DetNet Working Group | G. Mirsky |
Internet-Draft | ZTE Corp. |
Intended status: Standards Track | M. Chen |
Expires: January 9, 2020 | Huawei |
July 8, 2019 |
Operations, Administration and Maintenance (OAM) for Deterministic Networks (DetNet) with MPLS Data Plane
draft-mirsky-detnet-mpls-oam-00
This document lists functional requirements for Operations, Administration, and Maintenance (OAM) toolset in Deterministic Networks (DetNet) and, using these requirements; defines format and use principals of the DetNet service Associated Channel over a DetNet network with the MPLS data plane..
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[I-D.ietf-detnet-architecture] introduces and explains Deterministic Networks (DetNet) architecture and how the Packet Replication and Elimination function (PREF) can be used to ensure low packet drop ratio in DetNet domain.
Operations, Administration and Maintenance (OAM) protocols are used to detect, localize defects in the network, and monitor network performance. Some OAM functions, e.g., failure detection, work in the network proactively, while others, e.g., defect localization, usually performed on-demand. These tasks achieved by a combination of active and hybrid, as defined in [RFC7799], OAM methods.
This document lists the functional requirements toward OAM for DetNet domain. The list can further be used for gap analysis of available OAM tools to identify possible enhancements of existing or whether new OAM tools are required to support proactive and on-demand path monitoring and service validation. Also, this document defines format and use principals of the DetNet service Associated Channel over a DetNet network with the MPLS data plane [I-D.ietf-detnet-mpls].
The term "DetNet OAM" used in this document interchangeably with longer version "set of OAM protocols, methods and tools for Deterministic Networks".
CW Control Word
DetNet Deterministic Networks
d-ACH DetNet Associated Channel Header
d-CW DetNet Control Word
DNH DetNet Header
GAL Generic Associated Channel Label
G-ACh Generic Associated Channel
OAM: Operations, Administration and Maintenance
PREF Packet Replication and Elimination Function
POF Packet Ordering Function
PW Pseudowire
RDI Remote Defect Indication
TSN Time-Sensitive Network
F-Label A Detnet "forwarding" label that identifies the LSP used to forward a DetNet flow across an MPLS PSN, e.g., a hop-by-hop label used between label switching routers (LSR).
S-Label A DetNet "service" label that is used between DetNet nodes that implement also the DetNet service sub-layer functions. An S-Label is also used to identify a DetNet flow at DetNet service sub-layer.
Underlay Network or Underlay Layer: The network that provides connectivity between the DetNet nodes. MPLS network providing LSP connectivity between DetNet nodes is an example of the underlay layer.
DetNet Node - a node that is an actor in the DetNet domain. DetNet domain edge node and node that performs PREF within the domain are examples of DetNet node.
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 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here.
This section lists requirements for OAM in DetNet domain with MPLS data plane:
OAM protocols and mechanisms act within the data plane of the particular networking layer. And thus it is critical that the data plane encapsulation supports OAM mechanisms in such a way to comply with the above-listed requirements. One of such examples that require special consideration is requirement #5:
The Det Net data plane encapsulation in transport network with MPLS encapsulation specified in [I-D.ietf-detnet-mpls]. For the MPLS underlay network, DetNet flows to be encapsulated analogous to pseudowires (PW) over MPLS packet switched network, as described in [RFC3985], [RFC4385]. Generic PW MPLS Control Word (CW), defined in [RFC4385], for DetNet displayed in Figure 1.
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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |0 0 0 0| Sequence Number | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: DetNet Control Word Format
PREF in the DetNet domain composed by a combination of nodes that perform replication and elimination sub-functions. The elimination sub-function always uses the S-Label and packet sequencing information, e.g., the value in the Sequence Number field of DetNet CW (d-CW). The replication sub-function uses the S-Label information only. For data packets Figure 2 presents an example of PREF in DetNet domain.
