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Network Issues for Hybrid Ad Hoc Mobile Computer Networks

Network Issues for Hybrid Ad Hoc Mobile Computer Networks. Tzu-Chieh Tsai, Associate Professor (ttsai@cs.nccu.edu.tw) Department of Computer Science National Chengchi University Taipei, Taiwan. Outline. Hybrid Ad Hoc Mobile Computer Networks Disaster recovery or battle field

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Network Issues for Hybrid Ad Hoc Mobile Computer Networks

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  1. Network Issues for Hybrid Ad Hoc Mobile Computer Networks Tzu-Chieh Tsai, Associate Professor (ttsai@cs.nccu.edu.tw) Department of Computer Science National Chengchi University Taipei, Taiwan

  2. Outline • Hybrid Ad Hoc Mobile Computer Networks • Disaster recovery or battle field • Mobile Police Information System (MPIS) • Network Issues • MAC (Medium Access Control) • QoS (Quality of Service) • internet access • Our work + other works can be applied to MPIS • Implementation

  3. Introduction • Wireless/Mobile communication world is coming • information retrieval and two-way communication at any time, at any place • wireless network system: • voice: cellular phones, GSM • mobile data: CDPD(Cellular Digit Packet Data), GSM GPRS (General Packet Radio Service) • wireless LAN: IEEE 802.11, HIPERLAN • b/w  data rate  error rate 

  4. Introduction • Mobile computing: • multimedia: big challenge • QoS (Quality of Service): next-G telecom packet switching • security: EM wave can penetrate buildings • mobility: car speeds, network topology changing, control is dynamic

  5. A Real Mobile Information System • Goal: design and implement a mobile information system • Support real-time, multimedia traffic • with capability: • instant deployed infrastructure • internet access

  6. Network Components • Wireless LAN • free, no license (FCC regulations, spread spectrum) • 2 Mbps (will be upgraded to 10Mbps soon) • Mobile Data Network • CDPD (Cellular Digital Packet Data) technique 大通、義新 • expensive • 19.2 Kbps • coverage area (in the future, GSM GPRS or IMT-2000)

  7. MPIS Examples • Mobile Police Information System (MPIS) • integration of the above 2 network components • Examples • 110, 119: needs suspects’ pictures & information on the scene • Search: needs maps & keeps tracks of position (e.g. kidnapping) • Fire fighting: needs to know how dangerous (e.g. chemical factory) • On-line real-time query, consultation

  8. MPIS Architecture

  9. MPIS Attributes • Every policeman: equipped with a PDA that has multimedia capability (e.g. image, voice) • 2-level network architecture • Reason: • air-time is expensive • real-time vs. non-real-time • Advantages of Mobile Gateway (MG): • more mobility support • rapid deployment, mobile infrastructure • easy to management (compared to pure ad-hoc) • internet access

  10. Network Issues • Multihop Architecture Control • Channel Access • QoS, Multimedia Support • Routing • Roaming and Mobile IP

  11. Other MPIS Issues • Query and reply while an unstable, low-speed wireless connection is concerned • data replicate • security and authentication • mobile agent management

  12. Network Issues (Multihop Architecture Control) • MG: which mobile hosts are under its control • Mobile Hosts: which MG is nearest to it • Record: (timestamp) A MG send: hello MGIP+Seq # +hop number x, y, z register Record: CBA MGIP Seq # (timestamp) Hop = 1 Register node = MG Relay nodes for x, y, z (timestamp) abxyz hop = 2 register node = A

  13. Network Issues(Location Tracking Algorithm) • MG periodically sends out “hello” message (own IP, Sequence #, hop number distance to MG) • Node A,B,C receive “hello”: increase hop number by 1, update routing table and timestamp, then send out “register” message to MG • Node x, y, z receive “register”: update routing table, and repeat send “register”

  14. MPIS Issues(Channel Access) • Mobile Data Network for WAN • CDPD (Cellular Digital Packet Data) • Satellite • GSM GPRS (General Packet Radio Service) • IMT-2000 • Multihop Wireless LAN • IEEE 802.11 Standards • time-bounded service vs. datagram service

  15. Cellular Concept • Frequency Reuse • Channel Assignment Strategies • Handoff • Interference (SIR: Signal to Interference Ratio) • Power Control • QoS (Quality to Service) • uplink vs. downlink • control channel

  16. Cellular Frequency Reuse

  17. CDPD (Cellular Digital Packet Data) • Based on traffic engineering fact • 19.2 Kbps • connectionless service

  18. Why we choose CDPD as our mobile data network? • Currently, only CDPD is available in Taiwan • Support IP internet access • packet switching

  19. GSM GPRS • Provide packet data service over GSM infrastructure • 2 alternative approaches: • allocate specific GSM channels for packet transmission shared by all active packet subscribers • fast establishment of a GSM traffic channel on any radio resource available • Interworking with Public Switched Packet Data Networks and Internet

  20. IMT-2000 • Universal Mobile Telecommunications System (UMTS)/International Mobile Telecommunications (IMT-2000) • support 144kbps, preferably 384kbps for wide-area coverage(full mobility) and 2Mbps for local coverage(limited mobility) • 3rd Generation: W-CDMA, and/or TDMA • research is still going

  21. IEEE 802.11: infrastructure network

  22. IEEE 802.11: MAC • Contention Mode • All stations require to contend for access to the channel for each packet transmitted • Contention-free mode • During the contention-free period (CFP) • medium usage is controlled by the Access Point (AP)

