ETSF05 Internet Protocols PPP TDM Synchronous Optical Networks xdsl WLAN

Transcription

1 ETSF05 Internet Protocols PPP TDM Synchronous Optical Networks xdsl WLAN Jens A Andersson

2 Routing Konsten att bygga least costtrees Från sändare till mottagare Från varje nod till varje annan nod Tre principer Distance Vector Link State Path Vector Policy based routing ETSF05 Internet Protocols

3 Point to point protocol (PPP) Direct connection between two nodes Internet access Home user to ISP Telephone line Cable TV PPP ETSF05 Internet Protocols 3

4 State transitions in PPP We need more protocols LCP Link Control (LCP) Data Transfer Authentication Network Control (NCP) ETSF05 Internet Protocols 4

5 PPP frame format Support for several (sub)protocols Address & control not used Maximum payload 1500 bytes ETSF05 Internet Protocols 5

6 Link control protocol (LCP) Establish Configure Terminate Options Maximum receive unit (payload size) Authentication protocol (none/pap/chap) Protocol field compression (on/off), Address and control field compression (on/off) ETSF05 Internet Protocols 6

7 Authentication protocols (AP) Password authentication (PAP) ETSF05 Internet Protocols 7

8 Authentication protocols (AP) Challenge handshake authentication (CHAP) ETSF05 Internet Protocols 8

9 Network control protocols (NCP) Preparations for the network layer IPCP for Internet ETSF05 Internet Protocols 9

10 IP datagram encapsulation in PPP ETSF05 Internet Protocols 10

11 PPP session example ETSF05 Internet Protocols 11

12 PPP session example (cont.) ETSF05 Internet Protocols 12

13 Transmission modes ETSF05 Internet Protocols 13

14 Parallell transmission ETSF05 Internet Protocols 14

15 Serial transmission ETSF05 Internet Protocols 15

16 Transmission modes Asynchronous Synchronous ETSF05 Internet Protocols 16

17 Multiplexing, princip 1 link, n channels n inputs MUX DEMUX n outputs Figure 8.1 M ultiplexing ETSF05 Internet Protocols 17

18 FDM vs TDM Channel 1 Channel 2 Channel 3 Channel 4 Channel 5 Channel 6 Time f 1 f 2 f 3 f 4 f 5 f 6 Frequency (a) Frequency division multiplexing etc. Channel 5 Channel 4 Channel 3 Channel 2 Channel 1 Channel 6 Channel 5 Channel 4 Channel 3 Channel 2 Channel 1 Time Frequency (b) Time division multiplexing Figure 8.2 FDM and TDM ETSF05 Internet Protocols 18

19 Synkron TDM m 1 (t) m 2 (t) Buffer Buffer m 1 (t) m 2 (t) Scan Operation m c (t) Modem s(t) m n (t) Buffer m n (t) TDM stream modulated TDM stream (a) Transmitter Frame Frame 1 2 N 1 2 n Time slot: may be empty or occupied (b) TDM Frames Buffer m 1 (t) s(t) Modem m c (t) Scan Operation Buffer m 2 (t) modulated TDM stream TDM stream Buffer m n (t) (c) Receiver Figure 8.6 Synchronous TDM System ETSF05 Internet Protocols 19

20 TDM Link Control No headers and trailers Data link control protocols not needed Flow control Data rate of multiplexed line is fixed If one channel receiver can not receive data, the others must carry on Corresponding source must be quenched Leaving empty slots Error control Errors detected and handled on individual channel ETSF05 Internet Protocols 20

21 ETSF05 Internet Protocols 21

22 Framing No flag or SYNC characters bracketing TDM frames Must still provide synchronizing mechanism between source and destination clocks One control bit added to each TDM frame Added digit framing is most common Receivers compare incoming bits of frame position to the expected pattern Identifiable bit pattern used as control channel Alternating pattern unlikel y to be sustained on a data channel ETSF05 Internet Protocols 22

23 Pulse Stuffing is a common solution Have outgoing data rate (excluding framing bits) higher than sum of incoming rates Stuff extra dummy bits or pulses into each incoming signal until it matches local clock Stuffed pulses inserted at fixed locations in frame and removed at demultiplexer Problem of synchronizing various data sources Variation among clocks could cause loss of synchronization Issue of data rates from different sources not related by a simple rational number ETSF05 Internet Protocols 23

