Exam: Cisco 200-301 - Cisco Certified Network Associate (CCNA)
Ethernet is a LAN technology for physical and data link layers of OSI networking model. Data travels in Ethernet as frames. A number of standards have been defined by Institute of Electrical and Electronics Engineers (IEEE). Various Ethernet standards when combined together will allow you to get Local Area Network (LAN) that is combination of many different types of user devices, LAN switches, and cables.
Conventional Ethernet supports 10 Mbps data transfer rate. However, thesedaysnew Ethernet standards are developed such as Fast Ethernet and Gigabyte Ethernet.Fast Ethernet has taken the Ethernet speed to 100 Mbps and Gigabyte Ethernet has taken the speed of Ethernet upto1000 Mbps.
The network devices such as switches, hubs, PCs and routerscommunicate with each other by transferring Ethernet frames to each other on the same LAN or different LAN.
Ethernet has standard specifications for cables also that are used as a medium to transfer data from one device to another. To connect cables to computers, a network adaptor, also called NIC (Network Interface Card) is used. On Ethernet data may flow on different types of cables such as UTP Copper Cable, Fiber Optic strand, or over a Radiowave. The different types of cables may have different speeds. However, the properties of Ethernet are consistent for all the cable types. In addition, despite having different speeds of different cables, the Data Link Header and Trailer use the same format.
IEEE has defined Ethernet cabling standards for cables that can be used to connect switches to other network devices and hosts. The UTP cables have 8 wires within them that are connected from one end to the source device and from the other end to the destination device. The wires are connected to the connectors through pins. How the pins are positioned on both ends make different types of cables. The different types of cables that can be used are:
Straight-Through Cable
The straight-through cables are used to connect NICs of a host computer on a network and routers to switches and hubs. Computers are considered as1 and 2type devices and switches are considered as3 and 6type devices.
The NICs of host computers and the interface port of switches work on the basis of pin positions. There are two types of pins, Transmitter (TX) and Receiver (RX). In Straight through cables, all eight wires pass straight through the pins of RJ45 connector from one end to the same corresponding pin at the other end.
The NICs of host computer uses the pair connected to pins1 and 2to send data and Switch’s interfaceport uses a pair of wires connected at pin 1 and pin 2 to receive data. The switch on the other hand uses pins 3 and 6 to send data, which is received on pins 3 and 6 on PC. Thus Pin 1 on host computer connects to pin 1 on the switch and pin 3 on the host computer connects to pin 3 on the switch.
In other words, the Ethernet Straight-through cable connects pin 1 and 2 pinouts straight to 1 and 2 pinouts and pin 3 and 6 connects straight to 3 and 6 pinouts. Total two pairs of pins are used in straight-through cables.
Crossover Cable
Unlike straight through cables thatworks correctly when different types of devices such as a host computer and a switch/hub need to communicate with each other, the crossover cables are used to connect two similar devices such as a PC to PC, Switch to Switch, or a Hub to Hub. They can also be used to connectHub to switchand aRouterdirect to a host.
Just as straight through cables use four wires and 1,2, 3, and 6 pins, the cross over cable also use the same set of pins however instead of connecting 1 to 1, 2 to 2, 3 to 3 and 6 to 6, the crossover cables connect pins 1 to 3 and 2 to 6 on each side of the cable.
The NICs of a host computer uses the pair connected to pins1 and 2to send data and other computer’s interfaceport uses a pair of wires connected at pin 3 and pin 6 to receive data. Similarly, the other computer again uses pins 1 and 2 to send data, which is received on pins 3 and 6 on the first computer. Thus Pin 1 on host computer connects to pin 3 on the other computer and pin 2 on the host computer connects to pin 6 on the other computer
The Rollover wired cables
The Rollover wired cables are also called rollover cables. These cables are not used to connect devices together. Rather they are used to connect a host to a router console through serial communication (com) port. In other words the rollover wired cables are used to connect devices console port to make programming changes to the device. The rollover cables are not used to carry data but are used to create an interface with the device.
The rollover cables have opposite Pin assignments on each end of the cable. For example, the pin 1 of connector A is connected to pin 8 of connector B, pin 2 to pin 7 and so on, as shown in Figure below:
|
Connector A Connector B Pin 1 _______________________________ Pin 8 Pin 2________________________________Pin 7 Pin 3________________________________Pin 6 Pin 4________________________________Pin 5 Pin 5________________________________Pin 4 Pin 6________________________________Pin 3 Pin 7________________________________Pin 2 Pin 8________________________________Pin 1 |
Example questions
1. Determine which type of cable should be used if a PC connects to a Switch.
Correct Answer: A
The straight through cables are used to connecta PC to a Switch.
2. Determine which type of cable to be used if a PC connects to a PC.
Correct Answer B
The Crossover Cables are used to connecta PC to a PC.
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