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message to the client. Another benefit of the push approach is its low over-
head on the client host. Further, this pushing method allows the server to
control and filter message flows to each client host.
Finally, in order to reduce the bandwidth consumption, the game server
is implemented with a packet aggregation method. The packet aggregation
functions to accumulate several packets into one before messages are trans-
mitted and is able to reduce the number of headers on each transmission [24].
According to the study from Singhal and Zyda [21], this savings can achieve
50% of the required bandwidth depending upon different types of network
virtual environments. There are three aggregation policies generally consid-
ered: timeout-based transmission policy, quorum-based transmission policy,
and hybrid transmission policy [21]. Considering the wireless bandwidth
and latency, the timeout-based transmission policy was realized on the game
server. In summary, to reduce the transmission time and bandwidth con-
sumption at the same time, the game server periodically collects messages
from clients and then pushes aggregated packets to each client.
6.4.2 The Mobile Support Server
The most challenging issue of designing the MiMAR system was to enable
the mobile player to interact with other players in the same virtual world.
Due to the signal instability and the limited bandwidth of the wireless net-
work, messages from the server may easily jam the wireless network band-
width if the mobile player is directly connected to the game server. Further,
if the mobile player is directly receiving a message from the game server, the
limited computation power of the mobile device will be unable to proceed
with interactive messages as the number of simultaneous players increases.
To solve these problems, a MSS is designed as a data mediator between the
game server and the mobile player as shown in Figure 6.2. The MSS prin-
cipally adjusts the message flow between the game server and the mobile
player.
In addition to the prior research issues of the network virtual environment
[21], there are still other issues needed to be solved before the mobile player
can interact with a shared virtual space. These issues can be broadly classi-
fied into three categories. One is the instability and bandwidth problem of
the mobile network. The second issue is the limited computation resources
of the mobile device. The last one is the data correlation between the geo-
graphical coordinate system and the Cartesian coordinate system [25]. These
three problems further lead to more subproblems as depicted in Figure 6.3.
•
Mobile networking: The ultimate goal of MiMAR is to allow both
desktop players and mobile players to interact with each other in the
shared space. Since the desktop device is often connected by a fixed
location network, there is not much to be discussed due to signal
stability of such a network. On the other hand, the mobile player can
