Maximilian Riegel ICM Networks, Advanced Standardization
Prolog: The ubiquitous WLAN n Today’s road worriers require access to the Internet everywhere. n WLAN is more than just cable replacement, it provides hassle-free broadband Internet access everywhere. Office Railway Station Airport Hospital Congress hall, Hotel Semi-public WLAN Office Corporate WLAN Plant Remote Access Public WLAN Home WLAN Campus n Coverage in ‘hot-spots’ sufficient. n IEEE802.11b meets the expectations for easiness, cost and bandwidth. WLAN-IEEE802.
Prolog: WLAN has taken off ... n Lots of serious WLAN activities have been started – All big players have products (Cisco, Intel, …) – Integrated WLAN solutions appearing (Apple, IBM, ...) n The prediction have been exceeded by actual market. For comparison: Total PC world market in ‘01: ~ 120 Mio pcs.; > 30 % portable. 25 20 :/$1 UI L I >PLR@ Source: Frost&Sullivan (2000-03) 15 10 5 0 ’98 ’99 ’00 ’01 ’02 n Ruling technology is IEEE802.11b (Wi-Fi) [11Mb/s, 2.4 GHz]. WLAN-IEEE802.
Outline n Part 1: Wireless Internet System Architecture n Part 2: IEEE802.11 Overview n Part 3: Physical Layer n Part 4: Medium Access Control n Part 5: MAC Layer Management n Part 6: WLAN Mobility n Part 7: WLAN Security n Part 8: Public Hotspot Operations n Part 9: WLAN – UMTS Interworking WLAN-IEEE802.11 Tutorial (Maximilian Riegel), 021018-wlan-tutorial.
Part 1: Wireless Internet system architecture n n n n n n Generic Internet network architecture Layering means encapsulation IEEE802.11 – seamless integration into the Internet IP based network architecture Wireless LAN IEEE802.11 basic architecture What is unique about wireless? WLAN-IEEE802.11 Tutorial (Maximilian Riegel), 021018-wlan-tutorial.
Generic Internet network architecture 3ROLF\ 6HUYHU $$$ 6HUYHU :/$1 $FFHVV Peer Peer (Client) www http tcp ip 802.2 (Web-Server) Internet/Web Applications 802.2 802.2 802.3 ip ip 802.2 link 802.3 phy WLAN-IEEE802.11 Tutorial (Maximilian Riegel), 021018-wlan-tutorial.
Layering means encapsulation user data http appl. header tcp header HTML application data tcp TCP segment ip ip header IP datagramm Ethernet ip header 14 bytes 20 bytes tcp header appl. header user data 802.2 20 bytes Ethernet frame 64 - 1500 bytes WLAN-IEEE802.11 Tutorial (Maximilian Riegel), 021018-wlan-tutorial.
IEEE802.11 - seamless integration into the Internet W3C KWPO [PO [VO VPLO www +773 )73 6073 0 8$ 1)6 7&3 6&73 '16 6103 8'3 ,3 333 IETF ITU ETSI ATMF ,6'1 $70 6'+ *60 WLAN-IEEE802.11 Tutorial (Maximilian Riegel), 021018-wlan-tutorial.
IP based network architecture 193.175.26.92 www http N-DATA.request tcp ip link phy 131.34.3.35 N-DATA ip link phy ip link phy N-DATA ip link phy ip = connectionless, non-reliable, end-to-end, packet-oriented data delivery service WLAN-IEEE802.11 Tutorial (Maximilian Riegel), 021018-wlan-tutorial.
Wireless LAN IEEE802.11 basic architecture local distribution network Netscape http tcp ip 802.2 ppp Bluetooth 802.2 802.3 ip 802.2 802.2 802.3 802.3 internet apache http tcp ip 802.2 ppp Bluetooth 802.3 IEEE802.11 Client Access Point WLAN-IEEE802.11 Tutorial (Maximilian Riegel), 021018-wlan-tutorial.
What is unique about wireless? n Difficult media – interference and noise – quality varies over space and time – shared with “unwanted” 802.
Part 2: IEEE802.11 Overview n n n n n Wireless IEEE802.11 Standard IEEE802.11 Configurations IEEE802.11 Architecture Overview IEEE802.11 Protocol Architecture Wireless LAN Standardization WLAN-IEEE802.11 Tutorial (Maximilian Riegel), 021018-wlan-tutorial.
