Internet-Draft C. Tocci
<draft-tocci-ip-over-atm-00.txt> P. Conforto
Expires: February 2001 G. Losquadro
Alenia Spazio
ACCORD mobile multi-segment system: IP over ATM
performance and QoS trial results evaluation
STATUS OF THIS DOCUMENT
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ABSTRACT
This document reports upon the ACCORD Trial activity which aims at
investigating support of TCP/IP over mobile multi-segment system.
IP based applications and IP over ATM measurements have been
executed in order to obtain significant information about
intersegment service mobility.
1 Introduction
The ACCORD project, developed in the Advanced Communications
Technology and Services (ACTS) framework funded by the European
Union, is an integration project of four different Access Systems
and a Core Network, all coming from different ACTS projects:
SECOMS (Broadband Satellite Access System), MEDIAN ATM (Broadband
W-LAN Access System) SAMBA (Cellular W-ATM Access System) and
EXODUS (Enhanced-DECT Access System and Mobile Broadband Core
Network).
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The main goal of the ACCORD project is to investigate and validate
the possibility to create a Global Mobile Broadband (GMB)
communication system, consisting of multiple
(satellite/terrestrial) system components (or segments), able to
support a wide range of multimedia services (ATM native and IP
oriented applications).
The project has targeted its objectives through both a theoretical
and experimental activities, aiming at designing a Target Network
and executing field measurements on a trial platform,
respectively.
The scope of ACCORD Trial is to study and measure the
multi-coverage terrestrial and satellite environment. To this end
appropriate measurements, at various level (Physical, ATM, TCP/IP)
have been executed and the performance of the support of the ATM
network to the TCP/IP applications in the ACCORD environment has
been evaluated.
2 Overall Trial Strategy definition
Given that the ACCORD Trial aims at gathering as much as possible
significant information about the parameters involved in the
InterSegment HandOver (ISHO) between a variety of radio
terrestrial and the satellite radio access networks, the maximum
attention has been put on selecting combinations of coverage in
which the satellite access is available. Therefore the selected
trial scenarios are:
SECOMS/DECT trial which involves InterSegment HandOver (ISHO)/Dual
Mode Terminal Roaming (DMTR) study in the context of transitions
from Rural to Urban environment, from Outdoor to Dual coverage and
from Broadband to Narrowband and, of course, viceversa;
SECOMS/SAMBA trial which involves ISHO/DMTR study in the context
of transitions from Rural to Urban environment and from Broadband
to Wideband;
DECT/MEDIAN trial which aims at collecting data to characterise
typical transient coverage situations in the context of indoor
ISHO and transition from Narrowband to Wideband.
The DECT/MEDIAN trial has been selected instead of the
SECOMS/MEDIAN trial which, as there is not overlapping of indoor
MEDIAN and satellite SECOMS coverage, does not provide significant
results. The SECOMS/MEDIAN trial can be obtained from the logical
combination of the SECOMS/DECT and DECT/MEDIAN trials relying on
the intermediate "bridge" coverage provided by DECT.
The three trials SECOMS/DECT, SECOMS/SAMBA and DECT/MEDIAN,
consist in running two parallel connections with the simultaneous
execution of TCP/IP measurements on both the radio access systems
involved in the trial.
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In both SECOMS/DECT and SECOMS/SAMBA trials
the Dual Mode Terminal is in movement along
a predefined path, chosen in such a way to provide characteristics
ISHO and Dual Mode Terminal conditions. The goal is to take an
adequate number of measurements in significant conditions and for
validation purposes. In particular the measurements have been
executed at low speed (pedestrian) since the environment where the
measurement execution takes place is the near building area.
This environment has been chosen because it is the more
interesting as for the satellite/terrestrial complementary
access networks.
3 TCP/IP level measurement approach
The goal of the trial measurement campaign execution is to find
out what applications could be provided over a mobile multi-access
system. With reference to the OSI protocol stack the point for
measurement is on the User-Plane at application level. This is the
basic step to be done to identify the features of the applications
that can run over the system.
