Re: [Discuss-gnuradio] raw USRP2 interface vs the UHD interface

[Josh Blum]

On 10/10/2010 01:07 AM, Steve Mcmahon wrote:
> Hello:
>
> I want to make sure I understand the raw USRP2 interface and the new
> UHD interface correctly. I have USRP2, and I'm running GNU Radio
> 3.3.0 under Linux (Fedora 13), and if I use the default USRP2
> interface, it uses raw Ethernet (no UDP or TCP) by means of raw
> sockets, and there is no transport layer protocol used. But now there
> is a new UHD driver deing developed for USRP2. It uses UDP as the
> transport layer protocol. This means that the USRP2 will need to have
> an IP address and subnet mask, unlike before. What are the advantages

Talking over UDP is easily cross platform, unlike a raw ethernet 
interface. The raw ethernet interface for usrp2 in gnuradio was linux 
specific. Other unixs and windows were left out.

> to doing this?? Won't this reduce the bandwidth somewhat over raw

Yes, here is the break down of overheads on-top of the ethernet header:

- UHD overhead per packet: IP + UDP + VRT = 52 bytes
- Gnuradio raw-eth overhead: trans + fixed = 14 bytes

In the UHD implementation, thats 38 bytes more overhead per packet, 
which means an extra packet is needed for every (1500-52)/38 = 38.1 
packets (not exact).

In addition, the UHD driver adds inline and asynchronous message 
packets, further increasing the overhead.

> Ethernet, since UDP adds some overhead?? What is the motivation for

Cross platform support, and common API for all USRP devices that fully 
covers their functionalities.

> creating the UHD driver?? What's wrong or inadequate with the current

lacking functionality and completeness
tied to linux and other setup issues with raw ethernet
different firmwares for different daughter cards

-Josh

> raw Ethernet interface?? Any explanation and help in understanding is
> appreciated. Thanks.

http://en.wikipedia.org/wiki/Punctuation_%28chess%29#.3F.3F:_Blunder

> Steve McMahon
>
>
>
>
>
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