By Chris Bastian
SVP, Engineering/CTO, SCTE-ISBE
The cable operator’s access network is a key asset to providing Internet services to customers. Customers are astute, as they are constantly comparing service offerings between cable, telco, satellite, and wireless network operators. How does the cable operator stay ahead of this competitive curve? By pushing itself and its vendor partners to perpetually develop and assess the latest access network technologies and enhancements.
Three network architecture changes are making their way to the cable access network:
- Remote PHY
- Fiber deeper into the network
- CMTS/CCAP virtualization
All three are designed to continually support the services that the customers expect today and into the foreseeable future. Note that individual operators will choose to deploy these enhancements to varying degrees.
In today’s network, the PHY layer, or the part of the network equipment that is responsible for supporting the electrical interfaces connecting to the physical medium (IEEE), is located in the network hub site. Remote PHY will move this layer out of the hub site and into the fiber node, providing the following benefits and challenges:
- With the fiber node closer to the customer’s home, better network performance – less noise, higher modulation, more capacity, and higher speeds – is achieved.
- Significant rack units (RUs) are freed up in the hub site, so space, power, and HVAC demands are reduced.
- Lowering operational expenses associated with alignment and maintenance, while improving network visibility due to the Remote PHY distributed intelligence.
- Potential integration with alternative last-mile access technologies, including PON and wireless.
- The fiber node environment is harsher than the environmentally controlled hub site.
- Interoperability testing is crucial between the CCAP layers remaining in the hub site and the PHY layer in the fiber node. Complicating this will be that these elements could be from different vendors.
- Timing/synchronization, as elements which were once co-located in the hub site could now be split miles apart.
- Ability to perform software and maintenance upgrades, which were previously conducted in a hub environment but will now be in an outdoor fiber node environment. There are also many more fiber nodes than hub sites, usually by an order of magnitude.
Simply defined, “fiber deeper” is driving fiber closer to the customer’s home. The legacy HFC network had fiber nodes serving hundreds of homes, with “active” elements such as amplifiers and line extenders driving the signal down the coax segment. The nomenclature used is “N + x” where N is the node and x is the number of actives between the fiber node and the home. For example, N + 6 means there are six actives on the coax segment between the node and the home. Driving fiber deeper means driving toward N + 0. Fiber deeper is not a new access network development. Cable operators have been doing this for decades with node splits. Fiber deeper is just getting more attention now as cable operators are getting closer to N + 0 and setting service group targets fewer than 100 homes.
While the PHY layer is getting pushed out to the fiber node, network function, or CCAP, virtualization is focused on moving the remaining CCAP layers out of the hub site and into a centralized data center. As with Remote PHY, CCAP virtualization has its benefits and challenges:
- Innovative new services can be released more quickly due to focusing on developing software only at the data centers.
- Nodes in the data center become general computing hardware, which can be shared across multiple services and are more energy efficient.
- The simplified yet numerous nodes closer to the customer become less expensive.
- New, non-traditional developers may enter the marketplace to write service code.
- An “orchestrator” function is key to ensuring that the service functionality spread across the network stays in sync.
- Functions that were once self-contained within a node are now split across the network, exposing new network interfaces, so interoperability testing is key, just like it is for Remote PHY.
- Security is a prime concern as new interfaces are exposed and each network node must prevent unauthorized access or control.
- CCAP virtualization requires a high-performance network with deterministic behavior regarding throughput and latency.
The above-defined architecture changes are occurring simultaneously and in the next few years on the cable operators’ access networks. All are designed to continue to support the services that the customers expect today and into the foreseeable future.
- Remote PHY moves the PHY layer out of the hub site, into the fiber node.
- Fiber deeper brings fiber closer to the homes, removing network actives and improving network reliability.
- Network or CCAP virtualization moves the rest of the CCAP out of the hub and into the data center.