AeroMACS VoIP Characteristics
International Civil Aviation Organization
August 29, 2014
ACP-WG-S/Web Meeting 6
IP-02
29/8/2014
WORKING PAPER
AERONAUTICAL COMMUNICATIONS PANEL (ACP)
Sixth Web Meeting of the Surface Datalink Working Group WG-S
Web Meeting
Agenda Item XX:
AeroMACS VoIP Validation
Prepared and presented by Bruce Eckstein
SUMMARY
AeroMACS SARPs recommend that implementations support Voice
applications but do not contain specific requirements for the RF link to support
Voice. This paper notes AeroMACS capabilities with respect to Voice
implementation; it is not intended to present or validate requirements. This
paper contains proposed material for inclusion in the validation report that
supports using VoIP over AeroMACS. The paper reiterates prior testing
results of data packet performance characteristics obtained at NASA-Exelis
Cleveland AeroMACS test bed located at the Cleveland Hopkins Airport.
ACTION
The AeroMACS Working Group is invited to consider the information for
inclusion in the AeroMACS Validation Report.
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Contents
1.
INTRODUCTION: AEROMACS VOIP DATA PACKET TESTING ................................................. 3
2.
SEGREGATION OF DIFFERENT SERVICES IN CLE TEST BED .................................................. 4
2.1. Service Prioritization – Capability Area #1 .............................................................................................. 6
2.2. Segment Differentiation – Capability Area #2 ......................................................................................... 7
2.3. Mixed Traffic Types – Capability Area #3 ................................................................................................ 9
2.4. Preemption of Services – Capability Area #4 ........................................................................................ 10
List of Tables
Table 1. AeroMACS QoS Properties ........................................................................................................................ 5
Table 2. CLE Test Descriptions ................................................................................................................................ 5
Table 3. CLE Service Prioritization Tests ................................................................................................................. 7
Table 4. CLE Segment Differentiation Tests ............................................................................................................ 8
Table 5. CLE Mixed Traffic Type Tests ................................................................................................................. 10
Table 6. Preemption of Services Test Summary ..................................................................................................... 12
List of Figures
Figure 1 CLE Test Configuration .............................................................................................................................. 5
Figure 2. VLAN Data Segregation Test .................................................................................................................... 9
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1. INTRODUCTION: AEROMACS VOIP DATA PACKET TESTING
The AeroMACS SARPs recommends providing voice services for the aeronautical community. The voice
services that AeroMACS provides would be the transport of Voice over Internet Protocol (VoIP) data packets.
VoIP encoding and decoding is performed via processes outside of the AeroMACS standard and the resulting data
from the VoIP encoded packets would be provided to the AeroMACS for transfer to the VoIP application for
processing. VoIP data packets could be for transfer from one Mobile Station (MS) to another MS within the
AeroMACS system or an AeroMACS MS with a ground network connected VoIP subscriber station. The
AeroMACS standards recommendation for voice does not identify any specific performance requirements for
AeroMACS to meet. International Civil Aviation Organization (ICAO) has not developed any VoIP standards for
Air/Ground Communications and the ICAO VoIP standards for Ground/Ground do not indicate performance
requirements such as latency or dropped packet requirements typically important to VoIP systems and applicable
as AeroMACS allocated requirements. Voice quality is mainly a function of external systems processing of data
packets and as a result latency, dropped data packets and integrity of packet information are the important
parameters for AeroMACS. As such, the information presented in this paper for data packet performance reflects
AeroMACS characteristics for support of VoIP data packet transfer.
AeroMACS provides Quality of Service (QoS) capability for the transfer of data packets. Proper configuration of
QoS in AeroMACS is needed to minimize the key characteristics of data packet latency (including data packet
jitter) and dropped packets associated with VoIP. The tests that were performed were specifically to show the
separation of data streams with different priorities. This information is also applicable to VoIP as the results show
the characteristics associated with data packet transfer.
The tests were performed between AeroMACS MS and Base Stations (BS) on the surface of Cleveland Airport
and identified the packet jitter (which includes the latency of the data packets in these test) and dropped packets
response of the system. The prototype system did not have full mobility management implemented and therefore
tests of these parameters during MS handoff from BS to BS handoff did not occur.
