glossary
Networking Glossary
Alphabetized field terms for DNS, VoIP, email, subnetting, path testing, and packet capture work. Small definitions, less fog.
A
A Record
A DNS record that maps a hostname to an IPv4 address.
AAAA Record
A DNS record that maps a hostname to an IPv6 address.
ACK
A SIP request that confirms a final response, commonly the 200 OK that answers a call.
ASN
Autonomous System Number. It identifies a network or group of routes operated under one routing policy.
B
Blacklist
A reputation list that may flag an IP address or domain for spam, abuse, or suspicious sending behavior.
Broadcast Address
The last IPv4 address in a subnet, traditionally used to reach all hosts on that subnet.
C
CAA Record
Certification Authority Authorization record. It says which certificate authorities may issue certificates for a domain.
CIDR
Classless Inter-Domain Routing. CIDR notation writes an IP and prefix length, such as 192.168.1.10/24.
CNAME
Canonical Name record. It makes one DNS name an alias of another DNS name.
Codec
A media format used to encode and decode audio or video, such as G.711, G.729, or Opus.
D
DKIM
DomainKeys Identified Mail. DKIM signs email so receivers can verify that the message was authorized by a domain.
DMARC
Domain-based Message Authentication, Reporting, and Conformance. DMARC tells receivers how to handle mail when SPF or DKIM alignment fails.
DNS Propagation
The process of DNS changes becoming visible across recursive resolvers as cached answers expire.
DNSBL
DNS-based blacklist. A DNS-style lookup used by mail systems to check whether a sender appears on a reputation list.
DSCP
Differentiated Services Code Point. A packet marking used by QoS policies to classify traffic such as voice or video.
F
FQDN
Fully Qualified Domain Name. The complete DNS name for a host, such as pbx.example.com.
I
J
Jitter
Variation in packet arrival timing. High jitter can make VoIP audio sound uneven or robotic.
M
N
P
Packet Loss
Packets that do not arrive at the destination. In VoIP this can cause clipping, silence, or choppy audio.
PCAP
A packet capture file that stores network packets for analysis in tools such as Wireshark or TraceRoo PCAP tools.
PTR Record
Pointer record. It maps an IP address back to a hostname for reverse DNS.
Q
QoS
Quality of Service. Network policy used to classify, prioritize, or shape traffic.
R
S
SDP
Session Description Protocol. In SIP calls, SDP describes media addresses, ports, codecs, and related capabilities.
SIP
Session Initiation Protocol. SIP sets up, modifies, and tears down VoIP calls.
SPF
Sender Policy Framework. SPF lists which mail servers are allowed to send email for a domain.
SRTP
Secure RTP. SRTP encrypts and authenticates RTP media streams.
SRV Record
Service record. It advertises a service host, port, priority, and weight for protocols such as SIP.
STUN
Session Traversal Utilities for NAT. WebRTC uses STUN to discover a public-facing address and port for media connectivity.
Subnet Mask
A value that separates the network and host portions of an IP address.
T
T.30
The fax session protocol that negotiates capabilities, page transfer, confirmation, and call control between fax endpoints.
T.38
A real-time fax-over-IP protocol that relays fax data over IP networks, commonly using UDPTL instead of RTP audio passthrough.
TCP
Transmission Control Protocol. A connection-oriented transport protocol used by web, mail, and many application services.
TIFF
Tagged Image File Format. Fax systems often store received pages as TIFF files with resolution, compression, width, and height metadata.
TLS
Transport Layer Security. TLS encrypts connections such as HTTPS, SIP TLS, and secure mail submission.
TTL
Time To Live. In DNS, TTL controls how long resolvers can cache an answer.
TURN
Traversal Using Relays around NAT. TURN relays WebRTC media when direct peer connectivity cannot be established.