Wireless IEEE802.11 Standard n Operation in the 2.4GHz ISM band – North America: FCC part 15.247-15.249 – Europe: ETS 300 - 328 – Japan: RCR - STD-33A Approved June 1997 n Supports three PHY layer types: DSSS, FHSS, Infrared n MAC layer common to all 3 PHY layers n Robust against interference n Provides reliable, efficient wireless data networking n Supports peer-to-peer and infrastructure configurations n High data rate extension IEEE802.11b with 11 Mbps using existing MAC layer 802.
IEEE802.11 Configurations n Independent – one “Basic Service Set”, BSS – “Ad Hoc” network – direct communication – limited coverage area Station AH2 Station AH3 Ad Hoc Network Station AH1 n Infrastructure – Access Points and stations – Distribution System interconnects Multiple Cells via Access Points to form a single Network. Server DISTRIBUTION SYSTEM AP B AP A • extends wireless coverage area BSS-B Station A1 Station B2 BSS-A WLAN-IEEE802.11 Tutorial (Maximilian Riegel), 021018-wlan-tutorial.
IEEE802.
IEEE802.11 Protocol Architecture n Station Management – interacts with both MAC Management and PHY Management n MAC Layer Management Entity – power management – handover – MAC MIB LLC = 802.
Wireless LAN Standardization WIG IEEE 802.11 Wireless Interworking Group 802.11f: Inter Access Point Protocol ETSI BRAN 8076 ,QWHJUDWLRQ 802.11e: 4R6 (QKDQFHPHQWV 0$& 802.11i: 6HFXULW\ (QKDQFHPHQWV HiperLAN/2 IEEE 802.11 802.11h DFS & TPC 3+< 802.11a 5 GHz 54Mbit/s DFS & TPC 802.11g 802.11b 2,4 GHz 2,4 GHz 2,4 GHz 54Mbit/s 11Mbit/s 2 Mbit/s 5 GHz 54 Mbit/s Current standardization topics WLAN-IEEE802.11 Tutorial (Maximilian Riegel), 021018-wlan-tutorial.
Part 3: Physical layer n n n n n n n n n n n IEEE802.11 2.4 GHz & 5 GHz Physical Layers Frequency Hopping Spread Spectrum Direct Sequence Spread Spectrum DSSS Transmit Spectrum and Channels IEEE802.11a 5GHz PHY Layer IEEE802.11g: Further Speed Extension for the 2.4 GHz Band Spectrum Designation in the 5GHz range IEEE802.11h: Spectrum and Transmit Power Management ... when will 5 GHz WLANs come? PHY Terminology Physical Layer Convergence Protocol (PLCP) WLAN-IEEE802.
IEEE802.11 2.4 GHz & 5 GHz Physical Layers n Baseband IR, 1 and 2Mbps, 16-PPM and 4-PPM Frequency n 2.4 GHz Frequency Hopping Spread Spectrum – 2/4 FSK with 1/2 Mbps – 79 non overlapping frequencies of 1 MHz width (US) Frequency n 2.4 GHz High Rate DSSS Ext. (802.11b) – CCK/DQPSK with 5.5/11 Mbps WLAN-IEEE802.11 Tutorial (Maximilian Riegel), 021018-wlan-tutorial.ppt Frequency Power n 5 GHz OFDM PHY (802.
AMPLITUDE Frequency Hopping Spread Spectrum f5 f4 f3 FREQUENCY f2 f1 1 2 3 4 5 6 7 8 9 10 11 12 TIME n n n n 2.4GHz band is 83.
Direct Sequence Spread Spectrum RF Energy is Spread by XOR of Data with PRN Sequence 1 0 Data 1 bit period Out 11 Bit Barker Code (PRN*) 1011011100010110111000 0100100011110110111000 11 chips 11 chips 1 bit period PRN * PRN: Pseudorandom Number Signal Spectrum Transmitter baseband signal before spreading Transmitter baseband signal after spreading , Receiver baseband signal before matched filter (Correlator) Receiver baseband signal after matched filter (De-spread) © Siemens, 2002
DSSS Transmit Spectrum and Channels Transmit Spectrum Mask Unfiltered Sinx/x 0 dBr -30 dBr -50 dBr fc -22 MHz fc -11 MHz fc fc +11 MHz fc +22 Mhz &DQQHO WLAN-IEEE802.11 Tutorial (Maximilian Riegel), 021018-wlan-tutorial.
