Data From Stations example essay topic

Reason for design Data transfer over cable is a very important aspect of today's communication devices. Most cables used for data transfer in 1997 were used only for television purposes, and the direction of data flow was downstream, or from the head-end to the station. If this setup could be altered, then cables could also be used to receive data from stations, or upstream flow. In order for data to be transferable (able to go upstream as well as downstream), the cable must be upgraded to a combination of optical fiber and coaxial cable, or simply a hybrid fiber coax (HFC). In this concept lies the ability for high-speed digital data transfer between the head-end and the stations. The authors of this paper explore their idea for a media access protocol that can efficiently accomplish this task - high-speed digital data transfer over a cable.

How it works The concept to do this is simple, and involves two key players. One is the Head-End (HE). The HE can be thought of as the computer under the administrator's control. It is the main coordinator, distributor, and basically the "boss" of the whole system. The other key player in this system is the Station. There can be one or more of these (usually more than one), and they are pretty much individual systems connected to the HE.

They can be thought of as individual computers attached to the internet (which in turn is basically controlled by the HE), or as any other devices that have the purpose of sending and receiving data. These stations are dependent on the HE, and the HE itself is independent of the stations. The authors of this paper devised an efficient protocol they called a medium access control (MAC) protocol to accomplish their goals. The concept to understand the most basic scenario of the authors' MAC protocol is simple. First, imagine a made-up scene involving trains. Picture a train running on a circular track.

There is one central coordinating station where everything can be unloaded, scheduled, and shipped off. There are also many other minor stations, where things can be loaded on and off, but only after receiving permission from the central station to do so. If a person waiting at a minor station wished to send a package aboard the train, he would first have to wait for an empty space on the train to put in his request to send the package. When the request finally is put through, it gets sent to the central station. The central station, knowing the schedules for each route in the future, then knowingly sets aside a space for the package to be sent aboard the train. The person waiting to send the package is notified just before the train pulls in the minor station exactly how and when to send his package.

When the train arrives, the man can now send his package because there is an allotted space for him and he knows where it goes. This scenario is readily adapted to bi-channel data transfer between the HE and the station. The central station is the HE, the minor station is the station, the track is the hybrid fiber coax cable, and the individual available spaces on the train are data slots. The scene starts with a command for the station to transmit data (send a package). This request to transmit data is sent in the first available empty data slot, and it eventually arrives at the HE (central station). The HE then sends a confirmation, or acknowledgement, of receiving the station's request for data transfer to the station itself.

The HE makes use of its ranging mechanism (a property of the HE) to determine the round trip delay for the whole network (scheduling abilities) in order to know when a space will be available for the station to send its data. Upon finding an available space for the desired data to be transferred, the HE relays a grant of approval for the transmission which arrives right before the empty data slots. This way the station knows which slots to put its data inside of. If the available slots, however, are too small for the data the station wants to transfer, then the HE will allot more spaces later on to be used for the rest of the data (the data is cut in pieces and moved separately to be joined again later).

Performance The authors ran a simulation with 550,000 data slots in order to test their protocol and its effectiveness. Their results indicate a success for their protocol. The protocol performed well under heavy loads, and performance was not affected much by the number of stations connected to the HE. Other factors also proved this protocol to be an efficient way to transmit data. Comments This paper informed me about questions I had previously asked myself.

How data can be transferred over wires has puzzled me. However, I still do not know why it works, just that it does. The article cleared up how it works by explaining their method of using packets, or data slots, to transmit data. But, I still do not know why a cable is capable of sending data in the first place. Given that this article was not written to explain the reasoning for the mere possibility of data transfer through fiber optics and coaxial cables however, I should look elsewhere to answer the rest of my question. It amazes me that with the simple core ideas presented by the authors that something like data transfer through a HFC can work so well.

A Protocol for Efficient Transfer of Data Over Hybrid Fiber / Coax Systems. Limb, John. Sala, Dolors. I / ACM Transactions of Networking, vol. 5, no. 6: pp. 872-881. Dec. 1997.