MPLS Working Group G. Mirsky
Internet-Draft S. Ruffini
Intended status: Standards Track Ericsson
Expires: April 26, 2015 J. Drake
Juniper Networks
S. Bryant
Cisco Systems
A. Vainshtein
ECI Telecom
October 23, 2014
Residence Time Measurement in MPLS network
draft-mirsky-mpls-residence-time-03
Abstract
This document specifies G-ACh based Residence Time Measurement and
how it can be used by time synchronization protocols being
transported over MPLS domain.
Status of This Memo
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Conventions used in this document . . . . . . . . . . . . 3
1.1.1. Terminology . . . . . . . . . . . . . . . . . . . . . 3
1.1.2. Requirements Language . . . . . . . . . . . . . . . . 3
2. Residence Time Measurement . . . . . . . . . . . . . . . . . 3
3. G-ACh for Residence Time Measurement . . . . . . . . . . . . 4
4. Control Plane Theory of Operation . . . . . . . . . . . . . . 5
4.1. RTM Capability sub-TLV . . . . . . . . . . . . . . . . . 5
4.2. RTM Capability Advertisement in OSPFv2 . . . . . . . . . 6
4.3. RTM Capability Advertisement in OSPFv3 . . . . . . . . . 6
4.4. RTM Capability Advertisement in IS-IS . . . . . . . . . . 6
4.5. RSVP-TE Control Plane Operation to Support RTM . . . . . 7
5. Data Plane Theory of Operation . . . . . . . . . . . . . . . 8
6. Applicable PTP Scenarios . . . . . . . . . . . . . . . . . . 8
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
7.1. New RTM G-ACh . . . . . . . . . . . . . . . . . . . . . . 8
7.2. New RTM TLV Registry . . . . . . . . . . . . . . . . . . 9
7.3. RTM Capability sub-TLV . . . . . . . . . . . . . . . . . 9
7.4. IS-IS RTM Application ID . . . . . . . . . . . . . . . . 9
8. Security Considerations . . . . . . . . . . . . . . . . . . . 10
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 10
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 10
10.1. Normative References . . . . . . . . . . . . . . . . . . 10
10.2. Informative References . . . . . . . . . . . . . . . . . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 11
1. Introduction
Time synchronization protocols, Network Time Protocol version 4
(NTPv4) [RFC5905] and Precision Time Protocol (PTP) Version 2, a.k.a.
IEEE-1588 v.2, can be used to syncronized clocks across network
domain. In some scenarios calculation of time packet of time
syncronization protocol spends within a node, called Residence Time,
can improve accuracy of clock syncronization. This document defines
new Generalized Associated Channel (G-ACh) that can be used in Multi-
Protocol Label Switching (MPLS) network to measure Residence Time
over Label Switched Path (LSP). Transport of packets of a time
synchronization protocol over MPLS domain is outside of scope of this
document.
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1.1. Conventions used in this document
1.1.1. Terminology
MPLS: Multi-Protocol Label Switching
ACH: Associated Channel
TTL: Time-to-Live
G-ACh: Generic Associated Channel
GAL: Generic Associated Channel Label
NTP: Network Time Protocol
ppm: part per million
PTP: Precision Time Protocol
LSP: Label Switched Path
LSR: Label Switched Router
OAM: Operations, Administration, and Maintenance
RTM: Residence Time Measurement
IGP: Internal Gateway Protocol
1.1.2. Requirements Language
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
[RFC2119].
2. Residence Time Measurement
Packet Loss and Delay Measurement for MPLS Networks [RFC6374] can be
used to measure one-way or two-way end-to-end propagation delay over
LSP or PW. But none of these metrics is useful for time
syncronization across a network. For example, PTPv2 uses "residence
time", time it takes for a PTPv2 event packet to transit a node. The
residence times are accumulated in the correctionField of the PTP
event messages or of the associated follow-up messages (or Delay_Resp
message associated with the Delay_Req message) in case of two-step
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clocks. The residence time values are specific to each output PTP
port and message.
Note the delay of propagation over a link connected to a port
receiving the PTP event message is handled by IEEE 1588
[IEEE.1588.2008] by means of specific messages, Pdelay_Req and
Pdelay_Resp,or Delay_Req and Delay_Resp depending on the applicable
delay mechanism, peer-to-peer or delay request-response mechanism
respectively.
This document proposes mechanism to accumulate packet residence time
from all LSRs that support the mechanism across the particular LSP.
