Design and Prototyping of Location Management and ... - CiteSeerX

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Design and Prototyping of Location Management and Handoff Protocols for Wireless ATM networks A. Acharya, J.Li, A.Bakre, D. Raychaudhuri NEC USA, C&C Research Laboratories 4 Independence Way Princeton, NJ 08540, U.S.A. June 30, 1997 f

Abstract This paper deals with design and prototyping of mobility support protocols for mobile/wireless ATM networks. Specific ATM UNI/NNI protocol extensions for location management and handoff control are proposed and described in context of existing ATM networks. The viability of these protocols is established via implementation of a proof-ofconcept prototype mobile ATM network. The prototype system is used to validate the proposed location management and handoff protocols and/or to demonstrate support of both ATM and non-ATM mobile devices.

S1 connection2

connection1

Location Server

S3 S2

b4 Location Server

handoff

b1

name: m locn-id: b4.x

b3

b2

1 Introduction The use of ATM networks for wireless access services, proposed in [1], is currently under active consideration both at R&D[2-7] and standardization[8-11] levels. There are two major components in wireless access ATM networks: (a) A “radio access layer" providing high-bandwidth wireless transmission with appropriate medium access control, data link control, etc. and (b) a “mobile ATM" network for interconnection of base stations (access points) with appropriate support of mobility related functions capable of location management and handoff control. In this paper, we propose, prototype and verify extensions for such a “mobile ATM" network with location management and handoff control, supporting migration of terminal devices between wireless access points. Specific extensions to ATM signaling protocols for location management and handoff control are described and validated via proof-of-concept protoyping. An architecture for incorporating mobile terminals within an ATM network has been presented in [6,7]. Analogous to the solutions for terminal mobility in (connectionless) IP networks (eg. Mobile-IP), protocols are needed to support mobility in connection-oriented ATM networks. In contrast to IP, the connection-oriented nature of ATM requires lo-

ATM switch name: m locn-id: b3.x

Radio Port

Mobile terminal Static terminal

Figure 1: Mobile ATM Network Concept

cation resolution prior to establishing a connection with a mobile terminal, and needs handoff protocols to support dynamic re-routing of active connections as terminals migrate from one wireless access point to another. The solutions for location management and handoff control in ATM networks are conceptually different from those in the IP world. Extensions of ATM signaling protocols are necessary to support new functions in connection management, such as location resolution in location management and dynamic subpath rerouting in handoff control. They will be described in the following section. In section II, we briefly describe mobility functions and our proposed solutions. In section III, we introduce the new signaling syntax required for location management and handoff control. In section IV, We give the hardware/software configuration and explain the implementation

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2 Mobility Functions 2.1 Location Management Connection setup protocols in ATM (UNI/NNI signaling) have implicitly assumed that endpoints of a connection refer to static terminals, i.e. it is not necessary to determine dynamically a terminal’s current attachment point to the network before attempting to establish a connection to that terminal. However, with mobile ATM terminals, the location of such a terminal with respect to the network may no longer be deduced from its endpoint address. Additional addressing schemes and protocols are needed to locate and track mobile terminals, along with suitable modifications to the connection setup process. For example, in figure (1), a connection is setup to the mobile in each of the two cells (under radio ports b3 and b4). Under a possible addressing architecture, the name m is resolved to an address b3.x, that is specific to radio port b3, in order to setup the first connection. The mobile then moves to the cell under radio port b4. When the second connection is being setup, the name m is resolved to the address b4.x identifying its current location. In our proposed scheme[7], it is not necessary for a caller to determine a priori whether (a) the endpoint for connection setup is mobile and (b) the mobile is presently attached to its home switch or a foreign switch. The caller initiates a connection setup to the mobile using its home address. The SETUP message is routed to the mobile’s home switch, as before. But now, if the mobile is attached to the network via a switch other than its home, its home switch returns a response to the caller indicating the mobile’s current foreign address. This could be sent as a "cause" for failure to setup the connection using the mobile’s call reference: consequently, the resources reserved for the connection (during the forward path) are released on the return path of the response. As a result of this response, the caller receives the mobile’s current foreign address. The caller can then initiate a connection setup procedure using the mobile’s foreign address, which is then routed to the mobile’s current network attachment point.

