Our Proposed Mobility Management Algorithm

When the mesh client is associated with an any access point, QoS profile information is shared and the session is established and resources are reserved to satisfy the QoS requirement for this session. Session can be established using any signalling protocol such as Session Initiation Protocol (SIP) (Rosenberg et al., 2002). As an example, when a session is established between terminal T1 and gateway (node 7) in Figure 3.1, a route (1 → 5 → 6 → 7) will be reserved for this session only. Our handoff management scheme is based on selecting a new route for the Mobile Node (MN) before it moves and becomes disconnected from node 1. In order to reduce the handoff delay, this new route should be maximally jointed with the primary route.

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Figure 3.1 New Route Handoff Decision Taken from Khasawneh et al. (2014)

Three timing thresholds are introduced in our algorithm. Whenever the mobile node is moving and the Signal to Noise Ratio (SNR) reached a predefined threshold. The handoff preparation process is triggered by scanning and collecting information about the channels and the access points around the mobile node. After finishing this step, our proposed algorithm is trying to find the maximally jointed route with the old primary route. As shown in the figure below the new route is found which is maximally jointed with the primary old route. Location update messages are embedded in the routing packet header to avoid making an overhead in the network, this is done at the third time threshold.

As previously mentioned, at the first time threshold, and when the mobile client has an afforded throughput less than the minimum throughput acceptable for the mobile client the handoff preparation process is triggered. In order to calculate the throughput Shannon's formula is used as indicated below:

2 log (1 ) AP AP AP THR ₌W ₊SNR (3.1)

Where the THRAP is the maximum theoretical data rate for WLAN network, WAP is the bandwidth for the WLAN link and SNRAP is the Signal-to-Noise Ratio, which can be calculated as described below:

, , , APj i APj i APj i B G P SNR P = _(3.2)

Where GAPj,i is the channel gain between terminal i and the APj ; PAPj,i is the power transmitted from the APj and terminal i; and PB is the power of the noise at the terminal level.

As the radio wave is propagating over a distance, there is a path loss resulted which can be calculated by the following formula:

Pathloss dB( ) 20log ( ) 20log ( ) 32.44= 10 d + 10 f + −Gtx−Grx _(3.3)

Where d is the distance between the sender and the receiver in meters, f is the signal frequency in MHz, Gtx and Grx are the gains of the transmitter and receiver, respectively.

The newly selected route have to meet the QoS requirement for the mobile node session. When finding the maximally jointed path with the old primary path. This will save us time finding the complete route to the gateway which has to guarantee the same level of QoS and sometimes hard to find in case of highly congested network. The detailed mobility management scheme is given in the algorithm below.

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Algorithm 3.1 Handoff Management Scheme

1. if THRi < THRi , thresold then

2. Trigger handoff preparation scanning 3. process at time threshold 1.

4. Find all APs in MN transmission range. 5. Calculate the SNR for each AP and store 6. them in SNRAPs array.

7. end if 8.

9. At time threshold 2 10. for all AP(j)

11. if SNRAPs(j) >= SNRAcceptable then

12. Add AP(j) to the APCandidate array.

13. end if 14. end for 15.

16. for all APCandidate(k)

17. Find shortest path to the existing tree. 18. Add Pk to the PCandidate array.

19. end for 20.

21. for all PCandidate(t)

22. Find the number of common nodes

23. between Pprim and PCandidate(t).

24. end for 25.

26. Choose the optimal path with the maximum

27. number of common nodes.

28.

29. if multiple paths are found with the same 30. number of hops the existing tree then

31. choose the one with the shortest path to 32. the gateway.

33. end if 34.

35. At time threshold 3

36. Perform handoff process where a new route 37. satisfies QoS requirements for the session. 38. Send Link layer association message from 39. MN to the new AP.

40. Update all the routing tables up to the

42. packet.

43. Send Link layer de-association message from MN to the old AP.

Our handoff management sequence diagram is shown in the figure below. The Mobile Node (MN) has an established connection and a reserved resources through its route up to the destination gateway. This connection is passing through the old Access Router (AR). Whenever the predefined threshold is reached, a route discovery process is triggered based on our proposed algorithm, which will find the maximally jointed route with the old route and trigger multi-homing is needed. After the route is discovered, a link layer association is performed with the new AR selected as shown in the figure below.

Figure 3.2 Handoff Management Sequence Diagram Taken from Khasawneh et al. (2014)

The update process is taken place to update all the routing tables up to the first common router, which is the first router which is existing in both, the old and new selected route. All the uncommon routers in the old route should release the resources assigned to the user since the user traffic now is passing through different route, which is called the link layer de- association process. When this process is done all the upcoming traffic are going to be

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transferred through the new route. In some specific situations, where the congestion is at a high level, the mobile node does not find an access point to be associated with. In this case, multi-homing is triggered in order to avoid the hard handoff scenario. The multi-homing triggering conditions will be explained in more details in section 3.5 below.