{"id":83,"date":"2014-02-22T16:02:46","date_gmt":"2014-02-22T16:02:46","guid":{"rendered":"https:\/\/learncisco.net\/index.php\/ethernet-networking\/"},"modified":"2023-01-06T09:14:01","modified_gmt":"2023-01-06T02:14:01","slug":"ethernet-networking","status":"publish","type":"page","link":"https:\/\/www.learncisco.net\/courses\/ccna\/part-1-internetworking\/ethernet-networking.html","title":{"rendered":"Ethernet Networking"},"content":{"rendered":"

Ethernet is a contention media access method that allows all hosts on a network to share the same bandwidth of a link. Ethernet is popular because it’s readily scalable, meaning that it’s comparatively easy to integrate new technologies, such as Fast Ethernet and Gigabit Ethernet, into an existing network infrastructure. It’s also relatively simple to implement in the first place, and with it, troubleshooting is reasonably straightforward.<\/p>\n

Ethernet networking uses Carrier Sense Multiple Access with Collision Detection (CSMA\/CD), a protocol that helps devices share the bandwidth evenly without having two devices transmit at the same time on the network medium. CSMA\/CD was created to overcome the problem of those collisions that occur when packets are transmitted simultaneously from different nodes.<\/p>\n

When a host wants to transmit over the network, it first checks for the presence of a digital signal on the wire. If all is clear (no other host is transmitting), the host will then proceed with its transmission. The transmitting host constantly monitors the wire to make sure no other hosts begin transmitting. If the host detects another signal on the wire, it sends out an extended jam signal that causes all nodes on the segment to stop sending data (like a phone busy signal). The nodes respond to that jam signal by waiting a while before attempting to transmit again. Backoff algorithms determine when the colliding stations can retransmit. If collisions keep occurring after 15 tries, the nodes attempting to transmit will then time out.<\/p>\n

Half- and Full-Duplex Ethernet<\/h2>\n

Half-duplex Ethernet is defined in the original 802.3 Ethernet; Cisco says it uses only one wire pair with a digital signal running in both directions on the wire. Certainly, the IEEE specifications discuss the process of half duplex somewhat differently, but what Cisco is talking about is a general sense of what is happening here with Ethernet.<\/p>\n

It also uses the CSMA\/CD protocol to help prevent collisions and to permit retransmitting if a collision does occur. If a hub is attached to a switch, it must operate in half-duplex mode because the end stations must be able to detect collisions. Half-duplex Ethernet – typically 10BaseT – is only about 30 to 40 percent efficient as Cisco sees it, because a large 10BaseT network will usually only give you 3 to 4Mbps – at most. But full-duplex Ethernet uses two pairs of wires, instead of one wire pair like half duplex and full duplex uses a point-to-point connection between the transmitter of the transmitting device and the receiver of the receiving device. This means that with full-duplex data transfer, you get a faster data transfer compared to half duplex. And because the transmitted data is sent on a different set of wires than the received data, no collisions will occur. Imagine a freeway with multiple lanes instead of the single-lane road provided by half duplex. Full-duplex Ethernet is supposed to offer 100 percent efficiency in both directions – e.g., you can get 20Mbps with a 10Mbps Ethernet running full duplex, or 200Mbps for Fast Ethernet. But this rate is something known as an aggregate rate, which translates as “You’re supposed to get” 100 percent efficiency.<\/p>\n

Full-duplex Ethernet can be used in three situations:<\/p>\n