Questions and Answers of Computer Communications

The discussion of flow control with a reliable network service referred to a backpressure mechanism utilizing a lower-level flow control protocol. Discuss the disadvantages of this strategy.
It is common practice in most transport protocols (indeed, most protocols at all levels)for control and data to be multiplexed over the same logical channel on a per-userconnection basis. An
What does UDP provide that is not provided by IP?
What is a TCP implementation policy option?
Define the urgent and push features of TCP.
What is the benefit of the three-way handshake mechanism?
Explain the two-way and three-way handshake mechanisms.
What is the key difference between the TCP credit scheme and the sliding-window flow control scheme used by many other protocols, such as HDLC?
Briefly describe the credit scheme used by TCP for flow control.
Explain the use of multiplexing in the context of a transport protocol.
Describe four strategies by which a sending TS user can learn the address of a receiving TS user.
What addressing elements are needed to specify a target transport service (TS) user?
The original IPv6 specifications combined the Traffic class and Flow Label fields into a single 28-bit Flow Label field. This allowed flows to redefine the interpretation of different values of
The question arises as to which packets generated by a source should carry nonzero IPv6 flow labels. For some applications, the answer is obvious. Small exchanges of data should have a zero flow
The IPv6 flow mechanism assumes that the state associated with a given flow label is stored in routers, so they know how to handle packets that carry that flow label.A design requirement is to flush
The IPv6 standard states that if a packet with a nonzero flow label arrives at a router and the router has no information for that flow label, the router should ignore the flow label and forward the
Justify the recommended order in which IPv6 extension headers appear (i.e., why is the Hop-by-Hop Options header first, why is the Routing header before the Fragment header, and so on).
Compare the individual fields of the IPv4 header with the IPv6 header. Account for the functionality provided by each IPv4 field by showing how the same functionality is provided in IPv6.
In contemporary routing and addressing, the notation commonly used is called classless interdomain routing or CIDR. With CIDR, the number of bits in the mask is indicated in the following fashion:
Given a company with six individual departments and each department having ten computers or networked devices, what mask could be applied to the company network to provide the subnetting necessary to
Given a network address of 192.168.100.0 and a subnet mask of 255.255.255.192,a. How many subnets are created?b. How many hosts are there per subnet?
Is the subnet mask 255.255.0.255 valid for a Class A address?
What is the difference between the subnet mask for a Class A address with 16 bits for the subnet ID and a Class B address with 8 bits for the subnet ID?
Should internetworking be concerned with a network’s internal routing? Why or why not?
is to be used. What functions could be added to the routers to alleviate some of the problems caused by the mismatched local and long-haul networks?
The architecture suggested by Figure
A transport layer message consisting of 1500 bits of data and 160 bits of header is sent to an internet layer, which appends another 160 bits of header. This is then transmitted through two networks,
An IP datagram is to be fragmented. Which options in the option field need to be copied into the header of each fragment, and which need only be retained in the first fragment? Justify the handling
The IP checksum needs to be recalculated at routers because of changes to the IP header, such as the lifetime field. It is possible to recalculate the checksum from scratch. Suggest a procedure that
Consider a header that consists of 10 octets, with the checksum in the last two octets(this does not correspond to any actual header format) with the following content (in hexadecimal): 01 00 F6 F7
A 4480-octet datagram is to be transmitted and needs to be fragmented because it will pass through an Ethernet with a maximum payload of 1500 octets. Show the Total Length, More Flag, and Fragment
Because of fragmentation, an IP datagram can arrive in several pieces, not necessarily in the correct order. The IP entity at the receiving end system must accumulate these fragments until the
Describe some circumstances where it might be desirable to use source routing rather than let the routers make the routing decision.
What is the header overhead in the IP protocol?
In the discussion of IP, it was mentioned that the identifier, don’t fragment identifier, and time to live parameters are present in the Send primitive but not in the Deliver primitive because they
Although not explicitly stated, the Internet Protocol (IP) specification, RFC 791, defines the minimum packet size a network technology must support to allow IP to run over it.a. Read Section 3.2 of
What is the purpose of each of the IPv6 header types?
Briefly explain the three types of IPv6 addresses.
What is the difference between the Traffic class and Flow Label fields in the IPv6 header?
How is the IPv4 header checksum calculated?
Explain the function of the three flags in the IPv4 header.
What are the pros and cons of limiting reassembly to the endpoint as compared to allowing en route reassembly?
Give some reasons for using fragmentation and reassembly.
List the requirements for an internetworking facility.
Two documents related to safety concerns associated with wireless media are the FCC OET-65 Bulletin and the ANSI/IEEE C95.1-1999. Briefly describe the purpose of these documents and briefly outline
Compare and contrast wired and wireless LANs. What unique concerns must be addressed by the designer of a WLAN network?
Try this experiment: How far can you go and still be connected to your network? This will depend to a large extent on your physical environment.
