Network Working Group T. Mizrahi
Internet-Draft Marvell
Intended status: Informational G. Fioccola
Expires: September 6, 2017 Telecom Italia
M. Chen
L. Zheng
Huawei Technologies
G. Mirsky
March 5, 2017
Passive Performance Monitoring using a Multiplexed Marking Field
draft-mizrahi-ippm-multiplexed-alternate-marking-01
Abstract
This memo introduces a marking method that uses a single marking bit,
or two marking values, and allows accurate loss and delay
measurement.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on September 6, 2017.
Copyright Notice
Copyright (c) 2017 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
Mizrahi, et al. Expires September 6, 2017 [Page 1]
Internet-Draft Multiplexed Alternate Marking March 2017
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.1. Requirements Language . . . . . . . . . . . . . . . . . . 4
2.2. Abbreviations . . . . . . . . . . . . . . . . . . . . . . 4
3. Alternate Marking using a Multiplexed Marking Bit . . . . . . 4
3.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . 4
3.2. Timing and Synchronization Aspects . . . . . . . . . . . 5
4. Alternate Marking using Two Multiplexed Marking Values . . . 7
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
6. Security Considerations . . . . . . . . . . . . . . . . . . . 8
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 8
7.1. Normative References . . . . . . . . . . . . . . . . . . 8
7.2. Informative References . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9
1. Introduction
Alternate marking, defined in [I-D.ietf-ippm-alt-mark], is a method
for measuring packet loss, packet delay, and packet delay variation.
Typical delay measurement protocols require the two measurement
points (MPs) to exchange timestamped test packets. In contrast, the
alternate marking method does not require control packets to be
exchanged. Instead, every data packet carries a color indicator,
which divides the traffic into consecutive blocks of packets.
The color indicator may either be a single-bit binary indication, or
a two reserved values of a larger field, such as an IPv6 Flow Label
or an MPLS Label. Throughout the rest of the document it is assumed
that the color indication is a single-bit field, unless specified
otherwise. The color value is toggled periodically, as illustrated
in Figure 1.
Mizrahi, et al. Expires September 6, 2017 [Page 2]
Internet-Draft Multiplexed Alternate Marking March 2017
A: packet with color 0
B: packet with color 1
Packets AAAAAAAAAA BBBBBBBBBB AAAAAAAAAA BBBBBBBBBB AAAAAAAAAA
Time ---------------------------------------------------------->
| | | | |
| Block 1 | Block 2 | Block 3 | Block 4 | Block 5 ...
| | | | |
Color 0000000000 1111111111 0000000000 1111111111 0000000000
Figure 1: Alternate marking: packets are monitored on a per-color
basis.
Alternate marking is used between two MPs, the initiating MP, and the
monitoring MP. The initiating MP incorporates the marking field into
en-route packets, allowing the monitoring MP to use the marking field
in order to bind each packet to the corresponding block.
Each of the MPs maintains two counters, one per color. At the end of
each block the counter values can be collected by a central
management system, and analyzed; the packet loss can be computed by
comparing the counter values of the two MPs.
When using alternate marking delay measurement can be performed in
one of three ways (as per [I-D.ietf-ippm-alt-mark]):
o Single marking: the first packet of each block is used by both MPs
as a reference for delay measurement. The timestamp of this
packet is measured by the two measurement points, and can be
collected by the mangement system from each of the measurement
points, which can compute the path delay by comparing the two
timestamps. The drawback of this approach is that it is not
accurate when packets arrive out-of-order, as the two measurement
may have a different view of which packet was the first in the
block.
o Average delay: each of the MPs computes the average packet
timestamp of each block. The management system can then compute
the delay by comparing the average times of the two MPs. The
drawback of this approach is that it may be computationally heavy,
or difficult to implement at the data plane.
o Double marking: each packet uses two marking bits. One bit is
used as a color indicator, and one is used as a timestamping
indicator. This method resolves the drawbacks raised for the two
previous methods, at the expense of an extra bit in the packet
header.
Mizrahi, et al. Expires September 6, 2017 [Page 3]
Internet-Draft Multiplexed Alternate Marking March 2017
The double marking method allows for accurate measurement without
incurring expensive computational load. However, in some cases
allocating two bits for passive measurement is not possible. For
example, if alternate marking is implemented over IPv4, allocating 2
marking bits in the IPv4 header is challenging, as every bit in the
20-octet header is costly; one of the possible approaches discussed
in [I-D.ietf-ippm-alt-mark] is reserve one or two bits from the DSCP
field for remarking. In this case every marking bit comes at the
expense of reducing the DSCP range by a factor of two.
This memo extends the marking method of [I-D.ietf-ippm-alt-mark].
The method introduced in this document uses a single marking bit in
the packet header, while providing the advantages of the double
marking method. In a nutshell, the color indicator and the timestamp
indicator are multiplexed into a single bit. There is an underlying
assumption that the two MPs that take part in the measurement are
time-synchronized.