The followed approach foresees that the measurements are executed
with a spatial and temporal correlation. The spatial correlation
(measurements executed on same points/path) is intrinsically
provided by the Dual Mode Terminal emulation (co-location of two
mobile terminals) and the temporal correlation is guaranteed by
executing the two access system measurements at same time. This
approach not only studies what of the currently available
applications can be used over a Multi-mode/Multi-access platform,
but also allows to start considering applications specifically
designed for such platform. These applications are capable to run
over multiple user-plane belonging to different networks and take
full advantage as for user QoS both for bandwidth, mobility and
cost.
4 Measurement Tests executed over the ACCORD platform
In order to select a significant set of measurements to be done
during the ACCORD trials and in order to set up and tune a number
of tools to be used, preliminary tests, where only fixed systems
are involved in communication chain and no radio access are
included, have been executed.
The performance parameters selected for trial measurements are:
Throughput and Round Trip Delay at TCP/UDP/ICMP level, the
tools used are the netperf program and the ping program
respectively.
5 SECOMS/DECT joint-trial execution
SECOMS/DECT Trial aims at validating a mobile environment scenario
where an open area / urban area (near building) coverage is
assured by a dual-mode access network consisting of the
Broadband Satellite and of the DECT segments.
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The equipment for the SECOMS/DECT Trial consists of a dual
mode ACCORD Mobile Terminal (DECT and SECOMS), the corresponding
Base Stations, the ACCORD Core Network (ATM switch) and two
EXODUS Fixed Broadband Terminals (FBTs). The ACCORD Mobile
Terminal consists of two co-located subsystems: a SECOMS
Terminal and a DECT Portable Part. The Base Stations for
SECOMS and DECT are connected via ATM to the ACCORD Core Network.
The SECOMS/DECT joint-trial execution mainly aims at evaluating
the impact that different radio coverage environments have on
ATM connection, IP and TCP/UDP connection throughput and
transfer delay. The ACCORD mobile Terminal is mounted on
a van and two simultaneous calls towards the two different
EXODUS FBTs are established: one through the SECOMS access and
the other one through the DECT access.
The ATM switch is properly set in order to support two ATM
permanent cross-connections both identified by the couple
VPI/VCI=10/10 (as a required by the ATM card installed
in the EXODUS FBT). The same IP applications run on the two
connections. Once the two connections (one between the
SECOMS Terminal and FBT1 and one between the DECT Portable
Part and the FBT2) are set-up and the two applications
started up, the van is moved along a predefined path
which includes three different coverage areas: area A where the
sole satellite coverage is available (outdoor out of buildings
shadow area); area B where there is SECOMS/DECT coverage
overlapping; area C where the sole DECT coverage is
available. At each step data concerning TCP/IP are stored.
Tests to obtain throughput data at TCP/IP level are executed
while the van is actually mobile. The first run
(slow moving test) is done as slowly as possible and the
second run (fast moving test) is performed
at about 15 - 20 km/h. DECT worked well for both runs and we
got a few results from SECOMS for the second run. Data as
for DECT have been collected both at the Inter Working
Unit (IWU) and at FBT in the Laboratory.
6 SECOMS/SAMBA joint-trial execution
SECOMS / SAMBA Trial aims at validating a mobile environment
scenario where an open area / urban area (near and far building)
coverage is assured by a dual-mode access network consisting of
the Broadband Satellite and of the Digital Cellular W-ATM
segments. The equipment for the SECOMS/SAMBA Trial consists of a
dual mode ACCORD Mobile Terminal (SAMBA and SECOMS), the
corresponding Base Stations, the ACCORD Core Network (ATM switch)
and two EXODUS Fixed Broadband Terminals (FBTs). The ACCORD
Mobile Terminal consists of two co-located subsystems: a SECOMS
MBT (Mobile Broadband Terminal) and a SAMBA MBT.
The Base Stations for SECOMS and SAMBA are connected via ATM to
the ACCORD Core Network.
