VIRTUAL ROUTER Kien A. Hua Data Systems Lab School of EECS University of Central Florida

Outline Mobile Ad Hoc Networks Virtual Router Approach –Routing –Data Forwarding Cooperation Enforcement in Virtual Router Approach Simulation Results Conclusions 2

Wireline Communications Router S D Infrastructure Routers help forward data packets

What is Mobile Ad Hoc Network? →All nodes participate in the routing and data forwarding process. Source Node Destination Node Infrastructureless

Route Request Source Node Destination Node

Route Reply Source Node Destination Node

Data Transmission Source Node Destination Node The selected nodes participate in the data forwarding process

Link Break Source Node Destination Node

Issue Route Request Source Node Destination Node Selected New Route

Handling High Mobility Using Physical Nodes as Routers: Mobility → link breaks → reroute → overhead ! Using Virtual Routers: Virtual routers are stationary → links are robust → fewer reroute → less overhead ! Virtual Router S D S D

What is a Virtual Router ? A virtual router is a spatial area Physical nodes within this area alternate in forwarding data When a node leaves the area, it is no longer obliged to forward the data →Virtual router is stationary →More suitable for high mobility applications such as vehicular networks 11 Virtual Router S D X Y Z

Virtual Router – Example How to apply this concept to vehicular network ? Each cell is a virtual router Source Node Destination Node Each node has GPS & grid map

Street Environment: Mobility Model Streets constrain node mobility Nodes can pause and change direction at intersections. 13

Street Environment: Radio Range Buildings block radio signal → Often no link between nodes on different streets → Broadcast range is not a circle 14

Virtual Routers in Street Environment Streets are divided into small cells: –Each intersection is an intersection cell –A long road block can be divided into multiple block cells Radio range must cover any 2 consecutive cells Each cell is a virtual router 15

Vehicular Network Using Virtual Routers “Green” virtual routers form a connecting path between source and destination Data are transmitted from source to destination over these virtual routers 16 Source Destination

Location Discovery A source node broadcasts a Location Discovery (LD) packet This LD packet propagates until it reaches the destination node When the LD packet arrives at the destination, it replies with a Location Reply (LR) packet that includes the location of the destination router (i.e., destination cell). 17 Similar to standard route request Subsequently, every data packet carries the ID’s of the source and destination routers

Data Forwarding: Reference Line Every data packet carries the locations of Source and Destination Reference line (RL) is the straight line connecting the center of the source router and the center of the destination router 18

Data Forwarding: Reference Points Reference points (RP’s) are the intersections of the reference line and the streets 19

Data Forwarding: Forwarding Zones There is one forwarding zone for each reference point Three horizontal and two vertical forwarding zones in this example Some forwarding zones overlap The forwarding zones make up the grid path for data forwarding 20

Data Forwarding Virtual routers within the forwarding zones are selected for data forwarding When a node leaves the forwarding area, it is no longer obliged to forward data. If a node enters the forwarding area, this node must participate in the data forwarding. 21 How to do route maintenance

Connection Maintenance Destination node moves away from current router → Reference line changes → Reference points changes → Forwarding zones changes → Need a new connection path Route Maintenance: – The destination node periodically updates its location with the source node. – If this fails, source issues a location discovery packet 22 Essentially no overhead

Selfish and Malicious Behavior 23 Malicious Node It works as long as nodes cooperate Need cooperation enforcement !!

Cooperation Enforcement Step 1: Detect Malicious Node 24 Malicious node Malicious behavior detected

Cooperation Enforcement Step 2: Penalize Malicious Nodes 25 Malicious Node tries to establish connection by broadcasting Location Discovery packet radio range of malicious node Location Discovery packet is blocked by the building I know about the misbehavior No one will forward the Location Discovery packet for the malicious node.

