Information Systems: Computer Networks
Hardware Firewalls
Protect network against external, digital attacks.
Application Layer of Application Set of OSI Stack
Provides application services for things like file transfer and email. Telnet and FTP exist entirely on this layer.
Transport Layer of Transport Set of OSI Stack
Provides transparent transfer of data between end systems in addition to being responsible for end-to-end error recovery and flow control. The lowest layer to work between end computers to assure complete data transfer.
Enterprise Network
Refers to all systems and procedures a company uses to interconnect different departments and workgroups, facilitating insight and data accessibility. Deals with performance, reliability, and security of physical systems and components. Includes LANs and WANs and integrates all systems including Windows, Mac, and Unix. BYOD allows employees to bring their own device and connect creating security problems.
Network OS
Refers to two different things: 1.) the specialized OS for network devices like routers, switches, or firewalls. 2.) OS oriented to computer networking
Wired Communication
Transmission of data over a cable with common wired media like pairs of copper wires (twisted, shielded or unshielded), coaxial cables, and fiber optic cables.
Hop Counts in Data Packet Transmission
Under fault conditions, packets can end up following a closed circuit where, if there is no intervention, the number of packets recirculating could build up and contest the network to the point of failure. A time to live field is decreased by one each time a packet goes through the network node. If a field reaches zero, routing has failed and the packet was discarded. Ethernet packets don't have time to live fields and thus use a broadcast storm in the presence of a switch loop.
Host Application
Use all seven layers of the OSI stack.
Multi-mode Optical Fibers
Use cheaper light sources like LEDs with less bandwidth and more attenuation Primarily used for shorter distances
Data Link Layer of Transport Set of OSI Stack
Furnishes transmission protocol knowledge and management while also handling errors in the Physical Layer like flow control and dram synchronization. In charge of direct communication between two adjacent nodes. Data packets are encoded and decided into bits.
LAN Devices
Gateways, routers, network bridges, switches, hubs, and repeaters. Device classification depends on its OSI layer where a device working in a higher layer will be able to connect more networks, but will be slower having to decode and re-encode data units to a higher level.
Frame
The communication process in a computer network is organized in layers, the OSI stack, where frames are used in the lower layers
Ethernet over Fiber Optics
100MB/sg fast Ethernet had several versions for different types of fiber optic cabling: 100BASE-FX and 100BASE-SX for multi-mode fibers and 100BASE-LX10 for single-mode. For GB Ethernet, multi-mode: 1000BASE-FX and 1000BASE-SX single-mode: 1000BASE-LX and 1000BASE-LX10 Normally used for backbone communication in corporate networks In 2003 several 10GB/sg Ethernet standards were launched
Ethernet over Twisted Pair
10BASET standard was created to use Stuctured Cabling Systems for commercial premises based on shielded (STP) or unshielded (UTP) twisted pair cables for each station. At one time, computers had coaxial and TP network adapter cards. Eventually technology transitioned solely to TP. Began in Half-Duplex using one TP and a shared medium called a hub to provide access to individual stations connected with TP. Soon two pairs were used with Full-Duplex for simultaneous reception and transmission. This allowed for each connects device to have 10Mbits/sg instead of sharing. 100BASETX was introduced in 1995 with 100Mbits/sg transmission over TP, called fast Ethernet 1000BASET or GB Ethernet came in 1999 at 1000Mbits/sg The modern standard of network equipment for desktop access includes GB Ethernet switches and adapters. 10GBASET was launched in 2006 with 10GB/sg Ethernet
Client/Server Architecture
A sever provides function or service to one or many clients who initiate requests for them. Allows network administrators to centralize functions and applications in one or more dedicated servers. The server is the center of the system giving access to resources and instituting security. Servers are classified by the service they provide: web servers for web pages, file server for computer files, database server for database queries and requests. Computer can act as a client, server, or both depending on nature of the application.
Repeater
Devices that amplifies or regenerates digital signals. Goes to application layer of OSI stack. Used to regain signal strength lost due to long distance, usually positioned along path to maintain signal. First used in local area networks to extend range as first Ethernet standard used a shared coaxial cable as the transmission medium. The cable allowed for a maximum distance between connected computers; now unnecessary due to structured cabling. Still used in long distance transmission media Usually has 2 ports
Switch
A multi-port bridge with a high speed backbone able to assign full Ethernet bandwidth to each connected device instead of sharing. Able to split network traffic as it goes up to the datalink layer of the OSI stack sending through a port only traffic assigned to it.
