Rim Semiconductor Company (fka RSMI)

[spokeshave]

OSI Layers Redux:

Assuming that our technology is still a layer 1 (physical layer) technology, it may be helpful to point out the differences between the different layers.

For our purposes, the most important layers are 1, 2, 3 and 4. Let's start with layers 3 and 4 first. Layer 3, also called the network layer, is responsible for determining the route that data will take on a network. Sort of the traffic cop of data. It chooses the best path based on distance and delay. An example of a layer 3 technology is Internet Protocol (IP). We are all using IP right now.

However, IP is responsible only for routing the data. It has no idea if the data actually got there. That is the responsibility of the layer 4, or the transport layer. The transport layer essentially ensures that the data are received properly. It usually does this by assigning a sequential number to a data packet. If a packet arrives at the other end out of sequence, the error is detected and the packet resent. A common type of transport layer is Transport Control Protocol (TCP) and is commonly used with IP as a layer 3. The combination of these two layers is TCP/IP.

So, these two layers (3&4) basically rout your messages and make sure that they get to their destination.

Now, let's look at layer 1 and 2. When I post a message here and click submit, my typing is sent to my network interface card (NIC) by layer 3 (network layer) handled by my software. My NIC then uses a layer 2 (data link layer) to send the signal to the cable modem. In my case, the NIC is an Ethernet card thus Ethernet is the layer 2 protocol used. Layer 2 (Ethernet in this case) is responsible for compiling groups of bits into groups (frames) and adding error control bits to the front and back of the frame. These error control bits do such things as tell the receiving Ethernet device how many bits should be present. If the bits do not add up, the frame is resent.

This probably sounds similar to the responsibilities of the transport layer (layer 4). The idea is similar, and a simplified comparison is that they do sort of the same function, but with different sizes of data chunks.

OK. My NIC has now sent a signal to my cable modem. The cable modem must pass this signal on to the router at the cable company's office. However, it has to figure out a way to take a digital signal from the NIC, transform the signal into an analog waveform (here is your waveform generator, porscha) and send it down the cable wire. Then the receiving unit at the other end must take that analog signal, and reform it into a digital signal. The process of placing the signal on the wire is called MOdulation and the process of taking it off of the other end is called DEModulation. Thus the term MO-DEM. This process of taking a digital layer 2/3/4 signal and placing it on a different physical medium is called the physical layer, or layer 1.

OK. So why am I saying all of this? Well there seems to be some coonfusion about who might be the competition out there. A recent post of an Allied Telesyn PR was touting the speeds and distances of their technology. If you read the PR carefully, you will see that it is an Ethernet technology that has been developed, which is layer 2. I found no reference to a physical layer technology. It would seem that they have developed a layer 2 technology that increases the efficiency of ordinary ADSL.

ADSL is a conglomerate term for a number of different layer 1 technologies (plus other stuff). This type of technology could benefit greatly from a better DSL, and as such, each of these companies would potentially fall into the catagory of Cooper's "suppliers" that he referred to in his SHM address. If you were to crack open one of the Allied Telesyn products, you would find likely a chipset produced by Infineon, Alcatel, AMD, Broadcom, etc. Those chipsets are the target for NVEI. The more competitive this type of market becomes, the more successful an edge like the NVEI technology would make a company. More successful companies like Allied Telesyn is a good thing.

If you see a reference to companies that do fiber or wireless as potential competition, I suggest that you simply ignore the poster. They are uninformed. While fiber and wireless do have some niche "last mile" applications, they are not in the same ballpark. One of the main reasons for the "last mile" dilemma is that fiber is far too expensive to run to everyone's door. Wireless is developing nicely, with recent advances that allow non-line-of-site (NLOS) service at good data rates. However, this technology requires a significant physical plant investment on the part of the ISP or Telco. Those guys would *much* rather find an inexpensive way to use existing hardware.

For some more good info on OSI layers, see:

http://www.uwsg.iu.edu/usail/network/nfs/network_layers.html
http://www.rad.com/networks/1994/osi/layers.htm