6th European Conference - Academic Conferences

Hind Al Falasi and Liren Zhang
packets at once. Therefore, for every sequence of packets sent, only one piece of useful information
is sent via one acknowledgment. However, the high security network can set the size of the sliding
window to one which requires that every packet is acknowledged before the next one is sent, sending
us back to square one.
4. The covert channel analysis
4.1 Notations
The following acronyms are used in the paper: LSN stands for Low Security Network, and HSN
stands for High Security Network.
Table 1: The table contains the notations we will use throughout the paper, and in the illustration
figures
4.2 Assumptions
LSN SAFP: λ 1
SAFP LSN:µ1
LSN SAFP = T1
LSN SAFP = α1
RL: Ack rate from SAFP LSN
Arrival Rate = λ
Service Rate = µ
Packet Size = Ri
Queuing Delay = q
Transmission delay = Tx
Propagation Delay:
Acknowledgement Rate (Ack/sec):
SAFP HSN: λ 2
HSN SAFP: µ2
SAFP HSN = T2
SAFP HSN = α2
RH: Ack rate from HSN SAFP
T1 and T2 of the acknowledgment packets are ignored because the packet size is small. In addition,
the processing (service) time at SAFP is negligible.
4.3 Discussion
In this section, we investigate the time it takes one packet to travel from the low security network to
the high security network. In addition, we investigate the time it takes an acknowledgement of the
packet to reach the SAFP; as well as the time an acknowledgment from the SAFP to low security
network takes to reach its destination. Calculating the time from the SAFP point of view; the i th packet
is received at α1 + T1. Moreover, the i th packet is deleted from the buffer at α1 + T1 + 2α2 + T2 + 1/ µ2,
where α1 represents the propagation delay of the packets sent between the low security network and
the SAFP. Similarly, α2 represents the propagation delay of the packets sent between the SAFP and
the high security network. T1 and T2 represent the transmission delay from the low security network to
the SAFP, and the SAFP and the high security network, respectively. Finally, 1/ µ2 is the service time
at the high security network.
When we take the distance between the SAFP gateway and the high security network into
consideration, the time a packet stays in the SAFP buffer changes. For example, if the distance is
very large, then we can ignore T2 and 1/ µ2. Therefore, the i th packet is deleted from the buffer at α1 +
T1 + 2α2. As a result, the ability of the high security network to control the acknowledgment rates;
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