TDC 461 Basic Communications Systems

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TDC 461Basic Communications Systems

• Local Area Networks
• 29 May, 2001

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Agenda

• Local Area Networks
• Components
• Topologies
• Transmission Media
• Network Interface Cards (NICs)
• Network Operating System software
• Client vs Server functions
• Peer-to-Peer vs. Server-based

• Local Area Network Technologies
• Ethernet
• Token Ring
• LAN Interconnection
• LAN Switches
• Routers

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What is a LAN?

• Key Elements

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LAN Components

• Workstations (PCs, etc.)
• Interconnecting Cable
• Network Operating System (NOS) Software

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LAN Topologies

• How are Workstations connected together?

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Bus Topology
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Bus Topology Example10Base5 Ethernet
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Ring Topology
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Dual Ring ExampleFiber Distributed Data
Interface (FDDI)
Self healed after Link Failure
Self-healing
FDDI dual-
link failure
attached
adapters
GOLDMAN LAN
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Star Topology
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Star Topology Example10BaseT Ethernet
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LAN Cable

• LAN Cable can be of several types

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Twisted Pair

• Unshielded Twisted Pair (UTP)
• Similar to telephone cable, but
• Usually 4-pair cable is used
• UTP Category ratings
• Category 3 - 10 Mbps up to 100 meters
• Category 4 - 16 Mbps up to 100 meters
• Category 5 - 100 Mbps up to 100 meters
• Shielded Twisted Pair (STP)

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Coaxial Cable

• LAN coaxial cable is similar to Cable TV cable
  (and can be identical)
• Construction
• Advantages
• Disadvantages

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Coaxial Cable
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Fiber Optic Cable

• Transmits data using light rather than
  electricity
• Structure
• Advantages
• Disadvantages

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Fiber Optic Cable
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LAN Hardware

• Cabling and NIC card specs dictated by standards
  document for the particular LAN Access Method
• Ethernet
• Token Ring
• ARCNet
• Fiber Distributed Data Interface (FDDI)
• etc.

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NIC Card Sales - 1Q 1998(percentage of 10.9
millions units sold)
Source In-Stat
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Network Operating Systems

• Popular NOSes
• NOS determines workstation role

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Installed LAN Servers 2Q 1998
Source Dataquest
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New Servers Deployed Jan-June 1998
Source Network World
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File Servers

• A File Server
• Shared files accessed via

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Network Drives

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Security

• Login (Log on)
• Network Manager controls access rights for each
  user to each resource.

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File Servers

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Example Get File
Open File
File Opened
Read Data
Data
Close File
File Closed
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NOS Types

• Peer-to-Peer NOS
• Dedicated Server NOS

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LAN Standards

• IEEE 802 Committee Standards
• 802.3 - Ethernet
• 802.5 - Token Ring

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LAN Standards

• IEEE 802 Standards include
• Physical (Layer 1)
• Cable Types
• Maximum length restrictions
• Data rate and bit encodings
• Medium Access Control (Layer 2)
• Access control protocol (determines which device
  can transmit when
• Frame header/trailer format

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Ethernet

• Physical Standards
• 10Base5 (1985)
• 10 Mbps Thick Coaxial Cable (Bus)
• 10Base2 (1988)
• 10 Mbps Thin Coaxial Cable (Bus)
• 10BaseT (1990)
• 10 Mbps Twisted Pair (Star)

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Ethernet

• Physical Standards
• 100BaseT (1995)
• 100 Mbps Twisted Pair (Star)
• 100BaseF (1995)
• 100 Mbps Fiber (Star)
• 1000BaseX (1998)
• 1 Gbps Fiber (Star)

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Ethernet

• IEEE Naming System
• ltdata rategtltsignal typegtltlength of longest cable
  in 100s of metersgt
• Example 10Base5
• 10 Mbps data rate
• Baseband signal type
• Longest cable length 500 meters

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Ethernet

• IEEE Naming System
• ltdata rategtltsignal typegtltlength of longest cable
  in 100s of metersgt
• Example 10Base5
• 10 Mbps data rate
• Baseband signal type
• Longest cable length 500 meters

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10Base5 Ethernet
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10Base2 Ethernet
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10BaseT Ethernet
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100BaseT Ethernet (Fast Ethernet)

• Requires high-quality (Category 5) twisted pair
  cabling
• Requires 100 Mbps NIC cards in PC workstations
• Requires 100 Mbps hub

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100BaseT Ethernet (Fast Ethernet)
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Switched Ethernet

• Switched vs. shared
• Bandwidth to desktop
• Additional hardware
• Switches
• Switched 10
• Switched 100

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Gigabit Ethernet

• Requires fiber optic cabling
• Requires Gigabit NIC cards in PC workstations
• Requires Gigabit Ethernet hub or Gigabit Ethernet
  switch

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1000BaseX Ethernet
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Ethernet MAC Protocol

• Medium Access Control (MAC) layer protocol is
  identical for all Ethernets
• Ethernet Frame format
• Carrier Sense Multiple Access with Collision
  Detection (CSMA/CD) used to determine which
  workstation can send at any given time.

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Ethernet Frame Format
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Ethernet Frame

• Header
• Preamble - 8 bytes - alternating 1/0 bits for
  clock synchronization
• Dest. Address - 6 bytes
• Source Address - 6 bytes
• Length - 2 bytes - Packet length
• Trailer
• CRC - 4 bytes - Cyclic Redundancy Check

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MAC Protocol

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Carrier Sense Multiple Access with Collision
Detection

• To transmit data packet
• First, listen to see if any other station is
  transmitting (Carrier Sense)
• When network is quiet, start transmitting

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Carrier Sense Multiple Access with Collision
Detection

• Station Backoff
• Each station involved in collision
• As number of collisions grows, range of random
  values (N) increases (exponential backoff)

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Ethernet Enhancements

• Switched Ethernet
• Full-duplex Ethernet

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Ethernet Switches

• Ethernet Switch

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Switches vs. Routers

• How is Switch different than a Router?
• Addressing
• Switch uses layer 2 MAC addresses
• Router uses layer 3 IP address
• Speed security
• Switch forwards packets fast (50-100 nsec).
• Router takes more time (1-50 msec) and provides
  other security features

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Switched Ethernet
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Switches vs. Hubs

• How is Switch different than a Hub?
• Broadcasting (and Security)
• Hub broadcasts every packet to every device
• Switch forwards packet out single port
• Matching Data Rates
• All ports on hub must run at same data rate
• Switch ports can run at different rates (can
  buffer incoming packet at one data rate and
  re-transmit at another data rate).

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Full-Duplex Ethernet

• Full-Duplex Ethernet allows a workstation to send
  and receive data simultaneously.
• Requirements
• Must have a full-duplex NIC card
• Must be connected to Ethernet switch

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Switched Hierarchy

• Switches allow network manager to put bandwidth
  where it is needed.
• Some users get 10 Mbps shared (hub)
• Some users get 10 Mbps dedicated (switch)
• Some users get 100 Mbps shared (hub)
• Some users get 100 Mbps dedicated (switch)

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Token Ring

• Physical Layout
• Dual Ring of Stars
• Medium Access Control Protocol
• Token Passing

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Token Ring

• Advantages over Ethernet
• Disadvantages over Ethernet

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Token Ring Frames
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Access Control Byte
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Token Ring Operation