24 From source 1 2 khz, analog TDM PAM signal 16 ksamples/sec 4 bit A/D TDM PCM signal 64 kbps From source 2 f 4 khz, analog f = 4 khz From source 3 2 khz, analog From source kbps, digital Pulse stuffing 8 kbps, digital From source kbps, digital Pulse stuffing 8 kbps, digital Scan operation TDM PCM output signal 128 kbps From source kbps, digital Pulse stuffing 8 kbps, digital Figure 8.8 TDM of Analog and Digital Sources ETSF05 Internet Protocols 24

25 Table 8.3 North American and International TDM Carrier Standards Designation North American Number of Voice Channels Data Rate (M bps) DS DS-1C DS DS DS Level I nternational (I TU-T) Number of Voice Channels Data Rate (Mbps) ETSF05 Internet Protocols 25

26 Synchronous Optical Networks SONET, developed by ANSI Synchronous Digital Hierarchy SDH, developed by ITU T ETSF05 Internet Protocols 26

27 Digital hierarchy on optical links ETSF05 Internet Protocols 27

28 ETSF05 Internet Protocols 28

29 Network architecture Devices and connections ETSF05 Internet Protocols 29

30 Network architecture Devices and layers Data link layer Physical layer ETSF05 Internet Protocols 30

31 SONET add/drop multiplexer Replaces a signal with another one Operates at line layer Similar to a switch ETSF05 Internet Protocols 31

32 SONET/SDH Synchronous Optical Network (ANSI) Synchronous Digital Hierarchy (ITU T) High speed capability of optical fiber Defines hierarchy of signal rates Synchronous Transport Signal level 1 (STS 1) or Optical Carrier level 1 (OC 1) is 51.84Mbps Carries one DS 3 or multiple (DS1 DS1C DS2) plus ITU T rates (e.g., 2.048Mbps) Multiple STS 1 combine into STS N signal ITU T lowest rate is Mbps (STM 1) ETSF05 Internet Protocols 32

33 Table 8.4 SONET/SDH Signal Hierarchy SONET Designation ITU-T Designation Data Rate Payload Rate (Mbps) STS-1/OC Mbps Mbps STS-3/OC-3 STM Mbps Mbps STS-12/OC-12 STM Mbps Mbps STS-48/OC-48 STM Gbps Gbps STS-192/OC-192 STM Gbps Gbps STS-768 STM Gbps Gbps STS Gbps Gbps ETSF05 Internet Protocols 33

34 SONET frames Proportional to data rates ETSF05 Internet Protocols 34

35 SONET frames in transmission ETSF05 Internet Protocols 35

36 Section overhead 3 octets Line overhead 6 octets Transport overhead 3 octets 90 octets Synchronous payload envelope (SPE) 87 octets Path overhead 1 octet (a) STS-1 frame format Section overhead 9 N octets 270 N octets STM -N payload 261 N octets 9 octets (b) STM-N frame format Figure 8.10 SONET/SDH Frame Formats ETSF05 Internet Protocols 36

37 Multiplexing and byte interleaving ETSF05 Internet Protocols 37

38 Linear SONET topology Without add/drop multiplexer With add/drop multiplexer ETSF05 Internet Protocols 38

39 Automatic protection switching Failure protection through line redundancy ETSF05 Internet Protocols 39

40 Ring SONET topology ETSF05 Internet Protocols 40

41 Mesh SONET topology Better scalability Multiplexing/demultiplexing at switches ETSF05 Internet Protocols 41

42 Asymmetrical Digital Subscriber Line (ADSL) Link between subscriber and network Uses currently installed twisted pair cable Is Asymmetric bigger downstream than up Uses Frequency Division Multiplexing Reserve lowest 25kHz for voice (POTS) Uses echo cancellation or FDM to give two bands Has a range of up to 5.5km ETSF05 Internet Protocols 42

43 ETSF05 Internet Protocols 43

44 Discrete Multitone (DMT) Bits per hertz Line Gain Bits per hertz Frequency Frequency Frequency Figure 8.15 DM T Bits per Channel Allocation Multiple carrier signals at different frequencies Divide into 4kHz subchannels Test and use subchannels with better SNR 256 downstream subchannels at 4kHz (60kbps) In theory 15.36Mbps, in practice 1.5 9Mbps ETSF05 Internet Protocols 44

45 ETSF05 Internet Protocols 45

46 Internet Home Wireless LAN Router ATM switch Wireless modem Wireless modem Wireless modem/ router DSLAM G.DMT modem Set-top box Splitter Splitter Voice switch Telephone Customer Premises PSTN Central Office ATM = Asynchronous Transfer Mode DSLAM = Digital Subscriber Line Access Multiplexer PSTN = Public Switched Telephone Network G.DMT = G Discrete Multitone Figure 8.17 DSL Broadband Access ETSF05 Internet Protocols 46

