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Handling Mobility in a Wireless ATM Network Bora A. Akyol Donald C. Cox Department of Electrical Engineering Stanford University Stanford, CA 94040 [email protected]

Abstract

The world of wireless telecommunications is rapidly changing. The capabilities of wireless networks are improving at a steady pace. This paper presents a protocol implementation for implementing mobility in an Asynchronous Transfer Mode (ATM) network. The vision of the authors is of one \ATM-based wireless telecommunications network" that is capable of supporting a variety of today's applications with room to grow for advanced applications of the future.

1 Introduction

Wireless communication networks, e.g cellular telephony, have rapidly grown to be a sizable part of the world telecommunications market over the past two decades[2]. One reason for the rapid growth of wireless communication networks (WCN) is the mobility of a tetherless terminal. Next generation wireless networks are called Personal Communication Services (PCS) Networks and will provide for global user mobility, a life-long user identi cation numbering system and ability to accommodate varying data rates. The next generation xed network technology is Asynchronous Transfer Mode and we envision the communication needs of the next generation wireless networks to be accommodated by a xed Asynchronous Transfer Mode (ATM) network. An ATM network is designed to handle integrated voice, video, and data in a single protocol. Future wireless communicators may also handle voice, data, and perhaps images and video[4, 7]. It is then logical to consider an ATM network as the xed supporting network since ATM can carry wireless trac of varying data rates across long distances[5, 9, 10, 11]. We will refer to this combined network as the \ATM-based wireless PCS network." We should also note here that the di erentiating factor between wireless and xed network users is mobility and this paper concentrates on implementing mobility  Research supported by Motorola Inc., Schaumburg, IL. and Paci c Bell, San Ramon, CA.

within the xed ATM network (The authors are aware of the xed network user mobilityschemes such as callforwarding; however, mobility of the wireless users and the ability to place a call anywhere provides sucient reason to consider only the wireless network users.). We propose a possible implementation of mobility in a wireless network supported by an ATM network using the ATM User Network Interface (UNI) signaling and a two-tier database architecture to keep track of user movement.

2 Database Architectures to Support Mobility in an ATM Network

Mobility is a key advantage of a wireless network. In order to provide mobility, the wireless network must keep track of the location of its users. In a network where users are globally mobile, the tracking of users becomes one of the major functions of the wireless network. A database system is used in order to support the tracking process. The two-tier database architecture used in this research is advantageous in a geographically partitioned network such as a PCS network. We assume that the wireless network service area is partitioned into \zones". Each zone consists of a set of radio ports, the radio port controllers, and the xed network infrastructure that interconnects these radio ports and provides xed network access (See Figure 1). Two types of xed network connections exist in a zone. The rst is the ATM network that interconnects the zones in the wireless network. The second type of connection is the connection between the radio ports and the radio port controllers. This second type of connection is not considered in this paper, but will be addressed in our future research. Hence, in this paper, we assume that the ports and the port controllers are interconnected by an optimized communications link. There is also a database associated with every zone. This database is partitioned into two segments. One segment is reserved for the users that are permanently

independence provides for exibility in choosing service providers and changing home locations at the cost of increased complexity. We are not including the hierarchical structure in this research.

Radio Port Radio Port Radio Port Radio Port

Radio Port

Radio Port Controller To the ATM Network

Radio Port

Radio Port Controller Wireless-to-ATM Network Interface Database

Figure 1: A Zone in the PCS Network registered in that zone, i.e. the \home" segment. The second segment is for the users that are visiting the zone. The network databases do not keep track of the radio ports that connect the users to the network. The port controller keeps track of radio port and active user information. The user identi cation numbers determine the location of user's permanent registry and are used in tracking the users. The nearest database is the rst place to be searched in order to locate user information. If the desired information is not found at the nearest database then the permanent registry for that user is queried. We will refer to this architecture as the \twotier database architecture." The European GSM and U.S. IS-41 digital cellular standard of \Home Location Register/Visiting Location Register" is one example of a two-tier database architecture. One important advantage of a two-tier architecture as described above is the two-step deterministic search where a user's pro le is retrieved in at most two database look-ups.. An alternative to a two-tier database architecture is a hierarchical structure which takes advantage of the locality and motion patterns of users and organizes the distribution of data accordingly. The main di erence in terms of user identi cation numbers between a hierarchical scheme and a two-tier scheme is location dependence. In a hierarchical scheme, the user identi cation numbers do not carry any location information; therefore, the hierarchical scheme will also be referred to as a \Location Independent" scheme. The two-tier architecture is characterized as a \Location Dependent" database architecture. The location

