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Evaluating the Performance of Handoff Schemes in Wireless ATM Networks

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Evaluating the Performance of Handoff Schemes in Wireless ATM Networks Powered By Docstoc
					              Evaluating the Performance of Handoff Schemes in
                           Wireless ATM Networks
                                                                   Farouk Smith, Neco Ventura
                                                     Dept. of Electrical Engineering, University of Cape Town
                                                                 Rondebosch 7700, South Africa
                                                                 {fsmith, neco}@crg.ee.uct.ac.za


Abstract—The performance of handover schemes in a Wireless                                      The network architecture consists of three main parts as
ATM network is investigated and various handover schemes                                     shown in the figure 1.
are discussed that have been proposed in the literature.                                        The first part consists of ATM switches with standard
   The impact of handoff schemes in terms of Service disrup-                                 UNI/NNI and additional mobility support enhancements,
tion time, Handoff completion time, Buffer requirements at the
                                                                                             which form the mobility support ATM Network. These
Mobile Terminal (MT), Buffer requirements at the Access
Point (AP) and the excess bandwidth resources required dur-                                  ATM switches are termed Mobility Enhanced Switches
ing handoff are addressed.                                                                   (MES). The second part consists of ATM Access Points
   The testbed to study the performance of the various hando-                                with Mobility Enhanced UNI/NNI and radio interface capa-
ver schemes is based on a gigabit ATM switch. The signalling                                 bilities and lastly, Mobile Terminals with enhanced WATM
software of the ATM switch offers a direct many-to-many                                      UNI.
communication, with connections that can be modified dy-                                        One of the primary advantages of ATM is its ability to
namically.                                                                                   give QoS guarantees to connections. As mobile devices
   With the proposed evaluation platform the authors will                                    move between base stations, QoS re-negotiation may be
analyse the performance of the various handoff schemes and
                                                                                             required to maintain levels of service to the connections.
compare it to the analytical and simulation results obtained
from the literature.                                                                            The aim of the handover protocol is to enable a wireless
                                                                                             terminal to move between access points seamlessly while
                                                                                             maintaining the negotiated QoS of its active connections.
                            1. INTRODUCTION
                                                                                             The efficient handover and switching of the Mobile Termi-
                                                                                             nals (MT’s) virtual connections to the appropriate AP in the
   The architecture proposed for wireless ATM is composed
                                                                                             wired network can achieve this.
of a large number of small transmission cells. A base station
                                                                                                The methodology for implementing hand over is one of
(also called an Access Point, AP) serves each of these cells.
                                                                                             the most important parts of WATM to support mobility [1],
All the base stations in the network are connected via the
                                                                                             [12].
wired ATM network. As the cell size is reduced, hand over
                                                                                                The focus of the paper is on the performance of the new
rate also increases [1].
                                                                                             handoff schemes for integrated QoS based multimedia
   Wireless ATM networks can be implemented by adding
                                                                                             services in WATM networks [2, 8]. Because new connec-
mobility support functions to fixed ATM switches. The
                                                                                             tions setup and signaling are necessary during handoff, it is
Wireless ATM architecture makes provision for the most
                                                                                             difficult to provide guaranteed QoS. The key requirement
important mobility support function, the handover protocol
                                                                                             for QoS is the re-negotiation of VC parameters during the
for inter and intra – switch handovers.
                                                                                             course of a connection.
                                                                                                The remainder of this paper is organized as follows: In
                                                                                             section 2, various handoff schemes are presented together
                                                                                             with their features, advantages and disadvantages. In section
                                                                                             3, performance issues are discussed. In section 4, the per-
                                                                                             formance analysis for the various handoff schemes is given.
              Fixed ATM Network                  MES
                                                                                             In section 5 the evaluation platform is discussed. Finally,
                                                                                             section 6 concludes this paper.

