PROG1225-08 Lecture-Network Communication.pdf

1225 Unit Eight: Network Communication Overview A computer network is created when two or more computers can communicate with each other. Networks can be categorized by several methods, including the technology used and the size of the networks. Based on size:      PAN (Personal Area Network...

1225 Unit Eight: Network Communication Overview A computer network is created when two or more computers can communicate with each other. Networks can be categorized by several methods, including the technology used and the size of the networks. Based on size:      PAN (Personal Area Network) consists of personal devices communicating at close range such as a cell phone and laptop computer. PANs can use wired connections (such as USB) or wireless connections (such as Bluetooth or Wi-Fi). LAN (Local Area Network) covers a small local area, such as a home, office, other building, or small group of buildings. LANs can use wired (usually Ethernet) or wireless (usually Wi-Fi). A LAN is used for workstations, servers, printers, and other devices to communicate and share resources. Wireless LAN (WLAN) is used where network cabling is inconvenient to install or use – like most homes. MAN (Metropolitan Area Network) covers large campus or city. Uses wireless (commonly Wi-Fi indoors and LTE outdoors) and wired (Ethernet over fiber optic cable) connections. WAN (Wide Area Network) covers a large area and is made up of many smaller networks – like the Internet. Some technologies used to connect a single computer or LAN to the Internet include DSL, cable Internet, satellite, cellular, and fiber optic. Types of Network Connections Some connections are used to connect computers together locally (like a LAN) and some are used to connect to the Internet (through an ISP – Internet Service Provider).      Networks are built using one or more technologies that provide varying degrees of bandwidth – the theoretical number of bits that can be transmitted over a network at one time – usually in bits per second. o Kbps – thousands (Kilo) bits per second o Mbps – millions (Mega) bits per second o Gbps – billions (Giga) bits per second o Tbps – trillion (Tera) bits per second o Tbps < Pbps (Peta - Quadrillion) < Ebps (Exa - Quintillion) < Zbps (Zetta - Sextillion) < Ybps (Yotta - Septillion)  For more detail: https://en.wikipedia.org/wiki/Long_and_short_scales o Note: Some speeds use bits (like Mbps – megabits per second) and some use bytes (like MBps – megabytes per second).  Serial data transmissions (one bit at a time) will typically use bits per second.  Parallel data transmissions (more than one bit at a time) will typically use bytes per second. Data Throughput is the average of the actual speed where bandwidth is a theoretical speed. Latency is the delays experienced in network transmissions which accounts for the difference between bandwidth and the actual data throughput. Cellular – a wireless Internet connection used mostly for mobile phone service (a type of radio service). o 3G (third-generation cellular) – uses either CDMA (Code-Division Multiple Access) or GSM (Global System for Mobile communications) mobile phone services. Typical speeds: 200 Kbps to 4 Mbps. o 4G – uses either LTE (Long Term Evolution) or WiMAX (Worldwide Interoperability for Microwave Access) technology. Typical speeds: 100 Mbps to 1 Gbps Satellite – a wireless Internet connection that requires a dish to send and receive from a satellite. Typically used in remote locations with approximate speeds of up to 15 Mbps.      Telephone Line – a wired Internet connection technology. There are a number of sub-standards but the most common is ADSL. o ADSL (Asymmetric Digital Subscriber Line) – most bandwidth is from ISP to user. Typical speeds: 640 Kbps upstream (to ISP) and up to 24 Mbps downstream (from ISP). Cable Line – a wired Internet connection technology. Connects a home or small business to an ISP, and typically uses coaxial cable or sometimes fiber optic. Typical speeds: up to 160 Mbps depending on cable type. Dedicated Fiber Optic Line – direct connection from ISP to business or home. Typical speeds: up to 43 Tbps. Ethernet – most common wired connection technology for LANs. Uses twisted pair cabling. o Fast Ethernet (100BaseT) – typical speed: 100 Mbps o Gigabit Ethernet (1000BaseT) – typical speed: 1000 Mbps (or 1 Gbps) o Ethernet cabling comes in shielded and unshielded varieties – shielding protects from electromagnetic interference (caused by electrical motors, transmitters). o Ethernet cabling comes in different categories (abbreviated CAT). Examples:  CAT-5e (e for enhanced) is used for basic 100 Mbps and 1 Gbps networking.  CAT-7 is used for 1 Gbps and 10 Gpbs networking – and provides for extra shielding. Wi-Fi – most common wireless connection technology for LANs. o Based on IEEE (Institute of Electrical and Electronics Engineers) 802.11 standards. o 802.11g – typical speeds: up to 54 Mbps o 802.11n – typical speeds: up to 600 Mbps o 802.11ac – uses two frequencies to transmit data (2.4 GHz and 5 GHz).  2.4 GHz has a longer range than the 5 GHz range since the lower frequency has better penetration through materials that block wireless transmissions (walls, windows, floors, etc).  There are multiple 802.11ac sub-standards but as an example: AC5300 has a maximum 1000 Mbps at 2.4 GHz and 2167 Mbps (for each of 2 channels) at 5 GHz. Networking Hardware The focus here is on hardware found on local area networks, some of which can be found at home or a small office.   