3 Support of Mobility in an ATM Network

In this section we discuss the network transactions that are related to user mobility and suggest how they can be implemented using the ATM User Network Interface 1 (UNI) signaling protocol [1]. The network transactions related to user mobility are:  Registration,  Call Setup,  Hand-o . We refer to the operational software that manages a zone and the signaling systems in that zone as the \Zone Manager." The zone manager is responsible for database and connection management functions in the zone. There are two networks and two kinds of signaling in the ATM-based wireless PCS network architecture. The zones are interconnected by an ATM network. The zone managers must use the ATM signaling in order to establish connections through the ATM network. The radio ports and portables belong to the wireless network, and the zone managers exchange wireless network signaling messages in order to support the needs of the users and the network itself. The wireless network signaling messages are encapsulated into ATM cells and transmitted through the ATM network to their destinations. See gure 2 for a depiction of connection types and protocols between the layers in the wireless and ATM networks.

3.1 ATM Connection Setup Procedure

A procedure that is common to all of the wireless network transactions is establishing a connection through the xed ATM network. We will digress here and describe how an ATM connection is established in a xed network context[1], using current ATM protocols between two ATM network entities and then describe how registration, call setup and hand-o are implemented using this procedure. 1 ATM UNI (version 3.1) is an implementation agreement proposed by the ATM Forum and coincides with the ITUQ.2931 signaling protocol implementation. In this text the UNI signaling messages are typeset in BOLDFACE characters. Note also that the zones of the wireless network will appear as \users" to the xed ATM network hence use of ATM UNI signaling is justi ed.

Radio Ports

Radio Ports *

Radio Port Controllers

Radio Port Controllers Zone Manager (ZONES) ATM Network

Wireless Network Signaling Messages Using ATM ITU Q.2931B Signaling Messages Using ATM

Backbone Physical Link

Wireless Network Layers

Zone Manager (ZONES) ATM Network

Backbone Physical Link Layer Protocol

Physical Link

(*) The radio ports and port controllers can only communicate with the corresponding zone managers. The comm. between radio ports and port controllers is unspecified.

Figure 2: Protocol Layers in the Wireless and ATM Networks. The radio ports and the port controllers may only communicate with the zone managers. An ATM connection in a xed network context is established between two parties directly connected to the ATM network, the calling party that initiates the connection and the called party that is the destination. This process is discussed in the following paragraphs 2: 1. SETUP: The setup message is sent from the calling party 3 to the ATM network and from the ATM network to the called party. This message includes the called party address information, ATM user cell rate (ATM trac descriptor), broadband bearer capability and quality of service (QoS) parameters. The ATM network is responsible for selecting a connection identi er and sending a setup message to the called party. For network management purposes the connection is also assigned a call reference by the ATM network. This call reference is used in all of the following messages to refer to the ongoing connection setup. We will refer to this procedure as the ATM connectionsetup procedure throughout the text. Note that this procedure is in a xed network context and is used by all ATM network users. The zone managers will also use this procedure to establish ATM connections. 3 The calling/calledparties will be zone managersin the wireless access ATM network context. If the radio ports, and the port controllers are also interconnected by the ATM network, then the same procedure will be used by the ports and controllers as well. 2

2. CALL PROCEEDING: The ATM network upon receiving the SETUP message will determine whether the access to the requested service is authorized. If the access is authorized then the network sends a CALL PROCEEDING message to the calling user. The calling user then waits for the connection. 3. CONNECT: The connect message is sent by the called party to the ATM network to indicate call acceptance. The ATM network then sends a similar message to the calling party to indicate that a connection is established. If the called party is not able to send a CONNECT message in the allocated time, it sends a CALL PROCEEDING message to the ATM network while processing the connection request. If a CALL PROCEEDING message is sent by the called user to the ATM network, the ATM network waits for a CONNECT message until the connection setup timer expires. 4. CONNECT ACKNOWLEDGE: The calling user sends this message to the ATM network to acknowledge the successful connection, and goes into active state. The ATM network sends this message to the called party to acknowledge the successful connection setup. The state diagram for ATM connection setup is given in Figure 3. The ow of ATM signaling messages for a successful ATM connection setup is given in Figure 4. In a network where multiple hops are needed to establish a connection, this procedure is repeated at every hop. If an intermediate node does not have the resources to establish the connection, a RELEASE COMPLETE message will be sent to the initiating party to clear the call. If the called user is busy or if the incoming request is rejected the called user will send a RELEASE COMPLETE message which will include the reason for refusal. An active connection is terminated by the user by sending a RELEASE message to the network and the network will respond with a RELEASE COMPLETE message and both parties will enter the idle state.

