Cabling Encyclopedia | Cabling of Inter-Chassis Links (ICLs)

When it comes to cabling inter-chassis links (ICLs), it may be an afterthought for many people. Before discussing cabling, let's first understand what ICL ports are and why they are used.

●   ICL Port

The so-called ICL port can connect two chassis together to ensure redundancy.

ICL ports are located on the core routing blades of the chassis. Taking Broadcom's recently launched Gen7 product portfolio as an example, the X7-8s can accommodate 16 ICL ports per blade (32 total), while the X7-4s can accommodate 8 ICL ports per blade (16 total).

Organizations must adapt to continued data growth through a storage environment that can easily scale to meet their business needs. Broadcom Chassis Connect leverages dedicated ICLs to connect up to 12 directors, simplifying the fabric to increase consolidation while reducing complexity and cost.

Because ICL connections reside on the core routing blades instead of occupying ports on the port blades, up to 33% more device ports are available for server and storage connections. This maximizes overall port density in minimal rack space while freeing up front-end device ports for server and storage connections.

Wiring​

Now let’s talk about wiring!

The X7 supports cable distances up to 10 km at 32Gb/s using LWL optics in the Gen 7 blades. These ICL kits can provide connectivity for Gen 7 to Gen 7, Gen 7 to Gen 6, or Gen 7 to Gen 5.

For most applications in the data center, shortwave ICL will be used. Either 4x64Gb/s Gen7 to Gen7, 4x32Gb/s Gen7 to Gen6, or 4x16Gb/s Gen7 to Gen5, all support distances up to 100 meters.

In all of these scenarios, ICL QSFP requires OM4 12-core MTP (MPO) female/female assembly limited to 100M. MTP is the industry standard MPO connector of Conec brand in the United States.

For longer distances, long wave ICLs are used. Unlike short wave ICLs, starting with Broadcom's 5th generation portfolio (8510-4 and 8510-8s), these ICLs require an LC connector and single mode LC/LC fiber patch cords are used for the ICLs.

To simplify the connections and make them easier to manage, CABLExpress recommends using structured cabling and patch panels when implementing. This is especially true in cases where chassis switches may be located in different rows or locations in the data center. With LW ICLs, the switches can be located on different floors or PODs in the data center.

In these cases, long cables running directly to the ICL optics limit flexibility in performing any moves, adds, or changes.

However, there are two scenarios that can be used to optimize the ICL environment.

Scenario 1: X6/X7-X6/X7 with SW QSFP ICL optics

Using the CABExpress solution:

1. CABLExpress 96 Fiber MTP Male/MTP Male OM4 Trunk Cable
2. H Series 1U Cabinet
3. 16-MTP Adapter Panel
4. CABLExpress 12-core MTP female/MTP female OM4 trunk cable

To segment the connections, it is recommended to run a 96 fiber trunk as a “highway” so that short MTP/MTP patch cords can be connected into the ICL optics.

For example, instead of running a 50M ICL assembly directly connected to each active port, a 96 fiber trunk can be run to "set it and forget it."

This allows expansion with short jumpers, making it easier to add more ICL ports later, minimizing future installation time and eliminating risk variables.

Scenario 2: X6/X7-X6/X7 with LW QSFP ICL optics

Similar to Scenario 1 above, Scenario 2 will use structured cabling and patch panels:

1. CABLExpress 96-core MTP female/MTP female OS2 SM trunk cable
2. H Series 1U Cabinet
3. 16-port MTP/LC cassette module
4. CABLExpress Duplex LC/LC SM Fiber Optic Patch Cords

Again, it is recommended to use a 96-core MTP/MTP trunk to set up a “highway” in this case. However, since the SM LW ICL Optics use LC interfaces, it is recommended to use MTP/LC cassette modules.

This will allow LC/LC patch cords to be added as more ICL ports are added.As mentioned previously, environments using SM LW ICL optics will typically have their SAN directors farther apart due to exponential distance limitations.

The importance of wiring

Budget, resources, timelines and many other factors are involved when planning and prioritizing a data center project. Early on, there is no need to spend too much time planning the cabling infrastructure.

At the time, options were limited, copper cables were hard to break, and costs were low. Today, data speeds and access demands increase the cost of implementation, material and design requirements, as well as soft costs associated with MACs, troubleshooting, and installation issues.

When cabling is planned and installed according to best practices, the variables for problems and roadblocks in these high-profile projects are minimized.