1 / 59

CMPE 259 : Sensor networks/IoT

CMPE 259 : Sensor networks/IoT. Chen Qian Computer Engineering UCSC Baskin Engineering Lecture 2. 1. Introduction 2. Multiple access 3. Wireless links, characteristics 4. IEEE 802.11 wireless LANs ( “ Wi-Fi ” ) 5. Cellular Internet access 6. Mobility.

clamberson
Download Presentation

CMPE 259 : Sensor networks/IoT

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. CMPE 259 : Sensor networks/IoT Chen Qian Computer Engineering UCSC Baskin Engineering Lecture 2

  2. 1. Introduction 2. Multiple access 3. Wireless links, characteristics 4. IEEE 802.11 wireless LANs (“Wi-Fi”) 5. Cellular Internet access 6. Mobility Lecture 02 Wireless and Mobile networks Wireless, Mobile Networks

  3. network infrastructure Elements of a wireless network Wireless, Mobile Networks

  4. network infrastructure Elements of a wireless network wireless hosts • laptop, smartphone • run applications • may be stationary (non-mobile) or mobile • wireless does not always mean mobility Wireless, Mobile Networks

  5. network infrastructure Elements of a wireless network base station • typically connected to wired network • relay - responsible for sending packets between wired network and wireless host(s) in its “area” • e.g., cell towers, 802.11 access points Wireless, Mobile Networks

  6. network infrastructure Elements of a wireless network wireless link • typically used to connect mobile(s) to base station • also used as backbone link • multiple access protocol coordinates link access • various data rates, transmission distance Wireless, Mobile Networks

  7. Characteristics of selected wireless links 200 802.11n 54 802.11a,g 802.11a,g point-to-point 5-11 802.11b 4G: LTWE WIMAX 4 3G: UMTS/WCDMA-HSPDA, CDMA2000-1xEVDO Data rate (Mbps) 1 802.15 .384 2.5G: UMTS/WCDMA, CDMA2000 .056 2G: IS-95, CDMA, GSM Indoor 10-30m Outdoor 50-200m Mid-range outdoor 200m – 4 Km Long-range outdoor 5Km – 20 Km Wireless, Mobile Networks

  8. infrastructure mode • base station connects mobiles into wired network • handoff: mobile changes base station providing connection into wired network network infrastructure Elements of a wireless network Wireless, Mobile Networks

  9. Elements of a wireless network ad hoc mode • no base stations • nodes can only transmit to other nodes within link coverage • nodes organize themselves into a network: route among themselves Wireless, Mobile Networks

  10. Wireless network taxonomy multiple hops single hop host may have to relay through several wireless nodes to connect to larger Internet: mesh net host connects to base station (WiFi, WiMAX, cellular) which connects to larger Internet infrastructure (e.g., APs) no base station, no connection to larger Internet. May have to relay to reach other a given wireless node MANET, VANET no infrastructure no base station, no connection to larger Internet (Bluetooth, ad hoc nets) Wireless, Mobile Networks

  11. 1. Introduction 2. Multiple access 3. Wireless links, characteristics 4. IEEE 802.11 wireless LANs (“Wi-Fi”) 5. Cellular Internet access 6. Mobility Outline Wireless, Mobile Networks

  12. Random access protocols • when node has packet to send • transmit at full channel data rate R. • no a priori coordination among nodes • two or more transmitting nodes ➜“collision”, • random access MAC protocol specifies: • how to detect collisions • how to recover from collisions (e.g., via delayed retransmissions) • examples of random access MAC protocols: • slotted ALOHA • CSMA, CSMA/CD, CSMA/CA

  13. assumptions: all frames same size time divided into equal size slots (time to transmit 1 frame) nodes start to transmit only slot beginning nodes are synchronized if 2 or more nodes transmit in slot, all nodes detect collision operation: when node obtains fresh frame, transmits in next slot if no collision: node can send new frame in next slot if collision: node retransmits frame in each subsequent slot with prob. p until success Slotted ALOHA

