付録・索引

Network functionality depends on encoding, which is the process of converting a character sequence into the appropriate format to store or transmit the data (https://book.systemsapproach.org/direct/encoding.html). Encoding can be approached using compression, which seeks to encode bits of data in the smallest set possible. Compression techniques include run length encoding, differential pulse code modulation, and dictionary-based methods (https://book.systemsapproach.org/data/multimedia.html#lossless-compression-techniques). Encoding is also an important process to prepare files like JPEG (https://book.systemsapproach.org/data/multimedia.html#encoding-phase), MPEG (https://book.systemsapproach.org/data/multimedia.html#transmitting-mpeg-over-a-network), and videos (https://book.systemsapproach.org/data/multimedia.html#video-encoding-standards).

Wireless networks function similarly to wired networks, except all wireless links use the same medium. To ensure this medium is shared efficiently, it is divided using the dimension of frequency and space. Government agencies, such as the U.S. Federal Communications Commission make many of the determinations regarding which networks can use the medium, and this includes allocating certain frequency ranges for specific uses, such as television and cell phones (https://book.systemsapproach.org/direct/wireless.html#basic-issues). The physical properties of wireless networks include bandwidths (https://book.systemsapproach.org/direct/ wireless.html#physical-properties). Collision avoidance is a focus of wireless protocols (https://book.systemsapproach.org/direct/wireless.html#collision-avoidance), and wireless distribution networks use the link layer for operations (https://book.systemsapproach.org/direct/ wireless.html#distribution-system). As with all networks, security is a chief concern for wireless systems (https://book.systemsapproach.org/direct/wireless.html#security-of-wireless-links). Bluetooth is a popular wireless network (https://book.systemsapproach.org/direct/wireless.html#bluetooth-802-15-1).

Routing can be challenging for wireless, mobile devices. For example, IP addresses and mobile hosts must be handled differently in wireless networks, making it necessary to use different protocols when developing wireless networks (https://book.systemsapproach.org/scaling/mobile-ip.html#routing-among-mobile-devices).

Some networks use virtual circuit switching as an alternative technique for packet switching (https://book.systemsapproach.org/internetworking/switching.html#virtual-circuit-switching). Asynchronous Transfer Mode (ATM) is a well-known example of networking technology that relies on virtual circuit switching (https://book.systemsapproach.org/internetworking/switching.html#asynchronous-transfer-mode-atm). Another option is multiprotocol label switching, which leverages the robustness and flexibility found in datagrams with virtual circuit switching properties (https://book.systemsapproach.org/scaling/mpls.html).

Peer-to-peer networks are also useful in networks that allow a community of users to share their resources—including bandwidth, storage, and content—to give them greater network access than they would have individually. Examples of peer-to-peer networks include Gnutella and BitTorrent (https://book.systemsapproach.org/applications/overlays.html#peer-to-peer-networks).

Historically, the Internet has relied on specialized devices built with application-specific integrated circuits (ASICs), and this has made it time consuming to develop networks. Hardware switches have helped improve this situation (https://book.systemsapproach.org/internetworking/impl.html#hardware-switch). With this change, software-defined networks have become more common (https://book.systemsapproach.org/ internetworking/impl.html#software-defined-networks).

Metrics, or link costs, are an important consideration in routing and selecting the correct algorithm to handle the process. The ARPANET provided the testing ground to develop approaches for link-cost calculations (https://book.systemsapproach.org/internetworking/routing.html#metrics).

The Ethernet was developed in the mid-1970s and eventually dominated technology for local area networking. The basis for Ethernet was in Aloha, a packet radio network developed at the University of Hawaii as a support network to enable computer communications throughout the Hawaiian Islands (https://book.systemsapproach.org/direct/ethernet.html).