tcpdump mailing list archives
Speed specific Link-Layer Header Types for USB 2.0
From: Tomasz Moń via tcpdump-workers <tcpdump-workers () lists tcpdump org>
Date: Sun, 08 May 2022 13:48:20 +0200
--- Begin Message --- From: Tomasz Moń <desowin () gmail com>
Date: Sun, 08 May 2022 13:48:20 +0200
Hello, Back in 2019 I have requested Link-Layer Header Type for USB 2.0 [1]. Unfortunately, I didn't foresee the problems with dissecting packets at effectively "unknown" capture speed. That is, while the host, device and capture tool were all aware about the speed, the resulting pcap misses that information. For the most part speed does not really matter. It is the corner cases, and especially device and/or host misbehaviour where the speed matters. See [2] for example capture where the capture speed information would be useful. Differences between speeds include atleast (list is incomplete): * SPLIT transactions are only allowed at High Speed * Bulk endpoint wMaxPacketSize maximum value is 64 at Full Speed and 512 at High Speed (Bulk is not allowed at Low Speed) * SOF is send every 1 ms at Full Speed and every 125 us at High Speed (SOF is not send at Low Speed) * SOF is not send at Low Speed * Isochronous endpoint wMaxPacketSize maximum value is 1023 at Full Speed and 1024 at High Speed (Isochronous is not allowed at Low Speed) For existing LINKTYPE_USB_2_0 captures the analysis programs can ask the user to specify the capture speed but that is annoyance as the speed would have to be provided on per-capture basis. I would like to remedy the situation by requesting additional speed specific link layer header types, for example: * LINKTYPE_USB_2_0_LOW_SPEED * LINKTYPE_USB_2_0_FULL_SPEED * LINKTYPE_USB_2_0_HIGH_SPEED The description for existing LINKTYPE_USB_2_0 could be updated to mention that for new captures, the speed specific link layer header types should be used to enable better dissection. Best Regards, Tomasz Moń [1] https://www.mail-archive.com/tcpdump-workers () lists tcpdump org/msg08785.html [2] https://gitlab.com/wireshark/wireshark/-/issues/18062
--- End Message ---
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- Speed specific Link-Layer Header Types for USB 2.0 Tomasz Moń via tcpdump-workers (May 08)
- Re: Speed specific Link-Layer Header Types for USB 2.0 Guy Harris via tcpdump-workers (May 08)
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- Re: Speed specific Link-Layer Header Types for USB 2.0 Guy Harris via tcpdump-workers (May 08)
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- Re: Speed specific Link-Layer Header Types for USB 2.0 Tomasz Moń via tcpdump-workers (May 08)
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- Re: Speed specific Link-Layer Header Types for USB 2.0 Tomasz Moń via tcpdump-workers (May 09)
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- Re: Speed specific Link-Layer Header Types for USB 2.0 Tomasz Moń via tcpdump-workers (May 09)
- Re: Speed specific Link-Layer Header Types for USB 2.0 Guy Harris via tcpdump-workers (May 08)
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- Re: Speed specific Link-Layer Header Types for USB 2.0 Guy Harris via tcpdump-workers (May 09)
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- Re: Speed specific Link-Layer Header Types for USB 2.0 Tomasz Moń via tcpdump-workers (May 09)
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- Re: Speed specific Link-Layer Header Types for USB 2.0 Guy Harris via tcpdump-workers (May 09)
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- Re: Speed specific Link-Layer Header Types for USB 2.0 Tomasz Moń via tcpdump-workers (May 09)
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- Re: Speed specific Link-Layer Header Types for USB 2.0 Guy Harris via tcpdump-workers (May 09)