3.2 Registration

In Section 3.1 we discussed how an ATM connection in the xed ATM network is established. In the following sections we show how the ATM Connection Setup procedure may be used to implement Registration, Call Setup, and Hand-o transactions of the wireless network.

Receive (Rcv) Call Proc. from Network

Send SETUP to Network

IDLE

CALL INIT

Rcv. CONNECT from Network Send CONNECT ACK.

CALL PROC.

ACTIVE

Time Expired Call Rejected

Call completed

Figure 3: ATM Connection SETUP state diagram Calling Party

ATM Network Called Party

SETUP SETUP CALL PROC. CONNECT

CONNECT

CONNECT ACK. CONNECT ACK.

Figure 4: Signaling Message Flow for ATM connection setup. Registration is performed to maintain information about the mobile user locations. It is also used to ensure the validity of user location information. The registration is performed as follows: 1. The registration process starts with the transmission of the user identi cation number (UID) and user's previous zone identi cation from the portable that enters a new zone. The portable recognizes the zone change by comparing the current zone identi cation with the stored last zone identi cation. The radio ports are assumed to transmit zone identi cation beacon signals periodically to assist the registration process [3]. After exchange of authentication keys, user's password is also transmitted over the radio interface in an encrypted message. 2. Upon receiving the UID and the authentication information, the zone manager (ZM) of the new

zone establishes an ATM connection to the zone that contains the user pro le (\home" zone) 4. The location of the user pro le may be obtained by querying the user's previous known zone. The zone managers communicate by using the wireless network signaling protocol messages that are encapsulated into ATM cells. 3. After the ATM connection between the new and home zone managers is established, the zone manager of the user's current zone requests user's authentication record and upon receipt of this record, the user is authenticated. 4. If authentication is successful, the user's pro le is updated with the new location information and the updated pro le is transferred to the current zone. 5. The user's pro le in the previous zone is deleted by establishing an ATM connection to the previous zone manager. 6. If the authentication is unsuccessful then the user access is denied. 7. After the registration transaction is complete, the connection is released using RELEASE and RELEASE COMPLETE messages. Please see Figure 5 for message ows for a successful registration.

3.3 Call Setup

The call setup procedure is used to establish a connection between two wireless network users. In this section, the originating zone refers to the calling user's zone and the destination zone refers to the called user's zone. The call setup proceeds as follows: 1. Called user identi cation number (CUID) is transmitted from the portable to the originating zone manager together with call setup parameters such as required bandwidth, trac type, etc. 2. The originating zone manager (OZM) forms an ATM UNI protocol SETUP message using the incoming call parameters and proceeds as follows: (a) OZM requests the called user's location information from the wireless network. The procedure for this process is similar to what is described in sections 2, 3.2 and gure 5. 4 Note that if the user pro le is stored in a hierarchical database structure then a search has to be performed in order to locate the record; however, the steps involved in each step of the search will the same as what will be described in the following paragraphs.

Portable New Zone Registration Request

Home Zone Previous Zone

Establish ATM connection and obtain User Profile from Home Database



Call blocking may be checked at the same time as the user's pro le is obtained.



The connection setup for the user connection may be initiated by the OZM. Calling User

Zone Manager

Call Setup Request

User Profile

Notify user

ATM Network

User Database

Zone Manager

Called User

ATM Conn. Setup to called user DB.

User Loc. Data

If user is authenticated delete profile from previous zone.

ATM Conn. Setup to called user zone.

Page User Accept Conn.

Figure 5: Signaling Message Flow for Registration (b) When the called user's location information is retrieved from the network, an ATM connection is established to the called user's current zone manager using the ATM connection setup procedure. (c) After the connection is established, the originating zone manager (OZM) passes the calling user's identi cation number to the destination zone manager (DZM) and requests a connection setup. If the calling user's identi cation number is not in the call blocking list of the called user then the called user is paged, if the page is successful, the DZM requests an ATM connection between the two users. If the page is not successful then the called user is pronounced inactive and the proper record is updated. If the calling user is in the call blocking list of the called user, the connection is rejected. (d) Pending ATM user connection establishment, the calling user and the called user are noti ed and the connection is established. (e) If the called user is busy, the DZM noti es the OZM of the \busy" state and call attempt is terminated. The connection between the two zone managers is cleared. 3. After the call is complete, the ATM connection is released using RELEASE and RELEASE COMPLETE ATM signaling messages. See Figure 6 for the call setup transaction ow for a successful call. Remarks:

Respond

Setup User Conn.

