Tag Archives: DWDM channels

We all know that cascaded FCP/FICON directors use ISLs to connect the directors

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 8 way DWDM module. 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. 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 Equipments 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 ultra DWDM 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.


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Wavelength Multiplexing: CWDM and DWDM

CWDM: An optical industry interim standard uses up to eight wavelengths, this scheme is referred to as coarese wavelengtb division multiplexing(CWDM), in accordance with ITU-T(any channel spacing between 8 and 50 nm). ITU-T Recommendation approved in june 2014, extends this down to 1270 nm(18 wavelengths), anticipating the ready commercial availability of fiber with no “water peak” of loss between the 1310-nm and 1550-nm transmission windows, as discussed in Chapter. Such an extended-wavelength planis, of course, applicable only to nonamplified systems until such time as optical amplifiers with similarly extended bandwidths are developed.

DWDM: The International Telecommunications Union(ITU) has defined a usage plan that can scale to as many as 45 wavelengths in the third window and whose spacings have been further split in some systems to yield twice that number. The defined channel designations are for channels spaced 100 GHz apart (about 0.8 nm). Regardless of whether 200-GHz, 100-GHz, or 50-GHz spacings are used, the usage plan is referred to as dense wavelengtb division multiplexing(DWDM). (More about DWDM: DWDM WIKI)

A fwe properties are common to all the plans, each with obvious parallels in RF technology.

♦ The closer the wavelengths are spaced, the harder(and more expensive) it is to separate them in the demultiplexers and simultaneously achieve adequate adjacent channel isolation, minimal in-channel flatness variation, and low insertion loss.

♦ The closer the wavelengths are spaced,the more frequency stabillity is required of the transmitters.

♦ The closer the wavelengths are spaced, the better the signal transmission velocities will match. Four-wave mixing and cross-phase modelation are both maxmum when the signals travel at nearly the same velocity. The degree of matching is, of course, also dependent on fiber dispersionm with standard fiber having high dispersion at 1550 nm but low dispersion at 1310 nm. By contrast, close wavelength spacing leads to reduced crosstalk from stimulated Raman scattering. These mechanisms are discussed later.

♦ The more wavelengths that share a fiber, the lower must be the power per wavelength for a given amount of mutual interaction due to nonlinear glass properties.

As shown in figure shows the relationship of bands, CWDM channels, and DWDM channels. Gable systems using linear DWDM technology generally use 200-GHz-spaced channels from among the set of 20 listed in Table 1, though a few vendors offer 100GHz spacing. For network designs that use fewer than 20 of the listed wavelengths, various vendors have chosen to offer different subsets.


               Relationship of wavelength bands.


           Wavelength Division Multiplexing

Most offer C21 through C35 as the first eight, but noe vendor offers C39 through C53 as the second eight, another offers C45 through C59, and a third has chosen to offer C37 through C51. This is obviously inconvenient for operators who wish to have multiple sources for optical transmitters and DWDM Multiplexer.

WDM optical networking solutions

Fiberstore offers a number of WDM Optical Networking solutions that allow transport associated with a mix of services up to 100 GbE over dark fiber and WDM networks providing for the whole set of probably the most demanding CWDM and DWDM network infrastructure needs. Because the physical fiber optic cabling is expensive to implement for every single service separately, its capacity expansion using a WDM is a necessity.


WDM is a concept that describes combination of several streams of data/storage/video or voice on the same physical fiber optic cable by utilizing several wavelengths (or frequencies) of light with each frequency carrying a different sort of data. There’s two types of WDM architectures: CWDM (Coarse Wavelength Division Multiplexing) and DWDM (Dense Wavelength Division Multiplexing). CWDM systems typically provide 8 wavelengths, separated by 20 nm, from 1470nm to 1610nm. In order to increase the number of wavelength, it’s possible to also use the 1310 nm window therefore the CWDM channels can be increased to 16. Some DWDM network systems provide up to 96 wavelengths, typically without any more than 0.4 nm spacing, roughly over the C-band range of wavelengths.

CWDM Technology

CWDM proves to be the initial access point for many organizations due to its lower cost. Each CWDM wavelength typically supports as much as 2.5 Gbps and could be expanded to 10 Gbps support. This transfer rates are sufficient to aid GbE, Fast Ethernet or 1/2/4/8/10G Fibre Channel, along with other protocols. The CWDM is limited to 16 wavelengths and is typically deployed at networks as much as 80 km since optical amplifiers can’t be used due to the large spacing between channels.

