MRJ21 connectors are designed for improved packaging density, Gigabit Ethernet performance, and reduced installation time.
BY NYCHELLE HALLOCK & MICHAEL FOGG
As the benefits of operating networks at Gigabit Ethernet (GbE) speed become more evident, it is important to not ignore some of the fundamentals that can be overshadowed by the glamour and glitz of big-ticket system hardware like switches and routers. Some of the fine details, such as the connectors and cabling, have ramifications when upgrading to GbE or simply designing a new GbE network.
Recent developments in I/O connector technology can help many stakeholders in network upgrades and in new network designs.
Two of the primary I/O interconnects used in networking and telecommunications are the modular jack and “25-pair” connectors. They come in several varieties, with the RJ-45 and RJ-21 being most prevalent. These connectors offer reliability, familiarity and simplicity while allowing systems to operate at the 10/100Base-T bandwidth range.
But now that more people are utilizing GbE systems, shortcomings in many existing RJ-45 and RJ-21 interconnects are becoming evident. Many versions of gigabit-capable RJ-45 connectors are available on the market, but for those who prefer the 25-pair RJ-21 solutions, only one or two proprietary gigabit solutions exist.
To accommodate the jump to GbE, existing products have evolved, while new I/O connectors have emerged. One such connector, the MRJ21, was designed for GbE while tripling the density of the existing RJ-21, and has other attributes that ease the transition to GbE and other network upgrades (Fig. 1).
 FIGURE 1. Compact MRJ21 pc board connectors offer full shielding and positive-retention jackscrew hardware. (Tyco Electronics) |
MRJ21 connectors can be applied in nearly all network hardware that previously used standard stacked mod jack products or 50-position RJ-21 connector products (Fig. 2). OEMs who produce Ethernet switches, network closets, routers, digital cross-connects, DSLAM, and similar products can readily adapt their designs to accept this new connector.
 FIGURE 2. A comparison of MRJ21 and RJ-21 connectors illustrates the newer design’s packaging efficiency. (Tyco Electronics) |
In addition to allowing networks to operate at GbE, the MRJ21 is more compact than previous mod jack and RJ-21 designs. This higher density solution for networking I/O has been designed, tested and verified to reliably transmit not only simultaneous GbE transmissions, but also Power over Ethernet (PoE or PoLAN) as well.
For hardware designers, the connector density improvement means the I/O port density can be increased by 1.5 to 3 times, compared to stacked RJ-45 modular jacks. Compared to RJ-21, MRJ21 connectors are one-third the size. Further, these right-angle receptacles are 50% shorter than standard stacked jacks (Fig. 3).
Now, it’s possible to use 16 MRJ21 connectors to yield 96 GbE ports or 192 10/100 ports on a standard blade. This also translates to a doubling of GbE port density compared to RJ-45, and allows a total of 48 pluggable ports per 1RU breakout panel. As a result, patch cord bundles are reduced and simplified, which is a benefit to OEM, installer and user.
While the packaging advantages for the network hardware OEM are clear, in addition to being able to pack more I/O into a given box design, the MRJ21 offers other design improvements. For example, MRJ21 connectors have electrical properties that control alien crosstalk to meet or exceed Category 5e, and full shielding to mitigate EMI. Additionally, jackscrews are employed to provide positive latching.
With increases in port density, OEMs may choose to improve the functionality or features of their devices, but another advantage can be passed on to the user in the form of spare ports for future network growth or upgrades. With additional ports, users and installers can realize incremental cost reductions as they connect more users or devices to the network (Fig. 4).
Connector configurations
While system designers will be interested in the high-level technology advancements, such as density improvements and newfound speed capability, an MRJ21 connector is available in several configurations so that it can match the needs of a number of applications within the GbE and networking realm. These configurations include single-port MRJ21 (option of panel grounds and no panel grounds, thru-hole solder and press fit; both with the same board layout and dimensions), as well as dual and quad MRJ21 assemblies with integrated magnetics.
The MRJ21 is, by design, a simpler, quieter interconnect than the RJ-45 and RJ-21, minimizing introduction of alien crosstalk and creating an assembly that doesn’t suffer from the myriad of proprietary noise compensation approaches found on traditional RJ-45 products. These design features result in consistent and superior link electrical characteristics, making the product well suited for gigabit applications.
Installers will also see improvements with systems employing MRJ21 connectors and cable assemblies. First, cable management at the switch is improved since only one cable is required (compared to six for GbE or 10/100/1000 applications), and cable counts drop from 12 to 1 for 10/100. That single cable is also roughly 30% smaller in area than the corresponding six 4-pair cables. Further, because of the density improvements on the board and the resulting low I/O profile, visibility to activity indicators on hardware is improvef considerably. Total cost of ownership for end-users is likely to improve as well.
