Transcript Network Issues and Implementation for a Mobile Information System

Network Issues for Hybrid Ad
Hoc Mobile Computer Networks
Tzu-Chieh Tsai, Associate Professor
([email protected])
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 802.11, 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 IMT2000)
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
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Multihop Architecture Control
Channel Access
QoS, Multimedia Support
Routing
Roaming and Mobile IP
Other MPIS Issues
• Query and reply while an unstable, lowspeed 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:
MG
(timestamp) A
send: hello MGIP+Seq # +hop number
x, y, z
register
C
B
A
Record:
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 802.11 Standards
– time-bounded service vs. datagram service
Cellular Concept
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•
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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 802.11: infrastructure
network
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)
IEEE 802.11: MAC Architecture
IEEE 802.11: DCF w/o RTS/CTS
Hidden Terminal Problem
data
A
B
“hidden” to A
C
IEEE 802.11:DCF w/ RTS/CTS
CSMA/CA (Collision Avoidance)
IEEE 802.11: PCF
• Connection-oriented
• provide contention-free frame transfer
IEEE 802.11: PCF
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
Multimedia Support
• Different applications need different
QoS==> different protocol design
• Difficulty:
– control
– dynamic: traffic, network resource, mobility
– negotiate QoS, admission control
Network Issues
(Routing)
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•
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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:
MG
(timestamp) A
send: hello MGIP+Seq # +hop number
x, y, z
register
C
B
A
Record:
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 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 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
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-ofaddress with its home agent
– tunneling: encapsulate home address with careof-address
Mobile IP Concept
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
internet
MG
Multi- TCP/IP
hop
app.
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
telnet, http, ftp
• Disadvantage: not dynamic!
MG
internet
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: http://sparc1.cs.nccu.edu.tw/~s8427
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 802.11
• 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?