Chapter 10 - Network Technologies Flashcards
Ethernet
Ethernet is a family of frame-based technologies that is used to connect computers in a Local Area Network.
Ethernet is a data link layer standard that defines frames and error-correcting measures.
Ethernet Frame Layout
Ethernet is a frame-based network protocol, meaning data is transported in blocks of characters (frames) instead of one at a time.
An ethernet frame consists of a header, payload and checksum
Header
The ethernet header consists of 14 bytes that include:
- Preamble: 7 octets of 10101010
- start of frame: 1 octet
- 6-byte destination MAC address
- 6-byte source MAC address
- 2-byte Ethernet frame type
Payload
This is the data in the Ethernet frame that is of variable length, from 46 to 1500 bytes
Checksum
This is a 4-byte Cyclic Redundancy Check (CRC) that is used to verify the integrity of the entire frame.
The CRC is calculated by the sending node and placed in the header; the destination node calculates the CRC and compares it to the value in the header; if they match, the packet arrived correctly; if they do not match, the packet is dropped.
Interframe gap
After the frame is transmitted, the sending station pauses for 960 ns before sending the next frame.
MAC address
On an ethernet network, stations are uniquely identified by their Media Access Control (MAC) address.
A MAC address is 6 bytes in length and is permanently assigned to a device, such that no two devices in the world have the same MAC address.
Ethernet Error Detection
Ethernet, specifically the Carrier Sense Multiple Access with Collision Detection (CSMA/CD) protocol, operates by having stations listen for ongoing transmissions before attempting to send data. If a station detects another transmission, it stops, emits a jam signal to signal others to halt, and then waits for a random duration (backoff delay) before retrying. The delay uses a binary exponential backoff algorithm to prevent network crashes from excessive traffic. In Full Duplex Ethernet, collision detection isn’t used because every node is connected to a switch, eliminating the possibility of collisions. Instead, it functions as a point-to-point medium, not a shared one.
Token Ring
Token ring, an early LAN technology developed by IBM, used a physical star topology with large connectors. It operated at speeds like 4 Mbit/s and 16 Mbit/s and transmitted data using a logical token passed from station to station. When a station had data, it attached it to the token, which moved through stations to the destination. Multi-station Access Units (MAUs) managed situations like lost tokens and network changes. However, Ethernet’s simplicity and cost-effectiveness led to token ring’s decline in popularity.
USB
USB is a communication standard for connecting peripherals to computers, succeeding older standards like RS-232 and IEEE 1284. It has evolved through versions: USB 1.0/1.1 (1996), USB 2.0 (2000), and USB 3.0 (2008). USB allows hot-plugging, supporting various peripherals like keyboards, mice, printers, and more, often using a five-port hub.
RS-232
RS-232, an older serial communication technology, was widely used from the 1960s to the 2000s but has been replaced by USB. It served various purposes, including connecting terminals, printers, modems, mice, and other peripherals to computers. RS-232 supported speeds from 110 bps to 115 kbps and used different flow control methods, including hardware and software signaling. The computer end is referred to as DCE (Data Circuit-terminating Equipment), and the peripheral end as DTE (Data Terminal Equipment).