IEEE802.11a 5GHz PHY Layer n Specifications – Modulation type OFDM – Data rates: 6, 12, 18, 24, 36, 48, 54Mbps – 48 sub-carriers – Sub-carrier modulation: BPSK, QPSK, 16QAM, 64QAM – Bit interleaved convolutional coding, K=7, R=1/2, 2/3, 3/4 – OFDM frame duration: 4µs guard interval: 0.
IEEE802.11g: Further Speed Extension for the 2.4GHz Band n Mandatory: n Optional: n Optional: CCK w/ short preample (802.11b) and OFDM (802.11a applied to 2.4 GHz range). PBCC proposal for 22 Mbit/s from Texas Instruments CCK-OFDM proposal for up to 54 Mbit/s from Intersil Range vs. throughput rate comparison of n CCK (802.11b), n OFDM(“802.11a”), n PBCC, n CCK-OFDM (Batra, Shoemake; Texas Instruments; Doc: 11-01-286r2) WLAN-IEEE802.11 Tutorial (Maximilian Riegel), 021018-wlan-tutorial.
Spectrum Designation in the 5 GHz range -DSDQ 86$ ,QGRRU P: 2XWGRRU : (,53 (XURSH ')6 73& 0D[ SHDN 7[ SRZHU 2XWGRRU : (,53 ')6 73& ,QGRRU P: (,53 0D[ PHDQ 7[ SRZHU 2XWGRRU : (,53 ')6 '\QDPLF )UHTXHQF\ 6HOHFWLRQ 73& 7UDQVPLW 3RZHU &RQWURO )UHT *+] n Many European countries are currently opening the 5 GHz range for radio LANs.
IEEE802.11h: Spectrum and Transmit Power Management n TPC (Transmission Power Control) – supports interference minimisation, power consumption reduction, range control and link robustness.
… when will 5 GHz WLANs come? n IEEE802.11b (2.4 GHz) is now taking over the market. n There are developments to enhance IEEE802.11b for – more bandwidth (up to 54 Mbit/s) – QoS (despite many applications do not need QoS at all) – network issues (access control and handover). n 5 GHz systems will be used when the 2.4 GHz ISM band will become too overcrowded to provide sufficient service. – TCP/IP based applications are usually very resilient against ‘error proune’ networks.
PHY Terminology n FHSS n DSSS n OFDM Frequency Hoping Spread Spectrum Direct Sequence Spread Spectrum Orthogonal Frequency Division Multiplex n n n n n n n Pulse Position Modulation Gaussian Frequency Shift Keying Differential Binary Phase Shift Keying Differential Quadrature Phase Shift Keying Complementary Code Keying Packet Binary Convolutional Coding Quadrature Amplitude Modulation , PPM GFSK DBPSK DQPSK CCK PBCC QAM © Siemens, 2002
Physical Layer Convergence Protocol (PLCP) PLCP Protocol Data Unit n SYNC n n n n n SFD SIGNAL SERVICE LENGTH CRC (gain setting, energy detection, antenna selection, frequency offset compensation) (Start Frame Delimiter; bit synchronization) (rate indication; 1, 2, 5.5, 11 Mbit/s) (reserved for future use) (number of octets in PSDU) (CCITT CRC-16, protects signal, service, length field) WLAN-IEEE802.11 Tutorial (Maximilian Riegel), 021018-wlan-tutorial.
Part 4: Medium Access Control n n n n n n n n n n n Basic Access Protocol Features CSMA/CA Explained CSMA/CA + ACK protocol Distributed Coordination Function (DCF) „Hidden Node“ Provisions IEEE802.11e: MAC Enhancements for Quality of Service (EDCF) Point Coordination Function (PCF) IEEE802.11e: MAC Enhancements for Quality of Service (HCF) Frame Formats Address Field Description Summary: MAC Protocol Features WLAN-IEEE802.11 Tutorial (Maximilian Riegel), 021018-wlan-tutorial.
Basic Access Protocol Features n Use Distributed Coordination Function (DCF) for efficient medium sharing without overlap restrictions. – Use CSMA with Collision Avoidance derivative. – Based on Carrier Sense function in PHY called Clear Channel Assessment (CCA). n Robust for interference. – CSMA/CA + ACK for unicast frames, with MAC level recovery. – CSMA/CA for Broadcast frames. n Parameterized use of RTS / CTS to provide a Virtual Carrier Sense function to protect against Hidden Nodes.
