15.5 Blockchain
Blockchain is a network-based technology that was originally developed to support Bitcoin, a cryptocurrency that has been in use since 2009. A cryptocurrency is a currency that exists only in the digital world, instead of as paper money or some other physical representation. But the importance of blockchain is spreading beyond cryptocurrency; many think that it represents the future of online transactions.
Blockchain is like a public ledger, recording important data about economic transactions. Although originally designed for financial transactions, it can be used to record anything of value, such as contracts, medical data, or voting records.
A block is a record of new transactions. Once verified using established algorithms and encryption technology, a transaction is added to a block, and the block is added to the chain of ongoing sequential transactions (the blockchain).
One reason blockchain technology is so exciting is that the record of transactions is considered incorruptible. The ledger of transactions is decentralized—that is, it’s not stored in only one place, but across the Internet on many computers. It is also self-auditing: Every ten minutes, the ledger is reconciled across the network. Therefore, there is no single point of failure; no centralized version of the information exists that a hacker could corrupt. It cannot be controlled by any single entity.
Blockchain creates the ability to bypass traditional entities involved in these transactions, such as banks or even governments.
It is also thought that blockchain may have a significant impact on the economic status of people around the world. Just as anyone can have a voice on the Internet, blockchain promises to empower people economically, allowing anyone to register property rights, for instance, who wouldn’t otherwise have access to such services.
SUMMARY
A network is a collection of computers connected to share resources and data. Network technologies must concern themselves with underlying protocols and data transfer speeds. The client/server model has emerged as an important software technology given our ever-increasing reliance on networks.
Networks are often classified by their scope. A local-area network (LAN) covers a small geographic area and a relatively small number of connected devices. A wide-area network (WAN) embraces the concept of internetworking, connecting one network to another, and covers a large geographic area. A metropolitan-area network (MAN) is specially designed for large cities. LAN topologies include ring, star, and bus networks. Ethernet has become a standard topology for local-area networks.
Open systems are based on a common model of network architecture and protocols, allowing for interoperability. The OSI Reference Model is a seven-layer description of network processing based on open-system principles.
The Internet backbone is a set of high-speed networks provided by various companies. Internet service providers (ISPs) connect to the backbone or to other ISPs and provide connections for both home and business computing. Home connection technologies include phone modems, digital subscriber lines (DSL), and cable modems. Phone modems transfer data as audio signals and, therefore, are quite slow. DSL uses the same phone lines but transfers data digitally. Cable modems are also digital but use cable TV wiring to transfer data.
Messages are transferred over the Internet by breaking them up into packets and sending those packets separately to their destination, where they are reassembled into the original message. Packets may make several intermediate hops between networks before arriving at their destination. Routers are network devices that guide a packet between networks. Repeaters strengthen digital signals before they degrade too much.
Network protocols are layered so that a high-level protocol relies on lower-level protocols that support it. The key lower-level protocol suite for Internet traffic is TCP/IP. IP protocols and software deal with the routing of packets. TCP protocols and software divide messages into packets, reassemble them at the destination, and handle any errors that occur. High-level protocols include SMTP for email traffic, FTP for file transfers, telnet for remote login sessions, and HTTP for web traffic. Several high-level protocols have been assigned port numbers, which are used to help control and process network traffic. MIME types have been defined for many types of documents and special data formats.
A firewall protects a network from inappropriate access and enforces an organization’s access control policy. Some firewalls simply block traffic on specific ports; other, more sophisticated firewalls analyze the content of network traffic.
An Internet network address must pinpoint a particular machine among all possible ones in the world. A hostname uses readable words separated by dots. A hostname is translated into an IP address, which is a numeric address separated into four sections. One part of the IP address identifies the network, and another part identifies the specific host on that network. How the IP address is broken down depends on the network class (A, B, or C) that the address references.
The domain name system (DNS) translates hostnames into IP addresses. DNS has evolved from using a single file containing all of the information into a distributed system dividing the responsibility among millions of domain name servers. Top-level domains, such as .com and .edu, have become crowded, so some new top-level domains, such as .info and .biz, have been approved.
Cloud computing is a service that provides storage space and other resources on the Internet, largely freeing you from the responsibility of managing data and making it available wherever you are. There are various types of cloud services available at varying costs.
KEY TERMS
EXERCISES
For Exercises 1–6, match the word or acronym with the definition or the appropriate blank.
LAN
WAN
Gateway
Bus topology
Ethernet
Internet
For Exercises 7–15, match the word or acronym with the definition or the appropriate blank.
DSL
TCP/IP
UDP
IP
TCP
Broadband
For Exercises 16–20, match the protocol or standard with what it specifies or defines.
SMTP
FTP
Telnet
HTTP
MIME type
For Exercises 21–28, mark the answers true or false as follows:
True
False