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VIRTUAL CONNECTION TREE BASED ALGORITHMS FOR 3G MOBILECOMMUNICATION SYSTEMS
A. L. Heath and R. A. CarrascoSchool of Engineering and Advanced Technology, Staffordshire UniversityPO BOX 333, Beaconside, Stafford ST18 0DF, Staffordshire, U.K.Emails: [email protected], [email protected]
AbstractAn algorithm for mobile Asynchronous Transfer Mode(ATM) handover that offers serviceadaptability and efficient allocation of wired resources for connection rates is evaluated in this paper.In future 3G systems there is a requirement for wireless connection rates of up to 2Mbits/sec, it is theobjective of this paper to investigate the effects of this increase in rate on a service adaptable handoffalgorithm. The algorithm is based on the Virtual Connection Tree (VCT) and provides fast re-routing for delay sensitive services and cell sequencing for cell loss sensitive services. An ATMhandoff model is used to analyse the service adaptable algorithm in terms of cell loss and end-to-enddelay. Results are discussed proving the advantages of the algorithm for future ATM mobilecommunications.
1. IntroductionIn the near future bandwidths of up to 2Mbits/s will be available using 3G mobile communication
systems through IMT-2000 [1, 2], this will allow the most demanding of today’s internet applicationsto be carried out by portable devices allowing world wide roaming. With this trend it is important tohave an efficient signalling system and provision for handoffs to take place as the user travels fromone cell to another. Resources in a mobile environment are limited and therefore require efficientadministration if multimedia services are to be provided. The mobility that gives users freedom toroam complicates the management of calls at the central processor.
Handoff or handover is the process of changing a user’s reference BS, this makes transmission ofinformation difficult since a new path must be provided each time this process takes place [4].Seamless handover of ATM virtual connections is not currently supported in the ATM layeredprotocol; a new route is allocated each time a mobile changes BS. The delay introduced by the re-establishment of the routes is unacceptable for broadband services or delay sensitive connectionssince it can lead to disruptions or degradation of the connection [4].
In [4] a service adaptable handover algorithm was evaluated that avoids signalling and queuing ifthe service requires fast re-routing and assures the delivery most cells in order if the service can notsupport cell loss or cell delineation. The algorithm is based on the VCT which has been recognisedas the fastest method but requires incorporation of a lossless handover mechanism to assure cellsequencing. An ATM handover model is developed in [4] to simulate the effects of the algorithm interms of cell loss and cell delay. Connection rates of 64, 128 and 256kbits/sec were considered forconstant and variable rate services, advantages were provided at these values, however with futurerates increasing the ATM model will be used to evaluate the performance of the algorithm at thesehigher rates.
This paper is organised as follows; In section 2 the Virtual Connection Tree with a ServiceAdaptable Handoff Algorithm is described. In Section 3 the model used to simulate the HandoffAlgorithm is described. Results are obtained and analysed in Section 4 and the conclusions are drawnin Section 5.
2. Virtual Connection Tree with a Service Adaptable Handoff AlgorithmVCT is an ATM oriented strategy that avoids involving the central processor during handoffs. AVCT consists of cellular BSs with radio transceivers connected to switching nodes through an ATMwired infrastructure and mobile units, which transmit information over the shared radio channel. Theroot of the tree is the MSC and the leaves are the BSs, the area covered by the VCT is theNeighboring Mobile Access Region (NMAR).
The service adaptable algorithm [4] provides service adaptable handoffs, two options areconsidered, once the BS accepts the connection in it’s cell. If the service requires fast re-routing andthe loss of several cells is not inconvenient, then the standard VCT can be applied. Conversely, if theservice requires all cells to arrive in the correct order, then the VCT with extended cell sequencingalgorithm is employed.
Forward handoff has been considered, this is when the MS stops the wireless connection withthe BS and establishes a link with a new BS. The backward handoff where the new wireless link isestablished through the old BS is similar.
