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Trevor's View

Gigabit over Copper and VOIP

(Gigabit over Copper and VOIP:  Page 1 of 1 )

Gigabit over Copper, 1000 BaseTX, sends 10 times the amount of data over normal 100 BaseT (CAT-5, RJ45) cabling. VoIP allows voice traffic to be sent over the Internet. Both these technologies are entering mass-production, and are going to have a huge impact on computer networking.

Optical Fiber for the rest of us

Last week Intel started promoting 1000 BaseTX with a special offer of two PCI NICs for $219, while D-Link announced its new DES-1009G gigabit switch and a matching gigabit PCI Network Adapter. The switch, which interconnects eight full duplex 100 BaseT lines and one (half duplex) 1000 BaseTX connection, sells for under $300, almost an order of magnitude less than the cost of similar switches just a few months ago. The D-Link PCI Network Interface adapter is priced at $149, in line with Intel's list price, again reflecting a huge reduction in cost-of-ownership.

I had already been thinking about upgrading my own SOHO network to new adapters which can automatically sense whether a cross-over or normal CAT-5 cable is in use. I waste a lot of time fooling around with network cabling, and trying to crimp an RJ45 connector on a cross-over cable almost makes me go blind! The ability of the new Gig over Copper hardware to autosense inputs means I will never have to bother about cross-over cabling again, and that alone makes an upgrade look quite attractive. Add to that the 10x speedup of network data over my network, and the case for upgrade is very compelling indeed.

The Software Drivers Need Work

But there is still some way to go with 100 BaseTX driver development. E-Testing Labs showed that Intel's adapters maxed out at about 750 Mbits per second of throughput in typical Windows' servers.

Driver updates will also be needed to fully utilize some of the other features being integrated into this new network hardware.

IEEE Standards For 1000 BaseTX

The hardware on these new adapters complies with several IEEE standards previously implemented only in high end networking equipment:

802.3ab Gigabit Ethernet over Copper
802.1Q VLANs
802.3x flow control
802.1p Prioritization

The first of these defines the actual 1000 BaseTX technology, and ensures that equipment from one manufacturer will operate properly with equipment from another.

Flow control, 802.3x, defines a "pause packet" that is sent out by a switch (or adapter) just before it runs out of buffers. I haven't personally had a chance to test how the Intel and D-Link adapters generate or respond to flow control requests, and since there is considerable dissent over the various implementations of 802.3x, I will hold back my own opinions until a future column.

But VLANs (Virtual LANs) define a new TCP/IP packet that travels over the same wires as packets from normal adapters, and which can carry up to 8 levels of "priority". VLANs are going to become very important indeed as networking matures, and applications seek more and more bandwidth. Together with the prioritization allowed by 802.1p, these standards help to create 'Quality of Service' (QOS).

Quality of Service (QOS)

Microsoft has a very good description of QOS on its developer website. Microsoft considers it an industry wide initiative which uses 3 reserved bits on the MAC address associated with an Ethernet card to carry the eight levels of priority across a network. But QOS may also be derived from VLAN or IP tagging at points away from the OS and within the switches and routers on the network.

Software support for QOS is built into Windows 2000 and Windows 98, and is being incorporated into Linux drivers.

QOS is important because it allows network switches to be designed to give priority to the data coming from certain Ethernet adapters (recognized by their MAC address, their IP, or by their VLAN tag) and ensure that they travel across the network with as little added delay (latency) as possible. And of course QOS ensures that no data packets are lost from a priority source, even on a network that is fully loaded.

Multimedia streaming requires both minimal (constant) delay and constant data throughput no matter what level of traffic is moving across the network.

The D-Link switch does not have the ability to interpret QOS priorities, but the datasheet says it does have the ability to pass QOS packets through without damaging them.


Los Angeles recently hosted the Computer Telephony conference, a gathering for all involved in the movement to use the Internet to bypass the POTS (Plain Old Telephone Services) supplied by the Baby Bells.

The basic idea is to take digitized voice packets, feed them over the Internet to a POP (Point of Presence) close to the person you are calling, and then couple them onto the PSTN (Public Switched Telephone Network) at local call rates. (Engineers seem to use acronyms to hide the inherent simplicity of technology from their bosses. Certainly networking and telephony have more than their fair share of acronyms, IMHO).

