Electronic Design

Wired Communications Holds Its Own Against Encroaching Wireless Dominance

With wireless making continuous progress in replacing older wired technology, you might think that wires and cables are approaching obsolescence. Wrong! If anything, there are more wires and cables than ever as we dream up ever more applications that connect devices and exchange information.

Even as speeds have escalated into the upper-gigahertz ranges, cables still hold their own. Fiber-optic cables handle most of that higher-speed data, but even copper cables can deliver gigabit data over reasonable distances. There’s a wired infrastructure behind virtually every wireless application, too.

Copper Cables Hold Their Own

Who would have thought you could send data at hundred of megabits or even gigabits per second down a copper cable? We knew we could do it with coax if we were willing to put up with the high attenuation and fussy connectors. But how can you do it with twisted-pair cable or other formats?

Thanks to equalization, dispersion compensation, and other techniques implemented with DSP, megabit and gigabit cables are available. Several communications interface standards support the ever-increasing traffic, including Firewire, USB 2.0 and 3.0, HDMI, Ethernet, InfiniBand, HDBase-T, and Thunderbolt.

Firewire, the oldest standard, is on its way out now that Apple dropped it as an interface on its Mac PCs and laptops. It was used mainly for external disk drives and video cameras. USB 2.0 is there with its theoretical maximum rate of 480 Mbits/s up to 5 meters, but it can do a couple hundred megabits per second up to about 10 meters. USB 3.0 has a theoretical top rate of 5 Gbits/s up to 3 meters. These rates are great, but the range is too short for many applications.

Then there’s HDMI for audio and video media. It supports a bit rate to 10.2 Gbits/s up to about 10 meters, but there are multiple connector types and specifications. Repeaters and active cables support longer distances.

Ethernet has also been doing megabit and gigabit rates for years over unshielded twisted-pair (UTP) cable. It uses multiple pairs and all sorts of electronic modulation and other tricks to extend the range to 100 meters, including 10 Gbits/s—not bad for a cable.

The new interface, Thunderbolt, is a contender in the fast cable interface competition. Created by Intel as Light Peak and now adopted by Apple, Thunderbolt multiplexes both the PCI Express and DisplayPort interfaces on a single cable where both data and video can be carried at speeds up to 10 Gbits/s. Cable lengths up to 3 meters are supported. Up to six devices may be daisy-chained to extend range. Optional fiber-optic cables accommodate longer distances.

Intersil’s ISL37231 Thunderbolt transceiver chip boasts two differential 10.3125-Gbit/s full-duplex lanes that make it easy to build active cables where the interface circuitry is inside the cable connectors. The Intersil ISL80083 is a companion power management chip.

Fiber Optics Continue To Lead

The Internet backbone can’t keep up with the continued growth in data traffic thanks to the cloud, tablets, smart phones, the LTE expansion, and video. The continuous improvements in data rate and capacity help but never seem to quite catch up with demand. That’s why the push to 100-Mbit/s systems is accelerating.

All sectors including data centers, local-area networks (LANs), storage-area networks (SANs), metro networks, long-haul networks, and even undersea connections are targeting the 100-Gbit/s node. Many data centers wish they could move more quickly to 400 Gbits/s. The ultimate goal, 1000 Gbits/s or one terabit (1 Tbit/s), will require multiple fibers as well as new modulation formats like 16-phase quadrature amplitude modulation (16QAM) or orthogonal frequency division multiplexing (OFDM) on fiber.

The de facto standard for metro and long-haul 100-Gbit/s systems is single-wavelength (λ) polarization division multiplexing quadrature phase-shift keying (PDM-QPSK), or more specifically, dual polarization QPSK or DP-QPSK. It has a high tolerance to both polarization mode distortion (PMD) and chromatic dispersion, which are typical maladies affecting long fiber.

