IT Terminology to Know and Understand
Jul 11, 2014 3:29 PM, By Kevin Gross
A wide part of the gulf between IT and AV professionals is in vocabulary. The following IT terminology is relevant to AV applications.
Excess buffering of packets in network equipment such that during times of congestion, queuing delay becomes extreme and the network may become unable for time-critical applications such as media networking.
Differentiated Services (DiffServ)
An architecture for providing QoS on IP networks. DiffServ uses the DSCP field to classify and manage traffic through the network.
Differentiated Services Code Point (DSCP)
A 6-bit field in the header of IP packets that is used to indicate the importance of the packet to the network. Network equipment inspects this field to determine how to prioritize it.
The process of forwarding packets to all other destinations on a network. Network equipment floods messages when the location of the addressed destination (either unicast or multicast) is unknown. Network equipment that does not support PIM or IGMP may flood all multicast traffic.
The total time taken for a packet to traverse a network or piece of network equipment. Forwarding delay includes queuing delay and any other latency introduced in the path from source to destination.
High availability (HA)
Network systems engineered for high reliability. These systems typically contain redundant components and connections and a means for automatically switching in the event of failures or other disruptions.
A standard network protocol for distributing accurate time information. IEEE 1588 is used by a number of media networking systems and for networked industrial and financial systems that also require very accurate timing.
Internet Group Management Protocol (IGMP)
A protocol used by hosts to inform the network of the multicast transmissions in which they are interested.
Internet Protocol (IP)
The network transport protocol used to address and carry all data through the Internet and networks connected to the Internet.
IP Television (IPTV)
A method and set of protocols used to carry television programming over IT networks. IPTV may be used to replace live closed-circuit TV but also is able to provide less time-critical video-on-demand services.
Network engineering is done in layers. The first layer, Layer 1 or the data-link layer, is the physical circuits, wires, and connectors. The primary technology associated with Layer 2 is Ethernet. At Layer 2, basic communications is possible. Higher layers introduce additional flexibility and capability.
Layer 3 is known as the networking layer. The primary technology associated with Layer 3 is the Internet Protocol (IP). Layer 3 allows the formation of networks of Layer 2 networks. Networking at Layer 3 is more scalable and flexible.
Local Area Network (LAN)
A network spanning covering a campus area or smaller. LANs are typically built and maintained by the organization using the network.
Packets directed from a source, duplicated in the network equipment and delivered simultaneously to multiple destinations. Compare with unicast.
Network Hops (Or Switch Hops)
A count of the number of pieces of network equipment, such as switches and routers, a packet must pass through in traveling from source to destination. Some definitions of network hop count include an additional hop out of the source to the first piece of network equipment. A direct connection between source and destination can be considered zero or one network hops depending on the exact definition used.
The time required to deliver data across a network. Latency typically varies packet to packet (see packet delay variation) so receivers must buffer to the maximum expected network latency to absorb the variations.
Packet Delay Variation (PDV or DV)
Network latency is a sum of fixed and variable sources. Fixed sources include the speed of light through cables and optical fibers and minimum data processing time in network equipment. Variable sources include buffering behind higher-priority traffic (see queuing delay), time spent in contention with lower- or higher-priority traffic and different network paths taken for different packets.
Intentional or unintentional failure of network equipment or connections to deliver all packets from source to destination. Packet loss can be caused by electrical corruption of data but is more often caused by congestion in the network. Packet loss is measured in percent units. In typical IT network applications, packet loss is recovered from through retransmission of the data slightly delaying any transaction in progress. In realtime media networking systems, there is not time for retransmission ,so packet loss produces a brief drop out of the media signal.
Protocol Independent Multicast (PIM)
A family of routing protocols used to help move multicast traffic through an IP network.
Quality of Service (QoS)
Network features and standards that allow identification and prioritization of network traffic. Properly configured QoS can be critical to allowing high-performance media networking to coexist with other network applications.
The time a packet spends waiting in network equipment for its turn to transmit to the destination or next network hop. Queuing delay is usually considered on a per network hop basis.
Real-time Transport Protocol (RTP)
A standardized packet format used in the transport of time-sensitive data, such as that used in media networking or VoIP over an IP network.
Session Description Protocol (SDP)
A file format for describing media connections between devices. SDP is carried by SIP and is used by VoIP and AES67 to describe the sample rate, bit resolution, clocking, and other attributes of media streams.
Session Initiation Protocol (SIP)
A connection management protocol used by VoIP and AES67 that allows devices to find one another, exchange SDP “offers,” and negotiate and establish a media connection.
A prioritization scheme used in QoS systems in which higher-priority packets are always transmitted prior to lower-priority packets. This assures maximum responsiveness for high-priority traffic at the potential risk locking out and rendering lower-priority systems unusable.
Transmission Control Protocol (TCP)
The transmission system that allows for reliable communications across the Internet. TCP handles issues of timeouts, retransmissions, and accounting to ensure that all data arrives despite any hiccups in the underlying network.
Packets directed from a single source to a single destination. Compare with multicast.
User Datagram Protocol (UDP)
A generic packet format for carrying data on IP networks. Because it does not interfere with the timing of delivery, UDP is more appropriate for transmission of realtime data than the more commonly used TCP. RTP packets are carried inside UDP packets.
Voice over IP (VoIP)
A method and set of protocols used to carry telephone calls over IT networks. VoIP is used on local area networks to replace business telephone systems. It is used on wide area networks and over the Internet as an alternative to the public switched telephone network.
Wide area network (WAN)
A network spanning a metropolitan area or larger. WANs are typically constructed using leased connections from a telecommunications company.