The dual-mode terminal consisting of both the SECOMS MBT and
the SAMBA MBT is mounted on a van. The SECOMS MBT consists
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of an EXODUS FBT (Fixed Broadband Terminal) interconnected
to the SECOMS IWU connected to a CommQuest TDMA modem, model
CQM-248A. The SAMBA MBT consists of an EXODUS FBT interconnected
with the SAMBA MTA (Mobile Terminal Adapter).
The two EXODUS FBTs can be implemented either by 133 MHz PC's
running Windows NT 4.0 Operating System (OS) and containing NTUA
ATM card or by SUN workstations running UNIX OS and containing
commercial ATM card.
Two simultaneous calls towards two different EXODUS FBTs
(network side) are established: one through the SECOMS access
and the other one through the SAMBA access. Once the two
connections (one between the SECOMS MBT and FBT1 and the other
one between the SAMBA MBT and the FBT2) are set-up and the two
IP-based applications started up, the van is moved along a
predefined path . At each step data concerning TCP/IP
are stored. The van circulates in a predetermined
path were 3 different coverage areas are available: SAMBA only,
SAMBA and SECOMS simultaneously, SECOMS only.
7 DECT/MEDIAN joint-trial execution
The DECT/MEDIAN trial considers the indoor nature of
MEDIAN coverage and aims at testing it with the DECT
indoor coverage. The trial layout consists of a MEDIAN
Terminal, a DECT Portable Part, the corresponding Base
Stations, the ACCORD Core Network (ATM switch) and two
Fixed Terminals: a SUN Workstation running UNIX Operating
System (OS), an EXODUS Fixed Broadband Terminal (FBT) running
Windows NT 4.0 OS. The Base Stations for MEDIAN and DECT are
connected via ATM to the ACCORD Core Network.
One of the objective of this configuration is to evaluate
the TCP throughputs of two simultaneous calls evolving in
parallel on the two access systems.
Moreover, various test configurations have been used to
characterise the performance of the MEDIAN demonstrator
at TCP/IP level, both in stand-alone mode and in combination
with EXODUS equipment.
The comparison of the retrieved information with the
information collected on the other access systems
(especially for SECOMS) are very useful to investigate service
mobility through different access segments.
The configuration used for MEDIAN (stand-alone) TCP/IP
level testing includes two HP PCs which serve as
User Terminals, a MEDIAN Portable Station, a MEDIAN Base Station,
an ATM switch and an Internet Advisor inserted between the HP PC
and the MEDIAN Portable Station. The MEDIAN Base Station is
connected via ATM to the ATM switch. The PCs that serve as User
Terminals are equipped with ForeRunner PCA-200E ATM adapter
cards. The driver software for these cards allows the
specification of Peak Cell Rates on a per-PVC basis.
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The operation of Internet protocols over ATM is enabled on the
basis of the 'Classical IP' approach (PVC's) as specified in
RFC1577, using LLC/SNAP encapsulation of the IP packets as per
RFC1483. The Internet Advisor is put in monitor mode, thus making
it possible to inspect the bi-directional traffic flow at ATM and
higher levels. 'Ping' and 'Netperf' were used as tools for
TCP/IP level testing. Applications that were run over this
configuration include a Web browser / Web server with video
content, FTP and NetMeeting.
The MEDIAN/EXODUS test configuration consists of two SUN
Workstations which serve as User Terminals, a MEDIAN Portable
Station, a MEDIAN Base Station and a LightStream ATM switch.
The MEDIAN Base Station is connected via ATM to the LightStream
ATM switch. This configuration was used for TCP/IP level testing,
using 'Ping' and 'Netperf' as test tools. The 'Netperf' version
running on the SUN workstations made it possible to run UDP_STREAM
tests as well as TCP_STREAM tests. (Using the MEDIAN
configuration in stand-alone mode attempts to run UDP_STREAM tests
only produced error messages, despite the fact that NetMeeting (UDP)
worked). The overall transmit rate of the
SUN workstations had to be reduced to 40 Mbit/s to prevent cell
buffer overflows in the MEDIAN system.
