H.225
H.225, a key protocol in the H.323 VOIP architecture defined by ITU-T, is a standard to cover narrow-band visual telephone services defined in H.200/AV.120-Series Recommendations. It specifically deals with those situations where the transmission path includes one or more packet-based networks, each of which is configured and managed to provide a non-guaranteed QoS, which is not equivalent to that of N-ISDN, such that additional protection or recovery mechanisms beyond those mandated by Rec.
Standard Organization: ITU-T
Reference Document: H.225
H.225.0
H.225.0 is the specific document number for RAS, use of Q.931, and use of RTP under the H.323 VOIP architecture. It is also called as H.225.
Standard Organization: ITU-T
Reference Document: H.225.0
H.235
H.235 is the security recommendation for the H.3xx series systems. In particular, H.235 provides security procedures for H.323-, H.225.0-, H.245- and H.460-based systems. H.235 is applicable to both simple point-to-point and multipoint conferences for any terminals which utilize H.245 as a control protocol.
Standard Organization: ITU-T
Reference Document: H.235
H.245
H.245, a control signaling protocol in the H.323 multimedia communication architecture, is for the exchange of end-to-end H.245 messages between communicating H.323 endpoints/terminals. The H.245 control messages are carried over H.245 control channels. The H.245 control channel is the logical channel 0 and is permanently open, unlike the media channels. The messages carried include messages to exchange capabilities of terminals and to open and close logical channels.
Standard Organization: ITU-T
Reference Document: H.245
H.248
H.248, also known as Media Gateway Control protocol (Megaco), is for the control of elements in a physically decomposed multimedia gateway, enabling the separation of call control from media conversion. Megaco is a result of joint efforts of the IETF and the ITU-T Study Group 16. Therefore, the IETF defined Megaco is the same as ITU-T Recommendation H.248.
Standard Organization: ITU-T
Reference Document: H.248
H.261
H.261 is the video coding standard of the ITU. It was designed for data rates which are multiples of 64Kbit/s and is sometimes called p x 64Kbit/s (p is in the range 1-30). These data rates suit ISDN lines, for which this video codec was originally designed. H.261 transports a video stream using the real-time transport protocol, RTP, with any of the underlying protocols that carry RTP.
Standard Organization: ITU-T
Reference Document: H.261
H.263
The H.263, by the International Telecommunications Union (ITU), supports video compression (coding) for video-conferencing and video-telephony applications. H.263 was developed to stream video at bandwidths as low as 20K to 24K bit/sec and was based on the H.261 codec. As a general rule, H.263 requires half the bandwidth to achieve the same video quality as in the H.261. As a result, H.263 has largely replaced H.261. H.263 uses RTP to transport video streams.
Standard Organization: ITU-T
Reference Document: H.263
H.264
The H.264, also named Advanced Video Coding (AVC), is the MPEG-4 Part 10. H.264 is jointly developed by ITU and ISO. H.264 supports video compression (coding) for video-conferencing and video-telephony applications. The H.264 video codec has a very broad rang of applications that covers all forms of digital compressed video from, low bit-rate Internet streaming applications to HDTV broadcast and Digital Cinema applications with nearly lossless coding. H.264 is designed as a simple and straightforward video coding, with enhanced compression performance, and to provide a network-friendly video representation.
Standard Organization: ITU-T
Reference Document: H.264
H.323
H.323, a protocol suite defined by ITU-T, is for voice transmission over internet (Voice over IP or VOIP). In addition to voice applications, H.323 provides mechanisms for video communication and data collaboration, in combination with the ITU-T T.120 series standards. H.323 is one of the major VOIP standards, on a par with Megaco and SIP.
Standard Organization: ITU-T
Reference Document: H.323
H.450.2
H.450.2 is the call transfer supplementary service in the H.323 VOIP architecture.
Standard Organization: ITU-T
Reference Document: H.450.2
H.450.3
H.450.3 is the call diversion supplementary service in the H.323 VOIP architecture.
Standard Organization: ITU-T
Reference Document: H.450.3
HDLC: High Level Data Link Control
The High Level Data Link Control (HDLC) protocol, an ISO data link layer protocol based on the IBM SDLC, ensures that data passed up to the next layer has been received exactly as transmitted (i.e. error free, without loss and in the correct order). Another important function of HDLC is flow control, which ensures that data is transmitted only as fast as the receiver can receive it. There are two distinct HDLC implementations: HDLC NRM (also known as SDLC) and HDLC Link Access Procedure Balanced (LAPB). The later is the more popular implementation. HDLC is part of the X.25 stack.
