You are expanding your network. The goal is to ensure you won't regret this decision three years from now.
Start with four questions, not a product catalog
Before your first conversation with a supplier, answer four questions. They determine your choice of technology more than anything else.
The first question is: how many kilometers are your longest links along the cable route, not in a straight line? Cables don't run in straight lines. Routing through a city, through buildings, and including slack loops means the actual fiber length is often 20 to 40 percent greater than the geographical distance. Measure with an OTDR, don't count from a map.
The second question: how many channels do you need now and in five years? The architecture you choose today determines how easily you can scale in three years. CWDM has a ceiling of eighteen channels, while DWDM starts with a few and scales to eighty or more without replacing line equipment.
The third question: what are your bandwidth requirements per channel? 10G per channel means CWDM with standard modules. 100G without amplifiers over short distances means O-Band. 100G, 200G, and 400G over longer routes means DWDM with coherent modules. The fourth question: do you already have WDM infrastructure? If you have a working CWDM system, a hybrid of CWDM and DWDM is often the fastest and cheapest path for expansion, without replacing cables or existing passive components.
It is worth knowing the broader context of your options before focusing on choosing between WDM variants.
The first is a port on an operator's switch. You lease a 10G port for about 3,500 PLN per month. It's simple, requires no investment, but every new link means a new port and a new fixed cost, and the bandwidth is a specific speed that you cannot scale flexibly. The second is a port on a muxponder, or Alien OTN. Instead of a switch, you lease a port on an OTN device that supports the transport protocol. Costs for an OTU4 frame range from 5,000 to 6,000 PLN per month—about twice as much as a single switch port—but with significantly greater capabilities for aggregating various services and protocols.
The third is a port on a multiplexer, or Alien Lambda. You lease a specific DWDM wavelength directly from an operator. Bandwidth is not limited by the port, so you can transmit from 10G up to 400G on the same wavelength, with full protocol freedom. The fourth is dark fiber or your own infrastructure, which offers the greatest capabilities and complete independence. Dark fiber lease rates depend on the route and the operator, but the key is that with WDM, you only need one fiber or a pair, because you multiply bandwidth using technology rather than the number of leased fibers. The fifth is your own infrastructure with WDM, providing full independence and maximum cost-efficiency at scale.
A checklist: ten questions before signing an order
Each of the following questions can change the specification or uncover a hidden cost.
Tools that simplify management: SRD 5 and GBC Photonics S100
Two items from our portfolio that simplify the lives of optical network engineers in practice.
SRD 5 is an optical module programmer that allows you to save thousands of zlotys on network management. You program modules from your smartphone via the SRD Go app, and the device supports OSFP (400G, 800G, and 1.6T), QSFP-DD (400G and 800G), SFP-DD (100G), as well as the commonly used SFP+ (10G), SFP28 (25G), QSFP+ (40G), and QSFP28 (100G) interfaces. Salumanus engineers have calculated that when working with equipment from three different vendors across six network areas, the SRD environment can generate over $300,000 in annual savings.
GBC Photonics S100 is a new platform for building DWDM systems that provides real insight into what is happening in the optical layer. Signal power, wavelength, and OSNR are at your fingertips, accessible remotely via a browser or SNMP system. The OCM (Optical Channel Monitor) card checks the status of DWDM channels without physical access to the device, and the OLP (Optical Line Protection) module creates an automatic backup route, taking over all traffic in less than 50 ms in the event of a main link failure, without restarts or manual switching. The modular 1U and 2U architecture with three to seven slots allows you to purchase only what you actually need.
Three mistakes we see most often
How do we work with clients?
We don't start with a product catalog. We start by understanding your network: what you have, where it is, how much you are transmitting, and where it is going. Based on this, we calculate the optical budget for each route, recommend technology and components, and prepare a conceptual design with a quote and a five-year total cost of ownership calculator. All of this happens before any purchasing decision is made.
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What problems does 400G solve?
QSFP-DD 400G optical modules are the best choice for telecoms and large data centers with huge traffic growth.
How to Deploy a Coherent QSFP-DD Module in an Existing DWDM Network?
You have a working DWDM network. You want to plug a coherent QSFP-DD module straight into the router and remove the transponder from the architecture. It sounds simple and it really is — but only if you know about a few things that can block the project before you even order the hardware. This is a practical guide. Not theory, just the order of operations, a checklist, and the mistakes engineers regret after the fact.
400ZR, 800ZR, OpenZR+: What Are They and Which DCI Network Needs Them?
ZR standards are the technology that allowed companies to cut out external transponders and connect coherent optics directly to a router port. Less equipment, a lower energy bill, and more freedom when choosing partners.