Home Network Technologies
家庭網路相關網路技術 Home Networking Technology Computer Home Network Internet Broadband Access Technology ISP TV
Broadband Access Technologies • • • Digital Subscriber Line (DSL) Cable Modem Broadband Over Power Line (BOPL) Fiber-to-the-Home (FTTH) IEEE 802. 16 (Wi. Max) GPRS; 3. 5 G
Outlines • Broadband Over Power Line • Digital Subscriber Line (DSL) Technology • Cable Modem
Broadband Over Power Line (BOPL) • Use existing electrical lines to provide the medium for a high speed communications network • Superimposing voice or data signals onto the line carrier signal using OFDM • Two categories – In-house – access
In-House BPL • connecting machines within a building • Home. Plug: an alliance for in-house BPL
Access BPL • Delivers the last mile of broadband to the home
Access BPL Architecture Coupler Internet Vo. IP Backhaul Point Wireless link Coupler Bridge Medium-voltage lines Low-voltage lines
Coupler Bridge Backhaul Point
Advantages of BPL • Power lines are our most ubiquitous infrastructure • Lower cost of deployment – Existing wires
Main Concerns • Radio Frequency Interference (RFI) to licensed service • power lines are inherently a very noisy environment – Every time a device turns on or off, it introduces a pop or click into the line. – Energy-saving devices often introduce noisy harmonics into the line
Digital Subscriber Line (DSL) Technology • The key in DSL technology is modulation, a process in which one signal modifies a properties of another. • Hardware: DSL requires modems and splitters for endusers; carriers use DSLAMs (digital subscriber line access multiplexers) • Differences between x. DSL technologies: speed, operating distance, applications, ratio between up and downstream • Different approaches: ATM-based ADSL, ISDN DSL. • The important thing is what is running over x. DSL. . .
x. DSL - Digital Subscriber Line Technology
ADSL: Asymmetric Digital Subscriber Line • twisted pair copper (single loop) • asymmetric: most commonly: – downlink: 256 Kbps - 8 Mbps – uplink : 64 Kbps - 2 Mbps • limited distance (18000 feet over 26 -gauge copper)
RADSL: Rate-Adaptive Digital Subscriber Line • varying speeds depending upon line quality; asymmetric – downlink: 1. 5 Mbps - 8 Mbps – uplink : 176 Kbps - 1 Mbps • limited distance (18000 feet over 26 -gauge copper)
HDSL: High-speed Digital Subscriber Line • full-duplex, symmetric – 1. 544 Mbps or 2. 048 Mbps in each direction • two twisted pairs (for T 1) and 3 pairs (for E 1) • max distance 12, 000 feet
VDSL: Very-high-bit-rate Digital Subscriber Line (known as BDSL) • asymmetric – downlink: 12. 96 -51. 84 Mbps – uplink : 1. 6 - 2. 3 Mbps • max 4, 500 - 1, 000 feet • applications: High definition TV, multimedia
Cable Modem • primarily used to deliver broadband Internet access on Hybrid Fibre-Coaxial (HFC) Internet Cable Modem Computer Cable TV Cable CMTS Television Company
Cable Modem Standards • DOCSIS (Data Over Cable Service Interface Specification) – 1. 0 (1997): typical 2 Mbps upstream – 1. 1 (1999): 10 Mbps upstream – 2. 0 (2002) : 30 Mbps upstream
Hybrid Fibre-Coaxial (HFC) • combines optical fiber and coaxial cable
The Downstream & Upstream Path • The downstream data path of the cable modem uses a SINGLE 6 mhz TV channel, which is typically in the higher frequencies range (550 MHz and above) because higher frequencies can carry information faster. • The lower end of the radio frequency spectrum (5 MHz – 42 MHz) is used for the upstream or the return path. • In terms of data bandwidth, the typical upstream channel usually has a capacity of around 5 Mbps. • The total downstream bandwidth for a single channel is around 30 Mbps. Downstream Channel Multiple TV Channels Upstream signaling 5 -42 MHz . . . 50 MHz - 550 MHz - 750 and up MHz
Cable TV Spectrum
Cable Modem: Modulation & Demodulation Phase • Demodulation Phase: – tunes to the appropriate 6 MHz downstream channel (42 MHz – 850 MHz). – demodulates the signal and extracts the downstream data that is destined for it – converts the data into an Ethernet or USB signal to be fed into the user’s computer. • Modulation Phase: The cable modem receives data on its Ethernet or USB interface and modulates the data onto the upstream carrier frequency, negotiates channel access with the CMTS and sends the data.