Network Layer Structure 26

3C Module 27

3C Module - Overview It maintains three Counters: –Forward Request Counter: Number of forward requests (both discovery and data packets) received by a node. –Forward Counter: Number of packets forwarded by a node. –Location Discovery Counter: Number of Location Discovery packets initiated by a node (i.e., number of connections requested) It adds a 3C header which contains the values of these three counters to every Location Discovery packet. Based on this header, neighboring nodes analyze the behavior of the source node, and decide to forward or discard the packet (i.e., penalize the source node) 28

Misbehavior Detection: Overview 29 Add 3C header Examine 3C header for misbehavior Examine 3C header again before forwarding

Route Discovery Source node initiates Route Request packet Intermediate nodes forward the packet until it reaches the Destination node The Destination node receives the Route Request packet and sends back a Route Reply packet 30 SD Request Reply Let’s look at the operation at these nodes

Initiate Location Discovery 31 Routing Layer (Network) No Upper Layer Yes MAC Layer (Data Link) This is a new communication request This is a reroute request Add to Session Table Submit a route request

Routing Layer (Network) Receive Location Discovery 32 MAC Layer (Data Link) Yes No Yes No Yes No Yes MISBEHAVIOR DETECTION MODULE More on this module later… The forwarding node initiates this route request Penalize the requester Initiated by sender?

Routing Layer (Network) Forward Location Discovery (1) 33 Yes (Reply) No Yes No Yes No Yes (Forward) The Virtual Router has already forwarded the packet The route has been found

Forward Location Discovery (2) 34 Routing Layer (Network) Yes (Reply) Yes (Forward) MAC Layer (Data Link)

Network Attack: Sending Dummy Packets 35 Routing Layer (Network) No MAC Layer (Data Link) Generate & “forward” a dummy route request packet Flood the network with a dummy record

Data Transmission Source node transmits a data packet Intermediate nodes forward the packet until it reaches the Destination node 36 SD Data Let’s look at the data forwarding operation at a node

Receive Data Packet 37 MAC Layer (Data Link) Yes No Routing Layer (Network) Forwarding Procedure in VRA A node new to the virtual router might not know about this on- going session

Routing Layer (Network) VRA Protocol Forwarding Procedure (Data Packet) 38 No Yes No Yes No These steps are the same as in Location Discovery packet Yes The packet has reached its destination Yes

Forward Data Packet 39 Routing Layer (Network) MAC Layer (Data Link) Yes Receive Data Packet Packet arrives at destination

Network Attack: Dummy Packets 40 Routing Layer (Network) No MAC Layer (Data Link) Generate & “forward” a dummy data packet Flood the network with a dummy record

Routing Layer (Network) Receive Location Discovery 41 MAC Layer (Data Link) Yes No Yes No Yes No Yes MISBEHAVIOR DETECTION MODULE We now discuss this module

Misbehavior Detection Metrics 3C Module at each node i maintains the following information: –Forward Ratio (FR): Percentage of arriving packets forwarded FR i = –Local Average Forward Ratio (LAFR) LAFR i =, where, n is the number neighbor nodes of i –Request Ratio (RR): Offer enough service to use the network ? RR i = 42 Forward Request Counter Number of forward requests (both discovery and data packets) received by a node. Forward Counter Number of packets forwarded by a node. Location Discovery Counter Number of Location Discovery packets initiated by a node (i.e., number of connections requested)

Initiate Misbehavior Detection 43 mn Location Discovery packet Is the forwarder the initiator of this packet ? If m is not the source node, n proceeds to forward the packet else, n checks 3C header of this packet. Need to establish a communication connection with someone

m is a suspect Misbehavior Detection: Check Forward Ratio 44 mn Location Discovery packet FR m < FR n → n suspects m has been dropping packets FR n =FR m = FR m < FR n means that n is not forwarding enough packets

m is a suspect Misbehavior Detection: Check Request Ratio 45 mn Location Discovery packet RR m > 1.2*RR n → n suspects m has been dropping packets RR m > 1.2 ∙ RR n means that m made many connection requests; but it has not provided enough service to other nodes. RR m =RR n = n needs to exchange counter information with neighboring nodes

