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Learn about LAN topologies like bus, ring, and star networks, along with access methods like CSMA/CD and CSMA/CA. Explore token passing, multiple access protocols, and Ethernet standards.
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Local Area Network • Consists of a shared transmission mediumand a set of hardware and software • Regulating the orderly access to the medium
Topology • Bus • Interface hardware (tap) • Linear transmission medium (bus) • Terminator; at the end of a wire or cable to prevent a signal from being reflected back from the end, causing interference.
Topology • Ring • Point to point ring interface in a closed loop • Unidirectional link • IEEE 802.5: Token ring • Fiber distributed data interface (FDDI) American National Standards Institute (ANSI) (Institute of Electrical and Electronics Engineers (IEEE))
topology • Star • Stations connected to a common central node (Hub or switch) • Hub; broadcast to all stations • Switch; to the particular station,at the same time unused lines used for switching other traffic
Random-access protocol Collision detection Carrier sense multiple access Multiple access Collision avoidance
ALOHA network Any station sends a frame to the base station The base station relays it to the destination
CSMA Each station first listen to the medium Collision exists because of the propagation delay
Persistence strategies Nonpersistent If the line is busy, the station waits a random of time and then sense the line again
Persistent 1-persistent If the station find the line idle, the station send its frame immediately p-persistent If the station find the line idle, the station may or may not send It sends with probability p
CSMA/CD (used in Ethernet) Jam signal is to inform other stations All stations discard the part of the frame received
Reservation A station needs to make a reservation before sending data If there are N stations in the system, there are exactly N slots in the reservation frame
Token passing A station is authorized to send data when it receives a special frame called a token When no data are being sent, a token circulates around the ring
Channelization protocol Frequency division multiple access FDMA Time division multiple access TDMA Code division multiple access CDMA
CDMA Each station is assigned a code or Chips (Orthogonal sequences).
Ethernet A well-known and widely used network technology created in 1976 IEEE now controls Ethernet standards IEEE 802; Physical layer (802.3(Ethernet) 802.4 (Token Bus) 802.5 (Token ring)) Data link layer(802.2) Network layer(802.1)
IEEE standard 802.3 802.3 Cabling (10 Mbps, baseband signaling)
Ethernet • Access method: CSMA\CD • Addressing: Each station has its own Network Interface Card with a physical address • Line coding: • Manchester (10Base2) • MLT-3 • 4B5B,NRZI (100Base-TX)
Data link control: • Logical link control (LLC) • HDLC • Common to all LAN protocols • Medium access control (MAC) • Contention control for the shared media • Specific to the LAN using them (Ethernet, Token Ring, Token bus)
802.3 MAC frame Protocol data unit (PDU) data unit in The IEEE 802.2 logical link control (LLC) Length/type of PDUNumber of bytes in the coming PDU If the length is fixed, type is to identify the network layer protocol such as 0800 is Internet IP version 4
Function of a bridge Regenerate and filter traffic Check destination address Forwards the new copy to the segment to which the address belongs