47 Table 8.6 Comparison of xdsl Alternatives Data rate ADSL HDSL SDSL VDSL 1.5 to 9 Mbps downstream 16 to 640 kbps upstream or Mbps or Mbps 13 to 52 Mbps downstream 1.5 to 2.3 Mbps upstream Mode Asymmetric Symmetric Symmetric Asymmetric Copper pairs Range (24- gauge UTP) 3.7 to 5.5 km 3.7 km 3.0 km 1.4 km Signaling Analog Digital Digital Analog Line code CAP/DMT 2B1Q 2B1Q DMT Frequency 1 to 5 MHz 196 khz 196 khz 10 MHz Bits/cycle Varies 4 4 Varies UTP = unshielded twisted pair ETSF05 Internet Protocols 47

48 WLAN IEEE Trådlöst Ethernet Tre konfigurationsprinciper ETSF05 Internet Protocols 48

49 System med en accesspunkt ETSF05 Internet Protocols 49

50 System med flera accesspunkter ETSF05 Internet Protocols 50

51 Ad Hoc (ingen accesspunkt) ETSF05 Internet Protocols 51

52 Wireless LAN Requirements Throughput Number of nodes Connection to backbone LAN Service area Battery power consumption Transmission robustness and security Collocated network operation License free operation Handoff/roaming Dynamic configuration ETSF05 Internet Protocols 52

53 Wi Fi Alliance There is always a concern whether products from different vendors will successfully interoperate Wireless Ethernet Compatibility Alliance (WECA) Industry consortium formed in 1999 Renamed the Wi Fi (Wireless Fidelity) Alliance Created a test suite to certify interoperability for products ETSF05 Internet Protocols 53

54 Table 13.1 Key IEEE Standards St andar d IEEE a IEEE b IEEE c IEEE d IEEE e IEEE g IEEE i IEEE n IEEE T IEEE ac Scope Physical layer: 5-GHz OFDM at rates from 6 to 54 Mbps Physical layer: 2.4-GHz DSSS at 5.5 and 11 Mbps Bridge operation at MAC layer Physical layer: Extend operation of WLANs to new regulatory domains (countries) MAC: Enhance to improve quality of service and enhance security mechanisms Physical layer: Extend b to data rates >20 Mbps MAC: Enhance security and authentication mechanisms Physical/MAC: Enhancements to enable higher throughput Recommended practice for the evaluation of wireless performance Physical/MAC: Enhancements to support Gbps in 5-GHz band IEEE Physical/MAC: Enhancements to support 1 Gbps in the ETSF05 Internet Protocols ad GHz band (Table can be found on page 424 in the textbook)

55 Table 13.2 IEEE Terminology Access point (AP) Basic service set (BSS) Coordination function Distribution system (DS) Extended service set (ESS) Frame MAC protocol data unit (MPDU) MAC service data unit (MSDU) Station Any entity that has station functionality and provides access to the distribution system via the wireless medium for associated stations A set of stations controlled by a single coordination function The logical function that determines when a station operating within a BSS is permitted to transmit and may be able to receive PDUs A system used to interconnect a set of BSSs and integrated LANs to create an ESS A set of one or more interconnected BSSs and integrated LANs that appear as a single BSS to the LLC layer at any station associated with one of these BSSs Synonym for MAC protocol data unit The unit of data exchanged between two peer MAC entities using the services of the physical layer Information that is delivered as a unit between MAC users Any device that contains an IEEE conformant MAC and physical layer ETSF05 Internet Protocols 55 (Table can be found on page 424 in the textbook)

56 Extended service set (ESS) I EEE 802.x LAN portal Distribution System (DS) Basic service set (BSS) Access point (AP) STA1 Access point (AP) STA5 STA2 STA3 STA4 STA6 STA7 Basic Service Set STA = station Figure 13.4 I EEE Architecture ETSF05 Internet Protocols 56

57 Table 13.3 IEEE Services Ser vi ce Pr ovi der Used t o suppor t Association Distribution system MSDU delivery Authentication Station LAN access and security Deauthentication Station Dissassociation Distribution Integration Distribution system Distribution system Distribution system LAN access and security MSDU delivery MSDU delivery MSDU delivery MSDU delivery Station MSDU delivery Privacy Station LAN access and security Reassocation Distribution system MSDU delivery ETSF05 Internet Protocols 57

58 Medium Access Control Reliable data delivery Access control MAC layer covers three functional areas: Security ETSF05 Internet Protocols 58

