Tag Archives: CWDM chassis

Guide to CWDM MUX/DEMUX System Installation

CWDM (coarse wavelength division multiplexing) comes from the WDM system. It is designed to increase the capacity of a fiber optic network without adding additional fiber. The wavelengths of CWDM channels are spaced 20 nm apart which allows the use of low-cost, uncooled lasers. The wavelengths usually range from 1270 nm to 1610 nm.

Today, CWDM Mux/Demux (multiplexer/demultiplexer) module is an important device to increase the current fiber cable capacity by transmitting multiple wavelengths with up to 18 signal channels over a single fiber. When using a CWDM multiplexer at the beginning of the network, accordingly a CWDM demultiplexer should be used at the opposite end to separate the wavelengths and direct them into the correct receivers. This greatly reduces the number of fiber cables and other data links.


Basic Components of CWDM MUX/DEMUX System

Several basic components constitute a CWDM Mux/Demux system. They are a local unit, a remote unit, a rack-mount chassis, CWDM Mux/Demux modules, CWDM SFP transceivers and single-mode patch cables. The local unit and remote unit are two different switches. The rack-mount chassis is needed to be installed for holding the CWDM Mux/Demux module. As for the connections, CWDM SFP transceivers are usually used between a CWDM Mux/Demux module and a switch, and single-mode patch cables are used to connect transceivers to the module.

Preparation Before Installation

Multiple single-mode patch cables are needed for CWDM Mux/Demux system connection. And the transceivers used in the system must support the wavelengths from 1270 nm to 1610 nm. Make sure the installation environment is in a dry and interior space. The module should have enough room to create airflow for easier heat distribution. Any inappropriate arrangement that obstructs the ventilation holes should also be avoided.

CWDM MUX/DEMUX System Installation

Step one, mount the system chassis on the rack. The CWDM rack-mount chassis can be mounted in a standard 19-inch cabinet or rack. Make sure that you install the rack-mount chassis in the same rack or an adjacent rack to your system so that you can connect all the cables between your CWDM Mux/Demux modules and the CWDM SFP transceivers.


Step two, install the CWDM Mux/Demux modules. You should first loose the captive screws on the blank module panel and remove the panel. Then align the module with the slot of the chassis shelf and gently push the module into the slot. Finally, ensure that you line up the captive screws on the module with the screw holes on the shelf and tighten them up.


Step three, install CWDM SFP transceivers. Since each channel has a specific wavelength, transceivers must comply with the right wavelengths. Each wavelength must not appear more than once in the system. Device pairs must carry transceivers with the same wavelength.


Step four, install the CWDM Mux/Demux to the switch. After inserting the CWDM SFP transceiver into the switch, single-mode patch cables are used to connect the transceiver to the CWDM Mux/Demux module.

Step five, connect the CWDM MUX/DEMUX pairs. In a CWDM MUX/DEMUX system, multiplexer and demultiplexer must be installed in pairs. Two strands of single-mode patch cables are needed in the duplex Mux/Demux module, and one strand of single-mode patch cable is enough for the simplex Mux/Demux module.

When you finish all these steps, the installation of CWDM Mux/Demux system is successfully completed.


CWDM Mux/Demux system is definitely a good solution to high capacity data transmission. It is efficient for power, space, and cost-saving. And the installation procedure is easy to follow. All the components above are available in FS.COM. If you are interested, please come and visit our website for more information.

Make Use of DWDM Equipments by ISL Trunks

Inter-Switch Link (ISL) protocol, is a cisco proprietary protocol, Can only be used for interconnection between Cisco network equipment, it is mainly used for maintenance the VLAN information such as the traffic between the switches and routers. VLAN is a kind of agreement for solving the problem of Ethernet radio and safety. After the introduction of VLAN, the host to communicate across the switches in the VLAN. We all know that cascaded FCP/FICON directors use ISLs to connect the directors. In certain configurations, ISLs can be grouped or aggregated, typically for performance and reliability. Brocade calls this an ISL trunk (frame-based trunking), and Cisco calls this a Port Channel just as CWDM chassis. We will generically call this feature ISL trunking or just a trunk.

Each vendor might implement these trunks in a unique way to provide proprietary features. The vendors’ trunks ISLs might contain proprietary frames, proprietary frame formats, or special characters or sequences of characters in the inter-frame gaps.

Often, the difference between a cascaded environment contained in a signal data center or campus environment, and one in a metro environment, is the use of a DWDM Optical Amplifiers to carry the ISLs over the extended distance.

The primary concern when attempting to use trunked ISLs with a DWDM is that the ISL data streams must be unaltered by the DWDM for the proprietary functions to work correctly. This os sometimes called bits in, bits out, to indicate that there is no change to the signals, especially between the cascaded directors.

The challenge with non-symmetric transit times for the ISLs in a trunk is illustrated in following picture. The scale is time to arrive and not distance traversed per time unit (which would produce a great roughly the opposite of this). This diagram shows how the signals, sent at the same time on parallel ISLs, could arrive at the endpoint at different times. The director measure this difference at the time that the trunk is created. The difference is called skew.

ISL Skew

The director can accommodate a small skew, but an ISL with skew that is too large might be removes from the trunk by the director. An ISL that is carried on circuitry that introduces variable skew will not be detected, because the director does not re-measure the skew. If the variance of the skew becomes too large, the traffic on the trunk could be the cause of interface control checks (IFCCs), or could experience out-of-order frames.

It must be noted that the trunks between cascaded directors might appear to work without any issues during testing, because this is often performed with a relatively low I/O load. At that point, only oe or two ISLs in a trunk carry traffic with high I/O loads. Some DWDM optical transport equipment features can cause the skew to vary (that is, not be consistent), which can cause out-of-order frames or other issues with the I/O traffic.

Any alteration of the data stream introduced by circuitry or software in the DWDMs might affect the ISLs. The DWDM vendor might alter the data streams for different purposes. You should check with the DWDM and the FICON director vendors to determine basic ISL compatibility. Some of these features might be implemented in a way that alters the data stream that will not affect a single ISL, but would affect trunking. In general, these DWDM features should not be used on trunked ISLs.

IBM has experience with DWDMs that could not be used for ISL trunks because of the issues noted, and some experience where DWDMs appeared to support ISL trunking. There are many features on each DWDM and on each FICON director, giving a large number of permutations that would be difficult to test.

For a single example, and definitely not to provide an exhaustive test, Fiberstore tested a specific configuration with two Brocade FICON Directors whose trunked ISLs were carried on two ADVA FSP 3000s at a distance of 80 km. The test configuration, with significant and varying I/O load, did not find significant increases in IFCCs or out-of-order frames, and the skews between the ISLs in the trunk were within acceptable limits.

There are many DWDM vendors such as Fiberstore who has their own compatibility documents. Ask your DWDM vendors for this information if you are considering combining ISL trunking with a DWDM. In addition, Fiberstore is doing with a discount of 30% to CWDM/DWDM related products, if you have some needs, welcome to our Fiberstore.