Alert Calling User

Respond User Conn. Established

User Conn. Established

TWO WAY USER CONNECTION ESTABLISHED

Figure 6: Signaling Message Flow for Call Setup

3.4 Inter-zone Hand-o

The inter-zone hand-o process depends on its implementation in the wireless network. We will assume the following:  Hand-o is portable initiated. The portables monitor the link quality in terms of received signal power to candidate radio ports and when the link to another port becomes stronger that port is selected and hand-o is executed[3]. 

The hand-o process may be initiated in two ways: The portable may tune into the control channel of the candidate radio port and initiate a hand-o through the candidate port or the portable may use the existing link with the previous port to initiate the hand-o . The latter method is used more frequently in present systems[3]; however, both methods have merit and will be discussed.



The only kind of hand-o that generates network trac is an inter-zone hand-o . Therefore we will limit the discussion to inter-zone hand-o s. The intra-zone hand-o is performed in a similar manner by the radio port controller without generating network signaling trac.

Since we limit our discussion to the inter-zone hando s, the candidate radio port and the previous radio port are in di erent zones. The candidate radio port is controlled by the \candidate zone manager." The previous radio port is controlled by the \previous zone manager." Please refer to gures 7, 8 and 9 for details. The hand-o will proceed as described below:

3.4.1 Hand-o through the Previous Port

1. In this case, the portable realizes that a link of better quality exists to a candidate radio port. The portable records the identity of the candidate port. 2. The portable sends a message to the previous zone manager (PZM) desiring a hand-o to the candidate radio port. 3. The PZM establishes an ATM connection to the candidate zone manager (CZM) using the ATM connection setup procedure. 4. The PZM transfers a copy of the user pro le to the CZM, CZM assigns a channel to the user, relays the channel assignment information to the PZM. 5. The PZM contacts the end point for the user connection and requests re-routing to the candidate zone. 6. Once the re-routing is complete, the PZM contacts the portable and relays the channel assignment information. 7. The portable tunes to the new channel and contacts the CZM. 8. The CZM and the portable verify the connection. After veri cation the CZM noti es the PZM of the successful hand-o . If the connection is not veri ed, the portable tunes to the previous channel and starts scanning for candidate ports. The CZM deallocates the assigned channel. 9. If the hand-o is successful, the PZM deletes user pro le.

3.4.2 Hand-o through the Candidate Port

1. The portable initiates a hand-o by establishing a link with the candidate radio port in the candidate zone and requesting a hand-o from the candidate zone manager. This message includes the user's identi cation number and previous zone identi cation.

2. The candidate zone manager acknowledges this message. The candidate zone manager (CZM) establishes an ATM connection to the previous zone manager (PZM) using the ATM connection setup procedure. The portable tunes back to its previous channel after the acknowledgment is received. 3. Following the connection establishment, the CZM requests a hand-o . The PZM transfers the user pro le to the CZM using the ATM connection. The PZM shall also send a re-routing message to the ATM network so that the route to the candidate zone can be setup 5 . 4. The CZM provides the PZM with the channel assignment information for the portable. Pending re-routing success, the CZM starts to bu er the information for the portable. If the re-routing is not successful the hand-o attempt is dropped, the PZM is noti ed. The PZM in turn noti es the portable. 5. If the re-routing is accomplished, the PZM sends the proceed with hand-o message to the portable that is still tuned to the channel in the previous zone. The proceed with hand-o message includes the channel assignment information for the candidate zone. If the portable cannot be raised at the previous zone, the CZM will be noti ed and the CZM will page the portable to establish a link. This page includes the candidate channel assignment. 6. The portable, after receiving either the channel assignment information or the page from the CZM, tunes to the assigned channel and transmission is initiated. In either case the bu ered information is passed on to the portable in the order received. If the accepted time limits for the connection are exceeded then some information such as expired voice packets may be dropped, 7. When the stability of the new link is proven, and thus the hand-o is completed, the ATM connection between the zone managers is released. Upon release of this connection the PZM updates the user's pro le using a procedure similar to registration (authentication is not needed in this case) 5 Currently this can only be achieved using a SETUP message to establish the new connection. However, we can use the fact that the hand-o is most likely to occur between neighboring zones and perform the re-routing at the nearest common network point, this capability will need to be added into the ATM network signaling protocol.

and erase the information that is bu ered for the portable at the previous zone.

