Re: [Detnet-dp-dt] Flow-ID vs. scalability (further thoughts to dinner discussion)

[Lou Berger <[e-mail]>]

Works for me too - which?


On March 29, 2017 11:35:34 AM Jouni Korhonen <[e-mail]> 
wrote:

> Tomorrow 8-9 would be ok?
>
>
> --
> Jouni Korhonen, Broadcom, Core Switching Group
> [phone]
>
>
>
>> On Mar 29, 2017, at 9:33 AM, Jiangyuanlong <[e-mail]> wrote:
>>
>> I am available for both time slots.
>> Cheers,
>> Yuanlong
>>
>> From: Detnet-dp-dt [mailto:[e-mail]] On Behalf Of Lou 
>> Berger
>> Sent: Thursday, March 30, 2017 12:20 AM
>> To: Balázs Varga A; [e-mail]
>> Subject: Re: [Detnet-dp-dt] Flow-ID vs. scalability (further thoughts to 
>> dinner discussion)
>>
>> Great idea.  I can get a room assigned. How about 2pm today or first thing 
>> tomorrow -8 or 9?
>>
>> Lou
>>
>> On March 29, 2017 10:43:32 AM Balázs Varga A <[e-mail]> 
>> wrote:
>>
>> Hi All,
>> I have some thoughts below regarding the Flow-ID discussion at yesterday 
>> dinner.
>> Could we gain that we are at the same location and have a side meeting
>> today (afternoon or evening) or tomorrow (afternoon)?
>> Cheers
>> Bala’zs
>>
>> My interpretation on the Flow-ID and its scalability. Please comment.
>> Let’s list the end-systems together with their used encapsulation.
>> Starting with how it works with a TSN host and a TSN domain:
>> - TSN (L2) host: host is not IP aware, flow is directly encapsulated in 
>> Ethernet.
>> A StreamID is used constructed by “src-MAC + UniqueID” as per IEEE:
>> “The StreamID includes the following subcomponents:
>> - A 48-bit MAC Address associated with the Talker sourcing the
>> stream to the bridged network.
>> - A 16-bit unsigned integer value, Unique ID, used to distinguish
>> among multiple streams sourced by the same Talker.”
>> The UniqeID is not traveling with the Ethernet frame, but the multicast dst-MAC
>> can be used to find out the UniqueID. So the uniqueness of StreamID achieved,
>> it includes the source identification and scales well.
>>
>> We can do something similarly for IP hosts and a DetNet domain:
>> - DetNet aware IP host: flow is encapsulated in “PW over IP”. Seq.num and
>> Flow-ID added by the host. So if we would like to have an analogy with TSN, the
>> flow can be unambiguously identified by the “src-IP + Flow-ID”. That would 
>> scale
>> and is similar to TSN.
>>
>> However the difference is that in case of TSN we have just a single forwarding
>> paradigm: Ethernet bridging. The src-MAC and dst-MAC are visible for all
>> intermediate bridges, so the flow can be identified without any difficulties.
>>
>> In the “dp-sol-draft” we have defined the Flow-ID somewhat different to avoid
>> DPI (i.e., checking src/dst MAC/IP addresses) during transport to recognize 
>> the flows.
>> The Flow-ID is placed in the PW encapsulation header, so easy to find it 
>> and use it
>> whatever DetNet domain (IP or MPLS) you are crossing.
>>
>> In case of DetNet we have two forwarding paradigm: (i) IP routing and (ii) MPLS
>> switching. Therefore checking the “src-IP + Flow-ID” is somewhat more 
>> complicated
>> for intermediate nodes. For example, in case of MPLS the “src-IP” is in the
>> encapsulation payload, so we need DPI.
>> Furthermore if we interconnect TSN End-systems over DetNet there is no 
>> “src-IP”.
>> So we have solved the difficulties with “src-IP” by defining the “Flow-ID” 
>> as to be
>> unique with all the concerns regarding scalability.
>>
>> So what could be a better approach if we intend to solve scalability. We 
>> need two IDs.
>> (1) one identifying the source of the flow and (2) an other one to 
>> distinguish multiple
>> flows sent by the same source. For the second one we already have the Flow-ID.
>> What could be selected for the first one?
>> - src-MAC: not visible in many cases (e.g., source behind a routed domain, 
>> etc.)
>> - src-IP: may not present (e.g., in case of TSN host)
>> - PW-label: it is always present.
>> - new field: to be defined in the encapsulation
>> Making the PW-label source specific and constant during transport sounds 
>> similar as
>> segment routing, however here we have to allocate label space for hosts and not
>> per network nodes. So it may hurt scalability again.
>>
>> What about the new field? And we do not have to define a pretty new one just
>> extend and add structure to the already defined “DetNet flow identity word”.
>> - 16 bit Flow-ID: distinguish flows per source (same size as for TSN ! )
>> - 46 bit Src-ID: distinguish the source
>> - 1 bit: direction bit
>> - 1 bit: reserved
>> So we are adding 64 bit instead of 32 in order to ensure scalability …
>>       0                   1                   2                   3
>>       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
>>      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>>      |r|D|                           46 bit src identity             |
>>      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>>      |      src identity cont.       |     16 bit flow identity      |
>>      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>>
>> In the src-ID you can map a unique ID for sources. Some possible examples:
>> - L2 host: src-MAC without BC-bit and Local-administration-bit (48-2=46 bits)
>> - L3 (IPv4) host: src-IP address + zeros to fill up the field
>> - L3 (IPv6) host: IPv6 host have 128 bit src-IP, so we may need a preconfigured
>> ID for the IPv6 host used for DetNet purposes.
>>
>> Thanks if You have read so far …
>>
>> Note: For the scenario with DetNet unaware IP host(s): host sends flow needing
>> DetNet treatment. First DA-T-PE has to create the PW encapsulation (adding
>> seq.num and Flow-ID). It is a task of the DA-T-PE to create the field values as
>> specified above.
>>
>>
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