Table 1-1 shows the types of H3C low-end series Ethernet switches pluggable modules.
Table 1-1 Types of pluggable modules
Pluggable module type | Description | Connector type |
SFP (small form-factor pluggable) | Gigabit SFP optical module | SFP pluggable optical transceiver module | LC |
100 Mbps SFP optical module |
Gigabit BIDI (bi-direction) optical module | BIDI optical transceiver module |
100 Mbps BIDI optical module |
Gigabit CWDM (coarse wavelength division multiplexing) optical module | Gigabit CWDM optical transceiver module |
SFP electrical module | — | RJ-45 |
SFP stack module | SFP-STACK-Kit only, with fixed connection cable and dedicated for interconnecting devices. | — |
GBIC (Gigabit interface converter) | GBIC optical module | Pluggable optical transceiver module | SC |
GBIC electrical module | Hot-swappable | RJ-45 |
GBIC stack module | Hot-swappable, dedicated for interconnecting devices | HSSDC |
XFP (10-Gigabit small form-factor pluggable) | 10-Gigabit small form-factor pluggable transceiver module | LC |
XENPAK (10-Gigabit Ethernet transceiver package) | Optical transponder, hot-swappable | SC |
l Different models of the H3C low-end series Ethernet switches may support different pluggable modules. For details, see respective installation manuals.
l The types of pluggable module types are subject to changes. To obtain latest module type information, consult marketing or technical support personnel of H3C.
Optical modules are used for transmitting optical signals over optical fibers. Optical transmission features low loss and is fit for long distance transmission.
The H3C low-end series Ethernet switches support varied optical module models of different specifications. You can choose suitable optical modules as needed for data transmission over optical fibers.
At present, the commonly used optical modules include optical transmitters, optical receivers, transceivers, and transponders. The H3C low-end series Ethernet switches mainly support transceivers and transponders.
I. Transceiver
Transceivers are mainly used for optical-to-electrical and electrical-to-optical conversions and provide the following functions: optical power control, modulation transmission, signal probe, IV conversion, and limiting amplifier and decision regeneration. In addition, transceivers provide some other functions, such as counterfeit-prevention query and TX-disable. Common transceivers include SIP9, SFF, SFP, GBIC, and XFP.
II. Transponder
In addition to optical-to-electrical and electrical-to-optical conversions, a transponder has multiple signal processing functions, such as MUX/DEMUX, CDR, function control, and performance collection & monitoring. Common transponders include 200/300pin, XENPAK, and X2/XPAK.
Data rate is the number of bits transmitted per second. The unit of measure for data rate is Mbps (Megabits per second) or Gbps (Gigabits per second). The optical modules available for the H3C low-end series Ethernet switches mainly provide the following three levels of data rates: 100 Mbps, 1,000 Mbps, and 10 Gbps.
For optical modules, three types of transmission distances are available: short haul, middle reach, and long haul. Generally, a distance of 2 km (1.2 mi.) is considered as short haul, 10 km (6.2 mi.) to 20 km (12.4 mi.) as middle reach, and 30 km (18.6 mi.) and over as long haul.
Transmission distances provided by optical modules are mainly limited by certain loss and dispersion suffered during the transmission of optical signals over optical fibers.
l Loss is the optical energy loss due to the absorption, dispersion and leakage over the media when light travels through optical fibers. This loss increases in direct ratio to transmission distance.
l Dispersion happens mainly because electromagnetic waves of different wavelengths travel at different rates over the same medium, causing different wave components of optical signals to reach the receiving end early or late as the transmission distance increases, which in turn causes impulse broadening, making the signal values indistinguishable.
Therefore, you need to choose suitable optical modules according to actual networking conditions to meet different transmission distance requirements.
Central wavelength represents the wave band used for optical signal transmission. At present, there are mainly three central wavelengths for common optical modules: 850nm, 1310nm, and 1550nm, respectively representing three wavebands.
l The 850nm wave band is mainly used for short-reach transmission.
l The 1310nm and 1550nm wave bands are mainly used for middle- and long-reach transmission.
Depending on the mode of light transmission in fibers, fibers fall into two types: single-mode and multimode.
l Multimode fibers (MMFs) have thicker fiber cores and can transport light in multiple modes. However, the inter-mode dispersion is greater and worsens as the transmission distance increases. Other factors that influence the transmission distance of multimode fibers include data rate, core diameter, and mode bandwidth. For details, see Table 1-2.
Table 1-2 Multimode fiber specifications
Fiber mode | Data rate(bit/s) | Core diameter | Mode bandwidth (MHz*km) | Transmission distance |
Multimode | Gigabit per second | 62.5/125μm | — | < 275 m (902.2 ft.) |
50/125μm | — | < 550 m (1804.5 ft.) |
10 G per second | 62.5/125μm | 160 | < 26 m (85.3 ft.) |
200 | < 33 m (108.3 ft.) |
50/125μm | 400 | < 66 m (216.5 ft.) |
500 | < 100 m (328 ft.) |
2,000 | < 300 m (984.2 ft.) |
l Single-mode fibers (SMFs) have thinner fiber cores and can transmit light in only one mode. Therefore, single-mode fibers suffer little inter-mode dispersion and are suitable for long-reach communication.
