The cross-point is the core element used in making and breaking all connections. There are three different cross-point technologies available for copper cross-connects:

• Solid-state analog intermediate cross-connects (ICs)
• Latching relays (both standard and micro relays)
• Stepper motor with pin connect/disconnect control

Each of these technologies has its place in particular applications. The following sections compare these technologies.

Solid-State IC as Copper Cross-Point

Solid-state analog IC cross-points are practical when high-frequency signals are involved and physical size is an issue but are not recommended when high voltage such as plain old telephone service (POTS) ring voltage is required to be switched, nor when connections must be maintained during power outages.

Usage

These types of cross-connects are best suited for local-area network (LAN) and LAN/wide-area network (WAN) test access, digital subscriber line (DSL), trunk level 1 (T-1), etc. connectivity when power outage is not an issue.

Advantages

• Able to support high-frequency signals
• Minimal rack space requirement
• Fast cross-connect switching speed
• Cost-effective in both high- and low-density cross-connects
• Good meantime between failure (MTBF)

Disadvantages

• Cannot support high-voltage signals such as POTS ring voltage without special protection circuitry that would make it protocol- and/or signal-dependent
• Loses connections during power outages
• May alter the signal that is switched
• Consumes power at all times

Latching Relay as Copper Cross-Point (Standard and Micro Relays)

Latching relay–based products are bulky and not suitable for applications that require high port densities. Latching relays are sensitive to vibration that may cause unintended relay-state changes. Vibrations may be caused by physical contact or may be inherent to the location such as in earthquake regions. Unintended state changes are not communicated back to the control software, and as a result, the cross-point database may become incorrect. Frequencies in the signal transmitted through the relay or from external sources can equal the resonant frequency of the relay itself and may cause the relay to switch states uncontrollably (known as chattering).

Micro relays are smaller but are still bulkier than robotic technologies. Their small size dictates that micro relays have a lower breakdown voltage to the extent that products incorporating this technology may not properly support POTS ring voltage nor pass certain isolation voltage requirements.

Usage

These types of cross-points are best suited for small switches such as metallic test access units (MTAUs) for WAN, DSL, T-1, etc. or for exception switches. Advantages

• Able to support high-frequency signals
• Can support high voltage in the standard relay case
• Fast cross-connect switching speed
• Maintains connectivity during power outage
• Low power requirements
• Does not interfere with signals when designed properly
• Good MTBF

Disadvantages

• Relays are bulky
• Still an expensive alternative for larger cross-connects
• Micro relays may not support high voltage such as POTS ring voltage
• Microrelays may not pass isolation voltage requirements
• May be prone to larger crosstalk and return loss (reflections) values depending on the design (due to larger product size and thus longer printed circuit board [PCB] traces)
• Prone to vibration and can actually change state without warning
• Prone to resonance and may vibrate on and off uncontrollably (also know as chattering)

Stepper Motor with Pin Connect/Disconnect Control as Copper Cross-Point

Products designed around this technology allow for high port densities and extremely large matrix sizes, while keeping costs low and utilizing minimal rack space. Although switching speed is lower than the other solutions, this may only impact the speed of test access connection and has little to no significance in most other telecommunications applications. Overall cross-connect reliability can be designed to be extremely high even though mechanical wear limits the reliable lifetime of individual pins, holes, and robotic mechanisms. High MTBF levels have been achieved by using a multiple-path cross-connect architecture coupled with intelligent path selection.

Usage

These types of cross-points are best suited for higher-density cross-connects and lend themselves well to designing any-to-any cross-connects that require many cross-points. These designs keep port density high while keeping costs relatively low and physical rack space at a minimum.

Advantages

• Well suited for high density any-to-any cross-connects
• Maintains connectivity during power outage
• Able to support high-frequency signals
• Can support high voltage and current
• Low power requirements
• Efficient rack space usage
• Cost-effective
• Good MTBF

Disadvantages

• Slower cross-connect switching speed
• Cross-connect design must incorporate methods to maintain high reliability even though individual component life is limited by physical wear.