Standard Organization: IBM
HDSL: High Data Bit Rate DSL
High Data Bit Rate Digital Subscriber Line (HDSL), also known as High Speed DSL or High data-rate DSL, provides equal bandwidth for both downloads and uploads. HDSL is one of oldest DSL technologies. HDSL can carry as much on a single wire of twisted-pair cable as can be carried on a T1 line (up to 1.544 Mbps) in North America or an E1 line (up to 2.048 Mbps) in Europe over a somewhat longer range and is considered an alternative to a T1 or E1 connection.
Standard Organization: ETSI/ITU-T
HDSL2: 2nd generation HDSL
HDSL2, the 2nd generation HDSL (High Data Bit Rate Digital Subscriber Line), is a variant of HDSL which delivers 1.5 Mbps service each way, supporting voice, data, and video using either ATM (asynchronous transfer mode), private-line service or frame relay over a single copper pair. This ATIS standard (T1.418) for this symmetric service gives a fixed 1.5 Mbps rate both up and downstream. HDSL2 does not provide standard voice telephone service on the same wire pair. HSDL2 differs from HDSL in that HDSL2 uses one pair of wires to convey 1.5 Mbps whereas ANSI HDSL uses two wire pairs.
Standard Organization: ATIS
HDSL4: 4th generation HDSL
HDSL4, the 4th generation HDSL (High Data Bit Rate Digital Subscriber Line), is an enhanced version of HDSL2 which achieves about 30% greater distance than HDSL or HDSL2 by using two pairs of wire (thus, 4 conductors), whereas HDSL2 uses one pair of wires.
Standard Organization: ATIS
HELLO
HELLO protocol is an early version of routing protocol for TCP/IP network using a distance-vector algorithm. HELLO does not use hop count as a metric. Instead, it attempts to select the best route by assessing network delays and choosing the path with the shortest delay. HELLO protocols also contain routing information in the form of a set of destinations that the sending router is able to reach and a metric for each. The HELLO protocol was developed in the early 1980s and documented in RFC 891. The name “HELLO†is capitalized and it should not be confused with the hello process used by a few protocols.
Standard Organization: IETF
Reference Document: RFC 891
HPR-APPN: High Performance Routing for Advanced Peer-to-Peer Network
High Performance Routing for Advanced Peer-to-Peer Network (HPR-APPN), an IBM SNA component for dynamic routing across arbitrary network topologies, is an extension of the SNA APPN network. Two new components (Rapid Transport Protocol (RTP) and Automatic Network Routing (ANR)) in HPR-APPN provides some key advancements such as: Non-disruptive path switching; Better utilization of high-speed communication paths; An advanced congestion control methodology.
Standard Organization: IBM
HSRP: Hot Standby Router Protocol
Hot Standby Router Protocol (HSRP) is designed to support non-disruptive failover of IP traffic in certain circumstances and to allow hosts to appear to use a single router and to maintain connectivity even if the actual first hop router they are using fails. In other words, the protocol protects against the failure of the first hop router when the source host cannot learn the IP address of the first hop router dynamically. Multiple routers participate in this protocol and, in concert, create the illusion of a single virtual router.
Standard Organization: IETF and Cisco
Reference Document: RFC 2281
HTML: HyperText Markup Language
HyperText Markup Language (HTML) is a markup language designed for the creation of web pages with hypertext and other information to be displayed in a web browser. HTML is used to structure information denoting certain text as headings, paragraphs, lists and so on and can be used to describe, to some degree, the appearance and semantics of a document.
Standard Organization: IETF
Reference Document: RFC 1866
HTTP: Hypertext Transfer Protocol
The Hypertext Transfer Protocol (HTTP) is an application level protocol with the lightness and speed necessary for distributed, collaborative, hypermedia information systems. HTTP has been in use by the World-Wide Web global information initiative since 1990.
Standard Organization: IETF
Reference Document: RFC 2616
HTTPS: Hypertext Transfer Protocol Secure
Hypertext Transfer Protocol Secure (HTTPS) refers to the HTTP running on top of TLS or SSL for secured transactions. HTTPS is not to be confused with S-HTTP, a security-enhanced version of HTTP developed and proposed as a standard by IETF.
HVPLS: Hierarchical Virtual Private LAN service
Hierarchical Virtual Private LAN Service (HVPLS) is introduced to improve the scalability of VPLS, which is a layer 2 Virtual Private Network (VPN) services over Ethernet networks. The HVPLS standards allow the creation of hierarchies with a hub-and-spoke arrangement. The full mesh of tunnels is maintained between the hub sites (designated as PEs). The CE equipment is connected to an MTU-s router, which is connected to a PE router, thus providing the hierarchy.