SA-CA-MN Interaction

Since MN has two settings, AAA support and QoS option, hence the combination of these two values will result in three different types of interaction (QoS can be ON only when AAA is ON). We describe these interactions in three cases, including [AAA/QoS – OFF/OFF], [AAA/QoS – ON/OFF], and [AAA/QoS – ON/ON].

Case 1: [AAA/QoS – OFF/OFF]

Figure 3.6 Message flow in Case 1.

If both AAA and QoS are disabled in MN’s configuration, MN will behave as an ordinary mobile node in the wireless network. It seems that the AAA system never exists. However, there is still one action needed to be done by MN, the registration process. When MN enters the scope of CA-1, it soon hears the advertisement and then sends a MNReg message to CA-1. After checking the value of AAA field, CA-1 generates a CF+MNReg message to SA for updating the field, number of mobile users, in CA-record. When the CF+MNReg message arrives at SA, SA processes the request and modifies the corresponding records.

Once the alteration has been complete, a CF+MNAck message is created by SA to inform CA-1 of successful modification. Finally, CA-1 sends a MNAck message to terminate the registration procedure. The detailed message flow is elaborated in Figure 3.6.

Figure 3.7 Message flow in Case 2.

In case 2, the AAA support is turned on and QoS option is turned off. While a

SA CA-3 CA-4

MN gets into the wireless coverage of CA-1, it soon senses the advertisement and checks its AAA setting. Since the AAA is set as ON, then MN produces a ProbeReq message to CA-1 right away. The ProbeReq message contains MN’s ID, MN’s IP address, X-coordinate, Y-coordinate, Z-coordinates, and distance-sensitive option. The distance-sensitive option is used in the CalBest algorithm described below and is configured by MNs. CA-1 checks the type of arrival message and attaches its IP address to the end of message so as to generate a new message, CF+PbReq. The CF+PbReq message is forwarded to SA. SA recognizes the CF+PbReq message as an AAA query then makes use of the CalBest algorithm to output the recommended movement in the CF+BstAck message.

The CalBest algorithm takes four parameters as its input, including X-coordinate, Y-coordinate, Z-coordinate, and distance-sensitive option in the ProbeReq message. If the distance-sensitive option is OFF, which means to select a least-load AP without considering the distance between the mobile user and the new AP, CalBest sorts the CA-record based on the number of mobile users and available bandwidth. In table 3.1, CA-4 will be recommended to the MN in the end. On the other hand, if the distance-sensitive option is set as ON, CalBest algorithm first repeats the sort procedure described above. After that, the qualified finalists (with slighter load than current AP) are sorted again on the basis of the distance to the mobile user. In table 3.1, CA-2 replaces CA-4 to be the best choice.

Following the output of CalBest, SA generates a CF+BstAck message to CA-1.

CA-1 informs MN of recommended movement by sending a BstAck message. MN moves to the location as the message suggests and initiates the regular registration procedure present in Section 3.2.3. Figure 3.7 illustrates the message flow among SA, CA, and MN.

Case 3: [AAA/QoS – ON/ON]

With the AAA enabled (AAA support is ON), this guarantees mobile users the quality of service in the beginning. In order to keep monitoring and maintaining the quality of the ongoing connection, we introduce the QoS option to the MNs. The purpose of QoS option is to periodically check the throughput (delay or jitter) of a connection. Once the value of throughput (delay or jitter) is decreased below a specified threshold for accumulative sixty seconds, a ProbeReq messages will be automatically generated and sent to the corresponding CA on behalf of the MN.

For instance, a MN in case 2 accepts the suggestion thus moves from a dense area (CA-1) to a sparse area (CA-4). After arriving CA-4 area, MN starts the applications and the quality of service is definitely guaranteed in the beginning. As time passed by, there are some users who disable the AAA support and enter into the wireless coverage of CA-4. Nevertheless, MN was not aware of other users’ coming, and the throughput of the connection drop drastically. With the feature of QoS option, a monitor mechanism in MN will spontaneously be enabled and keep tracking the throughput of the connection. If the throughput is under the threshold for accumulative sixty seconds (can be changed by users), then the monitor mechanism will send a ProbeReq message to CA-4 for another AAA query (same procedure in case 2). Consequently, MN will soon be advised to move to another area to gain better services. Therefore, the joint use of AAA support and QoS option will ensure the quality of service for the entire connection.

The threshold setting is based on the class of service, and different services have different requirements for throughput, delay, and jitter. Table 3.2 shows the threshold for service class. Moreover, Figure 3.8 demonstrates the message flow in case 3.

SA CA-3 CA-4

Code Class of Service Throughput Delay Jitter

0 Default T_D D_D J_D

1 Best effort T_BE D_BE J_BE

2 Voice T_VO D_VO J_VO

3 Video T_VI D_VI J_VI

4 Reserved - - -

Table 3.2 Threshold for service class.

Figure 3.8 Message flow in Case 3.

In Figure 3.8, a ProbeReq message has been automatically created and sent to the CA-4. Meanwhile, MN waits for the BstAck message from SA. Once the BstAck

MNDReg

MNReg

SA CA-3 CA-4

message is received by a MN, MN deregisters with CA-4 before moving to the recommended area, CA-2. While the deregistration procedure is complete (MN receives the MNDAck message), MN immigrates to CA-2 and then initiates the regular registration process at the same time.