                                                                                                     2. HANDOFF REROUTING SCHEMES
                                                MES

                                                                                              There are two kinds of handoffs, namely intra-switch and
                                                                                             inter-switch handoff. In intra-switch handoff, the resulting
                             Mobile Terminal                    Wireless Link
                                                                                             route is optimal but in inter-switch handoff, the new con-
                                  Mobility Support
                                                                                             nection needs to be rerouted [1].
                                                              Access Point
                                                                                                Handoff Schemes for rerouting can basically be classified
                                                                                Fixed Host
                                   ATM Switch


                                                                                             into four main groups. The full, incremental, multipath and
Fig. 1. Wireless ATM Network architecture
                                                                                             path extension re-establishment schemes.
                                                                                                The full re-establishment (FR) requires a completely new
The authors would like to thank Telkom SA, Siemens, National Research Foundation
                                                                                             path to be setup during handover [2]. The incremental re-
(NRF) and The Department of Trade and Industry (DTI) for supporting this research
                                                                                             establishment (PR) scheme requires only that a partial new
project.
                                                                                             path be setup and allows circuits to be re-used [3]. This
scheme find the Cross Over Switch (COS) that is a cross                    All rerouting schemes have their advantages and disadvan-
point of the old path and the new path. The Multicast re-                  tages, but all are based on the following steps:
establishment (MR) scheme makes use of multicast in ATM
Networks [4], [5]. A controlling switch establishes a con-                     Select a handoff switch. (Not used in path extension
nection to the current serving AP and all AP’s in the neigh-                   scheme), Setup a new sub-path between a handoff
borhood of the serving AP. When the MT moves to one of                         switch and a new AP. (Not necessary in multicast
the neighboring AP’s, data is immediately available.                           scheme), Release old sub-path between a handoff
Handoff is fast, but there is wastage of resources and could                   switch and old AP.
result in call blocking for other MTs attempting to connect
to the neighboring APs. In the path extension re-                                                        TABLE 2
                                                                                          NETWORK PARAMETERS FOR HANDOVER SCHEMES
establishment (PE) scheme the route is extended from the
original connection at the old Mobility Enhanced Switch                                                                                         Value
                                                                                                  Parameter                       Symbol
(MES) to the destination connection at the new MES, where
                                                                               Number of hops from the
the new Access Point (AP) exist [6]. After several handoffs,                         i) New AP to the COS                       Hnew
path looping occurs which results in a non-optimized path.                           ii) Old AP to the COS                      Hold       variable
Hybrid Rerouting schemes have also been proposed that is a                           iii) New AP to the old AP                  Hctrl
combination of the connection extension and path rerouting                           through Signaling Channel
                                                                               Bandwidth of the wired backbone network          BWw        155Mb/s
schemes [7]. This technique is superior to the other handoff                   Bandwidth of wireless link                       BWwl       2Mb/s
schemes because path extension reduces handoff delay and                       Latency of the wireless link                     Lwl        3ms
path (partial) rerouting increases resource utilization. The                   Latency of the wired backbone                    Lw         500µs
various schemes can also make use of radio hints (ER) in                       Protocol processing time for signaling mes-
                                                                               sages                                            PTfix      0.3ms
order to pre-establish connections before the old connections                  Protocol processing time to find the COS         PTcos      2ms
are released, when the signal strength to the old AP becomes                   Time for a MT to acquire a wireless channel
weak [2].                                                                      to a base station                                Tacq       2ms
   Some of the features of the re-routing schemes are given                    Upper bound on the size of a signaling mes-
                                                                               sage (bytes)                                     Ssig       50
                            TABLE 1                                            Max size of a data packet (bytes)                Sdata      53
                SOME FEATURES OF HANDOVER SCHEMES                              Protocol processing time where admission
                                                                               control is to be performed, in excess of fixed
 Handover Schemes                                                              protocol processing time.                        PTadm      2ms
                                          Features

