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

5 A terminated bus topology network

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

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

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 15 A star-wired bus topology network

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 using single 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

21 A distributed backbone connecting multiple LANs 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

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

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. 31 MPLS shim within a frame

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

36 CSMA/CD process

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

38 Broadcast domains and collision domains

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 10Base-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

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

Ethernet Standards for Copper Cable 100Base-T (Fast Ethernet) –IEEE 802.3u standard –Similarities with 10Base-T Baseband transmission, star topology, RJ-45 connectors –100Base-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

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

Ethernet Standards for Copper Cable 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 44

Ethernet Standards for Copper Cable 10GBase-T –IEEE 802.3an –Pushing limits of twisted pair Requires Cat 6, 6a, 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 100Base-FX (Fast Ethernet) –IEEE 802.3u 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 1000Base-LX (1-Gigabit Ethernet) –IEEE 802.3z 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 1000Base-SX (1-Gigabit Ethernet) –Differences from 1000Base-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 802.3ae 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 10GBase-SR and 10GBase-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 10G Fiber (300 meters) 50

10-Gigabit Fiber-Optic Standards 10GBase-LR and 10GBase-LW –10G: 10 Gbps –Base: baseband transmission –L: long reach –Single-mode fiber –Medium segment length of 10G Fiber (10,000 meters, 6.2 miles) –10GBase-LR: WAN or MAN –10GBase-LW: SONET WAN links 51

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

Summary of Common Ethernet Standards 53 Common Ethernet standards

Ethernet Frames Four Ethernet frame types 1.Ethernet_802.2 (Raw) 2.Ethernet_802.3 (Novell proprietary) 3.Ethernet_II (DIX) 4.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 57 Ethernet II (DIX) frame

PoE (Power over Ethernet) IEEE 802.3af 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 PoE 58

PoE 59 PoE capable switch PoE adapters

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, PoE 60

End of Chapter 5 Questions 61