2. Terminology
2.1. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
2.2. Abbreviations
MP Measurement Point
MPLS Multiprotocol Label Switching
DSCP Differentiated Services Code Point
LSP Label Switched Path
SFL Synonymous Flow Label [I-D.bryant-mpls-sfl-framework]
3. Alternate Marking using a Multiplexed Marking Bit
3.1. Overview
This section introduces a method that uses a single marking bit that
serves two purposes: a color indicator, and a timestamp indicator.
The double marking method that was discussed in the previous section
uses two 1-bit values: a color indicator C, and a timestamp indicator
T. The multiplexed marking bit, denoted by M, is an exclusive or
between these two values: M = C XOR T.
Mizrahi, et al. Expires September 6, 2017 [Page 4]
Internet-Draft Multiplexed Alternate Marking March 2017
An example of the use of the multiplexed marking bit is depicted in
Figure 2. The example considers two routers, R1 and R2, that use the
multiplexed bit method to measure traffic from R1 to R2. In each
block R1 designates one of the packets for delay measurement. In
each of these designated packets the value of the multiplexed bit is
reversed compared to the other packets in the same block, allowing R2
to distinguish the designated packets from the other packets.
A: packet with color 0
B: packet with color 1
Packets AAAAAAAAAA BBBBBBBBBB AAAAAAAAAA BBBBBBBBBB AAAAAAAAAA
Time ---------------------------------------------------------->
| | | | |
| Block 1 | Block 2 | Block 3 | Block 4 | Block 5 ...
| | | | |
Color 0000000000 1111111111 0000000000 1111111111 0000000000
^ ^ ^ ^ ^
Packets | | | | |
marked for | | | | |
timestamping | | | | |
v v v v v
Muxed bit 0000100000 1111011111 0000100000 1111101111 0001000000
Figure 2: Alternate marking with multiplexed bit.
3.2. Timing and Synchronization Aspects
It is assumed that all MPs are synchronized to a common reference
time with an accuracy of +/- A/2. Thus, the difference between the
clock values of any two MPs is bounded by A. Clocks can be
synchronized for example using NTP [RFC5905], PTP [IEEE1588], or by
other means. The common reference time is used for dividing the time
domain into equal-sized measurement periods, such that all packets
forwarded during a measurement period have the same color, and
consecutive periods have alternating colors.
The single marking bit incorporates two multiplexed values. From the
monitoring MP's perspective, the two values are Time-Division
Multiplexed (TDM), as depicted in Figure 3. It is assumed that the
start time of every measurement period is known to both the
initiating MP and the monitoring MP. If the measurement period is L,
then during the first and the last L/4 time units of each block the
marking bit is interpreted by the monitoring MP as a color indicator.
During the middle part of the block, the marking bit is interpreted
as a timestamp indicator; if the value of this bit is different than
Mizrahi, et al. Expires September 6, 2017 [Page 5]
Internet-Draft Multiplexed Alternate Marking March 2017
the color value, the corresponding packet is used as a reference for
delay measurement.
+--- Beginning of measurement period
|
v
...BBBBBBBBB | AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA | BBBBBBBBB...
|<======================================>|
| L |
<========>|<========><==================><========>|<========>
L/4 L/4 L/2 L/4 L/4
<===================><==================><===================>
Detect color Detect timestamping Detect color
change indication change
Figure 3: Multiplexed marking field interpretation at the receiving
measurement point.
In order to prevent ambiguity in the receiver's interpretation of the
marking field, the initiating MP is permitted to set the timestamp
indication only during a specific interval, as depicted in Figure 4.
Since the receiver is willing to receive the timestamp indication
during the middle L/2 time units of the block, the sender refrains
from sending the timestamp indication during a guardband interval of
d time units at the beginning and end of the L/2-period.
+--- Beginning of measurement period
|
v
...BBBBBBBBB | AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA | BBBBBBBBB...
|<======================================>|
| L |
<========>|<========>|<================>|<========>|
L/4 L/4 | L/2 | L/4
<=>|<=> <=>|<=>
d d d d
<==========>
permissible
timestamping
indication
interval
Figure 4: A time domain view.
Mizrahi, et al. Expires September 6, 2017 [Page 6]
Internet-Draft Multiplexed Alternate Marking March 2017
The guardband d is given by d = A + D_max - D_min, where A is the
clock accuracy, D_max is an upper bound on the network delay between
the MPs, and D_min is a lower bound on the delay. It is
straightforward from Figure 4 that d < L/4 must be satisfied. The
latter implies a minimal requirement on the synchronization accuracy.
All MPs must be synchronized to the same reference time with an
accuracy of +/- L/8. Depending on the system topology, in some
systems the accuracy requirement will be even more stringent, subject
to d < L/4. Note that the accuracy requirement of the conventional
alternate marking method [I-D.ietf-ippm-alt-mark] is +/- L/2, while
the multiplexed marking method requires an accuracy of +/- L/8.
