Wireless IP Marko Ovaska 1998

1. Wireless IPMarko Ovaska1998 Introduction to the Wireless IP Basic concepts MOWGLI WAP

2. Levels of analysis in this presentation • Products • Wireless local network • Markets • wireless LANs • Specifications, RFCs, draft specs • Wireless LAN: IEEE 802.11, (MobileIP), WAP, Mowgli • Protocols • MOWGLI, WAP protocols • Principles, Requirements • wireless environment

3. Wireless IP • Wireless environment • networks • mobility • Internet protocol in wireless environment • Non-tcp/ip solutions • Mowgli • WAP

4. Wireless Networking • Wireless networking is the basic obstacle to be solved for the mobile computing • Wireless media has different characteristics than the current wired networks • Data networking protocols are optimized for the current wired networks • The protocols are not efficient in the wireless environments • Wireless network can be categorized to: • Wireless LAN’s • IEEE 802.11 • Wireless WAN’s • GSM, GPRS, CDPD, CDMA, PHS, DoCoMo, Ricochet • Microcell • Bluetooth

5. Wireless Network • The wireless network properties differ from the wireline one • latency • 802.11: round-trip 2 ms • normal tcp buffer size: 8KB, some W-WAN’s latency*bandwidth exceeds this • GSM: 0.7 s with one byte packet • extra kilo adds round trip time 0.6 seconds per kilo • tcp throughput is related to latency: high latency, low throughput • interactive applications suffer from long latency times • jitter • error rate • non-transparency data connection in GSM offers less than 10-8 bit error rate • however this results in highly variable transmission delays • example: 10Mbs LAN has an average of below 10-9 bit error rate • throughput: wireless networks could be characterized "thin” • unexpected disconnections • will the underlying protocol support recovery?

6. Mobility • The mobile wireless networking architecture • a wireless mobile device (mobile node) • a wireless link • a base station (access point) • a wireline link and landline internet • Wireless mobile device • a laptop, cellular phone, personal communicator • different communication needs: office workstation vs cellular phone vs pager • transmission: packet data vs circuit switched • level of mobility • travels from home network to foreign network • full mobility, roaming from network to network • Wireless link can consist of several hops • Base station is an intermediating agent • connects the mobile device to wirelined world, acts as a proxy

7. Mobile node Internet (HER, MGBR) Wireless components

8. PSTN/ISDN, (PR) PC PC PC PC PC PC ACCESS ROUTER HUB/SWITCH HUB/SWITCH SWITCH/ROUTER (BOR,MRR) EDGE ROUTER (MRR, HER, MGBR) Internet (HER, MGBR) Typical IP network architecture ADSL GSM ACCESS SERVER Mobile node

9. Internet Protocol • Internet protocols are optimized for megabit per second wireline connections • Wireless networking solutions • unrelated to IP • WAP, Mowgli, SNOOP • solutions on the top of the IP • MobileIP, optimized IP and TCP, modified TCP • researched: • LEO and GEO satellite links • IP packets checksum might not be strong enough • PPP has 16-bit CRC • IP is end-to-end protocol • designed to operate in a rather homogenous network

10. IP cont. • Purely IP based wireless internet • Link layer enchangements: • forward error correction • retransmissions • improved error detection • MobileIP solves the addressing and routing problem • Path MTU discovery helps to set more optimized end-to-end • TCP might be heavy solution to tackle the wireless problem • lightweight mobile devices: communication needs versus protocol overhead • Compatibility is a strong need

11. TCP/IP cont. • TCP optimization • slow start termination/modification • how will the networks congestion propagate, if slow start is abandoned? • Increased initial sending window • TCP header compression • IP payload compression • some or most of the data is already compressed • files transferred over ftp, published pictures in web • fast retransmit and fast recovery • multiple ACKs notify the sender to adjust the send window and initiate fast retransmissions of the lost packet • scheduling in TCP • fairness: fair queuing, class-based queues • throughput

12. Wireless LAN • Wireless LAN specified in IEEE 802.11 spec • Guarantees multi hardware vendor interoperability • Main features: • Robust • Data acknowledgement, RTS/CTS, data fragmentation • Multi channel roaming. Allows multiple cells resulting in higher capasitity • Power management • Automatic rate selection from 1Mbps to 2Mbps • Security WEP (wired equivalent privacy)

13. Wireless LAN architecture • Cell consists of work stations and an access point • Access points are interconnected via distribution system (ethernet) • The interconnected network forms an extended service set • Portal connects different 802 based LAN’s

14. Medium access control layer DSSS PHY FHSS PHY IR PHY Wireless LAN architecture • MAC similar to IEEE 802.3 (Ethernet) • Offers common access to three physical layer interfaces • Direct Sequence Spread Spectrum • Frequency Hopping Spread Spectrum • Infrared

