Figure 4.3
shows the flow of the email in the networking protocol. This email queue delay
period was set by the email system administrator. It can be set to minimum
value 0 and maximum value is 2147483647 due to maximum value for a 32-bit
signed integer (int32) supported by a SQL database. This means that the email
data can be kept in temporary storage for a maximum period of 2147483647
minutes equal to 4083 years. The user at the offline server will write and send
an email at application stage where the email data will be stored in the
offline mail server for a maximum period of 4083 years before it being
discarded. If the offline or online email server computer was shutdown or
restart, the pending email remains in the database and will eventually discard
when the time delay exceeded. Once the offline mail server connected to infomediary
device, the pending email data will move through TCP in Transport layer where
the application use NetBIOS over TCP/IP (NBT) to request NetBIOS name server to
send an IP address of the destination NetBIOS at infomediary device [20] . Link layer builds
an ethernet frame and pass it to the network operating system to be sent to the
NetBIOS name server. The NetBIOS name server sends back the NetBIOS name. After
the TCP connection is established, the application transfers the file to the
target host which is infomediary device.
Figure 4.3:
Networking Protocol flow
On the other
side, when infomediary device establishes a connection with an online mail server
computer, the email data is transferred to the mail server database. The data are
transferred packet by packet and when the last packet arrives, the files are
reassembled and completed files passed to the application layer. Figure 4.4
shows the Store and forward operation between mail server A, infomediary device
and mail server B. Each node contains storage to store the email data.
Figure 4.4:
Store and Forward
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