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11
The SpaceWire Internet Tunneland the Advantages It Provides
For Spacecraft Integration
Stuart Mills, Steve ParkesSpace Technology Centre
University of Dundee
Raffaele VitulliESA, ESTEC
22
Introduction
Spacecraft Integration The SpaceWire Internet Tunnel Technical Difficulties and Overcoming Them The SpaceWire Internet Tunnel Server The TopNet Pilot Study Advantages of the Tunnel Summary and Conclusions
Spacecraft Integration
33
Normal Integration Procedures
Integration Testing performed late in development process– Problems expensive to correct
Problem of geographical separation Importance of interface specifications Advantages of standard interfaces
– SpaceWire
Problems still possible at higher layers– Application level
44
Virtual Spacecraft Integration
Remote sub-systems connected using the Internet
Integration testing can be performed without bringing components to one physical location
Reduces travel Problems can be identified in interface
specifications and implementations Integration can be performed earlier in the
development process
55
The SpaceWire Internet Tunnel
66
SpaceWire Internet Tunnel
Developed by the University of Dundee under ESA contract
Now a commercial product available from STAR-Dundee
A Tunnel replaces a SpaceWire link with a connection over a network– Such as the Internet
Hardware and software solution Protocol Analysis software also provided
– Monitor the Tunnelled traffic
77
Example Network with Two Sub-Systems
88
Mass Memory Unit
Processor
Router
Camera Instrument 1
Camera Instrument 2
Router
SpaceWire Sub-System 1
SpaceWire Sub-System 2
Example Network with Tunnel
99
Internet
Mass Memory Unit
Processor
Router
Camera Instrument 1
Camera Instrument 2
Router
SpaceWire Sub-System 1
SpaceWire Sub-System 2
SpaceWireIP-Tunnel
PC running SpaceWireIP Tunnel Software
SpaceWireIP-Tunnel
PC running SpaceWireIP Tunnel Software
SpaceWire Internet Tunnel
Transparently replaces a SpaceWire link Traffic entering the Tunnel will exit in the
same order– A time-code will be between the same two data characters
Link start and disconnect are also represented
Only difference is in bandwidth and latency– Limitations of Internet
1010
SpaceWire Internet Tunnel Hardware
Connects to a PC using USB Provides two SpaceWire links
– Can create two Tunnels per device
1111
SpaceWire Internet Tunnel Software
Runs on Windows and Linux– Java software so doesn’t need recompiled for each platform– Dependant on hardware drivers
Secure connection used to ensure traffic cannot be viewed or modified– A password can also be specified for each Tunnel
Mechanisms provided to cope with bandwidth and latency limitations of the Internet– To avoid timeouts at routers
1212
SpaceWire Protocol Analyser Software
Protocol Analysis software built in to the SpaceWire Tunnel Software
Allows traffic crossing the Tunnel to be monitored and recorded
Traffic statistics can be viewed in real time Higher Layer Protocol Plug-Ins can be added
– Allows the properties of any protocol to be monitored and recorded
– RMAP packets or an application specific protocol– Can be written by users– Loaded at run-time
1313
SpaceWire Internet Tunnel Software
1414
Technical Difficulties andOvercoming Them
1515
Potential Limitations Identified
Issues relating to bandwidth and latency restrictions of the Internet
Security concerns related to sending data across the Internet
Problems establishing connections over the Internet
1616
Bandwidth and Latency Restrictions
Gaps in packets can cause SpaceWire routers to timeout
Mechanisms provided in Tunnel to avoid these timeouts– Present in both the Tunnel entrance and exit
Still some systems where a Tunnel is not appropriate– Packets expected within a restricted time period– High bandwidth
1717
Security Concerns
All traffic sent using Transport Layer Security (TLS)– Same mechanism used by secure websites– All traffic encrypted– Cannot be viewed or modified
Password used to ensure the other end is who they claim to be– Also sent encrypted using TLS
1818
Problems Establishing Connections
Proxy server issues Firewall restrictions Client-server limitations
– Firewall restrictions need to be relaxed at the server side of a Tunnel connection
Support for proxy servers added to software Software allows any TCP port to be used
– Using the port assigned for TLS web traffic can get Tunnel traffic through intelligent firewalls
Tunnel Server Software developed…
1919
The SpaceWire InternetTunnel Server
2020
SpaceWire Tunnel Server
Internet communication uses a client-server model
This requires one end to act as a server– Normally requires special firewall permissions– Many organisations will not allow this
Some users can only act as the client in a Tunnel connection– Can only connect to users in organisations which have the
necessary firewall permissions to act as the server
2121
SpaceWire Tunnel Server
Allows two PCs running the SpaceWire Internet Tunnel Software to connect
Neither PC must act as a server– Both are clients
