Network Issues for Hybrid Ad Network Issues for Hybrid Ad Hoc Mobile Computer NetworksHoc Mobile Computer Networks

Tzu-Chieh Tsai, Associate Professor (ttsai@cs.nccu.edu.tw)

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?