H¶

H.248¶

Gateway Control Protocol (Megaco). The ITU-T and IETF protocol with which a media gateway controller or softswitch controls media gateways, which convert between telephone circuits and IP media streams. It does the same job as MGCP.

H.248

H.248.

H.323¶

An ITU-T family of protocols for voice and video calls over packet networks, covering signalling, media and bandwidth control. It was the main VoIP standard before SIP replaced it.

H.323

H.323.

Half Duplex¶

Communication in which both ends can send, but only one at a time, like a push-to-talk radio.

Happy Path¶

See Nominal Path.

Hash Function¶

A function that maps data of any size to a fixed-size value. A cryptographic hash, such as SHA-256, is also one-way and collision-resistant. That makes it useful for integrity checks, digital signatures and storing passwords.

Hash Function

Hash Function.

HDF¶

Handover Distribution Frame. In UK local loop unbundling, the frame in the exchange where the copper pairs are handed over from the main distribution frame to another operator’s equipment.

HDF

HDF.

HDLC¶

High-Level Data Link Control. An ISO bit-oriented, synchronous data link protocol. Many other link protocols, including PPP framing, LAPB in X.25 and LAPD in ISDN, are based on it.

HDLC

HDLC.

HDSL¶

High-bit-rate Digital Subscriber Line. A symmetrical DSL that carries a 2 Mbit/s (E1) or 1.5 Mbit/s (T1) circuit over two or three copper pairs. It was used to deliver leased lines without new cable.

Heartbeat Retrospective¶

A retrospective held at a regular interval, such as the end of each iteration, in which the team reflects on recent events and agrees improvements.

HiFi Prototype¶

See High Fidelity Prototype.

High Fidelity Prototype¶

A prototype that looks and behaves much like the finished system, usually built with real development tools.

High Level Design¶

HLD. The design level between the architecture and the low-level design. It defines the components of the solution, their interfaces and how they interact, without going into how each is built.

See also: Low Level Design, Architecture.

HLD¶

See High Level Design.

HLR¶

Home Location Register. The central database of a GSM or UMTS network, holding each subscriber’s details: their IMSI, phone numbers, services and current location. In LTE and IMS, the HSS replaced it.

Hotfix¶

A small, urgent change, sometimes called a patch, that fixes a bug in released software outside the normal release cycle.

How Requirement¶

Usually a synonym for Non-functional Requirement; sometimes used for design constraints.

How Well Requirement¶

See Non-functional Requirement.

HSRP¶

Hot Standby Router Protocol. Cisco’s protocol for a fault-tolerant default gateway. Two or more routers share a virtual IP address; one is active and the others take over if it fails. VRRP is the open-standard equivalent.

HSRP

HSRP.

HSS¶

Home Subscriber Server. The master subscriber database for IMS and LTE, holding user profiles and authentication data and tracking where users are registered. It takes over the jobs of the HLR and the authentication centre.

HTTP¶

Hypertext Transfer Protocol. The request-response protocol of the web. A client asks for a resource by URL with a method such as GET or POST, and the server returns a status and content. HTTP/2 and HTTP/3 keep the same model with more efficient transports.

HTTPS¶

HTTP over TLS. It encrypts the traffic and lets the client check the server’s identity through its certificate, protecting against eavesdropping and tampering.

Hub¶

A network device that repeats every frame it receives to all its other ports, so all connected devices share one collision domain. It works at layer 1, and switches have replaced it.

Hub

Hub.

Human factors¶

The study of how people behave, physically and mentally, with products, systems and environments, and how to design for them.

Hungarian notation¶

A naming convention in which a prefix on an identifier shows its kind or type, such as cApples for a count or szName for a zero-terminated string. Most modern style guides advise against encoding the type in this way.