负压是什么意思
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A wide area network (WAN) is a telecommunications network that extends over a large geographic area. Wide area networks are often established with leased telecommunication circuits.[1]
Businesses, as well as schools and government entities, use wide area networks to relay data to staff, students, clients, buyers and suppliers from various locations around the world. In essence, this mode of telecommunication allows a business to effectively carry out its daily function regardless of location. The Internet may be considered a WAN.[2] Many WANs are, however, built for one particular organization and are private. WANs can be separated from local area networks (LANs) in that the latter refers to physically proximal networks.
Design options
[edit]The textbook definition of a WAN is a computer network spanning regions, countries, or even the world.[3][4] However, in terms of the application of communication protocols and concepts, it may be best to view WANs as computer networking technologies used to transmit data over long distances, and between different networks. This distinction stems from the fact that common local area network (LAN) technologies operating at lower layers of the OSI model (such as the forms of Ethernet or Wi-Fi) are often designed for physically proximal networks, and thus cannot transmit data over tens, hundreds, or even thousands of miles or kilometres.
WANs are used to connect LANs and other types of networks together so that users and computers in one location can communicate with users and computers in other locations. Many WANs are built for one particular organization and are private. Others, built by Internet service providers, provide connections from an organization's LAN to the Internet.
WANs are often built using leased lines. At each end of the leased line, a router connects the LAN on one side with a second router within the LAN on the other. Because leased lines can be very expensive, instead of using leased lines, WANs can also be built using less costly circuit switching or packet switching methods. Network protocols including TCP/IP deliver transport and addressing functions. Protocols including Packet over SONET/SDH, Multiprotocol Label Switching (MPLS), Asynchronous Transfer Mode (ATM) and Frame Relay are often used by service providers to deliver the links that are used in WANs. It is also possible to build a WAN with Ethernet.[5]
Academic research into wide area networks can be broken down into three areas: mathematical models, network emulation, and network simulation.
Performance improvements are sometimes delivered via wide area file services or WAN optimization.
Private networks
[edit]Of the approximately four billion addresses defined in IPv4, about 18 million addresses in three ranges are reserved for use in private networks. Packets addressed in these ranges are not routable on the public Internet; they are ignored by all public routers. Therefore, private hosts cannot directly communicate with public networks, but require network address translation at a routing gateway for this purpose.
Reserved private IPv4 network ranges[6] Name CIDR block Address range Number of addresses Obsolete classful description 24-bit block 10.0.0.0/8 10.0.0.0 – 10.255.255.255 16777216 Single Class A. 20-bit block 172.16.0.0/12 172.16.0.0 – 172.31.255.255 1048576 Contiguous range of 16 Class B blocks. 16-bit block 192.168.0.0/16 192.168.0.0 – 192.168.255.255 65536 Contiguous range of 256 Class C blocks.
Since two private networks, e.g., two branch offices, cannot directly communicate via the public Internet, the two networks must be bridged across the Internet via a virtual private network (VPN) or other form of IP tunnel that encapsulates packets, including their headers containing the private addresses, for transmission across the public network. Additionally, encapsulated packets may be encrypted to secure their data.
Connection technology
[edit]Many technologies are available for wide area network links. Examples include circuit-switched telephone lines, radio wave transmission, and optical fiber. New developments have successively increased transmission rates. In c.?1960, a 110 bit/s line was normal on the edge of the WAN, while core links of 56 or 64 kbit/s were considered fast. Today, households are connected to the Internet with dial-up, asymmetric digital subscriber line (ADSL), cable, WiMAX, cellular network or fiber. The speeds that people can currently use range from 28.8 kbit/s through a 28K modem over a telephone connection to speeds as high as 100 Gbit/s using 100 Gigabit Ethernet.
The following communication and networking technologies have been used to implement WANs.
AT&T conducted trials in 2017 for business use of 400-gigabit Ethernet.[11] Researchers Robert Maher, Alex Alvarado, Domani? Lavery, and Polina Bayvel of University College London were able to increase networking speeds to 1.125 terabits per second.[12] Christos Santis, graduate student Scott Steger, Amnon Yariv, Martin and Eileen Summerfield developed a new laser that potentially quadruples transfer speeds with fiber optics.[13]
See also
[edit]- Cell relay
- Internet area network (IAN)
- Label switching
- Low-power wide-area network (LPWAN)
- Wide area application services
- Wireless WAN
References
[edit]- ^ Mitchell, Bradley. "What Is a Wide Area Network (WAN)?". Lifewire. Archived from the original on 2025-08-04. Retrieved 2025-08-04.
- ^ Groth, David; Skandler, Toby (2005). Network+ Study Guide, Fourth Edition. Sybex, Inc. ISBN 0-7821-4406-3.
- ^ Forouzan, Behrouz (2025-08-04). Data Communications and Networking. McGraw-Hill. p. 14. ISBN 9780073376226.
- ^ Zhang, Yan; Ansari, Nirwan; Wu, Mingquan; Yu, Heather (2025-08-04). "On Wide Area Network Optimization". IEEE Communications Surveys & Tutorials. 14 (4): 1090–1113. CiteSeerX 10.1.1.459.4653. doi:10.1109/SURV.2011.092311.00071. ISSN 1553-877X. S2CID 18060. Archived from the original on 2025-08-04. Retrieved 2025-08-04.
- ^ CCNA Data Center DCICN 640-911 Official Cert Guide. Cisco Press. 14 November 2014. ISBN 978-0-13-378782-5.
- ^ Y. Rekhter; B. Moskowitz; D. Karrenberg; G. J. de Groot; E. Lear (February 1996). Address Allocation for Private Internets. Network Working Group IETF. doi:10.17487/RFC1918. BCP 5. RFC 1918.
- ^ "Selecting a WAN Technology (1.2) > WAN Concepts | Cisco Press".
- ^ "Selecting a WAN Technology (1.2) > WAN Concepts | Cisco Press".
- ^ "Selecting a WAN Technology (1.2) > WAN Concepts | Cisco Press".
- ^ "Selecting a WAN Technology (1.2) > WAN Concepts | Cisco Press".
- ^ "AT&T Completes Industry-Leading 400 Gb Ethernet Testing, Establishing A Future Network Blueprint for Service Providers and Businesses". www.att.com. September 8, 2017. Archived from the original on January 5, 2022. Retrieved August 20, 2018.
- ^ Maher, Robert; Alvarado, Alex; Lavery, Domani?; Bayvel, Polina (11 February 2016). "Increasing the information rates of optical communications via coded modulation: a study of transceiver performance". Scientific Reports. 6 (1): 21278. Bibcode:2016NatSR...621278M. doi:10.1038/srep21278. PMC 4750034. PMID 26864633.
- ^ "A New Laser for a Faster Internet - Caltech". Cal Tech. 19 February 2014. Archived from the original on 2025-08-04. Retrieved 2025-08-04.
External links
[edit]- Cisco - Introduction to WAN Technologies
- "What is WAN (wide area network)? - Definition from WhatIs.com", SearchEnterpriseWAN, archived from the original on 2025-08-04, retrieved 2025-08-04
- What is a software-defined wide area network?
