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					Data Link Protocols for Point-to-Point
                links
• SLIP (Serial Line IP)
     • First protocol for sending IP datagrams over dial-up links (from
       1988)
     • Encapsulation, not much else

• PPP (Point-to-Point Protocol):
  • Successor to SLIP (1992), with added functionality
  • Used for dial-in and for high-speed routers
• HDLC (High-Level Data Link) :
  • Widely used and influential standard (1979)
  • Default protocol for serial links on Cisco routers
  • Actually, PPP is based on a variant of HDLC
                   MAC and LLC
• In any broadcast network, the stations
  must ensure that only one station
  transmits at a time on the shared
  communication channel
• The protocol that determines who can
  transmit on a broadcast channel are
  called Medium Access Control (MAC)
  protocol
                                                                  to Network Layer
• The MAC protocol are implemented
  in the MAC sublayer which is the                      Logical Link



                                           Data Link
  lower sublayer of the data link layer                   Control



                                            Layer
• The higher portion of the data link                  Medium Access
  layer is often called Logical Link                      Control
  Control (LLC)
                                                                 to Physical Layer
     Channel Allocation Problem
• A single channel has to be shared among
  multiple users in broadcast networks.

Static Allocation :
• A user gets a channel for whole ‘conversation’
Dynamic Allocation:
• channel capacity allocated for a user is not
  fixed; depends on usage.
              IEEE 802 Standards
• IEEE 802 is a family of standards for LANs and MANs,
  which defines an LLC and several MAC sub layers

   IEEE 802 standard
                                         IEEE          Higher
                                       Reference       Layer
              802.1                     Model
                                       Logical Link
                 802.2                   Control      Data Link
                                        Medium         Layer
                                        Access
                              802.11
      802.3

              802.4

                      802.5




                                        Control
                                                      Physical
                                        Physical
                                                       Layer
                                         Layer
 IEEE 802 standards for LANs
• IEEE has standardized a number of LAN’s and
  MAN’s under the name of IEEE 802.
• The most important of the survivor’s are 802.3
  (Ethernet) and 802.11 (wireless LAN).
• Both these two standards have different physical
  layers and different MAC sub layers but
  converge on the same logical link control sub
  layer so they have same interface to the network
  layer.
                IEEE 802 standards
IEEE No Name                    Title

•   802.3      Ethernet    CSMA/CD Networks (Ethernet)
•   802.4                  Token Bus Networks
•   802.5                  Token Ring Networks
•   802.6                  Metropolitan Area Networks
•   802.11     WiFi        Wireless Local Area Networks
•   802.15.1   Bluetooth   Wireless Personal Area Networks
•   802.15.4   ZigBee      Wireless Sensor Networks
•   802.16     WiMax       Wireless Metropolitan AreaNetworks
               Ethernets
• Ethernet was originally based on the
  idea of computers communicating over
  a shared coaxial cable acting as a
  broadcast transmission medium e.g.
  radio system.
• The common cable providing the
  communication channel was likened to
  the ether and it was from this reference
  the name "Ethernet" was derived.
                  Ethernets

• From this early and comparatively simple
  concept, Ethernet evolved into the complex
  networking technology that today powers the
  vast majority of local computer networks.
• The coaxial cable was later replaced with point-
  to-point links connected together by hubs and/or
  switches in order to reduce installation costs,
  increase reliability, and enable point-to-point
  management and troubleshooting.
• Star LAN was the first step in the evolution of
  Ethernet from a coaxial cable bus to a hub-
  managed, twisted-pair network.
                Ethernets

• Above the physical layer, Ethernet stations
  communicate by sending each other data
  packets, small blocks of data that are
  individually sent and delivered.
• As with other IEEE 802 LANs, each
  Ethernet station is given a single 48-bit
  MAC address, which is used both to specify
  the destination and the source of each data
  packet.
     Different 10Mbps Ethernets used
  Name    Cable Type Max Segment Nodes per   Advantages
                     Length      Segment

• 10Base5 Thick coax   500 m     100     Original Cable; Obsolete
• 10Base2 Thin coax    185 m      30      No hub needed
• 10Base-T Twisted     100 m    1024     Cheapest system
            Pair
• 10Base-F Fiber       2000 m   1024    Best between buildings
           Optics
• Fast Ethernet is a collective term for a
           Fast Ethernet
  number of Ethernet standards that
  carry traffic at the nominal rate of 100
  Mbit/s, against the original Ethernet
  speed of 10 Mbit/s.
• Of the 100 megabit Ethernet standards
  100baseTX is by far the most common
  and is supported by the vast majority of
  Ethernet hardware currently produced.
             Gigabit Ethernet
• Gigabit Ethernet (GbE or 1 GigE) is a term describing
  various technologies for transmitting Ethernet packets
  at a rate of a gigabit per second, as defined by the
  IEEE 802.3-2005 standard.
• Gigabit Ethernet was the next iteration, increasing the
  speed to 1000 Mbit/s. The initial standard for gigabit
  Ethernet was standardized by the IEEE in June 1998 as
  IEEE 802.3z. 802.3z is commonly referred to as
  1000BASE-X (where -X refers to either -CX, -SX, -LX, or
  -ZX).
• IEEE 802.3ab, ratified in 1999, defines gigabit Ethernet
  transmission over unshielded twisted pair (UTP)
  category 5, 5e, or 6 cabling and became known as
  1000BASE-T.
           IEEE 802.3 Frame format


Preamble SOF   Destination   Source    lenght   data   pad   cheksum
               Address       Address

				
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