CSMA/CA Explained IFS: Inter Frame Space Free access when medium is free longer than DIFS DIFS Contention Window PIFS DIFS Busy Medium SIFS Backoff-Window Next Frame Slot time 'HIHU $FFHVV 6HOHFW 6ORW DQG 'HFUHPHQW %DFNRII DV ORQJ DV PHGLXP LV LGOH n Reduce collision probability where mostly needed. – Stations are waiting for medium to become free. – Select Random Backoff after a Defer, resolving contention to avoid collisions. n Efficient Backoff algorithm stable at high loads.
CSMA/CA + ACK protocol DIFS Src Data SIFS Dest Ack Contention Window DIFS Next MPDU Other Defer Access Backoff after Defer n Defer access based on Carrier Sense. – CCA from PHY and Virtual Carrier Sense state. n Direct access when medium is sensed free longer then DIFS, otherwise defer and backoff. n Receiver of directed frames to return an ACK immediately when CRC correct. – When no ACK received then retransmit frame after a random backoff (up to maximum limit). WLAN-IEEE802.
Distributed Coordination Function (DCF) Station 1 Tx Data to STA 2 Short interval ensures ACK is sent while other stations wait longer ACK to STA1 Short deferral Station 2 Rx data from STA 1 STA 3’s back-off is shorter than STA 4’s therefore it begins transmission first Distributed inter-frame deferral Station 3Detects channel busy 'HWHFWV FKDQQHO EXV\ Distributed interframe deferral Random back-off Tx Data Distributed inter-frame deferral Station 4Detects channel busy , 'HWHFWV FKDQQHO EXV\
“Hidden Node” Provisions Problem – Stations contending for the medium do not Hear each other Solution – Optional use of the Duration field in RTS and CTS frames with AP CTS-Range STA “B” cannot receive data from STA “A” DIFS STA A AP RTS-Range STA “B” Access Point Data RTS CTS Ack STA “B” cannot detect carrier from STA “A” STA B , STA“A” Time period to defer access is based on duration in CTS Next MPDU Back off after defer © Siemens, 2002
IEEE802.
Point Coordination Function (PCF) CFP repetition interval Contention Period Contention Free Period Access Point Stations Beacon D1+Poll D2+Poll U1+ACK CF end U2+ACK n Optional PCF mode provides alternating contention free and contention operation under the control of the access point n The access point polls stations for data during contention free period n Network Allocation Vector (NAV) defers the contention traffic until reset by the last PCF transfer n PCF and DCF networks will defer to each other
IEEE802.
Frame Formats 802.11 MAC Header Bytes: 2 2 6 6 Frame Duration Addr 1 Control ID Bits: 2 2 Protocol Type Version 4 SubType Addr 2 1 To DS 6 2 6HTXHQFH Addr 4 &RQWURO Addr 3 1 1 From DS More Frag 6 1 Retry 0-2312 4 Frame Body CRC 1 1 1 1 Pwr Mgt More Data WEP Rsvd n MAC Header format differs per Type: – Control Frames (several fields are omitted) – Management Frames – Data Frames n Includes Sequence Control Field for filtering of duplicate caused by ACK mechanism.
Address Field Description To DS 0 0 1 1 From DS 0 1 0 1 Address 1 DA DA BSSID RA Address 2 SA BSSID SA TA Address 3 BSSID SA DA DA Address 4 N/A N/A N/A SA n Addr 1 = All stations filter on this address. n Addr 2 = Transmitter Address (TA) – Identifies transmitter to address the ACK frame to. n Addr 3 = Dependent on To and From DS bits. n Addr 4 = Only needed to identify the original source of WDS (Wireless Distribution System) frames. WLAN-IEEE802.
Summary: MAC Protocol Features n Distributed Coordination Function (DCF) provides efficient medium sharing – Use Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) – MAC uses the PHY layer Clear Channel Assessment (CCA) function for CSMA/CA n Robust for interference – CSMA/CA + ACK for unicast frames, with MAC level recovery – CSMA/CA for broadcast frames n n n n , Virtual carrier sense function provided to protect against hidden nodes Includes fragmentation to cope with different PHY charac
Part 5: MAC layer management n n n n n n n n Infrastructure Beacon Generation Timing Synchronization Function Scanning Active Scanning Example Power Management Considerations Power Management Approach Power Management Procedure MAC Management Frames WLAN-IEEE802.11 Tutorial (Maximilian Riegel), 021018-wlan-tutorial.