Testing was performed using VLANs (an optional capability within the AeroMACS standards) to support
quantification of data transfer characteristics of an AeroMACS system between a BS and MS. To provide voice
data packet performance separation from other types of data packet transfer to a single MS, either Internet
Protocol Convergence Sublayer (ip.cs) or Ethernet Convergence Sublayer (eth.cs) can perform this function to
support VoIP within AeroMACS. Implementation and configuration of IP Differentiated Services Code Point
(DSCP) within the network may be required for use with ip.cs configurations of AeroMACS. The tests identify
the segregation of data packet characteristics by use of the notation of Air Traffic Control (ATC), Airline
Operational Control (AOC), and Logistics Control Traffic. The tests showed that the appropriate selection of QoS
services achieved low jitter and low loss of data packets when the total demand on the channel did not exceed the
capacity of the 5 MHz channel bandwidth (approximately 8 Mbit per second) at the Cleveland Airport
installation. The tests also showed data packets at one QoS service performance could be protected at the expense
of data packets transferred at a lower QoS service when the capacity of the link was exceeded. These tests indicate
the ability of the AeroMACS to provide the VoIP data packets with a quality of delivery for use by a VoIP
application assuming proper configuration of the QoS system. The tests did not explore MS to MS characteristics
(which would be through the BS) or MS to BS to different BS to MS as might be a typical airport surface VoIP
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operation. The following sections from the Exelis report SE2020 TO 0008 (TORP 1240) Task 3.1 describe the
applicable tests and results.
2. SEGREGATION OF DIFFERENT SERVICES IN CLE TEST BED
The ability for AeroMACS to segregate and prioritize traffic was evaluated using the Cleveland prototype
network in a series of tests. The tests evaluated the following capability areas:
1) Service Prioritization - control scheduling and network priority for traffic from multiple services
2) Segment Differentiation - segregate and maintain traffic segregation from multiple operational segments
like ATC and AOC operations
3) Mixed Traffic Types – simultaneous handling of multiple traffic types (continuous, burst, time-critical)
using the UDP and TCP protocols
4) Preemption of Services – use of QoS and network priority settings to assure that low priority traffic (Best
Effort) will be sacrificed to assure on-time delivery of higher-priority traffic in congested network
conditions
The AeroMACS prototype network built at the NASA Glenn campus and the Cleveland Hopkins airport (CLE) is
a full data network containing two base stations and eight fixed-site subscriber stations. The prototype network
uses IEEE802.16e based system components. Central servers for CSN functions contain a secure network router,
Network Management System (NMS) and Authentication, Authorization, and Accounting (AAA) functions.
Traffic segregation tests used a base station and two subscriber stations as illustrated in Figure 1. The
AeroMACS network was configured to operate with three VLANS to evaluate a method for traffic isolation.
Each VLAN was assigned a segment of traffic to represent ATC, AOC, and Control traffic as follows:

ATC traffic assigned to VLAN 90

AOC traffic assigned to VLAN 80

Logistics control traffic assigned to VLAN 54
The AeroMACS test network configuration and VLAN assignments are illustrated in Figure 1. Three Single
Board Computers (SBC’s) are used to generate test traffic. A SBC located at Building 110 (B110) receives traffic
that represents logistics control. A network switch at the B110 Subscriber Station (SS) is set up for port tagging
the traffic for VLAN 54.
Two SBCs at the Consolidated Maintenance Facility building (CMF) receive test traffic representing ATC and
AOC traffic carried over VLANS 90 (ATC) and 80 (AOC). Traffic in the three VLANS pass through Aircraft
and Firefighter’s building (ARFF) BS sector 2-3.
Network switches at the SSs and in B110 are configured for port tagging to establish traffic routing in the three
VLANS. With this configuration, two VLANS (90 and 80) are carried simultaneously over the CMF-to-BS air
link, and the ARFF BS sector 2-1 carries traffic from three VLANS simultaneously.
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The AeroMACS prototype network is set to operate as Layer 2 (Ethernet IP) for these tests because VLANS are
Layer 2 constructs. Operating as Layer 2 implements the Ethernet Convergence Sublayer (eth.cs) in the
AeroMACS radio Media Access Control (MAC) layer.
