Passing along for discussion

"Globally Synchronized Time via Datacenter Networks"  SIGCOMM '16=20

In this paper, we present Datacenter Time Protocol (DTP), a clock synchroni=
zation protocol that does not use packets at all, but is able to achieve na=
nosecond precision. In essence, DTP uses the physical layer of network devi=
ces to implement a decentralized clock synchronization protocol. By doing s=
o, DTP eliminates most non-deterministic elements in clock synchronization =
protocols. Further, DTP uses control messages in the physical layer for com=
municating hundreds of thousands of protocol messages without interfering w=
ith higher layer packets. Thus, DTP has virtually zero overhead since it do=
es not add load at layers 2 or higher layers. It does require replacing net=
work devices, which can be done incrementally. We demonstrate that the prec=
ision provided by DTP is bounded by 25.6 nanoseconds for directly connected=
 nodes, and in general, is bounded by 4TD where D is the longest distance b=
etween any two servers in a network in terms of number of hops and T is the=
 period of the fastest clock (=E2=89=88 6.4ns). Moreover, in software, a DT=
P daemon can access the DTP clock with usually better than 4T (=E2=89=88 25=
..6ns) precision. As a result, the end-to-end precision can be better than 4=
T D + 8T nanoseconds. By contrast, the precision of the state of the art pr=
otocol is not bounded: The precision is hundreds of nanoseconds when a netw=
ork is idle and can decrease to hundreds of microseconds when a network is =
heavily congested.

http://www.cs.cornell.edu/~vishal/papers/dtp_2016.pdf

Ki Suh Lee, Han Wang, Vishal Shrivastav, Hakim Weatherspoon
Computer Science Department

kimo wrote:
> Passing along for discussion
> 
> "Globally Synchronized Time via Datacenter Networks"  SIGCOMM '16 
> 
> In this paper, we present Datacenter Time Protocol (DTP), a clock synchronization protocol that does not use packets at all, but is able to achieve nanosecond precision. In essence, DTP uses the physical layer of network devices to implement a decentralized clock synchronization protocol. By doing so, DTP eliminates most non-deterministic elements in clock synchronization protocols. Further, DTP uses control messages in the physical layer for communicating hundreds of thousands of protocol messages without interfering with higher layer packets. Thus, DTP has virtually zero overhead since it does not add load at layers 2 or higher layers. It does require replacing network devices, which can be done incrementally. We demonstrate that the precision provided by DTP is bounded by 25.6 nanoseconds for directly connected nodes, and in general, is bounded by 4TD where D is the longest distance between any two servers in a network in terms of number of hops and T is the period of the fastest
 clock (≈ 6.4ns). Moreover, in software, a DTP daemon can access the DTP clock with usually better than 4T (≈ 25.6ns) precision. As a result, the end-to-end precision can be better than 4T D + 8T nanoseconds. By contrast, the precision of the state of the art protocol is not bounded: The precision is hundreds of nanoseconds when a network is idle and can decrease to hundreds of microseconds when a network is heavily congested.
> 
> http://www.cs.cornell.edu/~vishal/papers/dtp_2016.pdf
> 
> Ki Suh Lee, Han Wang, Vishal Shrivastav, Hakim Weatherspoon
> Computer Science Department

Haven't read all of this paper, yet, but sounds interesting.

Thanks for sharing it.

Martin
-- 
Martin Burnicki

Meinberg Funkuhren
Bad Pyrmont
Germany

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