portion of network where collisions occur

• Ethernet network design– Repeaters repeat

collisions• Result in larger

collision domain– Switches and routers

• Separate collision domains

• Collision domains differ from broadcast domains

Broadcast domains and collision domains

Collision Domains Demo

CSMA/CD (cont’d.)• Ethernet cabling distance limitations

– Effected by collision domains

• Data propagation delay– Data travel time too long

• Cannot identify collisions accurately

• 100 or 1000 Mbps networks– Three segment maximum connected with two

repeating devices

• 10 Mbps buses– Five segment maximum connected with four

repeating devices

Ethernet Standards for Copper Cable

• IEEE Physical layer standards– Specify how signals transmit to media– Differ significantly in signal encoding

• Affect maximum throughput, segment length, wiring requirements

BASE Terminology Demo

Ethernet Topologies (7:32)

Ethernet Network Types Demo

Ethernet Standards for Copper Cable (cont’d.)

• 10Base-T

– 10 represents maximum throughput: 10 Mbps

– Base indicates baseband transmission

– T stands for twisted pair

• Requires CAT3 or higher UTP

– Two pairs of wires: transmit and receive

• Full-duplex transmission

A 10Base-T network

– Follows 5-4-3 rule of networking• Five network segments

– Maximum segment length is 100 meters

• Four repeating devices (hubs)• Three populated segments maximum

Ethernet Standards for Copper Cable (cont’d.)

• 100Base-T (Fast Ethernet)– IEEE 802.3u standard– Similarities with 10Base-T

• Baseband transmission, star topology, RJ-45 connectors

– 100Base-TX• 100-Mbps throughput over twisted pair• Full-duplex transmission: doubles effective

bandwidth

Fast Ethernet Demo

A 100Base-T network

• Supports three network segments maximum

• Connected with two repeating devices• 100 meter segment length limit between

nodes

Ethernet Standards for Copper Cable (cont’d.)

• 1000Base-T (Gigabit Ethernet)– IEEE 802.3ab standard– 1000 represents 1000 Mbps– Base indicates baseband transmission– T indicates twisted pair wiring– Four pairs of wires in Cat 5 or higher cable

• Transmit and receive signals

– Data encoding scheme: different from 100Base-T

– Standards can be combined– Maximum segment length: 100 meters, one

repeater Gigabit Ethernet Demo

Ethernet Standards for Copper Cable (cont’d.)

• 10GBase-T– IEEE 802.3an– Pushing limits of twisted pair

• Requires Cat 6, 6a, or 7 cabling• Maximum segment length: 100 meters

– Benefits• Very fast data transmission• Cheaper than fiber-optic

– Uses• Connect network devices• Connect servers, workstations to LAN

Even Faster Ethernet Demo

Ethernet Over Copper Summary

Category Standard Bandwidth Cable TypeMaximum Segment Length

Ethernet 10BaseT10 Mbps (half duplex)20 Mbps (full duplex)

Twisted pair (Cat3, 4, or 5)

100 meters

Fast Ethernet

100BaseTX100 Mbps (half duplex)200 Mbps (full duplex)

Twisted pair (Cat5 or higher) Uses 2 pairs of wires

100 meters

Gigabit Ethernet

1000BaseT1,000 Mbps (half duplex)2,000 Mbps (full duplex)

Twisted pair (Cat5 or higher)

100 meters

10 Gigabit Ethernet

10GBaseT 10 Gbps (full duplex only)Twisted pair (Cat5e, 6, or 7)

100 meters

Ethernet Standards for Fiber-Optic Cable

• 100Base-FX (Fast Ethernet)

– 100-Mbps throughput, baseband, fiber-optic cabling

• Multimode fiber containing at least two strands

– Half-duplex mode

• One strand receives; one strand transmits

• 412 meters segment length

– Full duplex-mode

• Both strands send and receive

• 2000 meters segment length

– One repeater maximum

– IEEE 802.3u standard

Ethernet Standards for Fiber-Optic Cable (cont’d.)

• 1000Base-LX (1-Gigabit Ethernet)– IEEE 802.3z standard

– 1000: 1000-Mbps throughput

– Base: baseband transmission

– LX: reliance on 1300 nanometers wavelengths

– Longer reach than any other 1-gigabit technology

– Single-mode fiber: 5000 meters maximum segment

– Multimode fiber: 550 meters maximum segment

– One repeater between segments

– Excellent choice for long backbones

Ethernet Standards for Fiber-Optic Cable (cont’d.)

• 1000Base-SX (1-Gigabit Ethernet)– Differences from 1000Base-LX

• Multimode fiber-optic cable (installation less expensive)

• Uses short wavelengths (850 nanometers)

– Maximum segment length dependencies• Fiber diameter, modal bandwidth used to transmit

signals

Ethernet Standards for Fiber-Optic Cable (cont’d.)