  14. Pros: single active node can continuously transmit at full rate of channel highly decentralized: only slots in nodes need to be in sync simple Cons: collisions, wasting slots idle slots nodes may be able to detect collision in less than time to transmit packet clock synchronization 1 1 1 1 node 1 2 2 2 node 2 node 3 3 3 3 C E S C S E C E S Slotted ALOHA

  15. suppose:N nodes with many frames to send, each transmits in slot with probability p prob that given node has success in a slot = p(1-p)N-1 prob that any node has a success = Np(1-p)N-1 max efficiency: find p* that maximizes Np(1-p)N-1 for many nodes, take limit of Np*(1-p*)N-1 as N goes to infinity, gives: max efficiency = 1/e = .37 Slotted ALOHA: efficiency efficiency: long-run fraction of successful slots (many nodes, all with many frames to send) ! at best: channel used for useful transmissions 37% of time!

  16. ALOHA protocol • Was a pioneering computer networking system developed at the University of Hawaii. • ALOHA channels were used in a limited way in the 1980s in 1G mobile phones • Now in passive RFID systems • Why?

  17. CSMA (carrier sense multiple access) CSMA: listen before transmit: if channel sensed idle: transmit entire frame • if channel sensed busy, defer transmission • human analogy: don’t interrupt others!

  18. collisions can still occur: propagation delay means two nodes may not hear each other’s transmission collision: entire packet transmission time wasted distance & propagation delay play role in in determining collision probability CSMA collisions spatial layout of nodes

  19. CSMA/CD (collision detection) CSMA/CD:carrier sensing, deferral as in CSMA • collisions detected within short time • colliding transmissions aborted, reducing channel wastage • collision detection: • easy in wired LANs: measure signal strengths, compare transmitted, received signals • difficult in wireless LANs: received signal strength overwhelmed by local transmission strength

  20. CSMA/CD (collision detection) spatial layout of nodes

  21. 1. NIC receives datagram from network layer, creates frame 2. If NIC senses channel idle, starts frame transmission. If NIC senses channel busy, waits until channel idle, then transmits. 3. If NIC transmits entire frame without detecting another transmission, NIC is done with frame ! 4. If NIC detects another transmission while transmitting, aborts and sends jam signal 5. After aborting, NIC enters binary (exponential) backoff: after mth collision, NIC chooses K at random from {0,1,2, …, 2m-1}. NIC waits K·512 bit times, returns to Step 2 longer backoff interval with more collisions Ethernet CSMA/CD algorithm

  22. CSMA/CD efficiency • Tprop = max prop delay between 2 nodes in LAN • ttrans = time to transmit max-size frame • efficiency goes to 1 • as tprop goes to 0 • as ttrans goes to infinity • better performance than ALOHA: and simple, cheap, decentralized!

  23. 1. Introduction 2. Multiple access 3. Wireless links, characteristics 4. IEEE 802.11 wireless LANs (“Wi-Fi”) 5. Cellular Internet access 6. Mobility Outline Wireless, Mobile Networks

  24. Wireless Link Characteristics (1) important differences from wired link …. • decreased signal strength: radio signal attenuates as it propagates through matter (path loss) • interference from other sources: standardized wireless network frequencies (e.g., 2.4 GHz) shared by other devices (e.g., phone); devices (motors) interfere as well • multipath propagation: radio signal reflects off objects ground, arriving ad destination at slightly different times …. make communication across (even a point to point) wireless link much more “difficult” Wireless, Mobile Networks

  25. Wireless network characteristics Multiple wireless senders and receivers create additional problems (beyond multiple access): B A C C C’s signal strength A’s signal strength B A space Hidden terminal problem • B, A hear each other • B, C hear each other • A, C can not hear each other means A, C unaware of their interference at B Signal attenuation: • B, A hear each other • B, C hear each other • A, C can not hear each other interfering at B Wireless, Mobile Networks

  26. 1. Introduction 2. Multiple access 3. Wireless links, characteristics 4. IEEE 802.11 wireless LANs (“Wi-Fi”) 5. Cellular Internet access 6. Mobility Outline Wireless, Mobile Networks

