Ming-Yu Jiang and Wanjiun Liao,IEEE ICC 2002 Family ACK Tree (FAT): A New Reliable Multicast Protocol for Mobile Ad Hoc Networks. Speaker : Wilson Lai Date :

Outline Introduction FAT Protocol Performance Evaluation Concluding Remarks Question & Discussion My research

Introduction Family ACK Tree (FAT) support reliable multicast service in ad hoc networks. It employs a tree-based recovery mechanism that localizes ACKs and retransmissions to avoid feedback implosion. FAT constructs an ACK tree to maintain the family relation.

What is Reliable Multicast? S B J N A G E K D L O I F ACK ACK implosion S B J N A G E K D O I F NACK NACK implosion

Definition of a Family ACK Tree D A C B E FG GID Grandparent’s family PID Parent’s family CID Node’s family

Control message types Ad : sub-group ID advertisement –It is used to configure the ACK table of each node in a family ACK Tree. –Each mobile node periodically broadcasts beacons to its neighbors. RTQ : retransmission request –It is used to report s loss gap to its reliability agent and to request for a retransmission.

The construction of FAT S All nodes on the multicast tree are involved in the sub-group ID Advertisement process. Through this process, all nodes are able to acquire their GIDs/PIDs/CIDs to configure their ACK tables. (CID) (PID,CID) (GID,PID,CID)

The maintenance of FAT (1/4) Upon receipt a reliable multicast packet, a node caches it with a predefined timer Tc; otherwise, the node negatively acknowledges the packet for a retransmission upstream to its parent on the ACK tree and start a predefined timer Tr. –If no any retransmission request on expiry of Tc, the node removes the packet from the buffer; otherwise, retransmits the packet to the sender of NAK. –If no retransmission from its parent on expiry of Tr, an RTQ is resent.

When a node departs, the one hop neighbors will be informed. The nodes notified may include the parent node, the children nodes, and sibling nodes. The departing node forwards the packets in its cache upstream to its parent. This rollbacks the parent’s buffer and allows the grandparent to serve as the foster parent for its grandchildren. The maintenance of FAT (2/4)

The maintenance of FAT (3/4) S Sub-tree Request message Glue back Once an orphan node has reconnected to the tree, it reconfigures its ACK table and identifies the missing packets in which the new parent node is unable to repair. The node then negatively acknowledges the loss gaps to its previous GID and requests for retransmissions.

The maintenance of FAT (4/4) normal state (current ACK table) repairing state (previous and current ACK table) Detecting a departure of the parent Repair the missing packets A node receives an RTQ whose GID match its PID Discard the request Encapsulates the RTQ and forwards to its previous GID When a node,say F, receives an RTQ whose GID matches its CID, node F must be the grandparent of the requesting node. If the received request is encapsulated, node F decapsulates the request to identify the original requesting node, say node O; otherwise, the request sender must be the original requesting node. Node F then retransmits the requested packets directly to node O.

Simulation setup The packet transmission was error-free and all the loses were caused by node movements. A 100-by-100 mesh in which nodes were roaming across the mesh. The distance between two adjacent intersection points on the mesh is 20 meters. Randomly selected N nodes in the mesh, only one sender and the rest are group members.

Simulation setup… Each node stayed in a location with an exponentially distributed sojourn time with a mean of M. Each node had a transmission range is 20 meters. The sender generated data packets at a constant rate of one packet per second.

Simulation results(1/4) The inverse of the mean time that a node stays at a location. The ratio of the number of the granted requests to the total number of the received requests.

Simulation results(2/4)

Simulation results(3/4) The total number of retransmission Requests multiplied by the average Path length traversed by each Retransmitted packet.

Simulation results(4/4)

Conclusion FAT employs a tree-based recovery mechanism that localizes ACKs and retransmissions. The results show that FAT achieves the best performance in providing reliable service in ad hoc networks, in terms of reliability, scalability, and delivery efficiency.

Question & Discussion Cost + Control overhead ?

My Research All-to-all communication Load balance

Communication category AB Unicast : one-to-one Anycast : one-to-anyone A B C D Broadcast : one-to-all A BC D Multicast : One-to-some S1 R1 R2 R3 many-to-many S2 S1R2 R3 R1 all-to-all a e f b g

Protocol Introduction header gateway ordinary One-hop neighbor form a cluster and use adaptive TDMA in dense location. Per-source tree be created between cluster and cluster