Dear all,
I have a question (or actually a discussion) about networking, which we use to apply in a multi-channels experiment.
I am working on SpaceWire technology for a network with 62 detection channels. However, I also wonder: why people have to think about SpaceWire networking? Why not just use the traditional TCP/IP networking?
Some times, I think maybe SpaceWire is developed by FPGA technology, so it is more easy to change the function of the SpaceWire hardware just by programming. But is it true? If it's true, how about TCP/IP network? Can we make a TCP/IP network based on FPGA technology?
Thanks for spending your time on this discussion. This discussion is really helpful to a dummy as me.
Sincerely yours.
->SpaceWire is easy to implement and very well suited to the construction of highly fault-tolerant networks and systems.
->Ethernet offers a rich set of tried-and-tested protocols – and software.
->Ethernet and SpaceWire deliver largely similar low-level services – except multicast and broadcast
->Ethernet addressing has to be converted to (similar) SpaceWire addressing
I am allowing my self with Vishal sir
for sure transmission no one is better then ethernet
The software requirements described here can easily be implemented in a SpaceWire device driver which appears, to the operating system, to be a standard Ethernet driver
so if u ignore the complication of ethernet then you can say better over spacewire .
both are as a prons at there own requirment.
Spacewire defines the physical connections and transmission, but is not terribly well defined for protocols and higher level communication. TCP/IP is a networking protocol that rides on top of other lower-level protocols such as the 802.3 or MAC layer. Spacewire is more well defined at the equivalent MAC layer, but does not necessarily have higher level protocols like TCP/IP. In fact, you could probably embed TCP/IP in spacewire packets, if you wanted to and not know that you were using SpaceWire as the under lying medium.
SpaceWire does not need to be implemented in FPGAs, you can purchase hard IP from a small number of vendors. It is a little easier to obtain FPGAs and implement it this way. In either the case of TCP/IP or higher-level protocols on top of SpaceWire, you will likely need a soft-processor of some kind to handle the protocol implementation. Simple Spacewire protocols like RMAP can be implemented in FPGAs, but higher-level protocols with features like TCP/IP (reliable transmission, windowing, etc.) will need a processor to ensure packets get transmitted.
Normally, TCP/IP runs on something like gigabit ethernet or a similar medium. Nothing about the hardware guarantees that you will be able to transmit data. In fact, if the network becomes too busy, typically more than 30% of the overall bandwidth, transmission will start to fail. Spacewire requires that every link point in the system guarantee that there will be space to transmit before a transmission starts. In this way, it could be slightly more reliable than gigabit ethernet. However, there is nothing in Spacewire that says a given connection must give up transmitting. So, although two connections, once setup, will have bandwidth. These two connections can starve the network if there was only a single path between two parts of the network.
I've developed network drivers for some of our SpaceWire products in the past. The STAR-Dundee Brick and Router/Router Mk2 can be used on TCP/IP networks under Linux. Very good for multiplayer gaming over SpaceWire :-) There's no standard for transporting TCP/IP over SpaceWire, though, or for address resolution (SpaceWire to/from IP address), so our implementation probably won't work with other implementations.
Note that in the above case SpaceWire and Ethernet are being used in the same way. The TCP/IP protocols are network and transport protocols running over these two physical layers. SpaceWire provides a number of features which means it's not necessary to use additional protocols on top of SpaceWire, but that doesn't mean they can't still be used.
TCP/IP is very heavyweight for use onboard a spacecraft. Networks on spacecraft tend to be reasonably small, using only one or two bus types, and encounter very few errors. TCP/IP is designed to transport data between multiple networks, of different types, and with the possibility for packets to be lost, delivered out of sequence, or delivered with errors. The minimum header size of a TCP/IP packet is 40 bytes, which is quite an overhead if you're sending small amounts of data, for example.
Dear all,
Thanks for comment above.
Is there anyone use the SpaceWire/RMAP library of Prof. Yuasa? (https://galaxy.astro.isas.jaxa.jp/~yuasa/SpaceWire/)
Now, I want to try the multi-thread for reading data from RMAP memory to PC. But I don't know how to use ....
Thanks for your suggestion.
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