Re: [RFC net-next v3 00/10] net: bridge: mrp: Add support for Media Redundancy Protocol (MRP)

[JÃrgen Lambrecht]

On 1/25/20 10:18 PM, Vinicius Costa Gomes wrote:
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>
> Hi,
>
> "Allan W. Nielsen" <allan.nielsen@xxxxxxxxxxxxx> writes:
>
>> Hi Vinicius,
>>
>> On 24.01.2020 13:05, Vinicius Costa Gomes wrote:
>>> I have one idea and one question.
>> Let me answer the question before dicussing the idea.
>>
>>> The question that I have is: what's the relation of IEC 62439-2 to IEEE
>>> 802.1CB?
>> HSR and 802.1CB (often called FRER - Frame Replication and Elimination
>> for Reliability) shares a lot of functionallity. It is a while since I
>> read the 802.1CB standard, and I have only skimmed the HSR standard, but
>> as far as I understand 802.1CB is a super set of HSR. Also, I have not
>> studdied the HSR implementation.
>> Both HSR and 802.1CB replicate the frame and eliminate the additional
>> copies. If just 1 of the replicated fraems arrives, then higher layer
>> applications will not see any traffic lose.
>>
>> MRP is different, it is a ring protocol, much more like ERPS defined in
>> G.8032 by ITU. Also, MRP only make sense in switches, it does not make
>> sense in a host (like HSR does).
>>
>> [snip MPR explanation]
>>
>> Sorry for the long explanation, but it is important to understand this
>> when discussion the design.
> Not at all, thanks a lot. Now it's clear to me that MRP and 802.1CB are
> really different beasts, with different use cases/limitations:
>
>  - MRP: now that we have a ring, let's break the loop, and use the
>    redudancy provided by the ring to detect the problem and "repair" the
>    network if something bad happens;
indeed. MRP is IEC 62439-2
>
>  - 802.1CB: now that we have a ring, let's send packets through
>    two different paths, and find a way to discard duplicated ones, so
>    even if something bad happens the packet will reach its destination;

Not exactly, 802.1CB is independent of the network layout, according to the abstract on https://ieeexplore.ieee.org/document/8091139.

The IEC 62439-3 standard mentions 2 network layouts: 2 parallel paths and a ring:

- IEC 62439-3.4 Parallel Redundancy Protocol (PRP): this runs on 2 separated parallel paths in the network

- IEC 62439-3.5 HSR (High availability seamless redundancy): this runs on a ring: each host sends all data in 2 directions, and when it receives its own data back, it discards it (to avoid a loop).

(and it is better to implement IEEE, because the standard costs only 151$, and the IEC ones cost 2x410$)

Kind regards,

Jürgen