QoS‐oriented traffic management in multimedia satellite systems

Abstract

SUMMARYThe next generation of satellite systems will likely use some on-board switching techniques enabling the direct transmission of data from any up-link spot-beam to any down-link spot-beam. If the switch used in the payload of the system is an ATM-based shared buffer switch, some losses and delays can occur. Fortunately, these drawbacks can be fought thanks to some buffer management policies (HSPO, SMXQ, EPD) that either ensure low delay or low loss ratio.Real-time (voice or MPEG video streams) and non-real-time applications (file transfer, email, web browsing using TCP/IP protocols) should be carried over these satellite systems with different quality of service (QoS) requirements. Different combinations of buffer management policies are presented to guaranty the QoS required by the user. Especially, special emphasis is put on the way to transmit efficiently layer 3 messages (IP datagrams) within a mix of traffic in order to avoid some high layer retransmission techniques (provided in TCP for instance) wasting both time and bandwidth. Copyright The aim of this paper is to study the optimization of the transmission of layer 3 messages over an ATM UBR-like service provided by a geo-stationary satellite system with ATM-based onboard switching. This optimization will be performed while using different management schemes for the shared buffer of the ATM-like on-board switch. To achieve the transmission of data over the satellite system, all the layer 3 messages}potentially IP datagrams}and data streams are split into several layer 2 cells whose format is fixed (length, payload, addresses, etc.). The switch then handles these cells. If the buffer of the switch becomes overloaded, this kind of switch will react with the drop of some cells inside the buffer in order to avoid the congestion. If a dropped cell belongs to a sequence of cells that makes up a layer 3 message, its loss causes the definitive damage of the entire layer 3 message. This also implies the inefficient transmission of the remaining cells belonging to the same sequence of cells and often the use of a high layer retransmission policy (for example TCP). In Section 1, the ATM-like shared buffer switch will be detailed together with the buffer management policies we can implement to improve its performance. We have assumed in this

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