3. G-ACh for Residence Time Measurement
RFC 5586 [RFC5586] and RFC 6423 [RFC6423] extended applicability of
PW Associated Channel (ACH) [RFC5085] to LSPs. G-ACh presents
mechanism to transport OAM and other control messages and trigger
their processing by arbitrary transient LSRs through controlled use
of Time-to-Live (TTL) value.
Packet format for Residence Time Measurement (RTM) presented 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 1|Version| Reserved | RTM Channel |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Scratch Pad |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Value |
~ ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: G-ACh packet format for Residence Time Measurement
The Version field is set to 0, as defined in RFC 4385 [RFC4385]. The
Reserved field must be set to 0 on transmit and ignored on receipt.
The RTM G-ACh field, value to be allocated by IANA, identifies the
packet as such. The Scratch Pad field is 8 octets in length and is
used to accumulate the residence time spent in LSRs transited by the
packet on its path from ingress LSR to egress LSR. Its format is
IEEE double precision and its units are nanoseconds.
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The Type field identifies type of Value that the TLV carries. IANA
will be asked to create sub-registry in Generic Associated Channel
(G-ACh) Parameters Registry called "MPLS RTM TLV Registry". The
Length field is number of octets of the Value field. The optional
Value field may be used to carry a packet of a given time
synchronization protocol. If the packet carried in the RTM message,
then it accordingly identified by distinct Type, and may be NTP
[RFC5905] or PTP [IEEE.1588.2008]. It is important to note that the
packet may be authenticated or encrypted and carried over MPLS LSP
edge to edge unchanged while residence time being accumulated in the
Scratch Pad field. The TLV MUST be included in the RTM.
4. Control Plane Theory of Operation
The operation of RTM depends upon TTL expiry to deliver an RTM packet
from one RTM capable interface to the next along the path from
ingress LSR to egress LSR, which means that an LSR with RTM capable
interfaces needs to be able to compute a TTL which will cause the
expiry of an RTM packet at the next LSR with RTM capable interfaces.
However, because of Equal Cost Multipath, labels distributed by LDP
do not instantiate a single path between a given ingress/egress LSR
pair but rather a graph and different flows will take different paths
through this graph. This means one doesn't know the path that RTM
packets will take or even if they all take the same path. So, in an
environment in which not all interfaces in an IGP domain support RTM,
it is effectively impossible to use TTL expiry to deliver RTM packets
and hence RTM cannot be used for LSPs instantiated using LDP. In the
special but important case of environment in which all interfaces in
an IGP domain support RTM, setting the TTL to 1 will always cause the
expiry of an RTM packet on the next RTM capable downstream LSR and
hence in such an environment, RTM can be used for LSPs instantiated
using LDP.
Generally speaking, RTM is more useful for an LSP instantiated using
RSVP-TE [RFC3209] because the LSP's path can be known.
4.1. RTM Capability sub-TLV
Format for RTM Capailities sub-TLV presented in Figure 2
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type(TBA5) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| RTM | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: RTM Capability sub-TLV
o Type value will be assigned by IANA from appropriate registries.
o Length MUST be set to 4.
o RTM is three bit long bit map field.
o Reserved field must e set to all zeroes on transmit and ignored on
receive.
4.2. RTM Capability Advertisement in OSPFv2
The capability to support RTM on a particular link advertised in the
OSPFv2 Extended Link Opaque LSA [I-D.ietf-ospf-prefix-link-attr] as
RTM Capability sub-TLV, presented in Figure 2, of the OSPFv2 Extended
Link TLV.
Type value will be assigned by IANA from the OSPF Extended Link TLV
Sub-TLVs registry that will be created per
[I-D.ietf-ospf-prefix-link-attr] request.
4.3. RTM Capability Advertisement in OSPFv3
The capability to support RTM on a particular link in the OSPFv3 can
be advertised by including RTM Capability sub-TLV defined in
Section 4.2 in the following TLVs defined in
[I-D.ietf-ospf-ospfv3-lsa-extend] Intra-Area-Prefix TLV, IPv6 Link-
Local Address TLV, IPv4 Link-Local Address TLV when these are
included in E-Link-LSA.
4.4. RTM Capability Advertisement in IS-IS
The RTM capability logically belongs to a group of parameters
characterized as "generic information not directly related to the
operation of the IS-IS protocol" [RFC6823]. Hence the capability to
process RTM messages can be advertised by including RTM Capability
sub-TLV in GENINFO TLV [RFC6823]. The S bit of Flags MUST be cleared
to prevent the RTM Capability sub-TLV from leaking between levels.