Initiate Misbehavior Detection: Compare to Local Average 46 mn x y n exchanges counters information with neighboring nodes FR m < LAFR n → m is a suspect according to local average LAFR n = k is the number of neighbor nodes of n

Enter Detection Mode: Listening State 47 mn x y m is a suspect. Enter Detection mode – Listening State m is a suspect. Enter Detection model – Listening State m is a suspect. Enter Detection mode – Listening State n enters Detecting state by invoking Misbehavior Detection procedure. Radio range of m

Detection Mode: Detecting State (1) 48 mn x y x resets the delay timer and stays in Listening State y resets the delay timer and stays in Listening State n generates and broadcasts a Detection packet n broadcasts a Detection packet two more times Detection packet is just a dummy data packet

Detection Mode: Detecting State (2) 49 mn x y x exits Listening State y exits Listening State n exits Listening State If m forwards the Detection packet n forwards m’s Location Discovery packet

Detection Mode: Detecting State (3) 50 mn x y x marks m as misbehavior y marks m as misbehavior n marks m as misbehavior If m drops all three Detection packets x drops m’s Location Discovery pakcet n drops m’s Location Discovery packet y drops m’s Location Discovery packet

Simulation Setting Simulator: GloMoSim. Constant-bit-rate sessions of 512-byte packets. Radio propagation range is 375 meters, and channel capacity is 2 Mbits/sec. Street width is 10 meters, and building block size is 100m by 100m. Initial nodes placement: 2 nodes per intersection, and 8 nodes per block. Mobility model: At intersections, a node pauses for a period of time, and then probabilistically changes its direction of movement. Speed: random between 0 m/s and 25 m/s (or 56 miles/hr). Pause time: random between 0 and 20 seconds. 100 simulation runs with different seed numbers for each scenario. Number of misbehaving nodes: 5%, 10%, 20%, and 30% of total number of nodes. 51

Schemes and Malicious Behavior Schemes compared:  Reference scheme: All nodes act collaboratively and relay data for each other.  Defenseless scheme: No detection mechanism is implemented. The network is totally “defenseless”.  3CE (3-Counter Enforcement) scheme: misbehaving nodes are detected and punished. Malicious Behavior:  A malicious node recognizes that it is being punished when its Location Discovery packet has been dropped four consecutively times.  Once malicious nodes recognize the punishment, they participate in data forwarding to rejoin the network. 52

Performance Metrics Packet Delivered Ratio (P) –Percentage of data packets successfully delivered to their destination. Misbehaving Node Detection Ratio (D) –Percentage of misbehaving nodes detected False Accusation Rate (F) –Percentage of detected nodes incorrectly accused 53

Packet Delivered Ratio (P) 54 3CE is significantly better than the defenseless system 3CE incurs little overhead. Its performance does not decrease significantly compared to the Reference scheme. Reference VRA Defenseless

Misbehaving Node Detection Ratio (D) Detection Ratio Speed (m/s) % misbehaving nodes89%88%83%81% 10% misbehaving nodes93%91%86%88% 20% misbehaving nodes91%85%89%87% 30% misbehaving nodes91%87%84%85% 55 Average about 87%

False Accusation Rate (F) 56 False Accusation Ratio Speed (m/s) % misbehaving nodes0%2%3%2% 10% misbehaving nodes1%2% 3% 20% misbehaving nodes1% 2% 30% misbehaving nodes2% 4%5% Overall, false accusation is very low. False accusation is higher when nodes move faster.  Suspect node forwards the detection packet after moving out of the radio range of the detecting nodes causing false accusation (i.e., not forwarding the detection packet)

Forward detection packet Send detection packet False Accusation 57 mn m is bad False accusation

58 Conclusions The Virtual Router approach has been shown to provide better performance than standard routing based on physical nodes 3CE (3 Counters Enforcement) cooperation enforcement technique further improves the Virtual Router approach Our simulation results indicate: –improved network throughput (better data delivery rate) –effective detection of most (87%) misbehaving nodes –almost no false accusation