Homework Chapter 5

《Computer Networks and Internet》

Homework Chapter 5

1. How big is the LAN address space? The IPv4 address space? The IPv6 address space?

2^48，2^32，2^128

2. Suppose four active nodes—nodes A, B, C and D—are competing for access to a channel using slotted ALOHA. Assume each node has an infinite number of packets to send. Each node attempts to transmit in each slot with probability p. The first slot is numbered slot 1, the second slot is numbered slot 2, and so on.

假设四个活动节点，节点A，B，C和D-正在争夺访问使用时隙ALOHA的通道。假设每个节点有分组的无限号码发送。每个节点将尝试在每个时隙的概率为p传输。第一时隙编号为时隙1，第二时隙编号为2的插槽，并依此类推。

a. What is the probability that node A succeeds for the first time in slot 5? b. What is the probability that some node (either A, B, C or D) succeeds in slot 4? c. What is the probability that the first success occurs in slot 3? d. What is the efficiency of this four-node system?

1.节点A首次就成功插在插槽5的概率是多少？

2.某些节点（或A，B，C或D）成功插在插槽4的概率是多少？ 3.第一次成功发生在槽3的概率是多少？ 4.这四个节点系统的效率？

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3. Calculate the efficiency of slotted ALOHA and pure ALOHA as a function of p (p=0, 0.1, 0.2, 0.3, 0.4, 0.5, …, 1.0) for the following values of N: a. N=15. b. N=20. c. N=30. Answer: Equation pure ALOHA N=15 N=20 N=30 N=15 N=20 N=30 p=0 p=0 0.1 0.1 0.2 0.2 0.3 0.3 0.4 0.4 0.5 0.5 0.6 0.6 0.7 0.7 0.8 0.8 0.9 0.9 1.0 1.0 slotted ALOHA 2

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4. Consider three LANs interconnected by two routers, as shown in Figure 1. 考虑由两个路由器相互连接3个网，如图1。

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Figure 1

a. Assign IP addresses to all of the interfaces. For Subnet 1 use addresses of the form 192.168.1.xxx; for Subnet 2 uses addresses of the form 192.168.2.xxx; and for Subnet 3 use addresses of the form 192.168.3.xxx. b. Assign MAC addresses to all of the adapters.

c. Consider sending an IP datagram from Host E to Host B. Suppose all of the ARP tables are up to date. Enumerate all the steps, as done for the single-router example in ARP.

d. Repeat (c), now assuming that the ARP table in the sending host is empty (and the other tables are up to date).

1.将IP地址分配给所有的接口。对于子网1使用形如192.168.1.xxx的地址;子网2使用的形式192.168.2.xxx地址;而对于子网3使用形式192.168.3.xxx地址。 2.指定MAC地址的所有适配器。

3.考虑发送IP数据报从主机E至主机B.假设所有的ARP表是最新的。枚举所有的步骤，可用于在ARP单路由器为例。

4.重复（c）中，现在假定在发送主机ARP表是空的（和其他表是最新的）。

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1。在E转发表确定数据包应该被路由接口192.168.3.002。

2。在E的适配器创建和以太网目的地址88-88-88-88-88-88以太网数据包。

3。路由器2接收该分组，并提取该数据报。在该路由器的转发表指示数据报路由到198.162.2.002。

4。路由器2然后通过与198.162.2.003的IP地址，端口发送带有的55-55-55-55-55-5533-33-33-33-33-33和源地址到达目的地址的以太网数据包。 5。该过程继续，直至该分组到达主机B

5. Consider Figure 1 in above problem 4. Provide MAC addresses and IP addresses for the interfaces at Host A, both routers, and Host F. Suppose Host A sends a datagram to Host F. Give the source and destination MAC addresses in the frame encapsulating this IP datagram as the frame is transmitted (i) from A to the left router, (ii) from the left router to the right router, (iii) from the right router to F. Also give the source and destination IP addresses in the IP datagram encapsulated within the frame at each of these points in time.

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