Enhanced Alternate Marking Method

Abstract

This document extends the IPv6 Alternate Marking Option to provide enhanced capabilities and allow advanced functionalities. With this extension, it can be possible to perform thicker packet loss measurements and more dense delay measurements with no limitation for the number of concurrent flows under monitoring.¶

1. Introduction

The Alternate Marking [RFC8321] and Multipoint Alternate Marking [RFC8889] define the Alternate Marking technique that is a hybrid performance measurement method, per [RFC7799] classification of measurement methods. This method is based on marking consecutive batches of packets and it can be used to measure packet loss, latency, and jitter on live traffic.¶

The IPv6 AltMark Option [I-D.ietf-6man-ipv6-alt-mark] applies the Alternate Marking Method to IPv6, and defines an Extension Header Option to encode the Alternate Marking Method for both the Hop-by-Hop Options Header and the Destination Options Header. Similarly, SRv6 AltMark [I-D.fz-spring-srv6-alt-mark] defines how Alternate Marking data is carried as a TLV in the Segment Routing Header.¶

While the IPv6 AltMark Option implements the basic alternate marking methodology, this document defines extended data fields for the AltMark Option and provides enhanced capabilities to overcome some challenges and enable future proof applications.¶

It is worth mentioning that the enhanced capabilities are intended for further use and are optional.¶

Some possible enhanced applications MAY be:¶

1. thicker packet loss measurements: the single marking method of the base AltMark Option can be extended with additional marking bits in order to get shortest marking periods under the same timing conditions.¶
2. more dense delay measurements: than double marking method of the base AltMark Option can be extended with additional marking bits in order to identify down to each packet as delay sample.¶
3. increase the number of concurrent flows under monitoring: if the 20-bit FlowMonID is set independently and pseudo randomly, there is a 50% chance of collision for 1206 flows. The size of FlowMonIDcan can be extended to raise the entropy and therefore to increase the number of concurrent flows that can be monitored.¶

2. Data Fields Format

The Data Fields format is represented in Figure 1. An 4-bit NH(NextHeader) field is allocated from the Reserved field of IPv6 AltMark Option [I-D.ietf-6man-ipv6-alt-mark]. It is worth highlighting that remaining bits of the former Reserved field continue to be reserved.¶

 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
+---------------------------------------+-+-+-----------+-------+
|           FlowMonID                   |L|D|  Reserved |  NH   |
+---------------------------------------+-+-+-----------+-------+

The NH (NextHeader) field is used to indicate the extended data fields which are used for enhanced capabilities:¶

• NextHeader value of 0x00 is reserved for backward compatibility. It means that there is no extended data field attached.¶
• NextHeader values of 0x01-0x08 are reserved for private use or for experimentation.¶
• NextHeader value of 0x09 indicates the extended data fields. The format is showed in Figure 2.¶

 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
+---------------------------------------+-------+-------+-------+
|           FlowMonID Ext               | Flag  |  Len  |   R   |
+-------------------------------+-------+-------+-------+-------+
|           MetaInfo            |      Padding (variable)       |
+-------------------------------+-------------------------------+
//                    Padding (variable)                       //
+-------------------------------+-------------------------------+

where:¶

• FlowMonID Ext - 20 bits unsigned integer. This is used to extend the FlowMonID to reduce the conflict when random allocation is applied. The disambiguation of the FlowMonID field is discussed in IPv6 AltMark Option [I-D.ietf-6man-ipv6-alt-mark].¶
• Flag - A 4-bit flag to indicate the special purpose usage (see below).¶
• Len - Length. It indicates the length of the enhanced alternate marking extension in bytes.¶
• R - Reserved for further use. These bits MUST be set to zero on transmission and ignored on receipt.¶
• MetaInfo - A 16-bit Bitmap to indicate more meta data attached for the enhanced function (see below).¶
• Padding - These bits MUST be set to zero when not being used.¶

The Flag is defined in Figure 3 as:¶

• bit 0 - Measurement mode, M bit. M=0, indicates that it is for hop-by-hop monitoring. M=1, indicates that it is for end-to-end monitoring.¶
• bit 2 - Flow direction identification, F bit. This flag is used in the case backward direction flow monitoring is requested to be set up automatically. F=1, indicates that the flow direction is forward. F=0, indicates the flow direction is backward.¶
• others (shown as R) - Reserved. MUST be set to zero and ignored on receipt.¶

 0 1 2 3
+-------+
|M|R|F|R|
+-------+

The MetaInfo is defined in Figure 4 as a bit map as follows:¶

 0 1 2 3 4 5 6 7
+---------------+
|    MetaInfo   |
+---------------+

• bit 0: indicates a 6 bytes Timestamp is attached after the MetaInfo. Timestamp(s) stands for the number of seconds in the timestamp. It will overwrite the Padding after MetaInfo. Timestamp(ns) stands for the number of subseconds in the timestamp with the unit of nano second. This Timestamp is filled by the encapsulation node, and is taken all the way to the decapsulation node. So that all the intermediate nodes could compare it with its local time, and measure the one way delay.¶

   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
                                  +-------------------------------+
                                  |    Timestamp(s)               |
  +-------------------------------+-------------------------------+
  |                 Timestamp(ns)                                 |
  +---------------------------------------------------------------+
  

• bit 1: indicates the control information with the following data format is attached:¶

   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
  +---------------+---------------+-----------+-------------------+
  |  DIP Mask     |  SIP Mask     | Control   |    Period         |
  +---------------+---------------+-----------+-------------------+

  This is used to set up the backward direction flow monitoring. Where:¶

  • DIP Mask: is the length of the destination IP prefix.¶
  • SIP Mask: is the length of the source IP prefix.¶
  • Control: indicates more match fields to set up the backward direction flow monitoring.¶
  • Period: indicates the alternate marking period with the unit of second.¶

• bit 2: indicates a 4 bytes Sequence number with the following data format is attached after the MetaInfo. Sole Sequence cound be used to detect the out-of-order packets, in addition to the normal loss measurement. More over, the Sequence can be used together with the latency measurement, so as to get the per packet timestamp.¶

   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
  +---------------------------------------------------------------+
  |                          Sequence                             |
  +---------------------------------------------------------------+

It is worth noting that the meta data information specified above in Figure 5, Figure 6 and Figure 7 must be ordered according to the order of the MetaInfo bits.¶

5. References