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Bel Stewart Connector 11118 Susquehanna Trail South Glen Rock, PA 17327 Tel: 717.235.7512 Page 1 Bel Stewart Connector May 1 2012 Network Connectors Interfaces and Differential to Common Mode Conversion AN12012
Bel Stewart Connector 11118 Susquehanna Trail South Glen Rock, PA 17327 Tel: 717.235.7512 Page 2 Network Connector Interfaces and Differential to Common Mode Conversion Abstract The paper describes standard connector interfaces used in the networking including category 6a RJ45 and category 7a ARJ45. It discusses the differences between connectors within the networking equipment and premise wiring channels that share the same interface. The paper provides data for the Transverse Conversion Loss contribution of the interfaces within the twisted transmission media up to 2000 MHz. The effects of the Differential to Common Mode Conversion (DCMC) on the network performance are discussed . The TCL can be reduced by utilizing a balanced RJ45 interface and further improved by utilizing a higher level category 7a interface. The Ethernet systems from 1 to 40 GbE shall benefit from the reduction of the TCL and corresponding common mode noise Internet over Copper Wire Channels Close to 1 billion users are connected to the Internet today. Many of them are connected through copper-wire channels either leading to a final user or a part of the infrastructure. The Internet is built upon the standardized Ethernet protocols described in the IEEE 802.3 standards. The move toward the 40 and 100 GbE requires better and faster connectivity and lower noise. The Ethernet signals utilize differential mode transmission. Each differential channel consists of two conductors, and requires a balance within the transmitter or receiving pair, or, in electrical terms, the characteristic impedance of each conductor within the channel shall be equal, typically 50 Ohm. If the balance is violated that results in transformation of a portion of the original signal energy into the parasitic common mode noise. The common mode conversion worsens the transmission by reducing the signal strength and adding to the noise. In order to focus on the relation between the interfaces and DCMC we limit this discussion to the application spectra above 500 MHz. Interfaces and Connectors The interface between a network appliance and the premise wiring is an interface between the building cabling infrastructure and equipment such as a switch or computer. For the user, it is simply a port where a patch cord is plugged into the network device. Unfortunately it is not simple. In fact, there are two networking interfaces, which have rather complex electrical and mechanical characteristics where the mechanical structures directly impact the transmission performance. The networking equipment connectors are not covered by the premise wiring standards.
at the Premise Wiring cable side. The first interface is the interruption and disturbance of the twisted pair media. such connectors are referred to as Integrated Connector Modules (ICM). but look and function differently. What they have in common are the interfaces. particular, in the Power-over-Ethernet (POE) applications. be robust and be easy to use by millions of people. Table 1. Transmission classes, categories and interfaces
10 GbE
10 GbE over 100 m
Figure 1. The connector interfaces and applicable international standards of ARJ45 are identical to RJ45. opposite side of the cavity. mechanical switch within the category 7 connector, shown in figure 2.
interface is described by ISO 61076-3-114. Figure 2. Category 7a to 6a plugs combined in a single patch cord The Major Difference between Category 7a and Lesser Categories. shielded and unshielded designs.
the Transverse Conversion Loss (TCL), or Sdc11 as an S-parameter. Table 2. TCL in the standards Both standard expressions yield the same values shown in table 3 below.
such as ferrite, on all sides of the channels within the windings. not have a resistive component and consists of the inductance and capacitance. Figure 4. Differential Impedance of a balanced twisted pair
Figure 5. INTERFACE GEOMETRY vs. ELECTRICAL STRUCTURE differential pairs defined as contacts 1-2, 3-6, 4-5, 7-8. The result is a skew and the degradation of the TCL. balance of a twisted pair cable.
propagation velocity from the differential signal. It also has an arbitrary phase. EMI and jitter. As a contributor to the Alien NEXT it may cause bit errors. and potential increases in the useful channel length. established a theoretical limit for Sdc11 as 98 dB at 1000 MHz. used instead of data of unbalanced Category 6a connectors. Table 4. Test data: selected (worst) TCL values of Network Connectors, dB
Bel Stewart Connector 11118 Susquehanna Trail South Glen Rock, PA 17327 Tel: 717.235.7512 Page 12 Summary The Transverse Conversion Loss defines the interface as a source of Differential to Common Mode Conversion. The common mode noise negatively affects the network transmission. The Internet traffic from 1 GbE to 10 GbE and, in particular, new 40 GbE systems should benefit from balanced category 6a connectors. In the frequency spectra above 500 MHz the category 7a connectors can provide improvement of over 15 dB in comparison to category 6a and extend the channel bandwidth to 2000 MHz and above Authors Yakov Belopolsky , Manager, Research & Development, Member of the US TAG and a member of the ISO/IEC committees on Connectors and Cabling. Yakov published over 30 technical papers and awarded 78 US patents. Rich Marowsky, Principal Electrical Engineer, Member of the TIA committees. Rich has over 35 years experience in Development, Simulation, and Testing High Speed Connector Products for Computer Systems and the Premise Wire Industry Bel Stewart Connector, Glen Rock, PA , USA