Network Models

OSI, Open Systems Interconnection, broken down into Seven Layers

Layer 7  Application, code built into all operating systems that enables network-aware applications (Application Programming Interfaces)

Layer 6  Presentation, translates data from lower layers into a format usable by the Application layer. (data conversion)

Layer 5  Session, software that handles part of networking, connecting applications to other applications. (tracking / naming)

Layer 4 Transport, Segmentation and Reassembly software.

Layer 3 Network, containers called packets get created and addressed so they can go from one network to another. This is where the Router lives.

Layer 2 Data Link, any device that deals with a MAC address, switches

Layer 1 Physical, method of moving data between computers, cabling, copper cabling, fiber optics, radio, and central box hubs

(Physical, Data Link, Network, Transport, Session, Presentation, Application)

(Please,   Do,            Not,        Throw,      Sausage, Pizza,            Away)

TCP/IP, Transmission Control Protocol/Internet Protocol

CCENT, Cisco Certified Entry Network Technician

CCNA, Cisco Certified Network Associate

ISO, International Organization for Standardization

UTP, Unshielded Twisted Pair

NIC, Network Interface Card

MAC address, Media Access Control address, 48-bits address, also known as physical address, to view MAC address on a Windows system, type ipconfig /all from a command prompt.  For macOS, type ifconfig from a terminal window.  For Linux, type ip a in a terminal window.

OUI, Organizationally Unique Identifier

EUI, Extended Unique Identifier

Frame, Container for a chunk of data moving across a network

Frame Encapsulates, Puts a wrapper around the payload

FCS, Frame Check Sequence, trailer to payload

CRC, Cyclic Redundancy Check

LLC, Logical Link Control, Layer 2, NIC that talks to the system’s operating system usually via device drivers

Windows command   netstat –a    shows all TCP/IP sessions running on computer.

API, Application Programming Interfaces, that allow programs to be network aware.  Allow a standard way for programmers to enhance or extend an application’s capabilities.

Encapsulation, the process of preparing data to go onto a network.

De-Encapsulation, the revers process of Encapsulation.

The TPCP/IP Model, consists of four layers:

Layer 4, Application, Lumps together the top OSI layers, Session, Presentation, and Application.  The data or payload stats and ends here.

Layer 3, Transport, Segmentation and reassembly of data.  Connection-Oriented, Transmission Control Protocol, and connectionless communications, User Datagram Protocol. It is TCP/UDP

Layer 2, Internet, IP packet layer, anything that uses IP addressing. It is the IP packet.

Layer 1, Link / Network Interface, Lumps together the OSI model’s Layers 1 Physical, and Layer 2 Data Link.  Cabling, physical address, NICs, and switches all fall in the Link layer. It is the Frame.

IMAP Internet Message Access Protocol

VOIP Voice over IP

TCP, Transmission Control Protocol is connection oriented protocol

TCP segment (Destination port, Source port, Sequence number, Checksum, Flags, Acknowledgement, Data)

UDP, User Datagram Protocol is connectionless communications protocol

UDP datagram (Destination port, Source port, Length, Checksum, Data)

Windows command    netstat –n   shows all current sessions

Cabling and Topology

Network Topologies (Bus, Ring, Star, Hybrid, and Mesh)

Bus topology network used a single cable that connected all computers in a line, with termination at each end

Ring topology network connect all computer on the network with a ring of cable.

Star topology used a central connection box, fault tolerance, if one cable broke, all of the other computers kept working

Hybrid topology, physically looks like Star topology, internal electronics would show Ring, or Bus.  An example is Star-Bus wired network topologies.

Physical topology

Logical topology

Mesh topology, wired, or wireless.  Partially Meshed, Fully Meshed

Network Technology, is a practical application of a topology.

Copper cables, coaxial, and twisted pair

Coaxial cable (Coax) contains a central conductor wire, surrounded by an insulating material, surrounded by braided metal shield.

