The DOCSIS 3.1 suite of specifications supports capacities of at least 10 Gbps downstream and 1 Gbps upstream using 4096-QAM. Instead of 6 MHz or 8 MHz wide channel spacing, smaller 20 kHz to 50 kHz wide orthogonal frequency-division multiplexing (OFDM) subcarriers are used. These can be bonded inside a block spectrum that could end up being 200 MHz wide.
"(DOCSIS 3.1) is a much more complex signal to process and decode," said Alex Pelland, business line manager, Averna. "It also requires more throughput for processing, at least similar to 10 Gb in the downstream and 1 Gb in the upstream. (In addition) the upstream signal is defined in the (MAC layer)."
While protocol analysis is sometimes called packet sniffing, Averna says the tools can do much more by way of network management, including analyzing, debugging, maintaining and monitoring local networks and Internet connections. In a white paper titled, "Optimizing DOCSIS 3.1 Networks," the company explains how a protocol analyzer is not only a non-intrusive probe, meaning it will not impact live communications traffic, but it also can validate MAC-level communication and troubleshoot interoperability issues. By analyzing the content of MAC messages, the tool can either verify normal transactions between the CMTS and cable modem or can determine how either handles anomalies. This capability differs from the current monitoring devices on the market.
"(For example,) DOCSIS 3.1 spectrum analyzers (are) very different kind of product(s) that basically only monitor the PHY layer, making upstream monitoring very difficult," Pelland said.
In addition to the MAC layer coverage, a protocol analyzer must be able to handle the expanded frequency band DOCSIS 3.1 will enable and the complexities that wider OFDM channels and advanced modulation formats, including 4K QAM, will bring. To do so, the tool needs to have a "tremendous" amount of processing power to handle higher throughput, real-time demodulation of all sub-carriers, and the ability to monitor a specific downstream profile to focus on a targeted group of cable modems, the white paper says.
"(A DOCSIS 3.1 monitoring tool also should have) API for automation ... a GUI with an intuitive display, RF spectral shape with MER measurements, a lock indicator, and OFDM parameter detection," Pelland said.
An additional challenge facing operators is the need for analysis tools to bridge between DOCSIS 3.1 and 3.0, which operators continue to implement. Protocol analyzers can offer the ability to support both standards, capture legacy and OFDM channels, and monitor a mix of DOCSIS 3.0 and 3.1 channels on the same frequency while analyzing them as different channels on the MAC-layer level, the white paper says.