Protecting the Downstream Channel (and the upstream as well) • A component of the DOCSIS 1. 1 standard called Baseline Privacy Initiative+ (BPI+) is bi-directional encryption between cable modem and the CMTS • Each DOCSIS 1. 1 compliant cable modem has a digital certificate stored in its firmware. This allows for the cable modem to be authenticated onto the network. • The authentication takes place when the CMTS verifies the certificate presented by the modem. (The certificate is signed by the manufacturer’s private key). • Encryption is based on 56 -bit Triple-DES • This scheme effectively renders any sniffing attempts useless, unless cracking of the Triple-DES scheme is possible
DOCSIS Security Overview -- BPI+ -Internet CM Authentication (X. 509 Certificates) Key Management (RSA, Tri-DES) abcdef CMTS Data Encryption (DES) Mfg Certificate. . . Digitally Signed by: DOCSCSIS Root CM Certificate. . . Digitally Signed by: Mfg CA x$a 9 E! abcdef TFTP Server Secure Software Download CM New CM Code. . . (X. 509 Certificate) CM Code File Digitally Signed by: Manufacturer PC
The Device • The cable modem bridges Ethernet frames between a customer LAN and the coax cable network • It does, however, also support functionalities at other layers – Ethernet PHY and DOCSIS PHY – IP address – UDP, port-based packet filtering – DHCP, SNMP, TFTP
Fiber-to-the-Home (FTTH) // Copper Fiber CO/HE // Old networks, optimized for voice CO/HE // Optical networks, optimized for voice, video and data Note: network may be aerial or underground 24 kbps - 1. 5 Mbps 19 Mbps - 1 Gbps +
FTTH Characteristics • FTTH is an optical access network in which the optical network unit is on or within the customer’s premise. • Although the first installed capacity of a FTTH network varies, the upgrade capacity of a FTTH network exceeds all other transmission media. Optical Access Network CO/HE Optical Line Termination Source: www. ftthcouncil. org // Optical Network Unit
Why FTTH? • • • Enormous information carrying capacity Easily upgradeable Ease of installation Allows fully symmetric services Reduced operations and maintenance costs Benefits of optical fiber: – – – Very long distances Strong, flexible, and reliable Allows small diameter and light weight cables Secure Immune to electromagnetic interference (EMI)
Fiber versus Copper Glass Copper • Uses light • Transparent • Dielectric materialnonconductive – EMI immune • Low thermal expansion • Brittle, rigid material • Chemically stable • Uses electricity • Opaque • Electrically conductive material – Susceptible to EMI • High thermal expansion • Ductile material • Subject to corrosion and galvanic reactions • Fortunately, it’s recyclable
Architecture and Transport Architecture (Electronics) • PON • Active node • Hybrid Transport: ATM or Ethernet CO/HE //
FTTH Architectures • Passive Optical Networks (PONs) – Shares fiber optic strands for a portion of the networks distribution – Uses optical splitters to separate and aggregate the signal – Power required only at the ends • Active Node – Subscribers have a dedicated fiber optic strand – Many use active (powered) nodes to manage signal distribution • Hybrid PONs – Literal combination of an Active and a PON architecture
FTTH Technical Considerations • Data – – – How much per home? How well can you share the channel? Security – how do you protect the subscriber’s data? What kind of Qo. S parameters do you specify? Compatible business services? • SLAs • T 1 • Support for voice? • Support for video? – Broadcast – IPTV
FTTH Technical Considerations • Data – How much per home? – How well can you share the channel? – Security – how do you protect the subscriber’s data? – What kind of Qo. S parameters do you specify?
