Introduction to the communication technologies

Transcription

1 Introduction to the communication technologies

2 The Open System Interconnection (OSI) model

3 The OSI model (cont) Layer Description Ex. Application Interaction with the software application FTP Presentation Data format conversion XDR Session Connection management SIP Transport Transfer of data and reliability TCP, UDP Network Addressing between a source and a destination via one network ore more IP Data Link Access medium management, error detection and correction IEEE Physical Specifications to access the medium Signal processing

4 Network Classification Categorization by range WAN MAN LAN PAN BAN Categorization by network topology...

5 Network Classification (cont)

6 The WSI Reference Model for the Wireless World

7 The new vision of the Wireless World The multi sphere model Human is the center of the services Proposed by the Wireless Strategic Initiative Initial partners: Alcatel, Ericsson, Nokia, Siemens In 2001, it became the Wireless World Research Forum

8 The MultiSphere Model 6 spheres PAN The Immediate Environment Instant Partners Radio Accesses Interconnectivity CyberWorld (Community Area Network)

9 Building Blocks of the Wireless World 1. Augmented Reality/Cyberworld 2. Semantic Aware Services 3. Peer Discovery 4. End-to-End security and Privacy 5. Co-operative Networks and Terminal 6. Heterogeneous Ad-hoc networking 7. Radio Interfaces 8. Smart Antennas and Base Stations 9. Software Defined Radio

10 The Communication Element (CE) Four blocks:

11 The IEEE 802 Project

12 Introduction to the IEEE model IEEE is the world s largest professional association dedicated to advancing technological innovation in electricity electronic 802 Project Project began in February 1980 Standards for LANs and MANs (network with variable-size packets) Define the Physical and Link Layer of the OSI model developed by the ISO (International Organization for Standardization) The Link Layer is divided in 2 sub-layers The Logical Link Control (LLC): IEEE The Media Access Control (MAC): IEEE (Ethernet), IEEE (Token Bus), IEEE (Token Ring)

13 Introduction to the IEEE model (cont) ISO Applciation Layer Presentation Layer Session Layer Upper Layers Transport Layer Network Layer Logical Link Control Data Link Layer Media Access Control Physical Signal Pjysical Layer Transmission Medium

14 The OSI model and LAN protocols

15 The MAC Address 48 bits Address Composed by 2 parts: 0rganizationally Unique Identifier (OUI): 3 most significant bytes (see RFC1700 for a list) Network Interface Controller (NIC) Specific: 3 less significant bytes Ex A-BC Canonical Format Non-Canonical Format

16 The MAC Address (cont)

17 The Ethernet Case

18 A little bit of history IEEE Standards for wired Ethernet networks Beginning 70s, the University of Hawaii propose the Aloha Protocol Communication between different islands Collision of frames 2400bps In 1973, Xerox PARC propose a new standard In 1976, DIX (DEC, Intel and Xerox) allow Ethernet to become an open standard Coaxial cable 3Mbps 10Mbps 1985, the IEEE standard is officially published Allow the implementation of several nodes (CSMA/CD)

19 The CSMA/CD protocol Carrier Sense Multiple Access with Collision Detection

20 The CSMA/CD protocol (cont) The principle is when a host detects a collision, all the others computers in the LAN should detect it The Slot time (TS) is defined like the twice of the time needed by a signal to travel the length of the maximum theoretical distance between two nodes In Ethernet the TS = 51,2μs, which represents 512bits at 10Mbps Considering that the speed of electricity in a copper cable is 200,000,000 m/s, what is the maximum theoretical length of a network using this technology? Length of frames must be equal or higher than the TS Add a padding if needed Except for jammings (length = 32bits)

21 Propagation speed Medium Propagation Speed Thick Coax.77c (231,000 km/sec) Thin Coax.65c (195,000 km/sec) Twisted Pair.59c (177,000 km/sec) Fiber.66c (198,000 km/sec) AUI Cable.65c (195,000 km/sec) c refers to the speed of light in a vacuum (300,000 kilometers per second)

22 Ethernet Cable Types, Lengths and Data Rate Cable Name Cable Type Maximum Length Data Rate 10Base5 Coax 500m per segment 10Mbps 10Base2 Coax 185m per segment 10Mbps 10BaseT UTP 100m per segment 10Mbps 10BaseF Fiber 4km 10Mbps 100BaseT UTP 100m per segment 100Mbps 100BaseTX 2 pair Cat 5 UTP 100m (hub and network node) 100Mbps

23 The BEB algorithm

24 The BEB Algorithm BEB: Binary Exponential Backoff After a collision, hosts wait d TS before continue sending frames d = rand(0, 2i 1) 1 i < 10 d = rand(0, 210 1) 10 I < 16 After 16 retransmissions, the process is aborted and the upper layer is informed about this failure