DP-QPSK is the chosen method for OTU4, the 100-Gbit/s version of the Optical Transport Network (OTN). The format is either four lanes of 32 Gbits/s or four lanes of 28 Gbits/s depending on the protocol. Ethernet over shorter distances uses four lanes of 25.8 Gbits/s or 10 lanes of 10 Gbits/s (CFP).

The fastest growing sector of fiber serves shorter ranges under several kilometers, with growing use in data centers and access networks. Data centers are upgrading to 10-Gbit/s and 40-Gbit/s equipment and cabling. Line cards and switch density are increasing, along with port counts. As usual, requirements for lower power consumption and shorter latency are critical.

Cortina’s CS4343 incorporates electronic dispersion compensation (EDC) and clock and data recovery (CDR) plus the related amplifiers and drivers (Fig. 1). Protocol agnostic, the octal 15-Gbit/s physical-layer (PHY) chip works with Gigabit Ethernet (1/10/40G), Fibre Channel, InfiniBand, and Common Public Radio Interface (CPRI). It also provides full-duplex operation on eight independent channels and uses analog techniques for EDC. Dispersion compensation is needed at the higher data rates and long reaches of cables to offset the effect of pulse stretching due to the different rates of travel of different wavelengths of light.

1. Cortina’s CS4343 optical PHY interface incorporates eight full-duplex channels of transceivers capable of up to 15 Gbits/s. It includes CDR and well as electronic dispersion compensation (EDC).

Many data centers are already at the 100-Gbit/s level. Enterprise LAN and SAN installations are continuing their upgrades to 10-Gbit/s systems. Ethernet provides a path to upgrade to 40 Gbits/s and 100 Gbits/s. Only a few 100-Gbit/s metro and long-haul systems are in place. In these networks, the OTN standards leading to 100 Gbits/s are slowly replacing Sonet/SDH.

Fiber-optic cables provide even faster rates, with 40-Gbit/s and 100-Gbit/s rates possible at distances up into the kilometer range. Most of the need is for higher speeds over shorter distances up to 100 meters. Connections to servers, routers, and switches in data centers are a common application.

Avago Technologies offers active optical cables that deliver high-speed data over moderate distances. Copper Ethernet and InfiniBand interconnects dominate now with their large size, heavy weight, and power dissipation. Optical cables can replace them and greatly reduce the size and weight of the cables at no extra cost. And as a side benefit, they minimize electromagnetic interference (EMI).

The Avago AFBR-7CERxxZ uses standard multi-source agreement (MSA) standard small form-factor pluggable (SFP+) transceivers as terminations. This full-duplex cable offers a line rate to 10.3125 Gbits/s. The maximum cable length is 20 meters, but shorter versions are also available. It can be used with 10-Gigabit Ethernet (10GE), 8G Fibre Channel, Fibre Channel over Ethernet (FCoE), or InfiniBand single data rate (SDR), double data rate (DDR), and quad data rate (QDR) versions of 2.5, 5, and 10 Gbits/s. Power consumption is 25 mW per transceiver.

The Avago AFBR-7QERxxZ uses the QSFP+ MSA transceivers that feature four bidirectional links, each with a rate of 10.3125 Gbits/s, making it useful in applications like 40 GE-SR4 as well as the SDR, DDR, and QDR InfiniBand applications. Cable lengths to 20 meters are possible. The power consumption is only 1.5 W (maximum) for all four channels.

The AFBR-83DC/PDxxZ version meets the CXP MSA transceiver standard (Fig. 2). It provides 10 or 12 lanes of bidirectional data at 10.3125 Gbits/s with a reach of up to 100 meters. A 12-lane version capable of 12.5 Gbits/s is also an option. It’s good for use in 100GBASE-SR10 and CPPI or in InfiniBand applications. It also can be used to extend PCI3 Gen3 buses.

2. The Avago Technologies AFBR-83DC/PDxxZ active optical cable uses the CXP MSA connector standard and 10 or 12 fibers to achieve data rates to 100 Gbits/s. The cables are available in various lengths to 100 meters.

