Deterministic Networking (DetNet): OAM Functions for The Service Sub-Layer
Ericsson
Magyar Tudosok krt. 11.
Budapest
Hungary
1117
balazs.a.varga@ericsson.com
Ericsson
Magyar Tudosok krt. 11.
Budapest
Hungary
1117
janos.farkas@ericsson.com
DetNet
Operation, Administration, and Maintenance (OAM) tools are essential for
a deterministic network. The DetNet architecture
has defined two sub-layers:
(1) DetNet service sub-layer and (2) DetNet forwarding sub-layer. OAM
mechanisms exist for the DetNet forwarding sub-layer, nonetheless, OAM
for the service sub-layer requires a new mechanism. This draft introduces
OAM related procedures for the DetNet service sub-layer functions.
The DetNet Working Group has defined two sub-layers: (1) DetNet service
sub-layer, at which a DetNet service (e.g., service protection) is
provided and (2) DetNet forwarding sub-layer, which optionally provides
resource allocation for DetNet flows over paths provided by the
underlying network. In new DetNet-specific
functions have been defined for the DetNet service sub-layer, namely
PREOF (a collective name for Packet Replication, Elimination, and
Ordering Functions).
Framework of Operations, Administration and Maintenance (OAM) for
Deterministic Networking (DetNet) is described in
. OAM for the DetNet MPLS
data plane is described in and
OAM for the DetNet IP data plane is described in
.
This draft has been submitted as an individual contribution to OAM
discussions, in particular, to kick-off Working Group discussions on
introducing OAM functions for the DetNet service sub-layer. It is also
up to the Working Group discussions to which draft parts of this
contribution may go, if any.
The OAM functions for the DetNet service sub-layer allow, for example, to
recognize/discover DetNet relay nodes, to get information about their
configuration, and to check their operation or status.
The approach described in this draft introduces a new OAM shim layer to
achieve OAM for the DetNet service sub-layer. In the rest of the draft,
this approach is referred to as "DetNet PING", which is an in-band OAM
approach, i.e., the OAM packets follow precisely the same path
as the data packets of the corresponding DetNet flow(s) The OAM packets
provide DetNet service sub-layer specific information, like:
Identity of a DetNet service sub-layer node.
Discover Ingress/Egress flow specific configuration of a DetNet
service sub-layer node.
Detect the status of the flow specific service sub-layer
function.
DetNet PING is applicable both to IP and MPLS DetNet data planes.
This document uses the terminology established in the DetNet architecture
, and the reader is assumed
to be familiar with that document and its terminology.
The following abbreviations are used in this document:
Deterministic Networking.
Packet Elimination Function.
Packet Ordering Function.
Packet Replication, Elimination and Ordering Functions.
Packet Replication Function.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
BCP 14 when, and
only when, they appear in all capitals, as shown here.
The requirements on OAM for a DetNet relay node are:
to provide OAM functions for the DetNet service
sub-layer.
to discover DetNet relay nodes in a DetNet network.
to collect DetNet service sub-layer specific (e.g.,
configuration/operation/status) information from DetNet relay
nodes.
to work for both DetNet data planes: (1) MPLS and (2) IP.
The "DetNet PING" approach uses two types of OAM packets: (1)
DetNet-Echo-Request and (2) DetNet-Echo-Reply. Their encapsulation is
identical to that of the corresponding DetNet data flow, so
they follow precisely the same path as the packets of the
corresponding DetNet data flow. They target DetNet service
sub-layer entities, so they may not be recognized as OAM packet by
entities not implementing DetNet service sub-layer for a packet flow
(e.g., transit nodes). Other entities treat them as packets belonging
to the corresponding DetNet data flow.
The following relay node roles can be distinguished:
DetNet PING originator node,
Intermediate DetNet service sub-layer node,
DetNet PING targeted node.
An originator node sends (generates) DetNet-Echo-Request packet(s).
DetNet-Echo-Request packet contains an OAM specific "PINGSeqNum",
what can be used by the DetNet service sub-layer of relay nodes.
Note that "PINGSeqNum" is originator specific.
An intermediate DetNet service sub-layer node executes DetNet flow specific
service sub-layer functionality. Packet processing may be done in an
OAM specific manner (see details in in ).
A targeted node answers with DetNet-Echo-Reply packet for each
DetNet-Echo-Request. DetNet-Echo-Reply packet provides DetNet service
sub-layer specific information on
(i) identities of DetNet service sub-layer node (e.g., Node-ID,
local Flow-ID), (ii) ingress/egress flow related configuration
(e.g., in/out member flow specific information (including forwarding
sub-layer specifics)), and (iii) status of service sub-layer function
(e.g., local PxF-ID, Action-Type=x, operational status, value of key
state variable(s), function related counters).