FTTH Technical Considerations: Speed • Data requirements – Competition: ADSL, cable modem ~0. 5 to ~1. 5 Mb/s shared, asymmetrical – FTTH ~10 to 30 Mb/s non-shared or several 100 Mb/s shared, symmetrical – SDTV video takes 2 -4 Mb/s today at IP level – HDTV takes maybe 5 times STDV requirement – Pictures can run 1 MB compressed – 5. 1 channel streaming audio would run ~380 kb/s
FTTH Technical considerations: Security • Security – Data is shared in the downstream direction in most systems – Your Gateway filters out all packets not intended for you – But there is fear that someone will snoop on your data – FSAN has a low-complexity, low-security encryption scheme – 802. 3 ah has formed a committee to study security – Manufacturers have taken their own tacks on security, from none to robust
FTTH Data Flow and Security: Downstream Time division multiplex (TDM) – each subscriber’s data gets its turn. T // // D // H // // Tom // Box on side of home separates out only the data bound for that subscriber. But the fear is that someone will fool his box into giving data intended for another subscriber. Solution is to encrypt the data. H Harry D Dick
FTTH Data Flow and Security: Upstream Time division multiple access (TDMA) – similar to downstream, with gap for laser start/stop T // // D // H // // Tom // // Due to the physics of the network, Harry’s data flows upstream but does not come to Tom’s box, so Tom cannot see Harry’s data H Harry Dick
FTTH Data Flow and Qo. S If Dick has paid for more bandwidth, he gets more T // // D // // H // Tom // If Tom’s packets need higher priority (e. g. , telephone), they go first H Harry D Dick
Video Delivery with FTTH • several different ways – Broadcast (cable TV standards) • Analog or Digital • Benefit from high volume and rich applications of cable boxes – IPTV – TV transmitted over Internet Protocol • Feasible, and some people are doing it in place of broadcast • Bandwidth hog, but statistics can work for you – Interesting hybrid model awaits hybrid STTs, but can give the best of both worlds
IPTV Unicast (VOD)
Home Networking Technologies • IEEE 802. 3/Ethernet • IEEE 802. 11 a/b/g/n (Wi. Fi) • Bluetooth • In-House BPL (Home. Plug)
IEEE 802. 3 Family • Original IEEE 802. 3 (Ethernet) – 10 Mbps • Fast Ethernet – 1000 Mbps • Gigabit Ethernet – 1 Gbps • 10 G Ethernet – 10 Gbps
Gigabit Ethernet Networks • 1000 Mbps transmission rate • IEEE 802. 3 CSMA/CD frame format • Medium: Twisted pair (UTP, STP) or Fiber • Hub- or switch-based topology • Do not support priority scheme • Bandwidth utilization is not guaranteed to be fair • Do not support guaranteed delay service • Low bandwidth utilization under heavy loads • Suitable for multimedia communications
Gigabit Ethernet Architecture
Gigabit Ethernet Communication Structure Ethernet Upper Layers Logical Link Control (LLC) Media Access Control (MAC) Gigabit Media Independent Interface (GMII) 1000 BASE-T Codec 8 B/10 B Coding/Decoding 1000 BASE-LX 1270 -1355 nm 光傳送接收器 SMF 3 km 1000 BASE-SX 770 -860 nm 光傳送接收器 1000 BASE-CX STP 傳送接收器 1000 BASE-T 4 -Pair 傳送接收器 MMF 50 um MMF 62. 5 um Balance Shielded Copper Cat-5 UTP 550 m 300 m 25 m 100 m MMF
Gigabit Ethernet Physical Layer • 1000 BASE-T (UTP, IEEE 802. 3 ab) • 1000 BASE-CX (Short copper jumpers, IEEE 802. 3 z) • 1000 BASE-SX (Shortwave fiber, IEEE 802. 3 z) • 1000 BASE-LX (Longwave fiber, IEEE 802. 3 z)
Gigabit Ethernet Characteristics • Good fault tolerance – Hub/Repeater architecture • Carrier Extension for short frames. • Frame Bursting to increase performance (optional).
