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ABSTRACT
Non-geostationary (NGEO) satellite communication systems offer an array of advantages over their terrestrial and geostationary counterparts. They are seen as an integral part of next generation ubiquitous communication systems. Given the non-uniform distribution of users in satellite footprints, due to several geographical
And/or climatic constraints, some Inter-Satellite Links (ISLs) are expected to be heavily loaded with data packets while others remain underutilized. Such scenario obviously leads to congestion of the heavily loaded links. It ultimately results in buffer overflows, higher queuing delays, and significant packet drops. To guarantee a better distribution of traffic among satellites, this paper proposes an explicit exchange of information on congestion status among neighboring satellites. Indeed, a satellite notifies its congestion status to its neighboring satellites. When it is about to get congested, it requests its neighboring satellites to decrease their data forwarding rates by sending them a self status notification signaling message. In response, the neighboring satellites search for less congested paths that do not include the satellite in question and communicate a portion of data, primarily destined to the satellite, via the retrieved paths. This operation avoids both congestion and packet drops at the satellite. It also ensures a better distribution of
Traffic over the entire satellite constellation. The proposed scheme is dubbed “Explicit Load Balancing” (ELB) scheme. While the multi-path routing concept of ELB has many advantages, it may lead to persistent packet reordering. In case of connection- oriented protocols, this phenomenon results in unnecessary shrinkage of the data transmission rate. A solution to this issue is also incorporated in the design of ELB. The interactions of ELB with mechanisms that provide different QoS by differentiating traffic (e.g., Differentiated Services) are also discussed. The
Good performance of ELB, in terms of better traffic distribution, higher throughput, and lower packet drops, is verified via a set of simulations using the Network Simulator (NS).
Existing System:
ere is a possibility of missing of data packets when load on server is more.
2. Selecting shortest path is difficult until and unless we follow a proper algorithm.
Propesed System:
1.Basestation cares about data packets ,so that no missing of data packets.
2.Load is balanced by selecting shortest path.
I. INTRODUCTION
DESPITE the recent advances in terrestrial communication technologies, the ever-growing community of Internet users poses serious challenges to current terrestrial networks. Bandwidth-intensive services, with different Quality of Service (QoS), to a potential number of users, dispersed over extensively wide areas and requiring different degrees of mobility. To cope with this issue, network technicians and telecommunication
Operators have envisaged optical-fiber networks and have considered temporary solutions such as Asynchronous Digital Subscriber Line (ADSL) and High-rate DSL (HDSL)
Technologies. However, as the demand for advanced multimedia services is growing in terms of both the number of users and the services to be supported, applying such solutions to bridge the last mile between local service providers and end-terminals
Will require an immense investment in terms of time, infrastructure, and human resources. Building a cost-efficient global ubiquitous infrastructure is one of the major challenges before telecommunication industries in the current century. In this regard, and considering the fact that more than half of the world lacks a wired network infrastructure, satellite communication systems are seen as an attractive solution. The efficiency of
A satellite-based broadband service is strongly remarkable in remote zones and low-density population areas. The key technologies required to support broadband communications over satellite systems have been already developed [1], [2]. Indeed, with the recent advancements in satellite return channels and on-board processing technologies, satellites are now able to provide full two-way services to and from earth
Terminals [3]. Additionally, several techniques for on-demand onboard switching have been proposed to make efficient use of satellites capacity [4]. Unlimited connectivity can be accordingly guaranteed. The advent of ka-band guarantees more availability of spectrum to support broadband multimedia communication [5], [6]. This has spurred further on the expansion of multimedia satellite networks. To encourage the deployment of cost-effective terminals with small antennas (e.g., Very Small Aperture Terminals (VSATs) and Ultra Small Aperture Terminals (USATs)), satellite channels with higher frequencies, such as V-band (36–51.4 GHz) and millimeter wave (71–76 GHz), have also been developed. These high frequencies will enable scalable mobility and ubiquitous connectivity across the world. Various mechanisms have also been proposed to cope with the well-known problems associated with rain and atmospheric attenuation at these frequencies. Given these advancements and on-going enhancements in satellite communications, it is now possible to design and implement satellite based communication systems for high bit rate services. Satellite communication systems exhibit unique features and offer an array of advantages over traditional terrestrial networks. In addition to their inherent multicast capabilities and flexible deployment features, they are able to provide coverage to extensive geographic areas and to interconnect among remote terrestrial networks (e.g., islands). They can be also used as an efficient alternative to damaged terrestrial networks to recover from natural disasters. In the recent literature, a significant number of satellite communication constellations have been thus proposed using Geostationary (GEO), Medium Earth Orbit (MEO),
Or Low Earth Orbit (LEO) satellites. In addition to their long propagation delays, GEO systems cause mobile terminals in high latitude regions to experience frequent cut-offs of propagation signals by tall buildings, trees, or mountains possibly due to low elevation angles of the page link above the horizon. To provide global communication with reasonable
Latency and low terminal power requirements, constellations made of multi Non-Geostationary (NGEO) satellites (e.g., LEO and MEO) have been the focus of several researches in the recent literature [7]. Due to geographical and/or climatic constraints, the community of future NGEO satellite users will exhibit a significant variance in its density over the globe. Indeed, satellites covering urban areas dense with users will be more congested than satellites serving rural regions. This density variance, along with the highly dynamic feature of NGEO constellations, will yield a scenario where some satellite links are congested while others are underutilized. In the absence of an efficient routing algorithm that takes into account the traffic distribution, this unfair distribution of network traffic will lead to significant queuing delays and large number of packet drops at the congested satellites. Obviously, such performance will lead to poor throughput and will ultimately affect the QoS credibility of the entire system. All in all, support for IP routing in the satellite constellations is highly important for the implementation of
Integrated or Differentiated Services (DiffServ) architectures to support QoS over satellite systems. In the recent literature, a number of pioneering routing protocols
Have been specifically proposed for satellite networks. Most of these protocols search for the shortest path with the minimum routing cost. As will be discussed in the next section, a highly missing point in their design consists in their focus on searching for the shortest path with the minimum routing cost without any consideration of the total traffic distribution over the entire constellation. Indeed, while searching for only short paths for communication, some satellites may get congested while others are underutilized. This phenomenon leads to unfair distribution of the network traffic and ultimately to higher queuing delays and significant packet drops at some satellites in the constellation.
To cope with the aforementioned limitation of current routing protocols, this paper suggests that neighboring satellites should explicitly exchange information on their current congestion status. An Explicit Load Balancing (ELB) technique is developed.
In ELB, a satellite continuously monitors its queue size to determine its state which may be free, fairly-busy, or busy. A change in the state of a satellite is immediately notified
To its neighboring satellites via a Self-State Advertisement packet. As a consequence, the cost of the links between the busy satellite and its neighbors is then increased. To avoid an imminent congestion, a satellite with high traffic load requests its neighboring satellites to forward a portion of data, originally destined to travel through the satellite, via alternative paths that do not involve the satellite. The ELB scheme therefore alters
The traffic sending rate of neighboring nodes of the satellite in question before it gets congested. Since minimum cost links are preferred, packets will be routed on the least loaded links and busy links will therefore have less packets in the queues. In the ELB mechanism, satellites use three parameters to indicate their congestion status and to reduce their data transmission rates, respectively. These parameters consist of two queues
Ratio thresholds and a traffic reduction ratio, respectively. Appropriate adjustments of the parameters would result in efficient distribution of traffic over multi-hop satellite constellations.