3. ATM Based Handoff ModelA model was created in [4] to simulate the ATM handoff procedure, it simulates traffic in both
the wired and wireless environments. ATM cells are transmitted, simultaneously in both directionsfrom the end points of the system according to ATM technology to the other end point. Connectionsare interrupted momentarily and re-routed due to handoffs, the general system is shown in Figure 1.If initially BS1 was the serving BS, when a handoff occurs the connection is switched to BS2, andfor the next handoff switched back to BS1, this is repeated several times during the simulation. Thissimulates a MS travelling across multiple BSs using only two BSs. Figure 2 indicates the path takenby the information and the possible delays that can be encountered in the simulated model, for moreinformation refer to [4]. The model was built using BONeS Designer, a software package thatprovides an ATM library, that has been improved to allow ATM representation in the mobileenvironment.
The performance in terms of cell loss, loss of sequence and end-to-end delay have been modelledfor the two options considered in the VCT algorithm. Simulations were run for the VCT with andwithout the extended cell sequence algorithm, since the objective is to investigate the effect ofhandoff the simulations do not contemplate the effect of other users, either in the air link or the wiredpart. The general parameters used for the simulations are shown in Table 1. Mobile connections witha call duration of 360 seconds over a microcellular system were simulated. The number of handoffsconsidered during the simulation is high in order to obtain abundant results to complete a thoroughanalysis, a high velocity for the MS and a small cell size is therefore assumed. Different types ofconnection (constant and variable rate services) at different rates are considered.
4. Results and DiscussionFirstly, the standard VCT was analysed with the intention of detecting if cells were lost during
handover. The simulations were run for both constant and variable transmission rate connectionsbetween 64kbits/sec and 2Mbits/sec the results obtained are shown in Figure 3. The lost cells aredownlink cells that have been sent to the old BS when the MS is at the new BS, since there is noalgorithm to re-route these cells. With constant rate connections the relationship between the numberof cells lost due to handoff and transmission rate is linear, whereas for variable rate this relationshipcan be seen to be non-linear as shown in Figure 3. The reason for this is the bursty manner that thevariable rate traffic is generated since in some handoffs no cells are lost and in others many are lost.There are more cells lost for constant rate traffic (average values), but more cells are lost for burstytraffic in one instance for bursty traffic (peak values) these types of loses are more detrimental to theQoS.
The results show that cells can be lost during handoffs when the standard VCT is applied. If alow constant rate service such as voice is considered then the number of cells lost per handoff is
negligible. For services at higher rates the number of cells lost more cells are lost and for servicessuch as data this is not acceptable, so applying the VCT can present problems.
Secondly, the VCT with extended cell sequencing was examined, the same conditions wereapplied as in the previous case. This option maintains all cells, however the delay incurred due to theforwarded cells is important to some services. The algorithm prevents the loss of any cells byforwarding the wrongly routed cells to the new location. The delay for these cells is the largest sincethey are buffered and sent through a longer path, forwarding of the cells occurs in the downlink andtherefore this is the direction of study.
Next, the cell sequence was examined both with the standard VCT and the VCT with extendedcell sequencing, this is illustrated in Figure 4. The are more cell sequence errors for variable ratetraffic than constant rate traffic, this is also due to the bursty nature of the variable rate cell creation.The distribution of sequence errors for variable rate traffic is very similar for the standard VCT andextended cell sequence VCT, with the quantity of errors increasing with transmission rate, thisconcept requires further investigation. With constant rate traffic there are no sequencing errorsobtained for the extended cell sequence VCT, but there are random errors for the standard VCT.Even though the cell sequence errors for variable rate traffic are similar for both VCTs, they do nothave the same overall amount of errors, since with extended VCT there are no lost cells, therefore thecell error rate (CER) has been calculated for each condition. The CER was calculated, usingEquation 1.
ed transmittcells ofno.errors cell of no.
edtransmittcellsofno.errors sequencing of no. cellslost of no.CER Rate,Error Cell =+= (1)
The CER for the different conditions is illustrated in Figure 5a, the CER for constant rate traffic isrelatively constant with the standard algorithm (0.0046 slightly increasing with transmission rate)and no errors occurred with the extended VCT. The CER for variable rate traffic was higher than atconsequent transmission speeds than the constant rate traffic. The variable system is more unstabledue to the bursty nature of the traffic generation, there is not a linear relationship between CER andtransmission speed, this requires further investigation.