Local Area Network, LAN
Computer network that interconnects computers within a limited area such as a residence, school, lab, or office building. All components are locally managed with common transmission technologies like Ethernet over unshielded twisted pair, fiber optic for desktop access, and Wifi for wireless access. Simpler LANs consist of one or more LAN switches connected to computer hosts. Can be connected to a router, cable modem, or a DSL modem for Internet access OR other LANs via leased lines, special services, or Internet using VPN technology.
Bridge
Connects multiple network segments at the datalink layer of the OSI stack. Can transfer data from one physical medium to another, like transceivers. In Ethernet, were used to separate different sectors of a local network at a low OSI level.
Transport Set of OSI Stack
Consists of the remaining layers of the OSI Stack. Deals with processes needed when communicating in a computer network. Layers work with smaller chunks of data to facilitate communication and inter-networking.
Physical Layer of Transport Set of OSI Stack
Controls communication hardware by conveying a bit stream, electrical impulse, light or radio signal, through a network at an electrical and mechanical level. Provides hardware with a means of sending and receiving data on a carrier. Gigabit Ethernet, RS232, DSL, and ATM are protocols with Physical Layer components.
Ethernet
Created around 1973 by Xerox as a network standard for the communication of several computers using a shared cable. Accessing this shared medium uses a mechanism called CSMA-CD, Carrier Sense Multiple Access with Collision Detection, in which every station transmits then senses the cable to detect a collision with another transmitter. Originally competed to be the LAN standard with token ring and token bus: all three were included in the IEEE 802 project to create that standard. Assigned 802.3 code and became standard in 1985. Adapted to market by switching to twisted pair wiring to become the dominant network technology by the end of the 80s. Most modern wired LANs use Ethernet and fiber optic versions are used in local telecommunication carriers for backbone transmission. Goes up to the datalink layer of the OSI stack, specifying the transmission media along with the physical and datalink protocols. Has versions for coaxial, twisted pair, and fiber optic cabling.
Packet Framing
A packet or frame must carry control protocols where different communication protocols use different conventions to distinguish between elements and format data. Point to Point protocols structure packets into 8 bits, 1 byte, and has special characters to delimit different elements. Ethernet protocols structure a special sequence of bytes to mark the beginning of of a new frame Some protocols define packets at a bit level.
Data Packet Transmission Error Detection
Detection and correction performed at various layer in the protocol stack where all mechanisms are devised to detect and/or correct errors that occur during transmission. At the transmitter, a checksum, also referred to as a parity bit or Cyclic Redundancy Check code, is calculated before packet is sent. The code is then transmitted with the data and compared with one sent in packet at the receiver. A discrepancy will cause the packet to be corrected or discarded. Network protocol deals with packet loss.
Wide Area Network, WAN
A telecommunication or computer network extending over a large, geographical distance often established with leased telecommunication circuits. Used by business, education, and government entities to connect geographically spread out branches.
Central Computer with Terminals Distributed System
Developed in the early 1970s when mainframes adopted interactive user interfaces operating as timesharing computers where hundreds of users could be supported simultaneously. In addition, they featured batch processing using dumb local terminals connected with serial ports which soon transitioned into remote terminals connected as modems. All computing power lies in a central computer where remote systems act as input/output devices. Used with mainframes and supercomputers. Terminal emulation software is used to access a remote terminal with a PC. Modern example is a point-of-sale device connected to a central computer.
Hub
Device that connects multiple network segments making them act as one with shared media where only one connected computer is able to transmit at a time. Goes up physical layer of OSI stack. Used to be popular for Ethernet local area networking when structured cabling systems were introduced. Function, however, was superseded by Ethernet switches similar in appearance, but more powerful connecting every device with full instead of shared bandwidth.
Router
Allows for connection to different networks. Goes up to the Network Layer of the OSI stack.
Proxy Server
Allows network clients to make external connections through them.
TCP Transport Layer of TCP/IP Stack
Allows users to connect to a specific application in a computer host. TCP, Transmission Control Protocol, transmits data as a byte stream, provides flow control, and guarantees transferred data remains intact and arrives in same order UDP, User Datagram Protocol, allows for the connectionless transmission of data packets inidividuallly with no guarantee of order, but faster and more lightweight. Transport Layer addresses known as sockets or ports.