2.2 Handoff Control Once a connection has been established between a pair of endpoints, current protocols assume that the connection path does not change during the period of a connection lifetime (except due to failures of switches and links). This assumption is invalidated when the endpoint is mobile. The path of the connection for a mobile user needs to be frequently re-setup as the mobile user moves from one cell to another. For example, in figure (1), the connection that was setup to

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the mobile terminal through b3 is handed-off to b4 by deleting the sub-path from switch S3 to b3, and augmenting the truncated path from S3 to b4. An efficient handoff control protocol does dynamic path re-routing instead of whole path re-establishment. Handoff schemes can be classified into path re-routing and path extension. First scheme is based on removing a part of the existing connection and adding a new sub-path from the point of detachment (the "crossover" point). It is necessary to determine a crossover point in this scheme. How to select the crossover point is a fundamental problem in handoff control techniques and different methods give different performance for handoff control in terms of latency, data loss and resource utilization. The second scheme is based on extending the original connection from previous access point to new access point. This scheme is currently being used in the telephony networks. Although it looks relatively simple for a single handoff, the overall process has to include other complicated algorithms for loop removal and route optimazation. All mobility functions are dealing with connection management which is handled by ATM UNI/NNI signaling in existing ATM networks, so our proposal is to extend ATM UNI/NNI signaling syntax for mobility support. In next section, we will give the signaling syntax of the extensions of ATM UNI/NNI signaling for mobile ATM networks.

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Signaling syntax for mobile ATM networks

The new necessary functions for location management and handoff control are specified as incremental addition to available ATM UNI/NNI signaling syntax. Based on the primitives we have defined for mobility support [12], new messages and new information elements (IE) are introduced [13,14].

3.1

Location Management

The connection setup of a mobile ATM network is done in two phases. First is location resolution and second is connection establishment. As we described in last section, if a mobile is at home, the first SETUP message will accomplish connection establishment. While if a mobile is not at home, the first SETUP message is responsed by a RELEASE message with the mobile’s current foreign address. Then another SETUP message will make the connection established. There is no new message introduced for location management. However, some new information elements are introduced in SETUP/CONNECT and RELEASE messages. Home addresses of caller and callee can be used to generate a global connection ID, with BLLI IE for both caller

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Table 1: Information Elements for Location Management MSG SETUP/ CONNECT RELEASE

IE CALLER HOME CALLEE HOME CAUSE

Contents ATMaddr ATMaddr ATM MOBILE AWAY

and callee, for a mobility support connection. The global connection ID is not changed according to mobile user’s migration (re-location or handoff). It is an important element for handoff control. So even when caller is calling mobile’s current foreign address, there should be a field containing mobile’s home address. Foreign: B

Caller: Z.1

MT

Home: A

SETUP(A.1,0)

and the second is the new IE of MT’s current foreign ATM address.

3.2

Handoff Control

There are three phases in basic handoff control process. The first is setting up a new subpath between crossover switch (COS) and new basestation (BS2). We introduce two new messages HANDOFF REQUEST and HANDOFF RESPONSE for this action. The second is replacing the old subpath between COS and old basestation (BS1) with to the new subpath setup by phase I. Messages HANDOFF CONFIRM and HANDOFF CONFIRM COMPLETE are used for this phase. The third phase is completing the rerouted connection by setting up wireless subpath between MT and BS2. HANDOFF JOIN and HANDOFF JOIN COMPLETE messages are responsible for this function.

SETUP(A.1,0)

Table 2: New messages for handoff control CONNECT(Z.1,0)

CONNECT(Z.1,0)

MT at home, Foreign Addr=0 Global Conn-ID: (Z.1,A.1)

(a) mobile at home Foreign: B

Caller: Z.1

MT

Home: A

SETUP(A.1,0)

MT moves, UpdateForeign Addr=B.1

RELEASE(Z.1,B.1)

New message HANDOFF REQUEST HANDOFF RESPONSE HANDOFF CONFIRM HANDOFF COMPLETE

SETUP(B.1,A.1) SETUP(B.1,A.1) CONNECT(Z.1,0)

HANDOFF JOIN

CONNECT(Z.1,0) Global Conn-ID: (Z.1,A.1)

(b) mobile away from home

HANDOFF JOIN COMP

Functions select HOS /BS, SETUP newpath CONNECT new path, newpath ready inform HOS to enable new path respond to HANDOFF CONFIRM and RELEASE oldpath complete connection SETUP radio path between BS2 and MT CONNECT the radio path

Figure 2: Signaling sequence of location management In the cause IE of RELEASE, a new type of reason is introduced ATM MOBILE AWAY. If cause = ATM MOBILE AWAY, the current foreign address of the callee is returned to the caller in the new IE callee’s foreign address. The IE of callee’s foreign address has the same structure as IEs of callee’s number and subaddress in SETUP message. Upon receiving this message, caller will send another SETUP message with callee’s homeaddr being set with callee’s home address and callee’s number and subaddress being set with callee’s foreign address. The signaling sequence for location management is shown in figure 2. In SETUP(CONNECT), the first parameter is IE of callee’s(caller’s) ATM address and the second is the new IE of caller’s(callee’s) home address. In RELEASE, the first parameter is IE of caller’s ATM address

In addition to new messages, some existing hop-by-hop ACK messages are used for handoff control. CALL PROCEEDING is a response to HANDOFF REQUEST when new path is being SETUP. CONNECT ACK is a response to HANDOFF RESPONSE (also HANDOFF JOIN COMPLETE) when the new path is being CONNECT. RELEASE COMPLETE is a response to HANDOFF CONFIRM COMPLETE when the old path is being RELEASE. Since they are hop-by-hop local messages for acknowledgement only, new syntax definitions are not required for them. Some new messages are constructed based on existing messages, such as HANDOFF REQUEST/RESPONSE are based on SETUP/CONNECT, and others are based on General Message Organization. Additional IEs are introduced for each new message if necessary. Table 3 gives all such IEs. The IE of extended message type has three fields, referring to the functions the message provides[14].

