Globally Synchronized Time via Datacenter Networks
| Autor: | Vishal Shrivastav, Han Wang, Ki Suh Lee, Hakim Weatherspoon |
|---|---|
| Rok vydání: | 2016 |
| Předmět: |
Computer Networks and Communications
Computer science computer.internet_protocol Real-time computing Round-trip delay time 02 engineering and technology Synchronization Clock synchronization Scheduling (computing) Protocol stack Protocol overhead 020204 information systems Server 0202 electrical engineering electronic engineering information engineering Overhead (computing) Electrical and Electronic Engineering Jitter business.industry Network packet Physical layer 020206 networking & telecommunications Networking hardware Computer Science Applications Time Protocol State (computer science) business computer Software Computer network |
| Zdroj: | SIGCOMM |
| Popis: | Synchronized time is critical to distributed systems and network applications in a datacenter network. Unfortunately, many clock synchronization protocols in datacenter networks such as NTP and PTP are fundamentally limited by the characteristics of packet-switched networks. In particular, network jitter, packet buffering and scheduling in switches, and network stack overheads add non-deterministic variances to the round trip time, which must be accurately measured to synchronize clocks precisely. We present the Datacenter Time Protocol (DTP), a clock synchronization protocol that does not use packets at all, but is able to achieve nanosecond precision. In essence, the DTP uses the physical layer of network devices to implement a decentralized clock synchronization protocol. By doing so, the DTP eliminates most non-deterministic elements in clock synchronization protocols and has virtually zero protocol overhead since it does not add load at layer-2 or higher at all. It does require replacing network devices, which can be done incrementally and with very small amount of hardware resource consumption. We demonstrate that the precision provided by DTP in hardware is bounded by 4TD where D is the longest distance between any two nodes in a network in terms of number of hops and T is the period of the fastest clock. The precision can be further improved by combining DTP with frequency synchronization. By contrast, the precision of the state-of-the-art protocol (PTP) is not bounded: The precision is hundreds of nanoseconds in an idle network and can decrease to hundreds of microseconds in a heavily congested network. |
| Databáze: | OpenAIRE |
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