September 07, 2005
H.323 protocols and their applications - Part 3
H.261: It is basically a video coding standard that is used for transporting via the RTP with any of the protocols that support RTP. H.261 supports CIF and QCIF video frames that have luma resolutions of 176 x 144 and 88 x 72, respectively. An H.261 header consists of SBIT, EBIT, I, V, GOBN, MBAP, QUANT, HMVD, VMVD.
H.263: It defines the payload format for the H.263 bitstream in RTP. The RTP packet can use any of the three modes for the payload header of H.263. Fragmentation at the Group of Block (GOB) boundaries is supported by mode A, which is the shortest payload header. Fragmentation at the Macroblock (MB) boundaries is supported by the long payload headers, i.e. modes B and C. The H.263 payload header, whose size depends upon the modes, succeeds the RTP fixed header and the H.263 header is followed by the H.263 compressed bitstream. Payload header size is 4, 8, and 12 bytes for modes A, B, and C, respectively.
RAS: It stands for Registration, Admission and Status (RAS). It is a protocol that is used to carry out signaling functions such as registration, admission, disengagement actions, etc between the endpoints and the gatekeeper. A Request in Progress (RIP) message is used by an endpoint or a gatekeeper that is unable to respond to a request inside the timeout limits. This allows the receiving endpoint/gatekeeper to reset its timeout timer. Timeouts and retrys are particularly significant as the reliability of the RAS message channel is not very high. Important RAS messages include RegistrationRequest (RRQ), AdmissionRequest (ARQ), BandwidthRequest (BRQ), DisengageRequest (DRQ), InfoRequest (IR), etc.
RTCP: It stands for RTP control protocol and it monitors the QoS of an IPv6 RTP connection. It depends upon the multiplexing of data and the control packets. It works together with RTP in the delivery of multimedia data and provides an out-of-band control information. The RTCP header consists of the Version, P (Padding), Reception report Count, Length, etc.
RTP: It is a standardized packet format for the transmission of audio and video over multicast and unicast network services. RTP helps in payload-type identification, delivery monitoring, time stamping, and sequence numbering. The data transfer over RTP is facilitated by RTCP that enables the overseeing of data in such a manner so as to facilitate the same over multicast networks. RTP does not cover address resource reservation. RTP and RTCP function independently of the transport and network layers.
T.38: It is an Internet Fax Protocol. It deals with the transfer of fax documents in real-time over an IP network by using either TCP or UDP as per the service environment. The TCP/UDP payload carries the T.38 data. T.38 can manage fax as well as voice data over a single network. T.38 allows the use of H.323 in the same way as it is used in VoIP.
T.120: It is a family of protocols that cover the services for multilayer protocols, MCU, etc. It promotes greater operating powers that are not possible with H.231 and H.243. The Multipoint Communication Service Protocol (MCS) is covered under T.125. The procedures included in this protocol include the exchange of MCS data between two parallel MCS providers, exchange of MCS primitives between MCS providers and users. A single MAP connection or one or more transport connection make up an MCS connection.
--
Did you enjoy this post?
« Skype is to enter into a VoIP Joint Venture in China | Main | VoIP protocols - Part 1 »
