The twping RPC call has the following YANG definition.

    rpc twping {
        description "Measure the round trip time using TWAMP";
        typedef time-interval-ms {
            description "Floating point value representing a time interval";
            type decimal64 {
                fraction-digits 12;
            }
            units "milliseconds";
        }
        grouping min-max-time {
            leaf min {
                description "Minimum time observed during the sample period";
                type time-interval-ms;
            }
            leaf max {
                description "Maximum time observed during the sample period";
                type time-interval-ms;
            }
        }
        grouping addr-port {
            leaf address {
                description "IP address or domain name";
                type union {
                    type types:ip-address;
                    type types:domain-name;
                }
            }
            leaf port {
                description "Port number";
                type inet:port-number;
            }
        }
        grouping time-stats {
            uses min-max-time;
            leaf median {
                description "Median time observed during the sample period";
                type time-interval-ms;
            }
            leaf error {
                description "Calculated error for timing values";
                type time-interval-ms;
            }
            leaf pdv {
                description "Packet Delay Variation";
                type time-interval-ms;
            }
        }
        grouping hops {
            leaf diff-num-ttl {
                description "A count of how many different hop count values were observed during the test.";
                type uint32;
            }
            leaf min {
                description "Minimum number of hops taken by a test packet";
                type uint32;
            }
            leaf max {
                description "Maximum number of hops taken by a test packet";
                type uint32;
            }
        }
        input {
            leaf host {
                description "IP address or domain name of the test reflector";
                type union {
                    type types:ip-address;
                    type types:domain-name;
                }
                mandatory true;
            }
            leaf count {
                description "Number of test packets to send";
                type uint32 {
                    range 1..1000;
                }
                default 100;
            }
            leaf padding {
                description "Size of the padding to add to each test packet";
                type uint32 {
                    range 0..65000;
                }
                units "bytes";
            }
            leaf session-count {
                description "Number of test sessions to create and use";
                type uint32 {
                    range 1..65535;
                }
                default 1;
            }
            leaf test-dscp-value {
                description "RFC 2474 style DSCP value for TOS byte in test packets";
                type uint32 {
                    range 0..63;
                }
                default 0;
            }
            leaf control-port {
                description "Port to be used for the server control connection";
                type inet:port-number {
                    range 1..65535;
                }
                default 862;
            }
            leaf interval {
                description "Mean average time between
                         each test packet sent";
                type decimal64 {
                    fraction-digits 12;
                    range 0.0..max;
                }
                units "seconds";
            }
            container port-range {
                must "start <= end" {
                    error-message
                        "port-range start must be lower than or equal to port-range end";
                }
                must "(end - start + 1) >= ../session-count" {
                    description
                        "Each session uses a different port
                         number, therefore, there must be
                         at least as many available ports
                         in the port-range as sessions that
                         are going to be opened";
                    error-message "Size of the port-range must be at least as large as session-count";
                }
                leaf start {
                    description "The lowest port number that can be used during the test";
                    type inet:port-number {
                        range 1..65535;
                    }
                    default 8760;
                }
                leaf end {
                    description "The highest port number that can be used during the test";
                    type inet:port-number {
                        range 1..65535;
                    }
                    default 8960;
                }
            }
            container authentication {
                presence "Enables authentication";
                leaf mode {
                    description "Authentication mode";
                    type enumeration {
                        enum "authenticate";
                        enum "encrypt";
                        enum "mixed";
                    }
                    default "authenticate";
                }
                leaf user {
                    description "User name";
                    type string {
                        length 1..16;
                    }
                    mandatory true;
                }
                leaf passphrase {
                    description "Passphrase for user";
                    type string {
                        length 1..1024;
                    }
                    mandatory true;
                }
            }
        }
        output {
            list results {
                key sid;
                leaf sid {
                    description "Session Identifier";
                    type string;
                }
                container source {
                    description "Source address that test packets originated from";
                    uses addr-port;
                }
                container destination {
                    description "Destination address of the test reflector";
                    uses addr-port;
                }
                container packets {
                    leaf time-of-first {
                        description "Time that the first test packet was sent";
                        type ietf:date-and-time;
                    }
                    leaf time-of-last {
                        description "Time that the last test packet was sent";
                        type ietf:date-and-time;
                    }
                    leaf num-pkts-sent {
                        description "Number of test packets that were sent";
                        type uint32;
                    }
                    leaf num-pkts-lost {
                        description "Number of test packets that were lost";
                        type uint32;
                    }
                    leaf send-duplicates {
                        description "Number of duplicate test packets received by the reflector";
                        type uint32;
                    }
                    leaf reflect-duplicates {
                        description "Number of duplicate test packets received by the sender";
                        type uint32;
                    }
                }
                container round-trip-time {
                    description "Total round trip time, from when the test packet is sent from the test 
                                 client, until it is received back from the reflector";
                    uses time-stats;
                }
                container send-time {
                    description "Wire time for test packets to go from sender to reflector";
                    uses time-stats;
                }
                container reflect-time {
                    description "Wire time for test packets to go from the reflector, back to the sender";
                    uses time-stats;
                }
                container reflector-processing-time {
                    description "Time taken to process test packets within the reflector";
                    uses min-max-time;
                }
                container send-hops {
                    description "Number of hops taken by the test packets going from the sender to 
                                 the reflector.";
                    uses hops;
                }
                container reflect-hops {
                    description "Number of hops taken by the test packets going from the reflector back to 
                                 the sender";
                    uses hops;
                }
            }
        }
        configd:call-rpc "twamp-ping-rpc";
    }