Before you start
Objectives: learn what is Network Card, Transciever, Modem and Media Converter.
Prerequisites: no prerequisites
Key terms: media, transceiver, ethernet, signal, architecture, adapter, digital, modem, transmission, converter, gbic, copper, encoding
Network Adapters are architecture specific. In other words, if we are connecting to an Ethernet network we need to have an Ethernet NIC. They’re also transmission medium specific. For example, when using Ethernet we can use either copper cabling or fiber optic. We need to choose the right Networking Adapter that matches the transmission medium and network architecture we are connecting to. For some older computers we use NICs that plug in to the system’s expansion slots or which are external to the computer and connect through an existing computer port. Today, most computers come with built-in Network Adapters, and the most popular one is Ethernet NIC.
Image 219.1 – Ethernet NIC
The Network Adapter is responsible for taking the zeros and ones and converting them into a signal which can be sent on the transmission medium. On an Ethernet network, a Network Adapter has what’s called a Transceiver. The Transceiver is responsible for taking the digital data, which is represented by a series of zeros and ones, and converting that to an electrical, radio or a light signal. For example, a 0 might be represented as a zero voltage on the wire. A 1 might be represented by a positive voltage. The method that’s used to represent zeros and ones is often called the encoding scheme, which will depend on what kind of network architecture we’re using or which type of Transceiver is necessary for the transmission medium. Different Transcivers can sends light signals or electrical signals on a wire, and for wireless NICs can send radio signals. To receive signals, the Transceiver converts digital signals from the network to digital data for the PC. Time markers identify when each bit should occur.
Older Network Adapters used to have an external Transceiver. External Transceiver is just an adapter that took digital signals from an AUI port on one end and translated those into an electrical signal using RJ45 or some other port. When we ordered a network card we had to order the right transceiver that connected to the card. Network Adapters today usually have the the built-in Transceiver based on the media type that we need.
Image 219.2 – External Transceivers
One form of a Transceiver that is gaining in use is an SFP module. SFP stands for Small Form Factor Pluggable. SFPs are typically used on Switches and Routers to easily modify the media type used by a port. Instead of having a port with a fixed media type, the port accepts the SFP module. To change the media type simply plug in a different SFP module. For example, we can get an SFP to support copper or a different specifications of fiber optic.
Image 219.3 – Optical SFP Module
Another term we might hear is a GBIC. A GBIC is slightly larger than an SFP but performs the same function. A GBIC (GigaBit Interface Converter) is a larger-sized Transceiver that fits in a port slot and is used for gigabit media including copper and fiber optic. The SFP Transceiver is sometimes called a mini GBIC because it is smaller than the GBIC module. We should also mention an XFP transceiver, which is similar in size to an SFP but is used for 10 Gigabit networking.
Another type of Network Adapter is a Modem. Modem takes the digital zeros and ones and converts it to an analog sound signal that can be carried across the telephone wires. Modem is actually an abbreviated term that means modulator/demodulator. Modulation is happening on the sending end where binary data is converted to analog waves, and Demodulation is happening on the receiving end where the analog waves are converted back to binary data. Again, there’s an encoding scheme that identifies when the signal represents a 0 or a 1, and the Network Adapter must match both the architecture and the transmission medium that is used.
Image 219.4 – Dial-up Modem
In some cases we may need to convert from one media type to another. For example, let’s say that you had an Ethernet network that uses copper cabling but we had a server that had a fiber optic Network Adapter card. In this case we could use a fiber optic to Ethernet copper cable Media Converter. It’s important to remember that media converters work within the same network architecture. For instance, the Media Converter can convert from one type of Ethernet to another that uses a different transmission cable, but it is not used to convert from something such as Ethernet to a different networking standard, for example a WAN standard such as ATM (we use a Bridge or a Router to do this). Converting from one architecture to another would require modifying the Frame contents to modify the Data Link layer address. Media Converters operate at the Physical layer, since they simply transform the signal from one encoding scheme to another. Media Converters don’t read or modify the MAC address in any way.
Image 219.5 – Media Converter
Network Adapters are architecture and transmission medium specific. The Transceiver is responsible for taking the digital data, which is represented by a series of zeros and ones, and converting that to an electrical, radio or a light signal. The method that’s used to represent zeros and ones is called the Encoding Scheme. Modem takes the digital zeros and ones and converts it to an analog sound signal that can be carried across the telephone wires. Media Converters operate at the Physical layer, since they simply transform the signal from one encoding scheme to another.