15. data ack Wireless LAN architecture • MAC features • message fragmentation • CSMA/CD with acknowledgement • less impact for lost messages • handles interference • exponential random backoff after successful sending, in collision and retransmission • RTS/CTS protocol • permission to send • DSSS physical layer features • 2 Mbps raw data rate with a fallback to 1 Mbps • 2.4 GHz band • US - 11 overlapping channels • ETS - 13 overlapping channels • Japan - 1 channel

16. Wireless LAN architecture • Station joins a cell • find a cell: beacon frame or active probe request • authentication • association • Wireless distribution system • wireless bridges • Automatic rate selection 1Mbps / 2Mbps • Multi channel roaming • Roaming from cell to cell: • not in the specification! • Synchronization • beacon frames • frequency hopping • power saving

17. Frame control Duration / ID Address 1 Address 2 Address 3 Sequence control Address 4 Frame body CRC Frame control Duration RA CRC Wireless LAN architecture • Frame formats • MAC frame • header 30 octets • data 0 to 2321 octets • crc 4 octets • ACK frame • header 10 octets • crc 4 octets

18. Wireless LAN, prices

19. MOWGLI • Mowgli is a research project to connect a mobile office workstation to the internet • University of Helsinki’s CS department • funding by Nokia, Digital, Sonera and Ministry of Education • The mobile node is connected via a wireless link to the internet/office network • the link is GSM non-transparent data connection • Architecture: • Mobile node • Wireless link • Mobile-Connection host (MCH) • Fixed host

20. Mowgli architecture

21. Mowgli • Mowgli preserves the socket interface • tcp/ip is replaced • socket interface is modified: wireless environment related extensions • Mowgli data channel service (MDCS) • bidirectional data channel • streamed and message channels (similar to tcp and udp) • 256 simultaneous channels • independent per channel flow control • priorities • handles disconnections • closing if idle, reconnections • The MDCS properties are Mowgli socket API’s QoS services

22. Mowgli performance • Measurements: • One 100 Kb file transferred, times in seconds • Three 100 Kb file transferred concurrently, times in seconds

23. Wireless Application Protocol • Wireless Application Protocol (WAP) is developed by WAP Forum • WAP Forum is multivendor • grounded by Ericsson, Motorola, Nokia and Unwired Planet • First WAP specification 1.0 was released April 1998 • the work groups carry on to include a broader representation • WAP is aimed to • bring Internet content to wireless mobile device • create a global wireless protocol specification to work across different networks • The WAP model resembles WWW-model

24. WAP Model • The WAP model resembles WWW-model • The WAP Gateway contains the protocol conversion services • gateway has internet protocol specific WAP proxies

25. WAP defines • WAP defines • micro-browser, similar to web browser • scripting (WMLScript), similar to JavaScript • telephony support • formalized interfaces for different content types • business cards, calendar events etc. • telecommunication stack • transport • security • session

26. WAP network

27. WAP architecture • The WAP protocol stack replaces tcp/ip in mobile devices • The WDP unifies the different bearer properties • WDP and the bearer networks handle roaming • WDP has bearer specific profiles • WTLS is similar to SSL • denial-of-service protection • WSP offers two interfaces • stream data (TCP) • datagram (UDP)

28. WAP: WDP • Two different WDP bearer specifications: • WDP over GSM circuit switched data connection

29. WAP: WDP cont. • WDP over GPRS

30. WAP: WTA • The WTA (wireless telephony application) allows telephony functionality in the mobile device • calling, incoming call, voice mail • WTA interface contains subspecifications for different networks • for example: GSM, PDC, IS-136 • Examples of the WTA interface: <WML> <FORM> <DO TYPE=“ACCEPT” TASK=”GO” URL=”wtai:cc/mc;$(N)”/> Enter phone number: <INPUT TYPE=”TEXT” KEY=”N”/> </FORM> </WML>

31. WAP: WTA <WML> <COMMON> <SCRIPT> function checkNumber(N) { if (Lang.isInt(N)) WTAI.makeCall(N); else Dialog.alert(“Bad phone number”); } </SCRIPT> </COMMON> <FORM> <DO TYPE=”ACCEPT” TASK=”GO” URL=”wtai:cc/mc;$(N)”/> Enter phone number: <INPUT TYPE=”TEXT” KEY=”N”/> </FORM> </WML>

32. Markets • The broadband future of online services and Internet access in Europe (Datamonitor, 1997)

33. Markets • Worldwide LAN switch market split by technology, 1995-2001 (Datamonitor, 07/97)

34. Markets