http://dspace.cityu.edu.hk:80/handle/2031/707 2013-05-07T18:34:54Z http://dspace.cityu.edu.hk:80/handle/2031/4762 Title: Algorithms design for IPv6 address lookup and packet classification Authors: Li, Yiu Keung (李耀強) Abstract: In addition to the conventional 1-D address lookup used to determine the next-hop of an incoming packet, an IP router is also required to perform multi-field packet classification in order to support advanced functions, such as network security, quality of service, and virtual private network etc. Many algorithmic and Ternary Content Addressable Memory (TCAM) based approaches have been published for the address lookup and packet classification problems. In general, software implementations are suitable for low-end routers, whereas hardware search engines are employed in high-end routers that demand a very high packet-processing rate. Most of the existing algorithmic methods for address lookup exploit the characteristics of IPv4 routing tables to speed up the processing rate. The adoption of IPv6 with 128-bit addresses poses great challenges to the existing methods. In this research, we investigate the necessary modifications and extensions to several well-known address lookup algorithms for application to IPv6. It is found that a hybrid method that combines level-compressed trie with hashing will give the best performance. Multi-field packet classification is a much harder problem compares to the 1-D address lookup. TCAM-based approach is the dominant solution used in the industry. With the adoption of IPv6, the cost of TCAM-based search engine is jet up while the efficiency is degraded. In this research, we develop a novel encoding scheme, called prefix inclusion coding (PIC), which can compress a 5-tuple 296-bit IPv6 filter to 72 bits (or even 36 bits for classifiers with up to a few thousands filters). Hence, the overall TCAM storage requirement can be reduced by 90%. Notes: vii, 129 leaves : ill. ; 30 cm.; Thesis (M.Phil.)--City University of Hong Kong, 2005; Includes bibliographical references (leaves 123-129); CityU Call Number: TK5105.875.I57 L56 2005 2005-01-01T00:00:00Z http://dspace.cityu.edu.hk:80/handle/2031/4761 Title: Reliable multicast over wireless ad-hoc network Authors: Lau, Kwan Shek (劉鈞碩) Abstract: IEEE 802.11 is the de facto standard for wireless communications. According to the 802.1 1 medium access control protocol, multicast frames are transmitted over ad hoc networks without virtual channel reservation. Hence, multicast communications in ad hoc networks suffer from the hidden terminal problem, and may have low delivery ratio. Feedback implosion is another issue that need to be addressed. If each multicast group member sends feedback messages to the sender directly, the sender will be congested/overloaded. In this research, a tree-based reliable multicast communication protocol is proposed. Firstly, the virtual channel reservation technique for unicast communication is extended to multicast communications such that the packet loss probability can be reduced significantly. Secondly, a tree-based packet recovery protocol is developed. Feedbacks from the multicast group members are consolidated at the branch points of the multicast tree, and the workload of the packet recovery process can be distributed among the multicast group members. The performance of the proposed reliable multicast protocol is studied via simulation. It was found that the tree-based method performs better than gossip-based methods when node mobility is not high. Notes: ii, 56 leaves : ill. ; 30 cm.; Thesis (M.Phil.)--City University of Hong Kong, 2005; Includes bibliographical references (leaves 54-56); CityU Call Number: TK5105.887.L38 2005 2005-01-01T00:00:00Z http://dspace.cityu.edu.hk:80/handle/2031/4760 Title: 3D object model reconstruction from multiple views Authors: Wong, Sze Sze (黃思思) Abstract: This project aims to reconstruct a 3D object model from an image sequence captured by a mobile camera. Our system can be used to generate 3D model of any type of object. We are particularly interested in demonstrating the capability of the system in the reconstruction of 3D head model. An efficient method has been developed that can facilitate the reconstruction of a complex surface model. Conventional 3D reconstruction techniques, with the use of specialized equipment, are inflexible and very expensive. To reduce the cost and increase the flexibility, our system only requires consumer-type digital camera for image sequence acquisition. A new colored calibration pattern is designed to allow the object and the calibration pattern to be captured simultaneously. It can provide a higher convenience but lower cost for the set up of the system. The whole process of 3D object reconstruction consists of four major steps: camera calibration, volumetric model reconstruction, surface model reconstruction and