Next, the end-to-end cell delay is considered for the four different conditions, this isillustrated in Figure 5b. For constant rate connections the mean delays incurred are similar for thedifferent transmission rates. The mean delay of the standard VCT is 340µs for the at all transmissionrates and for the extended VCT a 470µs delay at 64 kbits/sec to a 570µs delay at 2M bits/sec this rateincreases linearly. The reason that the extended VCT has higher delays is that the forwarded cellshave to be buffered waiting for the algorithm. The first cell forwarded is the one with the highestdelay since it was the first cell to be buffered and had to wait longer for the algorithm than cellsarriving later. The difference between the end-to-end delay for successive forwarded cells is almostconstant, at higher transmission speeds more cells are forwarded. In variable rate connections theaverage and maximum delays are increased, this is due to the algorithm not only on the out of bandsignalling but also on the generation of ATM information cells (i.e. first cell in the uplink). Thegeneration of the cells is variable so it may be possible that no cells are transmitted in one directionwhen a handoff takes place, this increases the algorithm duration time and consequently the end-to-end delay of forwarded cells. The relationship between the transmission rate and the delay is notlinear.
These results show that if the VCT with extended cell sequencing algorithm is applied toevery type of service connection, significant delays may be introduced, this delay will not be suitablefor delay sensitive types of service such as voice.
5. ConclusionsA model has been used to evaluate the handover procedure in terms of cell loss, cell sequencing
and end-to-end delay at transmission speed of up to 2 Mbits/sec. The results obtained show thatdifferent services need to be treated differently when handoffs take place, for example, on averageabout 9 cells are lost in every handoff when the standard VCT is applied over a constant connectionat a rate of 64 kbits/sec. This can be acceptable for voice services where the loss of a few cells ispermitted as long as the delay is kept low. However data connections can not allow the loss ofinformation and will be damaged. When the VCT with extended cell sequencing option is appliedover the same connection no cells are lost at the cost of incurring peak delay of 0.075s in comparisonto the average delay measured to be 470 µs for this option and 340 µs for the standard VCT. In thissituation the opposite occurs voice can not tolerate delay and consequently the connection will beaffected.When the VCT extended cell sequencing is employed no cells are lost at all at any speed or withconstant or variable rate connections, however some cell sequencing errors do occur for variabletransmission rates at high speeds (2 Mbits/sec and 1.444 Mbits/sec), these have a similar distributionas the standard VCT at the same connection rates and service type, this phenomena requires furtherinvestigation. The performance of the extended VCT in terms of cell error rate is much better thanthe standard VCT.
5. References[1] Samukic A., ‘UMTS universal mobile telecommunications system: Development of standards for the third
generation’ IEEE Transactions on Vehicular Technology v 47, n 4, (Nov 1998), p 1099-1104[2] Godara, L.C.; Ryan, M.J.; Padovan, N. ‘Third generation mobile communication systems: Overview and
modelling considerations’ Annales des Telecommunications/Annals of Telecommunications v 54, n 1, (1999),p 114-136
[3] Karol, M., Veeraraghavan M. and Eng, K.Y., ‘Implementation and Analysis of Handoff Procedures in aWireless ATM LAN’ IEEE Globecomm London. 1996.
[4] Larrinaga, F. and Carrasco, R.A., ‘Virtual Connection Tree Concept Application over CDMA Based CellularSystems’ IEE Colloquium on ATM Traffic in the Personal Mobile Communications Environment, SavoyPlace, London 11 Feb. 1997.
