The Bits and Bytes of Computer Networking

Computer Networking

A group of computers that use a set of common communication protocols over digital interconnections for the purpose of sharing resources located on or provided by the network nodes.

Internetwork

The practice of interconnecting multiple computer networks, such that any pair of hosts in the connected networks can exchange messages irrespective of their hardware-level networking technology. The resulting system of interconnected networks are called an internetwork, or simply an internet.

Local Area Network (LAN)

Composed of computers connected together with ethernet cables, or with a hub or a switch as a central console. A computer network that links devices within a building or group of adjacent buildings.

Metropolitan Area Network (MAN)

Is a computer network that interconnects users with computer resources in a geographic region about the size of a typical metropolitan area.

Wide Area Network (WAN)

A computer network spanning regions, countries, or even the world.

Crosstalk

When an electrical pulse on one wire is accidentally detected on another wire.

Collision Domain

A network segment where only one device can communicate at a time. If multiple systems try sending data at the same time, the electrical pulses sent across the cable can interfere with each other. Ethernet as a protocol solved this problem by using a technique known as carrier sense multiple access with collision detection.

Autonomous System (AS)

Is a collection of connected Internet Protocol (IP) routing prefixes under the control of one or more network operators on behalf of a single administrative entity or domain that presents a common, clearly defined routing policy to the internet.

Node

Is either a redistribution point or a communication endpoint.

Modulation

Is the process of varying one or more properties of a periodic waveform, called the carrier signal, with a modulating signal that typically contains data being transmitted.

Line Code

(modulation in networking) Is a pattern of voltage, current, or photons used to represent digital data transmitted down a transmission line. This repertoire of signals is usually called a "constrained code" in data storage systems.

Duplex Communication

The concept that information can flow in both directions across the cable.

Full-Duplex

Both parties can communicate with each other simultaneously.

Half-Duplex

Allowing the transmission of signals in both directions but not simultaneously.

Simplex Communication

This concept that information can flow in one direction across the cable.

Octet

In computer networking, any number that can be represented by 8 bits.

Internet Protocol (IP) Address

A unique string of numbers separated by periods that identifies each computer using the Internet Protocol to communicate over a network. Belongs to the networks, not to the devices attached to those networks.

Static IP Address

Reserved for servers and network devices.

Dynamic IP Address

Reserved for clients.

Address Class System

A way of defining how the global IP address space is split up.

Class A

The first octet is used for the network ID and the last three are used for the host ID. 2^24 total addresses.

Class B

The first two octets are used for the network ID, and the second two are used for the host ID. 2^16 total addresses.

Class C

Those where the first three octets are used for the network ID and the last one is used for the host ID. 2^8 total addresses.

Network ID

The network number is used by routers to packets to the right network.

Host ID

Defines the host device (computer, server, printer, etc..).

Media Access Control (MAC) Address

Primarily assigned by device manufacturers, and are therefore often referred to as the burned-in address, or as an ethernet hardware address, hardware address, and physical address, each address is unique and should not be used twice.

Organizationally Unique Identifier (OUI)

The first three octets of a MAC address.

Hexadecimal Prefix

"0x" is meant to indicate that a value is being represented in hexadecimal.

Unicast

Transmission of a data package or an audiovisual signal to a single recipient.

Multicast

Is group communication where data transmission is addressed to a group of destination computers simultaneously. Multicast can be one-to-many or many-to-many distribution. Multicast should not be confused with physical layer point-to-multipoint communication.

Broadcast

Refers to transmitting a packet that will be received by every device on the network.

The ethernet broadcast address is all Fs; FF:FF:FF:FF:FF:FF.

Institute of Electrical and Electronics Engineers (IEEE)

Is a professional association for electronic engineering and electrical engineering. Its objectives are the educational and technical advancement of electrical and electronic engineering, telecommunications, computer engineering and allied disciplines.

Internet Engineering Task Force (IETF)

Is an open standards organization, which develops and promotes voluntary internet standards, in particular the standards that comprise the internet protocol suite (TCP/IP).

Internet Assigned Numbers Authority (IANA)

A non-profit organization that helps manage things like IP address allocation, also manages autonomous system numbers.

Internet Society (ISOC)

An American organization founded to promote the open development, evolution, and use of the Internet for the benefit of all people throughout the world.

