**3.1 Overview of L2 handoff**

For wireless communication, mobile terminal performs step-by-step layered procedures. First, when it is initially booted or located in new wireless network area, it scans L1 signal. As soon as it detects L1 signal, it performs L2 connection procedure. After successful L2 connection, mobile terminal can communicate or send/receive packets. The L3 handoff described in Section 2 initiates handoff after L2 connection. Our proposed L2 handoff procedure exploits L2 signaling messages transmitted during L2 connection setup. By acquiring packet flow path between network elements (e.g. PDSN and ACR in Fig. 3) while processing L2 messages, our method reduces packet loss occurred in handoff.

The proposed L2 handoff procedure considers the interworking network architecture as shown in Fig. 3. The cdma2000 and WiBro networks are loosely-coupled integrated through interworking between PDSN of cdma2000 and ACR of Wibro. So in exception of interworking of PDSN and ACR, each network is working and servicing independently. Our L2 handoff

(a) WiBro to cdma2000 L2 handoff (b) cdma2000 to WiBro L2 handoff

A Fast Handover Scheme for WiBro and cdma2000 Networks 59

should be setup, where ACR is the service anchor point in WiBro network. The origination message in (1) of Fig. 4(a) contains PANID field so that PDSN can connect to the appropriate anchor ACR using the field (3GPP2, 2002). To do this, a mapping function from the base station ID in WiBro network to ANID in cdma2000 network is required. A possible solution may be as follows: construct 48-bits base station ID in WiBro with SID (16 bits), NID (16 bits), PZID (8 bits), and base station number in a packet zone (8 bits), where SID, NID, PZID

Next, let us consider a mobile station moves from cdma2000 network to WiBro in Fig. 4(b). Similarly to the aforementioned case, when MS requests a communication channel to RAS, a bearer path MS-RAS-ACR-PDSN should be setup, where PDSN is the service anchor point in cdma2000 network. In order for ACR to connect to the right PDSN, PANID field should be delivered to ACR via RAS. It can be implemented by adding PANID filed in MAC

With this slight modification of standard specifications, the proposed L2 handoff scheme can be implemented as explained in this section. In addition, the fast handoff mechanism between PDSN and ACR will provide seamless services on vertical handoff. In the next section, we

The OPNET simulation, as shown in Fig. 5, has been conducted to examine the performance of the proposed scheme. We assume that there are 135 mobile stations used in the simulation

0, *<sup>v</sup> <sup>&</sup>lt;* <sup>0</sup> , *<sup>v</sup>* <sup>≥</sup> <sup>0</sup> (1)

<sup>−</sup> (*v*−*m*)<sup>2</sup> 2*σ*2

Fig. 4. L2 handoff procedure

validate its performance.

**4.1 Simulation model**

**4. Experimental evaluation**

and the traffic parameters are set as in Table 1.

*finit*(*v*) =

⎧ ⎪⎨

*k* √ 1 <sup>2</sup>*πσ <sup>e</sup>*

⎪⎩

comprise ANID in cdma2000 network.

management messages of WiBro standard specifications.

Fig. 3. Interworking Architecture between cdma2000 and WiBro networks

procedure exploits L2 signaling messages commonly existing in cdma2000 and WiBro. It does not require additional signaling messages so that our scheme can be implemented with ease.