Path                        Easy to implement
Extension                   Path is extended for every handoff
                            No end point determination process re-
                                                                                           3. PERFORMANCE ISSUES
                            quired
                            Handoff delay is the actual setup of the          The service disruption time, time taken to complete a
                            path extension                                 handoff, extra buffering needed to avoid data loss due to
                            Path     looping   occurs   after    several
                                                                           rerouting and extra bandwidth resources required are im-
                                                                           portant performance issues to be considered as they affect
                            handoffs
                                                                           the quality of service of the connections.
                            Results in inefficiency                           The five rerouting schemes in table 1 have been analyzed
Full Connection Re-         Most optimal and simplest scheme               by considering the signaling messages required to be ex-
routing                     Creates completely new route for each          changed during handoff in a common network structure [2],
                            handoff
                                                                           [8]. The performance measurements considered are (i)
                                                                           Service disruption time, (ii) Handoff completion time, (iii)
                            Higher handoff delay
                                                                           Buffer requirements at MT, (iv) Buffer requirements at AP
                            Maintains cell sequence through cell           and (v) The excess bandwidth resources required during
                            forwarding                                     handoff.
Partial Rerouting           Only a portion of the path is rerouted
                            Optimized path                                               4. PERFORMANCE ANALYSIS
                            Maintains cell sequence through cell
                                                                              The parameters we intend to evaluate in this work is
                            forwarding                                     based on the analytical and simulation analysis in [2] and
Multicast Rerouting         Multicast data to all neighboring AP’s         [8]. The Service disruption time, Handoff completion time,
                            Faster handoff                                 Buffer requirements at MT, Buffer requirements at AP and
                            Waste of resources                             the excess bandwidth resources required during handoff will
                                                                           be obtained from the evaluation platform and is based on the
Hybrid Technique            Path extensions and path rerouting ap-
                                                                           following analytical analysis.
                            plied                                             The parameters used in the analytical analysis are given
                            Lower handoff delay                            in table 2. It is assumed that the maximum throughput for a
                            Lower blocking                                 connection is limited by the throughput of the wireless con-
                                                                           nection. The analysis also assumes perfect delivery of sig-
                                                                           naling messages. We compute and measure the time taken
in the Table 1 [8].                                                        for each of the signaling messages to be transmitted, for-
                                                                           warded, and processed where necessary. Based on the time
                                                                           Message (7) is the last packet indication in the wireless
                                S e rv e r                              link from AP1 to the MT. The time delay is denoted by T7.
                                                                           Message (8) is the handoff completion and connection
                                                                        release message from the MT to the old AP. Denote this
                                 SW E                                   time delay by T8.
                                                                           Message (9) is the handoff completion and connection
                                                                        release message from the old AP to the COS hop by hop.
                                 SW D                                   The time delay is denoted by T9.
                                                                           Immediately after processing the last packet indication
                                                                        message (7), the MT acquires a channel to the new AP,
     9
                                 SW C                               5
                                                                        AP2. This time delay is denoted by T10.
         6
                   3
                                                     4                     Message (11) is the acknowledgement from AP2 to the
                                    2                                   MT. The time delay is denoted by T11.
                                                                           Based on the time taken by these control messages, vari-
             SW A                                             SW B
                                                                        ous performance measurements can be derived. Expressions
                                                                        for five measures are given in [2] and [8]. The disruption
                                                                        time, Tdisrupt, is the time interval between the instant the
             AP1                                              AP2       handoff completion command is received and the instant the
                                                                        first data packet is received by the MT in the new path. This
                       1
                                                10                      includes the time to process all the signaling messages at the
                       7
              8
                                   MT
                                                         11
                                                                        switches and the transmission time of the first data packet.
                                                                           The handoff completion time Tcomplete is the amount of
Fig. 2. The Partial Re-establishment Scheme with hints.                 time for all the rerouting to complete, i.e. from the time
                                                                        when the MT issues a handoff initiation request to the old
 taken by these signaling messages various performance                  AP to the time at which the connections to the previous AP
 measures will be obtained. Some of the parameters used are             is torn down or the connection established to the new AP.
 hardware and network specific (Table 2).                               All events except for the acknowledgement transmissions
    The handover schemes studied in this paper can be ana-              occur sequentially. Thus, the completion time is the sum of
 lyzed by considering the signaling messages required to be             the times taken for each of the events during rerouting.
 exchanged during handoff in a common network structure                    The amount of buffering required by the MT, BUFMT, is
 [2]. This is illustrated in Fig. 2 for the Partial Re-                 determined by the amount of time during which the MT
 establishment scheme with radio hints, and can similarly be            cannot transmit data on the wireless link. This includes the
 done for the other handover schemes.                                   time for the MT to greet the new AP to acquire a channel
    When the MT detects the handoff occurrence in advance               and the time for the new AP to acknowledge the greeting.
 by the receive signal dropping below a set value, it sends a              The amount of buffering required on the new AP for the
 handoff request (1) to the current serving AP, AP1. The time           downlink, BUFAP, down, is determined by the amount of data
 needed for this message, T1, is the sum of the transmission            that is transmitted in the new path before the MT is con-
 time of a signaling message, the propagation time on the               nected to the new AP.
 wireless link, and the fixed protocol processing time on                  The excess bandwidth resources, Rexcess, used for a single
 AP1.                                                                   conversation during handoff is the amount of highest band-
    After this AP1 communicates to AP2 through message                  width-space-time product among the two simultaneous
 (2) the list of connections about to be re-established. Its total      paths. The bandwidth space-time product is the product of
 time is the end-to-end delay through the control channel               the bandwidth provided to the connection, the length of the
 between AP1 and AP2 plus the fixed protocol processing                 connection and the amount of time that the connection is in
 time at AP2. This time delay is denoted by T2.                         existence [2, 8].
    Immediately after sending message (2), AP1 begins the                  For evaluation of the analytical model it is assumed that
 COS location algorithm process (3) to locate the COS be-
                                                                                        H ctrl
 tween AP1 and AP2. The time taken to locate the COS is                 Hnew = Hold =          (refer to table 2) for all the schemes
 equal to the transmission and propagation time along each                               2
 hop, plus the fixed signaling processing time in each switch           except the PE scheme. The values for Tdisrupt, Tcomplete,
 along the path from AP1 to the COS. Denote this time delay             BUFMT, BUFAP, and Rexcess depend on the specific hardware
 by T3.                                                                 being used and also the number of hops being considered.
    Message (4) is a partial channel establishment from the             Since the same hardware will be use to evaluate the various
 COS to the new AP, i.e. AP2. Admission control tests are               handoff schemes, comparisons can be made. Fig. 3, 4, 5 and
 carried out at each switch along each hop, plus the fixed              6 show the performance parameters of the rerouting
 protocol processing time at each switch along the path. De-            schemes as obtained from the analytical analysis in graphi-
 note this time delay by T4.                                            cal form.
    Message (5) is the acknowledgement of the partial chan-                The multicast scheme and schemes that makes use of
 nel establishment from AP2 to the COS. This signaling mes-             radio hints have low service disruption time, whereas for the
 sage retraces the path of the partial establishment, hop by            partial, full and path extension schemes it increases with the
 hop. Denote this time delay by T5.                                     increase in the number of hops from the old/new AP to the
    After the acknowledgement (5) the COS sends the last                COS or between the old and new AP. The reason for this is
 packet indication message to the old AP, AP1 hop by hop                that for the MR and the PE schemes the handoff latency will
 along the old path. This time delay is denoted by T6.                  not be affected due to multiple ATM switch handoff, since
the latency in the MR and PE schemes is determined only in                                                at the new AP to buffer data. Hence, smaller buffer require-
the last hop between the MES and the MT.                                                                  ments at the AP. This relationship can be seen by comparing
                                                                                                          figures 3 and 5 with the exception of the ER scheme. The
                                                                                                          reason for the exception is that depending on how far in
                                0.025
                                                                                                          advance a hint is available before the MT moves, the extra
                                                                                                          buffering required to complete the handoff may be signifi-
Service disruption time (Sec)