Enterprise and service provider customers can expect to receive additional benefits when using the MRJ21 connector for their infrastructure cabling. Studies focusing on four major cost-savings areas (labor, space, time and maintenance) have indicated that the MRJ21 cabling system offers a number of potential cost-saving opportunities.
In the labor study, it was determined that MRJ21 can provide immediate installed savings of $3.50 to $14 per port versus traditional RJ-45-based cabling. Also, studies indicate the space savings that result from MRJ21 amounted to ongoing floor space of up to $4.50 per port per year, since less space in data centers was necessary. Floor space savings of 50% or more were achieved in this study’s high-cost, mission-critical environment.
Furthermore, the study concluded that time for getting a data center wired up was roughly one-sixth of the time required for traditional cabling methods. Finally, the study showed reduced downtime for switch change-out or recovery.
Interconnectivity advances
One of the most advanced I/O applications for next-generation modular jacks could be where 10/100Base-T, GbE and powered Ethernet converge. Implications of 10/100Base-T and GbE are one thing, but passing power through Ethernet connectors is a relatively new issue, and the interconnect used for this type of application demands careful consideration.
Delivering high-speed signals throughout a network can be a challenge in itself, but adding the burden of low-power capability to a network imparts new challenges upon an interconnect system.
First, since the delivery of power through an interconnect that is already carrying signal is prone to interference, it’s important to protect the signal contacts from possible interference introduced by the low-power portion of the interconnect. Some designers may choose to filter the interconnect leads on the board. But by following this course, another level of complexity, cost, and effort is added to the board-processing portion of the manufacturing process.
Another option is to use an integrated MRJ21. The ganged MRJ21 connector allows 10/100/1000Base-T operation as well as PoE-enabled pins. Integrated magnetics and power management are combined, rendering costly and time-consuming board-level solutions unnecessary.
The integrated magnetics perform a variety of necessary functions:
- Provide DC isolation as mandated by IEEE 802.3 and IEC 60950;
- Provide common mode EMI suppression;
- Integrated magnetics allow for introduction of DC power for PoE applications.
In applying the press-fit ganged MRJ21 connector to Ethernet switches, the benefits of network-supported powered devices can proliferate throughout the network.
One of the important attributes of the MRJ21 ganged magnetics connector is that it can be flexible. The connector can be designed to incorporate both non-PoE and PoE-enabled options (see sidebar, “Why add PoE into the mod jack?”). With this design approach, the path to migrating networks from 10/100 and GbE 802.3af-compliant PoE is much easier.
Recent developments have taken seemingly simple, proven I/O interconnects and advanced them to new heights. These next-generation I/O connectors offer improved packaging density and performance while also improving handling and manufacturing, affecting not only the OEM, but also the installer and user.
Most importantly, these new I/O interconnects are designed to make Gigabit Ethernet and powered Ethernet easier to implement, further enhancing network functionality and improving overall network productivity.
NYCHELLE HALLOCK is product manager, and MICHAEL FOGG is a member of the technical staff (MTS2) at Tyco Electronics (www.tycoelectronics.com).
Why add PoE into the mod jack?
Adding PoE capability to the mod jack makes sense for its simplicity. Most PoE silicon has the ability to run in Auto Mode, so that once the connector is placed on the board, it is allowed to run by itself. This results in a significant reduction in board-level components, simplification of the bill of materials, and frees up valuable board space.
For those who wish to have additional control, but still retain the part number/bill of materials and board benefits, the product can be controlled in the Enhanced Mode, which allows control over power delivered, prioritization of ports, remote diagnostics, and compatibility with non-802.3af standard products.
A few words on signal integrity
Since RJ-45s with isolation magnetics are used only at the sourcing and receiving end of a system, they’re considered part of a device, and are allowed to have relaxed electrical requirements. Though all components between these devices are controlled by the stringent requirements of TIA/EIA-568/Category 5e requirements, the magnetic assemblies are not.
With migration to GbE, poor crosstalk performance has made it difficult to design robust systems, and virtually impossible to implement a mid-span PoE solution; therefore, the performance of RJ-45s with integrated magnetics must be improved.
Now, it’s possible to use 16 MRJ21 connectors to yield 96 GbE ports or 192 10/100 ports on a standard blade. This also translates to a doubling of GbE port density compared to RJ-45, and allows a total of 48 pluggable ports per 1RU breakout panel.