1111 11111111 111111 112212 112212 132213 CE1----EN1--------R1-------R2-------R3--------EN2----CE2 \2 22222/ 3 / \2222222 /----+ 3 / +------R4------------------------+ 333333333333333333333333
Figure 2: DetNet Data Plane Based on PW
+---------------------------------+ | | | DetNet App-Flow | | Payload Packet | | | +---------------------------------+ <--\ | DetNet Associated Channel Header| | +---------------------------------+ +--> DetNet active OAM | S-Label | | MPLS encapsulation +---------------------------------+ | | [ F-Label(s) ] | | +---------------------------------+ <--/ | Data-Link | +---------------------------------+ | Physical | +---------------------------------+
Figure 3: DetNet Active OAM Packet Encapsulation in MPLS Data Plane
DetNet OAM, like PW OAM, uses PW Associated Channel Header defined in [RFC4385]. Figure 3 displays the encapsulation of a DetNet MPLS [I-D.ietf-detnet-mpls] active OAM packet.
+---------------------------------+ | | | DetNet App-Flow | | Payload Packet | | | +---------------------------------+ <--\ | DetNet Associated Channel Header| | +---------------------------------+ +--> DetNet active OAM | S-Label | | MPLS encapsulation +---------------------------------+ | | [ F-label(s) ] | | +---------------------------------+ <--+ | UDP Header | | +---------------------------------+ +--> DetNet data plane | IP Header | | IP encapsulation +---------------------------------+ <--/ | Data-Link | +---------------------------------+ | Physical | +---------------------------------+
Figure 4: DetNet Active OAM Packet Encapsulation in MPLS-over-UDP/IP
Figure 4 displays encapsulation of a test packet of an active DetNet OAM protocol in case of MPLS-over-UDP/IP [I-D.ietf-detnet-mpls-over-udp-ip].
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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |0 0 0 1|Version|Sequence Number| Channel Type | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 5: DetNet Associated Channel Header Format
Figure 5 displays the format of the DetNet Associated Channel Header (d-ACH).
The meanings of the fields in the d-ACH are:
The DetNet flow, according to [I-D.ietf-detnet-mpls], is identified by the S-label that MUST be at the bottom of the stack. Active OAM packet MUST have d-ACH immediately following the S-label.
Special consideration for DetNet active OAM with MPLS data plane interworking with OAM in IEEE 802.1 Time-Sensitive Networking (TSN) domain based on [I-D.ietf-detnet-mpls-over-tsn]:
At the DetNet service layer, special functions MAY be applied to the particular DetNet flow - PREF to potentially lower packet loss, improve the probability of on-time packet delivery and Packet Ordering Function (POF) to ensure in-order packet delivery. As data and the active OAM packets have the same Flow ID, S-label, sub-functions that rely on sequencing information in the DetNet service layer MUST process 28 MSBs of the d-ACH as the source of the sequencing information for the OAM packet.
Hybrid OAM methods are used in performance monitoring and defined in [RFC7799] as: [RFC8321]. Reserving the field for the Alternate Marking method in the DetNet Header will enhance available to an operator set of DetNet OAM tools.
A hybrid measurement method may produce metrics as close to passive, but it still alters something in a data packet even if that is the value of a designated field in the packet encapsulation. One example of such a hybrid measurement method is the Alternate Marking method described in
TBA
TBA
TBA
This document lists the OAM requirements for a DetNet domain and does not raise any security concerns or issues in addition to ones common to networking.
Authors extend their appreciation to Pascal Thubert for his insightful comments and productive discussion that helped to improve the document.
[I-D.ietf-detnet-architecture] | Finn, N., Thubert, P., Varga, B. and J. Farkas, "Deterministic Networking Architecture", Internet-Draft draft-ietf-detnet-architecture-13, May 2019. |
[I-D.ietf-detnet-mpls] | Varga, B., Farkas, J., Berger, L., Fedyk, D., Malis, A., Bryant, S. and J. Korhonen, "DetNet Data Plane: MPLS", Internet-Draft draft-ietf-detnet-mpls-01, July 2019. |
[I-D.ietf-detnet-mpls-over-tsn] | Varga, B., Farkas, J., Malis, A., Bryant, S. and J. Korhonen, "DetNet Data Plane: MPLS over IEEE 802.1 Time Sensitive Networking (TSN)", Internet-Draft draft-ietf-detnet-mpls-over-tsn-00, May 2019. |
[I-D.ietf-detnet-mpls-over-udp-ip] | Varga, B., Farkas, J., Berger, L., Malis, A., Bryant, S. and J. Korhonen, "DetNet Data Plane: MPLS over UDP/IP", Internet-Draft draft-ietf-detnet-mpls-over-udp-ip-01, July 2019. |
[RFC2119] | Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997. |
[RFC8174] | Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017. |