VLAN 54
(Logistics)
Switch
SBC for
Logistics Traffic
test end point
B110 SS
• 3 VLANS
• 3 QoS
• 2 Traffic
types
VLAN 54
(Logistics)
• Represents
Port Authority
iPerf Client
for ATC
data flow
VLAN 90
(ATC)
VLAN 90
(ATC)
Switch
SBC for AOC
traffic test
endpoint
Switch
Secure
Router
BTS 2-3
(ARFF)
SBC for ATC
traffic test
endpoint
iPerf Client
for Logistics
Data Flow
VLAN 80
(AOC)
CMF SS
Backhaul
• Represents
Aircraft
VLAN 80
(AOC)
AeroMACS
Air Links
iPerf Client
for AOC
data flow
Figure 1 CLE Test Configuration
In addition to the establishment of VLANS, three service flows were established within the AeroMACS service to
establish QoS and priority settings for the simulated traffic from ATC, AOC, and Logistics services. These
settings are summarized in Table 1.
Table 1. AeroMACS QoS Properties
Traffic
Service
VLAN
Channel
Assigned QoS
ATC
90
nrtPS
Assigned
Network
Bandwidth
6-54 Mbps
AOC
Logistics
80
54
nrtPS
BE
1.5-7 Mbps
0-1 Mbps
The network tests listed in Table 2 were performed to evaluate the four listed traffic segregation and priority
criteria. A purpose and description is provided in the table for each test.
Table 2. CLE Test Descriptions
Purpose
Description
Segment Differentiation
Tests VLAN privacy by placing traffic simulating ATC, AOC, and Control
traffic on VLANS 90, 80, and 54 individually
Mixed Traffic Types
Mixed UDP and ATC protocol traffic types in high-priority ATC and
AOC VLANS (90 and 80)
Mixed Traffic Types
Mixed UDP and ATC protocol traffic types in high- and low-priority
ATC and Control VLANS (90 and 54)
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AeroMACS VoIP Characteristics
Purpose
August 29, 2014
Description
Service Prioritization
Mixed Traffic Types
Traffic prioritization in congested network conditions with mixed UDP
and TCP traffic
Service Prioritization
Mixed Traffic Types
Test #4 with high-priority VLANS 90 and 80 differentiated with nrtPS
bandwidth definitions
Preemption of Services
Mixed Traffic Types
Congested network tests with high- and low-priority ATC and Control
VLANS (90 and 54)
Preemption of Services
Mixed Traffic Types
Reference tests for traffic in single VLAN
Preemption of Services
Mixed Traffic Types
Traffic prioritization in congested network conditions with mixed UDP
and TCP traffic using all three VLANS
Preemption of Services
Mixed Traffic Types
Congested network tests with ATC, AOC and Control VLANS (90, 80
and
54) with mixed traffic types
Tests VLAN privacy by placing traffic simulating ATC, AOC, and Control
traffic on VLANS 90, 80, and 54 simultaneously
Segment Differentiation
The above tests were conducted in the four capability areas with the CLE prototype AeroMACS network
configured according to Figure 1. Highlights of test results for each capability area are discussed below.
2.1. Service Prioritization – Capability Area #1
Description: Based on Test 10A, described in Table 3. Three traffic streams were established simultaneously in
three VLANS for the purpose of testing correct service prioritization operation. The aggregate traffic rate of 7
Mbps is below the channel capacity of the service BS sector 2-3. Table 3 lists resulting link performance showing
that high-quality links are supported for all three levels of service prioritization, indicated by low levels of percent
dropped packets, out of order packets, and jitter. The delivered payloads are commensurate with the expected
average traffic rate for the test time period. As expected, higher jitter statistics occurred for low-priority traffic
using QoS of BE on VLAN 54. Overall, the results show proper operation for a BS sector channel operating
below capacity with three concurrent levels of traffic priority and three established VLANs.
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Table 3. CLE Service Prioritization Tests
Test Conditions
Test #
10A
Trial(s)
11
VLAN #
Service
QoS
BW (Mbps)
Protocol (UDP/TCP)
Set Rate (Mbps)
Set Period (S)
54
Ctl
BE
0-1
UDP
0.50
180
80
AOC
nrtPS
1.5-7.0
UDP
2.00
180
90
ATC
nrtPS
6.0-54.0
UDP
3.50
300
Test Results
No. Iterations
Rate Avg.(Mbps)
Period Avg.(S)
Out of Order Pkts.
