The Problem With Jitter

Jitter has been around for as long as the telecommunications industry has been trying to shift bits and bytes from A to B. Jitter is not cool, it’s unloved and nobody wants it and just like the bore at an office party it won’t go away. Now, just to be clear, we are talking about physical layer jitter here i.e. the ability of clock recovery circuits to function correctly and to determine if the data is a one or a zero or the closure of an eye diagram in the time domain. If you are expecting to hear about packets or packet jitter then this blog is not for you!

The higher speed circuitry, required for 100GbE, makes jitter a much bigger challenge than it was in the past. It’s much more difficult to have clean, open eye diagrams free of noise at 25GHz clock speeds. This is specified in IEEE 802.3. However, when the Ethernet clock is also used as part of the synchronization chain (i.e. Synchronous Ethernet, or SyncE), then there is another jitter standard which also has to be met, ITU-T G.8262. This places limits on jitter at much lower frequencies to ensure jitter doesn’t propagate down the synchronization chain.

G.8262 specifies that a SyncE clock must not generate more than 1.2UI pk-pk jitter measured over the 20kHz to 200MHz frequency range. This is hard enough, but the sting in the tail is the jitter tolerance limit – the amount of jitter a clock must tolerate on its input and still function correctly. Jitter tolerance is defined in the form of a mask from 10Hz to 100kHz, with as much as 6445 UI of jitter (250ns) at 10Hz.

Much of the industry focus has been on meeting the Jitter Generation requirements but, in reality, experience shows that much of the equipment out there can struggle to meet the tight Jitter Tolerance limits; especially at the top end of the mask at frequencies around 100kHz. If I was concerned about the quality of the equipment I was about to approve that’s where I’d look. Just saying.

Tim Frost
Strategic Technology Manager, Calnex Solutions.

Recent Blogs

Related Blogs

Four Boardroom Members

How to Optimise Your IT Network and Spend

Feb 06, 2019
Network emulation can be a key tool to overcome barriers in getting the most out of your…
4884 Read more

Responding to IT Network Issues

Jan 22, 2019
If simple remedial scripts are not enough to fix an IT network issue, a more…
5510 Read more

Keeping Audiences 'In the Moment'

Nov 16, 2018
Today’s broadcast audiences are seeking more. They want user defined, on demand content.…
1846 Read more

Archived Blogs

1644 More
1831 More

Timing not Telecoms

Nov 08, 2016
1225 More

5G Coming Soon

Aug 22, 2016
1232 More

What is 1588 PTP?

Aug 04, 2016
1651 More

5G on the Horizon

Aug 01, 2016
1262 More

What is a PTP Clock?

Apr 09, 2016
1548 More

What is Time Error?

Oct 21, 2015
1255 More

LTE-A & VoLTE Rollout

Sep 22, 2015
1199 More

LTE Picks Up Speed

Aug 22, 2015
1181 More

What is the Time?

Aug 22, 2015
1204 More

Mobile and Sync

Aug 22, 2015
1175 More

What is SyncE?

Aug 22, 2015
2402 More
1307 More

Microwave Update

Aug 22, 2015
1278 More

Unravelling Standards

Aug 22, 2015
1254 More

Partial Progress?

Aug 22, 2015
1172 More

Interpreting ITU

Aug 22, 2015
1192 More

Confusion Rules!

Aug 22, 2015
1244 More

Basestations Need Sync

Aug 22, 2015
1238 More

ITSF 2015 Edinburgh

Aug 22, 2015
1185 More

India to Follow China?

Aug 07, 2015
1198 More

Click your area of interest below for more tutorials and real-world case studies.