**3.3 Standardization issues**

Consider a mobile station moves from WiBro to cdma2000 networks as depicted in Fig. 4(a). When MS requests a communication channel to BSS, a bearer path MS-BSSPCF-PDSN-ACR

Fig. 4. L2 handoff procedure

4 Mobile Networks

Fig. 3. Interworking Architecture between cdma2000 and WiBro networks

**3.2 L2 handoff procedure**

being made.

**3.3 Standardization issues**

in standardization of each wireless network.

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.

In this section, we describe the proposed L2 handoff procedure. We consider two handoff scenarios. The first case is that the mobile station is moving from cdma2000 cellular network into WiBro. The second one is the reverse case. We do not consider the cases that handoff is occurring within its own wireless network, i.e., cdma2000 or WiBro. We also do not consider the initial call setup procedures for its own wireless network, since it is followed as described

Fig. 4 describes the proposed L2 handoff procedure. When the mobile station moves into a new network area, it processes L2 connection procedure. At this time, handoff information is transmitted to the network through the Origination message of cdma2000 or L2 REG-REQ message of WiBro as shown in (1) of Fig. 4(a) and (1) of Fig. 4(b), respectively. More specifically, the Origination message includes PANID (Previous Access Network ID). If the cdma2000 system receives the Origination message which contains PANID=ANID of WiBro, the cdma2000 system regards it as a vertical handoff from WiBro network. Similary, the REG-REQ message of WiBro can contain PANID=ANID of cdma2000 which means a vertical handoff from cdma2000 network. With such handoff information, the source PDSN or ACR detects the occurrence of handoff and extracts the target ACR or PDSN address for the handoff. Based on this address information, PDSN and ACR requests each other and generates tunnel for the handoff traffic. After the tunnel is setup, the corresponding PDSN or ACR is buffering packets destined to the mobile station while the requested L2 connection is

Consider a mobile station moves from WiBro to cdma2000 networks as depicted in Fig. 4(a). When MS requests a communication channel to BSS, a bearer path MS-BSSPCF-PDSN-ACR 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 comprise ANID in cdma2000 network.

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 management messages of WiBro standard specifications.

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 validate its performance.
