[Detnet-dp-dt] Providing unique Flow-ID

[Balázs Varga A <[e-mail]>]

Hi,

question to be answered:
- how to ensure that detnet flows can be unique recognized during transport?

Labels used by DetNet flows so far in our discussions:
- d-pw: DetNet flow specific
- l-label: FRER specific label to identify replica (member) flows
- t-label: transport label (FEC of T-PE or S-PE nodes)
Note: Text below assumes an l-label present, what may not be always the case.

Before discussing uniqueness/allocation/usage of these labels let's list the scenarios
requiring flow identification during transport. They can be separated in two groups:
1, DetNet function related scenarios:
- congestion protection: usage of allocated resources (queuing, policing, shaping).
- explicit routes: select/apply the flow specific path.
- service protection: recognize compound / member flows for replication an
elimination.

2, OAM function related scenarios:
- troubleshooting (e.g., identify misbehaving flows, etc.)
- recognize flow(s) for analytics (e.g, increase counters, etc.)
- correlate events with flows (e.g., volume above threshold, etc.)
- others ...

We can distinguish 3 node types:
- T-PE: d-pw starts/terminates here
- S-PE: place of detnet specific function (e.g., FRER)
- P: intermediate node (transport only functions)

T-PE and S-PE nodes are fully aware of both the DetNet service and transport layers.
In case of PHP, they receive only "d-pw + l-label", so the x-PE node should recognize
the DetNet flow based on these labels. DetNet specific functions are driven by the
"d-pw label" and "l-label" pair. The "d-pw"+"l-label" pairs have to be locally unique
on the x-PE.

The problematic points are the intermediate "P" nodes. Their detnet role is limited to
ensure congestion protection from the above listed DetNet functions. Additionally OAM
functions are also nice to have at each hop (as usual).

We have two options for P nodes:
- Option-A, P node can recognize only "t-label" and cannot consider the whole label
stack for flow recognition. This is the scenario, where we have pre-established
tunnels over the network, where the DetNet flows are mapped to appropriate tunnels to
be transported over the network. This can be treated as a form of aggregation as many
DetNet flows may use the same tunnel. Of course with this aggregation we lost per flow
identification, that is the price for scalability.
- Option-B, P-nodes can consider the whole label stack and they can identify each
individual flow. That represents additional requirement on P nodes, which may not be
acceptable in some network scenarios.

So, what labels should be unique and how should we allocate labels?
- d-pw: allocated by egress PE node. Label value is unique on that particular PE node.
Other PE nodes may allocate the same label value for a different detnet flow.
- l-label: allocated by the S-PE node. Label value is unique on that particular S-PE
node.
- t-label: allocated by P node. Refer to the tunnel endpoint node (FEC) and the
tunnel-ID. Value locally unique on the P node.

Such an allocation scheme ensure that all nodes in the network are able to identify
uniquely the DetNet flows (or aggregate flows) and support the above listed
functions:
- T-PE (egress): DetNet flow(s) identified based on the "d-pw" value.
- S-PE: DetNet flow(s) identified based on the "l-label" value
- P-node (option-A): aggregated DetNet flow(s) identified based on the "t-label"
- P-node (option-B): DetNet flow(s) identified based on the "l-label + t-label" (no
need to look for the "d-pw" label, unless "l-label" is not present)

Note, that as shown above globally unique "d-pw" labels are optional!

Good night and see You tomorrow early morning
Bala'zs