                                 0.02
                                                    FR, PR                                                cantly higher.
                                0.015




                                                                                                          Buffer Requirements at AP (bits)
                                                                           PE                                                                              40000
                                 0.01
                                                                                                                                                       35000
                                                                MR, ER
                                0.005                                                                                                                  30000                                       FR, PR                     ER

                                                                                                                                                       25000
                                        1   2      3       4       5            6       7        8
                                                                                                                                                           20000                                                    PE
                                            Number of hops from the AP to the COS
Fig. 3. Service disruption time for different handover schemes                                                                                             15000
                                                                                                                                                                                                                              MR
                                                                                                                                                       10000
  Handoff completion time for the path extension method is
lower than any other scheme; a reason for this is given in the                                                                                                       1       2         3           4        5   6         7         8
previous paragraph. The scheme with hints has handoff                                                                           Number of hops fromthe AP to the COS
completion time low compared to the full, partial and multi-                                              Fig.5. Buffer requirements at AP for downlink during handover
cast schemes. The reason for this result is that in the FR
scheme a completely new path is setup from the MT to the                                                     Extra bandwidth resources required are the most for full
FH, hence the new connection setup time is directly propor-                                               reconnection scheme and relatively constant compared to
tional to the number of switches between the MT and the                                                   the other schemes. The reason for this is that from the MT to
FH. The same can be said for the PR scheme, the only dif-                                                 the server (fig. 2) a new connection is setup and resources
ference being that the new connection setup time is propor-                                               are used in each connection. Extra bandwidth resources are
tional to the number of switches between the COS and the                                                  not required for the path extension scheme since only the
MT.                                                                                                       last hop is involved in the handoff process. The excess
                                                                                                          bandwidth resources required for the MR scheme depends
                                 0.1
                                                                                                          on the number of simultaneous paths setup for multicast
                                0.09
                                                                                                          purpose during handover. For the PR scheme the extra
Handoff completion time (Sec)