II. Fiber diameter
Fiber diameter is generally expressed as core diameter/cladding diameter, in μm. For example, 9/125 μm means the fiber core diameter is 9 μm and the fiber cladding diameter is 125 μm.
For the H3C low-end series Ethernet switches, the following fiber diameters are recommended:
l G.652 common single-mode fiber: 9/125 μm
l Common multimode fiber: 62.5/125 μm
l G.651 multimode fiber: 50/125 μm (for multimode VCSEL laser)
Connectors are used to connect pluggable modules to the corresponding transmission media. The optical modules available for the H3C low-end series Ethernet switches use two types of optical connectors: SC and LC.
I. SC connector
Figure 1-1 shows the appearance of an SC (subscriber connector standard connector).
Figure 1-1 Appearance of an SC connector
II. LC connector
Figure 1-2 shows the appearance of an LC (Lucent connector or local connector).
Figure 1-2 Appearance of an LC connector
Caution:
To keep the optical connector clean, make sure it is covered with a dust cap when it is not connected to any optical fiber.
I. Output optical power
Output optical power is the output power of the optical transmitter of an optical module, in dBm.
II. Receiving sensitivity
Receiving sensitivity is the minimum optical power that is needed at the receiving end for the optical module to receive optical signals at a given data rate and bit error rate, in dBm. Generally, the higher the data rate is, the worse the receiving sensitivity is, that is, the greater the minimum input optical power is; and a greater input optical power has higher requirements on the receiving components of the optical module.
III. Suppressed sensitivity
Suppressed sensitivity is the sensitivity measured when the jitter and vertical eye closure degradations are added to the input signals, in dBm. This concept applies to 10 Gbps interface modules (XENPAK and XFP modules) only.
IV. Optical saturation
Optical saturation (also known as saturated optical power) is the maximum input optical power at a given data rate and bit error rate range (10-10 to 10-12), in dBm.
Note that, saturated photocurrent occurs if a fiber probe is irradiated by intensive light. When this occurs, it takes the probe some time to recover. In this case, the receiving sensitivity worsens and the received signals may be decided incorrectly, causing bit errors. This will probably damage the receiving probe. Therefore, when you perform operations, try to maintain a normal saturated optical power level.
Caution:
Generally, the average output optical power of a long-haul optical module is greater than its maximum input optical power, namely, optical saturation. Therefore, be careful about the length of the optical fiber you use to ensure that the actual received optical power reaching the optical module is less than its optical saturation; otherwise, the optical module may be damaged.
Electrical modules are used for transmitting electrical signals over Category-5 unshielded twisted pair (UTP). UTP transmission cover shorter distances than optical transmission and therefore can be used in small-sized networks only.
The H3C low-end series Ethernet switches support the following two models of electrical modules:
l SFP electrical module: SFP-GE-T
l GBIC electrical module: GBIC-T-A
The data rates of the two models of electrical modules supported by the H3C low-end series Ethernet switches are both 1,250 Mbps.
Through UTP cables, electrical signals can be transmitted over a distance of 100 m (328 ft.) only. This is because electrical signals attenuate during transmission through the UTP cables.
Attenuation refers to the dissipation of the power of a transmitted signal as it travels over a cable. Attenuation occurs because signal transmission suffers certain resistance from the cable, which weakens the electrical signals as they travel over the cable. When signals are transmitted over a very long distance, signal strength decreases very significantly, causing the signal-to-noise ratio to drop below the accepted level. This makes it impossible to distinguish between signals and noise, resulting in decision errors.
Therefore, use electrical port modules only when signals are to be transmitted over a short distance.
RJ-45 (Registered Jack-45) twisted pair connectors are used as the connectors for electrical port modules. Figure 1-3 shows the appearance of an RJ-45 connector.
Figure 1-3 Appearance of an RJ-45 connector
Table 1-3 RJ-45 GE connector pin assignment
Pin | Signal | Function |
1 | MX_0+ | Data transmit/receive |
2 | MX_0- | Data transmit/receive |
3 | MX_1+ | Data transmit/receive |
4 | MX_2+ | Data transmit/receive |
5 | MX_2- | Data transmit/receive |
6 | MX_1- | Data transmit/receive |
7 | MX_3+ | Data transmit/receive |
8 | MX_3- | Data transmit/receive |
| | | |
A stack module provides one stack interface for connecting this switch to another switch to obtain higher port capacity. Stack modules are dedicated for interconnections between devices, generally over very short distances.
The H3C low-end series Ethernet switches support the following two models of Gigabit stack modules:
l SFP-STACK-Kit: SFP stack modules, using Category-5 UTP cables as the transmission media. An SFP-STACK-Kit module is fixed with a 1.5 m (4.9 ft.) transmission cable.
l GBIC-STACK: GBIC stack modules, using stack cables (External model: GBIC-STACK Cable) dedicated for HSSDC connectors. Figure 1-4 shows the appearance of this type of cables, with a transmission distance of 30 m (98.4 ft.).
Figure 1-4 Appearance of a GBIC-STACK Cable
