GLOSSARY
address resolution protocol (ARP) A TCP/IP protocol defined in the IETF (Internet Engineering Task Force) standard RFC 826. The purpose of ARP is to resolve logical IP addresses to physical MAC addresses. ARP falls under the Link Layer of the TCP/IP protocol stack and the Data Link Layer of the OSI (Open Systems Interconnection) model.
application security Any encryption or security measures performed at the Application Layer of the OSI model.
attack vector The means by which a malicious program or unauthorized user gains access to a system.
Audio Video Bridging (AVB) A suite of standards in development by an IEEE 802.1 task force to provide time-synchronized, low-latency streaming services.
automatic private IP addressing (APIPA) A form of link-local addressing defined in the IETF standard RFC 3927. APIPA automatically assigns locally routable addresses from the reserved network 169.254.0.0/16 to devices that do not have or cannot obtain an IP address. This allows devices to communicate with other devices on the same LAN. APIPA operates at the Network Layer of the OSI model and the Internet Layer of the TCP/IP protocol stack.
bandwidth (networking) The available or consumed data communication resources of a communication path, expressed in terms of bits per second. Also called throughput or bit rate.
bit depth The number of states you have in which to describe a sampled voltage level. Bit depth is also known as quantization. Quantization shares the same root as quantity; bit depth involves assigning a quantity to the signal being measured. Greater bit depth gives a more accurate representation of the sampled voltage level.
broadcast domain A set of devices that can send Data Link Layer frames to each other directly, without passing through a Network Layer device. Broadcast traffic sent by one device in the broadcast domain is received by every other device in the domain.
byte A group of eight bits. “B” is the abbreviation for byte.
caching server A type of proxy server that saves local copies of frequently or recently requested network resources. Caching servers have two benefits: they reduce latency by decreasing response time to repeated requests, and they limit wide area bandwidth usage by keeping traffic within the local area network.
Category 5 (CAT 5) The designation for 100-ohm unshielded twisted-pair (UTP) cables and associated connecting hardware whose characteristics are specified for data transmission up to 100 Mb/s (part of the EIA/TIA 568A standard).
Category 5e (CAT 5e) An enhanced version of the CAT 5 cable standard that adds specifications for far-end cross talk (part of the EIA/TIA 568A standard).
Category 6 (CAT 6) A cable standard for Gigabit Ethernet and other interconnections that is backward compatible with Category 5, CAT 5e, and CAT 3 cable (part of the EIA/TIA 568A standard). CAT 6 features more stringent specifications for cross talk and system noise.
central processing unit (CPU) The part of a computer system or control system that reads and executes commands.
classful (networking) Under IPv4, a classful network is a network that includes every host address in a full class network range. The size of a classful network is determined by its default netmask. A classful network can accommodate either 16.7 million devices (class A), 65,536 devices (class B), or 256 devices (class C).
classless interdomain routing (CIDR) A method of IP addressing that allows variable-length subnet masks. As opposed to the classful system, under CIDR, a network of any size can be issued on an as-needed basis.
client A device, computer, or workstation, typically with limited processing power, that depends on a server to perform certain functions.
CobraNet A combination of hardware, control software, and data transportation protocol technologies for sending real-time audio and control, but not video, over Ethernet. CobraNet is a Data Link Layer technology and can’t be routed outside a LAN. See also EtherSound.
codec An acronym for coder/decoder. An electronic device that converts analog signals, such as video and audio signals, into digital form and compresses them to conserve bandwidth on a transmission path.
collision domain A set of devices on a LAN whose packets may collide with one another if they send data at the same time.
common carrier topology A wide area network (WAN) topology wherein each LAN site runs a spoke to an Internet service provider (ISP) backbone.
content delivery network (CDN) A distributed network of caching servers that can provide hosted unicast distribution of media for an organization. They are most often utilized by organizations whose content is in high demand.
Dante A proprietary digital audio Network Layer protocol designed by Audinate. Dante sends audio information as Internet Protocol (IP) packets. It is fully routable over IP networks using standard Ethernet switches, routers, and other components. Dante traffic requires no separate infrastructure; it can coexist with other data traffic. Dante controller software manages data prioritization and audio routes.
device-management system A network server that manages a particular type of device or devices by collecting status information and alarms.
dial plan A set of configurations that instructs a gatekeeper or other call-processing agent on how to route calls.
differentiated service (DiffServ) A quality of service (QoS) strategy whereby data from specific applications or protocols are assigned a class of service. Data traffic assigned a high priority is given preferential treatment at the router, but delivery is not guaranteed.
domain name system (DNS) A hierarchical, distributed database that maps names to data such as IP addresses. A DNS server keeps track of all the equipment on the network and matches the equipment names so they can easily be located on the network or integrated into control and monitoring systems.