Detailed OAM packet processing rules of various DetNet relay nodes are
described in the next sections.
A DetNet relay node with PRF processes DetNet OAM packets in a stateless manner.
If the relay node with PRF is the target of a DetNet-Echo-Request packet,
then the DetNet-Echo-Request packet MUST NOT be further forwarded and
an DetNet-Echo-Reply packet MUST be generated. If the relay node with
PRF is not the target of a DetNet-Echo-Request packet, then the
DetNet-Echo-Request packet MUST be sent over all DetNet flow specific
member flow paths (i.e., it is replicated).
A DetNet-Echo-Reply packet MUST contain the following information:
Identities related to the DetNet service sub-layer node
(e.g., Node-ID, local Flow-ID),
Ingress/Egress flow related configuration (e.g., in/out member
flow specific information (including forwarding sub-layer specifics)),
Status of service sub-layer function (e.g., local PRF-ID,
Action-Type=Replication, operational status, value of the flow
related key state variable (e.g., "GenSeqNum" in
).
A DetNet-Echo-Reply packet MAY contain the following information:
PRF function related local counters.
A DetNet relay node with PEF processes DetNet OAM packets in a stateful manner.
If the relay node with PEF is the target of DetNet-Echo-Request packet,
then the DetNet-Echo-Request packet MUST NOT be further forwarded and
an DetNet-Echo-Reply packet MUST be generated. If the relay node with
PEF is not the target of DetNet-Echo-Request packet, then elimination
MUST be executed on the DetNet-Echo-Request packet(s) using the OAM
specific "PINGSeqNum" in the packet. So only a single
DetNet-Echo-Request packet is forwarded and all further replicas
(having the same originator's sequence number) MUST be discarded.
Note, that PEF MAY use a simplified elimination algorithm for
DetNet-Echo-Request packets (e.g., "MatchRecoveryAlgorithm" in
) as OAM is a slow protocol.
A DetNet-Echo-Reply packet MUST contain the following information:
Identities related to the DetNet service sub-layer node
(e.g., Node-ID, local Flow-ID),
Ingress/Egress flow related configuration (e.g., in/out member
flow specific information (including forwarding sub-layer specifics))
,
Status of service sub-layer function (e.g., local PEF-ID,
Action-Type=Elimination, operational status, value of the flow
related key state variable (e.g., "RecovSeqNum" in
).
A DetNet-Echo-Reply packet MAY contain the following information:
PEF function related local counters.
A DetNet relay node with POF processes DetNet OAM packets in a stateless manner.
If the relay node with POF is the target of DetNet-Echo-Request packet,
then the DetNet-Echo-Request packet MUST NOT be further forwarded and
a DetNet-Echo-Reply packet MUST be generated. If the relay node with
POF is not the target of DetNet-Echo-Request packet, then the
DetNet-Echo-Request packet(s) MUST be forwarded without any POF specific
action.
A DetNet-Echo-Reply packet MUST contain the following information:
Identities of the DetNet service sub-layer node (e.g., Node-ID,
local Flow-ID),
Ingress/Egress flow related configuration (e.g., in/out member
flow specific information (including forwarding sub-layer specifics))
,
Status of service sub-layer function (e.g., local POF-ID,
Action-Type=Ordering, operational status, value of the flow
related key state variable (e.g., "POFLastSent" in
).
A DetNet-Echo-Reply packet MAY contain the following information:
POF function related local counters.
A DetNet relay node without PREOF processes DetNet OAM packets in a stateless
manner.
If the relay node without PREOF is the target of DetNet-Echo-Request packet,
then the DetNet-Echo-Request packet MUST NOT be further forwarded and
an DetNet-Echo-Reply packet MUST be generated. If the relay node without
PREOF is not the target of DetNet-Echo-Request packet, then the
DetNet-Echo-Request packet(s) MUST be forwarded (as any data packets of
the related DetNet flow).
DetNet-Echo-Reply packet MUST contain the following information:
Identities of the DetNet service sub-layer node (e.g., Node-ID,
local Flow-ID),
Ingress/Egress flow related configuration (e.g., in/out member
flow specific information (including forwarding sub-layer specifics))
.
IEEE Standard for Local and metropolitan area
networks -- Frame Replication and Elimination for Reliability
IEEE