The D bit of the Flags field MUST be cleared as well. The I bit and
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the V bit MUST be set accordingly depending on whether RTM capability
being advertised for IPv4 or IPv6 interface of the node. Application
ID (TBA6) will be assigned from the Application Identifiers for TLV
251 IANA registry. The RTM Capability sub-TLV, presented in
Figure 2, MUST be included in GENINFO TLV in Application Specific
Information.
4.5. RSVP-TE Control Plane Operation to Support RTM
Though RTM capability is per interface throughout this document we
will refer to an LSR as RTM capable LSR when:
o ingress LSR's LSP interface is RTM capable;
o transient LSR's ingress and egress interfaces for the given LSP
are RTM capable;
o egress LSR's egress interface is RTM capable.
An ingress LSR that wishes to perform RTM along a path through an
MPLS network to an egress LSR verifies that the selected egress LSR
has an interface that supports RTM via the egress LSR's advertisement
of the RTM Capability sub-TLV. In the Path message that the ingress
LSR uses to instantiate the LSP to that egress LSR it places
initialized Record Route and RTM Set (see below) Objects, which tell
the egress LSR that RTM is desired for this LSP.
In the Resv message that the egress LSR sends in response to the
received Path message, it includes initialized Record Route and RTM
Set objects. The latter object will be defined in a subsequent
version of this document and it contains an ordered list, from egress
LSR to ingress LSR, of the RTM capable LSRs along the LSP's path.
Each such LSR will use the ID of the first LSR in the RTM Set Object
in conjunction with the Record Route Object to compute the hop count
to its downstream LSR with reacheable RTM capable interface. It will
also insert its ID at the beginning of the RTM Set Object before
forwarding the Resv upstream.
After the ingress LSR receives the Resv, it will begin sending RTM
packets to the first RTM capable LSR on the LSP's path. Each RTM
packet has its Scratch Pad field initialized and its TTL set to
expire on that LSR.
It should be noted that RTM can also be used for LSPs instantiated
using [RFC3209] in an environment in which all interfaces in an IGP
support RTM. In this case the RTM Set Object is not used.
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5. Data Plane Theory of Operation
After instantiating an LSP for a path using RSVP-TE [RFC3209] as
described in Section 4.5 or if this is the special case of
homogeneous RTM-capable IP/MPLS domain discussed in the last
paragraph of Section 4, ingress LSR MAY begin sending RTM packets to
the first downstream RTM capable LSR on that path. Each RTM packet
has its Scratch Pad field initialized and its TTL set to expire on
the next downstream RTM capable LSR. Each RTM capable LSR on the
explicit path receives an RTM packet and records the time at which it
receives that packet as well as the time at which it transmits that
packet; this should be done as close to the physical layer as
possible. Just prior to sending that packet, it takes the difference
between those two times and adds it to the value in the Scratch Pad
field. Note, for the purpose of calculating a residence time, a free
running clock may be sufficient, as, for example, 4.6 ppm accuracy
leads to 4,6 ns error for residence time in the order of 1 ms.
The RTM capable LSR also sets the RTM packet's TTL to expire on the
next downstream RTM capable LSR.
The egress LSR may then use the value in the Scratch Pad field to
perform time correction. For example, the egress LSR may be a PTP
Boundary Clock synchronized to a Master Clock and will use the value
in the Scratch Pad Field to update PTP's Correction Field.
6. Applicable PTP Scenarios
The proposed approach can be directly integrated in a PTP network
based on delay request-response mechanism. The RTM capable LSR nodes
act as end-to-end transparent clocks, and typically boundary clocks,
at the edges of the MPLS network, use the value in the Scratch Pad
field to update the correctionField of the corresponding PTP event
packet prior to performing the usual PTP processing.
Under certain assumptions the proposed solution in a network where
peer delay mechanism is used is also possible. The solution in this
case requires the definition of a specific protocol to be used to
calculate the link delays according to a peer delay link measurement
approach. This is not described in this version of the draft.
7. IANA Considerations
7.1. New RTM G-ACh
IANA is requested to reserve a new G-ACh as follows:
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+-------+----------------------------+---------------+
| Value | Description | Reference |
+-------+----------------------------+---------------+
| TBA1 | Residence Time Measurement | This document |
+-------+----------------------------+---------------+
Table 1: New Residence Time Measurement
7.2. New RTM TLV Registry
IANA is requested to create sub-registry in Generic Associated
Channel (G-ACh) Parameters Registry called "MPLS RTM TLV Registry".