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CT

BS2

SWITCH CONTROLLER

MT

MOBILE NNI

HANDOFF REQUEST(SELECT COS) HANDOFF REQUEST(SETUP) CALL PROCEEDING

Locn Mgmt ATM UNI 3.0 +Mobility

LINUX Pentium 180

ATM UNI 3.0 + Location Caching

HANDOFF RESPONSE(CONNECT)

ATM Radio Port

GSMP CLIENT

APPLICATION PROGRAM Native ATM Interface

CONNECT ACK (new path established)

HANDOFF RESPONSE

LINUX Pentium 180

NEC MODEL5 GSMP INTERFACE

"M" NNI

APPLICATION PROGRAM

WaveLAN wireless control

LINUX Pentium 180

IP interface

WaveLAN wireless control

IP Pac

kets

Mobile Client

HANDOFF CONFIRM (switch the connection to new path)

HANDOFF JOIN HANDOFF JOIN COMP (handoff complete)

ATM Radio Port

"M" NNI

HANDOFF CONFIRM COMP

SWITCH CONTROLLER

Locn Mgmt

NEC MODEL5 GSMP INTERFACE

MOBILE NNI GSMP CLIENT LINUX Pentium 180

ATM UNI 3.0 +Mobility

WaveLAN wireless control

LINUX Pentium 180

Figure 3: Signaling sequence of Path Extension Scheme

Figure 4: A prototype mobile ATM network

This syntax can be used for various handoff protocols. In [14], we gave three examples — Path Extension, Path Re-routing and BS-2 initiated Path Re-routing. In figure (3), the signaling sequence for Path Extension is given as an illustration.

ment and handoff control via limited extensions in ATM UNI/NNI signaling protocols to support terminal mobility. This system provides a two-fold functionality: Wireless ATM: The radio ports act as UNI termination points for the wireless terminals, and interact with the rest of the network through NNI signaling protocols, i.e. functionally, they behave as ATM switches with wireless ports in addition to wireline ports. This allows end-to-end ATM connections to and from mobile terminals. A generic platform for supporting mobility: A mbile ATM network can also function as a generic infrastructure network that provides mobility support to specialized mobility protocols such as packet data (Mobile-IP, GPRS), cellular telephony (CDMA/IS-95, TDMA/IS-136, GSM/DCS 1900, PHS), and PCS. The prototype system, as shown in figure 4, consists of two NEC Model5 2.4Gbps ATM switches and five Linux PCs with Zeinet ATM NIC card. One Linux PC is fixed host, two Linux PCs are basestations, which have also NCR Wavelan Cards, and the other two Linux PCs are used to control NEC Model5 switches through GSMP [15] protocol. An NEC Versa with Wavelan card is used as a mobile terminal. We use public domain Linux ATM software[16] on PCs. On ATM hosts, UNI signaling module was modified to support (a) location resolution and (b) location caching. On base stations, which terminate ATM signaling in our demostration, UNI signaling was modified to support (a) location resolution, (b) location caching and (c) handoff path extension. We developed an NNI signaling module for switch controllers, in which (a) COS selection, (b) subpath setup,

4 Proof of Concept Prototype The purposes of prototyping a mobile ATM network are (a) to validate the proposed signaling syntax and (b) to experiment different schemes for location management and handoff control. Our prototype system shows that an ATM backbone network can be enhanced with location manage-

Table 3: Information Elements in New Messages New MSG HANDOFF REQUEST

IE EXT MSG TYPE GCID

HANDOFF RESPONSE

ADDR TO GO EXT MSG TYPE RESULT

Contents operation flag, handoff protocol connection type Homeaddr& CallIDs MT/CT Newaddr of MT operation flag, handoff protocol connection type SUCCESS/FAILURE

