The GR-303 DS1 Line Mapping Table. The DS1 Line Mapping Table describes attributes for DS1 Line Termination and the mapping between the Interface Group and DS1 standard MIB (rfc2495). The maximum number of entries is determined by the maximum number of DS1 lines for the Interface Group, which is 28. Each Interface Group is associated with a ds1LineMapping Table indexed by (IG name, line group ID, ds1 channel number), where line group ID is either a physical T1 line group ID (eg, Dibrizzi) or a channelized DS3. DS1 channel number is one of 28 DS1s associated with a channelized DS3, that is being provisioned to the Interface Group. If line group ID is a T1, the associated DS1 channel number is 1. GR-303-CORE R12-508 [1377] The RDT is limited to a maximum of 28 DS1s per IG and each IG can support up to a maximum of 2048 two-wire terminations toward the customer's premises. Once a primary or secondary DS1 is provisioned for an IG it cannot be modified or deleted.