Network Issues for Hybrid Ad Hoc Mobile Computer Networks Tzu-Chieh Tsai, Associate Professor Department of Computer Science National Chengchi University Taipei, Taiwan

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

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 , HIPERLAN –b/w  data rate  error rate 

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

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

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)

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

MPIS Architecture

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

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

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

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: C B A MGIP Seq # (timestamp) Hop = 1 Register node = MG Relay nodes for x, y, z (timestamp) a b x y z hop = 2 register node = A

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”

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 Standards –time-bounded service vs. datagram service

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

Cellular Frequency Reuse

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

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

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

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

IEEE : infrastructure network

IEEE : 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)

IEEE : MAC Architecture

IEEE : DCF w/o RTS/CTS

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

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

IEEE : PCF Connection-oriented provide contention-free frame transfer

IEEE : PCF

Network Issues (QoS & Multimedia Support) Traffic Type: –datagram (e.g. , 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

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

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

Network Issues (Routing) Record: (timestamp) A MG send: hello  MGIP+Seq # +hop number x, y, z register Record: C B A MGIP Seq # (timestamp) Hop = 1 Register node = MG Relay nodes for x, y, z (timestamp) a b x y z hop = 2 register node = A

QoS Routing Example Bandwidth calculation is difficult and dynamic

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

Network Issues (Roaming and Mobile IP) IEEE 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

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

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

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

Smooth Handoff

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

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

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

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

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

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:

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

Current Status Roaming will be tested Query application programs will be integrated

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

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

Questions?