Infrastructure Beacon Generation Beacon Interval "Actual time" stamp in Beacon Time Axis X X X X Beacon Busy Medium n APs send Beacons in infrastructure networks. n Beacons scheduled at Beacon Interval. n Transmission may be delayed by CSMA deferral. – subsequent transmissions at expected Beacon Interval – not relative to last Beacon transmission – next Beacon sent at Target Beacon Transmission Time n Timestamp contains timer value at transmit time. WLAN-IEEE802.
Timing Synchronization Function (TSF) n All stations maintain a local timer.
Scanning n Scanning required for many functions. – finding and joining a network – finding a new AP while roaming – initializing an Independent BSS (ad hoc) network n 802.11 MAC uses a common mechanism for all PHY. – single or multi channel – passive or active scanning n Passive Scanning – Find networks simply by listening for Beacons n Active Scanning – On each channel • Send a Probe, Wait for a Probe Response n Beacon or Probe Response contains information necessary to join new network. WLAN-IEEE802.
Active Scanning Example n Initial connection to an Access Point – Reassociation follows a similar process Steps to Association: Access Point A Access Point C Station sends Probe. APs send Probe Response. Station selects best AP. Station sends Association Request to selected AP. AP sends Association Response. WLAN-IEEE802.11 Tutorial (Maximilian Riegel), 021018-wlan-tutorial.
Power Management Considerations n Mobile devices are battery powered. – Power Management is important for mobility. n Current LAN protocols assume stations are always ready to receive. – Idle receive state dominates LAN adapter power consumption over time. n How can we power off during idle periods, yet maintain an active session? n 802.
Power Management Approach n Allow idle stations to go to sleep – station’s power save mode stored in AP n APs buffer packets for sleeping stations.
Power Management Procedure TIM-Interval DTIM interval Time-axis TIM Busy Medium DTIM TIM AP activity TIM TIM DTIM Broadcast Broadcast PS Station PS-Poll Tx operation n Stations wake up prior to an expected DTIM (Delivery Traffic Indication Message). n If TIM indicates frame buffered – station sends PS-Poll and stays awake to receive data – else station sleeps again n Broadcast frames are also buffered in AP. – all broadcasts/multicasts are buffered – broadcasts/multicasts are only sent after DTIM.
MAC Management Frames n Beacon – Timestamp, Beacon Interval, Capabilities, ESSID, Supported Rates, parameters – Traffic Indication Map n Probe – ESSID, Capabilities, Supported Rates n Probe Response – Timestamp, Beacon Interval, Capabilities, ESSID, Supported Rates, pars – same for Beacon except for TIM n Association Request – Capability, Listen Interval, ESSID, Supported Rates n Association Response – Capability, Status Code, Station ID, Supported Rates n Reassociation Request – Capability, Listen Int
Part 6: WLAN Mobility n n n n IEEE802.11 Ad Hoc Mode IEEE802.11 Infrastructure Mode Mobility inside a WLAN ‚hotspot‘ by link layer functions... IEEE802.11f: Inter-Access Point Protocol (IAPP) WLAN-IEEE802.11 Tutorial (Maximilian Riegel), 021018-wlan-tutorial.
IEEE802.11 Ad Hoc Mode Peer-to-Peer Network n Independent networking – Use Distributed Coordination Function (DCF) – Forms a Basic Service Set (BSS) – Direct communication between stations – Coverage area limited by the range of individual stations WLAN-IEEE802.11 Tutorial (Maximilian Riegel), 021018-wlan-tutorial.
IEEE802.11 Infrastructure Mode Distribution System (DS) Server BSS-A BSS-B n Access Points (AP) and stations (STA) n BSS (Basic Service Set): a set of stations controlled by a single coordination function n Distribution system interconnects multiple cells via access points to form a single network n Extends wireless coverage area and enables roaming WLAN-IEEE802.11 Tutorial (Maximilian Riegel), 021018-wlan-tutorial.
Mobility inside a WLAN ‘hotspot’ by link layer functions...