All three basic versions specify a 1E-15 bit error rate (BER) and low power consumption. These active optical cables not only are keeping cabling alive, they’re also offering some unexpected benefits such as smaller size, lower weight, and EMI reductions at approximately the same cost as passive or active direct attached copper cables.

The growth of passive optical networks (PONs) such as Google’s new fiber optical network in Kansas City continues quietly in areas for new homes and in some rural areas with no cable. There are 7.3 million Gigabit PON optical network terminals (ONTs), and that’s expected to grow to 18 million by 2016, according to Infonetics Research. The ONTs are the service provider gateways.

With up to 32 customer premise optical networking units (ONUs) per ONT, their growth represents a huge increase in home or business coverage. GPON has a standard 2.488-Mbit/s downlink speed and 1.244-Mbit/s uplink speed. Already, the faster 10GPON or 10-Gbit/s version is being deployed in the U.S. Broadcom offers the BCM685xx series of GPON systems-on-chip (SoCs) for residential triple-play services including video on demand (VoD), HD-IPTV, voice over IP (VoIP), and high-speed Internet service.

EPON, the Ethernet version of a PON, is growing nicely in the world marketplace. This standard also supports a 10-Gbit/s version. It’s widely used in China, Japan, and South Korea. The PON approach is superior to wireless connections for residential access, especially in multi-dwelling units (MDUs) where thick walls and floors block wireless signals. EPON is also showing promise as a basestation backhaul solution because of its low cost.

Broadcom’s BCM5553x family of optical line terminal (OLT) chips for EPON support both 1-Gbit/s and 10-Gbit/s speeds (Fig. 3). They comply with the IEEE 802.3av standard as well as China Telcom 3.0 and CableLabs DOCSIS Provisioning over Ethernet.

3. Broadcom’s BCM5553x OLT is designed for new EPON fiber systems at the 1-Gbit/s and 10-Gbit/s rates.

The metro and long-haul optical networking sectors are doing moderately well. Older Sonet/SDH networking equipment is in decline as the industry switches over to OTN. However, according to Dell’Oro Group, wavelength division multiplexing (WDM) equipment sales are healthy as a number of service providers roll out their 40- and 100-Gbit/s services in response to the ongoing demand for more bandwidth. The metro and long-haul WDM sector grew by 14% in 2012 to $8 billion. Growth is expected in 2013.

POTS Continues Its Service

Plain-old telephone service (POTS) isn’t dead yet. All that telephone wiring is still there, and about 50% or the U.S. population still relies upon it for telephone service. Many have given up their POTS lines for cell-phone connections, yet those POTS connections are still present and useful for data services like DSL or over-the-top (OTT) TV and even new applications for machine-to-machine (M2M) communications or industrial monitoring and control.

M2M is growing rapidly as more companies and institutions find they need to monitor or control devices or facilities remotely. Most M2M connections today are cellular or some other wireless option. But for some cases, there’s no reason not to use the installed base of telephone wiring. It exists nearly everywhere, and phone line service is cheap and very reliable. Every traditional landline also supplies dc power, so it can power many devices instead of batteries or local ac power. Furthermore, connectivity is robust, as it typically remains connected even during storms and floods.

One company is taking advantage of this medium for both M2M and other industrial control. Global Monitoring’s GMU8120 modem offers related interfaces to transmit and receive data over POTS (Fig. 4). It uses traditional telephone dialup speeds from 1200 bits/s to 53 kbits/s. Interfaces include 4 to 20 mA, 0 to 5 V and dry contacts, ±1 V to ±10 V dc. Analog-to-digital converter (ADC) inputs have 14-bit resolution. Outputs are four relays.

4. Global Monitoring’s GMU8120 modem uses telephone lines for industrial monitoring and control. Standard interfaces and telephone modem data rates are available.

