When data packets leave the NIC, the medium that takes the packet from source to destination is called media. Media comes in various forms including copper wire, fiber optics, and wireless. Once the media access method, CSMA/CD or CSMA/CA, has been implemented, the data packets are on the media and sent to their destination. This process describes Layer 1 of the OSI model.
A media improvement over Ethernet is Fiber; however, it is very costly for installation and maintenance. Fiber optic cable operates by sending beams of light through fine strands of glass. These beams of light can be infrared or laser for example. Fiber is a major improvement on the speed and distance thresholds of Copper wire such as Coaxial UTP, STP.
Fiber is available in two different variants or types. Multimode (MMF) is used for shorter distances < 2km and can transmit data over multiple waveguide modes. Singlemode (SMF) used for longer distances > 2km and transmits data over a single path/mode. The term mode refers to rays of light.
Both multimode and singlemode fiber cables have a core, cladding, and a plastic covering for protection. The core is space in which light beams are sent (SM -10µm and MM – 50µm or microns). Cladding keeps the beams of light in the core by not reflecting the light within the cable. The plastic covering is used to protect the inner components of the cable.
Fiber cables can use multiple connector types as displayed here.
ST |
SC |
LC |
MTRJ |
Fiber Standards define the type of media used, speed, and distance limitations. Synchronous Optical Network (SONET) defines the carrier levels and transport signals used in fiber optic communications. Review the chart for details.
In some cases an electrical signal will have to be converted into an optical signal and vice versa. Some examples are converting from fiber to coaxial, singlemode to Ethernet, and multimode to Ethernet. SMF and MMF also need a way to convert their signals to the other mode being used.
Media Convertors make all of these conversions possible. A Gigabit Interface Converter (GBIC) is used to convert an optical signal into an electrical signal. XENPAK is used on fiber networks to convert wavelengths from MMF to SMF and vice versa. XENPAK and GBIC are often connected to routers and switches.
As LANs expand and develop using fiber and other high speed links, media convertors placed at strategic points can reduce costs. Fiber is expensive but it offers faster speeds and bandwidth than copper wire.
Wireless (RF)
Wireless is another major improvement over copper wire media due to mobility. A Wireless Access Point (WAP) is used to take a wired signal and transmit it via radio frequency (RF). Latency, or response time, is an issue that affects wireless networks due to the need to process the signal when received.
| Standard | 802.11a | 802.11b | 802.11g |
802.11n
|
| Data Rate (Speed) | 54 Mbps | 11 Mbps | 54 Mbps | Up to 600 Mbps |
| Distance (Range) | 150 feet | 300 feet | 300 feet | 300 feet |
| Frequency | 5 GHz | 2.4 GHz | 2.4 GHz | 2.4/5 GHz |
| Compatibility | 802.11 a/n | 802.11 b/g/n | 802.11 b/g/n | 802.11 a/b/g/n |
The IEEE standard for wireless media is 802.11x.
RF delivery methods describe ways to carry and maintain wireless communication. Wireless Standards are associated with each of the delivery methods and discussed within each defined method.
- Direct Sequence Spread Spectrum (DSSS) separates data into pieces, then “spreads” the data across 14 (22MHz) frequency channels using a mathematical equation. DSSS uses a chipping code when transmitting to resist interference and transmits using its full bandwidth of 90MHz.
- Frequency Hopping Spread Spectrum (FHSS) uses 79 (1MHz) channels and randomly sends data across these channels using a hopping sequence. In FHSS data packets are split up and transmitted in order.
- Orthogonal Frequency-Division Multiplexing (ODFM) takes single high frequency channels and converts them to low frequency parallel bit stream/channels to deliver data.
- Multiple Input Multiple Output (MIMO) uses space-division multiplexing where both the sender and receiver communicate utilizing multiple antennas.
Now that you have reviewed the various types of RF delivery methods it is important to be aware that a channel is a method of sending and transmitting data and RF spectrum is the bandwidth used as the delivery method. Channel bonding is when two channels are joined to increase the data rate/speed. Super G is a 108 Mbps standard that results from bonding two 802.11g channels together.
Alternative Media
There are other forms of media that are new or not very well known. Broadband over Power line (BPL) is an emerging media that uses electrical power lines to provide internet access. BPL uses modems at end points and also a section of the radio spectrum to provide network access.
RS-232 is a serial link between two hosts. The data rate is less than 20Kbps and is most commonly used when performing the initial configuring routers. RS-232 can be used to connect to computer however transmitting data will be slow. One end of the cable has DB-9 (Figure 23) or DB-25 (Figure 24) connection and the other end has either another DB-9/25 connector or an RJ-45, or USB.
Two types of serial connectors used are DB-9 and DB-25 displayed below.
DB-9 |
DB-25 |