Note that we assume that the middle L/2-period is designated as the
timestamp indication period, allowing a sufficiently long guardband
between the transitions. However, a system may be configured to use
a longer timestamp indication period or a shorter one, if it is
guaranteed that the synchronization accuracy meets the guardband
requirements (i.e., the constraints on d).
4. Alternate Marking using Two Multiplexed Marking Values
As mentioned above, the color indicator is not necessarily a single
bit, but may be implemented by using two well-known values in one of
the header fields. For example, as defined in
[I-D.bryant-mpls-rfc6374-sfl], two MPLS Label values can be used to
indicate the two colors of a given LSP: the original Label value, and
a Synonymous Flow Label (SFL) value.
The bit multiplexing approach of Section 3 is applicable not only to
single-bit color indicators, but also to two-value indicators;
instead of using a single bit that is toggled between '0' and '1',
two values of the indicator field, U and W, can be used in the same
manner, allowing both loss and delay measurement to be performed
using only two reserved values. Thus, the multiplexing approach of
Figure 2 can be illustrated more generally with two values, U and W,
as depicted in Figure 5.
Mizrahi, et al. Expires September 6, 2017 [Page 7]
Internet-Draft Multiplexed Alternate Marking March 2017
A: packet with color 0
B: packet with color 1
Packets AAAAAAAAAA BBBBBBBBBB AAAAAAAAAA BBBBBBBBBB AAAAAAAAAA
Time ---------------------------------------------------------->
| | | | |
| Block 1 | Block 2 | Block 3 | Block 4 | Block 5 ...
| | | | |
Color 0000000000 1111111111 0000000000 1111111111 0000000000
^ ^ ^ ^ ^
Packets | | | | |
marked for | | | | |
timestamping | | | | |
v v v v v
Muxed UUUUWUUUUU WWWWUWWWWW UUUUWUUUUU WWWWWUWWWW UUUWUUUUUU
marking
values
Figure 5: Alternate marking with two multiplexed marking values, U
and W.
5. IANA Considerations
This memo includes no requests from IANA.
6. Security Considerations
The security considerations of the alternate marking method are
discussed in [I-D.ietf-ippm-alt-mark]. Specifically, the method that
is defined in this document requires slightly more stringent
synchronization than the conventional marking method, potentially
making the method more vulnerable to attacks on the time
synchronization protocol. A detailed discussion about the threats
against time protocols and how to mitigate them is presented in
[RFC7384].
7. References
7.1. Normative References
[I-D.ietf-ippm-alt-mark]
Fioccola, G., Capello, A., Cociglio, M., Castaldelli, L.,
Chen, M., Zheng, L., Mirsky, G., and T. Mizrahi,
"Alternate Marking method for passive performance
monitoring", draft-ietf-ippm-alt-mark-04 (work in
progress), March 2017.
Mizrahi, et al. Expires September 6, 2017 [Page 8]
Internet-Draft Multiplexed Alternate Marking March 2017
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
7.2. Informative References
[I-D.bryant-mpls-rfc6374-sfl]
Bryant, S., Chen, M., Li, Z., Swallow, G., Sivabalan, S.,
Mirsky, G., and G. Fioccola, "RFC6374 Synonymous Flow
Labels", draft-bryant-mpls-rfc6374-sfl-03 (work in
progress), October 2016.
[I-D.bryant-mpls-sfl-framework]
Bryant, S., Chen, M., Li, Z., Swallow, G., Sivabalan, S.,
and G. Mirsky, "Synonymous Flow Label Framework", draft-
bryant-mpls-sfl-framework-02 (work in progress), October
2016.
[IEEE1588]
IEEE, "IEEE 1588 Standard for a Precision Clock
Synchronization Protocol for Networked Measurement and
Control Systems Version 2", 2008.
[RFC5905] Mills, D., Martin, J., Ed., Burbank, J., and W. Kasch,
"Network Time Protocol Version 4: Protocol and Algorithms
Specification", RFC 5905, DOI 10.17487/RFC5905, June 2010,
<http://www.rfc-editor.org/info/rfc5905>.
[RFC7384] Mizrahi, T., "Security Requirements of Time Protocols in
Packet Switched Networks", RFC 7384, DOI 10.17487/RFC7384,
October 2014, <http://www.rfc-editor.org/info/rfc7384>.
Authors' Addresses
Tal Mizrahi
Marvell
6 Hamada st.
Yokneam
Israel
Email: talmi@marvell.com
Mizrahi, et al. Expires September 6, 2017 [Page 9]
Internet-Draft Multiplexed Alternate Marking March 2017
Giuseppe Fioccola
Telecom Italia
Via Reiss Romoli, 274
Torino 10148
Italy
Email: giuseppe.fioccola@telecomitalia.it
Mach(Guoyi) Chen
Huawei Technologies
Email: mach.chen@huawei.com
Lianshu Zheng
Huawei Technologies
Email: vero.zheng@huawei.com
Greg Mirsky
USA
Email: gregimirsky@gmail.com
Mizrahi, et al. Expires September 6, 2017 [Page 10]