Broadband Jargon Glossary

A-F

ADSL (Asymmetric Digital Subscriber Line): The old, slow broadband delivered over copper telephone wires. Maximum speed around 24Mbps download, usually much less. Being phased out across the UK.

AltNet (Alternative Network): Any broadband infrastructure provider that is not Openreach or Virgin Media. CityFibre is the largest AltNet in the UK. See our AltNets guide.

Backhaul: The high-capacity connection between your local exchange and the wider internet. ISPs that buy more backhaul capacity deliver more consistent speeds at peak times.

CGNAT (Carrier Grade NAT): A technique where your ISP shares a single public IP address across many customers. This can cause problems for gaming and hosting. See our CGNAT guide.

Contention Ratio: The number of customers sharing the same bandwidth pipe. A lower ratio means less slowdown during busy periods.

CPI (Consumer Prices Index): The measure of inflation used by many ISPs to justify annual mid-contract price rises, often “CPI + 3.9%.”

CSP (Customer Splice Point): The small grey box mounted on the outside wall of your house during a fibre installation. It protects the join between the external and internal fibre cables.

DOCSIS (Data Over Cable Service Interface Specification): The technology Virgin Media uses to deliver broadband over coaxial cable. Fast, but not as reliable or symmetrical as full fibre.

FTTC (Fibre to the Cabinet): Fibre runs to the green street cabinet, but the final stretch to your house uses old copper wires. Maximum speed around 80Mbps. See our FTTC vs FTTP guide.

FTTP (Fibre to the Premises): Fibre runs all the way into your home. No copper involved. This is what CityFibre builds. Speeds of 1Gbps and above are standard.

G-O

GPON (Gigabit Passive Optical Network): An older fibre technology capable of up to 2.5Gbps shared across multiple homes. Being replaced by XGS-PON on newer networks.

IPv4 / IPv6: Internet Protocol version 4 and version 6. IPv4 addresses (like 192.168.1.1) have run out globally. IPv6 is the replacement with a virtually unlimited address space.

ISP (Internet Service Provider): The company you buy broadband from. On CityFibre’s network, ISPs include Vodafone, Zen, TalkTalk, Giganet, and many others.

Jitter: Variation in ping/latency over time. High jitter causes stuttering in video calls and rubber-banding in games. Full fibre connections have very low jitter.

Latency (Ping): The time it takes for data to make a round trip between your device and a server. Measured in milliseconds (ms). Lower is better. See our latency guide.

Mbps / Gbps: Megabits per second / Gigabits per second. The standard unit for measuring internet speed. 1 Gbps = 1000 Mbps. Note: this is bits, not bytes. Divide by 8 to get the file download speed in MB/s.

ONT (Optical Network Terminal): The small white box mounted inside your home during a fibre installation. It converts the light signal from the fibre cable into an electrical signal your router can use. Essentially your fibre “modem.”

Open Access: A network model where multiple ISPs can sell services over the same physical infrastructure. CityFibre operates an Open Access network, giving consumers a choice of provider.

P-Z

Packet Loss: When data packets fail to reach their destination. Causes buffering, disconnections, and lag. Almost non-existent on full fibre but common on old copper and wireless connections.

Peering: Direct connections between ISPs and content providers (like Netflix or gaming networks). ISPs with good peering arrangements deliver faster, more direct routes to popular services.

PON (Passive Optical Network): A fibre network architecture that uses unpowered splitters to serve multiple homes from a single fibre strand. “Passive” because no electricity is needed between the exchange and your home.

QoS (Quality of Service): A router feature that prioritises certain types of traffic (e.g., video calls or gaming) over less time-sensitive traffic (e.g., file downloads).

Static IP: A fixed IP address permanently assigned to your connection. Useful for hosting servers or remote access. See our static IP guide.

Symmetrical Speed: When your upload speed matches your download speed. Common on CityFibre, rare on Openreach and Virgin Media. See our symmetrical speeds guide.

VoIP (Voice over Internet Protocol): Phone calls made over your internet connection instead of a traditional copper phone line. See our VoIP guide.

WAN Port: The port on your router where you plug in the Ethernet cable from your ONT. Most routers have a 1 Gbps WAN port; for speeds above 1 Gbps you need a 2.5 Gbps port.

Wayleave: Permission granted by a property owner for infrastructure (like fibre cables) to pass through or be installed on their land. Renters need their landlord to agree to this.

XGS-PON (10-Gigabit Symmetric Passive Optical Network): The latest fibre technology deployed by CityFibre. Capable of 10 Gbps in both directions. This is the infrastructure that future-proofs the network for decades to come.