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The SpaceWire Internet Tunneland the Advantages It Provides

For Spacecraft Integration

Stuart Mills, Steve ParkesSpace Technology Centre

University of Dundee

Raffaele VitulliESA, ESTEC

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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

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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

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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

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The SpaceWire Internet Tunnel

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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

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Example Network with Two Sub-Systems

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Mass Memory Unit

Processor

Router

Camera Instrument 1

Camera Instrument 2

Router

SpaceWire Sub-System 1

SpaceWire Sub-System 2

Example Network with Tunnel

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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

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SpaceWire Internet Tunnel Hardware

Connects to a PC using USB Provides two SpaceWire links

– Can create two Tunnels per device

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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

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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

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SpaceWire Internet Tunnel Software

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Technical Difficulties andOvercoming Them

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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

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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

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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

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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…

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The SpaceWire InternetTunnel Server

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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

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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

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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

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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

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The TopNet Pilot Study

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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

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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

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Advantages of the Tunnel

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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

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Potential Limitations of Virtual Spacecraft Integration

Potential limitations identified earlier:– Bandwidth and latency restrictions of the Internet– Security concerns– Connection establishment problems

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Advantages of the SpaceWire Tunnel

Provides all the benefits of virtual spacecraft integration

Addresses most of the limitations

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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

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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

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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

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Summary and Conclusions

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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

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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

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