September 1997: Volume 13, Number 1

The "Bigger, Better" Last Mile

By Joan Burek

he last mile, the copper link from your home, your business to "the network" .... an exclusive territory previously held (and vigorously defended) by Stentor-member companies is now meeting competition from a variety of traditional (and not so traditional) competitors. Based on past and recent CRTC competitive rulings, cable companies, radio-based firms, long-distance carriers, fiber-providers and so on are lining up to provide their high speed alternative to the telco's copper last mile. (The last mile is defined as the connection from the customer premises telephone facilities to the serving central office, or C.O.).

As depicted in Table 1., the new definition of the "last mile" could include traditional copper facilities, radio-based communications or cable fiber (to name a few).

What does the "death" of the telco last mile mean to you? Good-bye to 14.4 Kbps and a competitive hello to 56 Kbps and beyond!

BEYOND V.34
SPEEDING UP TO 56 KBPS

Was it so long ago, when carrier and computer manufacturer alike refused to guarantee any data transmission at 9.6 Kbps (and never you mind about "the beyond"). Remember the cost of the 19.2 Kbps business modem? $5,000 if you were lucky (and bought about a million of them); $10,000 if you were part of the regular communicating crowd. Well, thanks to evolving and improving technology (and, of course, Rockwell), today's modem can achieve speeds beyond V.34 rates. Rockwell's K56 technology allows data transmission to approach and employ 56 Kbps - utilizing standard voice phone lines.

K56 digitally encodes (instead of modulates) downstream data (from the network to the K56 modem) and thus, allows 56 Kbps transmission to become a reality. However, K56 is based on asymmetrical communications, meaning:

• As mentioned earlier, downstream transmission utilizes the 56 Kbps rate.
• Upstream transmissions (from the K56 modem to the "network") utilize 33.6 Kbps rates.

Of course, in order to realize these speeds, the originating (where you're dialing from) and terminating (where you're dialing to) modems MUST both utilize the K56 technology. If only one (1) side has the K56 modem, then V.34 rates (or 33.6 Kbps and below) will be employed.

Remember that modem speed is always a factor of the line quality. A modem's rate adaption will occur regardless of (or in spite of) any hot, new technology. Rate adaption is the bandwidth / speed agreement, between originating and terminating modems, in which transmission quality is "more-or-less" assured. This means that slick new 56 Kbps modems, under adverse line quality conditions, may be no better than a $50 14.4 Kbps modem.

BIGGER, BETTER, FASTER WITH ADSL
(ASYMMETRIC DIGITAL SUBSCRIBER LINE SERVICES)

QUICK ....

• What's carrier compatible (minimal changes to existing carrier infrastructure)?
• What provides a broadcast medium in excess of 6 Mbps?
• What co-exists with POTS (Plain Old Telephone Service), on the same telephone line?
• What provides a full duplex channel of 640 Kbps?

TA - DA ....

Introducing ADSL or Asymmetrical Digital Subscriber Line Services, a (hopefully) soon-to-be released technology that will augment urban, high speed services. With two (2) ADSL transceivers…

• one located at the carrier central office (C.O.) and
• one located at the customer premises

...bandwidth (a.k.a. speed) is dramatically increased! How dramatically you ask? Well, with ADSL implemented at your home (and local C.O.) you could simultaneously:

• Hold a video-conference (that's 384 kbps)
• View up to four (4) movies (that's 1.5 Mbps per television set for each of the four TVs)
• Transfer data files over ISDN (that's 128 Kbps)
• Discuss this great new technology, with your neighbour, via a regular telephone call (that' 64 Kbps)

Or, pictorially speaking, see figure 3 ...

Sounds like you're going to be busy! (what with the TV, conferencing, downloading and discussing). Like every good idea, ADSL adheres to standards. Just like Frame Relay and X.25, standards ensure interoperability, and consistency throughout the regional, national and international forums. As the two (2) following tables suggest, ADSL rules for SIMPLEX and FULL DUPLEX transmission has been developed by the ANSI T1E1.4 committee (for ANSI Standard T1.413) and ETSI (the European Standards body). The shaded portions of the following tables denote the agreed rates that must be provided by the terminating ADSL equipment.

But there's more to come. ADSL's higher performance "brother", VDSL, is currently being studied by ANSI and ETSI. VDSL is believed to employ bit rates as high as 12 Mbps, 26 Mbps, and/or 52 Mbps over standard telephone "copper'.

SHARING THE CABLE PATH
TO HIGHER SPEED SERVICES

What started out as a "glint in the cable operator's eye" a few years ago, has become reality -- thanks, in part to the CRTC (Canadian Radio and Telecommunications Committee) and our ever evolving technology.

