The Physical Network
Cabling & Topology
- Network Topologies
- ‘Star-Bus’ topology is considered a hybrid topology.
- When each host is interconnected this is considered a fully meshed topology.
- Logical topology is the electronic circuit flow of frames.
- Topology is the organization of how the 1’s & 0’s (binary data) in the form of frames, move from host to host.
- Star-Bus topology is the primary topology that we use today. Ethernet uses exclusively ‘Star-Bus’. If you’re plugging a computer into a network, it’s probably using Ethernet, & it’s probably using ‘Star-Bus’.
- MESH is a topology that’s pretty much unique to wireless networks.
- Everybody connects to everybody else.
- Fully meshed vs partially meshed topology.
- Coaxial Cabling
- COAXial –> The conductors share the same center point or COmmon AXis.
- RG (Radio Grade) specifies the thickness of the conductors, insulation, & shielding.
- Coaxial cable has two conductors, one center point, and a tubular conducting layer.
- RG-59 has a 75ohm rating & uses a threaded F-type connector.
- RG-58 has 50ohm, RG-58 is an older type of cable.
- RG-8–Thicknet–50ohm
- RG-58–Thinnet–50ohm
- These were both used in early Ethernet installations.
- RG-6 has 75ohm, also. RG-6 is thicker than RG-59.
- RG-59 & RG-6 are classically used in cable modems.
- Twisted Pair Cabling (originally for telephone systems) (It’s the most common form seen on networks.)
- Modern twisted pair has 4 or more pairs of cable.
- UTP cable is unshielded and subject to signal interference from environmental factors.
- UTP–Unshielded Twisted Pair–No metal covering or aluminum cover-casing to protect from outside interference. But its less expensive!)
- 568A and 568B are wiring standards for how the wires are connected to a connector.
- STP–Shielded Twisted Pair
- Two-Standards–EIA/TIA 568A/568B
- STP has shielding to improve noise rejection compared to UTP.
- Because of the shielding; STP is more expensive.
- CAT Ratings (Category ratings) (Not to be confused with connectors like RJ-45 or RJ-11 (telephone) connectors.)
- UTP Cat ratings define the speed & cable length specifications.
- Cat ratings have a different number of twists per inch.
- Cat6a and Cat7 are both rated for 10 Gbps speed and up to 100-meter cable length.
- Cat3 (10 Mbps)–now obsolete
- Cat 5 (100 Mbps @ 100 meters)–quickly replaced w/ Cat 5e (100-1,000 Mbps @ 100 meters)
- Cat 6 (1 Gbps @ 100 meters)
- Cat6a (10 Gbps @ 100 meters)–Cat 6a is the current “king”. (Backwards compatible with 1gb sppeds)
- Fiber-Optic Cabling
- Multimode cables carry LED signals
- Single-mode cable carry laser signals
- For the test, be able to recognize the different types of fiber connectors.
- Multimode is almost always ORANGE!
- Single-mode is almost always YELLOW!
- Know connector types for the exam!
- ST connector–one of the earliest; it’s punched in & twisted to stay in place; ST is a round connector
- SC connector–equally as old & as popular as an ST connection; SC connectors are square; you punch them in & just pull them out;
- FC connector— similar in shape to ST (round); FC screws in like a TV cable.
- ST, SC, & FC are older generation connectors.
- LC connector–
- MT-RJ connector–
- LC & MT-RJ are more modern connectors.
- Duplex means two connectors in one cable.
- Polishing
- PC–physical contact; slightly rounded;
- UPC–ultra physical contact; more rounded;
- APC— angled physical contact;
- Fire Ratings
- Plenum-rated cable is the most fire resistant!
- Cable fire rating is normally clearly marked on the manufacturer’s box.
- Non-plenum is not considered fire/smoke resistant. It’s made of PVC and offers no fire protection at all.
- Riser-rated is designed to run between floors in a building; not as fire resistant as plenum.
- Legacy Network Connections
- DB-9 (9 pin) & DB-25 (25 pin) are legacy serial network connections.
- Parallel ports were typically used with printers.
- A Yost (or rollover) cable is a serial cable used to configure a router or switch.
- Know about both Serial Ports & Parallel Ports for the exam!
- Serial Ports are the oldest I/O connection in the world of computers!
- Low speed 2-way ports to allow us to make connections to 2 different types of things.
- Use a language called RS-232
- Parallel Ports (aka IEE 1284)–looks like a female DB-25 port.
- IEEE standards govern these things.
- Note: Parallel ports can send multiple bits out simultaneously, but serial ports only have one send pin, so data must be sent out serially (one after the other).