Portable

Previous Zone Mgr.

Hand-off Request

Radio Port Controller

Candidate Link

Establish ATM Conn. Request Re-routing

Portable

Candidate Radio Port

Channel Assignment Data

Re-route complete

Verify Radio Connection Notify end point Connection Verified

Radio Port Controller PREVIOUS ZONE

Establish ATM Conn. Request Hand-off Channel Assignment

Previous Link

Previous Radio Port

Candidate End point for Zone Mgr. user connection

CANDIDATE ZONE

Figure 7: The Hand-o : Basic Picture. Here the candidate zone is designated as a candidate for hand-o . The previous zone is the zone the portable is communicating with before the hand-o . The di erences between these two alternative methods are subtle; however, the former method (hand-o through the previous port) does not need synchronization to the control channel of the candidate port and uses the existing radio link to the previous port for hand-o related signaling. Note that if hand-o is being performed because the existing link is deteriorating, then the success of the former method is not assured; nevertheless, if the portables monitor the link quality frequently then this will be a minor problem. The latter method su ers from diculty of carrying on two connections at once but does not su er from the failing link problem of the latter. We have now outlined the proposed implementation of mobility within the xed ATM network. The next topic will the investigation of the impact of mobility on the xed ATM networks.

4 Impact of Mobility on the ATM Network

In this section we discuss the impact of mobility on the current ATM network technology. The current ATM networks are being designed to handle xed users. The user's identi cation number is used to determine where the user is and how to route a call to the user. However, in a mobile user environment the user numbers do not yield any information about the user's location. In such an environment the user's number

Re-routed data

Figure 8: Signaling Message Flow for Successful Hando , Case 1, Using Previous Port must be used as a means to retrieve the location information. Note that if the wireless and ATM networks were separate entities in which no cross-interaction between users occurred, then the discussions in the previous sections would provide a way of implementing a self-contained wireless network supported by an ATM network. However, the users in the respective networks need to interact with each other, so the ATM signaling protocols need to be modi ed to understand the existence of mobile users. In the following sections we will discuss methods which may be used to make ATM understand the existence of mobile users.

4.1 Making ATM Work with Mobile Users

4.1.1 The Interim Solution

The ATM signaling protocol currently understands only xed user numbers. These numbers are treated very much like a phone number to establish where to route a call to any given user. When xed ATM users are allowed to interact with mobile users we will face the following numbering system problem. When an ATM user desires to connect to a user that is a wireless network subscriber, the called user's number is useless for an ordinary ATM host. This implies that we need to have a numbering scheme that accommodates the mobile users. An interim solution is to to de ne PCS subscriber numbers as specially marked ATM numbers, e.g. special area codes, and have ATM to wireless user calls routed to designated wireless user switches that re-route the calls to their nal destinations. The calls from wireless network subscribers to xed ATM

Portable 1

Alternate Zone Manager

Initiate Hand-off Acknowledge

Previous Zone Manager

Hand-off Request

End Point for the User Connection

Re-routing User Information

Request

Acknowledge ATM Connection Setup

Acknowledge

User Data

User Data Sent to New Zone

Hand-off Proceed

Verify Radio Connection

Release Connection Release

Initiate Data Transfer

Hand-off Complete

Figure 9: Signaling Message Flow for Successful Hando , Case 2, Using Candidate Port hosts do not constitute a problem as the burden of establishing the connection lies with the wireless network which is aware of both kinds of numbering plans and users. This alternative is easy to implement and does not require any major modi cation to the ATM protocols. Because of ease of implementation this approach could provide a good interim solution. Unfortunately, this interim method may not scale well as the number of wireless network users grow and the wireless switching centers get congested. We might also face having to re-route calls across hundreds of miles to establish a connection to a user that is only 5 miles away. This leads the way to our next topic which relieve the problems discussed so far.

