Data Network

Data Network

1. Local Area Network (LAN)

   • owned by the organization that is using the network to interconnect equipment
   • Topology
   • Transmission medium
   • Wiring layout
   • Medium access control

2. Topologies

   • Tree
     • Multipoint medium
     • Branching cable with no closed loops
     • Tree layout(headend)
   • Bus
     • Multipoint medium
     • End of the bus is a terminator
     • Transmission medium (bus) through hardware interfacing (tap)
   • Ring
     • Repeaters joined by point-to-point links in closed loop
     • unidirectional
     • Stations attached to repeaters
     • Data transmitted in frames
       • Circulate
       • copies frame
       • back to source where it is removed
     • Medium access control
     • very high speed links over long distances
     • potential of providing best throughput
     • single link or repeater failure disables network
   • Star
     • central node
     • Two alternatives
       • Broadcast : Physical star, logical bus
         • retransmitted on all of the outgoing links
         • hub
       • Frame-switching device : Only one station can transmit at a time
         • buffered
         • retransmitted
     • uses natural layout of wiring in building
     • best for short distances
     • high data rates for small number of devices
   • Issues with bus & tree arrangements
     • Identify target station
     • mechanism to regulate transmission
     • Scheme to address issues
       • Transmit data in small blocks(frames)
       • control information
       • unique address/identifier
       • Destination address
       • Medium access control
   • Choice of Topology
     • Reliability
     • Expandability
     • Performance

3. LAN Protocol Architecture

   • IEEE 802 reference model
   • Physical Layer
     • physical layer of OSI Model
     • Encoding / decoding of signals
     • Preamble generation / removal for synchronization
     • Bit transmission / reception
     • Specification of transmission medium and topology
   • LLC Layer
     • • Logical Link Control
     • interface to higher layers
     • flow and error control
     • transmission of link level PDUs
     • characteristics
       • Support multi-access, shared medium
       • Relieved of some link access details by MAC layer
     • mechanisms for addressing stations
       • service access points
     • services
       • Unacknowledged connectionless service
       • Connection-mode service
       • Acknowledged connectionless service
   • MAC Layer
     • assemble data into a frame with address and error-detection fields
     • disassemble frame, and perform address recognition and error detection
     • Medium Access Control
     • controlling access to transmission medium,
     • Where
       • Centralized scheme
       • Distributed scheme
     • How
       • Synchronous
         • Specific capacity dedicated to connection
       • Asynchronous
         • Capacity allocated dynamically in response to demand
         • Round robin
         • Reservation
         • Contention
     • Frame Format
       • MAC Control
       • Destination MAC Address
       • Source MAC Address
       • LLC
       • CRC
     • MAC Address
       • unique number assigned to a network device
       • Globally unique addressed
       • first three bytes
         • manufacture

4. Transmission Media

   • Bus LAN Transmission Medium
     • Twisted pair
       • used voice grade cable
       • inexpensive
       • higher data rates not practical
     • Baseband coaxial cable
       • digital signaling
       • original Ethernet
     • Broadband coaxial cable
       • cable TV systems
       • analog signals
       • expensive
     • Optical fiber
       • expensive taps
       • better alternatives
   • Choice of Transmission Medium
     • Factors
       • LAN topology
       • Capacity
       • Reliability
       • Types of data supported
       • Environmental scope
     • Medium
       • Voice grade UTP cable : Cat 3
       • STP and baseband coaxial cables
       • Broadband coaxial cable
       • High performance UTP cable : Cat 5 and above
       • Optical fiber

Images and files in the map