Most wireless cards come with a small set of applications that can perform tasks similar to Netstumbler. Using your own client software, determine the same items you did with Netstumbler. Do they
There are many free tools and applications available for helping decipher wireless networks. One of the most popular is Netstumbler. Obtain the software at www.netstumbler.com and follow the links
Using what you know about wired and wireless networks, draw the topology of your network.
Answer the following questions about your wireless network:a. What is the SSID?b. Who is the equipment vendor?c. What standard are you using?d. What is the size of the network?
Show the locations of the FCS field in Figure 13.11.
The 802.11a and 802.11b physical layers make use of data scrambling (see Appendix 12B). For 802.11, the scrambling equation is P(X) = 1 + X4 + X7 In this case the shift register consists of seven
For IEEE 802.11a, show how the modulation technique and coding rate determine the data rate.
Consider the sequence of actions within a BSS depicted in Figure 13.14. Draw a timeline, beginning with a period during which the medium is busy and ending with a period in which the CF-End is
What is the difference between an access point and a portal?
Draw a figure similar to Figure 12.16 for the MLT-3 scrambler and descrambler.
a. Verify that the division illustrated in Figure 12.18a corresponds to the implementation of Figure 12.17a by calculating the result step by step using Equation (12.1).b. Verify that the
For the bit stream 0101110, sketch the waveforms for NRZ-L, NRZI, Manchester, and differential Manchester, and MLT-3.
Draw the MLT decoder state diagram that corresponds to the encoder state diagram of Figure 12.12.
With 8B6T coding, the DC algorithm sometimes negates all of the ternary symbols in a code group. How does the receiver recognize this condition? How does the receiver discriminate between a negated
With 8B6T coding, the effective data rate on a single channel is 33 Mbps with a signaling rate of 25 Mbaud. If a pure ternary scheme were used, what is the effective data rate for a signaling rate of
Analyze the advantages of having the FCS field of IEEE 802.3 frames in the trailer of the frame rather than in the header of the frame.
Describe the signal pattern produced on the medium by the Manchester-encoded preamble of the IEEE 802.3 MAC frame.
The binary exponential backoff algorithm is defined by IEEE 802 as follows:The delay is an integral multiple of slot time. The number of slot times to delay before the nth retransmission attempt is
For p-persistent CSMA, consider the following situation. A station is ready to transmit and is listening to the current transmission. No other station is ready to transmit, and there will be no other
A disadvantage of the contention approach for LANs, such as CSMA/CD, is the capacity wasted due to multiple stations attempting to access the channel at the same time. Suppose that time is divided
In the context of Ethernet, what is full-duplex operation?
How does Fast Ethernet differ from 10BASE-T, other than the data rate?
What are the transmission medium options for Fast Ethernet?
Explain binary exponential backoff.
What is CSMA/CD?
Explain the three persistence protocols that can be used with CSMA.
A station on a LAN that includes an attached bridge sends out a frame to a device that is not present on any of the segments of the total network. What does the bridge do with this frame?
Develop a spanning tree for the configuration of Figure 11.15.
For the configuration of Figure 11.8, show the central routing matrix and the routing tables at each bridge.
for a configuration in whicha. Two LANs are connected via two bridges that are connected by a point-to-point link.b. Two LANs are connected via two bridges that are connected by an ATM
Draw figures similar to Figure
Repeat Problem 15.4 for a data rate of 100 Mbps.
Consider a baseband bus with a number of equally spaced stations with a data rate of 10 Mbps and a bus length of 1 km.a. What is the mean time to send a frame of 1000 bits to another station,
Consider the transfer of a file containing one million 8-bit characters from one station to another. What is the total elapsed time and effective throughput for the following cases:a. A
An asynchronous device, such as a teletype, transmits characters one at a time with unpredictable delays between characters. What problems, if any, do you foresee if such a device is connected to a
Instead of LLC, could HDLC be used as a data link control protocol for a LAN? If not, what is lacking?
What is the difference between a hub and a layer 2 switch?
What is a spanning tree?
Why are there multiple LAN standards?
What is the purpose of the IEEE 802 committee?
List four common LAN topologies and briefly describe their methods of operation.
What is network topology?
What is the difference between fast and slow fading?
What is the difference between diffraction and scattering?
What is fading?
Explain the paging function of a cellular system.
List five ways of increasing the capacity of a cellular system.
What is the principle of frequency reuse in the context of a cellular network?
What geometric shape is used in cellular system design?
In order to support IP service over an ATM network, IP datagrams must first be segmented into a number of ATM cells before sending them over the ATM network. As ATM does not provide cell loss
when we look at a switch it is busy. Suppose that if there is a cell being transmitted by a switch, the average delay spent waiting for a cell to finish transmission is one-half a cell transmission
Consider compressed video transmission in an ATM network. Suppose standard ATM cells must be transmitted through 5 switches. The data rate is 43 Mbps.a. What is the transmission time for one cell
Another key design decision for ATM is the size of the data field for fixed-size cells.Let us consider this decision from the point of view of efficiency and delay.a. Assume that an extended

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