Dynamic Host Configuration Protocol (DHCP) An IP addressing scheme that allows network administrators to automate address assignment. When a device connects to the network, and the device has the “obtain IP address automatically” option activated, the DHCP service or server will take the MAC address of the device and assign an IP address to the MAC address that is unique within the domain address space supported by the DHCP service. The pool of available IP addresses is based on the subnet size and the number of addresses that have been allocated already. Addresses are leased for a preset amount of time. After the lease time has expired, the address may be assigned to another device. The network administrator sets the amount of the lease time. See also reserve DHCP.
E.164 The International Telecommunication Union (ITU)–recommended scheme for numbering public telecommunication systems. E.164 provides a universal dialing scheme. This is the numbering scheme that defines the format for telephone numbers.
electromagnetic interference (EMI) The improper operation of a circuit (noise) due to the effects of interference from electric and/or magnetic fields.
encryption The process of transferring data into an unreadable format for transmission or storage. Encrypted data must be decrypted by the data recipient.
Ethernet A LAN system used to transmit data at 10 MB/s, 100 MB/s, or 1 GB/s. Ethernet signals are transmitted serially, one bit at a time, over the shared signal channel to every attached station.
EtherSound A combination of hardware, control software, and data transportation protocol technologies for transporting real-time audio and control, but not video, via Ethernet. EtherSound is a Data Link Layer technology that can’t be routed outside a LAN. See also CobraNet.
firewall Any technology, hardware, or software that protects a network by preventing intrusion by unauthorized users and/or regulating traffic permitted to enter or exit the network. A firewall controls what traffic may pass through a router connecting one network to another. Firewalls control access across any network boundaries, including between an enterprise network and the Internet, or between LANs within an enterprise.
full-duplex A form of bidirectional data transmission in which multiple messages may travel on the same medium simultaneously.
fully qualified domain name (FQDN) A DNS name that specifies the exact location of an object in the DNS hierarchical database. The FQDN must contain at least three levels, including the top-level domain name, preceded by the organizational name, preceded by a service or host name. See also domain name system.
Group Management Protocol (GMP) A protocol that allows a host to inform its neighboring routers of its desire to start or stop receiving multicast transmissions. Without GMP, multicast traffic is broadcast to every client device on a network segment, impeding other network traffic and overtaxing device CPUs.
group of pictures (GoP) A group of successive pictures within a coded video stream. A coded video stream consists of successive GoPs. A GoP includes video frames, which represent the visible picture, as well as timing/sync and compression frames, such as I-frames, P-frames, and B-frames.
half-duplex A form of data transmission in which only one network node at a time sends data. Note that the International Telecommunication Union (ITU) uses this term to refer to simplex communications. See also simplex.
High-Bandwidth Digital Content Protection (HDCP) A form of digital rights management developed by Intel to control digital audio and video content as it travels across DVI or HDMI connections. It prevents transmission or interception of non-encrypted HD content. HDCP support is essential for the playback of protected HD content. Without the proper HDCP license, the material will not play. It is difficult but possible to distribute to multiple DVI or HDMI outputs; all the equipment used to distribute the material must be licensed. This is part of blanket negotiations between device manufacturers and film and media companies.
hub-and-spoke topology A wide area network (WAN) topology that locates shared network resources on a LAN in a central location, the hub. Smaller LANs, such as branch offices or remote workers, connect to the hub via a leased T1 line, virtual private network, or other secure, managed means.
Hypertext Transfer Protocol (HTTP) An Application Layer protocol used for website communication. HTTP is encapsulated in Transmission Control Protocol (TCP) for reliable two-way communication. Further encapsulation in Internet Protocol (IP) allows HTTP to pass through the Internet. The primary language of HTTP is Hypertext Markup Language (HTML).
ICANN Internet Corporation for Assigned Names and Numbers, a nonprofit organization chartered to oversee several Internet-related tasks. ICANN manages domain name system (DNS) policy, including the top-level domain space for the Internet.
ICMP echo request An administration utility used to test network connectivity and response time. An origin host sends the echo request to a device destination and waits for a response. IGMP echo request is also referred to as Ping.
IEEE The Institute of Electrical and Electronics Engineers.
