Network Transport Systems

1
Network Transport Systems

• Network transport system
• Sometimes referred to as the networks logical
  topology
• Describes networks logical interconnection
  between nodes, rather than its physical
  interconnection
• Switching
• Component of a networks logical topology that
  manages how packets are filtered and forwarded
  between nodes on a network

2
Network Transport Systems

• Circuit switching
• Connection is established between two network
  nodes before they begin transmitting data
• Message switching
• Connection is established between two devices in
  the connection path one device transfers data to
  the other, then breaks the connection
• Packet switching
• Data are broken into packets before they are
  transported

3
Network Transport Systems

• Shared Ethernet
• Carrier Sense Multiple Access with Collision
  Detection (CSMA/CD)
• Communication rules used by shared Ethernet
  networks

FIGURE 5-19 CSMA/CD process
4
Network Transport Systems

• Ethernet versions
• 10Base2
• Thin coaxial cable
• Simple bus topology
• 10Base refers to its network speed, 10 megabits
  per second (Mbps)
• BNC T connectors are used by nodes on a Thinnet
  cabling technology to tap into the network

FIGURE 5-20 10Base2 Ethernet network
5
Network Transport Systems

• 10Base5
• Thick coaxial cable
• Simple bus topology
• 10BaseT
• Twisted-pair cable
• Star-bus or hierarchical topology

FIGURE 5-21 10BaseT Ethernet network
6
Network Transport Systems
FIGURE 5-22 Enterprise-wide Ethernet 10BaseT
network
7
Network Transport Systems

• 100BaseT
• Also known as Fast Ethernet
• Enables LANs to run a 100 Mbps data transfer rate
• 100BaseTX
• Achieves its speed by sending the signal 10 times
  faster and condensing the time between digital
  pulses and the time a station is required to wait
  and listen in CSMA/CD

8
Network Transport Systems

• 100BaseT4
• Achieves its speed by breaking up the data stream
• Cannot support full duplexing, an enhancement
  allowing simultaneous two-way transmission
  between nodes while eliminating collisions
• 100BaseVG
• Can transmit data at 100 Mbps
• Uses a demand priority access method

9
Network Transport Systems

• Demand priority
• Each device on a star or hierarchical network
  sends a request to transmit to the central hub,
  which grants requests one at a time
• Intelligent hub
• Can manage transmissions by dictating which nodes
  can send and receive data at every instant

Figure 5-23 CSMA/CD versus demand priority
10
Network Transport Systems

• Switched Ethernet
• Enables multiple nodes to simultaneously transmit
  and receive data and individually take advantage
  of more bandwidth because they are assigned
  separate logical network segments through
  switching
• Switch manages network switching
• 1 Gigabit Ethernet
• Runs at 1000 Mbps
• Usually relies on fiber-optic cable

11
Network Transport Systems
FIGURE 5-24 Switched Ethernet network
12
Network Transport Systems

• Ethernet frame types
• Ethernet 802.2
• Default frame type for Novells IntraNetWare
  network operating system
• Defining characteristics of its data portion are
  the source and destination service access points
  that belong to the Logical Link Control layer

13
Network Transport Systems

• Service Access Point (SAP) identifies a node or
  internal process using the LLC protocol
• Frame Check Sequence (FCS) field ensures the data
  are received as sent
• Cyclical Redundancy Check (CRC) is an algorithm
  used by FCS field in Ethernet frames

FIGURE 5-25 Ethernet 802.2 frame
14
Network Transport Systems

• Ethernet 802.3
• Original NetWare Ethernet frame type
• Default frame type for networks running NetWare
  versions lower than 3.12

FIGURE 5-26 Ethernet 802.3 frame
15
Network Transport Systems

• Ethernet II
• Original Ethernet frame type developed by DEC,
  Intel, and Xerox, before the IEEE began to
  standardize the Ethernet

FIGURE 5-27 Ethernet II frame
16
Network Transport Systems

• Ethernet SNAP
• Adaptation of Ethernet 802.2 and Ethernet II
• SNAP stands for Sub-Network Access Protocol

FIGURE 5-28 Ethernet SNAP frame
17
Network Transport Systems

• Understanding frame types
• Autosense enables a NIC to automatically sense
  what types of frames are running on a network and
  set itself to that specification

18
Network Transport Systems

• Ethernet design considerations

TABLE 5-1 Characteristics of different Ethernet
versions
19
Network Transport Systems

• Token Ring networks use token passing routine and
  a star-ring hybrid physical topology
• Active monitor
• Maintains timing for token passing
• Monitors token and frame transmission
• Detects lost tokens
• Corrects problems when a timing error or other
  disruption occurs

20
Network Transport Systems

• Multistation Access Unit (MAU)
• Regenerates signals

FIGURE 5-29 Interconnected Token Ring MAUs
21
Network Transport Systems

• Token Ring switching
• Token Ring networks can take advantage of
  switching to better utilize limited bandwidth
• Token Ring frames
• IEEE802.5
• IBM Token Ring frame

FIGURE 5-30 IBM Token Ring frame
22
Design Considerations for Token Ring Networks

• Cabling
• Connectivity devices
• Number of stations
• Speed
• Scalability
• Topology

23
Chapter Summary

• Physical topology is a drawing that represents
  the basic physical layout of a network
• Physical topologies are categorized into three
  fundamental geometric shapes
• Few LANs use the simple physical topologies in
  their pure form
• Hubs that service star-wired bus or star-wired
  ring topologies can be daisy chained to form a
  more complex hybrid topology
• Hierarchical hybrid topology can designate hubs
  at different layers to perform different functions

24
Chapter Summary

• Cabling that connects each hub is called the
  backbone
• In mesh networks, routers are interconnected with
  other routers so at least two pathways connect to
  each node
• WAN topologies use LAN and enterprise-wide
  topologies as building blocks, but add more
  complexity
• Dedicated circuits are continuous physical or
  logical connections between two access points
  that are leased by a provider

25
Chapter Summary

• Network transport systems encompass a set of
  rules specifying which data are packaged and
  transmitted over network media
• Ethernet is a networking technology and is by far
  the most popular logical topology for LANs today
• Ethernet follows communication rules called
  CSMA/CD
• On heavily trafficked Ethernet networks,
  collisions are not uncommon
• Ethernet comes in a variety of implementations

26
Chapter Summary

• The actual transmission rate of an Ethernet
  network will vary and will likely be less than
  its rating
• Networks may use one or a combination of four
  kinds of Ethernet data frames
• Token Ring networks currently run at either 4 or
  16 Mbps, as specified by IEEE 802.5
• Token Ring networks use the token-passing routine
  and a star-ring hybrid physical topology