Half-Duplex vs. Full-Duplex • Gigabit Ethernet can operate in either halfduplex or full-duplex mode. • Half-duplex poses some difficult problems that can result in restrictions on the allowable topologies and/or changes to the Ethernet MAC algorithm. • Full-duplex is simpler to implement than a half-duplex MAC.
Limitations of Half-duplex Operation • CSMA/CD implies an intimate relationship between the minimum length of a frame (L, measured in bit-times, not absolute time) and the maximum round-trip propagation delay (2 a) of the network: L > 2 a transmission time A maximum hub distance B space round trip propagation delay
10 Mbps Ethernet • For the original 10 Mbps Ethernet, a compromise was struck. • Minimum frame = 512 bits (64 bytes), not including the preamble and Physical Layer overhead. • Minimum data field = 46 bytes rarely imposes a significant padding overhead (IP header + TCP header = 40 bytes). • At 10 Mbps, 512 bit-times is 51. 2 us. Depends on the type of cable used and the network configuration, the extent of a 10 Mbps Ethernet can be on the order of from 2 -3 Km. 7 1 Preamble SFD 6 6 DA SA 2 LEN 46 4 Data FCS Minimum Frame Length (512 bits) bytes
Network Extent • For a given minimum-length frame, the extent of a network scales inversely with data rate. 10, 000 m ~ 2800 m 1, 000 m ~ 205 m 100 m ~ 20 m 10 Mbps 1000 Mbps
100 Mbps Fast Ethernet • For 100 Mbps Fast Ethernet, a conscious choice had to be made to do one or more of the following: p. Increase the minimum frame length so that large networks (with multiple repeaters) could be supported. p. Change the CSMA/CD algorithm to avoid the conflict. p. Leave the minimum frame as is, and decrease the extent of the network accordingly.
Limitations of Half-duplex Operation • For Hub-based configuration (1995 ~), the only truly important distance was from the user to the wiring closet (<100 m, 200 m diameter). • A change to the minimum frame length would have required changes to higher-layer software, including device driver and protocol suite implementation. Also difficult to seamlessly bridge between 10 Mbps and 100 Mbps network with different minimum frame lengths. • A change to the CSMA/CD algorithm would have significantly delayed the release of the Fast Ethernet standard.
Limitations of Half-duplex Operation • Fast Ethernet uses ØThe same 512 -bit minimum frame. ØDecrease the network extent to the order of 200 m, using twisted-pair cabling. ØNo change to the CSMA/CD algorithm. • For Gigabit Ethernet, network extent is only about 20 m!!, if the same approach is used.
Carrier Extension • For Ethernet/Fast Ethernet, the minimum frame length = slot. Time = 512 bits. • Gigabit Ethernet keeps the 512 -bit minimum frame length but sets slot. Time to 512 bytes • In Gigabit Ethernet, frames that shorter than slot. Time are extended by appending a carrierextension field so that they are exactly one slot. Time long. • Frames longer than slot. Time are untouched
Carrier Extended Frame Format 512 -byte Short Frame 8 Preamble/SFD 6 6 2 DA SA LEN 46 - 493 Data 4 FCS 448 - 1 bytes Extension Minimum Nonextended Frame Length (64 bytes) Carrier-Extended Frame (64 -511 Bytes) 8 6 Preamble/SFD 6 2 DA SA LEN 494 - 1500 Data Non-Carrier-Extended Frame ( 512 Bytes) 4 bytes FCS
Channel Efficiency • The use of carrier extension for short frames imposes a significant performance degradation. • In the worst-case (a stream of minimum length frames of 512 bits with a 64 -bit preamble/SFD and a 96 -bit interframe gap), the channel efficiency is 512 length of = 12% slot time 4096 + 64 + 96 • For Ethernet (Fast Ethernet), 512 + 64 + 96 = 76%
Frame Bursting • The solution is to allow a station to send multiple frames, while extending only the first one with carrier extension (Frame Bursting). • No additional frames are sent if a collision occurs before the slot. Time expires. • After that time, the station can begin sending additional frames without contending again. • The interframe gap is filled with non-data symbols. • The bursting station may continue to start new frames for up to one burst. Length, which limits the maximum time that a station is allowed to dominate the channel.
