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Internetworking with TCP/IP: Pearson New International Edition

Douglas E. Comer

Chapter 15

Internet Multicasting - all with Video Answers

Educators

Chapter Questions

Problem 1

The IPv4 standard suggests using 23 bits of an IP multicast address to form a hardware multicast address. In such a scheme, how many IP multicast addresses map to a single hardware multicast address?

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Problem 2

Answer the question above for IPv6.

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Problem 3

Argue that IP multicast group IDs do not need as many bits as have been allocated. Suppose a group ID used 23 bits and analyze the disadvantages. (Hint: what are the practical limits on the number of groups to which a host can belong and the number of hosts on a single network?)

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Problem 4

IP software must always check the destination addresses on incoming multicast datagrams and discard datagrams if the host is not in the specified multicast group. Explain how the host might receive a multicast destined for a group to which that host is not a member.

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Problem 5

Multicast routers need to know whether a group has members on a given network because the router needs to know which multicast trees to join. Is there any advantage to routers knowing the exact set of hosts on a network that belong to a given multicast group? Explain.

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Problem 6

Find three applications that can benefit from IP multicast.

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Problem 7

The standard says that IP software must arrange to deliver a copy of any outgoing multicast datagram to application programs on the same host that belong to the specified multicast group. Does the design make programming easier or more difficult? Explain.

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Problem 8

When the underlying hardware does not support multicast, IP multicast uses hardware broadcast for delivery. How can doing so cause problems? Is there any advantage to using IP multicast over such networks?

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Problem 9

DVMRP was derived from RIP. Read RFC 1075 on DVMRP and compare the two protocols. How much more complex is DVMRP than RIP?

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Problem 10

Version 3 of IGMP and MLDV2 both include a measure of robustness that is intended to accommodate packet loss by allowing transmission of multiple copies of a message. How does the protocol arrive at an estimate of the robustness value needed on a given network?

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Problem 11

Explain why a multi-homed host may need to join a multicast group on one network, but not on another. (Hint: consider an audio teleconference.)

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Problem 12

Suppose an application programmer makes a choice to simplify programming: when joining a multicast group, simply join on each network to which the host attaches. Show that joining on all local interfaces can lead to arbitrary traffic on remote networks.

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01:19

Problem 13

Estimate the size of the multicast forwarding table needed to handle multicast of audio from 100 radio stations, if each station has a total of ten million listeners at random locations around the world.

Mayukh Banik
Mayukh Banik
Numerade Educator

Problem 14

Consider a cable TV provider using IP technology. Assume each set-top box uses IP and devise a scheme in which the cable provider broadcasts all channels to a neighborhood distribution point and then uses multicast to deliver to residences.

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Problem 15

Argue that only two types of multicast are practical in the Internet: statically configured commercial services that multicast to large numbers of subscribers and dynamically configured services that include a few participants (e.g., family members in three households participating in a single IP phone call).

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Problem 16

Consider reliable multicast achieved through redundant transmission. If a given link has high probability of corruption, is it better to send redundant copies of a datagram or to send one copy that uses forward error-correcting codes? Explain.

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Problem 17

The data-driven multicast routing paradigm works best on local networks that have low delay and excess capacity, while the demand-driven paradigm works best in a wide area environment that has limited capacity and higher delay. Does it make sense to devise a single protocol that combines the two schemes? Why or why not? (Hint: consider MOSPF.)

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Problem 18

Read the PIM-SM protocol specification to find how the protocol defines the notion of sparse. Find an example of an internet in which the population of group members is sparse, but for which DVMRP is a better multicast routing protocol.

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06:14

Problem 19

Devise a quantitative measure that can be used to decide when PIM-SM should switch from a shared tree to a shortest path tree.

Chris Trentman
Chris Trentman
Numerade Educator