Informer 278: 25 August 2015

In Informer 268 we advised you of a technical issue with Chorus' new Optical Network Terminal (ONT) that impacted end users using DHCP relay functionality. A second technical issue has been identified with the ONT affecting end users- sending packets modified due to mismatched MTU sizes across our NGA services.

View Informer 268 - DHCP relay issue with Chorus' new ultra-fast broadband ONT

What's happening?

As part of our wider network upgrade programme, we are deploying the next generation of Optical Network Terminal (ONT) for Ultra-Fast Broadband (UFB) installations. Despite rigorous testing of the new ONT before it was deployed, we have recently identified a further issue where the ONT does not forward packets with mismatched Maximum Transmission Unit (MTU) size.

MTU size is set by RSP network, RGW and/or end user equipment and as such, Chorus is unable to determine the scale and impact of this issue. To date the issue has only been picked it up in further testing and in one instance where RSP equipment was misconfigured. The previous version of the ONT forwarded these modified packets so misconfiguration issues were masked.

We have received a software fix for both the mismatched MTU issue and the previously identified DHCP relay issue. The fix has undergone pre-deployment testing prior to deployment into production, which is starting on the 25th August with completion by the 28th August. 

What's the detail?

While testing the software to fix the DHCP Relay problem, a second issue was identified where our new ONT does not forward packets modified in response to mismatched MTU sizes. This problem only occurs on our new ONT (G-240G-P model) which can be easily identified as it has “Type 200” on the top of the ONT and will also have a QR code. 

Packet modification where packets are divided into multiple packets is done to allow the transport of a larger frame size than the network between the source and destination can support. While our NGA services support a 2,000 Byte MTU, we have no visibility of either the hardware or software support or the configuration of the devices or applications outside of our network which may only support a smaller MTU. 

If End Users are using packet division to support applications or hardware then the impact of the ONT issue will be packet loss. This could appear as very low or broken throughput. 

Chorus and Alcatel-Lucent have managed to replicate, identify and solve the cause of the ONT discarding fragmented packets. The ONT software load which was being tested to resolve the DHCP Relay issue has been updated to also resolve this MTU mismatch issue. This software release has undergone detailed technical testing and is available in the CCIL for your testing on request. 

Starting on the 25th of August we will begin to roll out the new software to all G-240G-P ONTs in the network using BAU Service Event notifications. Your NOC will have already received notification of these planned changes which will involve a break in service of up to 5 minutes for affected ONTs during the maintenance window. 

All new installs from this date will automatically receive the new software version when the ONT is installed and connected to our network. 

This issue affects all NGA service variants – NGA Evolve (Bitstream 2), NGA Business (Bitstream 3/3a), NGA Education and NGA Voice.

Who do I contact?

For more information or specific updates, please contact your Service Delivery Manager.