Local Area Networks. Broadcast Networks. Hugh Melvin, Dept. IT, NUI,G 1. Hugh Melvin, Dept. IT, NUI,G 2. Hugh Melvin, Dept.

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1 Local Area Networks Broadcast Networks Hugh Melvin, Dept. IT, NUI,G 1 Hugh Melvin, Dept. IT, NUI,G 2 Hugh Melvin, Dept. IT, NUI,G 3 1

2 Recall Broadcast Networks Compare N nodes connected via.. P-to-point Broadcast Simplifies topology Wiring Costs Single channel/medium => access mechanism or protocol required Hugh Melvin, Dept. IT, NUI,G 4 Medium Access Control (MAC Layer) Sublayer of the DLL, closest to Physical layer that deals with this issue Different algorithms used to allocate channel among users Static Dynamic Hugh Melvin, Dept. IT, NUI,G 5 Hugh Melvin, Dept. IT, NUI,G 6 2

3 Static/Dynamic Static FDM /TDM FDM : Radio/TV broadcasts TDM : POTS GSM uses both Wasteful of b/w Dynamic Pure/ Slotted ALOHA Carrier Sense Multiple Access (CSMA) Protocols Collision free protocols Hugh Melvin, Dept. IT, NUI,G 7 Hugh Melvin, Dept. IT, NUI,G 8 Pure Aloha Each node sends data regardless of others If collision occurs, frames destroyed..nodes can detect this => wait a random time retransmit Vulnerable period = 2 x (time to send frame) Poor efficiency especially if demand is high Hugh Melvin, Dept. IT, NUI,G 9 3

4 Hugh Melvin, Dept. IT, NUI,G 10 Hugh Melvin, Dept. IT, NUI,G 11 Aloha G: Total frames sent/frame time (incl. retransmissions) S: successful throughput S = G e -2G Max. effic 18% at G =0.5 Hugh Melvin, Dept. IT, NUI,G 12 4

5 Slotted Aloha Time is divided into slots can only transmit at start of slot Vulnerable period halved => max. eff is doubled S = G e -G Max. effic 36% at G =1 Requires sync of clocks Still poor at hi-loads GSM : call setup Hugh Melvin, Dept. IT, NUI,G 13 Hugh Melvin, Dept. IT, NUI,G 14 CSMA Carrier sense Node on segment checks if channel is in use only transmits if channel is idle 1-persistent Once node detects an idle channel(segment) Transmits immediately (prob. of 1) Still get collisions Two waiting nodes start transmitting at exactly same time. Propagation delay If collision occurs, node waits random period Hugh Melvin, Dept. IT, NUI,G 15 5

6 CSMA Non-persistent Busy channel, it waits a random period before checking the channel (not continuous) less chance of problem 1 above Also have p-persistent Hugh Melvin, Dept. IT, NUI,G 16 Hugh Melvin, Dept. IT, NUI,G 17 CSMA with CD Collision Detection circuitry Once a station detects a collision whilst still transmitting a frame, it immediately aborts transmission transmits jamming signal Waits random period Max. period to wait to ensure collision is detected?? τ = time to transmit => 2 τ Hugh Melvin, Dept. IT, NUI,G 18 6

7 Hugh Melvin, Dept. IT, NUI,G 19 IEEE Standard 802 for LANs 802.1: Introduction 802.2: Defines LLC (Logical Link Control) 3 Phy.layer / MAC standards : CSMA/CD : Token bus : Token ring See Hugh Melvin, Dept. IT, NUI,G 20 LLC Operates on top half of D.L.L => interface to N.L. LLC provides service options Unreliable / Reliable etc.. Similar to HDLC Hugh Melvin, Dept. IT, NUI,G 21 7

8 802.3 CSMA/CD Family of 1-persistent CSMA/CD Ethernet is similar to (orig.xerox) Popular types 10Base-T, 10Base2 10Base-T 10Mbps Twisted pair, max seg.100m, stations connected to a hub, ease of installation & maintenance Most common type 10Base2 10Mbps Thin coax (Thinnet), max segment 200m Manchester encoding (+0.7V to -0.7V) Hugh Melvin, Dept. IT, NUI,G 22 Hugh Melvin, Dept. IT, NUI,G 23 Hugh Melvin, Dept. IT, NUI,G 24 8

9 Hugh Melvin, Dept. IT, NUI,G 25 Hugh Melvin, Dept. IT, NUI,G Frame format Preamble: used to synchronize Dest/source address : 6 byte(48bits) MAC address (Ethernet address) Broadcast => all 1 24 bit manuf. code + 24 bit ser. No Cisco 00000C 3Com 02608C / 00C04F Length data (Type field in Ethernet) Up to 1500 byte, Min 64byte CRC check field Hugh Melvin, Dept. IT, NUI,G 27 9