                                0.08
                                                                                                          bandwidth resources required depend on the number of hops
                                                                                                          between the COS and the MT and could be closely matched
                                0.07               FR
                                                                                                     ER   to the FR scheme depending on the number of hops between
                                0.06
                                                          PR                                              the COS and the APs.
                                0.05
                                                                                            MR
                                0.04
                                                                                                                                                              1e+6
                                0.03
                                                                           PE                                                                                90000
                                0.02                                                                                                                                                 FR
                                                                                                                                                            800000
                                0.01
                                                                                                                            Excess resources (bit links)




                                        1   2      3        4          5            6       7        8
                                                                                                                                                            700000
                                            Number of hops from the AP to the COS
                                                                                                                                                            600000                                                   MR
Fig. 4. Handoff completion time for different handoff schemes
                                                                                                                                                                                              PR                               ER
                                                                                                                                                            500000

   The buffer requirements at mobile terminal for uplink                                                                                                    400000

data during handoff are the same for all schemes. This is                                                                                                   300000

because the amount of buffering required by the MT,                                                                                                         200000

BUFMT, is determined by the amount of time during which                                                                                                     100000

the MT cannot transmit data on the wireless link. This in-                                                                                                     0
                                                                                                                                                                         1       2        3         4       5   6         7        8
cludes the time for the MT to greet the new AP to acquire a                                                                                                                      Number of hops from the AP to the COS

