network issues for hybrid ad hoc mobile computer networks tzu-chieh tsai, associate professor...
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Network Issues for Hybrid Ad Network Issues for Hybrid Ad Hoc Mobile Computer NetworksHoc Mobile Computer Networks
Tzu-Chieh Tsai, Associate Professor ([email protected])
Department of Computer Science
National Chengchi University
Taipei, Taiwan
OutlineOutline• 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
IntroductionIntroduction
• 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
IntroductionIntroduction
• 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 A Real Mobile Information SystemSystem
• Goal: design and implement a mobile information system
• Support real-time, multimedia traffic
• with capability:– instant deployed infrastructure– internet access
Network ComponentsNetwork 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 ExamplesMPIS 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 ArchitectureMPIS Architecture
MPIS AttributesMPIS 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 IssuesNetwork Issues
• Multihop Architecture Control
• Channel Access
• QoS, Multimedia Support
• Routing
• Roaming and Mobile IP
Other MPIS IssuesOther MPIS Issues
• Query and reply while an unstable, low-speed wireless connection is concerned
• data replicate
• security and authentication
• mobile agent management
Network Issues Network Issues (Multihop Architecture Control) (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 IssuesNetwork Issues(Location Tracking Algorithm)(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 IssuesMPIS Issues(Channel Access)(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
Cellular ConceptCellular 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 ReuseCellular Frequency Reuse
CDPD (Cellular Digital Packet CDPD (Cellular Digital Packet Data)Data)• Based on traffic engineering fact
• 19.2 Kbps
• connectionless service
Why we choose CDPD as our Why we choose CDPD as our mobile data network?mobile data network?
• Currently, only CDPD is available in Taiwan
• Support IP internet access
• packet switching
GSM GPRSGSM 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-2000IMT-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 802.11: infrastructure IEEE 802.11: infrastructure networknetwork
IEEE 802.11: MACIEEE 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)
IEEE 802.11: MAC ArchitectureIEEE 802.11: MAC Architecture
IEEE 802.11: DCF w/o RTS/CTSIEEE 802.11: DCF w/o RTS/CTS
Hidden Terminal ProblemHidden Terminal Problem
data “hidden” to A
A B C
IEEE 802.11:DCF w/ RTS/CTSIEEE 802.11:DCF w/ RTS/CTS CSMA/CA (Collision Avoidance) CSMA/CA (Collision Avoidance)
IEEE 802.11: PCFIEEE 802.11: PCF
• Connection-oriented
• provide contention-free frame transfer
IEEE 802.11: PCFIEEE 802.11: PCF
Network IssuesNetwork Issues(QoS & Multimedia Support)(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
Multimedia SupportMultimedia Support
• Different applications need different QoS==> different protocol design
• Difficulty:– control– dynamic: traffic, network resource, mobility– negotiate QoS, admission control
Network IssuesNetwork Issues(Routing)(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) 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 ExampleQoS Routing Example
• Bandwidth calculation is difficult and dynamic
MPIS: MG bandwidth MPIS: MG bandwidth managementmanagement
• 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
Network IssuesNetwork Issues(Roaming and Mobile IP)(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
Mobile IP ConceptMobile 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 ConceptMobile 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 ConceptMobile IP Concept
Mobile IP ConceptMobile 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 HandoffSmooth Handoff
MPIS ImplementationMPIS 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 NDISWindows NDIS
TCP/IPapp.
Multi-hop
MG
internet
Windows VxD approachWindows 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 approachWindows Sygate approach
• Sygate Proxy concept
remote client relay client MG
telnet, http, ftp internet
• Disadvantage: not dynamic!
Windows winsock approachWindows 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
LinuxLinux
• 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
Current StatusCurrent 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 StatusCurrent Status
• Roaming will be tested
• Query application programs will be integrated
ConclusionsConclusions
• 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
ConclusionsConclusions
• Implementation– location tracking algorithms– Windows
• NDIS, VxD• Proxy• Winsock
– Linux• ‘bridge’ relay• MG: IP encapsulation, Mobile IP
Questions?Questions?