Pkts. Sent
Dropped Pkts.
% Dropped
Jitter (mS)
Payload (Mbytes)
54
80
90
1
0.50
180
0
7655
0
0.00%
2.753
10.700
1
2.00
180
4
30611
8
0.03%
1.624
42.900
1
3.50
300
6
89287
30
0.03%
1.911
125.000
2.2. Segment Differentiation – Capability Area #2
Description: Based on Test #10B, described in Table 4. Three traffic streams were established simultaneously in
three VLANS for the purpose of testing traffic segregation. The test was designed to show that traffic stream
content is visible only within their assigned VLAN. Properties of the test traffic streams are described below and
in Table 4.

Test traffic stream #1 sent through VLAN 90 to represent ATC traffic using UDP protocol at 4.5 Mbps
and QoS of non-real-time poling service (nrtPS).

Test stream #2 sent through VLAN 54 to represent Logistics Control traffic using UDP protocol at 0.5
Mbps and Best Effort (BE) QoS.

Test stream #3 sent through VLAN 80 to represent AOC traffic using UDP protocol at 2 Mbps and nrtPS
QoS
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Table 4. CLE Segment Differentiation Tests
Test Conditions
Test #
10B
Trial(s)
9
VLAN #
Service
QoS
BW (Mbps)
Protocol (UDP/TCP)
Set Rate (Mbps)
Set Period (S)
54
Ctl
BE
0-1
UDP
0.50
180
80
AOC
nrtPS
1.5-7.0
UDP
2.00
180
90
ATC
nrtPS
6.0-54.0
UDP
4.50
300
Test Results
No. Iterations
Rate Avg.(Mbps)
Period Avg.(S)
Out of Order Pkts.
Pkts. Sent
Dropped Pkts.
% Dropped
Jitter (mS)
Payload (Mbytes)
54
80
90
1
0.50
180
0
7654
0
0.00%
5.748
10.700
1
2.00
180
10
30613
22
0.07%
3.468
42.900
1
4.50
300
4
114791
95
0.08%
2.130
161.000
Execution: Traffic flow through the three VLANs identified in Figure 1 was verified. ATC traffic was started
first and set to run for 5 minutes. The AOC and Logistics traffic streams were started at the one-minute mark
after the ATC data started. Both were set to run for 3 minutes. The performance data was recorded.
The next step that verified traffic segregation within a VLAN was completed by establishing traffic through one
VLAN route at a time to verify that this traffic could not be observed outside of the established VLAN
connection. The three Iperf client traffic sources to the right of the secure router in Building 110, shown in Figure
2, were activated one at a time. For each activated VLAN, a laptop computer located in the CMF Building was
sequentially connected to all active switch ports to test for connectivity with the three Iperf Clients in B110.
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AeroMACS VoIP Characteristics
VLAN 54
(Logistics)
Switch
SBC for
Logistics Traffic
test end point
B110 SS
August 29, 2014
• 3 VLANS
• 3 QoS
• 2 Traffic
types
VLAN 54
(Logistics)
• Represents
Port Authority
Secure
Router
Switch
BTS 2-3
(ARFF)
VLAN 90
(ATC)
iPerf Client
for Logistics
Data Flow
iPerf Client
for ATC
data flow
VLAN 54
(Logistics)
Switch
VLAN 90
(ATC)
VLAN 80
(AOC)
VLAN 80
(AOC)
CMF SS
• Represents
Aircraft
Backhaul
AeroMACS
Air Links
iPerf Client
for AOC
data flow
Building 110
CMF Building
Figure 2. VLAN Data Segregation Test
Results: The original test with three VLANS activated with traffic, operated as expected with traffic delivered to
the remote end points through AeroMACS. Correct VLAN operation was verified when each VLAN was
activated individually with traffic and all switch ports in the CMF building were probed. The remote laptop PC
was able to establish a connection and a traffic flow when switch ports of the same VLAN were probed, and no
connection or traffic flow occurred when mismatched VLAN channels were probed.
