LAN Technologies PDF

LAN Technologies CCN.1 Lecture Objective  To describe the operations of LAN operations  IEEE LAN standards  To describe the operations of Token Ring and FDDI  To introduce network interface cards (NIC) CCN.2 LAN Standards...

LAN Technologies CCN.1 Lecture Objective  To describe the operations of LAN operations  IEEE LAN standards  To describe the operations of Token Ring and FDDI  To introduce network interface cards (NIC) CCN.2 LAN Standards Covered in Lecture 3 Ethernet (IEEE 802.3) Token Bus (IEEE 802.4) Token Ring (IEEE 802.5) DQDB (IEEE 802.6) Falls into one of two categories: Contention (802.3, Ethernet, for example) Controlled access (802.5, Token Ring, for example) FDDI, another form of controlled access, is an ANSI/ITU-T standard CCN.3 Persistence Algorithms  Nonpersistent CSMA  1-persistent CSMA  P-persistent CSMA CCN.4 Nonpersistent CSMA  Non persistent CSMA rules: 1. if medium idle, transmit 2. if medium busy, wait amount of time drawn from probability distribution (retransmission delay) & retry  Random delays reduces probability of collisions  Capacity is wasted because medium will remain idle following end of transmission  Non persistent stations are deferential CCN.5 1-persistent CSMA  1-persistent CSMA avoids idle channel time  1-persistent CSMA rules: 1. if medium idle, transmit; 2. if medium busy, listen until idle; then transmit immediately  1-persistent stations are selfish  If two or more stations are waiting to send, a collision is guaranteed CCN.6 P-persistent CSMA  A compromise to try and reduce collisions and idle time  p-persistent CSMA rules: 1. if medium idle, transmit with probability p, and delay one time unit with probability (1–p) 2. if medium busy, listen until idle and repeat step 1 3. if transmission is delayed one time unit, repeat step 1  Issue of choosing effective value of p to avoid collision will not be stable under heavy load CCN.7 Which Persistence Algorithm?  IEEE 802.3 uses 1-persistent  both non persistent and p-persistent have performance problems  1-persistent seems more unstable than p-persistent because of greedy of the stations but wasted time due to collisions is short with random backoff unlikely to collide on next attempt to send CCN.8 Categories of Standard Ethernet CCN.9 10 Base 5: Thick Ethernet  10Base5 was the first Ethernet specification to use a bus topology with an external transceiver (transmitter/receiver) connected via a tap to a thick coaxial cable. CCN.10 10 Base 2: thin Ethernet  Also called Cheapernet  Use bus topology, but the cable is much thinner and more flexible. CCN.11 10Base-T and 10Base-F 10Base-T: Twisted-Pair Ethernet  Two pairs of twisted cable create two paths(one for sending and one for receiving) between the station and the hub. 10Base-F: Fiber Ethernet  Although there are several types of optical fiber 10-Mbps Ethernet, the most common is called 10Base-F. CCN.12 FAST ETHERNET  IEEE created Fast Ethernet under the name 802.3ae.  10 Gbps, is a fast ethernet std, can transmit data 10 times faster at a rate of 10,000 Mbps. CCN.13 Fiber Distributed Data Interface –FDDI (802.6)  LAN protocol using optical fiber as a medium with a 100Mbps data rate.  A token-ring-like network standard has been developed around fiber-optic cabling  FDDI implemented as a dual ring.  Data transmission is confined to the primary ring.  The secondary ring is provided in case the primary fails.  Nodes are connected to one or both ring. CCN.14 CCN.15 Fibre Channel Applications CCN.16 Advantages and disadvantages of FDDI Advantages:  High bandwidth: 250Gbps.  Secured, support 1000 terminals for 200km cable  Resistance to EMI Disadvantages  Costly  Installation and maintenance require a great deal of expertise. CCN.17  LAN Wiring and Physical Topology CCN.18 Network Interface Card  Internal NICs are plugged into an expansion slot on the computer’s motherboard  The PCI slots on this Intel motherboard could be used for an internal NIC PCI Slots in White CCN.19 Network Interface Hardware A computer CPU does not process of individual bits on the network  A network adapter card” or “Network Interface Card” (NIC) is a special-purpose hardware that connects a computer to a network, and handles all the details of packet processing  Most NICs contain Direct Memory Access (DMA) circuitry  To receive a packet, the CPU allocates buffer space in memory and then instructs the NIC to read the next incoming packet into buffer the NIC waits for a frame to cross the network makes a copy of the frame and process it CCN.20 NIC support all three kinds of connections. CCN.21 Review Questions  What is a token, and how are tokens used to control network access?  Explain the role of CSMA in LAN.  Why does CSMA/CD use a random delay?  With the help of diagram, briefly describe the contents of an Ethernet Frame.  Describe the operation of following non-persistent, 1-persistent and p- persistent CSMA/CD protocols.  Briefly describe the term “binary exponential backoff”. CCN.22 Review Questions What steps and precautions must be taken to assure reliable operation of a token ring network? State Shannon’s theorem that predicts the maximum data rate that can be achieved over a noisy communication channel of a given bandwidth. CCN.23 Reference  Chapters 8 and 9. Computer Networks and Internets, Douglas E. Comer, Prentice Hall. 4th Edition.  Chapters 16. Data and Computer Communications 8th Edition by William Stallings CCN.24