Wireless Media

The IEEE and telecommunications industry standards for wireless data communications cover both the Data Link and Physical layers. Four common data communications standards that apply to wireless media are:
Standard IEEE 802.11 - Commonly referred to as Wi-Fi, is a Wireless LAN (WLAN) technology that uses a contention or non-deterministic system with a Carrier Sense Multiple Access/Collision Avoidance (CSMA/CA) media access process.
Standard IEEE 802.15 - Wireless Personal Area Network (WPAN) standard, commonly known as "Bluetooth", uses a device pairing process to communicate over distances from 1 to 100 meters.
Standard IEEE 802.16 - Commonly known as Worldwide Interoperability for Microwave Access (WiMAX), uses a point-to-multipoint topology to provide wireless broadband access.
Global System for Mobile Communications

Standard IEEE 802.16 - Commonly known as Worldwide Interoperability for Microwave Access (WiMAX), uses a point-to-multipoint topology to provide wireless broadband access.
Global System for Mobile Communications (GSM) - Includes Physical layer specifications that enable the implementation of the Layer 2 General Packet Radio Service (GPRS) protocol to provide data transfer over mobile cellular telephony networks.

Other wireless technologies such as satellite communications provide data network connectivity for locations without another means of connection. Protocols including GPRS enable data to be transferred between earth stations and satellite links.

Wireless Media

Wireless media carry electromagnetic signals at radio and microwave frequencies that represent the binary digits of data communications. As a networking medium, wireless is not restricted to conductors or pathways, as are copper and fiber media.

Wireless data communication technologies work well in open environments. However, certain construction materials used in buildings and structures, and the local terrain, will limit the effective coverage. In addition, wireless is susceptible to interference and can be disrupted by such common devices as household cordless phones, some types of fluorescent lights, microwave ovens, and other wireless communications.

Further, because wireless communication coverage requires no access to a physical strand of media, devices and users who are not authorized for access to the network can gain access to the transmission. Therefore, network security is a major component of wireless network administration.

Single and Multimode

Single-mode optical fiber carries a single ray of light, usually emitted from a laser. Because the laser light is uni-directional and travels down the center of the fiber, this type of fiber can transmit optical pulses for very long distances.

Multimode fiber typically uses LED emitters that do not create a single coherent light wave. Instead, light from an LED enters the multimode fiber at different angles. Because light entering the fiber at different angles takes different amounts of time to travel down the fiber, long fiber runs may result in the pulses becoming blurred on reception at the receiving end. This effect, known as modal dispersion, limits the length of multimode fiber segments.

Multimode fiber, and the LED light source used with it, are cheaper than single-mode fiber and its laser-based emitter technology.

Copper Media

The most commonly used media for data communications is cabling that uses copper wires to signal data and control bits between network devices. Cabling used for data communications usually consists of a series of individual copper wires that form circuits dedicated to specific signaling purposes.

Other types of copper cabling, known as coaxial cable, have a single conductor that runs through the center of the cable that is encased by, but insulated from, the other shield. The copper media type chosen is specified by the Physical layer standard required to link the Data Link layers of two or more network devices.

These cables can be used to connect nodes on a LAN to intermediate devices, such as routers and switches. Cables are also used to connect WAN devices to a data services provider such as a telephone company. Each type of connection and the accompanying devices have cabling requirements stipulated by Physical layer standards.

Signal Patterns

One way to provide frame detection is to begin each frame with a pattern of signals representing bits that the Physical layer recognizes as denoting the start of a frame. Another pattern of bits will signal the end of the frame. Signal bits not framed in this manner are ignored by the Physical layer standard being used.

Valid data bits need to be grouped into a frame; otherwise, data bits will be received without any context to give them meaning to the upper layers of the networking model. This framing method can be provided by the Data Link layer, the Physical layer, or by both.

The figure depicts some of the purposes of signaling patterns. Signal patterns can indicate: start of frame, end of frame, and frame contents. These signal patterns can be decoded into bits. The bits are interpreted as codes. The codes indicate where the frames start and stop.

The three fundamental functions of the Physical layer are

The three fundamental functions of the Physical layer are:
The physical components
Data encoding
Signaling

The physical elements are the electronic hardware devices, media and connectors that transmit and carry the signals to represent the bits.

Encoding

Encoding is a method of converting a stream of data bits into a predefined code. Codes are groupings of bits used to provide a predictable pattern that can be recognized by both the sender and the received. Using predictable patterns helps to distinguish data bits from control bits and provide better media error detection.

In addition to creating codes for data, encoding methods at the Physical layer may also provide codes for control.

purposes such as identifying the beginning and end of a frame. The transmitting host will transmit the specific pattern of bits or a code to identify the beginning and end of the frame.

Signaling

The Physical layer must generate the electrical, optical, or wireless signals that represent the "1" and "0" on the media. The method of representing the bits is called the signaling method. The Physical layer standards must define what type of signal represents a "1" and a "0". This can be as simple as a change in the level of an electrical signal or optical pulse or a more complex signaling method.

Cisco RV120W Wireless-N VPN Firewall - Router

Cisco RV120W Wireless-N VPN Firewall - Router
The Cisco RV120W Wireless-N VPN Firewall combines highly secure connectivity - to the Internet as well as from other locations and remote workers - with a high-speed, 802.11n wireless access point, a 4-port switch, an intuitive, browser-based device manager, and support for the Cisco FindIT Network Discovery Utility, all at a very affordable price. The Cisco RV120W Wireless-N VPN Firewall's combination of high performance, business-class features and top-quality user experience takes basic connectivity to a new level.

What It Is and Why You Need It

High-speed, standards-based 802.11n wireless connectivity to help employees stay productive while away from their desks
Integrated 4-port 10/100 switch with quality of service (QoS) support for enhanced voice, video and data traffic
Support for separate 'virtual' networks enables you to control access to sensitive information and to set up highly secure wireless guest access
IP Security (IPsec) VPN support with hardware acceleration to deliver highly secure, high-performance connections to multiple locations and traveling employees.

Call or email today for a quote.