  23. IEEE 802.11: MAC Architecture

  24. IEEE 802.11: DCF w/o RTS/CTS

  25. Hidden Terminal Problem data “hidden” to A A B C

  26. IEEE 802.11:DCF w/ RTS/CTS CSMA/CA (Collision Avoidance)

  27. IEEE 802.11: PCF • Connection-oriented • provide contention-free frame transfer

  28. IEEE 802.11: PCF

  29. Network Issues(QoS & Multimedia Support) • Traffic Type: • datagram (e.g. email, file transfer): packet switching • 100% correctness • can suffer longer delay • bursty • time-bound traffic (e.g. voice): circuit switching • delay is very sensitive • loss may be acceptance • connection-oriented

  30. Multimedia Support • Different applications need different QoS==> different protocol design • Difficulty: • control • dynamic: traffic, network resource, mobility • negotiate QoS, admission control

  31. Network Issues(Routing) • With help of location tracking algorithm • Minimum hop routing • Spatial reuse (QoS) routing (load balance) • Internet traffic: choose the nearest MG • Traffic inside an MG coverage area: • distributed Bellman-Ford minimum hop routing • MG source routing: traffic up to MG, then down to destination; or by request, get routing path from MG • complexity vs. delay tradeoff

  32. Network Issues (Routing) • Record: (timestamp) A MG send: hello MGIP+Seq # +hop number x, y, z register Record: CBA MGIP Seq # (timestamp) Hop = 1 Register node = MG Relay nodes for x, y, z (timestamp) abxyz hop = 2 register node = A

  33. QoS Routing Example • Bandwidth calculation is difficult and dynamic

  34. MPIS: MG bandwidth management • 2 MAC mechanisms to support QoS (bandwidth) for real time traffic • reservation-TDMA (or PRMA) • polling as in IEEE 802.11 PCF (with Access Point case) • MG: (synchronization) • collection bandwidth information (done along with location tracking algorithm) • slot scheduling, or polling frequency assignment

  35. Network Issues(Roaming and Mobile IP) • IEEE 802.11 compliant wireless network adapters support roaming inside the same subnet • IP availability: can use “psuedo” IP • MG has 2 IPs: • legal IP on WAN mobile data card • “psuedo” IP on WLAN card • MG encapsulate its mobile nodes’ “psuedo” IP with its legal IP • Mobile IP: • MGs can work as foreign agents

  36. Mobile IP Concept • Goal: mechanism to deliver datagrams to the mobile node when it is away from home network without changing its original IP (gain a new IP address) • Home Agent: a router on a mobile node’s home network • Foreign Agent: a router on a mobile node’s visited network, cooperates with home agent

  37. Mobile IP Concept • Home address vs. Care-of-address • Protocol Overview: • Agent Discovery: mobile agents periodically broadcast • Registration: mobile node registers its care-of-address with its home agent • tunneling: encapsulate home address with care-of-address

  38. Mobile IP Concept

  39. Mobile IP Concept • Triangular routing problem • Route optimization: • mobile node may send binding warning control message to home agent indicating a correspondent node unaware of care-of-address • Correspondent node may send a binding request • Home Agent sends an authenticated binding update containing mobile node’s care-of-address • smooth handoff: mobile node sends a binding update

  40. Smooth Handoff

  41. MPIS Implementation • Issues: • Multihop (WLAN cards have no such functions) • TCP/IP socket transparent (all TCP/IP applications transparent) • MG (handles 2 cards, internet access) • roaming • 2 platforms: • Windows • Linux

  42. Windows NDIS internet MG Multi- hop TCP/IP app.

  43. Windows VxD approach • VxD (Virtual Device Driver): rawether • interface to NDIS • capture all TCP/IP packets passing NDIS • works closely with device driver • provide limited functions unless obtaining device driver source code

  44. Windows Sygate approach • Sygate Proxy concept remote client relay client MG telnet, http, ftp internet • Disadvantage: not dynamic!

  45. Windows winsock approach • Provide a special winsock function along with multihop relay daemon • make a winsock connection to relay client first then relay client makes another winsock to MG • with help of routing path • disadvantage: for our own applications only, not for all TCP/IP applications • Other approach is still being searched

  46. Linux • Use ‘bridge’ to support multihop • provide an interface program • on-line change routing path, i.e. decide if needs to relay or not • use ‘IP Masquerade’ • support IP transparency through MG (between WLAN and internet) • Details: http://sparc1.cs.nccu.edu.tw/~s8427

  47. Current Status • Location tracking program • implemented on socket level (due to Windows NDIS difficulty) • will tightly work with multihop platforms for both Windows and Linux • Routing algorithm • currently, minimum hop routing • QoS regarding bandwidth allocation (scheduling) will be developed

  48. Current Status • Roaming will be tested • Query application programs will be integrated

  49. Conclusions • MPIS architecture is presented • Mobile data systems introduced: • CDPD, GPRS, IMT-2000 • WLAN MAC protocols introduced: • IEEE 802.11 • Multihop Architecture • QoS Routing • Mobile IP

  50. Conclusions • Implementation • location tracking algorithms • Windows • NDIS, VxD • Proxy • Winsock • Linux • ‘bridge’ relay • MG: IP encapsulation, Mobile IP

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