A number of months ago, in a fit of competitive fervour, the CRTC granted cable companies the right to provide local termination services, which added two-way transmission services to their current one-way delivery (of television signals). Under some presumed badgering by the "telco-at-large", the CRTC has ruled that these two-way services, such as Internet access, must be "publicly filed" (for service descriptions and costs) via standard CRTC filing procedures. However. amid all this legalese and posturing, a true opportunity for higher speed access data is upon us.

Statistics suggest that over 75% of the homes and businesses within Canada are "cable-ready". And with this cable-readiness, comes a great opportunity to utilize some of the cable modem technology to connect your:

• Television - for one-way video broadcast
• Personal Computer - for two-way data communications
• Telephone - for two-way voice communications

While many cable modem manufacturers products individually vary, all employ (more-or-less) the same kind of components to deliver cable-ready two-way communications. They are:

• Subscriber "Interface" which "splits" the information stream to the appropriate repository (television, telephone and/or personal computer). In addition, PC software may be available to provide additional security/authorization.
• Cable Head End Components which interface the various input streams to the appropriate servers:
  • television / video server
  • telephone server for voice communications
  • data server for data communications
• Master Cable Interface Components which interface the various input streams for local / remote communications and provides network management and monitoring, authorization and control, security and other network features, including:
• television / video server for one-way television broadcast
• telephone server communications to the PSTN (Public Switched Telephone Network)
• data server communications to the appropriate private / public data network (Frame Relay, ATM, X.25 and so on).

Each subscriber / cable interface "shares" a high speed communications link which can range from 750 Kbps(for upstream communications) to 30 Mbps (for downstream communications). Remember this varies by cable modem manufacturer!

Just as many subscribers share a "cable leg" (for television signal delivery), the same sharing principles will be employed for two-way cable (data/voice) traffic - although with far less two-way subscribers than their video counterparts. Upstream routes are subject to noise and interference and thus, usually possess lower transmission rates then the Downstream path. (Remember -- Upstream is from the subscriber to the cable head-end). In this scenario, 750 Kbps is shared among many subscribers (all on the same cable leg) as the upstream channel. Downstream routes are not subject to the interference challenges as the Upstream and thus, possess much higher transmission rates - in this case 30 Mbps. (Remember - Downstream is from the cable head-end to the subscriber{s}).

Cable two-way services are similar (if not identical) to Ethernet environments. There may be greater sophistication to avoid collision (for data and/or voice services) within some cable modem manufacturers' products. Regardless, cable companies can offer substantial bandwidth improvements over traditional copper environments. The only challenge (or pause for thought) is a provision of voice services.

Similar to ISDN concerns, the subscriber / cable interface unit will, in all probability be powered by standard household current and thus, is subject to power failures. For this reason, cable voice services should be approached either with battery backup, an alternate power source, or with some level of caution.

LMCS: HIGH SPEED TO THE HOME, SOHO OR BUSINESS
(LOCAL MULTIPOINT COMMUNICATIONS SERVICES)

As with cable services, LMCS offers both high speed broadcast (one-way) and two-way (data and voice) services. However, instead of cable fiber or coax, LMCS employs "radio" technology.

The LMCS antenna is approximately the size of a paperback book, and is positioned at the customer premises to transmit / receive the radio signal. Multiple video channels (receiving the one-way broadcast) and T1 (two-way) can be received by the subscriber. (The T1 channel can, of course, carry data or voice services, dependent upon local configuration).

A radio tower, serving up to 10 Km, serves as the primary connection point, from the subscriber antenna. The radio tower (and associated communications interface equipment) is connected to a "long haul" network, such as ATM terrestrial services, high bandwidth satellite and so on.

LMCS is deployed on a city-by-city basis (since the construction of radio towers, electronics and long-haul network connection is necessary); and thus, Industry Canada has awarded Canada's sixty-six (66) largest cities and 127 of its medium to small city to the selected LMCS providers.

LMCS technology (called LMDS - Local Multipoint Distributions Services within the USA) is currently being "trialed" within Canada, and hence, is not yet commercially available. It is anticipated that LMCS will become available within selected cities within the next twelve (12) to eighteen (18) months. T < G

Footnotes:

• SIMPLEX pertains to a telephonic system in which communications between two (2) stations takes place in only one direction at a time.
• ETSI Annex requires 2.048 Mbps downstream and 176 Kbps upstream (160 Kbps + 16 Kbps control channel). All other rates are proposed.
• FULL DUPLEX pertains to a telephonic system in which communications between two (2) stations takes place in both directions (transmit / receive).

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