Encapsulation

In object-oriented programming, encapsulation refers to the bundling of data with the methods that operate on that data, or the restricting of direct access to some an object's components.

Subnetting

The process of taking a large network and splitting it up into many individual and smaller subnetworks, or subnets.

Demarcate

To set the boundaries or limits of; to separate or distinguish from.

Demarcation Point

The physical point where the public network ends and the private network of a customer begins. Simply put, the "demarc" marks the point where a customer's network interfaces with the network owned by another company or additional party.

Classless Inter-Domain Routing (CIDR)

A method for calculating IP addresses and for IP routing.

Subnet Mask

32-bit numbers (similar to the IP address) that are normally written out as four octets in decimal, a way for a computer to use AND operators to determine if an IP address exists on the same network.

Hop

Occurs when a packet is passed from one network segment to the next.

Routing Loop

Are formed when an error occurs in the operation of the routing algorithm, and as a result, in a group of nodes, the path to a particular destination forms a loop.

Vector

Are a logical element in programming languages that are used for storing data.

Autonomous System (AS)

An internetwork under the control of a single organization. Usually presents a common clearly defined routing policy to the internet.

Autonomous System Number (ASN)

Numbers assigned to individual autonomous systems, are 32-bit numbers.

Non-Routable Address Space

Private network addresses are not allocated to any specific organization. Anyone may use these addresses without approval from regional or local internet registries. Private IP address spaces were originally defined to assist in delaying IPv4 exhaustion. IP packets originating from or addressed to a private IP address cannot be routed through the public internet.

Request for Comments (RFC)

A publication from the internet society (ISOC) and its associated bodies, most prominently the IETF, the principal technical development and standards-setting bodies for the internet.

Handshake

A way for two devices to ensure that they're speaking the same protocol and will be able to understand each other.

Instantiation

The actual implementation of something defined elsewhere.

Flow Control

Process of managing the rate of data transmission between two nodes to prevent a fast sender from overwhelming a slower receiver.

Networking Devices

Hubs

Are devices commonly used to connect segments of a LAN. It contains multiple input/output ports. When a signal arrives at any input port, the signal will be reproduced and sent at all output ports except the one it is coming from.

Switch

Is a piece of networking hardware that connects devices on a computer network by using packet switching to receive and forward data to the destination device. A network switch is a multiport network bridge that uses MAC addresses to forward data at the data link layer.

Ethernet Cables

Are used to interconnect devices. Allows data to be transmitted point-to-point.

Coaxial Cable

Is a type of electrical cable consisting of an inner conductor surrounded by a concentric conducting shield, with the two separated by a dielectric.

Fiber Optic Cable

A flexible transparent fiber made by drawing glass or plastic to a diameter slightly thicker than that of a human hair.

Twisted Pair Cable

Is a type of wiring in which two conductors of a single circuit are twisted together for the purposes of improving electromagnetic compatibility.

Pinouts

A diagram showing the arrangement of pins on an integrated circuit and their functions.

8P8C Modular Connectors

The little plastic piece on the end of an ethernet cable, the plug.

Repeaters

Are used in transmission systems to regenerate analog or digital signals distorted by transmission loss.

Analog Repeater

Can only amplify the signal.

Digital Repeater

Can reproduce a signal to near its original quality.

Client

Is a piece of computer hardware or software that accesses a service made available by a server as part of the client-server model of computer networks. The server is often on another computer system, in which case the client accesses the service by way of a network.

Server

A computer or computer program which manages access to a centralized resource or service in a network. Serves data to a client that is requesting that data.

Router

A device that knows how to forward data between independent networks. A router receives and sends data on computer networks.

Media Converter

Is a simple networking device that makes it possible to connect two dissimilar media types such as twisted pair with fiber optic cabling.

RJ45 Port

The most common type of ethernet connection port.

Link LED

Flashes yellow when the cable is properly connected to two devices that are both powered on.

Activity LED

Flashes green when data is actively transmitted across the cable.

Patch Panel

Is a piece of hardware with multiple ports that helps organize a group of cables. Each of these ports contains a wire that goes to a different location. Patch panels can be quite small, with just a few ports, or very large, with many hundreds of ports.

Bridges

A type of computer network device that provides interconnection with other networks that use the same protocol, connecting two different networks together and providing communication between them.

Bridged Router

A network device that works as a bridge and as a router.

