CEG 2400 FALL 2012 Chapter 5 Topologies and

CEG 2400 FALL 2012 Chapter 5 Topologies and Ethernet Standards 1

Physical Topologies • Physical topology – Describes the physical network nodes layout – Does not specify: • Device types • Connectivity methods • Addressing schemes • Fundamental shapes – Bus, ring, star – Hybrid (combination of fundamental shapes) 2

Bus • Bus topology – – Single cable Connects all network nodes No intervening connectivity devices They share the communication channel • Physical medium – Usually coaxial cable • Passive topology – Node listens for, accepts data – Uses broadcast to send 3

Bus • Terminators – 50 -ohm resistors used to stop signal at end of wire • Signal bounce – Signal travels endlessly between two network ends – Happens if no terminator • One end grounded to removes static electricity 4

A terminated bus topology network 5

Bus • Advantage – Relatively inexpensive • Disadvantages – Does not scale well (adding more clients) – Difficult to troubleshoot (hard to tell where problem is) – Not very fault tolerant (one client can bring it down) 6

Ring • Ring topology – Node connects to nearest two nodes – Clockwise data transmission (circular network) • One direction (unidirectional) around ring – Active topology • Each workstation participates in data delivery – Physical medium • Twisted pair or fiber-optic cabling • Drawbacks – Malfunctioning workstation can disable network – Not very flexible or scalable 7

Ring A ring topology network 8

Star • Star topology – Node connects through central device • Usually a router or switch • Physical medium – Twisted pair or fiber-optic cabling • Single cable connecting two devices • Advantage – Fault tolerant – Flexible • Most popular fundamental layout 9

Star • A star topology network 10

Hybrid Topologies • Pure bus, ring, star topologies rarely exist • Hybrid topology – – – More likely Complex combination of pure topologies Several options Star-wired ring Star-wired bus (most common) 11

Star-Wired Ring • Star-wired ring topology – Star physical topology – Ring logical topology • Benefit – Star’s fault tolerance • Network use – Token Ring networks (not common anymore) • IEEE 802. 5 12

Star-Wired Ring A star-wired ring topology network 13

Star-Wired Bus • Star-wired bus topology – Star-connected devices – Central device networked via single bus • Advantage – Cover longer distances – Easily interconnect, isolate different segments • Drawback – More cabling, connectivity device expense • Basis for modern Ethernet networks 14

Star-Wired Bus A star-wired bus topology network 15

Logical Topologies • Refers to way data transmitted between nodes rather than physical layout • Does not necessarily match physical topology • Most common: bus and ring • Bus – signal travels from one device to all other devices – Broadcast domain • All nodes connected to single repeating device or switch • Ring – signal follows a circular path between sender and receiver 16

Network Backbone • Cabling that connects hubs, switches, routers • Has more throughput • Large organizations – Fiber-optic backbone – Cat 5 or better for hubs, switches • In an Enterprise – Significant building block: backbone • Enterprise-wide network backbones are – Complex, difficult to plan • Several different types – Serial, Distributed, Collapsed, and Parallel 17

Serial Backbone A serial backbone 18

Serial Backbone • Simplest backbone – Two or more devices connected usingle medium in daisy-chain fashion • Benefit – Logical growth solution • Modular additions – Low-cost LAN infrastructure expansion • Easily attach switches • Backbone components – Gateways, routers, switches 19

Serial Backbone • Standards – Limited number of repeating devices allowed – Limited distance spanned between each – Exceed standards • Intermittent, unpredictable data transmission errors • Not used in modern networks 20

Distributed Backbone A distributed backbone connecting multiple LANs 21

Distributed Backbone • Intermediate 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 (troubleshooting) – May include daisy-chain linked repeating devices • Drawback – Potential for single failure points 22

Collapsed Backbone 23

Collapsed Backbone • Uses router or switch – Single central connection point for multiple subnetworks – Single router or switch with multiprocessors to handle traffic • Disadvantage – Central router failure risk – Routers may slow data transmission • Advantages – Interconnect different subnetwork types – Central management 24

Parallel Backbone 25

Parallel Backbone • Most robust network backbone • A variation of collapsed backbone • Requires duplicate connections between connectivity devices • Advantage – Redundant links – Increased performance – Better fault tolerance • Disadvantage – Minor cost, more cabling (but usually worth it) 26

Switching • Logical network topology component • Three methods 1. Circuit switching 2. Packet switching 3. Multiprotocol label switching 27

Circuit Switching • Connection established between two network nodes – Before transmitting data • Dedicated bandwidth – nodes stay connected • Data follows same initial path selected by switch • Monopolizes bandwidth while connected even if not sending data – Resource wasted • Uses – Live audio, videoconferencing – Traditional telephone calls 28

Packet Switching • Most popular • 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 • Ethernet networks and the internet are the most common to use this type 29

Multiprotocol Label Switching(MPLS) • Based on short path labels rather than long network addresses thus avoiding complex lookups in a routing table • The labels identify virtual links (paths) between distant nodes rather than endpoints • Packet-forwarding decisions are made solely on the contents of this label, without the need to examine the packet itself. • Routers interpret label to predefined paths 30

MPLS • MPLS can encapsulate packets of various network protocols • Supports IP • MPLS operates at a layer that is generally considered to lie between traditional definitions of layer 2 (data link layer) and layer 3 (network layer), and is often referred to as a "layer 2. 5" protocol. MPLS shim within a frame 31

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 called CSMA/CD 32

CSMA/CD (Carrier Sense Multiple Access with Collision Detection) • Network access method – Controls how nodes access communications channel • Carrier sense (CS) – Ethernet NICs listen, wait until free channel detected • Multiple access (MA) – Ethernet nodes simultaneously monitor traffic or can access the media 33