Modem
Device used to adapt digital data from local networks or devices to be carried over public phone or cable networks. Goes to physical layer of OSI stack Analog modems used to connect computers to Internet, but now modem function is usually embedded in another connection device connected to it, usually a router that acts as a gateway.
Networking or Communication Device
Devices that act as the backbone of the data communication network. Routers, switches, hubs, LAN cards, gateways, modems, hardware firewalls, CSU/DSU, ISDN terminals, or transceivers.
Data Packets
The communication process in a computer network is organized in layers, the OSI stack, where packets are used to name data structures in the layers above frames.
ADSL
Asymmetric Digital Subscribe Line, offers different upload/download speeds where VDSL is the fastest version.
Asynchronous mode of communication using a computer that is more than 40 years old. The most used Internet application. Allows users to send and receive messages with an email client or webmail interface, access from an Internet web browser.
Coaxial Cables
Cable with central conductor, copper or aluminum, surrounded by a tubular insulating layer covered by a cylindrical conducting shield covered with a protective, plastic layer called a plastic jacket. Configuration protects signal from external electromagnetic interference guaranteeing good bandwidth. Used as transmission links for radio frequency signals. Can be found in feed lines protecting radio transmitters and receivers with antennas and computer network connections.
Cellphones
Changed telecommunications rules where use of SMS and voice calls were replaced with messages and calls over the Internet.
Session Layer of Application Set of OSI Stack
Establishes, manages, and terminates conversations and exchanges in addition to dealing with session and connection coordination between the application and counterpart in other computer. Dialogues between apps at each end.
Structured Cabling
In 1991 the TIA, Telecommunications Industry Association, developed a standard for structured cabling changing computer network business for LANs. TIA/EIA 568, now in revision c, was then adapted by ISO to become the international standard, ISO/IEC 11801. This created a standard for commercial buildings and their connections in a campus environment. Hierarchical structure The connection between a desktop and floor cabinet is made using 4 twisted pairs wrapped with insulating plastic material capable of connecting to a data network or regular telephone. Same infrastructure can be used for voice and data communications. Floor cabinet and building cabinet connection is made using long distance fiber-optic cables and/or twisted pair cables, In some cases, every pair has a conducting shield (STP) or all of the cable has a common shield (FTP) to minimize external interference. Connector has 8 wires called RJ-45 Cable components assigned to a category depending on quality: Standard- Cat3 guarantees 16MHz bandwidth and up to 100m - components used for telephony Cat5e 100MHz bandwidth and 100m - gigabit Ethernet, lowest category for Ethernet communications. Cat6, Cat6A 10GB/sg Up to Cat8 each working at higher frequencies
Packets in Data Transmission
In order for many users to transmit data at once quickly and easily across a network, data must be broken down into packets or frames.
ISDN
Integrated Services for Digital Networks, created in the late 80s as the future technology for digitalization of phone networks Has low bandwidth compared to DSL relegated technology.
Single-mode Optical Fibers
Need more expensive light sources like LASERs with more bandwidth and less attenuation
Optical Fiber Cables
Light, cheap, and durable made of silica glass with a diameter slightly larger than a human hair. Several fibers are bundled in a cable with components to protect and stiffen them. Uses light to transmit information with high bandwidth and low attenuations in order to carry a lot of information long distances. Single fiber links in commercial operations can carry 100Gbps up to 40km. Guides light inside them using variations of refraction indexes along the diameter where light will reflect inside the cable without escaping. Fiber optic materials are cheaper than twisted pairs, but the associated electronics are more expensive and connectorization process is more difficult and expensive. Used in backbones, where high bandwidth is needed, or where electrical interference can disrupt communications.
Virtual Private Network, VPN
Mechanism to extend a private network across a public, unsecure network like the Internet. Enables users to send and receive data across shared or public networks as is computing devices were directly connected to a private network. Created by establishing a point-to-point connection between a computer or remote network to a private network using virtual tunneling protocols that encrypt communication content. Allows employees to securely access corporate Internet outside of the office in addition to securely connecting geographically separated branches of an organization to a central network.
Video Conference, VC
Mode of communication using a computer that uses a set of telecommunication technologies that allow two or more locations to communicate by two-way video and audio transmissions. A type of groupware, also called visual collaboration. Popularized after introduction of high capacity broadband in the late 1990s and powerful computing processors in addition to video compression techniques.