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(c) re-routing subpath and (d) release subpath should be supported. The extensions of NNI signaling have not been supported yet at this moment. In addition, on switch controller we wrote a GSMP client program to control switches. In this specific demonstration, we showed IP data transmission on mobile terminal via Wavelan wireless access. The IP packets are converted from/to AAL5 ATM cells on basestations. We have shown following demonstrations with the prototype system. (1) When mobile terminal (MT) is at home, a caller setup a connection with MT as normal. (2) When MT migrates to another basestation. It sends a ’MOVE’ to its home basestation (BS1), in the home location registration file, the entry of MT is marked with ’AWAY’ and the current foreign ATM address is registered. (3) If a caller calls a MT which is ’AWAY’, the extended location management signaling is effected and a connection to MT through its current foreign ATM switch is setup without noticed by the caller. (4) While the connection is in active, MT send a ’HANDOFF’ to its current basestation (BS2), indicating it is moving back to BS1. And from BS2 an subpath is extended to BS1 via the extended handoff control signaling. Transmission can be kept on without being interrupted. The current handoff scheme does not guarantee zerocell loss during handoff procedure. We are designing a scheme on switch side to support zero-cell loss handoff. In addition, we are implementing other handoff protocols(only Path Extension scheme is available in the demonstration).

5 Concluding Remarks This paper presented the design and prototyping of a mobility support ATM network. We briefly described the major functions of location management and handoff control and proposed the necessary extensions in ATM UNI/NNI signaling syntax for these new functions. With the implemention of the extensions, the prototype system validates our mobile ATM network concept. The future work will be the experiments of different schemes and performance measurement.

6 References [1] D. Raychaudhuri and N. D. Wilson, “ATM-Based Transport Architecture for Multiservices Wireless Personal Communication Networks," IEEE Journal on Selected Areas of Communications. vol. 12, No. 8 pp. 1401-1414. 1994. [2] K.Y.Eng, M.J.Karol, M.Veeraraghavan, E.Ayanoglu, C.B.Woodworth, P.Pancha, and R.A.Valenzuela, “BAHAMA: A broadband ad-hoc wireless ATM local area network,” in Proc. ICC ’95, pp.1216-1223, June 1995.

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[3] E.Hyden, J.Trotter,P.Krzyzanowski,M.Srivastava, and P.Agarwal, “SWAN: An indoor wireless ATM network,” in Proc. ICUPC ’95, (Tokyo, Japan), pp.853-857, Nov. 1995. [4] J. Mikkonen, and J. Kruys, “The Magic WAND: a wireless ATM access system”, ACTS Mobile Summit 96Proceedings, Granada, Spain, Nov. 96. [5] A. Acampora and M. Naghshineh, “An Architecture and Methodology for Mobile-Executed Handoff in Cellular ATM Networks,” IEEE Journal on Selected Areas of Communications. vol. 12, No. 8 pp. 1365-1375. 1994. [6] R. Yuan, S. K. Biswas, L. J. French, J. Li, and D. Raychaudhuri, “A Signaling and Control Architecture for Mobility Support in Wireless ATM Networks,” ACM/Baltzer Mobile Networks and Applications, Vol. 1, No. 3 Dec 96 [7] A.Acharya, S.K.Biswas, L.J.French, J.Li, and D.Raychaudhuri, “Handoff and location management in mobile ATM networks,” in Proc. 3rd Intl Workshop on Mobile Multimedia Communications (MoMuC-3), (Princeton, NJ), Sept. 1996. [8] D.Raychaudhuri et al., “Technical Scope Outline for Mobile ATM Specification Items.” ATM Forum Contribution/96-0216/PLEN. [9] D. Raychaudhuri (NEC), Lou Dellaverson (Motorola), M.Umehira(NTT), J. Mikkonen (Nokia), T. Phipps (Symbionics), J. Porter (ORL), C. Lind (Telia), H. Suzuki (NEC), “Charter, Scope and Work Plan for Proposed Wireless ATM Working Group,” ATM Forum/96-0530/PLEN, April 96 . [10] T.Phipps,J.Loraine,N.Shipp,L.Neal and M.Leach, “Wireless ATM Physical Layer Requirements,” ATM Forum/96-1004, Aug 96. [11] M.Veeraraghavan, M.Karol and K.Y.Eng, “A combined Handoff Scheme for Mobile ATM Networks,” ATM Forum/96-1700, Dec 96. [12] A. Acharya, J. Li, D. Raychaudhuri, “Primitives for Location Management and Handoff in Mobile ATM Networks,” ATM Forum/96-1121, Aug 96. [13] A. Acharya, J. Li, D. Raychaudhuri,”Signaling syntax extensions for location management in mobile ATM,” ATM Forum/96-1624, Dec 96. [14] J. Li, A. Acharya, D. Raychaudhuri, “Signaling syntax extensions for handoff control in mobile ATM,”ATM Forum/96-1625, Dec 96. [15] P.Newman et al., “Ipsilon’s General Switch Management Protocol Specification,” RFC1987, Aug 96. [16] Linux ATM software: “http://lrcwww.epfl.ch:80/”.