channel and the time for the new AP to acknowledge the                                                    Fig. 6. Excess bandwidth resources required during handoff
greeting. The message sequence is the same for all schemes
(messages 10 and 11, fig 2).                                                                               The objective of the paper is to verify on an experimental
   The buffer requirements at AP for the downlink are low-                                                testbed the impact of the handoff schemes in terms of the
est for the MR and PE schemes. The reason for this behavior                                               performance measurements mentioned above and compare
is due to the fact that the amount of buffering required on                                               the results with those obtained analytically.
the new AP for the downlink, BUFAP, down, is determined by
the amount of data that is transmitted in the new path before                                                                                                            5. EVALUATION PLATFORM
the MT is connected to the new AP. This is directly related
to the service disruption time, since the service disruption                                                The testbed consists of hardware and software compo-
time is the time interval between the instant the handoff                                                 nents and tools to monitor the handover operation. The test-
completion command is received and the instant the first                                                  bed would consist of at least two AP’s, a fixed host, a net-
data packet is received by the MT in the new path. Hence                                                  work node (WUGS) and a node controller [4, 14]. As seen
the lower the service disruption time, the less time is needed                                            on Fig. 7, the network node consists of the Washington
University Gigabit Switch (WUGS) [9] intended for ex-                                                                                                                                                                                                                    However, packet losses using the wireless configuration
perimental research. The switching and control functionality                                                                                                                                                                                                          are slightly higher. On further investigation, it was found
are separated. The Node Controller (NC) allows remote                                                                                                                                                                                                                 that the reason for the higher packet losses in the wireless
control, the modification of the signaling software for mo-                                                                                                                                                                                                           link was due to occasional burst losses suffered in the wire-
bility purposes and a flexible environment for development                                                                                                                                                                                                            less medium. It is for this reason that our choice of using
and testing.                                                                                                                                                                                                                                                          Ethernet is revalidated to eliminate the wireless specific
                                                                                                                                                                                                                                                                      effects and concentrate on the losses due to mobility and
                                                                                                                                                                                                                                                                      connection rerouting in isolation.
     Fixed Host
                                                                                                                                                                                                                                                                         The protocol stack at the fixed host and the MT are dif-
                                                                                  FH
                                                                                                                                                                                                                                                                      ferent (Fig. 8). The fixed host uses AAL5 over ATM
                                                                                                                                                                                                                                                                      whereas the MT uses UDP/IP over Ethernet. The AP’s per-
                                                                                                                                                                                                                                                                      form the bridging function between the different protocol
   WUGS Node
                                                                                                                                                                                                                                                                      stacks. In an end-to-end ATM system, the mobile host
                                                                                                                                                  NC                                                                                                                  would be responsible for reassembling the ATM cells.
    Controller
                                                                                                                                                                                                                                                                         At first the scenario with a single switch between the FH
                                                                                                                                                                                                                                                                      and the AP’s will be considered. Later a more complex sce-
                                                                                                                                                                                                                                                                      nario will be considered where one more switch can be lo-
                                                                                                                                                                                                                                                                      cated between the fixed host and the MT, Fig 8, in order to
                                                                                                                                                                                                                                                                      demonstrate the path extension scheme.
       Access
       Points           AP1                                                                                                              AP2                                                                                                                            At this stage it is worthwhile mentioning why the use of
                                                                                                                                                                                                                                                                      one or even two ATM switches in the experimental setup is
                                                                                                                                                                                                                                                                      sufficient in evaluating the performance of the various
Fig. 7. Logical Testbed                                                                                                                                                                                                                                               handoff schemes.
                                                                                                                                                                                                                                                                         The effect of multiple switches on packet loss can be ex-
   The evaluation platform for this work consists of the fol-                                                                                                                                                                                                         plained as follows with regards to the various handoff
lowing hardware configuration. Five end stations, three                                                                                                                                                                                                               schemes. The period during which the translation tables in
serving as AP’s, one as the fixed host and the last one serv-                                                                                                                                                                                                         the COS are modified in order to reroute the connections,
ing as the Node Controller (NC), are connected via multi-                                                                                                                                                                                                             has the biggest impact on packet loss, [15]. Even when the
mode fibre to the WUGS switch ports. The two WUGS                                                                                                                                                                                                                     connections span multiple ATM switches, the single COS at
switches are also connected via multimode fibres. The Mo-                                                                                                                                                                                                             which the translation tables are altered will be mainly re-
bile Terminal is connected to the AP’s via Ethernet to emu-                                                                                                                                                                                                           sponsible for packet loss.
late the wireless access portion of the network.                                                                                                                                                                                                                         The reason for this is that the handoff schemes first up-
   There are no wireless ATM cards available for experi-                                                                                                                                                                                                              date all the switches in the new route and only then alter the
mentation. However, this is not an obstacle, as in this inves-                                                                                                                                                                                                        entry at the COS (Section 4). Hence, it does not matter
tigation we are primarily interested in the effect of handover                                                                                                                                                                                                        where in the connection the COS is located and the losses
on the backbone ATM network portion of the connection.                                                                                                                                                                                                                suffered due to multiple switch rerouting will be similar to
Hence, experiments can be conducted with the Mobile Ter-                                                                                                                                                                                                              our one hop experimental setup.
minal connected to the AP’s via Ethernet, Fig 8. This would                                                                                                                                                                                                              The effect of multiple switches on handoff latency can be
allow us to focus on the consequences of connection re-                                                                                                                                                                                                               explained as follows with regards to the various handoff
routing: loss, duplication, and reordering of packets.                                                                                                                                                                                                                schemes. It can be noted that for the MR and the PE
   Past experiments were performed to evaluate the per-                                                                                                                                                                                                               schemes the handoff latency will not be affected due to
formance of handoff schemes using both Wavelan wireless                                                                                                                                                                                                               multiple ATM switch handoff, since the latency in the MR
Ethernet cards and conventional wired Ethernet, [15]. It was                                                                                                                                                                                                          and PE schemes is determined only in the last hop between
found that the results of the performance evaluation are                                                                                                                                                                                                              the MES and the MT. This can also be seen in fig. 3 where
similar using both configurations.                                                                                                                                                                                                                                    the service disruption time is relatively constant with the
                                                                                                                                                                                                                                                                      increase in the number of hops for the MR and PE schemes.
                                                                        Application
                                                                          AAL5
                                                                                                                                               Fixed Host
                                                                          ATM
                                                                         Physical
                                                                                                                                                                                                                                                                         In the FR scheme a completely new path is setup from the
                                                                                                                                                                                                                                                                      MT to the FH, hence the new connection setup time is di-
                                                                                                                                                                                                                                                                      rectly proportional to the number of switches between the
                                                                                                                                                                                                                                                                      MT and the FH (Section 4). The same can be said for the PR
   Switch Controller
                                                                                                                                                                                                                                                                      scheme, the only difference being that the new connection
                                                                                                                                                       PVC
                                                         7x   8x   9x       10x   11x   12x   7x   8x   9x       10x   11x   12x                                                            7x   8x   9x       10x   11x   12x   7x   8x   9x       10x   11x   12x

