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Technology Stocks : LAST MILE TECHNOLOGIES - Let's Discuss Them Here -- Ignore unavailable to you. Want to Upgrade?

To: Bernard Levy who wrote (5978)	11/15/1999 8:57:00 PM
From: P2V	Read Replies (1) \| Respond to of 12823

Hi Bernard, Page 8 of the following ( PDF format) document, from Mot.) -- indicates that their proposed PHY upstream protocol is derived from the DOCSIS 1.1 RF interface specification. I have found no references to DOCSIS 1.1 in the Media Access Protocol documents that I have so far been able to download. grouper.ieee.org Now a question (for ANYONE) regarding the MAC documents -- I have been unable to find to an answer to Frank C's questions (or to satisfy my own curiosity) about Channel Contention, or a Collision Avoidance scheme in the xOFDM proposals. My assumption would be that the MAC is the place to include something like CSMA/CA (the 802.11x Carrier Sensing and Collision Avoidance scheme) . If there is no need for such a specification, why not ? Best Regards, Mardy.

To: Bernard Levy who wrote (5978)	11/15/1999 9:59:00 PM
From: ftth	Respond to of 12823

I can't really say at this point what portions of the DOCSIS MAC are or aren't transferrable. If you'd care to propose a requirements list—-even if it's a 10,000 foot view--for your ideal MMDS/xOFDM MAC I'm all ears. The essence of the upstream is this: The upstream channel uses TDMA, and the time reference is provided by the CMTS. CMTS also controls channel utilization. The scheduling algorithm isn't mandated by the spec; it is open to vendor-specific implementation. The spec only defines the protocol elements that must be used to implement the scheduling, in order to give it maximum flexibility and allow for vendor differentiation. I'll just provide this admittedly general overview snippit from the spec, which is expanded into literally hundreds of pages in the DOCSIS 1.1 RFI spec: The upstream Physical Media Dependent (PMD) sublayer uses a FDMA/TDMA burst modulation format, which provides five symbol rates and two modulation formats (QPSK and 16QAM). The modulation format includes pulse shaping for spectral efficiency, is carrier-frequency agile, and has selectable output power level. The PMD sublayer format includes a variable-length modulated burst with precise timing beginning at boundaries spaced at integer multiples of 6.25 msec apart (which is 16 symbols at the highest data rate). Each burst supports a flexible modulation, symbol rate, preamble, randomization of the payload, and programmable FEC encoding. All of the upstream transmission parameters associated with burst transmission outputs from the CM are configurable by the CMTS via MAC messaging. Many of the parameters are programmable on a burst-by-burst basis. Some of the MAC protocol highlights include: • Bandwidth allocation controlled by CMTS • A stream of mini-slots in the upstream (A “mini-slot” is the unit of granularity for upstream transmission opportunities) • Dynamic mix of contention- and reservation-based upstream transmit opportunities • Bandwidth efficiency through support of variable-length packets • Extensions provided for future support of ATM or other Data PDU • Quality-of-service including: • Support for Bandwidth and Latency Guarantees • Packet Classification • Dynamic Service Establishment • Extensions provided for security at the data link layer. • Support for a wide range of data rates. I hesitate to even open this can of worms, since I'm kind of short on bandwidth at the moment and hate to post and run. I'll try to field any questions, but it may be later in the week or the weekend before I have a chance to do them justice. I believe you can download the DOCSIS 1.1 RFI spec (which is but one of several DOCSIS specs in the family) from www.cablemodem.com, but I'm not sure if the most recent 11/5 updates are there. The changes in the 11/5 update are pretty low level details so probably aren't critical to the level of discussion. Enjoy? dh PS aside from my bandwidth deficiency, my good old @Home cable modem service reliability is at an all time low (and that's saying something!), with outages nearly every day for the past few weeks. This tends to limit my posting also.

To: Bernard Levy who wrote (5978)	11/16/1999 11:01:00 PM
From: jack bittner	Respond to of 12823

i've been kept mute for a few days because my subscription ran out, and when i tried to renew by telephone and credit card, the people at SI's office were as stunned as if i'd hit them upside the head with a bat. using some ingenuity and with the kind help of john busby over there, i finally did so. i never put my card on the Web because i know a bit about cryptography and i don't have faith that no one has, or soon will have, the ability to factor the product of 2 primes, (i know, at 10 to the 129 it takes x billion years when tried by brute trial and error; and we all know that's the only possible solution) - which is the heart of RSA. but i am tardily posting now to thank Dr. Levy, petere, wireless wonk and mardy for their thorough responses to my queries which are based on a solid core of ignorance.