Note: Fiberstore’s WDM optical networking goods are designed to support both CWDM and DWDM technology by utilizing standards based pluggable CWDM Transceiver/DWDM Transceiver such as SFP, XFP and SFP . The technology used is carefully calculated per project and according to customer requirements of distance, capacity, attenuation and future needs.

DWDM Technology

DWDM is a technology allowing high throughput capacity over longer distances commonly ranging between 44-88 channels/wavelengths and transferring data rates up to 100 Gbps per wavelength. Each wavelength can transparently have a wide range of services. The channel spacing from the DWDM solutions is defined by the ITU standards and can range from 50 GHz and 100 GHz (the most widely used today) to 200 GHz. DWDM systems can provide up to 96 wavelengths (at 50 GHz) of mixed service types, and can transport to distances up to 3000 km by deploying optical amplifiers (e.g., DWDM EDFA) and dispersion compensators thus enhancing the fiber capacity with a factor of x100. Due to its more precise and stabilized lasers, the DWDM technology tends to be more expensive in the sub-10G rates, but is really a more appropriate solution and it is dominating for 10G service rates and above providing large capacity data transport and connectivity over long distances at affordable costs.


The main benefit of CWDM is the price of the optics that is typically 1 / 3 of the price of the equivalent DWDM optics. This difference in economic scale, the limited budget that lots of customers face, and typical initial requirements to not exceed 8 wavelengths, means that CWDM is a popular entry point for a lot of customers. With Fiberstore’s WDM equipment, a customer can start with 8 CWDM wavelengths however grow by introducing DWDM wavelengths in to the mix, utilizing the existing fiber and maximizing roi. By utilizing CWDM and DWDM network systems or the mixture of thereof, carriers and enterprises are able to transport services as much as 100 Gbps of data.

Typically CWDM solutions provide 8 wavelengths capability enabling the transport of 8 client interfaces over the same fiber. However, the relatively large separation between your CWDM wavelengths allows growth of the CWDM network with an additional 44 wavelengths with 100 GHz spacing utilizing DWDM technology, thus expanding the present infrastructure capability and making use of the same equipment included in the integrated solution.

FiberstoreAdditionally, the normal CWDM spectrum supports data transport rates as high as 4.25 Gbps, while DWDM is utilized more for large capacity data transport needs as high as 100 Gbps. By mapping DWDM channels inside the CWDM wavelengths spectrum as demonstrated below, higher data transport capacity on the same fiber optic cable is possible without any requirement for changing the existing fiber infrastructure between the network sites. As demonstrated through the figure beside, CWDM occupies the following ITU channels: 1470 nm, 1490 nm, 1510 nm, 1530 nm, 1550 nm, 1570 nm, 1590 nm, and 1610 nm, each separated from the other by 20 nm. Fiberstore can insert into the of the 4 CWDM wavelengths (1530 nm,1550 nm,1570 nm and 1590 nm), a set of additional 8 wavelength of DWDM separated from one another by only 0.1 nm. By doing so up to 4 times, the CWDM network capability can easily expand by up to 28 additional wavelengths.

The other figure below further demonstrates in detail the expansion capabilities via the DWDM spectrum. As seen below, just one outgoing and incoming wavelength of the existing CWDM infrastructure can be used for 8 DWDM channels multiplexing in to the original wavelength. Since this DWDM over CWDM network solution is integrating the DWDM transponders, DWDM MUX/DeMUX and EDFA (optical amplifier if needed), the entire solution is delivered simply by adding a really compact 1U unit. This expansion is achieved with no service interruption to the remaining network services, or to the data, and with no need to change or replace any of the working CWDM infrastructures.



Fiberstore’s CWDM and DWDM network equipment is a serious contender for today’s optical transport requirements. It provides the following advantages: 1. Low-cost initial setup with targeted future growth path2. Easy conversion and upgrade capabilities up to 44 wavelengths3. Easy upgrade to support 10G, 40G and 100G services4. Seamless, non traffic effective network upgrades5. Reliable, secure, and standards based architecture6. Easy to install and maintain7. Full performance monitoring

With Fiberstore’s compact CWDM solutions, you could get all of the above benefits and much more (such as remote monitoring and setup, integrated amplifiers, protection capabilities, and integration with 3rd party networking devices, etc.) inside a cost effective 1U unit, enabling you to expand as you grow, and utilize your financial as well as physical resources towards the maximum.

Fiberstore’s full scale WDM product suite is ideal for not only services providers, but additionally dark fiber developers, data centers, financial institutions, campuses and enterpirses. Our WDM optical networking goods are supported and implemented by partners, distributors, VARs and customers all over the world.