Gateway
Network device that goes up to the application layer of the OSI stack. This enables the interconnection of two networks working with completely different sets of protocols. Most versatile of the network devices, but also the slowest having to decode and re-encode completely every data packet in each new protocol set.
Network Layer of Transport Set of OSI Stack
Offers services to Transport Layer by providing switching and routing technologies, managing a multi-node network, creating logical paths or virtual circuits to transmit data from node to node. Works in end computers and intermediate network devices. Routing and forwarding, addressing, inter-networking, error handling, congestion control, and packet sequencing functions.
LLC, Logical Link Control Layer of Data Link Layer of Transport Set of OSI Stack
One of two sublayers of the Data Link Layer that controls frame synchronization, flow control, and error checking.
MAC, Media Access Control Layer of Data Link Layer of Transport Set of OSI Stack
One of two sublayers of the Data Link Layer that controls how a computer on a network gains access to data and permissions for transmission.
OSI Stack
Open System Interconnection, defines the networking framework to implement protocols in seven layers where control is passed from one to the next. Stack does not perform functions in networking, but provides a conceptual framework that breaks down the complex problem of computer inter-networking into a vertical stack, usually divided into two sets. OSI no longer used to develop communication software, but still used for educational purposes and can be seen in use when system administrators troubleshoot a network problem.
Data Packet Components
Packets and frames include header, body, and footer. Header: provides destination address, length information, originating address, packet number in sequence, protocol, and information to perform error checking operations. Body: or payload, contains the message Footer (optional): contains a sequence of bits to the end of the message and maybe some information to perform error checking operations at the receiver end.
Symmetric DSL Technology
SDSL HDSL
Value Added Network, VAN
Service from network providers that allow connection to a proprietary WAN with additional services specific to a business application.
Presentation Layer of Application Set of OSI Stack
Sometimes called the syntax layer, provides independence from differences in data representation, like encryption, by translating between application and network formats. Transforms data into a form that the Application Layer can accept. Formats and encrypts data to be sent across a network in order to solve compatibility problems.
Router
Specialized network device that goes up to the network layer of the OSI stack. Able to determine the next network node to which a data packet has to be sent to reach its ultimate destination. Acts as core switching device of the Internet performing the inter-networking function between different networks: based on TCP/IP protocol stack. Gateway of LAN to Internet.
WebChat
Synchronous, real-time mode of communication using a computer. Provides a system for exchanging typed electronic messages in an instant via an Internet or cellular network using a shared application. Microsoft Messenger, WhatsApp are a mixture of chat and email.
Ethernet over Coaxial Cable
The first specifications were based in using a shared coaxial cable to transmit 10Mbit/sg, detecting collisions between transmitting stations. Only one station could transmit at a time, call Half or Semi-Duplex, where each station can transmit and receive, but not at the same time. To better detect collisions there is a maximum network station distance. 10BASE5 Ethernet standard using thick coaxial cable (first standard, later used for backbones) 10BASE2 Ethernet or Cheapernet standard using thinner coaxial cable.
TCP/IP Stack
The most common family of protocols that rule current Internet. Provides a simpler and more efficient implementation of the seven layer model of the OSI stack. Deals with four layers of communications where data packets are passed top down for transmission. TCP/IP doesn't have Network Access Layer like OSI stack.
Application Set of the OSI Stack
The top three layers of the OSI stack that deals with the communication between applications where partners are identified, quality of service agreed, user authenticated, privacy considered, and restraints on data syntax are identified.
Phone Networks
Used copper pairs for more than 100 years where one or several pairs would connect a home with a street node connected to a multi-pair cable with 50 to 500 pairs. That is then connected in another node to a larger cable going to a local exchange office of the public switched telephone network with up to 2400 pairs. Originally developed for narrow band voice communication and was first used for data transmission by employing low bandwidth modems to adapt digital signal to the voice channel DSL, Digital Subscriber Line, has kept growing possible bandwidth from copper wires using modulation techniques that allow the transmission of data in parallel with voice calls using different parts of the frequency spectrum.
Metropolitan Area Network, MAN
WAN confined to a city or part of a city.
Transceiver
When using more than one transmission media, it is necessary to have devices that convert signal from one media to another, called a transceiver. Can be incorporated as expansion cards in some higher level networking devices like modems, CSU/DSUs. Used to adapt the signal of a local network to be carried over a public network.
Switch
Works inside local networks. Only goes up to Datalink Layer of OSI stack