Table 1 – Simulation Parameters
Parameter ValueService Type Variable or ConstantMean Rate 64, 128, 256, 394, 512, 1024, 1444 2000
(kbits/sec)Call Duration 360 (sec)Air Link Capacity 5 106 (bit/sec)Radio Capacity Delay, δair rate ATM cell size/Capacity air link (sec)Fabric Delay (Switch) S
iδ 2.5 10-5 (sec)Capacity or Rate of the Link 100 or 150 (Mbit/sec)Link Rate Delay linkrate
iδ ATM cell size/Capacity of link (sec)Link Propagation delay per unit length 5 10-6 (sec/miles)Transmission Link Delay .linktrans
iδ Link propagation delay per unit length * Lengthof the link (sec)
Wireless Connection EstablishmentDelay δwirelessest
Between 25 and 75 (msec)
Velocity of Mobiles Between 20 and 70 (miles/hour)Diameter of Cells 0.1 (miles)
BS2BS1
MSC
FixedNetworks
Endpoint
Figure 1 – ATM Handover simulation Model
MSRadio
Channel
LinkBS
oldBS
Link
IntermediateNodes & Links
Fixed-endTerminalMSC
IntermediateNodes & Links
Link IntermediateNodes & Links
Link IntermediateNodes & Links
linkrateBSδ
.linktransBSδ
linkrateMSCδ .linktrans
MSCδ.twirelessesδ
linkrateoldBSδ
.linktransoldBSδ
rateairδ
.retransδ
.transairδ
intairδ
SBSδQBSδ
Normal Routing
Downlink Forwarded Cells
Delays
��
���
� ++�=
l
k
linktransk
linkratek
Sk
0
.δδδ
��
���
��
=
l
k
Qk
0
δ
��
���
� ++�=
n
i
linktransi
linkratei
Si
0
.δδδ
��
���
��
=
n
i
Qi
0
δ
��
���
�++�
=
m
j
linktransj
linkratej
Sj
0
.δδδ
��
���
��
=
m
j
Qj
0
δ
SMSCδQMSCδ
SoldBSδQoldBSδ
Figure 2 – End-to-End mobile connection and delay
Cells Lost per Handoff
0
100
200
300
400
0 500 1000 1500 2000
Transmission Rate (kb/s)
Num
ber
of C
ells
Lost
AVG-Const PEAK-Const AVG-Var PEAK-Var
Figure 3 – Cells lost due to handover, standard VCT
64 128
256
394
512
1024
1444
2000
0
25
50
75
100
Cel
ls L
ost
Transmission Rate (kbits/sec)
Total Cell Sequence Errors
Std Alg (Const) Ext Alg (Const) Std Alg (Var) Ext Alg (Var)
Figure 4- Cell sequencing errors
a)
Cell Error Rate for ATM Handoff System
0.00001
0.0001
0.001
0.01
0.1
0 500 1000 1500 2000
Transmission Rate
Cel
l Err
or R
ate
Std Alg (Const) Ext Alg (Const) Std Alg (Var) Ext Alg (Var) b)
Mean End-to-End Cell Delay
0
200
400
600
800
64 128 256 394 512 1024 1444 2000
Transmission Rate (kbits/sec)
Tim
e ( µµ µµ
s)
Std Alg (Const) Ext Alg (Const) Std Alg (Var) Ext Alg (Var)
Figure 5 – a) Cell Error Rate, b) End-to-end Cell Delay
11 April 2000
Alison HeathMEng, BEng (Hons), [email protected]
andProfessor Rolando CarrascoBSC(Hons), PhD, CEng, [email protected]
http://www.staffs.ac.uk/personal/engineering_and_technology/alh2/
School of Engineering& Advanced Technology
VIRTUAL CONNECTION TREE BASEDVIRTUAL CONNECTION TREE BASEDALGORITHMS FOR 3G MOBILEALGORITHMS FOR 3G MOBILE
COMMUNICATION SYSTEMSCOMMUNICATION SYSTEMS
11 April 2000
2
IndexIndex
� Introduction, to 3G communication systems� Research Objectives� Background Theory
– Asynchronous Transfer Mode,Virtual Connection Tree, Bandwidth
