**4. User based Call Admission Control (CAC) algorithm**

Call admission control (CAC) plays a very important role in the IEEE 802.16 based wireless network. WiMAX networks aim to ensure that the QoS requirements for each service class are met. In order to provide QoS, the network should have a robust CAC algorithm.

When an SS/MS wants to establish a connection for a particular service class, it sends a DSA (Dynamic Service Addition) request to BS. This DSA request also contains the QoS parameters for the service class. Upon receiving the DSA request the BS decides to accept or reject the connection. If BS accepts the connection then it has to support the QoS needs of that connection.

When a BS decides to accept a connection, various factors need to be considered. For example the minimum and maximum data rates on the connection, the delay and jitter parameters for the connection etc. There can be other criteria like fairness, revenue per connection that can also play a role while admitting a connection.

Many CAC algorithms have been proposed both for wired and wireless medium. Because of the unique characteristics of wireless medium, many of the CAC algorithms of wired world cannot be applied to the wireless networks. Researches have proposed some CAC algorithms for WiMAX. In (Chen et. al, 2005) a simple bandwidth based CAC algorithm is proposed. A new connection is accepted if the bandwidth requirements for the connection can be satisfied by the BS. This algorithm does not take into consideration the deadline consideration of the connections. Once the bandwidth is allocated to the connection, the available bandwidth is calculated using the below equation:

$$BVV\_{avail} = BVV - \sum\_{s \in \{\text{LGS, RTPS, } nRTPS\}} \sum\_{l=1}^{N^s} C\_l^s \{rate\} \tag{13}$$

Where *rateC* ][*<sup>s</sup> <sup>i</sup>* represents the data rate for the ith connection which belongs to s service class. In (Chandra & Sahoo, 2007) a QoS aware CAC is proposed. BS contains CAC queues for each service class. So there shall be 5 CAC queues (one each for UGS, RTPS, eRTPS, nRTPS and BE). When an SS makes a CAC request for a particular connection, the BS shall queue the request in one of queues based on the QoS requirements for the Class. BS then goes through each of the queues and accepts the connections. (Chandra & Sahoo, 2007) also provides criteria for call admission for each of the service class. In (Shu'aibu et. al, 2010) (Shu'aibu et. al, 2011) a partition based CAC algorithm is proposed. The total bandwidth is divided into many partitions like constant bit rate partition (CBR), variable bit rate partition (VBR) and Handover partition (HO) etc. CAC is applied to each of these partitions. CAC algorithms proposed above, are all service class based algorithms. In this section we shall look at user based CAC algorithm. The algorithm is based on (Chandra & Sahoo, 2007).

#### **4.1 User based CAC algorithm**

Fig. 14 shows the control flow at the SS when a new connection request is sent.

Fig. 14. User based CAC at SS.

Many CAC algorithms have been proposed both for wired and wireless medium. Because of the unique characteristics of wireless medium, many of the CAC algorithms of wired world cannot be applied to the wireless networks. Researches have proposed some CAC algorithms for WiMAX. In (Chen et. al, 2005) a simple bandwidth based CAC algorithm is proposed. A new connection is accepted if the bandwidth requirements for the connection can be satisfied by the BS. This algorithm does not take into consideration the deadline consideration of the connections. Once the bandwidth is allocated to the connection, the

{ , , }1

*<sup>i</sup>* represents the data rate for the ith connection which belongs to s service

*avail i s UGS RTPS nRTPS i BW BW C rate* 

class. In (Chandra & Sahoo, 2007) a QoS aware CAC is proposed. BS contains CAC queues for each service class. So there shall be 5 CAC queues (one each for UGS, RTPS, eRTPS, nRTPS and BE). When an SS makes a CAC request for a particular connection, the BS shall queue the request in one of queues based on the QoS requirements for the Class. BS then goes through each of the queues and accepts the connections. (Chandra & Sahoo, 2007) also provides criteria for call admission for each of the service class. In (Shu'aibu et. al, 2010) (Shu'aibu et. al, 2011) a partition based CAC algorithm is proposed. The total bandwidth is divided into many partitions like constant bit rate partition (CBR), variable bit rate partition (VBR) and Handover partition (HO) etc. CAC is applied to each of these partitions. CAC algorithms proposed above, are all service class based algorithms. In this section we shall look at user based CAC algorithm. The algorithm is based on (Chandra & Sahoo, 2007).

Fig. 14 shows the control flow at the SS when a new connection request is sent.

Start

Crease DSA request

Add the service flow specific QoS parameters to the DSA request

Send DSA request to BS

End

[ ] *<sup>s</sup> <sup>N</sup> <sup>s</sup>*

<sup>13</sup>

available bandwidth is calculated using the below equation:

Where *rateC* ][*<sup>s</sup>*

**4.1 User based CAC algorithm** 

Fig. 14. User based CAC at SS.

Fig. 15 shows the classification of DSA request into different queues based on the priority of user.

Fig. 15. Classification of DSA request at BS based on priority of User.

Because of lack of space, the control flow of eRTPS service class cannot be shown. However the logic for classifying the DSA request for eRTPS would be similar to UGS.

Once DSA requests are classified into the respective queues, BS goes through the DSA requests in each queue to admit the connection. High Level view of Admission control algorithm is given in Fig 16.


Fig. 16. User Based Admission control.

So, first, connections of priority UGS shall be accepted, followed by Non priority UGS. Priority RTPS and Non Priority RTPS follow next. Once RTPS connections are taken care, priority and Non priority eRTPS connection as admitted in that order. Subsequently priority and Non priority nRTPS connections are admitted. And finally priority and non priority BE connections are admitted.