Independent Group Management Protocol (IGMP) The IPv4 group management protocol. IGMPv1 allowed individual clients to subscribe to a multicast channel. IGMPv2 and IGMPv3 added the ability to unsubscribe from a multicast channel. See also Internet Protocol.
Internet Control Messaging Protocol (ICMP) A TCP/IP protocol defined in the IETF standard RFC 792. ICMP sends error messages and carries messages for network diagnostic programs. ICMP falls under the Internet Layer of the TCP/IP protocol stack and the Network Layer of the OSI model.
Internet Protocol (IP) A TCP/IP protocol defined in the IETF standard RFC 791. IP defines rules for addressing, packaging, fragmenting, and routing data sent across an IP network. IP falls under the Internet Layer of the TCP/IP protocol stack and the Network Layer of the OSI model.
latency The response time of a network, expressed as the amount of time in milliseconds between a data packet’s transmission from the source application and its presentation to the destination application.
layer (digital signage) The order in which the graphics will be displayed on the screen. Layers may be placed in front of or behind one another. See also zone.
local area network (LAN) A computer network limited to a single, openly routable location, usually the same building or floor of a building. A LAN typically connects devices within a small geographical area. LANs are generally owned and/or operated by the end user.
MAC address The actual hardware address, or number, of an NIC device. Each device has a globally unique media access control (MAC) address to identify its connection on the network.
management information base (MIB) A document that defines all the objects and traps that a particular device or subsystem offers to a Simple Network Management Protocol (SNMP) manager/collector. MIB files are text files, formatted according to the SNMP standard, that define a data interface between managers and devices or subsystems. See also Simple Network Management Protocol.
manager of managers (MoM) A network management system that can manage both devices and device-management systems via a unified user interface that can be accessed directly or through a web interface, enabling use from remote locations. A manager of managers can also be configured to send alert messages to key personnel either through email, SMS, SNMP traps, or other notification protocols.
maximum transmission unit (MTU) The size in bytes of the largest frame that can pass over a Data Link Layer connection. Any header information must be included within the MTU.
meshed topology A network topology in which every node or network is connected to every other node or network for the purpose of relaying data.
Multicast Listener Discovery (MLD) The IPv6 group management protocol. Multicast is natively supported by IPv6; any IPv6 router will support MLD. MLDv1 performs roughly the same functions as IGMPv2, and MLDv2 supports roughly the same functions as IGMPv3.
multicast streaming A one-to-many transmission: one server sends out a single stream, which can then be accessed by multiple clients. Class D IP addresses are set aside for multicast transmissions. In multicast streaming a server sends the stream to a designated class D IP address, called the host address; clients subscribe to the host address; and routers send the stream to all clients subscribing to the host address. Multicast streams require UDP transport. They can only be sent over LANs or private networks; they cannot be sent over the open Internet. See also Universal Datagram Protocol.
Multiprotocol Label Switching (MPLS) A networking protocol that allows any combination of Data Link Layer protocols to be transported over any type of Network Layer. MPLS routes data by examining each packet’s MPLS label without examining packet contents. Implementing MPLS improves interoperability and routing speed.
network (computing) Two or more interconnected nodes that can share meaningful data.
network address translation (NAT) Any method of altering IP address information in IP packet headers as the packet traverses a routing device. NAT is typically implemented as part of a firewall strategy. The most common form of NAT is port address translation (PAT). See also port address translation.
network bridge A means for connecting two different types of networks together. A network bridge translates one network protocol to another protocol. An example of a bridge is a computer modem. A cable modem converts, or bridges, the Ethernet protocol to a cable TV protocol.
network interface card (NIC) An interface that allows you to connect a device to a network. Many NICs are now integrated into the device’s main circuitry.
network security Security that controls access to a LAN at the logical network boundaries. Network security is generally accomplished using multiple technologies.
network segment Any single section of a network that is physically separated from the rest of the network by a networking device, such as a switch, router, or hub. A segment may contain one or more hosts.
Nyquist-Shannon sampling theorem A theorem that states that an analog signal can be reconstructed if it is encoded using a sampling rate that is greater than twice the highest frequency sampled. For example, since the range of human hearing extends to 20 kHz, the sampling rate for digital audio should be greater than 40 kHz.