Frame Bursting Maximum Time to start of Last frame in Burst (8192 Bytes) Slot. Time (512 Bytes) Carrier detection 傳送 訊框 Carrier extension Inter-Frame Spacing (96 bit time) frame 1 Preamble frame 2 SFD DA SA frame 3 LEN LLC PAD FCS frame 4
Frame Bursting • Transmitters are not required to implement frame bursting. • A trade-off between complexity and performance. • Receiver must be prepared to receive bursted frames. • Even if the first frame in a burst is longer than a slot. Time (no carrier-extension), a station may still continue to burst frames up to the burst. Length time. • Normally, no collision should occur after the first slot. Time during a burst of frames.
Half-Duplex Operational Parameters Slot. Time (Bit times) inter. Frame. Gap (us) attemp. Limit backoff. Limit jam. Size max. Frame. Size min. Frame. Size extend. Size burst. Length (bits) Ethernet Type 10 Mbps 1 Mbps 512 9. 6 100 Mbps 1000 Mbps 512 4096 96 0. 096 16 10 32 1518 64 0 16 10 32 1518 64 448 - - - 65, 536
Full-Duplex MAC • When an Ethernet operates in full-duplex mode, all of the complexity of carrier sense, collision detection, carrier extension, frame bursting, backoff algorithm, and so on, has no bearing !! • Only shared medium needs these. • The full-duplex MAC is not really a MAC at all. • With a dedicated channel, a station may transmit at will.
Limitations of Full-duplex Operation • The underlying physical channel must be capable of supporting simultaneous, bi-directional communications without interference (1000 BASE-X and 1000 BASE-T families). • Exactly two devices on the LAN segment. • The interfaces in both devices must be capable of and configured to use full-duplex mode. • If all of these conditions are met, then full-duplex mode not only can be used, it should be used.
Operation of Full-Duplex MAC • A station can send a frame any time there is a frame in its transmit queue and it is not currently sending a frame. • Stations should similarly receive frames at any time, subject to interframe spacing. • Do not defer transmissions to received traffic. • No need for carrier-extension in full-duplex mode !! • No explicit need for frame bursting !! • Full-duplex MAC can “burst” at any time (not just after an extended carrier) and for any length of time (not just for a burst. Length period) !!
Gigabit Ethernet Protocol Stack • • CS: Convergence Sublayer MDI: Medium Dependent Interface MII: Medium Independent Interface GMII: Gigabit Medium Independent Interface
10 Gigabit Ethernet Protocol Stack
IEEE 802. 11 Family • Differs in Physical Layer • IEEE 802. 11 b – 2. 45 GHz / 11 Mbps (100 m) • IEEE 802. 11 a – 5. 8 GHz / 54 Mbps (70 m) • IEEE 802. 11 g – 2. 4 GHz / 54 Mbps (100 m) • IEEE 802. 11 n – 2. 4/5 GHz / 100+ (max. 600) Mbps (100+ m)
2. 4 GHz Radio Licenses NOT required in these bands 5 GHz Direct Sequence Spread Spectrum IEEE 802. 11 Standard for WLAN operations at data rates up to 2 Mbps in the 2. 4 GHz ISM band. DSSS modulation. IEEE 802. 11 a Standard for WLAN operations at data rates up to 54 Mbps in the 5 GHz band. Proprietary “rate doubling" has achieved 108 Mbps. Realistic rating is 20 -26 Mbps. IEEE 802. 11 b Wi-Fi™ or “high-speed wireless” 1, 2, 5. 5 and 11 Mbps in the 2. 4 GHz band. All 802. 11 b systems are backward compliant. Realistic rating is 2 to 4 Mbps. IEEE 802. 11 g 802. 11 a backward compatible to the 802. 11 b 2. 4 GHz band using OFDM. Orthogonal Frequency Division Multiplexing
Adaptive Rate Selection • Performance of the network will also be affected by signal strength and degradation in signal quality due to distance or interference. • As the signal becomes weaker, Adaptive Rate Selection (ARS) may be invoked.
