Network+ : From Physical Topologies to Media and Network Devices

  1. Network+ Certification
  2. Network+ Certification – Introductions and Resources
  3. Network+ : From Physical Topologies to Media and Network Devices
  4. Network+ : Networking Variants, Physical Installation
  5. Network+ : TCP/IP and Network Operations
  6. Network+ : Network Naming and Sharing Resources
  7. Network+ : IPv6
  8. Network+ : Remote, Secure and Cross-Platform Networking
  9. Network+ : Servers and Support
  10. Network+ : WiFi
  11. Routing and Firewalls
  12. Network+: Routing Protocols
  13. Network+: Network Monitoring

Day 2: Chapters 3, 4 and 5

Client / Server Model


Clients: Either a physical machine like your PC or workstation, or more accurately, a “receiving end” application like your web browser. The client will connect to the server’s IP address and the service’s port number, eg.

Servers: either physical machines or service daemons, like web servers, mail servers, streaming servers, etc.). The server will accept connections from clients at the server’s IP address and port number.

There’s more to this, so don’t forget this model.

Local Area Networks (LANs)

Layer 1 of the OSI Model: the Physical Layer

Physical media: What carries the signal (think of telegraph wire)

            • Wire
            • Fiber optic cable
            • Radio waves
            • Infrared

Layer 2: The Data Link Layer

Layer 2 of the OSI is … a mistake. ISO ignores the fact that there are two protocols at work there: a Logical Link Control layer that sets up sessions and handles multiplexing, and a Media Access Control layer that handles addressing using MAC addresses.

Logical Link Control (LLC)

Media Access Control (MAC)

MAC Addresses

NICs have “permanent” hardware addresses (Physical Addresses in Windows): MAC Addresses.

All local network traffic is sent to and from MAC Addresses. Think of them as the room numbers in a hotel, used for things like Room Service.


Mac Addresses are written in hexadecimal:

Base 16 notation, using 0-9 and A-F to express numbers from 0-15:

0 1 2 3 4 5 6 7 8 9 a b c d e f

Grouped in six pairs of hex numbers with a separator in between:

Generic hex numbers in the wild look like this:

0f38  – just the number

0x0f38 – “0x” means “hex”

0f38h – “h” means “hex”

So actual MAC addresses look like this:




The formal specification for MAC addresses calls for them to be lower-case letters, BUT: Microsoft will and CompTIA may show them as upper-case letters.
And the delimiter can be a colon ( : ), a dash ( – ), or anything else. The delimiters aren’t really there; they are put in for our feeble human minds.

Signal Protocols: How the message gets passed (think of Morse Code)

Ethernet, Token Ring, DECnet, X.25, IPXSPX, Banyan Vines, etc.

Today, mostly Ethernet

Ethernet passes frames. (You could call them packets, but the other kids on the playground will make fun of you.)

Ethernet cards are NICs (network interface cards, also called “host adapters”).

Full vs. Half-duplex

It wasn’t until we got switches that we could use full duplex communication. In other words, both hosts can talk non-stop, and listen non-stop, full-time, with no collisions!

This was a huge step. Every session between hosts is on its own private collision domain: there ARE no collisions. Ethernet became hugely faster with this innovation.

LAN Topologies

Bus Topology


Ring Topology

Ring: Token Ring


Star Topology

Mesh Topology

Mesh: Full vs Partial Mesh

Hybrid Topology


Physical vs. Logical

Now we go one layer deeper.

A bus is a linear network – both physically and logically.

A star topology is physically a star (think of a hub or switch at the center of a group of hosts.

But a star topology in Ethernet physically looks like a start – but at the logical level, the way it actually functions, it uses a bus topology. Think of it this way: if you took all the wiring out of a hub and laid it out, you’d find it’s actually arranged as a bus.

This creates a “Physical Star but Logical Bus” topology. Ethernet hubs and switches use it, but so do Token Ring concentrators.



RG-8 – 10Base5

RG-58 – 10Base2


Vampire Tap

Connectors: BNC (“bayonet”) – a steel, stick and twist connector

RG-6 – Cable TV service, analog service, security cameras

RG-62 – TV

RG-59 – Cable service : Siamese (TwinAxial) cable: coax bonded to two conductor wires (primitive “power over ethernet” – analog)

Twisted Pair Ethernet

Twisted pair Ethernet cable has 4 pairs (8 wires), but only 2 pairs are used. Theoretically this supports 2 Ethernet ports per cable, though this feature usually goes unused. Ports and jacks use the RJ-45 standard, similar to the telephone RJ-11 jack.

Get familiar with the T-568A & B jack and plug pinout configuration. Memorize the B pinouts and learn to use the acronym GO to get the A pinouts. For some reason everyone uses B most of the time. This site is clear and to-the-point:

Almost all standards for Twisted Pair call for runs of a maximum of 100 meters. In-wall cable is usually limited to 90 meters to allow patch cables at both ends.


Shielded Twisted Pair

Was mostly used with Token Ring.

Use in high-EMI/RFI areas where shielding is needed.


Unshielded Twisted Pair

10BaseT: minimum Cat 3

100BaseTX, which became simply
100BaseT: minimum Cat 5

100BaseT4: an early alternative that used all 4 pairs in a Cat 3 cable

1000BaseT or 1GBaseT: Cat5e

10GBaseT: Cat 6 will get you 55 meters, Cat 6a will get you 100 meters.

Fiber Optic

LEDs – short distance

Lasers – long distance

Multimode fiber: usually orange; short distance; uses multiplexing, for instance three different signals: red, green and blue

Single-mode fiber: usually yellow; long distance; simplex: only one signal stream

Physical Contact (PC) Connectors

Flat-surface connector

Ultra Physical Contact (UPC)

Angled Physical Contact (APC)

Media converter

10BaseFL – early fiber optic


1000BaseSX: “S for short” distance, up to 500 meters

1000BaseLX: “L for long” distance, up to 5 kilometers

ATM over SONET rings

The national long-distance telephone system.

10 Gbps

ATM used 53 byte cells

Fading away…

Metro Ethernet over SONET

Uses SONET rings, so 10GB

10GBaseSR: S for short; R is for eth-R-net; multimode; 300 meters

10GBaseSW: W is for WAN (meaning ATM signaling, not Ethernet); multimode; 300 meters

10GBaseLR: Ethernet, single-mode; 10 kilometers

10GBaseLW: WAN/ATM; 10 km

10GBaseER: E is for extra-long; ethernet; 40 km

10GBaseEW: WAN/ATM; 40 km


ST – Stick and Twist
SC – Stick and Click
LC – the “Little Connector” (actually Lucent)

Early Gigabit Media

1000BaseCX (copper, 25 yd)
1000BaseSX (“short” fiber-optic)
1000BaseLX (“long” fiber-optic)


Repeater – Layer 1 – usually for coaxial, but there are twisted pair repeaters too.

Bridge – Layer 2 – also usually for coax, and essentially a 2-port switch, i.e. it keeps a MAC table.

Hub – Layer 1 – has no MAC filtering.

Switch – Layer 2 – isolates traffic based on MAC addresses.

Router – Layer 3 – routes internet traffic based on IP addresses. This is the only Layer 3 box in this list.