Packet Probe Hardware Timestamping for Transit Delay Precision
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Solution Overview
Problem
Packet-switched networks face challenges in achieving precise time alignment due to their statistical nature, leading to significant transit delay variations, which can cause client devices to fall out of alignment and result in measurement errors when using conventional time-stamping methods.
Innovation Solution
A method and apparatus for precise time-stamping packets in packet networks, involving a packet probe that generates and updates time stamps in hardware based on a reference time source, with offsets to account for transmission and reception delays, enabling accurate measurement of transit delay and variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional time-stamping methods are used in packet-switched networks, then the measurement process is simple, but measurement precision deteriorates due to statistical nature of packet switching and transit delay variations
Solution Approach 1:
The patent applies preliminary action by pre-calculating and storing offset values that compensate for transit delay variations in packet-switched networks. The system performs preliminary measurements of delay variations and stores compensation offsets in lookup tables, so that when packets are timestamped, the pre-computed offsets are already available to correct for statistical variations in packet switching delays, thereby improving measurement precision without adding complex real-time processing.
Solution Approach 2:
The patent introduces an intermediary compensation mechanism that acts between the raw timestamp and the final measurement. Offset values serve as intermediaries that mediate the effect of packet switching statistical variations on the timestamp. The system inserts these offset corrections into the timestamping process, effectively filtering out the harmful statistical variations while preserving the deterministic timing information needed for precise measurements.
2Measurement precision
If hardware-based time-stamping is implemented, then measurement precision improves, but device complexity increases
Solution Approach 1:
The hardware timestamping system applies preliminary action by pre-computing offset values and storing them in lookup tables before actual timestamping operations. The complex calculations for compensating packet switching variations are performed in advance and stored, so the hardware timestamping unit only needs to perform simple table lookups and additions, thereby achieving high precision without requiring complex real-time hardware processing.
Solution Approach 2:
The hardware timestamping apparatus applies self-service by automatically selecting and applying the appropriate offset values from lookup tables based on current network conditions. The system monitors packet delay variations and automatically updates the offset compensation values without requiring external intervention or complex control logic, making the hardware implementation more manageable while maintaining high precision.
3Measurement precision
If offset compensation is applied to account for transmission delays, then measurement precision improves, but calculation complexity increases
Solution Approach 1:
The patent applies preliminary action by pre-calculating offset compensation values and storing them in lookup tables before actual timestamping operations. The complex calculations for determining appropriate offsets are performed in advance based on measured delay variations, and the results are stored for rapid retrieval during timestamping, thereby achieving high measurement accuracy without requiring complex real-time calculations.
Solution Approach 2:
The patent uses simple, easily computable offset values that can be rapidly calculated and discarded after use. Each offset value is a straightforward numerical compensation factor that requires minimal computational resources to calculate and apply. After being used to correct a timestamp, the offset value is discarded and replaced with a new one, allowing the system to achieve high precision through simple, disposable calculations rather than complex persistent computations.
Data Source
AI summary
A packet probe for a packet network accurately generates and monitors packets within the network. The packet probe supports packet generation and packet transmission. When a packet is ready for transmission, a hardware-based time stamp unit affixes a time stamp to the packet reflecting an actual transmission time. The packet probe also supports receiving, filtering, and time stamping received packets. When a packet is received, a packet filter determines whether the received packet should be stored in memory along with a time stamp reflecting an actual reception time.