All code points within this registry shall be allocated according to
the "IETF Review" procedure as specified in [RFC5226] This document
defines the following new values RTM TLV type
+-------+-------------+---------------+
| Value | Description | Reference |
+-------+-------------+---------------+
| 0 | Reserved | This document |
| TBA2 | No payload | This document |
| TBA3 | PTPv2 | This document |
| TBA4 | NTP | This document |
+-------+-------------+---------------+
Table 2: RTM TLV Type
7.3. RTM Capability sub-TLV
IANA is requested to assign a new type for RTM Capability sub-TLV
from future OSPF Extended Link TLV Sub-TLVs registry as follows:
+-------+----------------+---------------+
| Value | Description | Reference |
+-------+----------------+---------------+
| TBA5 | RTM Capability | This document |
+-------+----------------+---------------+
Table 3: RTM Capability sub-TLV
7.4. IS-IS RTM Application ID
IANA is requested to assign a new Application ID for RTM from the
Application Identifiers for TLV 251 registry as follows:
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+-------+-------------+---------------+
| Value | Description | Reference |
+-------+-------------+---------------+
| TBA6 | RTM | This document |
+-------+-------------+---------------+
Table 4: IS-IS RTM Application ID
8. Security Considerations
Routers that support Residence Time Measurement are subject to the
same security considerations as defined in [RFC5586] and [RFC6423].
9. Acknowledgements
TBD
10. References
10.1. Normative References
[I-D.ietf-ospf-ospfv3-lsa-extend]
Lindem, A., Mirtorabi, S., Roy, A., and F. Baker, "OSPFv3
LSA Extendibility", draft-ietf-ospf-ospfv3-lsa-extend-04
(work in progress), September 2014.
[I-D.ietf-ospf-prefix-link-attr]
Psenak, P., Gredler, H., Shakir, R., Henderickx, W.,
Tantsura, J., and A. Lindem, "OSPFv2 Prefix/Link Attribute
Advertisement", draft-ietf-ospf-prefix-link-attr-01 (work
in progress), September 2014.
[IEEE.1588.2008]
"Standard for a Precision Clock Synchronization Protocol
for Networked Measurement and Control Systems", IEEE
Standard 1588, March 2008.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3209] Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V.,
and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP
Tunnels", RFC 3209, December 2001.
[RFC3630] Katz, D., Kompella, K., and D. Yeung, "Traffic Engineering
(TE) Extensions to OSPF Version 2", RFC 3630, September
2003.
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[RFC3784] Smit, H. and T. Li, "Intermediate System to Intermediate
System (IS-IS) Extensions for Traffic Engineering (TE)",
RFC 3784, June 2004.
[RFC4385] Bryant, S., Swallow, G., Martini, L., and D. McPherson,
"Pseudowire Emulation Edge-to-Edge (PWE3) Control Word for
Use over an MPLS PSN", RFC 4385, February 2006.
[RFC5085] Nadeau, T. and C. Pignataro, "Pseudowire Virtual Circuit
Connectivity Verification (VCCV): A Control Channel for
Pseudowires", RFC 5085, December 2007.
[RFC5329] Ishiguro, K., Manral, V., Davey, A., and A. Lindem,
"Traffic Engineering Extensions to OSPF Version 3", RFC
5329, September 2008.
[RFC5586] Bocci, M., Vigoureux, M., and S. Bryant, "MPLS Generic
Associated Channel", RFC 5586, June 2009.
[RFC5905] Mills, D., Martin, J., Burbank, J., and W. Kasch, "Network
Time Protocol Version 4: Protocol and Algorithms
Specification", RFC 5905, June 2010.
[RFC6423] Li, H., Martini, L., He, J., and F. Huang, "Using the
Generic Associated Channel Label for Pseudowire in the
MPLS Transport Profile (MPLS-TP)", RFC 6423, November
2011.
[RFC6823] Ginsberg, L., Previdi, S., and M. Shand, "Advertising
Generic Information in IS-IS", RFC 6823, December 2012.
10.2. Informative References
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226,
May 2008.
[RFC6374] Frost, D. and S. Bryant, "Packet Loss and Delay
Measurement for MPLS Networks", RFC 6374, September 2011.
Authors' Addresses
Greg Mirsky
Ericsson
Email: gregory.mirsky@ericsson.com
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Stefano Ruffini
Ericsson
Email: stefano.ruffini@ericsson.com
John Drake
Juniper Networks
Email: jdrake@juniper.net
Stewart Bryant
Cisco Systems
Email: stbryant@cisco.com
Alexander Vainshtein
ECI Telecom
Email: Alexander.Vainshtein@ecitele.com
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