IEEE802.11f: Inter-Access Point Protocol (IAPP) n IAPP defines procedures for – context transfer between APs when stations move – automatic configuration handling of access points 5$',86 6HUYHU Distribution System ,$33 $'' WLAN-IEEE802.11 Tutorial (Maximilian Riegel), 021018-wlan-tutorial.
Part 7: WLAN security n n n n n n n IEEE802.11 Privacy and Access Control WEP privacy mechanism Shared key authentication Shortcomings of plain WEP security IEEE802.11i: Robust Security Network (RSN) A last word about WLAN security: Summary: MAC Functionality WLAN-IEEE802.11 Tutorial (Maximilian Riegel), 021018-wlan-tutorial.
IEEE802.11 Privacy and Access Control n Goal of 802.11 was to provide “Wired Equivalent Privacy” (WEP) – Usable worldwide n 802.11 provides for an authentication mechanism – To aid in access control. – Has provisions for “OPEN”, “Shared Key” or proprietary authentication extensions. n Shared key authentication is based on WEP privacy mechanism – Limited for station-to-station traffic, so not “end to end”. – Uses RC4 algorithm based on: • a 40 bit secret key • and a 24 bit IV that is send with the data.
WEP privacy mechanism 6HFUHW .H\ ,9 6HFUHW .H\ ,9 :(3 351* 7; + 3ODLQWH[W ,9 &LSKHUWH[W :(3 351* 3ODLQWH[W + &LSKHUWH[W ,QWHJULW\ $OJRULWKP ,QWHJULW\ $OJRULWKP ,&9 ,&9 3UHDPEOH 3/&3 +HDGHU 0$& +HDGHU ,9 . ,' 3D\ORDG (QFU\SWHG &\SKHUWH[W ,&9 ,&9" &5& ,&9 n WEP bit in Frame Control Field indicates WEP used. – Each frame can have a new IV, or IV can be reused for a limited time. WLAN-IEEE802.11 Tutorial (Maximilian Riegel), 021018-wlan-tutorial.
Shared key authentication Station 6WDWLRQ VHQGV DXWKHQWLFDWLRQ UHTXHVW Access Point $3 VHQGV FKDOOHQJH WH[W JHQHUDWHG ZLWK WKH :(3 DOJRULWKP 6WDWLRQ HQFU\SWV FKDOOHQJH WH[W DQG VHQGV LW WR WKH $3 Secret Key Loaded Locally $3 GHFU\SWV WKH HQFU\SWHG FKDOOHQJH WH[W $XWKHQWLFDWLRQ VXFFHVVIXO LI WH[W PDWFKHV RULJLQDO Secret Key Loaded Locally n Shared key authentication requires WEP n Key exchange is not specified by IEEE802.
Shortcomings of plain WEP security n WEP unsecure at any key length – IV space too small, lack of IV replay protection – known plaintext attacks n No user authentication – Only NICs are authenticated n No mutual authentication – Only station is authenticated against access point n Missing key management protocol – No standardized way to change keys on the fly – Difficult to manage per-user keys for larger groups n WEP is no mean to provide security for WLAN access, – … but might be sufficient for casual use
IEEE802.11i: Robust Security Network (RSN) Additional enhancement to existing IEEE802.11 functions: n Data privacy mechanism: – TKIP (Temporal Key Integrity Protocol) to enhance RC4-based hardware for higher security requirements, or – WRAP (Wireless Robust Authenticated Protocol) based on AES (Advanced Encryption Standard) and OCB (Offset Codebook) n Security association management: – RSN negotiation procedures for establishing the security context – IEEE802.
A last word about WLAN security: n Even IEEE802.11i may not be sufficient for public hot-spots: Netscape http tcp IPSEC, TLS, SSL ip ip 802.2 ppp 802.2 802.2 802.2 802.11 WEP 802.3 802.3 802.3 apache http tcp ip 802.2 ppp Bluetooth 802.3 n Only VPN technologies (IPSEC, TLS, SSL) will fulfil end-to-end security requirements in public environments. n VPN technologies might even be used in corporate WLAN networks. WLAN-IEEE802.11 Tutorial (Maximilian Riegel), 021018-wlan-tutorial.
