Twisted Pair Cable

• Relatively slow speed
• Two insulated wires can be shielded (STP0 or unshielded (UTP)
• UTP is four-pair medium and comes in several categories
• UTP can be easily tapped by eavesdroppers than the other cable types
• Category based on how tightly wound the wires are, the tighter the wind the higher the rating and the higher the resistance to interference
• Cat 1 UTP – was used for telephone lines, not good for data
• Cat 2 UTP – up to 4 MBps
• Cat 3 UTP – Used for 10BaseT networks up to 10 MBps
• Cat 4 UTP – Used in Token Ring Networks up to 16 MBps
• Cat 5 – Current UTP standard for new installations up to 100MBps
• Cat 6 UTP – up to 155MBps
• Cat 7 UTP – up to 1 GBps

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Coaxial Cable

• Hollow outer conductor surrounds inner wire conductor
• Currently two types of LAN
  • 50-ohm Cable for digital signaling
  • 75-ohm Cable for analog signaling and high-speed digital signaling
• More expensive, but is more resistant to Electromagnetic Interference (EMI)
• Used rarely except in Broadband communications
• Comes in two types:
  • Thinnet – RG58
  • Thicknet RG8 and RG11
• Two common types of coaxial transmission methods:
  • Baseband – The cable carries a single channel
  • Broadband – Cable carries several channels

Fiber Optic Cable

• Conducts modulated light transmission
• Light waves are faster and travel greater distances
• Difficult to tap
• Resistant to EMI
• Usually connects backbones in larger networks
• Can be used to connect workstations to the network
• Expensive to install and to terminate

LAN Transmission Protocols

• Rules for communication between computers on a LAN
• Formatting of the data frame, the timing and sequencing of packet delivery, and resolution of error states

Carrier Sense Multiple Access (CSMA)

• Foundation of the Ethernet protocol
• Workstation continuously monitors the line waiting until it thinks it is free
• If the workstation doesn’t receive an acknowledgement from the destination to which it sent the packet, it assumes a collision has occurred and it resends the packet
  • Persistent Carrier Sense – Unless it receives an acknowledgement it will resend
  • Non-persistent Carrier Sense – Waits a random amount of time before it resends

CSMA/CA

• Carrier Sense Multiple Access / Collision Avoidance
• Workstations connected to two coax cables, one to send and one to receive data

CSMA/CD

• Carrier Sense Multiple Access / Collision Detection
• If the host detects another signal while transmitting it will send a jam signal causing all nodes to stop sending data
• Nodes will wait to resend
• Designed to avoid collisions

Polling

• A primary workstation polls another at a predetermined time to determine if it has data to transmit
• Primary must give permission to others to transmit

Token Passing

• Token Ring, FDDI and ARCnet
• Cannot transmit without the token
• Each station can hold token for maximum predetermined amount of time

LAN Transmission Methods

• Refer to the way packets are sent on the network
• Unicast – from single source to single destination
• Multicast – source copied and sent to multiple destinations
• Broadcast – source copied and sent to all nodes on the network

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