The Gigabit WAN Connectivity Era

In this fast-changing and complex world, it is easy to lose track of progress and milestone achievements in wired and wireless broadband connectivity.

IEEE 802.3ab 1000BASE-T Gigabit Ethernet over twisted pair copper (using Cat 5 and Cat 6 cabling), on segment lengths up to 100 meters, has been essentially ubiquitous in wired LANs for the past five years or so. And IEEE 802.11ac “Wave 2” Wi-Fi, using four spatial streams and wide channels, offers wireless maximum PHY data rates above 1 Gbps, as does the emerging IEEE 802.11ad WiGig standard, both within maximum ranges of perhaps 50 meters. These consumer technologies are relatively well known and broadly appreciated by everyday users.

The Wide Area Network (WAN) standards we rely on to feed corporate and home local area networks have made remarkable strides forward as well, while generally flying under the radar of popular appreciation. WAN physical layer technologies need to support longer range or reach, and must deal with impairments in existing infrastructure.

A great example of WAN innovation is the G.fast digital subscriber line (DSL) standard, set for deployment this year. ITU-T G.9700/9701 G.fast can be thought of as an extension to older ADSL2/ADSL2+ and VDSL2 specifications, and utilizes similar ingredient technologies, including discrete multi-tone modulation, trellis and Reed-Solomon forward error correction. In order to mitigate the crosstalk typically found in multiple twisted pair wiring comprising legacy telephone bundles, G.fast uses far-end crosstalk self cancellation, referred to as vectoring. G.fast supports both linear precoding and advanced non-linear precoding vectoring algorithms. This combination of innovations can squeeze 106 MHz of bandwidth from plain old analog phone lines, enabling theoretical maximum aggregate (combined upstream and downstream) data rates of 500 Mbps at a reach of 100 meters. Forthcoming enhancements, including a 212 MHz operating profile, hold the potential to double throughput to 1 Gbps.

Another prime example of WAN innovation is the CableLabs DOCSIS 3.1 specification for hybrid fiber-coaxial (HFC) networks. A combination of QAM and OFDM techniques, 192 MHz wide channels and channel bonding methods constitute the key ingredient technologies. The first DOCSIS 3.1 cable modem equipment certifications were announced this week, and cable modem services with gigabit per second downstream data rates are anticipated to be deployed before the end of this year.

Of course, no surprise, optical WAN standards have evolved as well. The IEEE 802.3ah Ethernet Passive Optical Network (EPON) standard, which dates from 2004, specifies 1 gigabit per second upstream and downstream rates. The ITU-T G.984 GPON standard typically operates at 2.488 Gbps downstream and 1.244 Gbps upstream. GPON is a point-to-multipoint technology using optical splitters, with each optical line terminal (OLT) typically serving up to 32 subscriber side optical network terminals (ONTs). Verizon’s fiber to the home (FTTH) Fios service is based on GPON technology – single mode fiber and wavelength division multiplexing (1310 nm for upstream traffic, 1490 nm for downstream traffic, 1550 nm for cable television). The current top tier Fios service is 500 Mbps downstream, 500 Mbps upstream.

Google Fiber is also based on GPON, with a single 1 Gbps downstream, 1 Gbps upstream service plan for all users. The next stops for passive optical networks are the ITU-T G.987 10G-PON and IEEE 802.3av 10G-EPON standards, which both provide 10 Gbps of downstream point-to-multipoint data bandwidth.

Whether over decades old analog telephone lines, more recent coax cable, or brand new passive fiber, communication engineers have managed to deliver magical levels of wide area data bandwidth to consumers and enterprises across the world. While local area connectivity technologies such as Wi-Fi get most of our attention and affection, let’s not forget to tip our hats to the gigabit WAN innovations that pipe the internet hot into our local living and working spaces.