8 ATM Level Measurement execution for SECOMS, SAMBA and
MEDIAN Access Networks
In the framework of the ACCORD trial activity, besides to evaluate
the network performance at TCP/IP level, also ATM level
measurements have been executed for satellite SECOMS, Digital
Cellular W-ATM SAMBA and W-LAN MEDIAN access segments.
As matter of fact the above mentioned access networks can be seen
as mobile (SECOMS and SAMBA) and portable (MEDIAN) wireless ATM
networks which access an Internet core network.
In order to evaluate the ATM connectivity performance that each
access segment is able to provide a set of ATM performance
parameters has been selected for trial measurements. These
parameters are: Cell Transfer Delay (CTD), Cell Delay Variation
(CDV), Cell Loss Ratio (CLR), Cell Error Ratio (CER).
The performance evaluation at ATM level of the different access
networks includes the verification of the ACCORD network
compliance with the ITU-T network performance objectives defined
in the ITU-T Recommendation I.356. Therefore in the ACCORD trial
activities only the ATM user information transfer performance
parameters are measured, moreover no international backbone
capabilities are taken into account.
The SECOMS, SAMBA and MEDIAN test-bench configurations set to
execute the ATM measurements have been implemented following the
same approach: each test-bench configuration consists of the
relevant access segment integrated with the ACCORD ATM switch
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which in turn is connected to a Protocol Analyzer (ATM
Measurement Equipment) configured in the loop-back mode.
The protocol analyzer performs the twofold task of generating
ATM traffic and analyzing the network performance.
9 IP over ATM performance and QoS trial results evaluation
On the basis of the measurements executed in the above described
trials, ATM and TCP/IP over ATM performance in multi-segment
application can be evaluated. Moreover both subjective and
objective QoS evaluation can be derived.
As far as the DECT system is concerned the TCP Throughput
measurements executed on the DECT access show that the actual
rate available at TCP level is about 15 Kbps for single
slot DECT available in the demonstrator.
This is likely to be enough for signalling and control in
the frame of Multi-access Multi-media network. Anyway limitation
to single slot DECT was only for the demonstrator and the rate
can be easily increased using Multi-slot DECT in the Target
System. The available throughput over DECT is always quite
good even with the terminal in motion. There can be anyway
drop in the throughput and this implies that it has to foresee
buffering and re-transmission in the data or signalling
application to cope with instantaneous gaps in the throughput,
and it has to limit the actual speed of the mobile.
The second issue is likely not to be a problem in the actual
context of complementary terrestrial satellite coverage that
is near building. Also the use of multi-slots could significantly
improve the behaviour of DECT. Moreover the throughput of the
DECT despite being low has a high availability also where no
Line of Sight is present, this suggests the use of DECT as
preferred application control channel in the design of
multi-segment/multi-access specific applications.
As far as the SECOMS system is concerned the data gathered
and processed show that the delay is a significant issue
for satellite since it is higher than terrestrial links.
The Round Trip Delay is not dependent on either the terminal
position or the ICMP packet size, it is a constant delay of
510-530 ms. This implies that ATM transport does not affect
the delay figures.
Also the same is for IP if we do not exceed the MTU size
(here MTU size at IP level was 1500 bytes). Anyway the effect of
IP fragmentation on Round Trip Delay is not very impressive
(consider also that the path is run two times). As a hint on
Target Network signalling this means that the signalling message
used on satellite will suffer significant delay (impact on
signalling state machine timers). The effect of satellite link
delay actually sums up for each fragment but is not dramatic
(that is ~ 10 msec over 520 msec that is 2%). It is estimated
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that also fragmentation in 2 or 3 fragment can be supported
(packet size exceeding 2 times the MTU size).
The ATM level measurements executed for the SECOMS access
segment show that the CTD parameter is 252 ms, the CDV is
0.584 ms, the CLR is 2.41E-7, the CER is 1.3E-6.
The measurements on SAMBA were targeted to have information
for the case in which a complete access network inclusive of its
own ATM switch interfaces with a Global Core Network supporting
multi-segment mobility. The above allowed to study the impact
of multi access radio when more than a network and operator
is involved. This pointed out that problems can arise in ATM
buffer management (ATM switches owned by different players).