4.1.2 Wireless-aware ATM Interface Approach

A wireless-aware ATM interface approach will distribute the wireless switching center functionality to all xed ATM end-points including ATM switches and ATM interface equipment at user terminals. This is accomplished by designating a special numbering scheme which identi es the wireless users as \mobile" and cause a di erent signaling mechanism to be employed for voice and data calls that are to or from wireless users. These mechanisms are similar to the wireless network messages discussed in section 3. For example, if an ATM user needs to establish a data connection to a wireless network user, the protocol recognizes that the user is mobile and try to obtain

the location information for that user using wireless network signaling procedures. Once the location information is obtained, a connection is setup and the users start exchanging information. This distributes the intelligence to the xed network user interfaces and will result in more e ective use of network resources. The following are a few additional issues that need to be addressed for implementation of ATM-based wireless PCS networks.

4.2 Wireless users in a Multi-tier Environment

A multi-tier network environment is de ned as one that will provide di erent bandwidth capacities to users depending on their locality. An example of a multi-tier architecture is given in [8]. In a campuswide setting the users may be able to attain a few megabits per second data rates. As they leave the campus and go into a wider area, the wireless network may change the available data rate to a lower value but still will allow the connection to continue in a seamless manner. Accommodating changing data rates on a pre-established connection may cause a problem to the supporting xed ATM network. In some environments a tier change could cause the available channel bandwidth to decrease or to increase by an order of magnitude or more. Currently, using ATM UNI signaling, once an ATM connection is established the only way to change the allocated bandwidth is to reestablish the connection. Clearly, we need to de ne a procedure by which the bandwidth allocated for an established connection may be changed. One approach to solving this problem can be classi ed as an extension of ATM ow control algorithms. When the user changes a tier in the multi-tier network, the ATM ow control mechanisms will either detect an extreme congestion in the case of a bandwidth decrease or they may be programmed to detect a completely empty packet queue in case of a bandwidth increase. This in turn could trigger the network to send a message to either party asking for renegotiation of ATM trac descriptors. We shall call this method the Autonomous Bandwidth Negotiation Algorithm. Alternatively, the wireless access network could notify the ATM network of the tier change. Upon noti cation the ATM network may change the parameters for the established connection.

4.3 Handling Bursts of Errors in the Wireless Network

The wireless environment su ers from stochastic channel degradation; therefore, occasional bursts of errors may occur for data that is transmitted over a

radio interface. In the current ATM adaptation layer implementations, the only recovery from such an error burst is re-transmitting the complete information packet through the network. In order to prevent the excessive use of network resources the wireless network zone managers may need to be able to bu er large amounts of data so that such errors only result in a re-transmit over the radio interface.

4.4 Re-routing Strategy for Hand-o

A hand-o is performed when a portable unit determines that a better quality radio link is available. Typically hand-o results in switching to a neighboring zone. When the hand-o process is handled by the network, we may make use of the locality of hand-o and choose to re-route at the nearest common network node between the two zones. However, the current ATM signaling does not permit a re-routing at an intermediary point of an ATM connection[1]. In order to handle hand-o in an ecient manner we need to de ne the protocol that needs to be added to the existing ATM protocol set so that the concept of nearest common node is de ned. Once the nearest common node is de ned then what needs to be done for hando is to adjust the routing and translation tables at the nearest common node and the nodes between the nearest common node and the zone where the hand-o is performed. This strategy is Nearest Common Node Re-routing. Some alternative hando approaches are discussed in [10, 11].

5 Conclusion

The integration of the xed Asynchronous Transfer Mode and the next generation wireless personal communications networks is a challenging problem. The current ATM networks do not have the means to understand or to support mobile users. On the other hand, the speci cations for current wireless networks are still being designed to interface with the plain old telephone networks. In this paper we proposed a protocol implementation to integrate mobility into the ATM protocol stack. Our vision is of one network that is an integration of today's xed and mobile networking technologies; namely, an ATM-based wireless PCS network. Also in this paper, we have established a database architecture to support mobility in the ATM network, we have de ned the signaling structure needed to support the mobility and we have given counterparts for these signaling messages in terms of ITU-Q.2931 signaling messages. We also identi ed the issues involved in the interactions between wireless and xed ATM users, and wireless users in multi-tier environments. Other remaining issues are:









An alternative wireless network architecture which will use the ATM protocol not only in the backbone but also on links between the radio port controllers and the ATM network and perhaps also from radio ports to port controllers. A radio-access structure that is able to accommodate varying data rates in a multi-tier environment. An addendum proposal to current ATM UNI speci cations to incorporate the solutions for the issues raised in Section 4. A complete wireless network signaling speci cation which solidi es the procedures described in this paper.

References

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