Bandwidth is the capacity of a medium to carry data.

The practical bandwidth of a network is determined by a combination of factors:

  • The properties of the physical media
  • The technologies chosen for signaling and detecting network signals

Throughput is the measure of the transfer of bits across the media over a given period of time.

Due to a number of factors, throughput usually does not match the specified bandwidth in physical layer implementations. Many factors influence throughput including:

  • The amount of traffic
  • The type of traffic
  • The latency created by the number of network devices encountered between source and destination


Usable data. Goodput is the measure of usable data transferred over a given period of time. Goodput is throughput minus traffic overhead for establishing sessions, acknowledgements, and encapsulation.


Fiber-optic cables can be broadly classified into two types:

  • Single-mode fiber (SMF): Consists of a very small core and uses expensive laser technology to send a single ray of light. Popular in long-distance situations spanning hundreds of kilometers such as required in long haul telephony and cable TV applications.
  • Multimode fiber (MMF): Consists of a larger core and uses LED emitters to send light pulses. Specifically, light from an LED enters the multimode fiber at different angles. Popular in LANs because they can be powered by low cost LEDs. It provides bandwidth up to 10 Gb/s over link lengths of up to 550 meters.

Fiber-optic connectors include:

  • Straight-Tip (ST): An older bayonet style connector widely used with multimode fiber.
  • Subscriber Connector (SC): Sometimes referred to as square connector or standard connector. It is a widely adopted LAN and WAN connector that uses a push-pull mechanism to ensure positive insertion. This connector type is used with multimode and single-mode fiber.
  • Lucent Connector (LC): Sometimes called a little or local connector, is quickly growing in popularity due to its smaller size.
  • Other fiber connectors such as the Ferrule Connector (FC) and Sub Miniature A (SMA) are not popular in LAN and WAN deployments. Obsolete connectors include biconic (obsolete) and D4 connectors.

Optical Time Domain Reflectometer (OTDR) can be used to test each fiber-optic cable segment. This device injects a test pulse of light into the cable and measures back scatter and reflection of light detected as a function of time. The OTDR will calculate the approximate distance at which these faults are detected along the length of the cable.



  • Standard IEEE 802.11: Wireless LAN (WLAN) technology, commonly referred to as Wi-Fi, uses a contention or non-deterministic system with a Carrier Sense Multiple Access/Collision Avoidance (CSMA/CA) media access process.Various 802.11 standards have evolved over the years. Standards include:
    • IEEE 802.11a: Operates in the 5 GHz frequency band and offers speeds of up to 54 Mb/s. Because this standard operates at higher frequencies, it has a smaller coverage area and is less effective at penetrating building structures. Devices operating under this standard are not interoperable with the 802.11b and 802.11g standards described below.
    • IEEE 802.11b: Operates in the 2.4 GHz frequency band and offers speeds of up to 11 Mb/s. Devices implementing this standard have a longer range and are better able to penetrate building structures than devices based on 802.11a.
    • IEEE 802.11g: Operates in the 2.4 GHz frequency band and offers speeds of up to 54 Mbps. Devices implementing this standard therefore operate at the same radio frequency and range as 802.11b but with the bandwidth of 802.11a.
    • IEEE 802.11n: Operates in the 2.4 GHz and 5 GHz frequency bands. The typical expected data rates range from 150 Mb/s to 600 Mb/s with a distance range of up to 70 meters. It is backward compatible with 802.11a/b/g devices.
    • IEEE 802.11ac: Operates in the 5 GHz frequency band providing data rates ranging from 450 Mb/s to 1.3 Gb/s (1300 Mb/s.) It is backward compatible with 802.11a/n devices.
    • IEEE 802.11ad: Also known as “WiGig”. It uses a tri-band Wi-Fi solution using 2.4 GHz, 5 GHz, and 60 GHz and offers theoretical speeds of up to 7 Gb/s.
  • Standard IEEE 802.15: Wireless Personal Area Network (WPAN) standard, commonly known as “Bluetooth”, uses a device pairing process to communicate over distances from 1 to 100 meters.
  • Standard IEEE 802.16: Commonly known as Worldwide Interoperability for Microwave Access (WiMAX), uses a point-to-multipoint topology to provide wireless broadband access.


crossover or straight-through


To specify when we use crossover cable or straight-through cable, we should remember:

  • Group 1: Router, Host, Server
  • Group 2: Hub, Switch

One device in group 1 + One device in group 2: use straight-through cable

Two devices in the same group: use crossover cable