                                                                                                                                                                                                                                                                      setup time is proportional to the number of switches be-
                            E thernet




                                                                                                                                                              E thernet




                                        C                                                                                                                                 C
                                                    12
                                            7 8 91011                                                                                                                                  12
                                                                                                                                                                              7 8 9 1011

                                        A   12 3456                                                                                                                       A   12345 6




                                                                                                                                                                                                                                                                      tween the COS and the MT. Hence, meaningful results can
                                                         1x   2x   3x       4x    5x    6x    1x   2x   3x       4x    5x    6x                                                             1x   2x   3x       4x    5x    6x    1x   2x   3x       4x    5x    6x
                                                                        A                                    B                                                                                             A                                    B




                                                                              WUGS 1                                                                                             WUGS 2

                                                                                                                                                                                                                                                                      be obtained for the various performance parameters regard-
                                                 AP 1                                                                                          AP 2                                                                                                 AP 3              less of the number hops involved in the handover procedure.
                            Bridge                                                                                                      Bridge                                                   Bridge

    Access Points
                        AAL5
                        ATM
                                UDP/IP
                                Ethernet
                                                                                                                                    AAL5
                                                                                                                                    ATM
                                                                                                                                            UDP/IP
                                                                                                                                            Ethernet
                                                                                                                                                                                             AAL5
                                                                                                                                                                                             ATM
                                                                                                                                                                                                     UDP/IP
                                                                                                                                                                                                     Ethernet
                                                                                                                                                                                                                                                                         The signaling protocols used in this experimental hando-
                       Physical Physical                                                                                           Physical Physical                                        Physical Physical                                                         ver investigation are part of the WUGS environment, Fig. 9.
                                                                                                                                                                                                                                                                         The Node Controller (Node/Switch Management) pres-
                                                                                  Application
                                                                                                                                                             Ethernet
                                                                                                                                                                                                                                                                      ents the same switch control API as the switch controller. It
                                                                                   UDP/IP
                                                                                   Ethernet
                                                                                                                                                                                                                                                                      allows several switches to be treated as one switch, i.e. the
                                                                                   Physical
                                                                                                                                                                                                                                                                      node controller hides the details of how the individual
                                                                              Mobile Host
                                                                                                                                                                                                                                                                      switches are connected together.
Fig.8. Experimental Testbed
   The Connection Management Layer implements a dis-               ment. Its signaling software offers a direct many-to-many
tributed control for a network with multiple nodes. Connec-        communication and switching with connections that can be
tion Managers communicate with each other using a general          modified dynamically.
signaling protocol.                                                   The authors expect to report results of the evaluation
   The Call Management Layer implements a session ab-              based on the experimental setup to verify the results ob-
straction (MCALL) used by signaling clients to request and         tained analytically [2], [7], [8]. Results will be presented at
manage connections in an ATM network. It allows general,           SATNAC 2003.
dynamic, multi-connection, multicast sessions. The sessions
are supported through the UNI signaling protocol, Connec-                                     7. REFERENCES
tion Management Access Protocol, CMAP [10].                        [1] IEEE Journal on Selected Areas in Communications, Special Issue on
                                                                   Wireless ATM, 1997.
                              Call Management                      [2] K. Keeton, B. Mah, S. Seshan, R. Katz and D. Ferari. Providing Con-
                                                                   nection-Oriented Network Services to Mobile Hosts. August 1993.

