Both Cat-5 and Cat-5e cables are defined by TIA/EIA standards, but with critical differences:

// Standards reference:
TIA/EIA-568-A (Legacy) → Cat5
TIA/EIA-568-B (Current) → Cat5e

While both operate at 100MHz bandwidth, Cat-5e implements stricter specifications:

• Improved Near-End Crosstalk (NEXT) performance: Minimum 3dB better than Cat5
• Power Sum NEXT (PSNEXT) requirements (new in Cat5e)
• Return Loss and Equal Level Far-End Crosstalk (ELFEXT) specifications

The practical difference manifests in 1000BASE-T support:

// Network interface check (Linux example)
$ ethtool eth0 | grep -i speed
    Speed: 1000Mb/s (requires Cat5e for reliable operation)
    
// Cisco switch port configuration
interface GigabitEthernet0/1
 speed auto  (auto-negotiates based on cable quality)

While not visually distinguishable, Cat5e typically uses:

• Tighter pair twists (varies by manufacturer)
• Improved insulation materials
• Sometimes includes a spline (not required by spec)

Proper certification requires specialized equipment:

// Sample cable test results (simplified)
Test Parameter      Cat5 Pass  Cat5e Pass
-----------------------------------------
NEXT @ 100MHz       ≥32.3dB    ≥35.3dB
PSNEXT @ 100MHz     N/A        ≥32.3dB
Return Loss         ≥8.0dB     ≥10.0dB

For modern networks:

1. Always use Cat5e or better for new installations
2. Existing Cat5 may work for Gigabit over short runs (<25m)
3. For PoE applications, Cat5e provides better heat dissipation

The fundamental difference lies in the TIA/EIA-568-B standard's enhanced specifications for Cat-5e. While both support 100MHz bandwidth, Cat-5e implements stricter requirements for:

• Crosstalk reduction (NEXT/FEXT improvements of 3dB minimum)
• Impedance stability (100±15Ω vs Cat-5's looser tolerance)
• Return loss (minimum 20.1dB at 100MHz vs Cat-5's 16dB)

While Cat-5 can sometimes handle 1000BASE-T, Cat-5e guarantees it through four-pair signaling:

// Example cable test output (simplified)
void testCableSpecs(CableType type) {
    if (type == CAT5E) {
        assertTrue(crosstalk <= -35.3dB);
        assertTrue(returnLoss >= 20.1dB); 
    } else {
        // Cat-5 has no formal gigabit requirements
    }
}

Marketing claims about "350MHz Cat-5e" refer to proprietary enhanced cables, not the TIA standard. True Cat-5e certification requires:

• 100MHz base bandwidth
• PSNEXT (Power Sum NEXT) compliance
• ELFEXT (Equal Level FEXT) measurements

Despite popular belief, the wiring pattern doesn't determine category rating. Both standards work with either cable type:

// Correct RJ45 pinout implementation
enum WiringStandard {
    TIA_568A = [3,2,1,4,5,6,7,8], // Green pair first
    TIA_568B = [1,2,3,4,5,6,7,8]  // Orange pair first
}

When upgrading infrastructure:

1. Existing Cat-5 may work for gigabit in short runs (<50m)
2. New installations should use Cat-5e minimum
3. Test for actual performance, not just printed ratings