  27. 802.11b 2.4-5 GHz unlicensed spectrum up to 11 Mbps direct sequence spread spectrum (DSSS) in physical layer all hosts use same chipping code 802.11a 5-6 GHz range up to 54 Mbps 802.11g 2.4-5 GHz range up to 54 Mbps 802.11n: multiple antennae 2.4-5 GHz range up to 200 Mbps IEEE 802.11 Wireless LAN • all use CSMA/CA for multiple access • all have base-station and ad-hoc network versions Wireless, Mobile Networks

  28. Internet 802.11 LAN architecture • wireless host communicates with base station • base station = access point (AP) • Basic Service Set (BSS) (aka “cell”) in infrastructure mode contains: • wireless hosts • access point (AP): base station • ad hoc mode: hosts only hub, switch or router BSS 1 BSS 2 Wireless, Mobile Networks

  29. 802.11: Channels, association • 802.11b: 2.4GHz-2.485GHz spectrum divided into 11 channels at different frequencies • AP admin chooses frequency for AP • interference possible: channel can be same as that chosen by neighboring AP! • host: must associatewith an AP • scans channels, listening for beacon frames containing AP’s name (SSID) and MAC address • selects AP to associate with • may perform authentication [Chapter 8] • will typically run DHCP to get IP address in AP’s subnet Wireless, Mobile Networks

  30. IEEE 802.11: multiple access • avoid collisions: 2+ nodes transmitting at same time • 802.11: CSMA - sense before transmitting • don’t collide with ongoing transmission by other node • 802.11: no collision detection! • difficult to receive (sense collisions) when transmitting due to weak received signals (fading) • can’t sense all collisions in any case: hidden terminal, fading • goal: avoid collisions: CSMA/C(ollision)A(voidance) B A C C C’s signal strength A’s signal strength B A space Wireless, Mobile Networks

  31. DIFS data SIFS ACK IEEE 802.11 MAC Protocol: CSMA/CA 802.11 sender 1 if sense channel idle for DIFSthen transmit entire frame (no CD) 2 if sense channel busy then start random backoff time timer counts down while channel idle transmit when timer expires if no ACK, increase random backoff interval, repeat 2 802.11 receiver - if frame received OK return ACK after SIFS (ACK needed due to hidden terminal problem) sender receiver Wireless, Mobile Networks

  32. Avoiding collisions (more) idea:allow sender to “reserve” channel rather than random access of data frames: avoid collisions of long data frames • sender first transmits small request-to-send (RTS) packets to BS using CSMA • RTSs may still collide with each other (but they’re short) • BS broadcasts clear-to-send CTS in response to RTS • CTS heard by all nodes • sender transmits data frame • other stations defer transmissions avoid data frame collisions completely using small reservation packets! Wireless, Mobile Networks

  33. RTS(B) RTS(A) reservation collision RTS(A) CTS(A) CTS(A) DATA (A) ACK(A) ACK(A) Collision Avoidance: RTS-CTS exchange B A AP defer time Wireless, Mobile Networks

  34. H1 remains in same IP subnet: IP address can remain same switch: which AP is associated with H1? self-learning (Ch. 5): switch will see frame from H1 and “remember” which switch port can be used to reach H1 802.11: mobility within same subnet BBS 2 H1 BBS 1 Wireless, Mobile Networks

  35. 802.11: advanced capabilities power management • node-to-AP: “I am going to sleep until next beacon frame” • AP knows not to transmit frames to this node • node wakes up before next beacon frame • beacon frame: contains list of mobiles with AP-to-mobile frames waiting to be sent • node will stay awake if AP-to-mobile frames to be sent; otherwise sleep again until next beacon frame Wireless, Mobile Networks

