up:: [[Computing MOC]] tags:: #note/develop #on/computing/networking # Network Cables ## Copper UTP Cables The most common type of network cable is the copper UTP cable. It is a cable with 8 copper wires inside. These wires are twisted together into 4 pairs. There is also no metal shield around the wires to protect against electromagnetic interference. UTP stands for *Unshielded Twisted Pair*. - Port and connector commonly called RJ45 (Registered Jack 45) - Actually called 8 Position 8 Contact (8P8C) - Shielded twisted pair exists, but is less common ### IEEE 802.3 (Ethernet) Standards for UTP Cables Some Ethernet standards for UTP cables: | Speed | Speed-derived name | IEEE task group | Informal name | Max cable length | Cable name | | -------- | ------------------ | --------------- | ------------- | ---------------- | ---------- | | 10 Mbps | Ethernet | IEEE 802.3i | 10BASE-T | 100 m | Cat 3 | | 100 Mbps | Fast Ethernet | IEEE 802.3u | 100BASE-T | 100 m | Cat 5 | | 1 Gbps | Gigabit Ethernet | IEEE 802.3ab | 1000BASE-T | 100 m | Cat 5e | | 10 Gbps | 10 Gig Ethernet | IEEE 802.3an | 10GBASE-T | 100 m | Cat 6a | ### Straight-Through and Crossover Cables - Not all Ethernet standards use all four pairs of wires in a cable - Straight-through and crossover cables differ in which pins on one end of a cable connect to which pins on the other end - Straight-through cables - 10BASE-T and 100BASE-T use two wire pairs, one for each direction of communication - The pair connected to pins 1 and 2 - The pair connected to pins 3 and 6 - For devices connected with a straight-through cable, a pin pair on one connector connects to the same pin pair on the other connector - For example, when connecting a PC to a switch: - The PC uses pins 1 and 2 to transmit data (Tx) - The switch uses pins 1 and 2 to receive data (Rx) - The PC uses pins 3 and 6 to receive data - The switch uses pins 3 and 6 to transmit data - Connecting two of the same type of device with a straight-through cable will not work because the Tx pins of one are connected to the Tx pins of the other; there's no Rx pins involved. That's what crossover cables are for. - Crossover cables - Connect opposite pin pairs - Pins 1 and 2 on one end connect to 3 and 6 on the other end - Allows devices that transmit data on the same pin pair to communicate with each other - Below is a table of common device types and their Tx/Rx pin pairs | Device type | Transmit (Tx) pins | Receive (Rx) pins | | ----------- | ------------------ | ----------------- | | Router | 1 and 2 | 3 and 6 | | Firewall | 1 and 2 | 3 and 6 | | PC/Server | 1 and 2 | 3 and 6 | | Switch | 3 and 6 | 1 and 2 | - Usually don't have to worry about whether a cable is straight-through or crossover because of Auto MDI-X (Auto Medium-Dependent Interface Crossover) - Allows a device to change which pins are used for send/receive - 1000BASE-T and 10GBASE-T use all 8 pins in both directions (full duplex), so cable type doesn't matter ## Fiber-Optic Cables - More common for longer-distance connections - Transmit light signals along a glass fiber - Must be handled with care, or you could damage the glass fiber - Fiber-optic cables - Actually uses two cables instead of just one - One for transmitting data, one for receiving data - Connect to Small Form-Factor Pluggable (SFP) transceiver - SFP transceivers are modular and must be purchased separately from devices themselves - Must connect transmitter on one end to the receiver on the other end; no Auto MDI-X here - Two main types - Multimode Fiber (MMF) - Light travels through the cable at multiple angles - Has a wider core than SMF cables - Max distance of up to several hundred meters - Uses LEDs - Single-Mode Fiber (SMF) - Laser points straight through the cable at one angle - Max distance of up to tens of kilometers - More expensive than MMF - Uses lasers ## UTP vs. Fiber - Fiber supports greater distances but at increased cost - UTP more common for end hosts - UTP is vulnerable to EMI - UTP can leak signal; security risk ## References McDowell, Jeremy. *Acing the CCNA Exam*. Vol. 1. Acing the CCNA Exam. Manning, 2024. --- > [!createdat] Created at: [[2025-11-10]]