Data Link Layer Protocols

(1). Answer

Data Link Layer Protocols always put CRC in there trailer rather than in the header. Because, because in its header source and destination physical address are present and the CRC is evaluated during transmission and appended to the output stream as soon as the last bit goes out onto the physical medium. If the CRC were in the header, it would be necessary to make a pass over the frame to compute the CRC before transmitting. The CRC is computed while the packet is being transmitted and then incorporated in a trailer. Similarly, the receiver computes the CRC and compares it with the transmitted one. It is better to have the CRC in a trailer. Because then we can compute the CRC as you transmit the packet. If we put it in the header, we would have to make one pass over the packet computing the CRC, then send the CRC, and then a second pass actually stuffing each byte out the interface.


In terms of collision that is there was less collision ratein pure aloha the throughput is about 19 % and in case of sorted it is approximately doubled is 38%.

An improvement to the original ALOHA protocol was "Slotted ALOHA", which introduced discrete timeslots and increased the maximum throughput Slotted Aloha essentially advertises the availability of a time slot in a channel. In slotted ALOHA we divide the time into slots and force the station to send only at the beginning of the time. A station can send only at the beginning of a timeslot, and thus collisions are reduced. In this case, we only need to worry about the transmission-attempts within 1 frame-time and not 2 consecutive frame-times, since collisions can only occur during each timeslot


It is possible Somewhere in some cases. If data is 01111110 -> 011111010 is send if the second 0 is lost due to transmission error, 01111110 will received, which can be interpreted as end of frame. With the change in one bit there is no balancing of that change with any bit else so sum will be different from the information and frame will be discarded because of error. The bits before the end of the frame will then be interpreted as the check-sum. If the check-sum is 4 bits, there is only one chance in 24 that these random bits will be interpreted as a valid check-sum. Due to bit stuffing, the possible problem if the data contains the flag byte pattern(0111 1110) is eliminated .Generally speaking, the longer the checksum, the lower the probability of an error getting through undetected, but the probability is never zero.

(4). Answer:-

Network might use an error correcting code instead of error detection and retransmission due to:

(a) It is easy to detect error rather than error correcting.

(b)It is very lengthy process to detect an error and retransmit. Because, if the no of bit is less than It is easy but if no of bit is more than it is difficult.

(5). Answer:-

Wireless transmission and wired transmission use different set of multiple channel allocation strategies. When detection was already available there was a need of avoidance because in wireless transmission because does not use an electrical or optical conductor. . This is not useful for effective collision detection. When the collision avoidance strategy fails such schemes cannot detect collisions, and corrupted data frames are still transmitted in their entirety, thereby wasting the channel bandwidth and significantly reducing the network throughput and Wireless transmission is used when distance make cable media difficult and in wired transmission the selection of networking media depends on various factors such as connectivity & bandwidth The basic idea of the proposed protocol is the use of pulses in an out-of-band control channel for exploring channel condition and medium reservation and achieving both collision avoidance and collision detection.. So there was a need of avoidance when detection was already available.

(6). Answer:-

Bluetooth: Bluetooth is the name of a new technology that is no becoming commercially available. It promises to change significantly the way we What is Bluetooth whatis called blue tooth cable replacement technologyuse machines.It is use to transfer and share the data.


Two types of links between slave and master are as follows:

1) SCO (Synchronous connection-oriented)link: The SCO link is a symmetric point-to-point link . The master maintains the SCO link by the reserved slots at regular intervals and it is used for packet-switched data available at irregular intervals.

2) ACL (Asynchronous connectionless link): The ACL link is a point-to-multipoint link and it is used in real time such as telephone connections.

the master shall always start at even numbered slots and slave transmission shall always start at odd numbered slots (though they may continue to transmit regardless of the number of the slot). Baseband also manages asynchronous and synchronous links, handles packets and does paging and inquiry to access and inquire the Bluetooth devices..

(7). Answer:-

For 5-bit sequence numbers the maximum size of the sender and receiver windows for each of protocols is following

(a) 25=32 maximum size of the send and receive window is 1

(b) N=2m-1 maximum size of the send is 31and receive window is 1

(c) 2m-1, 25-1=16 maximum size of the send 16 and receive window is16

(8). Answer: -

An Ethernet destination address 07:01:02:03:04:05 is multicast.

The first byte in binary is 00000111. The least significant bit is 1. This means that the pattern defines a multicast address.

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