RTLoss_Passive_IP-TCP_RFC8912sec10_Packet_Count All section numbers below refer to RFC 8912  10.1. Summary    This category includes multiple indexes to the Registry Entries: the    element ID and Metric Name. 10.1.1. ID (Identifier)   26 10.1.2. Name    RTLoss_Passive_IP-TCP_RFC8912sec10_Packet_Count 10.1.3. URI    URL: https://www.iana.org/assignments/performance-metrics/RTLoss_Passive_IP-TCP_RFC8912sec10_Packet_Count 10.1.4. Description    RTLoss:  This metric assesses the estimated loss count for TCP packets     constituting a single connection, exchanged between two hosts. We consider     the measurement of round-trip delay based on a single Observation Point (OP)  [RFC7011] somewhere     in the network. The output is the estimated loss count for the measurement interval. 10.1.5. Change Controller    IETF 10.1.6. Version (of Registry Format)    1.0 10.2. Metric Definition    This category includes columns to prompt the entry of all necessary    details related to the metric definition, including the RFC reference    and values of input factors, called "Fixed Parameters". 10.2.1. Reference Definition    Almes, G., Kalidindi, S., and M.  Zekauskas, "A Round-trip Delay    Metric for IPPM", RFC 2681, DOI 10.17487/RFC2681, September 1999,    .  [RFC2681]    Although there is no RFC that describes Passive Measurement of round-    trip delay, the parallel definition for Active Measurement is    provided in [RFC2681].    This metric definition uses the terms "singleton" and "sample" as    defined in Section 11 of [RFC2330].  (Section 2.4 of [RFC2681]    provides the reference definition of the singleton (single value)    round-trip delay metric.  Section 3.4 of [RFC2681] provides the    reference definition expanded to cover a multi-singleton sample.)    With the OP [RFC7011] typically located between the hosts    participating in the TCP connection, the round-trip delay metric    requires two individual measurements between the OP and each host,    such that the Spatial Composition [RFC6049] of the measurements yields    a round-trip delay singleton (we are extending the composition of    one-way subpath delays to subpath round-trip delay).    Using the direction of TCP SYN transmission to anchor the    nomenclature, host A sends the SYN, and host B replies with SYN-ACK    during connection establishment.  The direction of SYN transfer is    considered the Forward direction of transmission, from A through the    OP to B (the Reverse direction is B through the OP to A).    Traffic Filters reduce the packet streams at the OP to a Qualified    bidirectional flow of packets.    In the definitions below, Corresponding Packets are transferred in    different directions and convey a common value in a TCP header field    that establishes correspondence (to the extent possible).  Examples    may be found in the TCP timestamp fields. The definition of round-trip loss count uses the nomenclature developed above, based on observation of the TCP header sequence numbers and storing the sequence number gaps observed. Packet losses can be inferred from: Out-of-order segments:     TCP segments are transmitted with monotonically increasing sequence numbers, but these segments may be received out of order. Section 3 of [RFC4737] describes the notion of "next expected" sequence numbers, which can be adapted to TCP segments (for the purpose of detecting reordered packets). Observation of out-of-order segments indicates loss on the path prior to the OP and creates a gap. Duplicate segments:     Section 2 of [RFC5560] defines identical packets and is suitable for evaluation of TCP packets to detect duplication. Observation of segment duplicates a segment previously observed (and thus no corresponding observed segment gap) indicates loss on the path following the OP (e.g., the segment overlaps part of the octet stream already observed at the OP). Each observation of an out-of-order or duplicate segment infers a singleton of loss, but the composition of round-trip loss counts will be conducted over a measurement interval that is synonymous with a single TCP connection. With the above observations in the Forward direction over a measurement interval, the count of out-of-order and duplicate segments is defined as RTL_fwd. Comparable observations in the Reverse direction are defined as RTL_rev. For a measurement interval (corresponding to a single TCP connection) T0 to Tf, the REQUIRED Composition Function for the two single-direction counts of inferred loss is: RTLoss = RTL_fwd + RTL_rev 10.2.2. Fixed Parameters    Traffic Filters:       IPv4 header values:          DSCP:  Set to 0          Protocol:  Set to 06 (TCP)       IPv6 header values:          DSCP:  Set to 0          Hop Count:  Set to 255          Next Header:  Set to 6 (TCP)          Flow Label:  Set to 0          Extension Headers:  None       TCP header values:          Flags:  ACK, SYN, FIN, set as required          Timestamps Option (TSopt):  Set.  See Section 3.2 of [RFC7323] 10.3. Method of Measurement    This category includes columns for references to relevant sections of    the RFC(s) and any supplemental information needed to ensure an    unambiguous method for implementations. 10.3.1. Reference Methods    The foundational methodology for this metric is defined in Section 4    of [RFC7323] using the Timestamps option with modifications that    allow application at a mid-path OP [RFC7011].  Further details and    applicable heuristics were derived from [Strowes] and [Trammell-14].    The Traffic Filter at the OP is configured to observe a single TCP    connection.      