                           Connection Management
                                                                   [3] R. Yuan, S Biswas and D. Raychaudhuri. A Signaling and Control
                                                                   Architecture for Mobility Support in Wireless ATM Networks, 1997.
                                                                   [4] A. Festag, A. Wolisz, MOMBASA: Mobility Support – A Mulitcast-
                          Node/Switch Management                   based Approach. Proceedings of European 2000, Sept 2000.
                                                                   [5] D. Kim and C. Toh. Mobile Multicasting in Wireless ATM Networks.
                                                                   Mobile Networks and Applications 5 (2000) 103-110.
                                                                   [6] J. Porter, D. Gilmurray, A. Massarella, and J. Naylon, Wireless ATM
              Client                               Client
                                                                   handover requirements and issues. http://www.cam-orl.co.uk/radio/atm97-
                               Physical Network                    0153.html.
Fig. 9. Signaling protocols in the WUGS environment                [7] W.S.V. Wong, H.C.B. Chan, and V.C.M. Leung, Performance Evalua-
                                                                   tions of Path Optimization Schemes for Inter-Switch Handoffs in Wireless
   When a signaling client opens a MCALL, the connections
(could be several) are set up. The client manages the              ATM Networks, July 2000.
MCALL and is designated the owner. Additional clients can          [8] P. Marichamy, S. Chakrabarti and S.L Maskara. Performance Issues in
be added to the MCALL on request of the owner. Once a              Rerouting for Handoff in Wireless ATM, 2000.
MCALL is opened, connections can be added, modified and            [9] WUGS – Washington University Gigabit Switch, URL:
dropped to/from the MCALL. MCALL features can be set
                                                                   http://www.arl.wustl.edu/gigabitkits/kits.html
according to the user needs. Signaling clients can be imple-
mented to perform rerouting of connections when handover           [10] K. Cox, et al: Connection Management Access Protocol (CMAP)
occurs.                                                            Specification. URL:http://www.arl.wustl.edu/gigabitkits/kits.html
   As already mentioned the performance measurements to            [11] J. De Hart. Connection Management Software (CMSS) Architecture.
be considered with the experimental setup are (i) Service          URL:http://www.arl.wustl.edu/gigabitkits/kits.html
disruption time, (ii) Handoff completion time, (iii) Buffer
                                                                   [12] A. Acompora and M. Naghshineh, An Architecture and methodology
requirements at MT, (iv) Buffer requirements at AP and (v)
The excess bandwidth resources required during handoff.            for mobile-executed handoff in cellular ATM networks, IEEE Journal on
   It is intended to perform experiments with audio and low        Selected Areas in Communications 12(8) (October 1994) 1365 – 1375.
bit rate video, in order to quantify the service disruption due    [13] C. Chiasserini and R. Lo Cigno. Handover in Wireless ATM Net-
to the handover. Audio traffic can be characterized by its         works: In-Band Signaling Protocols and Performance Analysis. IEEE
timing component. Every T milliseconds, a 160-byte packet
                                                                   Transactions on Wireless Communications, Vol. 1, No. 1, January 2002.
will be transmitted by the source. For T = 20, this corre-
sponds to telephone quality audio of 64 kb/s. In a typical         [14] A. Festag, L. Westerhoff and A. Wolisz. The MOMBASA Software
audio conversation, there will be silence periods during           Environment – A Toolkit for Performance Evaluation of Multicast-Based
which no packets will be transmitted. If this occurs during a      Mobility Support. Proc. of Performance Tools 2002, London, UK, April
handoff, there would be no disruption of traffic. It is for this   2002.
reason that we will make use of continuous traffic, so that
                                                                   [15] R. Ramjee, T. La Porta, J. Kurose, D. Towsley. Performance Evalua-
we can detect all potential disruptions during a handoff.
   The Video traffic can be characterized by a Constant Bit        tion of Connection Rerouting Schemes for ATM-based Wireless Networks.
Rate source sending packets every 30 ms. This would corre-         IEEE/ACM Transactions on Networking, 1998.
spond to a frame rate of approximately 30 frames per sec-
ond, the frame rate for full motion video.

                       6. CONCLUSION

   In this paper, an evaluation platform has been presented
to study the handover schemes, and its components have
been fully justified to serve as a tool for the performance
evaluation of the various handoff schemes.
   For experimental purposes a testbed will be setup, which
is based on an open, non-proprietary, networking environ-

				
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