Draft: draft-ietf-detnet-dp-sol-mpls-00

Commentary: Signed - off - by : Korhonen , Jouni
TSN End Systems send and receive packets over the DetNet.  The
supported packet types are IP and Ethernet.
Edge Nodes are responsible for the imposition and disposition of the
required DetNet encapsulation.  These are functionally similar to
pseudowire (PW) Terminating Provide Edge (T-PE) equipment.
Relay nodes are strategically placed and used enhance the reliability
of delivery by enabling the replication of packets so that multiple
copies, possibly over multiple paths.  They also reduce the impact of
replication by the eliminating surplus copies of DetNet packets.
Replication and elimination may also be performed at ingress and
egress edge nodes respectively.
Edge nodes, and relay nodes are aware of the needs of particular
DetNet flows and take care to process them in accordance with the
required performance needs.
Transit nodes are normal MPLS Label Switching Routers (LSRs).  They
are unaware of the special requirements of DetNet flows, although
they have to be configureable to provide traffic engineering services
to them to enhance the prospect of them meeting the required service
level agreement (SLA).
The MPLS LSP may be provided by any MPLS method (LSP, RSVP-TE, MPLS-
TP, or MPLS Segment Routing (SR)).
fig_pw_detnet illustrates how end to end MPLS-based DetNet service
can be provided.  In this case, the end systems are able to send and
receive DetNet flows.  For example, an end system sends data
encapsulated in MPLS.  Like earlier the 'X' in the end systems, edge
and relay nodes represents potential DetNet flow packet replication
and elimination points.  Here the relay nodes may change the
underlying transport, for example tunneling IP over MPLS, or simply
interconnect network segments.
fig_pw_detnet illustrates how end to end MPLS-based DetNet service is
provided in a more detail.  In this case, the end systems are able to
send and receive DetNet flows.  For example, an end system sends data
encapsulated in MPLS.  The 'X' in the end systems, edge and relay
nodes represents potential DetNet flow packet replication and
elimination points.  Here the relay nodes may change the underlying
transport, for example tunneling MPLS over IP [draft-xu-mpls-sr-over-
ip], or simply interconnect network segments.
An example MPLS DetNet network fragment and packet flow is
illustrated in fig_mpls_example .
Customer Equipment CE1 send a packet into the DetNet enabled MPLS
network.  Edge Node EN1 makes a copy of the packet and encapsulates
each copy as a DetNet packet (packet 1 and packet 2).  It sends one
copy (1) to Relay Node R1 and the other copy (2) to Relay Node R4.
R1 sends packet copy 1 to R2.  R4 sends one copy to R2, and a further
copy (3) to EN2.  R2 receives copy (2) before copy 1, and so
eliminated copy (1) sending only (2) to EN2.  EN2 receives copy (3)
first sending it to CE2 and eliminating copy (2).  Note the number
illustrates the replication instance and should not be confused with
the sequence number which remains unchanged in all packet copies.
The above is of course illustrative of many network scenarios that
can be configured.  Between a pair of relay nodes there may be one or
more transport nodes that simply forward the DetNet traffic, but
these are omitted for clarity.
The DetNet data plane encapsulation MUST include two DetNet specific
information elements in each packet of a DetNet flow: (1) a flow
identification and (2) a sequence number.
The DetNet data plane encapsulation may consists further elements
used for overlay tunneling, to distinguish between DetNet member
flows of the same DetNet compound flow or to support OAM functions.
A method of identifying the MPLS payload type.
A method of identifying the DetNet flow group to the processing
element.
A method of distinguishing DetNet OAM packets from DetNet data
packets.
A method of carrying the DetNet sequence number.
A suitable LSP to deliver the packet to the egress PE.
A method of carrying queuing and forwarding indication.
In this design an MPLS service label (the S-Label), similar to a
pseudowire (PW) label [RFC3985], is used to identify both the DetNet
flow identity and the payload MPLS payload type satisfying (1) and
(2) in the list above.  OAM traffic discrimination happens through
the use of the Associated Channel method described in [RFC4385].  The
sequence number is carried in the DetNet Control word which carries
the Data/OAM discriminator.  The LSP used to transport the DetNet
packet may be of any type (MPLS-LDP, MPLS-TE, MPLS-TP[RFC5921], or
MPLS-SR[I-D.ietf-spring-segment-routing-mpls]).  The LSP (T-Label)
label and/or the S-Label may be used to indicate the queue processing
as well as the forwarding parameters.
Note that when the network consists only of DetNet enabled nodes with
no aggregation, Penultimate Hop Popping (PHP) means that the only
label in the label stack is the S-label.
DetNet control word (d-CW) containing sequencing information for
packet replication and duplicate elimination purposes.  There MUST
a separate sequence number space for each DetNet flow.
DetNet Label (S-label) that identifies a DetNet flow within a
DetNet Edge or a Relay node.  The DetNet label MUST be at the
bottom of the label stack.
An optional DetNet service label (S2-Label) that represents DetNet
Service LSP used between DetNet Egde and/or Relay nodes.  One
possible use of an S2-Label is to identify DetNet member flows
used to provide protection to a DetNet compound flow, perhaps even
when both LSPs appear on the same link for some reason.
One or more MPLS transport LSP label(s) (T-label) which may be a hop-
by-hop label used between LSR and MUST appear higher in the label
stack than S-labels.  A top of stack T-label may be PHPed before
arriving at a DetNet node.  In general T-labels should be considered
to be part of the underlying transport network rather the actual
DetNet data plane encapsulation.
DetNet control word (d-CW) containing sequencing information for
packet replication and duplicate elimination purposes, and the OAM
indicator.  There MUST a separate sequence number space for each
DetNet flow.
DetNet service Label (S-label) that identifies a DetNet flow to
the peer node that is to process it.  The S-Label is allocated
from the platform label space.
Zero or more MPLS transport LSP label(s) (T-label) used to direct
the packet along the label switched path (LSP) to the next peer
node along the path.  When Penultimate Hop Popping is in use there
will be no label T-label in the protocol stack on the final hop.
The necessary data-link encapsulation is then applied prior to
transmission over the physical media.
DetNet flow identification at a DetNet service layer is realized by
an S-label.  It maps a Detnet flow to a specific d-CW in a DetNet
node.  The S-label used for flow identification MUST be bottom label
of the label stack for a DetNet-s- or DetNet-st-flow and MUST precede
the d-CW.
DetNet flow identification at a DetNet service layer is realized by
an S-label.  It maps a Detnet flow to a specific d-CW in a DetNet
node.  For a data flow the S-label used for flow identification MUST
be bottom label of the label stack for a DetNet-s- or DetNet-st-flow
and MUST precede the d-CW.