Simple LAN Topologies

1
Simple LAN Topologies

• Terminators stop signals after they have reached
  their destination
• Signal bounce
• Phenomenon in which signals travel endlessly
  between the two ends of a bus network

FIGURE 5-2 Terminated bus network
2
Hybrid LAN Topologies

• Star-wired bus
• In a star-wired bus topology, groups of
  workstations are star-connected to hubs and then
  networked via a single bus

FIGURE 5-6 Star-wired bus network topology
3
Enterprise-wide Topologies

• Serial backbone
• Two or more hubs connected to each other by a
  single cable
• Distributed backbone
• A number of hubs connected to a series of central
  hubs or routers in a hierarchy

FIGURE 5-9 Simple distributed backbone network
4
Enterprise-wide Topologies
FIGURE 5-10 Distributed backbone connecting
multiple LANs
5
Enterprise-wide Topologies

• Mesh networks
• Routers are interconnected with other routers
  with at least two pathways connecting each router

FIGURE 5-13 Example of a mesh network
6
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

7
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

8
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
9
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
10
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
11
Network Transport Systems
FIGURE 5-22 Enterprise-wide Ethernet 10BaseT
network
12
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

13
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

14
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
15
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

16
Network Transport Systems
FIGURE 5-24 Switched Ethernet network
17
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

18
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
19
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
20
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
21
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
22
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

23
Network Transport Systems

• Ethernet design considerations

TABLE 5-1 Characteristics of different Ethernet
versions