Optical Transport Networks are transitioning to an intelligent Next-Generation Optical Transport Network (NG-OTN) to improve operational efficiency, deploy more cost-effective optical transport, and enable dynamic bandwidth services.
Future high-speed networks will be very complex and use many sophisticated tra c control mechanisms. This paper investigates the performance of interactive TCP services over large scale ATM networks with many TCP connections by means of simulation. A simulation environment has been developed, which allows the automatic creation of large simulation scenarios on the basis of a tabular description. The network under study consists of 8 ATM switches, interconnected by a mesh of ATM links and attached Fast Ethernet LANs with TCP end systems. The switches allow CBR, VBR.1, VBR.3 and UBR tra c. To separate di erent tra c streams, Weighted Fair Queueing has been used. In the case of congestion Virtual Queue Discard allows to discard low priority cells. Furthermore the in uence of EPD and PPD has been investigated. All tra c control mechanisms are used in combination, which causes interactions between several algorithms. Data packets as well as TCP acknowledgements ow o ver congested links. The results showgoodoverall performance but unfairness for the service category UBR. For small bu er size the performance decreases and the unfairness increases. As CBR does not allow for multiplexing gain, VBR.1 is better suited than CBR for interactive TCP services. TCP cannot bene t from using VBR.3. For competing VBR.3 streams no guarantees can be given on frame level. Using PPD has a positive impact on performance, however additionally using EPD has only a small impact. In a tra c mix of VBR.3 and UBR tra c, VBR.3 tra c can be transported without QoS degradation. UBR is able to use the remaining bandwidth, but in an unfair manner.
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