� ATM Model– Mobility and Handoff Problem,– Algorithm and Delay– Improve QoS by measuring cell loss, delay and sequencing errors– Results
� Conclusions and Future Work
11 April 2000
3
IntroductionIntroduction
� Evolution to 3G mobile communications
� High bw, broadband systems
– Single set of services– Anytime, anyplace communications– Packet based transport mechanisms
IS-95
HSCSD
GPRS
Cdma2000 WCDMA
IMT-2000, UMTS
Voice
EDGE
GSM
Data
Voice Data
IS-136
SecondGeneration
Systems
ThirdGeneration
Systems
ATM TCP
IPTransportMedium
TransportMechanism
USAKorea
EuropeJapanKorea
11 April 2000
4
Research ObjectivesResearch Objectives
� Investigate the issues affecting the access to mobileATM networks
� Accommodate mixed types of information– Voice, data, images - Multimedia, and Mobility
� Simplify re-routing of information (handoffs)
� Minimise time delay, and loss of cells
11 April 2000
5Asynchronous TransferAsynchronous TransferMode (ATM)Mode (ATM)
� Different types of services at different traffic rates using the same uniqueUniversal Network
� Common Network Layer for all types of traffic
� Intelligent Network that assures QoS
� UMTS and Wireless ATM (Mobile)
Physical &Convergence
Layer
ATM Layer
ATM Adaptation Layer
HigherLayers
HigherLayers
ControlPlane
UserPlane
Management Plane
ATM Protocol Reference Model
11 April 2000
6Virtual Connection TreeVirtual Connection Tree(VCT)(VCT)
Static PartDynamic PartPre-establishedRoutes
Endpoint
BS2BS3
BS4
BS5
MS1
MSCroot
Neighbouring MobileAccess Region
leaves
MS1 associated to BS2
vc9
vc8BS1
vc1 12
3 4
5 6A
vc14
vc10vc2
vc7vc13
Switch A Look Up Table
vc3
vc6
vc4
vc5
vc11
vc12
VCN-in Port-in VCN-out Port-outvc1 1 vc2 3vc9 5 vc10 3vc7 4 vc8 2
vc13 4 vc14 6
11 April 2000
7VCT WiredVCT WiredBandwidth AllocationBandwidth Allocation
4 Mbit/sec
MSCMSC20 Mbit/sec
8 Mbit/sec 8 Mbit/sec 8 Mbit/sec 8 Mbit/sec
4 Mbit/sec 4 Mbit/sec 4 Mbit/sec
BS 2BS 1 BS 3 BS 4
20 Mbit/sec
11 April 2000
8NewNewBandwidth AllocationBandwidth Allocation
VP switches
PVP between BSs
Reserve PVP for BSs
vp2
vp1-2
vp1
BS 1 BS 2
4 Mbit/sec 4 Mbit/sec
vp3
vp3-4
vp4
BS 4BS 3
4 Mbit/sec4 Mbit/sec
MSC
20 Mbit/sec
8 Mbit/sec 8 Mbit/sec 8 Mbit/sec 8 Mbit/sec
20 Mbit/sec
11 April 2000
9
0 100 200 300 400 500 600 700 8000
200
400
600
800
1000
1200
1400Band-W idth Allocation(MSC)
Active Users in VCT
Ban
d-W
idth
(Mbi
t)
16 BSs50 Channels
0 100 200 300 400 500 600 700 8000
10
20
30
40
50
60
70
80Band-Width Allocation(BS)
Active Users in VCT
Ban
d-W
idth
(Mbi
t)
Old VCT
New VCT
Old VCT
New VCT
Bandwidth ComparisonBandwidth Comparison
•1 Mbit/s per connection
11 April 2000
10ATM-BasedATM-BasedHandoff ModelHandoff Model
BS2BS1
MSC
FixedNetworks
EndpointObjectives•Test AlgorithmPerformance•Compare to SimpleVCT
Conditions•Diff. Call Rates•Diff. Services •Mobility
Measurements•Cell Loss•Cell mis-orderring•Cell Error Rate•Cell Delays
11 April 2000
11Service AdaptableService AdaptableHandoff AlgorithmHandoff Algorithm
Handoff requestat BS
Wireless bwavailable
?