10 Hugh Melvin, Dept. IT, NUI,G 28 Hugh Melvin, Dept. IT, NUI,G 29 ipconfig / all DOS Command C:\>ipconfig /all Windows NT IP Configuration Host Name : bibio.nuigalway.ie DNS Servers : Node Type : Broadcast NetBIOS Scope ID : IP Routing Enabled..... : No WINS Proxy Enabled..... : No NetBIOS Resolution Uses DNS : No Hugh Melvin, Dept. IT, NUI,G 30 10

11 ipconfig /all..contd Ethernet adapter El90x1: Description : 3Com 3C90x Ethernet Adapter Physical Address : 00-C0-4F DHCP Enabled : No IP Address : Subnet Mask : Default Gateway : Note: ifconfig command in Unix/Linux similar Hugh Melvin, Dept. IT, NUI,G 31 64bytes 10Mbps Need to ensure that a collision will be detected before frame transmission ends Max distance between stations 2.5km (10Base 5) Max wait : 51.2µs 51.2µs * = 512 bits = 64 bytes => use padding if necessary Hugh Melvin, Dept. IT, NUI,G 32 LLC IEEE / SNAP LLC header embedded in data field 4 bytes Dest/Source network protocols TCPIP or NetWare Control field Seq. No Flow control Similar to HDLC SNAP (Subnetwork Access Proto) Limited alternative to LLC (temporary) Hugh Melvin, Dept. IT, NUI,G 33 11

12 802.5 Token Ring Competitor to Ethernet/802.3 Lost significant ground Uses a 3 byte token Only transmit when node has token => no collisions Speeds up to 16Mbps (100Mbps also possible) Token circulates when ring is idle Centralised monitor station Station has data to send => Seizes token Inverts one bit => token converted into starting frame fields Can transmit for token time (typ. 10ms) Hugh Melvin, Dept. IT, NUI,G No terminator => once bits propagate the ring Removed by the sender No limit on size of frames (once within token holding time) Priority Represented by bit sequence in token Can be set by frames awaiting use of the channel Frame of priority n must wait until the priority of the token is also n or lower Good hi-load performance Hugh Melvin, Dept. IT, NUI,G Frame format AC : Contains Priority bit FC : distinguishes between data/control frames FS : Contains two bits that inform the sender if Destination present Frame copied okay possible to resend Hugh Melvin, Dept. IT, NUI,G 36 12

13 Hugh Melvin, Dept. IT, NUI,G 37 Hugh Melvin, Dept. IT, NUI,G 38 Comparison of standards Simplest to install and operate.. No waiting for token Not suitable for real-time applications non-deterministic and no priorities Collisions.poor performance at high loads Requires CD circuitry Minimum frame length of 64bytes Easily upgradeable (Fast/Gigabit Ethernet) 85% of all network connections Hugh Melvin, Dept. IT, NUI,G 39 13

14 Comparisons No collisions, reasonable priority system Large frame sizes Token delay Centralised monitoring Maintenance issues Good hi-load performance Overall much more complex than Limited b/w..compared to Ethernet scalability Hugh Melvin, Dept. IT, NUI,G 40 LAN Terminology NIC Repeater Hub Bridge Switch Router General Description (not definitive) Hugh Melvin, Dept. IT, NUI,G 41 Network Interface Card Connects workstation to network Internal bus ISA/PCI (Hardware Module??) MAC address stored in ROM Function Form data frames and place on network Receive data frames and pass to NL Implement access protocol eg. CSMA/CD Hugh Melvin, Dept. IT, NUI,G 42 14

15 Repeater Operates at physical layer not concerned with frames Amplify / reshape signals Ensure signal degradation does not cause bit errors Hugh Melvin, Dept. IT, NUI,G 43 Hub Multiport Repeater Does not filter traffic Centralised connection to network Physical star topology Logical Bus topology Hugh Melvin, Dept. IT, NUI,G 44 Bridge Operates at MAC address level Maintains table of of MAC address Examines destination MAC add forward iff address not on originating segment Reduces collision domain Connect multiple (diff) LANs at D.L.L. Partitions network: Benefits?? Org. Depts Load Distribution Filtering.. Security?? Hugh Melvin, Dept. IT, NUI,G 45 15

16 Hugh Melvin, Dept. IT, NUI,G 46 Hugh Melvin, Dept. IT, NUI,G 47 Switch (Switched Hub) Very fast, intelligent Hub Directs traffic to another segment iff the dest. MAC address is on that segment Effectively increases b/w Software on Switch segments traffic depending on connection Desktop Switch Connected directly to nodes Segment Switch Connects diff segments Hugh Melvin, Dept. IT, NUI,G 48 16