Access Point (AP) • Usually connects wireless and wired networks – if not wired • acts as an extension point (wireless bridge) • consists of a radio, a wired network interface (e. g. , 802. 3), and bridging software conforming to the 802. 1 d bridging standard • Number of clients supported – device dependent
AP as a Wireless Bridge fixed terminal mobile terminal server infrastructure network access point application Application TCP IP IP LLC LLC 802. 11 MAC 802. 3 MAC 802. 11 PHY 802. 3 PHY
Basic Service Set (BSS) Coordinated function BSS
Independent Basic Service Set (IBSS) A BSS without Access Point IBSS Ad hoc mode
Extended Service Set (ESS) • ESS: one or more BSSs interconnected by a Distribution System (DS) • Traffic always flows via Access Point • allows clients to seamlessly roam between APs
Distributed System (DS) • A thin layer in each AP – embodied as part of the bridge function – keeps track of AP-MN associations – delivers frames between APs • Three types: – Integrated: A single AP in a standalone network – Wired: Using cable to interconnect APs – Wireless: Using wireless to interconnect APs
ESS: Single BSS (with integrated DS) A cell Access Point 91. 44 to 152. 4 meters BSS
ESS: BSS’s with Wired Distribution System (DS) 20 -30% overlap BSS Di st r Sy ibu st tio em n BSS
ESS: BSS’s with Wireless Distribution System (DS) BSS Di st Sy ribu st tio em n BSS
ESSID in an ESS • ESSID differentiates one WLAN from another • Client must be configured with the right ESSID to be able to associate itself with a specific AP • ESSID is not designed to be part of security mechanism, and it is unfitted to be one • AP broadcast the SSID(s) they support • Client association requests contain the ESSID • Transmitted in the clear
ESSID
Connecting to the Network Access Point Client Probe Request Probe Response Authentication Request Authentication Response Association Request Association Response Probing 802. 11 Authentication Association
Probing Phase • Find an available AP • APs may operate at different channels (11 channels in total in case of 802. 11 a) • Should scan a channel at least Min. Channel. Time • If an AP is found, should last Max. Channel. Time
Active Scanning AP MN probe request with SSID probe response If SSID matches Service Set Identifier (SSID)
Passive Scanning AP MN beacon with SSID Service Set Identifier (SSID)
Full Scanning MN AP 1 AP 2 Scan channel 1 AP 3 Min. Channel. Time Scan channel 2 Beacon or Probe Resp Scan channel 3 … Scan channel 11 Max. Channel. Time
Authentication and Association Types WLAN authentication occurs at Layer 2. It is the process of authenticating the device not the user. Authentication request Authentication response (Accept or Reject)
802. 11 Authentication Methods • Open Authentication (standard) • Shared key authentication (standard) • MAC Address authentication (commonly used)
Open Authentication • The authentication request contain a NULL authentication protocol. It must have the AP SSID. • The access point will grant any request for authentication Access Point Client Authentication Request Authentication response
Shared Key Authentication • Requires that the client configures a static WEP key Access Point Client Authentication Request Authentication response (challenge) Authentication Request(encrypted challenge) Authentication response(Success/Failure)