Type ofservice
?VCT with extended
cell sequencingAlgorithm
BlockedConnection
StandardVCT
Algorithm
Transmission fromnew BS (VPI)
DelaySensitive
Cell LossSensitive
No
Yes
11 April 2000
12End-to-End mobileEnd-to-End mobileconnection and delayconnection and delay
MSRadio
Channel
LinkBS
oldBS
Link
IntermediateNodes & Links
Fixed-endTerminalMSC
IntermediateNodes & Links
Link IntermediateNodes & Links
Link IntermediateNodes & Links
Normal Routing
Downlink Forwarded Cells
11 April 2000
13
Parameter ValueService Type Variable or ConstantMean Rate 64, 128, 256, 394, 512, 1024, 1444 2000 (kbits/sec)Call Duration 360 (sec)Air Link Capacity 5 106 (bit/sec)Radio Capacity Delay, δair rate ATM cell size/Capacity air link (sec)
Fabric Delay (Switch)S
iδ 2.5 10-5 (sec)
Capacity or Rate of the Link 100 or 150 (Mbit/sec)
Link Rate Delay linkrateiδ ATM cell size/Capacity of link (sec)
Link Propagation delay per unit length 5 10-6 (sec/miles)
Transmission Link Delay .linktrans
iδ Link propagation delay per unit length * Length of thelink (sec)
Wireless Connection Establishment Delayδwirelessest
Between 25 and 75 (msec)
Velocity of Mobiles Between 20 and 70 (miles/hour)Diameter of Cells 0.1 (miles)
Simulation ParametersSimulation Parameters
11 April 2000
14
Cell Loss MeasurementCell Loss Measurement
No cells are lost using Extended VCT Algorithm15 31 57 68 10
2
116
0
50
100
150
200
250
Los
t Cel
ls
Time (sec)
Lost Cells Due to HandoverStd Alg (Variable)
10 17 30 47 64 82 93 108
119
050100150200250300350400
Time (sec)
Lost Cells Due to HandoverStd Alg (Constant)
256kb/s394kb/s512kb/s1024kb/s1444kb/s20000kb/s
bits/sec Constant Variable256k 49 0
1024k 198 2032M 387 215
At first handover
11 April 2000
15
Cell Loss MeasurementCell Loss Measurement
Average number of Cells Lost per Handoff
0
100
200
300
0 500 1000 1500 2000
Transmission Rate (kb/s)
Los
t Cel
ls
AVG-Const AVG-Var
Linearrelationship
11 April 2000
16Cell SequenceCell SequenceLoss (Constant)Loss (Constant)
Cell Sequence Errors - Std Alg (Constant)
0 60 120 180 240 300 360
Time (sec)
Handoff Time
1024 kb/s
512 kb/s
394 kb/s
Random loss of sequence
11 April 2000
17Cell SequenceCell SequenceLoss (Variable)Loss (Variable)
Cell Sequence Errors -Ext Alg (Variable)
0 25 50 75 100
Time (sec)
Handofftime
2Mb/s
144 kb/s
Cell Sequence Errors - Std Alg (Variable)
0 25 50 75 100
Time (sec)
HandoffTime
2 Mb/s
1444 kb/s
1024 kb/sMore errors
as speed increaseswith both
variations ofthe Algorithm
11 April 2000
18
Cell sequence errorsCell sequence errors
64
256
512
1444
0
25
50
75
100
Cel
ls L
ost
Transmission Rate (kb/s)
Total Cell Sequence Errors
Std Alg (Const) Ext Alg (Const) Std Alg (Var) Ext Alg (Var)
76 cells out of sequence forStandard Algorithm and75 cells out of sequence forExtended Algorithm for variablerate traffic at 2Mbit/sec
11 April 2000
19
Cell Error RateCell Error Rate
edtransmittcellsofno.errors cell of no.