25 The BEB Algorithm

26 The 802.3D protocol CSMA/CD cannot guarantee a bounded access delay to frames transmitted Not adapted for real-time applications The CSMA/CDR protocol is the CSMA/CD version for real-time applications This protocol reverts to a toking passing algorithm when a collision is detected

27 Ethernet frame format

28 Frame Format Preamble 7 bytes with value Start Frame Delimiter 1 byte =

29 Some possible values of the Type Ethernet field

30 Example of an Ethernet Frame

31 Address Resolution MAC - IP

32 The ARP protocol ARP (Address Resolution Protocol) allow to know the MAC address of host from its IP address

33 The ARP packet Hardware Type IP = 0x0800 Hardware Address Length Ethernet = 1 Protocol Type Ethernet = 6 Protocol Address Length IPv4 = 4 Operation Request = 1 Reply = 2 Sender Hardware Address Sender IP Address Target Hardware Address Request = Target IP Address

34 Example of ARP frames Example 1 ADDR HEX 0000 FF FF FF FF FF FF C0 48 8C C0 48 8C Example 2 ADDR HEX C0 48 8C C0 E5 8C C0 E5 8C C0 48 8C

35 ARP messages and the Case of Multicast ARP Probe Gratuitous ARP The Case of Multicast: Conversion of a Class D IP address

36 Introduction to the Wireless Networks

37 Categorization of Wireless networks according to the range TAGGING RFID WPAN Wireless Personal Area Network (<10m) WLAN Wireless Local Area Network (<150m) WMAN Wireless Metropolitan Area Network (<5km) WRAN Wireless Regional Area Network (<100km)

38 IEEE standards for wireless networks WPAN IEEE Bluetooth IEEE UWB (Ultra Wide Band) IEEE ZigBee IEEE (Wi-Fi) IEEE b, a, g IEEE n IEEE s WMAN WLAN IEEE IEEE IEEE IEEE e/IEEE (Wi-Mobile) WRAN IEEE : Unused spaces in TV frequency spectrum MHz (Wi-RAN)

39 Wireless Networks: Data Rate vs Range

40 Wireless Networks: The Frequency bands

41 Wireless Metropolitan Area Network

42 Example of a WMAN: WiMAX

43 Example of a WMAN: WiMAX Network architecture Point to Point Point to MultiPoint Frequency band 2GHz et 11GHz Channel bandwidth 1.25 MHz, 5 MHz, 10 MHz or 20 MHz Up to 70Mbps New alternative for last Mile Networks

44 Example of a WMAN: WiMAX

45 Wireless Local Area Network

46 Example of a WLAN: IEEE Network architecture Point to Point Point to MultiPoint Frequency band Channel bandwidth 2.4GHz or 5GHz 22 MHz Rate: 11Mbps 54Mbps TM

47 Example of a WLAN: IEEE

48 Example of a WLAN: HomeRF Frequency band 2.4 GHz Maximum Rate HomeRF1 1.6Mbps HomeRF2 10 Mbit/s Range Between 50m and 100m

49 Example of a WLAN: HiperLAN Released in 1991 Frequency band Maximum Rate 5Ghz 20-54Mbps Range + 30 m

50 Wireless Personal Area Network

51 Example of WPAN: Bluetooth Frequency band Maximum rate 1Mbps Range 2.4GHz 10m Standards IEEE (Bluetooth) IEEE (Bluetooth 2)

52 Example of WPAN: Wireless USB Frequency band Maximum rate 53Mbps - 480Mbps Range 3.1GHz 10.6GHz 3m 10m Specification Wireless USB Specification Rev 1.1 (September 2010)

53 Example of WPAN: Wireless Z-Wave Frequency band Maximum Rate MHz (USA) 40Kbps Range 30m

54 Example of WPAN: ZigBee Frequency band Maximum rate 250Kbps Range 2.4GHz 10m Standard IEEE

55 Wireless Body Area Network

56 Example of WBAN: NFC Near Field Communication (NFC) Very low range Rate Similar to RFID (Radio Frequency Identification): HF 13.56MHz Applications ~424Kbps Frequency Range Only a few centimeters Access control NFC Forum:

57 The IEEE standard

58 Introduction The IEEE standard describes the characteristics of a Wireless LAN The term Wi-Fi is a contraction for Wireless Fidelity. Wireless Fidelity is the name that the Wi-Fi Alliance gave to the first specification Wi-Fi Alliance was founded in 1999 by 3com, Aironet, Intersil, Lucent Technologies, Nokia and Symbol Technologies The yin-yang logo indicates the certification of a product for interoperability

59 Introduction More specifically, IEEE defines the two lowest layer of the OSI model The Physical Layer (sometimes called the PHY Layer). The PHY Layer proposes 3 modulations techniques. This layer defines the technologies to transfer raw bits over a physical medium The Data Link Layer, which is composed by 2 sub-layers Logical Link Control (LLC) Media Access Control (MAC)

