
Ethernet Media
4-26 Connector Types
Figure 4-18. RJ21 Pinout Mapping for 10BASE-T
Punchdown Blocks
While not strictly a connector type, the punchdown block is a fairly common
component in many Ethernet 10BASE-T installations that use 25-pair cable. The
punchdowns are bayonet pins to which UTP wire strands are connected. The
bayonet pins are arranged in 50 rows of four columns each. The pins that make up
the punchdown block are identified by the row and column they are members of.
Each of the four columns is lettered A, B, C, or D, from leftmost to rightmost. The
rows are numbered from top to bottom, one to 50. Thus, the upper left hand pin is
identified as A1, while the lower right hand pin is identified as D50.
49
27
26
2
1
+-
TransmitTransmit
ReceiveReceive
50
48
47
46
45
44
43
42
41
40
39
38
37
36
35
34
33
32
31
30
29
28
27
26
25
24
23
22
21
20
19
18
17
16
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
1845n18
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