Networks questions....!!!!
dear all,
can you please explain these questions below in networking....
your help is really appreciated...
best regards,
DHCP
To configure a new computer to be attached to the Internet without using autocon figuration services such as DHCP, you need to specify four parameters in order to make the Internet working part work properly. Name these parameters, and for each parameter describe why it is important.
DNS
Assuming that an attack would succeed in bringing down all of the root servers in the DNS system, what implications would that have to the operation and usability of the Internet?
Multiple Access
1)
a) Protocols like ALOHA and CSMA/CD are also called statistical multiplexing protocols.
Why? What are the advantages as compared to TDMA, FDMA, and CDMA?
b) Suppose nodes A and B are on the same 10Mbit/s Ethernet segment (CDMA/CD).
Node A begins transmitting a frame and, before it finishes and before the frame reaches B, also node B begins transmitting a frame. What is the condition that both A and B
can detect the collision? Assuming that the propagation delay between the two nodes is 225 bit times (1 bit time = 1 bit / 10Mbit/s), what is the minimum frame size allowing collision detection?
2)
In this problem you will derive the efficiency of a CSMA/CDlike multiple access protocol. In this protocol, time is slotted and all adapters are synchronised to the slots. Unlike slotted ALOHA, however, the length of a slot (in time) is much less than a frame time (the time to transmit a frame). Let T be the length of a slot. Suppose all frames are of constant length L = kRT, where R is the transmission rate of the channel and k is an integer. Suppose there are N nodes,each with an infinite number of frames to send. We also assume that P (propagation time) is smaller than T, so that all nodes can detect a collision before the end of a slot time. The protocol is as follows:
• If, for a given slot, no node has possession of the channel, all nodes contend for the channel; in particular, each node tranmits in the slot with probability p. If exactly one node transmits in the slot, that node takes possession of the channel for the subsequent k − 1 slots and transmits its entire frame.
• If some node has possession of the channel, all other nodes refrain from transmitting until the node that possesses the channel has finished transmitting its frame. Once this node has transmitted its frame, all nodes contend for the channel.
Note that the channel alternates between two states: the productive state, which lasts exactly k slots, and the nonproductive state, which lasts for a random number of slots. Clearly, the channel efficiency is the ratio of k/(k+x), where x is the expected number of consecutive unproductive slots.
(a) For fixed N and p, determine the efficiency of this protocol.
(b) For fixed N, determine the p that maximises the efficiency.
(c) Using the p (which is a function of N) found in (b), determine the efficiency as N approaches infinity.
(d) Show that this efficiency appraoches 1 as the frame length becomes large.
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