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Datacommunications Tutorial
  • What are networking products?
    Networking products consist of active (powered) communications devices such as Ethernet switches and routers, protocol converters and copper to fiber media converters.
  • How are networking products used?
    These products are used to connect users and devices to a network. Other uses include extending the distance of a network and translating protocols between two different network types.
  • Where are networking products used?
    Networking products are used in many voice, video and data communications applications including Ethernet networks, video surveillance, Internet access applications, and for monitoring and controlling devices in process and automation industries.
Datacommunications Terms
Asynchronous Transfer Mode (ATM): A very high speed network utilizing SONET optical transmission methods through the public telecommunications system.
Baseband Transmission: A transmission method where direct current signals are placed directly onto the transmission medium (cable). Ethernet is a baseband network type, hence, the “Base” in 10Base-T, etc.
Baud Rate: A measure of signal changes per second. Commonly used to rate the speed of a modem.
Bridge: A networking component that links two or more network segments. Bridges are used to split busy networks into separate, less congested segments.
Broadband Transmission: A transmission method where multiple channels are modulated onto separate carrier frequencies. The result is multiple communications channels that occupy specific frequency ranges.
Bus: Also called a "Daisy Chain". A network topology where each node is connected to one another in line. A major disadvantage is that when there is a break in the bus the entire network goes down.
Client Server: A network architecture where multiple user workstations (Clients) communicate with backend servers through a network. Clients are fully operating systems that are capable of processing data.
CODEC: An acronym for COder/DECoder. A device used for converting analog signals to digital signals. For example, telephone companies use codecs to convert binary signals transmitted on their digital networks to analog signals converted on their analog networks.
Converter: A device used to convert from one transmission media to another (Ex. Fiber/Copper Media Converter). Converters are usually externally powered as they physically “repeat” or regenerate the signal.
CSMA: Carrier Sense Multiple Access
Ethernet: The most common of the network standards established in the early 1980's by the IEEE committee under standard 802.3
Fiber Distributed Data Interface (FDDI): A 100Mbps fiber optic cabling standard developed by ANSI. FDDI utilizes a dual counter rotating ring topology for network redundancy.
Hub: A network device that receives a signal from one station and retransmits to all other connected stations.
Local Area Network (LAN): A network that remains within one facility (department, office, building, campus).
MODEM: An acronym for MOdulate/DEModulate. Modems are data communications devices that convert digital signals to analog signals for transmission over analog public telephone networks.
Network Interface Card (NIC): Network devices that are installed in computers so that they can be connected to a network. Ethernet NICs come in different speeds as well as with connections to different media types.Node: A device or station connected to a network.
Node: A device or station connected to a network.
Peer to Peer: A network architecture where computers connect directly with other computers without the need for servers.
Redundancy: Utilizing multiple access methods so that if one goes down the systems still operate.
Repeater: A network device that regenerates the signal to increase a cabling run.
Router: A network device that interconnects networks. Routers provide traffic control and filtering functions, they are commonly used to connect a LAN to the Internet.
Server: A computing device that provides a service to users on a network (clients). An example is a file server that stores and maintains documents for retrieval.
Small Computer System Interface (SCSI):
A peripheral interface that is used to connect devices to a computer.
Star: The most common network topology where each node is connected to a central point. Advantageous because if one part of the star is lost the network remains intact.
Switch: A switch is a multiport bridge that segregates different portions of a network for faster network access (See Basic Ethernet Theory - right).
Synchronous Optical Network (SONET): A Bellcore and ANSI standard that defines transmission of synchronous and time sensitive (ex: real time video) information. SONET provides a way for worldwide carriers to connect equipment.
Token Ring: A networking standard that utilizes a ring topology. Information is put onto the ring which is then passed (Token Passing) to the different stations. The amount of time that a station possesses the token is variable which gives some users priority on the network. Token Ring was standardized by IEEE under the 802.5 standard.
Transceiver: A device used to change one media type to another. Transceivers usually get their power from the NIC.
Wide Area Network (WAN): A network that spans a greater distance and needs the involvement of a public carrier.

What is Ethernet?
In the early 1980s, Digital Equipment Corporation, Intel, and Xerox developed the Ethernet Local Area Networking format. This technology was soon accepted by the IEEE Committee, creating the 802.3 standard. This standard dictates the use of CSMA/CD (Carrier Sense Multiple Access with Collision Detection) as its accessing scheme. Networks use a variety of NICs (Network Interface Cards), hubs, transceivers, converters, repeaters & switches, as well as different types of transmission media for carrying signals.

Accessing Scheme:
CSMA/CD - Carrier sense multiple access
with Collision Detection.
Speed:10 Mbps/100 Mbps/1000 Mbps (1 GBps).
Network Architecture:Coax Bus, UTP Star, Fiber Star


Connectors Commonly Used in Ethernet Environments
Connectors Commonly Used in Ethernet Environments

Basic Ethernet Theory

1. Ethernet operational theory is quite easy to understand and a simple analogy is helpful to visualize the basics. Imagine a long hallway lined with offices. The hallway represents the physical network, the offices represent the attached stations. When an occupant wishes to speak to another occupant they would lean into the hallway, listen to make sure no one else is engaging in a conversation, then speak out addressing the desired recipient. All other occupants hear the conversation but ignore it knowing it is not directed to them.
 In essence, the above analogy describes the medium access method standardized under IEEE802.3 known as Carrier Sense Multiple Access with Collision Detection (CSMA/CD). Carrier Sense is analogous to the ability to listen to all conversations (network traffic). Multiple Access is the ability for multiple users to access the medium while data is transmitted.
2. Returning to our analogy, what if two or more occupants decide to speak at the same time? Naturally the overlapping voices would become garbled and indistinguishable. With Ethernet this is known as a collision. In the CSMA/CD method, CD stands for Collision Detection. If a collision is detected by a transmitting station(s) the rule states: stop transmitting immediately, transmit a jamming signal to inform all other stations to stop, then wait a random period (binary exponential backoff) and re-transmit.
 Unfortunately, as the quantity of stations increases so does the amount of collisions. This causes the average access time to increase proportionally. This is referred to in the industry as network congestion.
3. Fortunately, there are several ways to alleviate network congestion. One way is that the entire network can be upgraded to Fast Ethernet (100 Mbps) which represents a 10 fold increase in transmission speed. This, however requires upgrading of all components and can be rather expensive. Another approach is to add an Ethernet Switch.
 In the above analogy, the long hallway represents the network. Adding a two port switch is analogous to dividing the hallway into two shorter hallways separated by a door. This creates two segments (collision domains) where messages that are directed for occupants within the same area are not allowed to pass through the door. Only when a message is directed to another segment does the door open allowing the message to pass.
 An Ethernet switch reduces collisions by creating multiple collision domains. This, in most cases, is the most economical approach. A switch can be added to any network without the need to upgrade existing equipment.

The difference between standard/fast Ethernet
and switched/shared equipment
  
    
 
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