edtransmittcellsofno.errors sequencing of no. cellslost of no.CER Rate,Error Cell =+=
ConstantCER
0.0045
Cell Error Rate for ATM Handoff System
0.00001
0.0001
0.001
0.01
0.1
0 500 1000 1500 2000
Transmission Rate
Cel
l Err
or R
ate
Std Alg (Const) Std Alg (Var) Ext Alg (Const) Ext Alg (Var)
Higher CER,bursty sourcesmax = 0.085
11 April 2000
20End-to-EndEnd-to-EndCell Delay (Constant)Cell Delay (Constant)
Downlink Cell Delay (Constant 256 kb/s)
0.00048(Alg)
0.00034-0.01
00.010.020.030.040.050.060.070.080.09
0 25 50 75 100Time (sec)
Del
ay (s
ec)
Handoff Time Forwarded cells
Downlink Cell Delay (Constant 2 Mb/s)
0.00057(Alg)0.00034
-0.010
0.010.020.030.040.050.060.070.080.09
0 25 50 75 100Time(sec)
Del
ay (s
ec)
Handoff Time Forwarded cells
Std Algorithm has constant delay, Ext Algorithm delay increaseswith transmission rate, more packets are forwarded at higher rates
50 cells 388 cells
11 April 2000
21
Downlink Cell Delay (Variable 256 kb/s)
0.00077 (Alg)0.00061
-0.010
0.010.020.030.040.050.060.070.080.09
0 25 50 75 100
Time (sec)
Del
ay (s
ec)
Handoff Time Forwarded cells
Downlink Cell Delay (Variable 2 Mb/s)
0.000610.00078(Alg)
-0.010
0.010.020.030.040.050.060.070.080.09
0 25 50 75 100
Time(sec)D
elay
(sec
)
Handoff Time Forwarded cells
End-to-EndEnd-to-EndCell Delay (Variable)Cell Delay (Variable)
Variable traffic delays are higher, traffic is bursty
0 cells at1st
handover
232 cells
11 April 2000
22Mean End-to-EndMean End-to-EndCell DelayCell Delay
Mean End-to-End Cell Delay
0
200
400
600
800
0 500 1000 1500 2000
Transmiss ion Rate (kbits /se c)
Tim
e ( µµ µµ
s)
Std Alg (Const) Std Alg (Var) Ext Alg (Const) Ext Alg (Var)
Variable traffic larger mean delay than constant traffic
11 April 2000
23
ConclusionsConclusions
� Service adaptable ATM handover algorithm with reducebandwidth reservation and seamless inter-VCT handover(ATM level)
� Cell Loss– Constant rate Std Alg number cells lost increases as transmission speed
increases (49@256kb/s, 387@2Mb/s)
– More cells lost for constant rate traffic but more cells are lost in eachinstance with variable traffic (387 const, 215 var @2Mb/s).
– No cells lost with the Extended VCT� At the cost of increased time delay
11 April 2000
24
ConclusionsConclusions
� Cell Sequencing Errors– Constant rate: Std Alg there are small number of errors and none for Ext Alg– Variable rate: similar distribution for both Algorithms at high speeds, no
errors at low speeds (75 errors @2Mb/s)
� Cell Error Rate– Constant rate Std Alg, CER stays relatively constant as transmission speed
increases (0.0045)– Variable rate Std Alg, CER is variable, in the same order as constant Variable
rate for Ext Alg has low CER (5.83x10-5)
� End-to-End Delay– Higher values for Ext Alg than Std - due to forwarding of cells and higher
values (780µs extended 610µs std @2Mb/s)– slight increase in delay as transmission speed increases
11 April 2000
25
Future WorkFuture Work
� Investigate reasons for cell sequence errors at high speeds
� Implement similar Algorithm for TCP
� Implement a packet switched B-ISDN system to run on topof IP
� Investigate multiple access schemes such as cdma2000,WCDMA, TDMA, FDMA
11 April 2000
Any Questions ?Any Questions ?
School of Engineering& Advanced Technology
Thank you for Listening
11 April 2000
School of Engineering& Advanced Technology
VIRTUAL CONNECTION TREE BASEDVIRTUAL CONNECTION TREE BASEDALGORITHMS FOR 3G MOBILEALGORITHMS FOR 3G MOBILE
COMMUNICATION SYSTEMSCOMMUNICATION SYSTEMS
Alison HeathMEng, BEng (Hons), [email protected]
andProfessor Rolando CarrascoBSC(Hons), PhD, CEng, [email protected]
http://www.staffs.ac.uk/personal/engineering_and_technology/alh2/
