RJ21 Amphenol to BIX

RJ21 connectors are typically used for Telephone/PBX applications and support up to 25 Tip/Ring twisted pairs.
Eg: a Media Gateway will have a number of RJ21 Amphenol connectors, for connecting card slot ports to the MDF.

Male connector (rear) shown.
RJ21 Male: Pair 1 is at cable end.
RJ21 Female: Pair 25 is at cable end.

The 25 Tip/Ring twisted pairs are punched down to BIX in the following order (25-pair color code):

RJ21	26	1	27	2	28	3	29	4	30	5	31	6	32	7	33	8	34	9	35	10	36	11	37	12	38	13	39	14	40	15	41	16	42	17	43	18	44	19	45	20	46	21	47	22	48	23	49	24	50	25
BIX	1	2	3	4	5	6	7	8	9	10	11	12	13	14	15	16	17	18	19	20	21	22	23	24	25	26	27	28	29	30	31	32	33	34	35	36	37	38	39	40	41	42	43	44	45	46	47	48	49	50
Pair	pr1		pr2		pr3		pr4		pr5		pr6		pr7		pr8		pr9		pr10		pr12		pr12		pr13		pr14		pr15		pr16		pr17		pr18		pr19		pr20		pr21		pr22		pr23		pr24		pr25

The tip color is always placed first, and pairs should never be split. Eg:

White/Blue represents pair 1: eg, White with a Blue band is the tip, Blue with a White band is the ring.
Violet/Slate represents pair 25: eg, Violet with a Slate band is the tip, Slate with a Violet band is the ring.

See also: 25 Pair Color Code, and BIX Cable Termination.