CSMA/CD • Collision – Two nodes simultaneously: • Check channel, determine it is free, begin transmission • Collision detection (CD) – Way nodes respond to collision – Collision detection routine • Enacted if node detects collision – Jamming – What happens if collision • NIC issues 32 -bit sequence • Indicates previous message faulty 34

CSMA/CD • Heavily trafficked network segments – Collisions are common • Collisions corrupt data, truncate data frames – Network must detect and compensate • Segment growth – too many devices – Performance suffers – “Critical mass” 35

CSMA/CD process 36

CSMA/CD • 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 37

Broadcast domains and collision domains 38

Ethernet Standards for Copper Cable • IEEE Physical layer standards – Specify how signals transmit to media • How to specify – Number transmission type cable • Ex. 10 base T 39

Ethernet Standards for Copper Cable • 10 Base-T – – 10 represents maximum throughput: 10 Mbps Base indicates baseband transmission T stands for twisted pair Two pairs of wires: transmit and receive • Full-duplex transmission • Two wires for transmit • Two wires for receive – Baseband transmission, star topology, RJ-45 connectors – Not common anymore 40

5, 4, 3 rule – max 5 segments, 4 repeating devices, 3 segments populated, 500 meters max between nodes A 10 Base-T network 41

Ethernet Standards for Copper Cable • 100 Base-T (Fast Ethernet) – IEEE 802. 3 u standard – Similarities with 10 Base-T • Baseband transmission, star topology, RJ-45 connectors – 100 Base-TX (most common) • 100 -Mbps throughput over twisted pair • Full-duplex transmission: doubles effective bandwidth • where X is a placeholder for the FX and TX variants 42

max 3 segments, 2 repeating devices, 300 meters max between nodes A 100 Base-T network 43

Ethernet Standards for Copper Cable • 1000 Base-T (Gigabit Ethernet) – – – IEEE 802. 3 ab 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 44

Ethernet Standards for Copper Cable • 10 GBase-T – IEEE 802. 3 an – Pushing limits of twisted pair • Requires Cat 6, 6 a, or 7 cabling – Benefits • Very fast data transmission • Cheaper than fiber-optic – Uses • Connect network devices • Connect servers, workstations to LAN 45

Ethernet Standards for Fiber-Optic Cable • 100 Base-FX (Fast Ethernet) – IEEE 802. 3 u standard – 100 -Mbps throughput, baseband, fiber-optic cabling • Multimode fiber containing at least two strands – Half-duplex mode • One strand receives; one strand transmits – Full duplex-mode • Both strands send and receive 46

Ethernet Standards for Fiber-Optic Cable • 1000 Base-LX (1 -Gigabit Ethernet) – – – IEEE 802. 3 z standard 1000 -Mbps throughput Base: baseband transmission LX: Long wavelengths Single-mode fiber: 5000 meters maximum segment (3. 1 miles) – Multimode fiber: 550 meters maximum segment (0. 34 miles) 47

Ethernet Standards for Fiber-Optic Cable • 1000 Base-SX (1 -Gigabit Ethernet) – Differences from 1000 Base-LX • Multimode fiber-optic cable • Uses short wavelengths – Maximum segment length dependencies • Fiber diameter – 50 micron fibers: 550 meter maximum length (0. 34 miles) – 62. 5 micron fibers: 275 meter maximum length (0. 17 miles) 48

10 -Gigabit Fiber-Optic Standards • 802. 3 ae standard – Fiber-optic Ethernet networks transmitting data at 10 Gbps – Several variations (will discuss next) – Common characteristics • Star topology, allow one repeater, full-duplex mode – Differences • Signal’s light wavelength; maximum allowable segment length 49

10 -Gigabit Fiber-Optic Standards • 10 GBase-SR and 10 GBase-SW – – 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 – Shortest segment length of 10 G Fiber (300 meters) 50

10 -Gigabit Fiber-Optic Standards • 10 GBase-LR and 10 GBase-LW – – – 10 G: 10 Gbps Base: baseband transmission L: long reach Single-mode fiber Medium segment length of 10 G Fiber (10, 000 meters, 6. 2 miles) – 10 GBase-LR: WAN or MAN – 10 GBase-LW: SONET WAN links 51

10 -Gigabit Fiber-Optic Standards • 10 GBase-ER and 10 GBase-EW – E: extended reach – Single-mode fiber – Longest fiber-optic segment reach • 40, 000 meters (25 miles) – 10 GBase-EW • Encoding for SONET transmission format – Best suited for WAN use 52

Summary of Common Ethernet Standards Common Ethernet standards 53

Ethernet Frames • Four Ethernet frame types 1. 2. 3. 4. Ethernet_802. 2 (Raw) Ethernet_802. 3 (Novell proprietary) Ethernet_II (DIX) Ethernet_SNAP • Frame types differ slightly in format – Coding and decoding packets • Framing – Independent of higher-level layers 54

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 55

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 56

Ethernet_II (DIX) • Developed by DEC, Intel, Xerox (abbreviated DIX) • Contains 2 -byte type field – Identifies the Network layer protocol (ex. IP) • Most commonly used on contemporary Ethernet networks Ethernet II (DIX) frame 57

Po. E (Power over Ethernet) • IEEE 802. 3 af standard – Supplying electrical power over Ethernet connections • Two device types – PSE (power sourcing equipment) – PDs (powered devices) • Ex. Wireless access point, outdoor camera • Requires Cat 5 or better copper cable • Connectivity devices must support Po. E 58

Po. E capable switch Po. E adapters 59

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 – Circuit switching, Packet switching, MPLS • Ethernet – Cabling specifications, data frames, Po. E 60

End of Chapter 5 Questions 61