Fibre Channel Connectors
Data transfer rates over the Fibre Channel infrastructure are measured in gigabits. As a result, the data transported over Fibre Channel links is sometimes referred to as gigabit transport. Fibre Channel connectors play an important role in facilitating the gigabit transport between two communicating ends. The connectors provide an interface that converts any type of communication transport into gigabit transport.
Four types of Fibre Channel connectors are used to interconnect Fibre Channel devices:
- Gigabit Interface Converters (GBICs)
- Gigabit Link Modules (GLMs)
- Media Interface Adapters (MIAs)
The following sections discuss each of these connectors.
Fibre Channel devices use electronic signals known as differential serial data signals. These signals are encoded according to the 8B/10B encoding method. However, the link between two communicating devices is either copper-based or fiber-optic. Copper and fiber-optic links are not capable of transmitting differential serial data signals. Using GBICs solves this problem.
GBICs are hot-pluggable and easily replaceable interface modules that are responsible for converting differential serial data signals into corresponding optical or copper signals that can be transported to the destination. At the sender end, a GBIC takes differential serial data signals as input and converts them according to the Fibre Channel link on which the data is transmitted in the form of signals. At the recipient end, the GBIC receives the optical or copper signal and delivers it to the device as differential serial data signals.
On optical links, GBICs support two modes of optical operations depending on the wavelength of the laser being used. The two optical modes of a GBIC are ShortWave (SW) mode and LongWave (LW) mode.
ShortWave GBICs provide connectivity for comparatively short distancesup to 500 meters. The 50-micron fiber-optic cables offer SW mode at a distance of 2 to 500 meters. The 62.5-micron fiber-optic cables offer the SW mode at a distance of 2 to 175 meters. The 9-micron fiber-optic cables do not support the SW mode.
For more information on SW and LW Fibre Channel connections, see Chapter 5, "Fibre Channel Cabling."
As the name suggests, GBICs that function in LW mode offer long connectivity distances of up to 10 kilometers. The 9-micron fiber-optic cables offer LW mode up to a distance of 10 kilometers. Both 50-micron and 62.5-micron fiber-optic cables offer the LW mode up to a distance of 550 meters.
GBICs are external pull-push type connectors that need to be attached to the HBA as shown in Figure 4-2. GBICs plug into the Fibre Channel device. Fibre Channel cables, or links, are then attached to the GBIC. They are commonly used with HBAs, switches, and gate-ways and support transfer rates of 1063 Mbps and above. Prices of GBICs range from $250 to $3000.
Apart from Fibre Channel networks (such as SANs), GBICs can also be used in Gigabit Ethernets.
Figure 4-2 GBIC
Also referred to as Gigabaud Link Modules, GLMs are the low-cost predecessor of GBICs. GLMs facilitate full-duplex communication between Fibre Channel devices. They convert differential serial data signals to optical or copper signals so that the signals can be trans-mitted over the Fibre Channel link. At the recipient end, GLMs reconvert the optical or copper signals to differential serial data signals that the recipient can understand and process.
Although the GLMs function similarly to the GBICs, there are differences between the two. Table 4-1 enumerates the differences between GLMs and GBICs.
Table 4-1 The Differences Between GBICs and GLMs
GBICs offer transfer rates of 1063 Mbps and above.
GLMs offer transfer rates of 266 Mbps and 1063 Mbps.
GBICs are hot-pluggable. This means that the GBICs can be attached to or removed from the Fibre Channel device while the device is still operational.
GLMs are not hot-pluggable. The Fibre Channel device needs to be shut down before GLMs can be attached, replaced, or repaired.
GBICs are easy to configure and use.
GLMs are difficult to configure and use.
GBICs are more expensive than GLMs.
GLMs are comparatively cheaper than GBICs.
Similar to GBICs, GLMs also use two types of lasers for transportation of data over fiber-optic links. These include the following:
You can attach GLMs to the Fibre Channel devices as external connectors, or you can build GLMs into the HBA. Figure 4-3 shows an external GLM. Figure 4-4 shows a GLM that is a part of the HBA. The price of GLMs ranges from $900 to $2500.
Figure 4-3 External GLM
Figure 4-4 GLM as a Part of the HBA
Transceivers are hot-pluggable Fibre Channel connectors that are generally used in switch implementations. They facilitate high-speed, bidirectional, point-to-point communication between Fibre Channel devices. Transceivers support communication speeds of 2 Gbps and above (3.25 Gbps to 10 Gbps). Some transceivers can also provide transaction speeds up to 10 Gbps.
Commonly used Fibre Channel transceivers include the following:
- 1 ∴ 9 transceivers
- Small Form Factor (SFF) transceivers
- 1 ∴ 28 transceivers
1 ∴ 9 optical transceivers are the most commonly used transceivers. Transceivers are preferred over GBICs because they are roughly two times faster and are much easier to maintain than GBICs. However, transceivers are also more expensive than GBICs and GLMs. The price of transceivers ranges from $350 to $2000.
Figure 4-5 shows a 1 ∴ 9 transceiver.
Figure 4-5 1 ∴ 9 Transceiver
SFF transceivers are small, laser-based optical connectors that are the same size as RJ-45 connectors. These transceivers offer high data transfer rates (1063 Mbps) and are well suited for networking applications that require a high-speed serial interface. Being small in size, SFF transceivers are highly recommended for environments where devices are squeezed in less space. The performance of SFF connectors is directly related to the precision of fiber align-ment. Therefore, take special care while connecting these transceivers to Fibre Channel devices. The price of SFF transceivers ranges from $450 to $3000.
Figure 4-6 depicts an SFF transceiver.
Figure 4-6 SFF Transceiver
1 ∴ 28 transceivers are high-speed optical transceivers that can support data transfer rates up to 1.25 Gbps. In addition to facilitating connections between Fibre Channel devices and links, 1 ∴ 28 transceivers are also capable of providing link status information and diagnosing link problems. This helps the Fibre Channel device that they are connected to promptly diagnose transmission- and link-related problems.
Figure 4-7 depicts a 1 ∴ 28 transceiver.
Figure 4-7 1 ∴ 28 Transceiver
Some vendors, such as Vixel, 3Com, and Finisar, categorize GBICs as transceivers.
MIAs, a cost-effective category of Fibre Channel connectors, are responsible for the conversion of DB9-based copper signals into corresponding optical signals and vice versa. MIAs are useful in the following situations:
Extending a Fibre Channel copper link distance beyond the stipulated 30 meters.
Currently, optical MIAs are available only for SW lasers. Therefore, the cables supported by MIAs can stretch up to a maximum of 500 meters.
Connecting the copper interface to a Fibre Channel hub or switch.
MIA prices range from $50 to $1500. Although MIAs are cost-effective compared to other Fibre Channel connectors, they are not considered to be good Fibre Channel solutions for the following reasons:
MIAs are not hot-pluggable. Therefore, the Fibre Channel to which they are connected must be powered down before they can be removed or replaced.
MIAs are difficult to manage.
MIAs do not provide support to the High Speed Serial Data Connectors (HSSDC) copper interface, which is often used in Fibre Channel networks.
MIAs are dependent on DB-9 connectors for power supply. However, not all DB-9 connectors are capable of supplying power to MIAs.
Figure 4-8 shows a Fibre Channel MIA.
Figure 4-8 A Fibre Channel MIA
The next section discusses Fibre Channel hubs in detail.