60 Introduction The LLC sub-layer provides the multiplexing and flow control mechanisms that make possible the coexistence of several network protocols on the same physical interface Same as IEEE802.3 The MAC sub-layer provides the addressing and channel access control mechanisms that make possible share the same link between different terminals

61 WLAN devices and operating modes WLAN devices Wireless Adapters Access Points (AP) Wireless routers Wireless network bridges Wireless repeaters defines two operating modes Infrastructure mode Ad-hoc mode

62 Operating modes

63 Infrastructure mode Wireless Stations (STAs) connect to the Access Point (AP) via a wireless link Basic Service Set (BSS): set of STAs connected to the same AP Each BSS is identified by a BSSID. In the infrastructure mode case, this BSSID correspond to the AP's MAC address It is possible to connect two BSSs by mean of a Distribution System (DS) Extended SS (ESS)

64 Infrastructure mode

65 Infrastructure mode An ESS is identified by an ESSID (also called SSID) 32B length (coded in ASCII) ESSID can be considered like the first level of security STAs can transparently change between APs in an ESS (ex. choice the AP with the highest signal quality) Roaming

66 Infrastructure mode To join a cell, STAs sends a probe request on each channel The probe request message indicates the ESSID to join and others characteristics like the supported data rate Upon reception of a probe request, the AP checks whether the ESSID matches its ESSID and if so, the AP sends a probe response containing synchronization information, supported data rate, etc. In absence of the requested ESS, the STAs can listen the medium to find a BSS APs can be configured to frequently send a beacon frame to diffuse the characteristics of the network

67 Ad-hoc networks In ad-hoc mode, nodes connect to one another to form a peer-to-peer network There is not Access points Self-organizing network without the need of fixed network infrastructure Multi-hop communication Nodes MAY behave like routers and forward packets on behalf of other nodes Decentralized, mobility-adaptive operation The set of nodes forms an Independent BSS (IBSS)

68 Ad-hoc networks In ad hoc networks, the coverage area depends on the range of each station in a IBSS

69 From infrastructure mode to ad-hoc networks As we move away from the BS, we move ourselves to pure ad-hoc operations Ad hoc networks can be used in several areas

70 IEEE802.11: The Physical Layer

71 Radio spectrum Radio frequency bands are usually regulated by the government Free spectrum Licensed spectrum Reserved for Astronomy observations

72 Radio spectrum Organizations that regulate the radio spectrum are ETSI (European Telecommunications Standards Institute) in Europe FCC (Federal Communications Commission) in USA MKK (Kensa-kentei Kyokai) in Japan l ART (Autorité de Régulation des Télécommunications (ART)) in France

73 The ISM band In 1985, the FCC designated 3 frequency band for the Industry, Scientific and Medical purposes. These parts of radio spectrum can be used without license The ISM bands (adopted later in several countries) are MHz, GHz and GHz In Europe, the frequency band between 890MHz and 915MHz is reserved for mobile communication (GSM). Only the bands at 2.4GHz and 5GHz can be used without license

74 PHY Layer IEEE defines 3 Physical Layer DSSS Physical Layer FHSS Physical Layer Infrared (IR) Physical Layer

75 Direct Sequence Spread Spectrum The ISM band at 2.4GHz is divided in 14 channels (13 channels In France and 11 channels in US), each one with a 22MHz bandwidth There are only 3 non overlapping channels Channel Frequen cy band

76 Direct Sequence Spread Spectrum DSSS may deliver frames at 1, 2, 5.5 and 11Mbps. The original standard specified only 1 and 2 Mbps data rates The only coding/modulation used is Baker code (pseudo-random noise, PN). PN = The chip sequence allow to detect errors during the transmission and introduce error correction techniques

77 Frequency Hopping Spread Spectrum FHSS consists in rapidly changing the transmission frequency in a predetermined pseudo random pattern Initially proposed for military activities FHSS uses Gaussian Frequency Shift Keying (GSFK) 75 channels with a 1MHz bandwidth Transmitter and receiver must be synchronized 78 hopping sequences grouped in 3 sets of 26 sequence each. Sequence from same set encounter minimum collision (suitable for collocated systems) To lower the amount of collision to acceptable levels, the actual number of collocated systems should be around 15

78 Frequency Hopping Spread Spectrum FHSS Consist in rapidly changing the transmission frequency in a predetermined pseudo random pattern Initially proposed for military activities FHSS uses Gaussian Frequency Shift Keying (GSFK) 75 channels with a 1MHz bandwidth Transmitter and receiver must be synchronized 78 hopping sequences grouped in 3 sets of 26 sequence each. Sequence from same set encounter minimum collision (suitable for collocated systems) To lower the amount of collision to acceptable levels, the actual number of collocated systems should be around 15