2.3. Mixed Traffic Types – Capability Area #3
Description: Based on Test #8 described in Table 5. Three traffic streams are established to flow simultaneously
with one stream per VLAN. The established flows are a mixture of QoS and IP protocol. Test results show that
AeroMACS channel capacity and quality of link is maintained when carrying mixed traffic types.
Test #8 uses the following three traffic flows:

Test traffic stream #1 sent through VLAN 90 to represent ATC traffic using UDP protocol at 6 Mbps and
QoS of non-real-time poling service (nrtPS).

Test stream #2 sent through VLAN 54 to represent Logistics Control traffic using TCP protocol and Best
Effort (BE) QoS.

Test stream #3 sent through VLAN 80 to represent AOC traffic using TCP protocol and nrtPS QoS
AOC and Logistics Control traffic are assigned to use TCP protocol. TCP is a guaranteed-delivery protocol so it
will transfer at the fastest rate that it can achieve within the limits set by the services granted. The ATC traffic is
assigned the nrtPS QoS that provides higher-priority scheduling than the BE Logistics Control traffic.
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ATC and AOC traffic are both assigned nrtPS QoS. However, the traffic is differentiated by the committed
bandwidth setting; ATC with 6.0 to 54 Mbps and AOC with 1.5 to 7.0 Mbps bandwidth. Traffic is also
differentiated through use of UDP protocol for ATC and TCP protocol for AOC traffic.
Channel capacity for traffic rate will not be exceeded because the ATC traffic with UDP protocol is assigned a
rate below the expected 8 Mbps channel capacity and the two additional traffic flows are assigned TCP protocol.
Table 5. CLE Mixed Traffic Type Tests
Test #
8
Trial
1,2,3,4,5
VLAN #
Service
QoS
BW (Mbps)
Protocol (UDP/TCP)
Set Rate (Mbps)
Set Period (S)
54
Ctl
BE
0-1
TCP
n/a
180
80
AOC
nrtPS
1.5-7.0
TCP
n/a
180
90
ATC
nrtPS
6.0-54.0
UDP
6.00
300
Test Results
No. Iterations
Rate Avg.(Mbps)
Period Avg.(S)
Out of Order Pkts.
Pkts. Sent
Dropped Pkts.
% Dropped
Jitter (mS)
Payload (Mbytes)
54
80
90
5
0.060
180.36
n/a
n/a
n/a
n/a
n/a
1.32
5
2.07
180.28
n/a
n/a
n/a
n/a
n/a
44.56
5
6
300.00
2
153058.60
67.40
0.04%
1.86
214.60
Total Bandwidt
Test Conditions
8.13
Execution: The ATC test traffic is launched first and is set to run for 5 minutes (300 seconds). AOC traffic is
launched at the 1 minute mark, closely followed within approximately 2 seconds by start of the Logistics Control
traffic, with both set to run for 3 minutes (180 seconds).
Results: High-priority ATC traffic is reliably delivered across AeroMACS while the lower-priority traffic is
adjusted according to the total channel capacity of 8.13 Mbps. ATC traffic is reliably delivered using UDP
protocol in the presence of two simultaneous TCP streams.
2.4. Preemption of Services – Capability Area #4
Description: Based on Test #6 described in Table 6. Test traffic stream #1 is sent through VLAN 90 to represent
ATC traffic using UDP protocol initially at 6 Mbps rate and non-real-time polling service (nrtPS) QoS. Test
stream #2 is sent through VLAN 54, representing Logistics Control traffic, using TCP protocol initially at 1 Mbps
and Best Effort (BE) QoS.
Simultaneous use of UDP and TCP protocols tests the behavior of mixed data types. Test trials with increasing
traffic rates on the VLANS explore the effects of QoS on preemption of services. It is expected that higherpriority ATC traffic, set to nrtPS QoS, will be delivered with priority over Logistics traffic that is assigned BE
QoS.
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Execution: ATC traffic is set to run for 5 minutes (300 seconds) and begins first. The Logistics traffic is set to run
for 3 minutes (180 seconds) and starts 1 minute after ATC traffic starts. Therefore, ATC traffic has no
competition for network resources for the first minute. ATC data continues for the final minute after Logistics
traffic finishes. This test sequence is performed at three traffic rates to test prioritization.