Summary: MAC Functionality n Independent and Infrastructure configuration support – Each BSS has a unique 48 bit address – Each ESS has a variable length address n CSMA with collision avoidance – – – – MAC-level acknowledgment allows for RTS/CTS exchanges (hidden node protection) MSDU fragmentation “Point Coordination” option (AP polling) n Association and Reassociation – station scans for APs, association handshakes – Roaming support within an ESS n Power management support – stations may power thems
Part 8: Public hotspot operation n n n n n n n Serving customers in public hot spots... One solution for every place (hotspot) Becoming a WLAN operator is easy. Selling WLAN access in public hot-spots: Probably to consider...
Serving customers in public hot spots... Office Hospital Congress hall, Hotel Railway Station á Airport Campus WLAN-IEEE802.11 Tutorial (Maximilian Riegel), 021018-wlan-tutorial.
One solution for every place (hotspot) n There is a wide variety of notebooks each having more or less its unique configuration. n Only a very common dominator can be assumed for the software installations available on all notebooks. Office Railway Station Airport Hospital Congress hall, Hotel Semi-public WLAN Public WLAN Office Corporate WLAN Plant Remote Access Home WLAN Campus n Most WLAN-enabled notebooks will use DHCP for basic IP configuration.
Becoming a WLAN operator is easy. n Legal aspects (in Germany): – Usage of license free spectrum (2,4 GHz ISM band) – No telecommunication license necessary, as long as • not providing telephony services, • not providing network access across borders of private premises. n Cost issues: – The lower bound: Investment: WLAN Access Point /w DSL Router (~ 350 ¼ Monthly operation cost: ~ 60 ¼ IRU '6/ )ODW 5DWH – Most commercial installations are much more expensive due to charging and billing.
Selling WLAN access in public hot-spots: Probably to consider … n How does your favorite storefront look like? Too much security might hinder your business! WLAN-IEEE802.11 Tutorial (Maximilian Riegel), 021018-wlan-tutorial.
Using a web page for initial user interaction Free local content services Authentication for Internet access Selection of billing method WLAN-IEEE802.11 Tutorial (Maximilian Riegel), 021018-wlan-tutorial.
How does it work: Web based access control html Username: max.riegel Password: ********** RADIUS client auth auth '+&3 6HUYHU 0RELOH &OLHQW $$$ 6HUYHU $FFHVV *DWHZD\ WLAN-IEEE802.11 Tutorial (Maximilian Riegel), 021018-wlan-tutorial.
Web based access control: Enabler for mCommerce and location based services n Puting a mCommerce application into a web-page for WLAN access control enables further services to be billed. => there is far more business for the operator than just WLAN access n Due to its limited coverage services delivered by WLAN in hot-spots can easily tailored to their locations. => Operators can start with location based services without huge investments for full geographic coverage. WLAN-IEEE802.
Functions of an integrated access gateway (User management) n Authentication via secure (HTTPS) web-based GUI for registered and unknown users based on – External database, supports ISP roaming via RADIUS – Integrated LDAP directory – GSM phone (Transmission of one-time passwords by SMS) – Credit card n Authorization based on user profiles assigned to different user groups having particular access – Dynamic subscribtion to additional services – Personalized portal page n Real-time accounting based on servic
Functions of an integrated access gateway (Network services) n DHCP server for assigning IP addresses to WLAN clients – Retaining session if user is temporarily out of WLAN coverage – Detection of session end n Policy engine – Loadable user profiles – User-specific routing configuration – Dynamic firewalling rules n IP router with NAT engine – Assignment of private addresses for free services – Must allow IPSEC connections WLAN-IEEE802.11 Tutorial (Maximilian Riegel), 021018-wlan-tutorial.
Part 9: WLAN – UMTS Interworking n n n n n n n n n UMTS and Wireless LAN are different WLAN – UMTS Interworking: Ancient approach: ‚tight coupling‘ WLAN as an exension of a mobile network WLAN is much cheaper than 2G/3G Conclusions for Mobile Network Operators WLAN – UMTS Interworking: Now widely accepted: ‚loose coupling‘ WLAN loosely coupled to a Mobile Network E.g.: Web based authentication and mobile network security Standards for WLAN – UMTS Interworking WLAN-IEEE802.
