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Mac protocols


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Mac protocols

  1. 1. IEEE 802 Standards forLAN & MAN Network Security
  2. 2. IEEE 802 Standards Define physical network interfaces such as NICs, bridges, routers, connectors, cables etc. Describe the three lowest layers of network architecture: physical layer, MAC sublayer & Data link layer. Network Security
  3. 3. Famous IEEE Standards 802.2 : LLC 802.3 : Ethernet 802.4 : Token Bus 802.5 : Token Ring 802.6 : DQDB (MAN standard) 802.11 : Wireless LAN (CSMA) 802.14 : Cable Modem Network Security
  4. 4. 802.3 - Ethernet Modes of operation: half-duplex and full-duplex Four data rates defined for operation over optical fiber and twisted-pair cables:  10 Mbps - 10Base-T Ethernet (IEEE 802.3)  100 Mbps - Fast Ethernet (IEEE 802.3u)  1000 Mbps - Gigabit Ethernet (IEEE 802.3z)  10-Gigabit - 10 Gbps Ethernet (IEEE 802.3ae). Three basic elements:  physical medium  a set of medium access control rules, and  an Ethernet frame that consists of a standardized set of bits used to carry data over the system. Network Security
  5. 5. Ethernet Frame•Preamble (PRE)- 7 bytes. To synchronize the frame-reception portions of receivingphysical layers with the incoming bit stream.•Start-of-frame delimiter (SFD)- 1 byte.•Destination address (DA)- 6 bytes•Source addresses (SA)- 6 bytes•Length/Type- 2 bytes. This field indicates the number of data bytes that are contained inthe data field of the frame.•Data- Is a sequence of n bytes (46=< n =<1500) of any value. (The total frame minimum is64 bytes.)•Frame check sequence (FCS)- 4 bytes. Contains a 32-bit cyclic redundancy check(CRC) value to check for damaged frames. Network Security
  6. 6. Ethernet Specifications 10Base2 : thin wire coax cable 10Base5 : thick wire coax cable 10BaseF : Optical fiber cable 10BaseT : Twisted pair cable Network Security
  7. 7. 802.4 –Token Bus It a network implementing the token ring protocol over a "virtual ring" on a coaxial cable. A token is passed around the network nodes and only the node possessing the token may transmit. If a node doesnt have anything to send, the token is passed on to the next node on the virtual ring. Token Bus suffered from two limitations:  Any failure in the bus caused all the devices beyond the failure to be unable to communicate with the rest of the network.  Adding more stations to the bus was somewhat difficult. Network Security
  8. 8. Token Bus FrameFrame Control (FC):This field is used to distinguish data frames from controlframes.For data frames, it carries the frames priority indicatorrequiring destination to acknowledge the frame receipt.For control frames, it is used to specify the frame type. Theallowed types include token passing, entrance of any newstation and various ring maintenance functions. Network Security
  9. 9. 802.5 –Token Ring The principle used in the token ring network is that a token is circulating in the ring and whichever node grabs that token will have right to transmit the data Each link is terminated with an active repeater that detects a data packet on the in-bound link and re- transmits it on the outbound link. At the end of the packet transmission, the data equipment unit issues another idle token. Network Security
  10. 10. Token Ring FrameToken consists of – Start delimiter - which alerts the stations of a token arrival. Access control byte - which contains the priority and reservation fields, a token bit to differentiate token from data/command frame and a monitor bit checking whether a frame is circling the ring endlessly. End delimiter - which signals the end of a frame, end of a logical sequence and damaged frames. Network Security
  11. 11. Things to do LAN transmission modes LLC, Hiper LAN Ethernet cables & connectors CSMA/CD, Frame Relay & X.25 protocol Comparison of various IEEE Standards Merits & demerits of IEEE Standards Network Security