Hub – connects multiple networking devices together. Transmits data to all attached devices at the same time – except the device that generated the data. o Works on Level 1 of the OSI model (physical layer). Switch – connects multiple networking devices and networks together. Transmits data only to the intended device. o A switch keeps a table of all MAC addresses connected to it – it uses this table to determine which device to send the data to. o Works on Level 2 of the OSI model (data-link layer) and uses MAC addresses to do its job.    Bridge – a device that stands between two segments of a network and manages network traffic between them (uses MAC addresses). The two segments must be using the same protocols (like Ethernet, Wi-Fi, Cellular). Could think of it as a simple switch. o Works on Level 2 of the OSI model (data-link layer) and uses MAC addresses to do its job. Router – a device that manages traffic between two or more networks and can help to find the best path for traffic to get from one network to another (using IP addresses). Routers can communicate to one another. o Works on Level 3 of the OSI model (network layer) and uses IP addresses to do its job. Access Point – various definitions but generally allow wireless devices to connect to a wired network (and sometimes to the Internet) Networking Topologies Network topology is the arrangement of the elements on a network (how things are connected).     Star Topology – all devices connect to one central device (like a switch). Bus Topology – all devices are connected in a line – like three switches which are connected to each other (sometimes called daisy-chained). o Backbone is a central conduit that connects segments of a larger network – this can also lead to a bus topology. Star-Bus Topology – a hybrid topology that combines aspects of both star and bus topologies. Most networks use a star-bus topology. Ring Topology – an older type of connection where devices are connected to a ring backbone. Network Storage In the world of servers, storage takes on special importance since it contains the most critical portion of a company’s business – the data. Several technologies are used mainly for server and/or networking environments:     Fault Tolerance – refers to techniques that allow data storage (or other operations) to continue in the event of a failure or fault of one of its components. NAS (Network Attached Storage) – a separate standalone device on a local area network – its only role is providing fault tolerant data storage. SAN (Storage Area Network) – larger version of a NAS used in local and wide area networks. Multiple storage devices are connected to multiple, identical servers. RAID (Redundant Array of Independent Disks) – a way to use more than one storage device for fault tolerance: o RAID Level 0 – Striping  File data is written simultaneously to multiple drives in the array, which act as a single larger drive.  Provides a performance increase but no fault tolerance.  Minimum of two hard drives are required. o RAID Level 1 – Mirroring  Data written to one drive is duplicated on another. Hence, no increase in drive capacity.  Provides fault tolerance but no performance increase.  Minimum of two hard drives are required. o RAID Level 5 – Blocked Data with Distributed Parity  Files are broken up and distributed to multiple hard drives.  A parity file is created for each file stored is also distributed to the multiple hard drives.  The parity file can be used to recreate a missing piece of a file as long as only one piece is missing.  Improved performance.  Minimum of three hard drives. o    RAID Level 10 – actually Level 1+0  4 drives – first two drives are striped (Level 0) then both are mirrored to the other two drives (Level 1) SCSI (Small Computer System Interface) – a parallel storage technology used in servers. The server equivalent of PATA but with more capabilities. SAS (Serial Attached SCSI) – a serial storage technology used in servers. The server equivalent of SATA but with more capabilities. FC (Fiber Channel) – a transport layer protocol used on fiber-optic media instead of TCP or UDP. Also replaces the Ethernet connection with its own connection. Used mainly for storage on a SAN. o   FCoE (Fiber Channel over Ethernet) – a newer standard that allows FC to use Ethernet devices which saves money but tends to be slower than a dedicated FC device. iSCSI (Internet SCSI) – a transport layer protocol that runs on top of TCP to allow fast transmissions over LANs, WANs, and the Internet. Uses Ethernet connections and is used mainly for storage on a SAN. o iSCSI is newer than FC and is cheaper since it can use existing Ethernet devices but FC tends to be faster. Tape Drives – still used for backing up data. Sometimes called WORM (Write Once – Read Many) drives. Other Networking/Server Hardware One of the main themes in networking and server hardware is redundancy (having multiple copies) and fault tolerance. The following are some ways to achieve this:   UPS (Uninterruptible Power Supply) is a device that raises the voltage when it drops during brownouts or sags (temporary voltage reductions). It also acts as a surge suppressor to protect against power surges or spikes. A UPS also serves as a battery backup to provide power for a brief time during a blackout to properly shutdown a computer. Redundant Hardware – multiple processors, drives (RAID), power supplies, NICs, and other hardware devices including redundant servers are commonly used.