Media diagnostics · Primary-source explanation; no UK IPTV implementation or account test. Instructions are based on publisher guidance; a UK IPTV account was not tested on this platform.
Work through the clocks first
Suppose a packet really spends five milliseconds travelling between two points. The receiving clock is accurate for this example, while the sending clock reads ten milliseconds ahead. At real time zero the sender stamps the packet as ten milliseconds. It arrives at real time five milliseconds, carrying that stamp. Subtracting the sender value from the receiver value gives minus five milliseconds. The journey was positive; the simple subtraction included a clock offset larger than the journey being measured.
Separate a measurement problem from a transport claim
RFC 7679 treats clock synchronization and its uncertainty as part of one-way delay measurement. Save the timestamp sources, synchronization method, resolution and available error estimate with any result. A clock adjustment during a session can also change how observations should be interpreted. None of this is established by noticing that two devices show the same minute on their home screens. Millisecond claims require information at a finer scale than that visual comparison can provide.
Choose a useful next comparison
If the clock relationship is unknown, describe the result as an unvalidated timestamp difference and keep the raw observations. A round-trip measurement from one clock can answer a different question without claiming to recover either one-way value. Do not repair a negative reading by silently changing its sign or setting it to zero; either operation hides the evidence. This example supports checking the measurement before blaming a stream or router. It supplies no measured delay for UK IPTV and no universal threshold for acceptable viewing.