EMI, Electromagnetic interference

BNC connectors, special bayonet-style connector

F connector, F-Type connector

ISP Internet service provider

RG Radio Guide rating

RG-58 50 Ohms ratting, RG-59, and RG-6 75 Ohms rating

STP Shielded twisted pair, protected from EMI

UTP Unshielded twisted pair

Cat 3      16 MHz                 16 Mbps             

Cat 5      100 MHz              100 Mbps

Cat 5e   100 MHz              1 Gbps

Cat 6      250 MHz              10 Gbps

Cat 6a    500 MHz              10 Gbps

Cat 7      600 MHz              10+ Gbps

ISO International Organization for Standardization

ANSI The American National Standards Institute

TIA Telecommunications Industry Association

RJ Registered Jack

RJ-11 Telephones connector

RJ-45 (RJ45S 8P8C) network cable connector

Fiber-Optic cable transmits light rather than electricity, it has four components, glass fiber (the core), the cladding that help reflect the light, buffer that gives strength, and insulating jacket.  The most common fiber-optic cable size is 62.5/125

LED Light Emitting Diodes

MMF Multimode Fiber, uses LED, 850-NM wavelengths

SMF Single-Mode Fiber, uses laser, 1310-NM or 1550-NM wavelengths

Modal Distortion problem unique to multimode fiber

RS Recommended Standard, RS-232, DB-9 connector serial cable, 56,000 bps

Parallel cable, DB-25 connector, 2 Mbps

Fire Ratings

UL Underwriters Laboratories

PVC Polyvinyl Chloride,

NEC National Electrical Code

Plenum-Rated cable creates much less smoke and fumes.

IEEE The Institute of Electronics Engineers

IEEE 802.1            Higher Layer LAN Protocols

IEEE 802.3            Ethernet

IEEE 802.11          Wireless LAN (WLAN)

IEEE 802.15          Wireless Personal Area Network (WPAN)

IEEE 802.18

IEEE 802.19

IEEE 802.20

IEEE 802.21         

IEEE 802.22          Wireless Regional Area Networks

Ethernet Basics

802.3 Standards

802.3i                   10 Mbps Ethernet using twisted pair cabling (1990)

802.3ab                Gigabit Ethernet over twisted pair (1999)

802.3by                25 Gigabit Ethernet over fiber (2016)

Ethernet Frames

Frames, broken down data transmitted between computer

Preamble, 7-byte series of alternating ones, and zeroes followed by a 1-byte start frame



Type, helps the receiving computer interpret the frame contents

Data, part of the frame that carries the payload

Pad, the minimum Ethernet frame is 64-bytes in size.  Extra data will fill up this area

FCS, Frame Check Sequence enables Ethernet nodes to recognize when bad things happen to data

UTP, Unshielded Twisted Pair cable

Half-Duplex mode, NICs that only communicate in only one direction at a time

Full-Duplex mode, enable NICs to send and receive at the same time, both directions.

TIA/EIA 568C the current standard includes the same wiring 568A, 568B

568A                                      568B

Brown                                   Brown

Brown/White                    Brown/White

Orange                                 Green

Blue/White                         Blue/White

Blue                                       Blue

Orange/White                   Green/White

Green                                   Orange

Green/White                     Orange/White

10BaseT Summary

Speed                   10Mbps

Signal type          Baseband

Distance               100 meters

Node Limit          No more than 1024

Topology             Star-Bus, Physical Star, Logical Bus

Cable type          Cat 3 with RJ-45

10BaseFL Summary

Speed                   10Mbps

Signal type          Baseband

Distance               2000 meters

Node Limit          No more than 1024

Topology             Star-Bus, Physical Star, Logical Bus

Cable type          Multimode fiber-optic with ST, or SC connectors

CSMA/CD Carrier Sense Multiple Access/Collision Detection

Carrier Sense, means each node on the network examines the cable before sending

Multiple Access, means that all machines have equal access to the wire

Collision Detection, NIC sense overlapping signals will know a collision has occurred, they generate a random number to determine how long to wait before trying again.