Open Systems Interconnection (OSI) model A reference model developed by the ISO (International Organization for Standardization) in 1984 as a conceptual framework of standards for communication in the network across different equipment and applications by different vendors. Network communication protocols fall into seven categories, or “layers.”
packet filtering A firewall technique that uses rules to determine whether a data packet will be allowed to pass through a firewall. Rules are configured by the network administrator, and implemented based on the protocol header of each packet.
packet switching A method of data transmission in which data is divided into small, individual units (i.e., packets) before it is transmitted.
polling A request to a subsystem or a device to send back a specified set of information.
port (IP networking) In a TCP/IP network, a port is a 16-bit number included in the TCP or UDP Transport Layer header. The port number typically indicates the Application Layer protocol that generated a data packet. A port may also be called by its associated service (e.g., port 80 may be called HTTP, or port 23 may be called telnet).
port address translation (PAT) A method of network address translation (NAT) whereby devices with private, unregistered IP addresses can access the Internet through a device with a registered IP address. Unregistered clients send datagrams to a NAT server with a globally routable address (typically a firewall). The NAT server forwards the data to its destination and relays responses back to the original client. PAT is also known as one-to-many NAT, network and port translation (NAPT), or IP masquerading. See also network address translation.
program report A document that describes a client’s specific needs, system purpose, and functionality, and the designer’s best estimate of probable cost, in a nontechnical format for review and approval by the owner. Also known as an AV narrative, discovery phase report, return brief, or concept design report.
protocol-independent multicast (PIM) Allows multicast routing over LANs, WANs, or even the open Internet. Rather than routing information on their own, PIM protocols use the routing information supplied by whatever routing protocol the network is already using: hence, protocol-independent.
Q-Sys A proprietary networked audio transport protocol that operates at the Network Layer. It packages audio data inside IP packets so that they can be routed from one LAN to another.
quality of service (QoS) A term used to refer to any method of managing data traffic to preserve system usefulness and provide the best possible user experience. Typically, QoS refers to some combination of bandwidth allocation and data prioritization.
radio frequency interference (RFI) Radiated electromagnetic energy that interferes with or disturbs an electrical circuit.
Real-Time Control Protocol (RTCP) A Session Layer protocol used in conjunction with Real-Time Transport Protocol (RTP) to monitor quality of service for streaming data. RTCP periodically reports on packet loss, latency, and other delivery statistics. See also Real-Time Transport Protocol.
Real-Time Transport Protocol (RTP) A Transport Layer protocol used in conjunction with the Universal Datagram Protocol (UDP) to provide additional robustness for streaming applications. RTP packets include sequence, timing, and source information in addition to the data payload. See also Universal Datagram Protocol.
reflecting server A server that takes in a unicast stream and broadcasts a multicast stream. Often used for live data streams.
reserve DHCP A hybrid approach to IP addressing. Using reserve DHCP, a block of statically configured addresses can be set aside for devices whose IP addresses must always remain the same. The remaining addresses in the subnet may be assigned dynamically. The total pool of dynamic addresses is reduced by the number of reserved addresses. See also Dynamic Host Configuration Protocol.
Resource Reservation Protocol (RSVP) A Transport Layer protocol used to reserve network resources for a specific application. The reservation is initiated by the host receiving the data. The reservation must be periodically renewed by the host in order to be maintained. RSVP is used in combination with differentiated service. See also differentiated service.
risk The potential for a problem. You have a risk when there is a probability that a threat will exploit a vulnerability in your system or project.
root-cause analysis The ability to isolate and identify a problem and determine the cause of the problem using all pertinent available data.
router A device that works on the OSI Layer above the Network and Transport Layers. A router knows the IP address of sent packets, and it can send them to specific locations on the network. The IT manager can use a router to change how the network works and allows for redundancy in the network.
sampling rate Describes the number of samples taken per unit of time (typically seconds) when converting a continuous (analog) signal to a discrete signal (typically a digital signal). The sample is described by its bit depth.
server A powerful computer, typically with large amounts of storage, and more memory, computing capacity, and redundancy than a desktop computer.
service-level agreement (SLA) The documentation of agreements between an IT service provider and a customer. An SLA describes the services to be provided, documents service-level targets, and specifies the roles and responsibilities of the service provider(s) and the customer(s). It may cover one service or many and may apply to one customer or many.
Session Description Protocol (SDP) A standardized method of representing information about media sent over the Internet. SDP information generally includes the session name, purpose, and active time(s), along with the media being transported and the contact information for session attendees. The information transmitted via SDP is utilized by other protocols to initiate and maintain a conferencing session.
