Principles of Operation4-233610-A2-GB41-70 July 1999Line and Channel SpeedsThe MCMP capability operates only on a 56 kbps DDSmultipoint circuit. Speeds of any channel can be set to thesynchronous speed of 1.2, 2.4, 4.8, 7.2, 9.6, 12, 14.4, 16.8,19.2, 38.4, or 48 kbps full-duplex.A channel can be used either synchronously orasynchronously. Possible asynchronous rates include allrates available to synchronous operation ( 1.2 through48 kbps). Asynchronous rates of 150, 300, and 1200 bpsrequire the allocation of 1200 bps. The asynchronousspeed of 600 and 1800 bps requires the allocation of2400 bps.The sum of the allocated channel speeds (aggregate bitrate) must not exceed 48 kbps.MCMP Overhead CompositionOf the 56 kbps capacity (bandwidth) available toMCMP operation, 48 kbps is allocated to user-transmitted data and 8 kbps is overhead. The MCMPoverhead consists of a management channel to control theproprietary MCMP framing process and a nondisruptivein-band secondary channel.Management ChannelDuring MCMP operation, the control DSU is inconstant communication with each tributary DSU via themanagement channel. Since the management channel isembedded in the MCMP overhead, it transmitsinformation without disrupting user-transmitted data.When the MCMP capability is activated for the firsttime, the control DSU with MCMP determines theroundtrip delay parameters that are critical to MCMPoperation. MCMP sends these parameters to thetributaries in the network to synchronize theirtransmissions. Refer to MCMP Operation in this chapter.After initialization, the control DSU continues tomonitor these delay parameters. Upon detecting changes,the control DSU sends corrected roundtrip delayparameters to the tributaries.The management channel is also used for framing,where selection of an underspeed channel is not required.This framing technique differs markedly from the in-bandframing scheme used by the TDM capability, whereframing bits may be implemented by reducing the datarate of one of the channels.In-Band Secondary Channel TransportThe MCMP capability supports in-band secondarychannel transport between the control and tributary DSUsthat can transport diagnostics without disruptinguser-transmitted data.Some tests transmitted over the in-band secondarychannel transport may result in primary channeldisruptions when the test is executed ( i.e., a Device Testto a tributary DSU). There is no routine health and statuspolling unless configured for nondisruptive diagnostics.Number of TributariesThe MCMP capability can support up to40 addressable tributary devices (40 DSUs or 20 DSUswith DBMs).
