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Wireless Communication - Internet
The advent of the Internet has caused a revolutionary change in the use of computers and the search for information. The Internet has affected the traditional way of information exchange and now almost every city, every town, and every street has access to the Internet.
Homes, schools and businesses connect to the Internet today using a variety of different methods. One method, wireless Internet service, provides Internet access to customers without the need for underground copper, fiber, or other forms of commercial network cabling. Compared to more established wired services like DSL and cable Internet, wireless technology brings added convenience and mobility to computer networks.
The below sections describe each popular type of wireless Internet service available.
Satellite Internet
Introduced in the mid1990s, satellite became the first mainstream consumer wireless Internet service. Compared to other forms of wireless Internet service, satellite enjoys the advantage of availability. Requiring only a small dish antenna, satellite modem and subscription plan, satellite works in almost all rural areas not serviced by other technologies.
However, satellite also offers relatively low performing wireless Internet. Satellite suffers from high latency (delay) connections due to the long distance signals must travel between Earth and the orbiting stations. Satellite also supports relatively modest amounts of network bandwidth.
Public Wi-Fi Networks
Some municipalities have built their public wireless Internet service using Wi-Fi technology. These so-called mesh networks join numerous wireless access points together to span larger urban areas. Individual Wi-Fi hotspots also provide public wireless Internet service in select locations.
Wi-Fi is a low-cost option relative to other forms of wireless Internet service. Equipment is inexpensive (many newer computers have the needed hardware built in), and Wi-Fi hotspots remains free in some locales.
Fixed Wireless Broadband
Fixed wireless is a type of broadband that utilizes mounted antennas pointed at radio transmission towers.
Mobile Broadband
Cell phones have existed for decades, but only recently have cellular networks evolved to become a mainstream form of wireless Internet service. With an installed cellular network adapter, or by tethering a cell phone to a laptop computer, Internet connectivity can be maintained in any area with cell tower coverage. Mobile broadband service will not function without having an Internet data subscription in place from some provider.
The classical wired networks have given rise to a number of application protocols such as TELNET, FTP and SMTP. The wireless application protocol (WAP) architecture aims at bridging the gap at the application level, between the wireless users and the services offered to them.
Wireless Internet
Wireless Internet refers to the extension of the services offered by the Internet to mobile users, enabling them to access information and data irrespective of their location. The inherent problems associated with wireless domain, mobility of nodes, and the design of existing protocols used in the Internet, require several solutions for making the wireless Internet a reality.
The major issues that are to be considered for Wireless Internet are the following −
- Address mobility
- Inefficiency of transport layer protocols and
- Inefficiency of application layer protocols
Address Mobility
The network layer protocol used in the Internet is Internet Protocol (IP) which was designed for wired networks with fixed nodes. IP employs a hierarchical addressing with a globally unique 32-bit address which has two parts Network identifier and Host identifier.
The network identifier refers to the subnet address to which the host is connected. The addressing scheme was used to reduce the routing table size in the core routers of the Internet, which uses only the network part of the IP address for making routing decisions.
This addressing scheme may not work directly in the wireless extension of the Internet, as the mobile hosts may move from one subnet to another, but the packets addressed to the mobile host may be delivered to the old subnet to which the node was originally attached.
Inefficiency of Transport Layer Protocols
The transport layer is very important in the Internet and it ensures setting up and maintaining end-to-end connections, reliable end-to-end delivery of data packets, flow control and congestion control. TCP is the predominant transport layer protocol for wired networks, even though UDP, a connectionless unreliable transport layer protocol is used by certain applications.
Wireless Internet requires efficient operation of the transport layer protocols as the wireless medium is inherently unreliable due to its time varying and environment dependent characteristics. Traditional TCP invokes a congestion control algorithm in order to handle congestion in the networks. If a data packet or an ACK packet is lost, then TCP assumes that the loss is due to congestion and reduces the size of the congestion window by half.
With every successive packet loss, the congestion window is reduced, and hence TCP provides a degraded performance in wireless links. Even in situations where the packet loss is caused by link error or collision, the TCP invokes the congestion control algorithm leading to very low throughput.
The identification of the real cause that led to the packet loss is important in improving the performance of the TCP over wireless links. Some of the solutions for the transport layer issues include −
- Indirect TCP (ITCP)
- Snoop TCP and
- Mobile TCP
Inefficiency of Application Layer Protocols
Traditional application layer protocols used in the Internet such as HTTP, TELNET, simple mail transfer protocol (SMTP), and several markup languages such as HTML were designed and optimized for wired networks. Many of these protocols are not very efficient when used with wireless links.
The major issues that prevent HTTP from being used in Wireless Internet are its stateless operation, high overhead due to character encoding, redundant information carried in the HTTP requests, and opening of a new TCP connection with every transaction.
The capabilities of the handheld devices are limited, making it difficult to handle computationally and bandwidth wise expensive application protocols. Wireless application protocol (WAP) and optimizations over traditional HTTP are some of the solutions for the application layer issues.