UMTS and Wireless LAN are different. GSM/GPRS/UMTS n n n n n n n n anytime / everywhere voice, realtime messaging QoS precious bandwidth carrier grade operator driven huge customer base high revenues WLAN IEEE802.11 n n n n n n n n sometimes / somewhere standard web applications best effort cheap bandwidth corporate technology market driven casual users low revenues WLAN-IEEE802.11 Tutorial (Maximilian Riegel), 021018-wlan-tutorial.
WLAN – UMTS Interworking: Ancient approach: ‘tight coupling’ BTS MSCS MSCS TDM / ATM / IP BTS BSC HSS Node B PLMN access PSTN SCPLNP IN PLMN core RNC Node B AUC VLR SGSN GGS N internet wlan local access network WLAN as just another radio access technology of UMTS n All UMTS services become available over WLAN. but: n PLMN is burdened with high bandwidth WLAN traffic. n Wi-Fi does not provide all the functionality needed (QoS, security). WLAN-IEEE802.
WLAN as an extension of a mobile network tight coupling AP WLAN-IEEE802.11 Tutorial (Maximilian Riegel), 021018-wlan-tutorial.ppt n WLAN just as another radio access technology n MNOs are the WLAN operators – OA&M – agreement with siteowner – very dense PLMN n Full competition with open ISP market. n Mobile network is carrier of the WLAN traffic. n Dynamics of growth may differ.
WLAN is much cheaper than 2G/3G Transfer cost/duration of an 1 Mbytes .ppt/.doc/.xls File... ORJDULWKPLF VFDOH ¼ 7UDQVIHU &RVW >¼@ Duration [min] 4 min 4 min 5 sec -99,6% * *356 *60 +6&6' :/$1 *356 *60 +6&6' :/$1 based on current IP volume prices of 40¼ *%\WH Time based pricing results in similar costs, e.g. MobileStar Pulsar pricing plan: $0,10/min WLAN-IEEE802.11 Tutorial (Maximilian Riegel), 021018-wlan-tutorial.
Conclusions for Mobile Network Operators When you can’t stop them, when you can’t beat them, then you should join them. n The most complicated and appealing task of a WLAN operator is charging and billing. n MNOs have large customer bases, secure authentication and accounting facilities and they like to go into mobile business. n Providing electronic payment services to WLAN operators can be an important market entry into mobile business for MNOs.
WLAN – UMTS Interworking: Now widely accepted: ‘loose coupling’ Siemens contributed ‚loose coupling‘ to standardization. BTS MSCS MSCS TDM / ATM / IP BTS BSC HSS Node B PLMN access PSTN SCPLNP IN PLMN core RNC Node B AUC VLR SGSN Authentication Accounting internet wlan local access network Only Authentication, Authorization and Accounting of WLAN access is performed by the mobile network operator. n Revenues without competing against aggressive WLAN operators.
WLAN loosely coupled to a Mobile Network loose coupling (SIM) loose coupling (RADIUS) HLR SGSN HLR RADIUS SIM n Each hotspot is SS7 endpoint – SIM cards required – SGSN or MSC functionality at access network WLAN-IEEE802.11 Tutorial (Maximilian Riegel), 021018-wlan-tutorial.
E.g.: Web based authentication and mobile network security SMS containing Password html Username: 0172-3456789 Password: ********** RADIUS client auth auth '+&3 6HUYHU 0RELOH &OLHQW WLAN-IEEE802.11 Tutorial (Maximilian Riegel), 021018-wlan-tutorial.
Standards for WLAN/UMTS interworking n 3GPP – R5: SA1 Requirements of 3GPP system – WLAN interworking. – R6: SA2 Continuation with architectural considerations n ETSI BRAN Subgroup on “Interworking between HiperLAN/2 and 3rd generation cellular and other public systems”. – Detailed architectural description mainly based on the Siemens ‘loose coupling’ principle established – IEEE802.11 and MMAC are now joining this effort. => Wireless Interworking Group (WIG).
The end n Thank you for your attention. n Questions and comments? Maximilian Riegel (maximilian.riegel@icn.siemens.de) Literature: n The IEEE 802.11 Handbook – A Designer‘s Companion Bob O‘Hara, Al Patrick; IEEE press, ISBN 0-7381-1855-9 n 802.11 Wireless Networks – The Definitive Guide Matthew S. Gast; O‘ Reilly, ISBN 0-596-00183-5 WLAN-IEEE802.11 Tutorial (Maximilian Riegel), 021018-wlan-tutorial.