Simple Network Management Protocol (SNMP) A set of IETF standards for network management, including an Application Layer protocol, a database schema, and a set of data objects. SNMP exposes management data in the form of variables on the managed systems, which describe the system configuration. These variables can then be queried, and sometimes set, by managing applications.
simplex As defined by the American National Standards Institute (ANSI), a form of data transmission whereby communication is available in only one direction. Data is sent from one node to others, but the other nodes cannot respond. The International Telecommunication Union (ITU) uses the term “half-duplex” to refer to this type of data transmission.
socket In a TCP/IP network, a socket is the combined port numbers and IP addresses of communicating end systems. A socket uniquely identifies a session of a given transport protocol.
source-specific multicast (SSM) A method for allowing clients to specify the sources from which they will accept content. This has the dual benefit of reducing demands on the network while also improving network security. Any device that has the host address can try to send traffic to the multicast group, but only content from the specified source will be forwarded to the group. This is in contrast to any-source multicast (ASM), which sends all multicast traffic sent to the host address to all subscribed clients.
streaming video/streaming audio Sequence of moving images or sounds sent in a continuous, compressed stream over the Internet and displayed by the viewer as they arrive. With streaming video or audio, a web user does not need to wait to download a large file before seeing the video or hearing the sound.
subnet A logical group of hosts within a LAN. A LAN may consist of a single subnet, or it may be divided into several subnets. Additional subnets may be created by modifying the subnet mask on the network devices and hosts.
subnet mask A binary number whose bits correspond to IP addresses on a network. Bits equal to 1 in a subnet mask indicate that the corresponding bits in the IP address identify the network. Bits equal to 0 in a subnet mask indicate that the corresponding bits in the IP address identify the host. IP addresses with the same network identifier bits as identified by the subnet mask are on the same subnet.
syslog A standard for sending real-time messages to a log collection server. Essentially, it is a data dump of a system log.
thin server A server that offers only one service. Typically, a thin server resides on a dedicated computer configured with only the functionality required to perform the service.
traffic policing A bandwidth management strategy that drops any excess packets beyond a preset maximum throughput. It may be applied to either inbound or outbound traffic.
traffic shaping A bandwidth management strategy that places any excess packets beyond the preset maximum throughput in a queue and schedules them for later transmission. This “smooths out” traffic to a predictable average throughput. Traffic shaping can only be applied to outbound traffic.
Transmission Control Protocol (TCP) A connection-oriented, reliable Transport Layer protocol. TCP transport uses two-way communication to provide guaranteed delivery of information to a remote host. It is connection oriented, meaning it creates and verifies a connection with the remote host before sending it any data. It is reliable because it tracks each packet and ensures that it arrives intact. TCP is the most common transport protocol for sending data across the Internet.
trap A mechanism within a subsystem or device programmed to generate an alert after an error or other specified event has taken place.
unicast streaming A one-to-one connection between the streaming server sending out the AV data, and client devices listening to the stream. Each client has a direct relationship with the server. The client sends a request to the server, and the server sends the client a stream in response. Since the server is sending out a separate stream for each client, each additional client takes up more bandwidth. Streaming media to three clients at 100 Kbps actually uses 300 Kbps of bandwidth. IP unicast streams may use either UDP or TCP transport, although with TCP transport, there will always be some buffering.
Universal Datagram Protocol (UDP) A connectionless, unacknowledged Transport Layer protocol. UDP begins sending data without attempting to verify the origin device’s connection to the destination device, and continues sending data packets without waiting for any acknowledgment of receipt.
virtual local area network (VLAN) A network that is created when network devices on separate LAN segments are joined together to form a logical group that can communicate via switching. Devices on a VLAN form a single, isolated broadcast domain.
virtual private network (VPN) A network that uses the Internet to create a tunnel between two or more LANs. VPNs are used to create virtual wide area networks and for remote monitoring, troubleshooting, and control. They are typically controlled and configured by the enterprise network administrator. Each host requires the proper software, access rights, and password to log in to the client network.
web service integration (WSI) A device-to-device communication method that treats every device or subsystem on a network as a “service.” Any other device or system on the same network can interact with the service through “Post” or “Get” messages through the XML protocol using open standards of message formatting.
wide area network (WAN) A network that spans large geographical distances, connecting several LANs via leased lines, packet switching, VPNs, or other means. LANs are connected to a WAN through a router.
wireless access point (WAP) A network device that allows wireless devices to connect to a wired network.
zone In digital signage, an area on a screen where separate content may be placed. A different playlist must be created for each zone. See also layer.