The major telecom companies would love to abandon their wireline business to focus on the more lucrative wireless and broadband markets, but state and federal regulations require them to maintain their existing lines. AT&T, which serves 76 million homes in 22 states, recently indicated a desire to phase out its landline business. The company is trying to get local and federal regulations changed. Verizon, the other largest wireline company, also serves millions but would prefer to move on to more profitable broadband services.

Landlines are here to stay for the time being, though, so take advantage of this low-cost and reliable medium while it lasts. In addition, landlines are still widely used to supply high-speed Internet connections via DSL to a huge population not only in the U.S. but also in Asia and Europe. Cable TV-based Internet connections still dominate in the U.S., but DSL is a close second.

AT&T uses the connection to the home for its U-verse TV service. This OTT Internet TV service is a strong competitor with cable TV services in some parts of the country. U-verse is a hybrid service with fiber to local nodes and existing telephone UTP to the homes. Advanced DSL technology like ADSL2 or VDSL2 is used to achieve the speeds needed for compressed HDTV delivery.

Broadcom’s BCM63168 mulitmode ADSL2+/VDSL2 chip further extends the reach and speed of DSL lines. DSL technology uses discrete multitone (DMT) technology, which is a form of OFDM, to achieve high speeds on UTP telephone cable. In VDSL2 format, it uses up to 30 MHz of bandwidth on the line with up to 3479 carriers, each 8.625 MHz wide, to deliver data rates to 200 Mbits/s over limited distances. The speed depends mainly on cable length. Maximum data rate at 0.5 km is about 100 Mbits/s, for example.

This chip also uses vectoring and channel bonding to further improve speed and reliability over longer distances. Vectoring is a technique for reducing crosstalk and noise on adjacent cables using DSP. With a single vectoring connection, VDSL2 can deliver up to 50 Mbits/s up to 1 km. Channel bonding permits the use of two or more pairs of cables to deliver parallel paths, further increasing the data rate up to 100 Mbits/s with some combinations. Such techniques keep DSL competitive speed-wise with cable TV systems. The BCM63168 also includes a full dual-band 802.11n/ac Wi-Fi transceiver.

Cable TV Upgrades

U.S. cable TV companies will maintain their dominance in high-speed Internet service over DSL. They offer higher speeds and more channels than ever. This capability comes as a result of the ongoing upgrade of cable modem termination systems (CMTS), the stilted name of the cable head-end system that feeds the network of connected homes and businesses. Cable systems are hybrid fiber coax (HFC) networks that put multiple channels on a fiber that terminates at neighborhood nodes that convert the connection to RG-6/U coax for attachment to the customer’s cable STB. Each fiber node serves about 500 homes.

Over the past several years, the cable companies have gradually changed from an all-analog system to an all-digital format. The more recent upgrades are to the latest version of the Data Over Cable Service Interface Specification (DOCSIS), an international standard from CableLabs that specifies how to supply video and Internet service over the HFC system.

DOCSIS 3.0 aims to provide 50- to 100-Mbit/s data service to customers and address the need for more IP identification with IPv6. It also provides stronger encryption and should help reduce the number of HFC node splits needed to cover a given area. In the downstream from the CMTS to the customer, the standard 6-MHz wide channels are still used.

Total cable bandwidth is commonly up to 1 GHz wide, meaning it can accommodate up to about 166 channels, mostly downstream. 64QAM and 256QAM provide a data rate in the 26- to 38-Mbit/s range per channel. The upstream data occurs in the 5- to 42-MHz space on the cable and uses QPSK or 16QAM to get rates ranging up to about 30 Mbits/s but averaging 1 to 3 Mbits/s. More than 80% of all U.S. cable systems have upgraded to DOCISS 3.0.

Aiding the DOCSIS 3.0 transition, the Analog Devices ADS9129 14-bit digital-to-analog converter (DAC) supports up to 2.8 Gsamples/s. It’s designed for CMTS infrastructure equipment and can handle as many as 158 carriers at a time. The ADS9129 and the 11-bit AD9119 are expected to reduce total systems power consumption, component count, and overall cost.