MAC Address Authentication • Not specified in the 802. 11 standard, but supported by many vendors (e. g. Cisco) • Can be added to open and shared key authentication Client Access Point Auth. Request Auth. Response (Success/Reject) RADIUS Server Access-Request (MAC sent as RADIUS req. ) Access-Success/Reject
實際驗證 Open Authentication
WEP Encapsulation 1. 2. 3. 4. Initialization Vector (IV) P = M || checksum(M) Key. Stream = RC 4 (IV || k) C = XOR (P, Key. Stream) Transmit (IV, C) {p=plaintext} {k=shared-key} {c=ciphertext} {IV=init-vector} IV || seed WEP Key Plaintext RC 4 PRNG Key Stream Å || C Ciphertext P CRC-32 Integrity Check Value (ICV) Message
WEP Decapsulation 1. 2. 3. WEP Key IV Ciphertext Message Key. Stream = RC 4 (IV || k) P’ = XOR (C, Key. Stream) = M’ || checksum(M) If checksum(M’) = (checksum(M))’ Then P’ is accepted M’ || Seed RC 4 PRNG Key stream P’ Å Plaintext CRC 32 ICV’ ICV' = ICV?
802. 1 X • based on EAP (extensible authentication protocol, RFC 2284) – still one-way authentication – initially, MN is in an unauthorized port – an “authentication server” exists – after authorized, the MH enters an authorized port – 802. 1 X ties it to the physical medium, be it Ethernet, Token Ring or wireless LAN.
Three Main Components • supplicant: usually the client software • authenticator: usually the access point • authentication server: usually a Remote Authentication Dial-In User Service (RADIUS) server
Extensible Authentication Protocol (EAP) • the AP does not provide authentication to the client, but passes the duties to a more sophisticated device, possibly a dedicated server, designed for that purpose. Authentication server Authentication request Authentication response
802. 1 X – How it works Client AP Auth Server “RADIUS” Let me in! (EAP Start) What’s your ID? (EAP-request identity message) ID = xxx@yyy. local (EAP Response) The answer is “ 47” Is xxx@yyy. local OK? Prove to me that you are xxx@yyy. local EAP Challenge/ Authentication Let him in. Here is the session key. Come in. Here is the session key. http: //yyy. localindex. htm network Encrypted session
Distributed Coordination Function: CSMA/CA • CSMA: Carrier Sense Multiple Access – physical carrier sense: physical layer – virtual carrier sense: MAC layer • network allocation vector (NAV) • CA: Collision Avoidance – random backoff procedure • shall be implemented in all stations and APs
Contention Window random 1 data frame The winner contention window busy DIFS random 2 All stations must wait DIFS after medium is free random 3 time
SIFS: Giving Priority to RTS/CTS/ACK data frame Source busy Destination contention window ACK DIFS Others SIFS Defer access
SIFS: Transmitting Fragments Source DIFS SIFS Fragment 1 SIFS Fragment 2 Destination SIFS ACK Others Defer access SIFS ACK Contention Window
EIFS: Low Priority Retransmission data frame Source busy Destination contention window DIFS SIFS can resend EIFS DIFS No ACK SIFS Others Defer access contension
CSMA/CA with RTS/CTS SIFS data frame Source RTS busy Destination ACK contention window CTS DIFS SIFS Others NAV (RTS) NAV (CTS)
RTS/CTS is Optional • system parameter RTSThread – RTS/CTS is used only when frame size RTSThread
Throughput Issues • When a source node sends a frame, the receiving node returns a positive acknowledgment (ACK). – This can consume 50% of the available bandwidth. • This overhead, combined with the collision avoidance protocol (CSMA/CA) reduces the actual data throughput to a maximum of 5. 0 to 5. 5 Mbps on an 802. 11 b wireless LAN rated at 11 Mbps.
