Ethernet Switching

1. A user message is split into 15 frames, each of which has an 80% chance of arriving error-free. If no error control is used by the data link layer, how many times must the message be sent on the average to get the entire message through? 2. A communication channel has a bit rate of 14 kbps and an one-way propagation delay of 10 msec. If the sender sends one frame and waits for an acknowledgment before proceeding, what range of frame sizes gives an efficiency of at least 50%? 3. A 200 km long cable operates at T1 rate. The propagation speed in the cable is 2/3 of speed of light (200,000 km/sec). How many bits can fit in the cable? 4. A group of N stations share a 64 kbps pure ALOH... click for more

Ethernet Switching

1. For a 10Gigabit network operating over 4,000 km, the delay becomes the limiting factor, rather than the bandwidth. Consider a MAN with the average distance (between the source and destination) of 20 km. At what rate does the round-trip delay due to the speed of light equal the transmission delay for a 1,000-byte packet? 2. A group of N stations share a 56 kbps slotted ALOHA channel. Each station generates a 1000-bit frame on an average of once every 10 second, even if the previous frame has not yet been sent (i.e. frame is buffered). What is the maximum value of N? 3. Consider building a supercomputer network with a very high speed technology. The data path is 64-bit wide, an... click for more

Ethernet Switching

1. ATM networks use a token bucket scheme to regulate traffic (traffic shaping). A new token is put into the bucket every 1 usec so ATM cells can be sent during this period. The data payload of ATM cells is 48 bytes. What is the maximum sustainable net (or effective) data rate? 2. A bridge between an 802.3 LAN and an 802.4 LAN has a problem with intermittent memory errors. Can this problem cause undetected errors with transmitted frames, or will these all be caught by the frame checksum? 3. A virtual circuit is newly set up in an ATM network. Between the source and destination hosts lie 3 ATM switches. How many messages (including acknowledgments) will be sent to establish the circu... click for more

Erlang

1. A company needs to provide sufficient private trunks between two switches to accommodate 90% of call attempts among employees during the busy hour. Assume that there will be 560 callers at random times during that hour, and that call duration averages 3 minutes. Employees are instructed to attempt to call using a trunk; if blocked, callers will use a more expensive company-issued calling card. How many trunks will be needed? 2. In order to eliminate the cost of calling cards, the company in the above problem is considering a new policy that requires blocked callers to redial over and over until they get a trunk. Assuming the same number of callers and the same call duration, ... click for more

data link question

In order to delimit messages from a stream of bits being exchanged on a data link, a sender marks the beginning and end of each message with a control flag. In order to prevent the receiver from inadvertently detecting the end of a message when a pattern in the data matches the control flag, the sender stuffs extra bits or characters into the data as necessary, while the receiver removes these extra bits or characters. Assume that a sender and receiver are exchanging data on a link using bit stuffing. (a) Given a message containing the following bits: 1111101010000111111110001 what bit pattern (including the beginning and ending flags and any stuffed bits) will the transmitter send?... click for more