• 1000Base-SX (cont’d.)– Modal bandwidth measurement

• Highest frequency of multimode fiber signal (over specific distance)

• MHz-km• Higher modal bandwidth, multimode fiber caries signal

reliably longer

– 50 micron fibers: 550 meter maximum length– 62.5 micron fibers: 275 meter maximum length– One repeater between segments– Best suited for shorter network runs

10-Gigabit Fiber-Optic Standards

• Extraordinary potential for fiber-optic cable– Pushing limits

• 802.3ae standard– Fiber-optic Ethernet networks– Transmitting data at 10 Gbps– Several variations– Common characteristics

• Star topology, allow one repeater, full-duplex mode

– Differences• Signal’s light wavelength; maximum allowable segment

length

10-Gigabit Fiber-Optic Standards (cont’d.)

• 10GBase-SR and 10GBase-SW– 10G: 10 Gbps– Base: baseband transmission– S: short reach– Physical layer encoding

• R works with LAN fiber connections• W works with SONET fiber connections

– Multimode fiber: 850 nanometer signal transmission– Maximum segment length

• Depends on fiber diameter

10-Gigabit Fiber-Optic Standards (cont’d.)

• 10GBase-LR and 10GBase-LW– 10G: 10 Gbps– Base: baseband transmission– L: long reach– Single-mode fiber: 1310 nanometer signal

transmission– Maximum segment length

• 10,000 meters

– 10GBase-LR: WAN or MAN– 10GBase-LW: SONET WAN links

10-Gigabit Fiber-Optic Standards (cont’d.)

• 10GBase-ER and 10GBase-EW– E: extended reach– Single-mode fiber

• Transmit signals with 1550 nanometer wavelengths

– Longest fiber-optic segment reach• 40,000 meters (25 miles)

– 10GBase-EW• Encoding for SONET

– Best suited for WAN use

Ethernet Over Fiber SummaryCategory Standard Bandwidth Cable Type

Maximum Segment Length

Fast Ethernet

100BaseFX100 Mbps (multimode cable)

Fiber optic 412 meters

Gigabit Ethernet

1000BaseSX (short)1,000 Mbps (half duplex)2,000 Mbps (full duplex)

Fiber optic

220 to 550 meters depending on cable quality

1000BaseLX (long)

550 meters (multimode)10 kilometers (single-mode)

10 Gigabit

Ethernet

10GBaseSR/10GBaseSW

10 Gbps (full duplex only)

Multimode fiber optic

300 meters

10GBaseLR/10GBaseLWSingle mode fiber optic

10 kilometers

10GBaseER/10GBaseEWSingle mode fiber optic

40 kilometers

Multiple types of Ethernet on a WAN

Ethernet Frames

• Four types– Ethernet_802.2 (Raw)– Ethernet_802.3 (Novell proprietary)– Ethernet_II (DIX)– Ethernet_SNAP

• Frame types differ slightly– Coding and decoding packets

• No relation to topology, cabling characteristics• Framing

– Independent of higher-level layers

Using and Configuring Frames

• Ensure all devices use same, correct frame type– Node communication

• Ethernet_II used today• Frame type configuration

– Specified using NIC configuration software– NIC autodetect

• Importance– Know frame type for troubleshooting

Frame Fields

• Common fields– 7-byte preamble, 1-byte start-of-frame delimiter– SFD (start-of-frame delimiter) identifies where data

field begins– 14-byte header– 4-byte FCS (frame check sequence)– Frame size range: 64 to 1518 total bytes

• Larger frame sizes result in faster throughput

• Improve network performance– Properly manage frames

Ethernet_II (DIX)• Developed by DEC, Intel, Xerox (abbreviated DIX)

– Before IEEE• Most commonly used on contemporary Ethernet networks

• The preamble is a set of alternating ones and zeroes terminated by two ones (i.e., 11) that marks it as a frame.

• The destination address identifies the receiving host's MAC address. • The source address identifies the sending host's MAC address. • The 2-byte type field identifies the Network layer protocol• The data, or the information that needs to be transmitted from one host to the other.

– Optional bits to pad the frame. Ethernet frames are sized between 64 and 1518 bytes. If the frame is smaller than 64 bytes, the sending NIC places "junk" data in the pad to make it the required 64 bytes.

• The FCS/CRC (frame check sequence/cyclic redundancy check) is the result of a mathematical calculation performed on the frame. The CRC helps verify that the frame contents have arrived uncorrupted.

Ethernet Frames Demo

PoE (Power over Ethernet)• IEEE 802.3af standard

– Supplying electrical power over Ethernet connections

• Two device types– PSE (power sourcing equipment)

– PDs (powered devices)

• Requires Cat 5 or better copper cable

• Connectivity devices must support PoE

• Compatible with current 802.3 installations

PoE capable switch

PoE adapters

Power over Ethernet (3:45)

Summary• Physical topology describes basic network

physical layout– Examples: bus, ring, star, hybrid

• Logical topology describes signal transmission

• Network backbones– Serial, distributed, collapsed, parallel

• Switching– Manages packet filtering, forwarding

• Ethernet– Cabling specifications, data frames, PoE

The End