What is Bluetooth? • Major joint computing and telecomm industry initiative • Plan to deliver a revolutionary radio-based solution – Cable replacement, no line of sight restrictions – Prefect for mobile devices - small, low power, low cost – Open specification (license free)
Bluetooth Characteristics • • • Data/voice access Cable replacement technology 1 Mbps symbol rate Range 10+ meters Low cost Low power
Ultimate Headset (Voice Access)
Cordless Computer (Cable Replacement)
Automatic Synchronization In the Office At Home
Bluetooth World
Application of Bluetooth • Integrated in – – mobile phones PDA/handhelds Computers Wireless peripherals • Handsets • cameras – Network access devices • universal bridge to other networks or internet
Masters and Slaves • Each Bluetooth device may be either a Master or Slave at any one time, thought not simultaneously. s m • Master — the device which initiates an exchange of data. • Slave — the device which responds to the master.
Piconet • Two or more units sharing the same hopping sequence form a piconet (similar to a LAN). • Each piconet can have – only one master. – up to seven slaves. • Each piconet has max capacity (1 Mbps). m s s s
Piconet Structure Master Active Slave Parked Slave Standby
Scatternet • Multiple piconets form a scatternet. • Same device can be shard by two different piconets m s s s m s Max 256 piconets s m s s
Frequency Hop Spread-Spectrum • Bluetooth channel is represented by a pseudo random hopping sequence through the entire 79 RF frequencies • Nominal hop rate of 1600 hops per second • Channel Spacing is 1 MHz
Time Division Duplex (TDD) • Bluetooth is a Time Division Multiplexed system • 625 s/slot Slot k master slave 625 s Slot k+1 Slot k+2
Multi-Slot Packets • Bluetooth defines data packets which are 1, 3, or 5 slots long 1 -slot packet 3 -slot packet 5 -slot packet f(k) f(k+1) f(k+2) f(k+3) f(k+4) f(k+5) f(k+6)
Time Division Multiplexing • Slaves must listen to the master • A slave can send only after receiving a poll 1 2 Master TX RX Slave 1 RX TX TX RX RX 1 TX Slave 2 TX
Putting It Altogether channel 78 77 76 75 Master … Slave 1 5 4 3 2 1 0 Slave 2 time
Asynchronous Connection-Less (ACL) Links • One ACL link can exist between any two devices. • No slots are reserved. • Every even-slot is Master transmission & every old-slot is Slave response • Broadcast packets are ACL packets not addressed to any specific slaves.
Synchronous Connection Oriented (SCO) Links • a symmetric link between Master and Slave with reserved channel bandwidth and slots. • Typically used for voice connection • A Master can support up to three SCO links. • A slave can support – up to 3 SCO links from the same master – two SCO links if the links are originated from different masters. • SCO packets are never retransmitted.
SCO Traffics • Master reserves slots for SCO links Slot no master 0 1 SCO TX SCO RX 3 SCO RX SCO TX TX RX RX Slave 1 Slave 2 2 4 5 0 1 RX SCO TX SCO RX SCO TX TX TX RX 2
Mixed Link Packets SCO MASTER SLAVE 1 SLAVE 2 SLAVE 3 ACL SCO ACL
RFID • What is RFID? – RFID is an ADC (Automatic Data Capture) technology that uses radio-frequency waves to transfer data between a reader and a movable item to identify, categorize, track … – RFID is fast, reliable, and does not require physical sight or contact between reader/scanner and the tagged item
An RFID System
RF Tag
Variations of RF Tags • Basic types: active vs. passive • Memory – Size (16 bits - 512 k. Bytes +) – Read-Only, Read/Write or WORM • • Arbitration (Anti-collision) Ability to read/write one or more tags at a time Frequency : 125 KHz - 5. 8 GHz Physical Dimensions – Thumbnail to Brick sizes – Incorporated within packaging or the item • Price ($0. 50 to $150)
RFID Frequencies
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