In turn this indicated that high level protocols need to have
packet handling as TCP while datagram protocols as UDP do not
behave well unless a fine tuning of all the resources on
the transmission path is performed.
As for round trip delay the executed measurement clearly
show that for the SAMBA access segment the mobile terminal
position and the ICMP packet size have significant impact on
round trip delay.
The SAMBA round trip delay figures are all not exceeding
250 ms (half of the average on SECOMS access); this implies
that the delay impairment at SECOMS/SAMBA radio access change
is foreseen to be a major requirement to be handled in design
of both multi-segment/multi-access application as well as in
design of target network signalling. The TCP throughput of
SAMBA is good whenever good coverage is provided.
The measurements show that the actual value for TCP throughput
is 5 Mbps nevertheless when the radio condition worsened the
actual average TCP throughput figure dropped to 2 Mbps.
The ATM level measurements executed for the SAMBA access
segment show that the CTD parameter is 1.1 ms, the CDV is
1.37 ms, the CLR is 1.32E-4, the CER is 1.95E-4.
As far as the MEDIAN system is concerned the TCP Throughput
measurements executed on the MEDIAN/EXODUS test configuration
show that the actual rate available at TCP level is about 30
Mbps in downlink and 14 Mbps in uplink direction respectively.
The ATM level measurements executed for the MEDIAN access
segment show that the CTD parameter is 1.4 ms, the CDV is
1.7 ms, the CLR is 7.4E-6 and it includes also the errored
cells.
>From the obtained results of the ATM level measurements
executed for broadband satellite, W-LAN and cellular W-ATM
access segments, it can be deduced that the network
performances guaranteed by the satellite SECOMS
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and W-LAN MEDIAN access segments are compliant with the
ITU-T network performance objectives defining the
QoS class 1 and class 2. This implies that a network
configuration for portable services obtained complementing
the broadband satellite with the W-LAN segment, can
support, on both access networks, services requiring QoS
class 1 and 2. Service mobility between open and indoor
environment is therefore assured.
On the contrary SAMBA access segment performances are not
compliant with the QoS class 1 and class 2 recommended
figures. This implies that service mobility in a network
configuration for mobile services based on the broadband
satellite and cellular W-ATM segment, is not guaranteed.
A possible reason of this situation can be found in the
still prototypal nature of the SAMBA demonstrator and in the
hostile atmospheric conditions at the moment of measurements.
The above described ACCORD trial execution and the relevant
obtained results along with the ACCORD Target Network design
represent a first step toward the definition
and the implementation of an advanced network supporting
mobile IP QoS sensitive services.
The ACCORD project results will be further expanded in the
framework of the IST SUITED project which aims at developing
and demonstrating an Internet based multi-segment (satellite/
terrestrial) network for business class and mobile services.
10 References
[1] Gianfranco Ferrari, Lino Moretti, Paolo Conforto,
Vincenzo Schena, Stefan Wolters, Steve Pitchers,
Eliseu Macedo, Manuel Dinis, Nikolas Georgantas,
"Trial Strategy Description", CEC Deliverable Number
AC348-IT-ITL-DS-DS-R-031.
[2] AC348 ACCORD Annual Project Review Report
(Parts A1 and A2), November 1999.
[3] ITU-T Recommendation series I.350, "B-ISDN ATM layer
cell transfer performance".
[4] M. Laubach, "Classical IP and ARP over ATM",
RFC 1577, Hewlett-Packard Laboratories, January 1994.
[5] J. Heinanen, "Multiprotocol Encapsulation over ATM
Adaptation Layer 5", RFC 1483, Telecom Finland,
July 1993.
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11 Contact
Clementina Tocci
Alenia Spazio
Via G. V. Bona, 85
00156 - Roma
Phone: +39/06/ 4151-275
Fax: +39/06/ 4151-297
E-mail: c.tocci@rmmail.alespazio.it
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