unit 4 Flashcards
What does dynamic channel allocation not assume?
dependent traffic
What is a difference between slotted ALOHA and pure ALOHA?
with slotted aloha a station is not permitted to send whenever the user wants while with pure aloha they can.
Explain a hidden terminal problem.
“The problem of a station not being able to detect a potential competitor for the medium because the competitor is too far away”
What cable is used for 10GBase-SR?
multimode fiber cables?
Systems in which multiple users share a common channel in a way that can lead to conflicts are know as __________.
contention system
When a station has data to send, it first listens to the channel to see if anyone else is transmitting at that moment. If the channel is idle, the stations sends its data. Otherwise, if the channel is busy, the station just waits until it becomes idle. Then the station transmits a frame. If a collision occurs, the station waits a random amount of time and starts all over again. What is this protocol called?
1- persistent csma
________________ is the basis of the classic Ethernet LAN, so it is worth devoting some time to looking at it in detail. It is important to realize that collision detection is an analog process. The station’s hardware must listen to the channel while it is transmitting. If the signal it reads back is different from the signal it is putting out, it knows that a collision is occurring.
csma/cd
As a collision-free protocol, this protocol consists fo exact N slots. If station 0 has a frame to send, it transmits a 1 bit during the slot 0. No other station is allowed to transmit during this slot. Regardless of what station 0 does, station 1 gets the opportunity to transmit a 1 bit during slot 1, but only if it has a frame queued. In general, station j may announce that it has a frame to send by inserting a 1 bit into slot j. After all N slots have passed by, each station has complete knowledge of which stations wish to transmit. At that point, they begin transmitting frames in numerical order. What is this protocol called?
basic bit map
Now let us look at a different situation: station B transmitting to station A at the same time that station C wants to transmit to station D. If C senses the medium, it will hear a transmission and falsely conclude that it may not send to D. In fact, such a transmission would cause bad reception only in the zone between B and C, where neither of the intended receivers is located. What is this problem called?
exposed terminal problem
A ____________ is a physical layer device that receives, amplifies (i.e., regenerates), and retransmits signals in both directions. As far as the software is concerned, a series of cable segments connected by repeaters is no different from a single cable
repeater
