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Sunday, January 3, 2010

Day 26: Network Physical Media

Before finally moving on to working with swiches, we can review a bit by viewing a short study video available at the Cisco Learning Home page:

Understanding the TCP/IP Internet Layer:

A directed-broadcast address is an address that has all 1s in the host field. It allows the network administrator to address every host on a subnet. When directed broadcast is enable (directed-broadcast command) a router translate of layer 3 broadcast into layer 2 broadcast. It can be use to target all host in subnet to perform remote management or administration services (WOL, DHCP relay).

Unshielded twisted-pair (UTP) cabling is a type of twisted-pair cable that relies solely on the cancellation effects produced by the twisted wire pairs to limit electromagnetic interference (EMI) and radio frequency interference (RFI). UTP cable is often installed using an RJ-45 connector, and UTP cabling must follow precise specifications dictating how many twists are required per meter of cable. The advantages of UTP are ease of installation and low cost. A disadvantage of UTP is that it is more prone to EMI than other types of media.
Shielded twisted-pair (STP) cable combines the twisting techniques of UTP, but each pair of wires is wrapped in a metallic foil. The four pairs of wires are then wrapped in a metallic braid or foil. STP reduces electrical noise and EMI. STP is installed with an STP data connector but can also use an RJ-45 connector. An advantage of STP is that it is more resistant to outside interference; a disadvantage is that it is more expensive and difficult to install.
Both UTP and STP have a maximum cable length of 100m.

A coaxial cable carries electrical signals over a copper wire and is capable of longer lengths than UTP.
Fiber-optic cables send and receive data with pulses of light. Multimode is less expensive than single-mode but cannnot go such long distances (2000m for multimode).

TIA/EIA defines the wiring schemes T568A and T568B for network cables.
A straight-through cable is used to connect unlike devices, like switch to router, hub to pc, switch to pc - think of it things that are meant to be connected! They're wired the same way at both ends. This cable uses pins 1, 2, 3, and 6. The send and receive wires are not crossed.
Crossover cables are used to connect like devices, like pc to pc, hub to hub, switch to switch but also hub to switch! It's a cable that has the send and receive wires crossed at one of the ends. In a Category 5 cable, the 1 and 3 wires are switched and the 2 and 6 wires are switched at one end of the cable.
A console cable is used to connect to the console port on a router or switch for configuring the device. It's also called a rolled cable.
A serial cable is used to connect a router to an Internet connection.

Ethernet IEEE 802.3 (10BASE or baseband signal rate of 10Mbps)
  • 10BASE2: Known as thin Ethernet, this specification uses thin coaxial cable as its medium and provides access for multiple stations on the same segments.
  • 10BASE5: Called thick Ethernet, this specification uses a thick coaxial cable as its medium. The maximum segment length of 10BASE5 is over twice that of 10BASE2.
  • 10BASE-T: This specification provides access for a single station only, so all stations connect to a switch or hub. The physical topology of 10BASE-T is that of a star network. It uses unshielded twisted-pair (UTP) cable Category 3, 4, 5, and 5e as its network medium.
Fast Ethernet IEEE 802.3u (raises Ethernet standard of 10Mbps to 100Mbps)
  • 100BASE-FX: Uses two strands of multimode fiber-optic cable as its medium and has a maximum segment length of 400 meters. 
  • 100BASE-T: Defines UTP as its medium and has a maximum segment length of 100 meters. 
  • 100BASE-T4: Uses four pairs of Cat 3 to 5 UTP as its medium. It maximum segment length is 100 meters. 
  • 100BASE-TX: Specifies two pairs of UTP or shielded twisted-pair (STP) cable as its medium with a maximum segment distance of 100 meters.
We also have these Gigabit possibilities:
  • 1000BASE-T: 100 meters 
  • 1000BASE-LX: 550 meters for multimode fiber, 10 km for single-mode fiber 
  • 1000BASE-SX: 250 meters for multimode fiber, 550 meters for single-mode fiber 
  • 1000BASE-CX: 25 meter

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