PLC Still Connecting

Power-line communications (PLC) uses the existing ac power lines to carry data. Sophisticated modulated signals ride on top of the 60-Hz power sine wave along with all the attendant noise to carry any form of data. While the attenuation is significant, whole home coverage is possible at data rates that heretofore were considered impossible. Most PLC standards specify OFDM, which provides for high noise tolerance and good spectral efficiency to deliver high speeds at reasonable distances.

Multiple PLC standards have been developed, but only a few of them have survived. The leading PLC technology, HomePlug, has been around for years and has gradually advanced the state of the PLC art to a new level. Its latest version, HomePlug AV2, extends the signal bandwidth from its usual maximum of 30 MHz to 86 MHz and boosts modulation higher-level QAM to produce near 1-Gbit/s rates over reasonable distances.

Most home applications involve video distribution between STBs, HDTV sets, DVD players, and other consumer products. HomePlug also has a lower-speed standard called HomePlug Green PHY that’s used for home-area networks (HANs).

The main competing standard is the ITU’s G.hn. This broader standard uses the power line, but it also can use any existing coax cable or twisted pair in the home to carry the signal. G.hn is designed primarily for home networking, with video transmission being the main use. Speeds to 1 Gbit/s are possible with some configurations.

G.hn has not yet been as widely adopted as HomePlug, but it is fighting for some of the potential consumer market. Lower-speed PLC standards like G3 target applications like industrial communications and smart meter/Smart Grid connections.

PLC’s real battle is with wireless, which is so well entrenched in the home with Wi-Fi and ZigBee that it’s is hard to see PLC as other than a niche technology. There is no questioning its convenience with a connection via any ac plug, but wireless may be even easier and more portable. However, PLC does have its place.

In some situations, PLC can be more reliable than wireless. PLC and wireless also can complement each other. Greenvity Communications makes PLC and wireless technologies available on a single chip. Both can be used in smart meters and other HAN equipment, but neither technology fits all possible potential uses.

The Greenvity GV7011 Hybrii-XL integrates a full ZigBee radio and a HomePlug Green PHY transceiver (Fig. 5). This combination reduces the cost of HAN equipment and accelerates product design. Furthermore, this integrated device uses less power than multiple separate chips and boards to support both standards.

5. The Greenvity GV7011 Hybrii-XL integrates a full ZigBee radio and a HomePlug Green PHY transceiver including the full analog front end, RF, baseband, media access controller (MAC), and embedded memory. An 8051 microcontroller implements low-power energy management.

The Hybrii chip automatically selects the best medium to transmit data, wirelessly or on the power line. If the power line is too noisy, the wireless nodes will be enabled and vice versa, always ensuring reliable communications under most circumstances.

PLC’s greatest potential is probably in the smart meter and Smart Grid space since it is so closely tied to the ac power line. It will also see greater adoption if it gets embedded in STBs and other consumer gear, but it will continue to battle the wireless vendors for those cherished spots.

Potential Worldwide Internet Control

One chilling development is the potential for the Internet to come under management by the International Telecommunications Union (ITU). The Internet currently isn’t controlled by any one country or entity. It is an open system with various committees and task forces to handle technical standards and interfaces, like the Internet Engineering Task Force.

The United Nations has been lobbying for the Internet to be controlled by the ITU, an organization that already develops standards for other communications systems. Most of the UN’s 193 member states favor worldwide regulation and control. The basic idea is to tax the sender to raise revenue.

The World Conference on International Telecommunications of the ITU in Dubai is expected to develop and approve a treaty for ITU Internet control. The U.S. will lobby heavily for keeping its open nature, which has been so successful so far. No good can come from having one organization or some authoritarian countries start making rules and changing its systems and access methods. For example, the ITU could levy taxes on international traffic, which is a scary prospect for all of us.

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