Access 4.0: A valuable lesson in network transformation

The Access 4.0 broadband deployment by Deutsche Telekom has deepened its understanding of the intricacies of network transformation. The Access 4.0 team discusses what it has learnt and reflects on the issues a mass deployment raises.

Deutsche Telekom’s Access 4.0 platform has been delivering broadband services for nearly half a year.

But the operator has deliberately limited the deployment of the next-generation fibre-to-the-x platform to one central office in Stuttgart.

Robert SoukupThe system is fully functional, says Robert Soukup, senior program manager at Deutsche Telekom, but the operator wants to understand the processes involved so they can be automated before it starts the widescale deployment.

“Now we can see where the gaps are and what we need to adapt internally,” says Hans-Jörg Kolbe, chief engineer and head of SuperSquad Access 4.0 at Deutsche Telekom.

This will take the rest of the year. Only if this final check is successful will the Access 4.0 platform be rolled out across the operator’s 1,000 central offices in Germany.

Disaggregation

The Access 4.0 platform uses all the ingredients of network transformation: the platform is a disaggregated design running software-based network functions on white-box switches and servers as well as stackable white-box passive optical networking (PON) equipment.

The Access 4.0 programme came about after the operator conducted a detailed study of the costs involved in building networks. At the same time, the Central Office Re-architected as a Datacentre (CORD) industry initiative began.

Deutsche Telekom decided to assess CORD to determine how combining cloud technologies with access hardware would work and the possible cost benefits.

The operator quickly realised that CORD would reduce costs and once it built an Access 4.0 prototype, further cost savings and operational benefits were identified. CORD has since evolved to become the ONF’s Software Defined Networking (SDN) Enabled Broadband Access (SEBA) solution on which Access 4.0 is based.

But given its focus on networking costs, the operator hadn’t considered the far-reaching changes associated with adopting white boxes and software-hardware disaggregation, nor how a software-based architecture could shorten service introduction times. Both have since been confirmed.

Source: Deutsche Telekom

Architecture

The Access 4.0 platform uses two components developed by the Open Networking Foundation (ONF): Voltha and the SEBA reference design.

Voltha provides a common control and management system for PON white boxes while making the PON network look to the SDN controller as a programmable switch. In effect, the PON optical line terminal (OLT) is abstracted so it can be treated as a switch.

SEBA supports several fixed broadband technologies including the GPON and XGS-PON standards. Both Voltha and SEBA continue to be developed by the ONF; a Voltha version 2.7 has been announced as has a version 2.0 of SEBA.

Deutsche Telekom has now interfaced the Access 4.0 architecture to its IP core that is based on equipment from different vendors. 

Challenges

Soukup stresses that a working system in the lab is very different to having a platform ready for widescale deployment.

One issue to address is security. The platform must also go through a series of planning processes and be integrated with the telco’s IT systems. Both issues were the focus of the Access 4.0 work in 2020.

“In the lab, all the wiring, cabling and planning doesn’t have to be documented that much,” says Soukup. But a field deployment requires the involvement of many staff in Deutsche Telekom’s infrastructure organisation.

“Each is responsible for a certain piece that you need in your chain, and they need to be aligned to get the maximum outcome,” says Soukup.

The Stuttgart deployment uses DT’s business support system/operations support system (BSS/OSS) stack without needing any tweaks but it is still highly manual. “This year we want to learn to do the processes right and then automate,” says Soukup. “There is a zoo of microservices in there that need to be managed and tested.”

Cloud-native

The ONF’s Voltha framework is a cloud-native design that uses containers and microservices which Deutsche Telekom has embraced for its own SDN control framework, what it calls PAO (POD access orchestrator). “Voltha is just the tip of the iceberg,” says Soukup. “The PAO is the heavy thing above and is the orchestrator that uses Voltha for the OLT/ONU.”

“We have a microservice approach, we use Docker containers and it is run on a distributed Kubernetes platform,” says Kolbe. “It allows us to slice the problem into digestible units.”

The POD’s business processes, written by the operator, also use microservices. The approach has an inherent messaging system whereby a microservice takes a message, acts on it, and returns it before being picked up by another microservice. “By doing so, you can implement any kind of business logic,” says Kolbe.

Orchestration, automation and OSS

The orchestration of the service at the point of delivery, as performed by the PAO SDN controller, is a local one while Kubernetes orchestrates the microservices. Deutsche Telekom is also investigating orchestration across sites but that is not a priority of the Access 4.0 work.

As for automation, first efforts didn’t work as expected. “When cloud stuff hits networking with VLANs, UDP (User Datagram Protocol) traffic, NATs (network address translations) and ACLs (access control lists); this we had to learn the hard way,” says Kolbe.

For the OSS, Deutsche Telekom has deliberate demarcation lines between process and production IT. The process IT involves the execution and management of the business processes while the production IT manages the live network.

“If you have the process and production mixed, if you have technology-specifics in the OSS, then if you replace a line card, for example, you have to amend the OSS,” says Soukup. “Access 4.0 does this differently and much smarter.”

The operator’s IT department for the fibre rollout has thus separated the technology-specific aspects from the service side, he says.

Learnings

When Access 4.0 went live late last year, intense videoconferencing calls took place each day to tackle the teething problems, and this lasted 10 days.

Hans-Jörg Kolbe“One thing I realised was that whenever we ran into something, we could fix it ourselves,” says Kolbe. “Even I fixed something.”

Because the operator understood the system’s workings, it could solve issues, and quickly. “No calling someone and waiting for a binary to be delivered,” says Kolbe.

Soukup highlights the cost savings. “Deutsche Telekom has issued request-for-quotations (RFQs),” says Soukup. “At least for the hardware, the numbers are even lower than we anticipated.”

The Access 4.0 team also confirmed that disaggregation works. Deutsche Telekom has connected a bare metal router/ Broadband Network Gateway (BNG) from RtBrick to its IP core network. “This phone would ring if something was broken,” says Kolbe, touching his handset. “It hasn’t.”

As for SDN and microservices, the operator stresses that the system has yet to be scaled in the live network but what is deployed works end-to-end.

Network transformation

Access 4.0 has been Deutsche Telekom’s forerunner disaggregation project but now other teams are working on projects, says Kolbe, including home gateways and disaggregated routing.

Deutsche Telekom is working with Vodafone, Orange and Telefonica to promote Open RAN that disaggregates the radio access network (RAN).

“Disaggregation has become very important and Open RAN as well as 5G core are other big disaggregation topics,” says Gero Schultz, head of Supersquad Packet Core that includes 5G.

Gero SchultzDeutsche Telekom stresses the importance of collaborating with fellow CSPs, even ones that compete in shared markets, citing Open RAN and the Telecom Infra Project (TIP) as examples.

“If we have a thought, we go to other operators and test the waters to see if they, and the vendors, are interested,” says Kolbe.

“We need to share with other operators,” adds Soukup. “We are just too small, one cog in the system.”

One issue that the Access 4.0 work has raised is that the operator has to be selective in what it chooses to do in-house.

“We have shown with Access 4.0 that a telco can go very far in what it can do,” says Soukup. “The question is: do we want to do this in-house and what is the core technology that we must keep for good?”

Deutsche Telekom is also addressing the ecosystem at key spots to make sure all the pieces it needs are available.

“There are going to be vendors, start-ups, consultants, operators, all software-driven,” says Kolbe. “The set-up is changing dramatically but there will always be these roles.”