Rack of Ethernet switches.

Network and Telecommunication Cables

Cables, cables, cables!

High-speed serial, Ethernet, Fiber, DS3, OC3, and even telco punchdown cables. Here is how to make sense of data communication cables used for raw device-to-device connections and also for running TCP/IP network protocols.

First, the fundamentals: Below is an ANSI/TIA/EIA-422-B (formerly RS-422) or ITU-T V.35 serial cable for connecting a Cisco router's serial port to a T1/DS1 interface.

Cisco V.35 or ANSI/TIA/EIA-422-B (formerly RS-422) or ITU-T V.11 serial cable.

The V.35 interface is now specified as ITU-U V.11. V.35/V.11 is for data communication at speeds up to 10 Mbps.

This type of cable has a DB-60 connector at the router end, and a Winchester block connector at the network interface end. Cisco's description including pinouts is here.

Cisco V.35 or ANSI/TIA/EIA-422-B (formerly RS-422) or ITU-T V.11 serial cable.
Category 6 (or cat-6) Ethernet cable.

Here is one end of a Category 6 Ethernet cable, or more formally, ANSI/TIA/EIA-568-C.1. The connector is informally known as an RJ45. To be pedantic, it is really an 8P8C modular connector.

Why is "RJ45" incorrect? The RJ45 standard refers to the physical connector and the wiring pattern. A true RJ45 was used for an analog telephone connection and was intended for use with a high-speed modem. Pins 5 and 4 were the tip and ring, respectively, of a single telephone line, and pins 7 and 8 were a programming resistor.

The wiring of a true 8P8C connector is:

Pin EIA T568A EIA T568B
Wire, of pair Color Wire, of pair Color
1 1 of 3 white/green 1 of 2 white/orange
2 2 of 3 green 2 of 2 orange
3 1 of 2 white/orange 1 of 3 white/green
4 2 of 1 blue 2 of 1 blue
5 1 of 1 white/blue 1 of 1 white/blue
6 2 of 2 orange 2 of 3 green
7 1 of 4 white/brown 1 of 4 white/brown
8 2 of 4 brown 2 of 4 brown
To make a crossover cable, wire one end as T568A and the other as T568B.

Right to left in the picture above, or top to bottom in the picture below, are pins 1 through 8.

10BASE-T (Ethernet) and 100BASE-TX (Fast Ethernet) use wire pairs 2 and 3, or wires 1/2 and 3/6.

10BASE-T uses two differential voltages: +2.5V or -2.5V, signalling at 10 Mbaud.

Electrical characteristics for Cat.5e
Property Value
Impedance at 100 MHz 100±15Ω
Capacitance at 800 Hz 52 pF/m
Inductance 525 nH/m
DC resistance ≤0.188Ω/m
Propagation speed 0.64c
Propagation delay 4.8-5.3 ns/m

100BASE-TX uses three differential voltages: +1V, 0V or -1V. 4B5B binary encoding generates a signal clocked at a 125 MHz symbol rate. Data bits are grouped into groups of 4 bits each, each data block converted to a 5-bit block guaranteed to have at least two transistions and solve problems of receiver clock synchronization, DC equalization, and spectrum shaping.

1000BASE-T (Gigabit Ethernet) uses all four wire pairs, signaling with 5-level pulse amplitude modulation at a 125 Mbaud symbol rate.

Category Bandwidth
3 16 MHz
4 20 MHz
5, 5e 100 MHz
6 250 MHz
6a 500 MHz
7 600 MHz
7a 1000 MHz

All these standards should be able to communicate over cables up to 100 meters long. Cables are rated in terms of their RF bandwidth rather than supported bit rate, as listed in the table at right.

The wire pairs are twisted together to create a bundle of balanced transmission lines and reduce crosstalk between pairs. The twisting is at 1.5-2 cm per turn.

The wires are #24 AWG or 0.205 mm², rated for 0.577 A maximum current.

Category 6 (or cat-6) Ethernet cable.

8P8C connector, pins 1 through 8 from top to bottom.

Category 6 (or cat-6) Ethernet cable.
Category 6 (or cat-6) Ethernet cable.
Category 6 (or cat-6) Ethernet cable.

The blue and green cables here are Category 6 Ethernet cables plugging into a bank of Cisco switches, along with four fiber optic lines (smaller diameter yellow and orange lines).

Category 6 (or cat-6) Ethernet cable plugging into Cisco switches.
Category 6 (or cat-6) Ethernet cable plugging into Cisco switches.
Fiber optic network interfaces.
Fiber optic network interfaces.

Above are fiber optic network connections.

Below are, first, ANSI/TIA/EIA-422-B serial connections to three Cisco routers.

Then, a Fujitsu FLM 600 MD / 2400 LS OC-12 SONET ring and FLM-150 SONET interfaces.

ANSI/TIA/EIA-422-B (formerly RS-422) or ITU-T V.11 serial connections to a bank of three Cisco routers.
Fujitsu OC-12 SONET ring.
Fujitsu OC-12 SONET ring.
Fiber optic network interfaces.

This is a Tsunami 100 5.3/5.8 GHz wireless Ethernet bridge mounted above a Cisco Catalyst 2950 switch with 24 Ethernet ports and two fiber ports.

Tsunami 100 5.3/5.8 GHz wireless Ethernet bridge.

Below is an ATM switch and a Cisco Catalyst 48-port Ethernet switch.

ATM switch
Cisco Catalyst 48-port Ethernet switch.

At below are DS3 and OC3 router interfaces on a Lucent Packetstar AX 600 and a Cisco 7204.

Cisco DS3/OC3 interfaces.
AX600 DS3/OC3 interfaces.
AX600 DS3/OC3 interfaces.
AX600 DS3/OC3 interfaces.

Here are some telecommunications punchdown blocks.

The first panel is relatively simple and widely spaced as these things go.

The large panel shown overall and in detail below is at a major conference center.

Telecommunications or telco punchdown blocks.
Telecommunications or telco punchdown blocks.
Telecommunications or telco punchdown blocks.

Finally, here is a random collection of dangling Ethernet and fiber lines:

Yellow and orange network cables and fiber optic lines hanging from stacks of networking equipment in multiple racks.
Yellow and orange network cables and fiber optic lines hanging from stacks of networking equipment in multiple racks.
Telecommunications and networking room with racks of switches and routers, telco punchdown blocks, and a Linux firewall.

If you like this, make sure to see my page showing the telecommunications infrastructure in Manhattan.

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