d integrity of the timing solution. There are several parameters described in Annex J of IEEE 1588- 2019 that can be used for performance monitoring. By observing those parameters and analyzing them for anomalies, such as unexpected values or unforeseen variations, alerts can be generated and acted upon. Chapter 12 provides more on the topic of operational deployments and timing verification. 11.5.1 Integrity Verification from IEEE 1588-2019 The ICV (from prong A) is calculated by applying a cryptographic hash function to ensure that un- authorized modifications of a message can be detected by the receiver. The AUTHENTICATION_TLV that carries this value is appended to the PTP message that it is validat- ing. The ICV is calculated according to a security algorithm selected and shared during the negoti- ation of the security parameters by the key distribution mechanism. Figure 11-15 shows the format of the TLV. TLV Type Security Key Identifier or Current Key Sequence ICV based on Parameter Disclosure Interval, depending number hash algorithm Pointer on verification scheme (optional) secParam keyID disclosedKey sequenceNo tlvType lengthField Indicator (optional) (optional) TLV length Security Parameter Disclosed key from Reserved field Indicator previous interval (optional) (optional) Figure 11-15 The AUTHENTICATION TLV The implementors of the ICV mechanism are required to support at least the HMAC-SHA256-128 algorithm, as defined in Federal Information Processing Standards (FIPS) PUB 198-1, which uses the SHA-256 hash combined with a keyed-hash message authentication code (HMAC) shortened to 128 bits of output. HMAC codes are also used in IPsec implementations as well as the Transport Layer Security (TLS) encryption package that is the basis of web browser, email, and other network encryption schemes. An HMAC is a type of message authentication hash or checksum that combines a cryptographic hash function and a secret cryptographic key. By doing this, the HMAC can be used to validate the integrity of the data as wel