Routes data from one client to the other Avoids firewall restrictions
– Any PC can operate as a client– Only the Tunnel Server PC has to have special firewall
permissions
Makes testing of multiple sub-systems simpler– Users do not have to know the address of each client they
are connecting to, only the server’s address2222
SpaceWire Tunnel Server
Capable of managing multiple client pairs A single Tunnel Server could manage
connections from multiple organisations Alternatively an organisation could run their
own Tunnel Server to manage all their connections
2323
SpaceWire Tunnel Server
Restrictions can be applied to connecting clients based on– IP address– TCP port– Password
Uses same secure connections as SpaceWire Tunnel Software (TLS)
Completely transparent to the clients running the Tunnel Software– Has no effect on the mechanisms used to cope with
bandwidth and latency restrictions
2424
SpaceWire Tunnel Server Software
Runs on all platforms which support Java– Java software so doesn’t need recompiled for each platform– Doesn’t use any hardware, so not dependant on hardware
drivers
Distributed with the Tunnel software and hardware
2525
The TopNet Pilot Study
2626
TopNet Pilot Study
ESA pilot study to investigate benefits and limitations of virtual spacecraft integration and the SpaceWire Internet Tunnel
A number of organisations in several countries involved
Performed experiments, integrated components virtually using the Tunnel
Reported back on their results and experiences
2727
TopNet Pilot Study
Summary of findings:– Virtual spacecraft integration and the SpaceWire Internet
Tunnel can be very useful for integration testing– Still improvements that can be made
Feedback from pilot contractors has lead to improvements to the Tunnel software and hardware– Some improvements made during study– Others have been made following final presentations
2828
Advantages of the Tunnel
2929
Advantages of Virtual Spacecraft Integration
Earlier integration– Identify and correct problems earlier– Saves time and money as easier to correct problems
identified at an earlier stage
Less travel– With associated financial and environmental savings
Improved flexibility– Integration testing can be performed at any time– Sub-systems can easily be replaced by simulations
Improved cooperation– Allows multiple organisations (or a single organisation with
multiple sites) to work on the same system
3030
Potential Limitations of Virtual Spacecraft Integration
Potential limitations identified earlier:– Bandwidth and latency restrictions of the Internet– Security concerns– Connection establishment problems
3131
Advantages of the SpaceWire Tunnel
Provides all the benefits of virtual spacecraft integration
Addresses most of the limitations
3232
Features of the SpaceWire Tunnel
Bandwidth and Latency Restrictions– Software provides mechanisms to cope with poorer and
varying bandwidth and latency– But still some SpaceWire systems where the Tunnel is not
suitable E.g. a camera which expects to continually send images
at a high rate and expects the SpaceWire link to never be blocked
– Pilot users found that it was often possible to perform limited integration testing for such systems
– Some suggested the addition of specific software and hardware modes to a system under test to allow virtual integration testing E.g. with relaxed timing requirements
3333
Features of the SpaceWire Tunnel
Security– All traffic sent over a Tunnel is encrypted using TLS/SSL– A password for the Tunnel can be specified– A password can also be specified for the Tunnel Server
Connection Establishment Issues– Software allows any TCP port to be used
Using an appropriate port, a firewall will see the traffic as no different to a secure web page
– Use of a Tunnel Server avoids the client-server limitations on the end users
3434
Features of the SpaceWire Tunnel
Other issues from the Pilot Study– Many improvements suggested to the Protocol Analysis
software Highlighted the importance of analysis tools when
performing integration testing
Additional advantages identified– Virtual integration testing can take a fraction of the time of
full integration testing– Not necessary to transport EGSE to an integration site– Some users now use the Protocol Analyser software to
monitor SpaceWire traffic Without actually Tunnelling
3535
Summary and Conclusions
3636
Summary and Conclusions
Tunnel has been successfully demonstrated across Europe
The benefits of virtual spacecraft integration and the SpaceWire Internet Tunnel are clear
Recent improvements to the SpaceWire Tunnel and the addition of the SpaceWire Tunnel Server increase these benefits
Feedback from Pilot activity– Validated concept and implementation– Allowed improvements to be made
3737
Summary and Conclusions
TopNet Pilot Study has shown that virtual spacecraft integration can be used in real projects
Although physical integration testing is still essential, virtual integration testing can be an important and beneficial stage in future projects
3838