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We study and compare topology aggregation techniques used in QoS routing. Topology Aggregation (TA) is defined as a set of techniques that abstract or summarize the state information about the network topology to be exchanged, processed, and maintained by network nodes for routing purposes. Due to scalability, aggregation techniques have been an integral part of some routing protocols. However, TA has not been studied extensively except in a rather limited context. With the continuing growth of the Internet, scalability issues of QoS routing have been gaining importance. Therefore, we survey the current TA techniques, provide methodology to classify, evaluate, and compare their complexities and efficiencies. Categories and Subject Descriptors: A.1 [Introductory and Survey]; C.2.1 [Computer-Communication Networks]: Network Architecture and Design--Network topology, Network communications, A Packet-switching networks; C.2.4 [Computer-Communication Networks]: Distributed Systems--Distributed applications; D.4.4 [Operating Systems]: Communications Management--Message sending, Network communication; E.1 [Data Structures]:--Graphs and networks General Terms: Algorithms, Design, Performance Additional Key Words and Phrases: Topology aggregation, QoS routing, routing, bandwidth, delay, inaccuracy, networks, topology, hierarchical networks, path selection ACM Reference Format: Uludag, S., Lui, K.-S., Nahrstedt, K., and Brewster, G. 2007. Analysis of topology aggregation techniques for QoS routing. ACM Comput. Surv. 39, 3, Article 7 (August 2007), 31 pages DOI = 10.1145/1267070.1267071 http://doi.acm.org/10.1145/1267070.1267071.

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.comnet.2005.01.011 Byline: Tat Wing Chim, Kwan L. Yeung, King-Shan Lui Keywords: Traffic engineering; Traffic splitting; ECMPs; Packet reordering; Load balancing Abstract: To effectively manage the traffic distribution inside a network, traffic splitting is needed for load sharing over a set of equal-cost-multi-paths (ECMPs). In this paper, a new traffic splitting algorithm, called Table-based Hashing with Reassignments (THR), is proposed. Based on the load sharing statistics collected, THR selectively reassigns some active flows from the over-utilized paths to under-utilized paths. The reassignment process takes place in such a way that the packet out-of-order problem is less severe. Simulations show that THR provides close-to-optimal load balancing performance but suffers about 5% of packets arrived out-of-order. Although additional traffic monitoring function is needed by THR, we show that the extra complexity incurred is marginal. Author Affiliation: Department of Electrical and Electronic Engineering, The University of Hong Kong, Pokfulam Road, Hong Kong Article History: Received 28 April 2004; Revised 11 October 2004; Accepted 10 January 2005 Article Note: (miscellaneous) Responsible Editor: H.-L. Truong

In a tracking system, an object of interest is monitored continuously in a sensor network. Information about the object is kept in the sensors and sensors transmit the information upon request. In this paper, we consider the scenario where all sensors around a targeted object capture images of it and these pictures will be sent to a mobile agent upon request. Due to the size and energy limitations in sensors, images kept in sensors are often small and highly compressed. We describe a framework to facilitate a mobile agent in the sensor network to request images of the object of interest. As sensors are limited in energy, it is desirable to reduce the energy used in transmitting the images. We observe that, in a sensor network that is sufficiently dense, images from neighbor cameras would likely overlap, and therefore intermediate sensors can process and combine overlapping portions so as to reduce the energy spent on image transmission. We develop a protocol for involved sensors to determine how to transmit the images they have kept to the mobile agent in an energy efficient manner. Our protocol is truly distributed and does not require any global information. We evaluate our protocol through extensive simulations.

Satellite networks have great potential in providing global ubiquitous broadband communication. In this paper, we explore the capacity of both single-layered and two-layered satellite networks. Closed-form approximate expressions of network capacity are derived, which provide insights into the impact of different network parameters, such as number of orbits, number of satellites in each orbit, link bandwidth, existence of the seam, the relative position between the two layers, etc. We investigate the advantages of two-layered structure by comparing the capacity of single-layered and two-layered networks. The results show that the network capacity of two-layered networks is always no less than the total capacity of the two layers. Moreover, we obtain the network parameter condition under which the network capacity of two-layered networks is strictly larger than the sum capacity of the two layers. The results obtained in this paper can serve as a guideline for the design of efficient multi-layered satellite networks. [ABSTRACT FROM AUTHOR]