![](bg3.png)
= 1, means this MRN is alive and it has sent
heart-beat message to the router
= 0, means this MRN is not alive
[ MRN_load ]
= (int) N, the sent packet amount to this MRN
(from the router), it is statistical value.
= 0, if MRN_live = 0, this value will be
cleared to 0.
[ MRN_buffer_usage ]
= (int) M, indicates how many packets are
queued in this MRN, the packet amount value
is sent with heart-beat message from this
MRN.
The MRN selection rule is
(MRN_alive=1) AND Min(MRN_load) AND
Min(MRN_buffer_usage)
Each MRN is connected to healthcare server in
the hospital, and finally healthcare server should
handle the data from the selected MRN.
2.1.3 Healthcare Server
It is used to receive the vital sign data from the
ambulance. Since stateless protocol is used to
transmit the data, call setup procedure is not applied.
While the first data packet comes to the server, one
session table is automatically built to route the
following data packets to the specified line. The
session table contains three columns: source address,
3G’s IMUI data, and the sequence number of
received UDP packet. To have this information in
the server, the extra IMUI data should be added to
the packet while the ambulance is sending the vital
sign data and connects with the application layer of
the hospital.
Since each packet and its duplicate are sent via
two respective paths, one sequence number field
should be added in the payload of UDP. In the
receiving side, the packet-duplication-removal
procedure should be applied in the application layer.
That is, each time the UDP packet (payload) is
received and the sequence number should be
compared with the one in the session table of the
same source address. If the sequence number of the
received UDP is greater than the current sequence
number in the session table, the UDP packet
handling procedure can go on; otherwise, the
received packet is spare and should be dropped.
In this paper, we aim at providing reliable and
stable message transmission while the ambulance is
on the way to the hospital. Therefore it is not the
intension to further describe the received data
handling in the healthcare server.
2.2 System Behaviours
When the patient at the event place was taken care
and moved into the ambulance, the healthcare
monitor system starts its operations and transmits the
data to the hospital, the data includes the vital sign
data (heart-beat rate, blood pressure, etc.) retrieved
from the sensors and the monitoring video view of
the patient. The vocal communication between the
nursing people (in the ambulance) and the hospital
uses normal 2G/3G mobile phone system, and is
totally separated from the healthcare monitor
system.
Each data is divided into several UDP packets
for transmission and the destination address is
MRG’s anycast address. Each UDP packet should
insert the IMUI of the healthcare monitor system
and the sequence number of this UDP packet. The
packets are transmitted through the TDs to the
MRNs (of the same anycast address) of the target
hospital. In the system, three TDs are equipped in
the healthcare monitor system and each time two out
of three TDs are selected to transmit the UDP packet
and its duplicate, thus to enforce the possibility of
successful data transmission. Supposed that the
index number of TD is from 0 to 2, and
i
TD
stands
for transmission device i, each time the selected
transmission devices are
i
TD
and
3mod)1( +i
TD
,where
i= (Sequence_Number) mod 3.
The reason for each time having two TDs with
two separated paths is to make trade-off between the
bandwidth saving and the data loss possibility.
When the UDP packet finally arrived at the specified
MRN, it would judge to accept that packet by
checking the buffer usage of this node. And the
packet should be kept in the FIFO buffer, until it is
finally transmitted to the healthcare server.
3 ANALYSIS
First, the analysis on the packet loss rate of the
system is explained. Second, the hardware cost
comparison using between anycast and multicast to
build up MRG is described.
3.1 Data Loss Probability and
Required Min. MRN Node Number
For easy explanation, Figure 3 is used as the basis of
the system architecture for message reliability
analysis.
A VEHICULAR HEALTHCARE SYSTEM USING ANYCAST AND PERVASIVE COMPUTING - One Pervasive
Computing Application on Mobile Software and Services
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