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 Stars 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 using single medium
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 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 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 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 max 3 segments, 2 repeating devices, 300 meters max between nodes A 100 Base-T network 43 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 Signals 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
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 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
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