VoIP data is only 20Kbps, why does it need QOS?

VoIP has been in its infancy for several years now, held back by a number of problems.

Firstly, most TCP/IP networks are designed to buffer packets during times of high traffic, sending them along when bandwidth permits. Multimedia players buffer up a clip into memory so that short breaks in the data transmission will not be audible. But you can't really do this with telephone traffic. A 10 second buffer delay on something you are downloading from the web is fine, but when you have a two way conversation with each person waiting 10 seconds before they can hear what is being said to them, and another 10 seconds for their response to return, you have a system that is inoperable.

I have used an extreme example here, but every router and switch on the Internet backbone, or on the backbone of a Corporate Internet, contributes a small "latency", or delay, that can add up to quite significant values. This is where QOS can help.

There are several providers of VoIP services, the one that I have used most is Deltathree. Over the last few years they have contracted for their own International TCP/IP "backbone" to pass along the VoIP traffic without it having to travel along the main (slow) Internet Backbone.

I get good voice quality and acceptable delays with Deltathree, whether I use my DSL or Cable Modem. A call to Europe gave about a one second delay, to Australia about 1.5 seconds. Echo cancellation in their "PC-to-Phone" software was excellent, so the delays didn't really get in the way of my conversation.

Mass Produced VoIP hardware

At the conference the PC VoIP hardware pioneers, such as Quicknet, were selling their wares to the roadwarriors, but over in a corner were some Taiwanese businessmen taking orders for inexpensive hardware that even a consumer can afford, and selling low cost, PC based, VoIP PABX switchboards for small businesses.

Why does PC VoIP need any hardware? Surely the computer's microphone and speakers are plenty good enough? In answer to this question the President of City-Netek slipped me an engineering sample of a yet-to-be-released product and suggested I try it when I got home.

This 'thing' had a socket for me to plug a telephone handset at one end, and a USB connector at the other. I dutifully plugged the USB into my PC and Windows told me that it had identified a USB Audio input device and a USB Audio output device.

When I connected the handset and made a VoIP call I suddenly realized how much a DSP based audio system (for that is what was in the box) could improve the quality of VoIP telephone conversations. I placed several calls, and nobody realized that I was calling using the Internet.

DSP Hardware for PC VoIP

It wasn't long before the cover had been popped off the "thing" and I was searching the Internet looking to identify the ICs in it. In this case I found that the whole device was a reference design from a company called "Tiger Jet Network", containing a 'Tiger' USB interface and a Motorola Digital Filter and Codec.

The Motorola MC14LC5480 Codec chip filters out any incoming audio frequencies outside a 200Hz-3400Hz voiceband range (the same as a normal telephone) and then converts it to PCM digital for the USB interface chip, bypassing the A-D converter already in your PC.

The frequency shaping makes for more efficient digital conversion, resulting in more "talk power". Only the data needed for efficient voice communication is transmitted, low and high frequencies have been removed.

Look to see equipment like this DSP system implemented inside headsets over the next few months (the first 'Digital Headsets' are already on the market, but their frequency range is designed for speech recognition, and not for VoIP).


Networking technologies have been slower to adapt to the increased speeds of modern PCs than other hardware. I am sure that the advent of Gig over Copper 1000 BaseTX is going to change that, and upgrade the network speeds to match the Gigahertz CPUs that seem to be selling for 'dime a dozen' these days.

VoIP is the obvious way to add communications capabilities to a PC, and hardware like Tiger's will make PC VoIP easy and efficient. The low cost PC based VoIP PABX systems should increase the amount of VoIP traffic towards critical mass, taking the industry beyond the profitability threshold that has proved so elusive over the last few years.

Trevor Marshall is an engineering management consultant, with interests ranging from RF and Hardware design to Linux internals, Internet infrastructure, MPEG, and Digital Video. He started his career in the '70s, designing the Maplin Electronic Music Synthesizers. When the Microcomputer came along, he got sidetracked into computer software, programming the 2650, 8080, Z80, Z8000, 8048, 8306, 6805, 80x86, and Power PC families. Along the way, he also picked up a little expertise in RF system design, biomedical engineering, and the printing industry. His web site is

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A list of all 75 papers Trevor has published is available at this link.

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