1-2 Media and Topologies

1.2 Specify the main features of 802.2 (Logical Link Control), 802.3 (Ethernet), 802.5 (token ring), 802.11 (wireless), and FDDI (Fiber Distributed Data Interface) networking technologies, including:

> 802.3 (Ethernet) Carrier Sense Multiple Access with Collision Detection (CSMA/CD) LAN Ethernet

Access method

• CSMA/CA (Carrier Sense Multiple Access/Collision Avoidance)
• CSMA/CD (Carrier Sense Multiple Access / Collision Detection)

A type of media access control. With CSMA/CD, a computer listens to the network to determine whether another computer is transmitting a data frame. If no other computer is transmitting, the computer can then send its data. While the computer is listening for a data signal, that would be the carrier sense part. Multiple access means, there are multiple computers trying to access or send data on the network at the same time. Collision detection indicates that the computers are also listening for collisions, if two computers try to send data at the same time and a collision occurs, they must wait a random period of time before transmitting again.

> 802.5 (token ring)

The IEEE 802.5 Token Ring standards define services for the OSI physical layer and the MAC sublayer of the data link layer. Token Ring computers are situated on a continuous network loop. A Token Ring controls access to the network by passing a token, from one computer to the next. Before they can transmit data they must wait for a free token, thus token passing does not allow two or more computers to begin transmitting at the same time.

> 802.11b (wireless)

802.11b is a wireless Ethernet technology operating at 11MB. 802.11b devices use Direct Sequence Spread Spectrum (DSSS) radio technology operating in the 2.4GHz frequency band.

An 802.11b wireless network consists of wireless NICs and access points. Access points act as wireless hubs to link multiple wireless NICs into a single subnet. Access points also have at least one fixed Ethernet port to allow the wireless network to be bridged to a traditional wired Ethernet network.. Wireless and wired devices can coexist on the same network.

802.11b devices can communicate across a maximum range of 50-300 feet from each other.

> FDDI networking technologies

Fiber Distributed Data Interface, shares many of the same features as token ring, such as a token passing, and the continuous network loop configuration. But FDDI has better fault tolerance because of its use of a dual, counter-rotating ring that enables the ring to reconfigure itself in case of a link failure. FDDI also has higher transfer speeds, 100 Mbps for FDDI, compared to 4 - 16 Mbps for Token Ring.

Unlike Token Ring, which uses a star topology, FDDI uses a physical ring. Each device in the ring attaches to the adjacent device using a two stranded fiber optic cable. Data travels in one direction on the outer strand and in the other direction on the inner strand. When all devices attached to the dual ring are functioning properly, data travels on only one ring. FDDI transmits data on the second ring only in the event of a link failure.