Modem

Stands for MOdulator/DEModular. A modem converts digital signals generated by the computer into analog signals which, then can be transmitted over cable lines and transforms incoming analog signals into digital equivalents.

Network Interface Card (NIC)

Network interface card is an electronic device that is mounted or integrated on the motherboard. Information is stored in the ROM. Known as a network interface card, network adapter, LAN adapter, or physical network interface; is a computer hardware component that connects a computer to a computer network.

Multiplexer

Also known as a data selector, is a device that selects between several analog or digital input signals and forwards it to a single output line.

Demultiplexer

A device taking a single input and selecting signals of the output of the compatible multiplexer, which is connected to a single input, and shared selection line. A multiplexer is often used with a complimentary demultiplexer on the receiving end.

Gateway

Is a component that is part of two networks, which use different protocols. The gateway is a protocol converter which will translate one protocol into the other. A router is a special case of gateway.

Transmission Control Protocol (TCP)

Is a standard that defines how to establish and maintain a network conversation through which application programs can exchange data. TCP works with the Internet Protocol (IP).

Internet Protocol (IP)

Is the principal communications protocol in the Internet Protocol Suite for relaying datagrams across network boundaries. Its routing function enables networking, and essentially establishes the internet.

Physical Layer (1, TCP/IP)

Represents the physical devices that interconnect computers. It sends and receives signals on the physical wire or the antenna to transmit the bits found in the frames. There are physical components at the end of every network interface (wire or antenna).

Modulation

Is the process of varying one or more properties of a periodic waveform, called the carrier signal, with a modulating signal that typically contains data being transmitted.

Data Link Layer (2, TCP/IP)

Network Interface, Network Access Layer; Responsible for defining a common way of interpreting these signals so network devices can communicate.

Ethernet Protocol

Is a family of computer networking technologies commonly used in local area networks (LAN), metropolitan area networks (MAN), and wide area networks (WAN). Responsible for getting data to nodes on the same network or link.

Carrier Sense Multiple Access with Collision Detection (CSMA/CD)

Used to determine when the communication channels are clear, and when a device is free to transmit data. Uses carrier-sensing to defer transmissions until no other stations are transmitting.

Medium Access Control (MAC) Layer

Responsible for controlling how devices in a network gain access to a medium and permission to transmit data.

Logical Link Control (LLC)

Responsible for identifying and encapsulating network layer protocols and containing error checking and frame synchronization.

Network Layer (3, TCP/IP)

Allows different networks to communicate with each other through devices known as routers.

Address Resolution Protocol (ARP)

Is a communication protocol used for discovering the link layer address, such as the MAC address, associated with a given internet layer address, typically an IPv4 address. This mapping is a critical function in the internet protocol suite.

ARP Table

A list of IP addresses and the MAC addresses associated with them. This is typically stored on the network switch. ARP table entries generally expire after a short amount of time to ensure changes in the network are accounted for.

ARP Broadcast

A message sent by a network switch requesting a device's MAC address.

ARP Response

When a device responds to an ARP broadcast, and sends the native MAC address to the network switch.

Router Table

In computer networking a routing table, or routing information base (RIB), is a data table stored in a router or a network host that lists the routes to particular network destinations, and in some cases distances associated with those routes.

Interior Gateway Protocols (IGP)

A type of protocol used for exchanging routing information between gateways within an autonomous system. This routing information can then be used to route network-layer protocols like IP.

Link State Protocol (LSP)

Router knows the state of all links (interfaces) in the internetwork, and selects the best path. Used in packet switching networks for computer communications.

Intermediate System to Intermediate System (IS-IS) Protocol

Is a routing protocol designed to move information efficiently within a computer network, a group of physically connected computers or similar devices. It accomplishes this by determining the best route for data through a packet switching network.

Open Shortest Path First (OSPF) Protocol

Calculate the shortest route to a destination through the network based on an algorithm.

Distance-Vector Protocols (DCP)

Measures the distance by the number of routers a packet has to pass, one router counts as one hop. Distance-Vector Protocols also require that a router informs its neighbors of network topology changes.

Enhanced Interior Gateway Routing Protocol (EIGRP)

Is an advanced DVP routing protocol that is used on computer networks for automating routing decisions and configuration. The protocol was designed by Cisco Systems as a proprietary protocol, available only on Cisco routers. Includes link state like features as well.