1-20
z
Before using an optical fiber to connect a network device, verify that the optical fiber connector
matches the optical module.
z
Before connecting an optical fiber, make sure the received optical power at the local end does not
exceed the upper threshold of the receiving optical power of the optical module. Otherwise, the
optical module may be damaged.
Cable connecting electrical Ethernet interfaces
Usually, you can use a Category-5 twisted pair cable to connect an electrical Ethernet interface. Figure
1-12 shows an Ethernet cable.
Figure 1-12
Ethernet cable
Ethernet cables fall into two categories:
z
Standard cable: Also known as straight-through cable. At both ends of a standard cable, wires are
crimped in the RJ-45 connectors in the same sequence. A straight-through cable is used for
connecting a terminal (for example, a PC or router) to a hub or LAN switch. The cables delivered
with the firewall are straight-through cables.
z
Crossover cable: At both ends of a crossover cable, wires are crimped in the RJ-45 connectors in
different sequences. A crossover cable is used for connecting two terminals (for example, PC or
router). You can make crossover cables by yourself as needed.
Table 1-23
Straight-through cable connector pinouts
RJ-45
Signal
Category-5
twisted pair
Signal direction
RJ-45 pin
1 TX+
White
(Orange)
Æ
1
2 TX–
Orange
Æ
2
3 RX+
White
(Green)
Å
3
4 — Blue
— 4
5 — White
(Blue)
— 5
6 RX–
Green
Å
6
7 — White
(Brown)
— 7
8 — Brown
— 8