Results: Table 6 summarizes the Preemption of Services test conditions and results. Tests are listed in three
groups as 6A, 6B, and 6C. Test 6A used an aggregate traffic rate below the AeroMACS link capacity, while 6B
and 6C used progressively higher rates in congested network conditions where the test traffic rate exceeds the
AeroMACS link capacity.
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Table 6. Preemption of Services Test Summary
Test #
6A
6B
6C
Test Results
VLAN #
Service
QoS
BW (Mbps)
Protocol (UDP/TCP)
Set Rate (Mbps)
Set Period (S)
54
Ctl
BE
0-1
TCP
n/a
180
80
AOC
nrtPS
1.5-7.0
TCP
n/a
90
ATC
nrtPS
6.0-54.0
UDP
6.00
300
54
80
90
No. Iterations
Rate Avg.(Mbps)
Period Avg.(S)
Out of Order Pkts.
Pkts. Sent
Dropped Pkts.
% Dropped
Jitter (mS)
Payload (Mbytes)
5
0.96
180.86
0
n/a
n/a
n/a
n/a
20.6
0
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
5
6.00
300.00
0
153062
105
0.07%
2.7
214.000
Protocol (UDP/TCP)
Set Rate (Mbps)
Set Period (S)
TCP
n/a
180
TCP
n/a
UDP
8.00
300
No. Iterations
Rate Avg.(Mbps)
Period Avg.(S)
Out of Order Pkts.
Pkts. Sent
Dropped Pkts.
% Dropped
Jitter (mS)
Payload (Mbytes)
5
0.14
184.48
n/a
n/a
n/a
n/a
n/a
3.01
0
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
5
7.99
300.00
2
204080
353.2
0.17%
1.760
286.000
Protocol (UDP/TCP)
Set Rate (Mbps)
Set Period (S)
TCP
n/a
180
TCP
n/a
UDP
10.00
300
No. Iterations
Rate Avg.(Mbps)
Period Avg.(S)
Out of Order Pkts.
Pkts. Sent
Dropped Pkts.
% Dropped
Jitter (mS)
Payload (Mbytes)
5
0.010
202.5
0
n/a
n/a
n/a
n/a
0.33
0
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
Total Bandwidth
Test Conditions
6.96
8.13
5
8.14
8.15
300.00
0
255085.80
47289.00
18.54%
1.87
291.00
Test 6A results: ATC data transferred at an average rate of 6.0 Mbps, matching the set rate for the test. The total
data transfer was 214 Mbytes with a packet loss rate of .07%, which is under the 1% threshold considered to be
the limit for a well-performing UDP channel. Logistics data transferred at an average of .96 Mbps (maximum
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rate was set for 1 Mbps). The total Logistics data transferred was 20.6 Mbytes. These rates and total transfers are
consistent with a channel that is operating below its capacity.
Test 6B results: Tests are repeated with ATC traffic rate increased to 8 Mbps while the Logistics traffic rate
remained at 1 Mbps. ATC traffic at 8 Mbps is near channel capacity by itself. These test trials resulted in ATC
traffic throughput rate increasing to 7.99 Mbps and a total payload transfer of 286 Mbytes. The packet loss rate
increased slightly to 0.17%, which is still an acceptable rate for a UDP link. However, the Logistics traffic with
BE QoS was not able to sustain the 1 Mbps rate; averaging 0.14 Mbps instead. The total payload transfer over the
length of the test was limited to 3 Mbytes. These results clearly show that high-priority ATC traffic was
transferred without impact, while lower-priority Logistics data rate was sacrificed for the ATC traffic.
Test 6C results: Tests are repeated with ATC traffic rate having an additional increase to 10 Mbps which exceeds
the expected AeroMACS channel capacity. The Logistics traffic rate remained 1 Mbps. These test trials resulted
in ATC traffic throughput rate increasing to 8.14 Mbps and a total payload transfer of 291 Mbytes. The achieved
rate of 8.14 Mbps indicates that the intended traffic rate of 10 Mbps exceeds channel capacity and resulted in an
18.5% packet loss rate. In addition, the BE Logistics traffic reduced to 0.010 Mbps average rate and total payload
transfer was reduced to 0.33 Mbytes. These results show that traffic continued to be transferred when highpriority ATC traffic exceeded channel capacity, and that ATC traffic was again given priority over Logistics BE
traffic which was severely restricted.
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