SAT, Source Address Table

Broadcast Domain

Uplink Port enable you to connect two switches using a Straight-Through cable.

Crossover Cable reverses the sending and receiving pairs on one end of the cable

Bridging Loops or Switching Loops create redundant connections in a network.

STP, Spanning Tree Protocol, used to eliminate the problem of accidental bridging loops.

BPDU, Bridge Protocol Data Units, switches communicate with other switches to prevent loops from happening

TCN, Topology Change Notification, allows switch to network themselves around the failed interface

Root Guard, will move a port into a root-inconsistent state RSTP, Rapid Spanning Tree Protocol, faster convergence time following some kind of network change.

Modern Ethernet

100BaseT Summary

Speed                   10Mbps

Signal type          Baseband

Distance               100 meters between Hub/Switch/Node

Node Limit          No more than 1024

Topology             Star-Bus, Physical Star, Logical Bus

Cable type          Cat 5 or better, UTP or STP, with RJ-45/8P8C connectors

Baseband Network, means that only a single signal travels over the wires of the network at one time.

Broadband Network, multiple signals to flow over the network

100BaseFX Summary

Speed                   100 Mbps

Signal type          Baseband

Distance               Two Kilometers between Hub/Switch/Node

Node Limit          No more than 1024

Topology             Star-Bus, Physical Star, Logical Bus

Cable type          Multimode fiber-optic cabling with ST or SC connectors

Full-Duplex Ethernet

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Gigabit Ethernet, two different versions:

IEEE 802.3ab standard, 1000BaseT, uses four pair UTP, STP cable (Gigabit Ethernet)

IEEE 802.3z standard 1000BaseLX

1000BaseSX, uses multimode fiber-optic cabling to connect systems. 850-nm (nanometer) wavelength LED, 220 to 500 meters

Wavelength of a particular signal refers to the distance the signal has to travel before it completes its particular shape and starts to repeat

1000BaseLX, is for Long-Distance carrier for Gigabit Ethernet uses laser

SFF Fiber Connectors, Small Form Factor

MT-RJ, Mechanical Transfer Registered Jack

Standard              Cabling                                 Cable Details                      Connectors                                         Length

1000BaseSX        Multimode Fiber              850-nm                                 Variable commonly LC                    220-500 m

1000BaseLX        Single Mode Fiber            1300-nm                             Variable commonly LC, SC            5 km

1000BaseT           Cat 5e/6 UTP                      Four-Pair/Full Duplex     RJ-45                                                     100 m

PC, Physical Contact connector, replace the Flat-Surface connector

UPC, Ultra Physical Contact

APC, Angled Physical Contact

Media Converters

                Single-mode fiber (SMF) to UTP/STP

                Multimode fiber (MMF) to UTP/STP

                Fiber to coaxial

                SMF to MMF

GBIC, Gigabit Interface Converter

SFP, Small Form-Factor pluggable

SONET, Synchronous Optical Network

Standard                              Fiber Type                           WaveLength                      Physical Layer Signaling                 Maximum Signal Length

10GBaseSR                         Multimode                         850-nm                                 LAN                                                        26-300 m

10GBaseSW                        Multimode                         850-nm                                 SONET/WAN                                      26-300 m

10GBaseLR                          Single-mode                      1310-nm                              LAN                                                        10 km

10GBaseLW                        Single-mode                       1310-nm                              SONET/WAN                                      10 km

10GBaseER                         Single-Mode                      1550-nm                              LAN                                                        40 km

10GBaseEW                        Single-Mode                      1550-nm                              SONET/WAN                                      40 km

MSA, Multisource Agreements

SFP+, Enhanced Small Form-Factor pluggable

WDM, Wave Division Multiplexing

BiDi, Single Strand Fiber Transmission Bidirectional Transceivers

QSFP, Quad Small Form Factor Pluggable optics