AT&T DS1/DMi/ISDN-PRI manual CDMs, CEMs, System, DS1 or DMI

SAMPLE INSTALLATION AND MAINTENANCE PROBLEMS B-5

the REC or NEC to ensure compatibility between these devices and the associated communications systems.

CDMs

The CDM is used to drop or insert one or more DS1/DMI channels from the transmission facility. These channels may be used for external data or voice applications, depending on the channel units that are used in the CDM. Channel 1, for example, can be selected for drop or insert by the CDM. Channels 2 through 24 would then be left for use by the switch endpoints. Figure B-5, System 75 or System 85 with CDMs, shows a CDM configuration.

				TRANSMISSION	FACILITY
	SYSTEM	75						SYSTEM	75
	OR							OR
	SYSTEM 85			CDM		CDM		SYSTEM	85
	DS1 OR DMI							DS1 OR DMI
EXTERNAL DEDICATED			CHANNELS
						EXTERNAL	DEDICATED CHANNELS
	(FOR	DATA OR VOICE)				(FOR	DATA OR VOICE)

Figure B-5.System 75 or System 85 with CDMs

The effects of translations to the endpoint switches is in accommodating the channels used by the CDM. The recommended method is to translate those channels, which are drop/inserted, into an unused (dummy) trunk group.

CEMs

The CEM takes the output of two DS1/DMIs and compresses them for transmission on one facility. Compression of two DS1 facilities can be as simple as translating 48 voice-grade trunks with robbed- bit signaling or as complex as the mixing of compressed voice-grade trunks with uncompressed alternate voice/data (AVD) trunks and using bundling signaling between the CEMs. Figure B-6,Translation Effects on the CEM, shows a simple CEM configuration using two DS1 facilities from each switch. The DS1/DMIs on each switch must be translated the same, and compatible options must be administered for the CEMs (for example, the CEMs must match one another).