Simulation of the SCTP Failover Mechanism
Some features of SCTP provide opportunities for creating redundancies for signalling over IP networks. This paper presents the behaviour of SCTP in failover scenarios, based on literature review and simulations. Simulations were carried out using NS2 in a multi-homing environment. It was found, as expected, that when failover took place, the undelivered chunks were retransmitted to the secondary path while new messages were still transmitted to the primary path until the error count was exceeded whereupon the primary path was declared inactive and a new primary path was chosen. The simulations raised some concerns regarding the duration of failover for different PRL values. *
On the Use of SCTP in Failover-Scenarios
The new general purpose transport protocol SCTP (Stream Control Transmission Protocol) has been developed for transport of signaling data, such as Signaling System No. 7 MTP level 2 or 3 user primitives, over IP networks. Since this application has especially high requirements towards the underlying transport protocol concerning reliability and fast recognition and recovery from failures, SCTP-based transmission must provide a high degree of network level fault tolerance. In our contribution we look at a typical link failure scenario in a multi-homed setup, and investigate two options for fast recovery from such an event, namely seamless SCTP switch-over, and a user level switch-over as has been suggested for the MTP Level 2 peer adaptation layer. Moreover, we will analyze necessary parameter settings for fast recovery from the failure situation. 1
The microscale obstacle-resolving meteorological model MITRAS v2.0: model theory
Abstract. This paper describes the developing theory and underlying
processes of the microscale obstacle-resolving model MITRAS version 2. MITRAS
calculates wind, temperature, humidity, and precipitation fields, as well as
transport within the obstacle layer using Reynolds averaging. It explicitly
resolves obstacles, including buildings and overhanging obstacles, to
consider their aerodynamic and thermodynamic effects. Buildings are
represented by impermeable grid cells at the building positions so that the
wind speed vanishes in these grid cells. Wall functions are used to calculate
appropriate turbulent fluxes. Most exchange processes at the obstacle
surfaces are considered in MITRAS, including turbulent and radiative
processes, in order to obtain an accurate surface temperature. MITRAS is also
able to simulate the effect of wind turbines. They are parameterized using
the actuator-disk concept to account for the reduction in wind speed. The
turbulence generation in the wake of a wind turbine is parameterized by
adding an additional part to the turbulence mechanical production term in the
turbulent kinetic energy equation. Effects of trees are considered
explicitly, including the wind speed reduction, turbulence production, and
dissipation due to drag forces from plant foliage elements, as well as the
radiation absorption and shading. The paper provides not only
documentation of the model dynamics and numerical framework but also a solid
foundation for future microscale model extensions.