79 DSSS vs FHSS

80 IR PHY specifies also one alternative to the radio communication: the use of an infrared light IR PHY was proposed for short- and medium-range communication Systems may operate in line-of-sight mode or in diffuse mode (scatter mode) Unlike RF (radio frequency), IR cannot pass through walls IR support 1Mbps (using 16-PPM scheme) and 2Mbps (using 4-PPM scheme)

81 IR PHY

82 The MAC sub-layer

83 The Data Link Layer 2 sub-layer Logical Link Control Media Access Control The MACL sub-layer defines two methods to ensure all STAs get access to the medium Distributed Coordination Function (DCF) All STAs must implement DCF Point Coordination Function (PCF) Optional

84 CSMA/CA DCF is a method to access the media without synchronization or priority management DCF relies on the CSMA/CA alorithm CSMA/CA stands for Carrier Sense Multiple Access / Collision Avoidance While in wired networks, one station can know when one another is using the medium, this is not possible in Wireless networks CSMA/CA is the equivalent of CSMA/CD for wired networks CSMA/CA is a contention-based protocol making certain that all stations first sense the medium before transmitting Avoid collisions Avoid retransmissions

85 DCF DCF uses PCS (Physical Carrier Sensing) and VCS (Virtual Carrier Sensing) to avoid collisions The PCS implementation is based on the Clear Channel Assessment (CCA) function When the station senses an energy above a specific threshold the medium is busy VCS uses two different mechanisms to reserve the medium By mean of the RTS/CTS frames: the overhead may be important By mean of a timer (NAV)

86 Inter-Frame spacing The time elapsed between two frames is known like Inter-Frame Spacing (IFS) There are 4 types of IFS Short IFS (SIFS). Depend on the kind of PHY FHSS = 28microsec DSSS = 10microsec Distributed IFS (DIFS) = SIFS + 1TS Point Coordination IFS (PIFS) = SIFS + 2TS Extended IFS (EIFS)

87 The hidden/exposed node problem MS-D ignores the communication between MS-B and MS-C. MS-D sends data to MS-C MS-A listen the communication between MS-C and MS-B. MS-A cannot communicate with MS-D

88 BEB Algorithm

89 Timers and Constants Congestion Window Advised min = 15 Advised max = 1023 CWi = min(cwmax, CWmin*2i 1) Back-off T = random(0,cw)*ts Timeslot FHSS = 50μs DHSS = 20μs OFDM = 9μs...

90 DCF

91 Error Control In wireless networks, checking for data corruption is important due to the unreliability nature of the medium The MAC sub-layer usually implement the Cyclic Redundancy Check (CRC) to detect errors in the MAC frames Polynomial of order 32 x32+x26+x23+x22+x16+x12+x10+x8+x7+ x5+x4+x2+x+1

92 Frame format frames have the following format Preamble 80-bit sequence of alternating zeros and one Start Frame Delimiter (SFD) which consist of a 16-bits binary pattern ( ) PLCP (Physical Layer Convergence Protocol) header PLCP_PDU Length Word. Number of bytes in the packet PLCP Signaling Field. Rate information Header Error Check Field. 16-bit CRC MAC Data MAC frame

93 MAC frame format General format of a MAC frame The Frame Control Field contains the following information

94 Frame Control Protocol version Type and subtype with a length of 2 and 4 bits respectively Management type (00). Association/disassociation messages Control messages (01). Access control to the media Data messages (10). Contains data sent by the upper layer ToDS = 1 when the frame is addressed to a Distribution System (the AP). FromDS = 1 when the frame comes from a DS 2 bits = 00 What is the value for ToSD ans FromDS in an ad-hoc network? More fragments One Fragment belonging to the same frame follows current frame

95 Frame Control Retry = 1 indicates that this frame is a retransmission Power Management = 1 indicates that the station enters in power save mode More Data. Used by the AP to indicate to a STA that some frames are buffered WEP. Set to 1 when the frame body is encrypted with the WEP algorithm

96 MAC frame format Duration/ID. In Power-Save Poll messages this field indicate the ID of the STA In all other messages, this is the duration value used for the NAV calculation Address 1. The recipient address Address 2. Transmitter address Address 3. if FromDS=1, then this is the original Source Address. If ToDS = 1, then this is the Destination Address Address 4. Wireless Distribution System frame distributed from one AP to another AP

97 MAC Frame Format Sequence Control is used to re-assembly several fragments corresponding to a same frame Sequence number (12 bits) contains the ID of the fragmented frame Fragment number (4 bits). Number of each frame sent of a fragmented frame CRC

98 RTS and CTS frames

99 Type and subtypes (summary)