Chapter 6 Review Questions
1. In infrastructure mode of operation, each wireless host is connected to the larger
network via a base station (access point). If not operating in infrastructure mode, a
2. a) Single hop, infrastructure-based
3. Path loss is due to the attenuation of the electromagnetic signal when it travels
through matter. Multipath propagation results in blurring of the received signal at the
4. a) Increasing the transmission power
b) Reducing the transmission rate
5. APs transmit beacon frames. An AP’s beacon frames will be transmitted over one of
7. APs transmit beacon frames. An AP’s beacon frames will be transmitted over one of
8. False
9. Each wireless station can set an RTS threshold such that the RTS/CTS sequence is
10. No, there wouldn’t be any advantage. Suppose there are two stations that want to
transmit at the same time, and they both use RTS/CTS. If the RTS frame is as long as
11. Initially the switch has an entry in its forwarding table which associates the wireless
station with the earlier AP. When the wireless station associates with the new AP, the
AP.
12. Any ordinary Bluetooth node can be a master node whereas access points in 802.11
14. “Opportunistic Scheduling” refers to matching the physical layer protocol to channel
15. UMTS to GSM and CDMA-2000 to IS-95.
16. No. A node can remain connected to the same access point throughout its connection
17. A permanent address for a mobile node is its IP address when it is at its home
19. The home network in GSM maintains a database called the home location register
(HLR), which contains the permanent cell phone number and subscriber profile
information about each of its subscribers. The HLR also contains information about
20. Anchor MSC is the MSC visited by the mobile when a call first begins; anchor MSC
thus remains unchanged during the call. Throughout the call’s duration and regardless
21. a) Local recovery
Chapter 6 Problems
Problem 1
Problem 2
Sender 2 output = [1,-1,1,1,1,-1,1,1]; [ 1,-1,1,1,1,-1,1,1]
Problem 3
Problem 4
Problem 5
a) The two APs will typically have different SSIDs and MAC addresses. A wireless
station arriving to the café will associate with one of the SSIDs (that is, one of the
APs). After association, there is a virtual link between the new station and the AP.
Problem 6
Suppose that wireless station H1 has 1000 long frames to transmit. (H1 may be an AP
that is forwarding an MP3 to some other wireless station.) Suppose initially H1 is the
only station that wants to transmit, but that while half-way through transmitting its first
Problem 7
A frame without data is 32 bytes long. Assuming a transmission rate of 11 Mbps, the time
Problem 8
a) 1 message/ 2 slots
b) 2 messages/slot
c) 1 message/slot
Problem 10
a) 10 Mbps if it only transmits to node A. This solution is not fair since only A is getting
served. By “fair” it means that each of the four nodes should be allotted equal number
of slots.
b) For the fairness requirement such that each node receives an equal amount of data
10t n1 = 5t n2 = 2.5t n3 = t n4
Hence,
n2 = 2 n1
n3 = 4 n1
n4 = 10 n1
= (10N/17 + 5 * 2N/17 + 2.5 * 4N/17 + 1 * 10N/17)/N
= 40/17 = 2.35 Mbps
c) Let node A receives twice as much data as nodes B, C, and D during the sub-frame.
Hence,
10tn1 = 2 * 5tn2 = 2 * 2.5tn3 = 2 * tn4
Problem 11
a) No. All the routers might not be able to route the datagram immediately. This is
because the Distance Vector algorithm (as well as the inter-AS routing protocols like
BGP) is decentralized and takes some time to terminate. So, during the time when the
Problem 12
If the correspondent is mobile, then any datagrams destined to the correspondent would
Problem 13
Because datagrams must be first forward to the home agent, and from there to the mobile,
Problem 14
First, we note that chaining was discussed at the end of section 6.5. In the case of
chaining using indirect routing through a home agent, the following events would
happen:
x The mobile node arrives at A, A notifies the home agent that the mobile is now
datagrams it receives (from the foreign agent in A) that are addressed to the
mobile’s COA in B to the mobile’s COA in C.
Note that when the mobile goes offline (i.e., has no address) or returns to its home
network, the datagram-forwarding state maintained by the foreign agents in A, B and C
must be removed. This teardown must also be done through signaling messages. Note
home agent will forward datagrams it receives that are addressed to the mobile’s
COA in B.
x The mobile node moves to C. The foreign agent at C must notify the foreign
agent at B and the home agent that the mobile is no longer resident in B but in fact
is resident in C and has the specified COA in C. The foreign agent in B can
Problem 15
Two mobiles could certainly have the same care-of-address in the same visited network.
Problem 16
If the MSRN is provided to the HLR, then the value of the MSRN must be updated in the