For payload-bearing packets,  each observation of an out-of-order or     duplicate segment infers a loss count, but the composition of round-trip loss     counts will be conducted over a measurement interval that is synonymous     with a single TCP connection.        Method for Inferring Loss:    *  The OP tracks sequence numbers and stores gaps for each direction       of transmission, as well as the next expected sequence number as       discussed in [Trammell-14] and [RFC4737].  Loss is inferred from       out-of-order segments and duplicate segments.    Loss Measurement Filtering Heuristics:    *  [Trammell-14] adds a window of evaluation based on the RTDelay.    *  Distinguish reordered packets from out-of-order segments due to       loss, because the sequence number gap is filled during the same       RTDelay window.  Segments detected as reordered according to       [RFC4737] MUST reduce the loss count inferred from out-of-order       segments.    *  Spurious (unneeded) retransmissions (observed as duplicates) can       also be reduced in this way, as described in [Trammell-14].   Sources of Error:    *  A key source of RTLoss error is observation loss, as described in       Section 3 of [Trammell-14]. 10.3.2. Packet Stream Generation    N/A 10.3.3. Traffic Filtering (Observation) Details    The Fixed Parameters above give a portion of the Traffic Filter.    Other aspects will be supplied as Runtime Parameters (below). 10.3.4. Sampling Distribution    This metric requires a complete sample of all packets that qualify    according to the Traffic Filter criteria. 10.3.5. Runtime Parameters and Data Format    Runtime Parameters are input factors that must be determined,    configured into the measurement system, and reported with the results    for the context to be complete.    Src:  The IP address of the host in the host A Role (format       ipv4-address-no-zone value for IPv4 or ipv6-address-no-zone value       for IPv6; see Section 4 of [RFC6991]).    Dst:  The IP address of the host in the host B Role (format       ipv4-address-no-zone value for IPv4 or ipv6-address-no-zone value       for IPv6; see Section 4 of [RFC6991]).    T0:  A time, the start of a measurement interval (format "date-time"       as specified in Section 5.6 of [RFC3339]; see also "date-and-time"       in Section 3 of [RFC6991]).  The UTC Time Zone is required by       Section 6.1 of [RFC2330].  When T0 is "all-zeros", a start time is       unspecified and Tf is to be interpreted as the duration of the       measurement interval.  The start time is controlled through other       means.    Tf:  Optionally, the end of a measurement interval (format       "date-time" as specified in Section 5.6 of [RFC3339]; see also       "date-and-time" in Section 3 of [RFC6991]), or the duration (see       T0).  The UTC Time Zone is required by Section 6.1 of [RFC2330].       Alternatively, the end of the measurement interval MAY be       controlled by the measured connection, where the second pair of       FIN and ACK packets exchanged between host A and host B       effectively ends the interval.    TTL or Hop Limit:  Set at desired value. 10.3.6. Roles    host A:  Launches the SYN packet to open the connection.  The Role of       "host A" is synonymous with the IP address used at host A.    host B:  Replies with the SYN-ACK packet to open the connection.  The       Role of "host B" is synonymous with the IP address used at host B. 10.4. Output    This category specifies all details of the output of measurements    using the metric. 10.4.1. Type    For RTLoss: The count of lost packets. 10.4.2. Reference Definition    For all output types:    T0:  The start of a measurement interval (format "date-time" as       specified in Section 5.6 of [RFC3339]; see also "date-and-time" in       Section 3 of [RFC6991]).  The UTC Time Zone is required by       Section 6.1 of [RFC2330].    Tf:  The end of a measurement interval (format "date-time" as       specified in Section 5.6 of [RFC3339]; see also "date-and-time" in       Section 3 of [RFC6991]).  The UTC Time Zone is required by       Section 6.1 of [RFC2330].  The end of the measurement interval MAY       be controlled by the measured connection, where the second pair of       FIN and ACK packets exchanged between host A and host B       effectively ends the interval.    RTLoss_Passive_IP-TCP_RFC8912sec10_Packet_Count: The count of lost packets.    Observation of an out-of-order segment or duplicate segment infers a    loss count, after application of the Definitions of Section 10.2.1 and the Loss Measurement     Filtering Heuristics of Section 10.3.1.  The composition of round-trip loss counts will    be conducted over a measurement interval that is synonymous with a    single TCP connection.    For a measurement interval (corresponding to a single TCP connection)    T0 to Tf, the REQUIRED Composition Function for the two single-    direction counts of inferred loss is:    RTLoss = RTL_fwd + RTL_rev    Packet count:  The numeric value of the result is expressed in units       of lost packets, as a positive value of type uint64 (represents       integer values between 0 and 18446744073709551615, inclusively       (see Section 9.2 of [RFC6020]).  10.4.3. Metric Units    The round-trip loss count is expressed as a number of packets.     10.4.4. Calibration    Passive Measurements at an OP could be calibrated against an Active    Measurement (with loss emulation) at host A or host B, where the    Active Measurement represents the ground truth. 10.5. Administrative Items 10.5.1. Status    Current 10.5.2. Requester    RFC 8912 10.5.3. Revision    1.0 10.5.4. Revision Date    2021-11-17 10.6. Comments and Remarks    None