  36. P P P P P M M Master device Slave device Parked device (inactive) S S S S 802.15: personal area network • less than 10 m diameter • replacement for cables (mouse, keyboard, headphones) • ad hoc: no infrastructure • master/slaves: • slaves request permission to send (to master) • master grants requests • 802.15: evolved from Bluetooth specification • 2.4-2.5 GHz radio band • up to 721 kbps radius of coverage Wireless, Mobile Networks

  37. 1. Introduction 2. Multiple access 3. Wireless links, characteristics 4. IEEE 802.11 wireless LANs (“Wi-Fi”) 5. Cellular Internet access 6. Mobility Outline Wireless, Mobile Networks

  38. connects cells to wired tel. net. • manages call setup • handles mobility Mobile Switching Center Mobile Switching Center • covers geographical region • base station(BS) analogous to 802.11 AP • mobile usersattach to network through BS • air-interface:physical and link layer protocol between mobile and BS Public telephone network MSC cell wired network Components of cellular network architecture Wireless, Mobile Networks

  39. time slots frequency bands Cellular networks: the first hop Two techniques for sharing mobile-to-BS radio spectrum • combined FDMA/TDMA: divide spectrum in frequency channels, divide each channel into time slots • CDMA: code division multiple access Wireless, Mobile Networks

  40. Base transceiver station (BTS) Base station controller (BSC) Mobile Switching Center (MSC) Mobile subscribers 2G (voice) network architecture Base station system (BSS) MSC G BTS BSC Public telephone network Gateway MSC Legend Wireless, Mobile Networks

  41. Serving GPRS Support Node (SGSN) Gateway GPRS Support Node (GGSN) 3G (voice+data) network architecture MSC G Public telephone network radio network controller Gateway MSC G Public Internet SGSN Key insight: new cellular data network operates in parallel (except at edge) with existing cellular voice network • voice network unchanged in core • data network operates in parallel GGSN Wireless, Mobile Networks

  42. 3G (voice+data) network architecture MSC G Public telephone network radio network controller Gateway MSC G Public Internet SGSN GGSN radio interface (WCDMA, HSPA) core network General Packet Radio Service (GPRS) Core Network public Internet radio access network Universal Terrestrial Radio Access Network (UTRAN) Wireless, Mobile Networks

  43. 4G (LTE) network architecture Wireless, Mobile Networks

  44. 4G (LTE) network architecture Wireless, Mobile Networks

  45. 1. Introduction 2. Multiple access 3. Wireless links, characteristics 4. IEEE 802.11 wireless LANs (“Wi-Fi”) 5. Cellular Internet access 6. Mobility Outline Wireless, Mobile Networks

  46. no mobility high mobility What is mobility? • spectrum of mobility, from thenetworkperspective: mobile wireless user, using same access point mobile user, passing through multiple access point while maintaining ongoing connections (like cell phone) mobile user, connecting/ disconnecting from network using DHCP. Wireless, Mobile Networks

  47. Mobility: vocabulary home network:permanent “home” of mobile (e.g., 128.119.40/24) home agent: entity that will perform mobility functions on behalf of mobile, when mobile is remote wide area network permanent address:address in home network, can always be used to reach mobile e.g., 128.119.40.186 Wireless, Mobile Networks

  48. Mobility: more vocabulary visited network:network in which mobile currently resides (e.g., 79.129.13/24) permanent address:remains constant (e.g., 128.119.40.186) care-of-address:address in visited network. (e.g., 79,129.13.2) wide area network foreign agent: entity in visited network that performs mobility functions on behalf of mobile. correspondent: wants to communicate with mobile Wireless, Mobile Networks

  49. How do you contact a mobile friend: Consider friend frequently changing addresses, how do you find her? • search all phone books? • call her parents? • expect her to let you know where he/she is? I wonder where Alice moved to? Wireless, Mobile Networks

  50. Mobility: approaches • let routing handle it: routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange. • routing tables indicate where each mobile located • no changes to end-systems • let end-systems handle it: • indirect routing:communication from correspondent to mobile goes through home agent, then forwarded to remote • direct routing:correspondent gets foreign address of mobile, sends directly to mobile Wireless, Mobile Networks

More Related