154 internetworking in order to connect wired and

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Chapter UECC / Exercise 33
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1.5.4 Internetworking In order to connect wired and wireless networks together they must share a common networking protocol such as as TCP/IP and ATM. As we have seen TCP has problems operating over wireless links, mainly due to its use of congestion control in response to packet delays. However, wireless links can experience large and variable delays, sporadic error bursts, and in- termittent connectivity due to handoffs. Large and variable link delays cause large oscillations in the TCP sending rate, resulting in large and variable end-to-end delays. Error bursts can result in unnecessary retransmissions by TCP, since these errors are usually corrected at the link layer, and also cause significant throughput degradation, since flow is reduced in response to every error burst. The effect of intermittent connectivity on TCP is similar to that of error bursts, resulting in unneces- sary retransmissions and throughput reduction. Various modifications to TCP have been proposed to address this issue, but none has emerged as a clear solution. ATM provides QoS guarantees, which are required for some applications. But it is not clear that the QoS guarantees of ATM can be achieved in a wireless network. 1.5.5 Security Wireless communication systems are inherently less private than wireline systems because the wire- less link can be intercepted without any physical tap, and this interception cannot be detected by the transmitter or the receiver. This lack of link security also makes wireless networks more subject to usage fraud and activity monitoring than their wireline counterparts. Opportunities for fraudulent attacks will increase as services like wireless banking and commerce become available. Thus, secu- rity technology is an important challenge. Security issues can be broken down into three categories: network security, radio link security, and hardware security. Network security includes countermeasures to fraudulent access and monitoring of network ac- tivity, and end-to- end encryption. Radio link security entails preventing interception of the radio signal, ensuring privacy of user location information and, for military applications, anti-jam and low probability of interception and detection capabilities. Hardware security should prevent fraudulent use of the mobile terminal in the event of theft or loss, and user databases should also be secure against unauthorized access. 1.5.6 A New Paradigm for Wireless Network Design Network design using the layered OSI architecture has worked well for wired networks, especially as the communication links evolved to provide gigabit-per-second data rates and BERs of 10 - 12 . Wireless channels typically have much lower data rates (tens or hundreds of Kbps for typical chan- nels with high user mobility), higher BERs ( 10 - 2 - 10 - 6 ), and exhibit sporadic error bursts and in- termittent connectivity. These performance characteristics also vary over time, as does the network topology and user traffic. Consequently, good end-to-end wireless network performance will not be possible without a truly optimized, integrated, and adaptive network design.
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Enhanced Microsoft Office 2013: Illustrated Fundamentals
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Chapter UECC / Exercise 33
Enhanced Microsoft Office 2013: Illustrated Fundamentals
Cram/Duffy
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1.5. NETWORK DESIGN

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