17 Router Operate at network layer Examine network layer addresses Slower than bridge Communicate with each other Generate an accurate picture of the subnet Determine best route Routing algorithms later Forward traffic iff have info on that destination Hugh Melvin, Dept. IT, NUI,G 49 High Speed LAN Developments Some solutions Fast Ethernet IEEE 802.3u IEEE VG-AnyLAN FDDI Gigabit Ethernet IEEE 802.3x Hugh Melvin, Dept. IT, NUI,G 50 Fast Ethernet Based mostly on 10Base T wiring (tw.pair) 10 times faster (theory!) Same frame format & basic operation Use either category 3 (100 Base 4T) category 5 tw. pair (100 Base TX) Fibre (100 Base FX) Hugh Melvin, Dept. IT, NUI,G 51 17

18 Fast Ethernet 100 Base TX Easy to upgrade from 10Base T Cat.5 tw. pair => can take 125 MHz and 2 tw. pairs (1 + 1) Encoding scheme derived from FDDI..4B5B => 100Mbps 100 Base FX Fibre Optic Distance 2000m => requires special set-up for CD Hugh Melvin, Dept. IT, NUI,G 52 Hugh Melvin, Dept. IT, NUI,G 53 IEEE VG-AnyLAN Developed by HP mainly Different access scheme Round-robin priority based Called Demand Priority Access Method (DPAM) Some RealTime traffic features Integrates with 10Base T Hugh Melvin, Dept. IT, NUI,G 54 18

19 FDDI Fibre Distributed Data Interface Ring topology.. protocol similar to => Suffers from complexity issues 2 fibre cables, each at 100Mbps.. primary and secondary ring Supports some Time-sensitive data Sync frames generated every 125µs 96 bytes of data => compatible with E1 / T1 carriers 3 E1 = 3 x 32 Hugh Melvin, Dept. IT, NUI,G 55 FDDI Primarily used as a backbone Losing ground to Fast/Gigabit Ethernet Encoding scheme 4 of 5 group code i.e. 5 clock periods used to send 4 bits => redundancy for signalling etc Hugh Melvin, Dept. IT, NUI,G 56 Hugh Melvin, Dept. IT, NUI,G 57 19

20 Hugh Melvin, Dept. IT, NUI,G 58 Gigabit Ethernet Defined standard 1998 Gigabit Ethernet Alliance GEA..est Com, Bay Networks (Nortel), Cisco etc See Initial objectives Operation at 1000Mbps Standard frame format & CSMA/CD Compatible with 10Base T/Fast Ethernet Multiple gigabit products now available Hugh Melvin, Dept. IT, NUI,G 59 Gigabit Ethernet Gigabit Switches extend b/w further Enhanced CSMA/CD method Required with standard hubs Extend packet to 512 bytes (via extension field) Physical Layer Alternatives 1000Base-SX : fibre short distances, low-cost fibre 1000 Base-LX : fibre 1000 Base T : 4 pairs of CAT 5 UTP Hugh Melvin, Dept. IT, NUI,G 60 20

21 Fast / Gigabit or VG-AnyLAN not shown..plus developments in Wireless LANs Hugh Melvin, Dept. IT, NUI,G 61 Wireless LANs Requirements for mobility Wiring issues Mobility Issues Previous development issues Cost/Bandwidth/Reliability/Security Range of standards eg. IEEE Hiperlan HomeRF Large growth market.. 2 => 4 million Units between 2000=>2004 Hugh Melvin, Dept. IT, NUI,G 62 Wireless LAN IEEE Original std 2Mbps b Up to 11 Mbps Range m Depends on product & operating environment Operates in ISM band (915MHz, 2.4 & 5.7 GHz) Industrial, Scientific & Medical 2.4 GHz Globally available Support for 128 bit Wired Equivalent Privacy (WEP) Encryption Hugh Melvin, Dept. IT, NUI,G 63 21

22 HiperLAN Developed by ETSI European Telecommunications Standards Inst. 5 GHz Up to 23.5 Mbps Supports WEP Gaussian Minimum Shift Keying Encoding Not widely implemented (802.11b most popular) Also HomeRF Hugh Melvin, Dept. IT, NUI,G 64 Bluetooth Concept developed initially by Ericsson 1994 Wireless PC 10th Century Danish King! Expanded scope Personal Area Network (PAN) Network of devices Phone, PDA, PC,..toaster Bluetooth Special Interest Group (2000 org) IEEE PAN Working GRoup Hugh Melvin, Dept. IT, NUI,G 65 Bluetooth 2.4 GHz ISM band 10 metre range (100m) Circuit & packet switch data Asynchronous link Asymmetric: 721 kbps / 57.6 kbps Symmetric :432.6 kbps Plans for 20Mbps link Overhyped? Billion units by 2005 Interoperabilty issues main stumbling block Blue Unit : Test unit Hugh Melvin, Dept. IT, NUI,G 66 22