texture mapping. Camera calibration is an important step to determine the relationship between 3D world coordinates and the corresponding 2D image coordinates. The volumetric model is reconstructed from the image sequence (multiple views) of the object by Shape-from-Silhouette/Photo-consistency. The volumetric model in the real world space is converted to surface model. Finally, a single texture map is created from the original multiple camera views of the object. The linear camera calibration method can be done in high speed and with high accuracy. The camera can be calibrated either by using the coplanar calibration pattern or the non-coplanar calibration pattern with on-line lens distortions compensation. Both radial and tangential lens distortion compensation can improve the linear camera calibration. For the 3D model reconstruction, a novel reconstruction algorithm "Shape-from- Silhouette/Photo-consistency" is implemented. This algorithm combines the voting-localizing operations of the Shape-from-Silhouette in a novel space, and the Photo-consistency constraint among neighboring views of the object. It overcomes the shortcomings of each algorithm. A 2D voxel mask in 3D space is proposed that can effectively locate the concavity of the object surface. The volumetric model is then converted to the surface model by the marching cubes algorithm. To give the object model a realistic appearance, two texture mapping methods are developed. One is a view-independent method and the other is a view-dependent method. The view-independent method is to combine the individual photographs together. The view-dependent texture mapping is to combine and blend different input photographs to form a single texture. The results of camera calibration and volumetric modeling are shown. Some reconstructed 3D photorealistic models are presented to demonstrate the performance of the system. Notes: xii, 138 leaves : ill. (some col.) ; 30 cm.; Thesis (M.Phil.)--City University of Hong Kong, 2004; Includes bibliographical references (leaves 129-135); CityU Call Number: TA1637.W664 2004 2004-01-01T00:00:00Z http://dspace.cityu.edu.hk:80/handle/2031/4759 Title: Graph-based stereo correspondence algorithms and occlusion detection Authors: Chen, Shifeng (陳世峰) Abstract: Stereo matching, or 3D reconstruction from two or multiple 2D images of a scene, is one of the most active research areas in computer vision. Due to its ill-posed nature, stereo matching problem still remains challenging although many stereo algorithms have been developed. Amongst recent algorithms, graph-based methods are the most popular because of their excellent performance. On the other hand, occlusion detection is an important part in stereo problem. Many heuristics have been presented to handle occlusions. In this dissertation, three stereo algorithms are presented. The first one is a local occlusion detection algorithm, so called the competitive approach. The objective of this algorithm is to label occlusions in the obtained dense disparity map without occlusions after matching. This algorithm has two main steps: first, all matching conflicts are labelled in a dense disparity map after matching without occlusions; second, occlusions are extracted from matching conflicts via a maximum-value rule. In this dissertation, an improved cooperative algorithm is presented to improve the original cooperative algorithm by using the competitive occlusion detection approach. This algorithm is implemented on some standard test image pairs to demonstrate its improvement. The second part of this dissertation proposes two global stereo algorithms, named left-right consistency graph cuts (LRC-GC) algorithms, to solve correspondence problem with occlusions. Our objective of this part is to design good stereo matchers for accurate correspondence computation including occlusion labelling. These two algorithms are based on graph cuts and handle occlusions within the global energy minimization process by enforcing the left-right matching consistency constraint, which states that only the non-occluded pixels have correspondences and each pair of correspondences should have the same disparity value. The two novel algorithms give unique and symmetric results. We compare them with another graph-based stereo algorithm, which handles occlusions by enforcing the uniqueness constraint. Experimental results are reported to demonstrate the excellent performance of the two novel algorithms and to show that they outperform the algorithm based on the uniqueness constraint. In the conclusion part, some limitations of these novel algorithms are discussed and some directions for further research are suggested. Notes: xiii, 108 leaves : ill. ; 30 cm.; Thesis (M.Phil.)--City University of Hong Kong, 2005; Includes bibliographical references (leaves 97-108); CityU Call Number: TA1634.C445 2005 2005-01-01T00:00:00Z