The following assumptions regarding the reference satellite network are made: • All aircrafts, maritime vessels, etc., are each equipped with an mRCST, GPS
(or Galileo) receiver and the global satellite network map. The GPS (or Galileo) receiver and the global satellite network map enable the aircrafts (or maritime vessels) to perform the analysis of their position information and then signal handover recommendation whenever necessary with a specified target beam to be used in the handover decision process by the NCC.
• A handover detection/recommendation technique adopted here is the position based distributed approach [17] which is the recommended approach in the DVB-RCS specification [17]. In this approach, the aircraft knows its location at any time and therefore the target GW whenever it enters the overlapping area of any two beams belonging to different GWs. Since the satellite GWs, NCC and the NMC are all connected by terrestrial private networks and the global terrestrial Internet, communication between any of them is done through terrestrial networks. The satellite link (network) is only used for connection to a remote RCST or mRCST which of course has no access to terrestrial networks.
Figure 4.1 Reference network architecture for IP multicast mobility support over satellites
Figure 4.1 shows the reference satellite network architecture adopted for IP multicast mobility support. While a minimum of three GEO satellites are required to provide global coverage, for simplicity the reference network architecture only shows two satellites. In order to cover various possible
aspects of IP mobile multicast in a global GEO multi-beam satellite network, the reference network architecture is designed as follows:
• Considering the fact that the new generation of High-Throughput Satellites have capacities in excess of 100 Gbps per satellite [67], one GW per satellite footprint may not be able to efficiently handle the high density traffic. So, for maximum spectrum usage and high-throughput in the system, each of the GEO satellites in this network is designed to have two GW Beams, each representing a separate IP network. A GW Beam is a wide beam or regional beam which normally has a GW that interconnects the satellite network to terrestrial networks. Each GW Beam shown in Figure 4.1 is sub- divided into multiple spot beams in order to further enhance the overall satellite capacity and to support higher data rate as explained in Chapter 2. • Satellites A and B are controlled by NCC-A and NCC-B respectively,
providing real-time control and monitoring functions e.g., session control, connection control, terminal access control to satellite resources, routing, etc. The NMC is in charge of the whole global satellite network.
• The multicast source is located on the terrestrial network and the receivers are both on terrestrial network and satellite network (i.e. in the aircraft). The aircraft is currently located at GW-B1 (i.e. IP network 1) which is its home network.
• The mRCST on board the aircraft is configured to support IGMP/MLD proxy with the upstream interface towards the satellite and the downstream interface towards the aircraft. The actual multicast subscribers on board the aircraft are the user terminals (UT) located behind the mRCST as shown on Figure 4.1.
The MIP HS/RS-based approaches are each implemented during a handover when the aircraft in Figure 4.1 crosses the overlapping areas of:
• GW_B1 and GW_B2; GW_B3 and GW_B4 for GWH. • GW_B2 and GW_B3 for SH.
Handover latency, signalling cost and the number of packets lost due the handover process are some of the most important factors in performance evaluation of any mobility protocol. Handover latency is defined here as the time period during a handover process where the mobile node (IP multicast receiver/source) cannot receive or send user traffic through its satellite interface due to the handover process from one point of attachment in a satellite network (i.e. GW) to another. The one way message transmission (end-to-end) delay,
Dm from a node on the ground segment to the remote satellite terminal (e.g., in
the aircraft) via the satellite over wired and wireless (satellite) links is given by [38, 68, 69]: + + + = − −
L
d
h
M
L
d
h
M
sl sl Z Y S wd wd Y X S m D (4.1)Where Ms = message size; hX-Y = number of hops between nodes X and Y in
wired links; hY-Z = number of hops between nodes Y and Z in satellite links;
Lwd/Lsl = Latency on wired and satellite links respectively; dwd/dsl = data rate on
the wired and satellite links respectively.
Handover signalling cost (Cs) is the signalling overhead incurred as a result of
the handover process from one point of attachment in a satellite network (i.e. GW) to another. Here, the handover signalling cost is mainly the location update cost that a network suffers as consequence of supporting mobility. Handover signalling cost depends on the handover signalling messages and the distances
these messages have to travel in terms of number of hops. The signalling cost C is calculated as the product of the message size and the number of hops traversed by the message and has the units of bytes hops [38, 70],:
h M
C= S SD (4.2)
Where Ms = message size in bytes and hSD = number of hops from source node
to destination node.
To develop analytical mobility modelling for the MIP HS/RS-based approaches at GWH and SH, the standard GWH procedure in mobile satellite systems defined in the DVB-RCS specification in [17] and the IP address acquisition process for DVB-RCS in [17] are used. The MIP HS/RS-based approaches are each integrated into the standard DVB-RCS GWH handover signalling sequence given in [17].