59 Reliable Data Delivery Can be dealt with at a higher layer More efficient to deal with errors at MAC level includes frame exchange protocol Station receiving frame returns acknowledgment (ACK) frame Exchangetreated as atomic unit If no ACK within short period of time, retransmit physical and MAC layers unreliable Noise, interference, and other propagation effects result in loss of frames Even with error correction codes, frames may not successfully be received ETSF05 Internet Protocols 59

60 Hidden Node/Station Problem ETSF05 Internet Protocols 60

61 Four Frame Exchange RTS alerts all stations within range of source that exchange is under way CTS alerts all stations within range of destination Other stations don t transmit to avoid collision RTS/CTS exchange is a required function of MAC but may be disabled Can use four frame exchange for better reliability Source issues a Request to Send (RTS) frame Destination responds with Clear to Send (CTS) After receiving CTS, source transmits data Destination responds with ACK ETSF05 Internet Protocols 61

62 LOGICAL LINK CONTROL (LLC) MAC layer Contention-free service Point Coordination Function (PCF) Contention service Distributed Coordination Function (DCF) PHYSI CAL LAYER (802.11a, b, g, n, ac, ad) Figure 13.5 I EEE Protocol Architecture ETSF05 Internet Protocols 62

63 Distributed Coordination Function (DCF) DCF sublayer uses CSMA algorithm Does not include a collision detection function because it is not practical on a wireless network Includes a set of delays that amounts as a priority scheme If station has frame to send it listens to medium If medium is idle, station may transmit Else waits until current transmission is complete ETSF05 Internet Protocols 63

64 Wait for frame to transmit Medium idle? No Yes Wait IFS Still idle? No Wait until current transmission ends Yes Transmit frame Wait IFS Still idle? No Yes Exponential backoff while medium idle Transmit frame Figure 13.6 I EEE M edium Access Control Logic ETSF05 Internet Protocols 64

65 Priority IFS Values SIFS (short IFS) PIFS (point coordination function IFS) DIFS (distributed coordination function IFS) For all immediate response actions Used by the centralized controller in PCF scheme when issuing polls Used as minimum delay for asynchronous frames contending for access ETSF05 Internet Protocols 65

66 Point Coordination Function (PCF) Alternative access method implemented on top of DCF Polling by centralized polling master (point coordinator) Uses PIFS when issuing polls Point coordinator polls in round robin to stations configured for polling When poll issued, polled station may respond using SIFS If point coordinator receives response, it issues another poll using PIFS If no response during expected turnaround time, coordinator issues poll Coordinator could lock out asynchronous traffic by issuing polls Have a superframe interval defined ETSF05 Internet Protocols 66

67 MAC octets 2 Frame Control ramformat 2 6 Duration/I D Addr ess 1 Två ramtyper Kontroll Data Management Addr ess 2 Addr ess 3 Sequence Control Addr ess 4 QoS Control High Throughput Control MAC header Notera fyra adressfält! Frame Check Sequence (FCS) Always present Present only in certain frame types and subtypes Figure 13.8 I EEE M AC Frame Format ETSF05 Internet Protocols 67

68 Table 13.4 IEEE Physical Layer Standards Standard a b g n ac ad Year introduced Maximum data transfer speed Frequency band Channel bandwidth Highest order modulation Spectrum usage Antenna configuration Mbps 11 Mbps 54 Mbps 5 GHz 2.4 GHz 2.4 GHz 20 MHz 20 MHz 20 MHz 65 to 600 Mbps 2.4 or 5 GHz 20, 40 MHz 78 Mbps to 3.2 Gbps 6.76 Gbps 5 GHz 60 GHz 40, 80, 160 MHz 2160 MHz 64 QAM 11 CCK 64 QAM 64 QAM 256 QAM 64 QAM DSSS OFDM DSSS, OFDM 1 1 SISO 1 1 SISO 1 1 SISO Up to 4 4 MIMO OFDM SC-OFDM SC, OFDM Up to 8 8 MIMO, MU- MIMO 1 1 SISO (Table is on page 436 in textbook) ETSF05 Internet Protocols 68

69 25 Throughput (M bps) n g Simultaneous users/ap Figure Average Throughput per User ETSF05 Internet Protocols 69

70 Access and Privacy Services Deauthentication and Privacy Privacy Used to prevent messages being read by others allows optional use of encryption Original WEP security features were weak Subsequently i and WPA alternatives evolved giving better security Deauthentication Invoked whenever an existing authentication is to be terminated ETSF05 Internet Protocols 70