Networking & Telecommunications Vocabulary: 100 Key English Terms
Networks run on English: device commands, vendor documentation, RFCs, certification exams and trouble tickets all use the same core vocabulary. Network and telecom engineers who know these terms can configure equipment with confidence, follow vendor guides and explain an outage clearly to colleagues, customers and operators abroad.
100 terms
11 topics
41 core terms
200 example sentences
Read, understand, keep going
No account needed. Read the meaning, see where the term is used, then study the examples. Click any word in the lesson for help. You can also select a word and press Alt + Enter.
Network Fundamentals
network
noun
Meaning
A group of computers, phones and other devices that are connected by cables or radio signals so that they can exchange data and share resources.
Where you use it
The most basic word in the field. Engineers design, build, manage and monitor networks, and talk about the office network, the guest network, the core network or the mobile network. As a verb, 'to network' usually means meeting people for your career, not connecting devices.
Examples
The printer isn't on the office network, so nobody can send print jobs to it.
We keep visitors on a separate guest network with internet access only.
Short for local area network: a network that connects devices in a limited area such as a home, an office floor or a single building.
Where you use it
Said as one word, 'lan'. Used for the internal side of a network: LAN ports, LAN cabling, the LAN interface of a router. It is the opposite of WAN. Wireless LAN (WLAN) means the Wi-Fi part of the local network.
Examples
All the PCs on the LAN can see the shared printer, but the laptops on Wi-Fi can't.
Connect the cable to one of the yellow LAN ports, not to the WAN port.
Common phrases
local area network · LAN port · wireless LAN · LAN cable · LAN segment
Short for wide area network: a network that links sites across cities or countries, usually over lines leased from a telecom operator or over the internet.
Where you use it
Said as one word, 'wan'. Companies talk about WAN links between branches, WAN costs and WAN optimisation. On a home router the WAN port is the one that goes to the internet; the other ports are LAN ports.
Examples
Each branch connects to the head office over a 200 Mbps WAN link.
The WAN port on the router is not getting an address from the ISP.
Common phrases
wide area network · WAN link · WAN port · WAN optimisation · WAN connection
A small unit of data sent across a network, made of a header with addressing and control information and a payload that carries part of the actual content.
Where you use it
One of the most frequent words in the field. Packets are sent, received, forwarded, dropped, lost and captured. Strictly speaking, 'packet' is used at layer 3 (IP) and 'frame' at layer 2 (Ethernet), but in conversation people say 'packet' for both.
Examples
The firewall is dropping packets from that subnet.
Large files are split into thousands of packets that may take different paths.
Common phrases
drop packets · forward packets · packet header · packet size · packet loss
Either a physical socket on a device where a network cable is plugged in, or a number from 0 to 65535 that identifies a particular service on a host, such as 443 for HTTPS.
Where you use it
Context tells you which meaning is used. On a switch, ports are up or down, enabled or shut down. In firewall and application work, ports are opened, closed, blocked or listened on: 'Is port 22 open?'
Examples
Port 12 on the second-floor switch is down; can someone check the cable?
The web server only listens on port 443, so plain HTTP requests fail.
Common phrases
open a port · port number · switch port · block a port · listen on a port
A reference model that splits network communication into seven layers, from the physical cable (layer 1) up to the application (layer 7), so that problems and technologies can be described clearly.
Where you use it
Used in training, interviews and everyday shorthand. Engineers say 'it's a layer 1 issue' for a cable problem, or talk about layer 2 and layer 3 switches. The seven layers are physical, data link, network, transport, session, presentation and application.
Examples
Let's go through the OSI model from the bottom: is the cable even plugged in?
In the interview they asked me to explain the seven layers of the OSI model.
Common phrases
OSI layer · layer 2 · layer 3 · OSI reference model · seven-layer model
The layout of a network: how its devices and links are arranged and connected, for example in a star, ring or mesh shape.
Where you use it
Used in design documents, diagrams and change plans. Engineers draw, document and redesign the network topology. Physical topology shows the actual cables; logical topology shows how traffic flows. Most office LANs use a star topology built around switches.
Examples
Please update the topology diagram after you add the new firewall.
The operator uses a ring topology, so traffic can go the other way round if one fibre is cut.
Common phrases
network topology · star topology · ring topology · mesh topology · topology diagram
Any device on a network that has an IP address and sends or receives data, such as a computer, server, phone or printer.
Where you use it
Used in technical documents, commands and error messages: 'host unreachable', 'host not found', the number of hosts in a subnet. In server work 'host' can also mean the physical machine that runs virtual machines, so check the context.
Examples
A /26 subnet gives you 62 usable host addresses.
The scan found 140 active hosts on the office network.
Common phrases
host address · destination host unreachable · remote host · number of hosts
A message sent to every device on the local network segment at once, instead of to a single address; routers do not forward broadcasts to other networks.
Where you use it
Used as a noun and an adjective: broadcast traffic, broadcast address, broadcast domain. DHCP and ARP rely on broadcasts. Engineers keep broadcast domains small with VLANs, because too many broadcasts, or a broadcast storm caused by a loop, can slow down or stop a LAN.
Examples
The loop caused a broadcast storm that took down the whole floor.
Each VLAN is its own broadcast domain, so broadcasts from the cameras don't reach the PCs.
A device that connects different networks and decides, packet by packet, the best path for data to reach its destination, usually based on IP addresses.
Where you use it
Used in every networking context, from home internet to operator backbones. Engineers configure, reboot, replace and upgrade routers, and talk about edge routers, core routers and the router at a branch office. A switch works inside one network; a router moves traffic between networks.
Examples
The branch router lost its connection to headquarters at 9:40.
We need to replace the core routers before traffic doubles next year.
Usage note
Americans usually say /ˈraʊtər/, rhyming with 'outer'; many British speakers say /ˈruːtə/, like 'route' plus -er. Both are correct.
Common phrases
edge router · core router · configure a router · reboot the router · wireless router
A device with many ports that connects computers, phones, printers and other equipment inside the same local network and forwards each frame only to the port where its destination is.
Where you use it
A daily word in LAN work. Engineers talk about access switches on each floor, core switches in the server room, managed and unmanaged switches, and 24- or 48-port switches. The verb 'switch' (to change) also appears often, so context matters.
Examples
Plug the new phones into the access switch on the third floor.
We replaced the old unmanaged switch with a managed one so we can create VLANs.
To set up a device or service by entering the settings it needs, such as addresses, passwords, VLANs and routing, so that it works the way the network requires.
Where you use it
A daily verb. Engineers configure interfaces, ports, VLANs and routing; the noun 'configuration' is usually shortened to 'config': the running config, a config backup. A misconfigured device is behind many outages.
Examples
I've configured the new switch, but I haven't saved the config yet.
Port 8 was configured in the wrong VLAN, so the phone couldn't get an address.
Common phrases
configure an interface · configure a VLAN · running configuration · misconfigured device · save the configuration
A device that converts digital data into signals that can travel over telephone, cable TV or mobile networks, and converts incoming signals back; the name comes from modulator-demodulator.
Where you use it
In strict technical English, a modem only handles the line signal; routing and Wi-Fi are done by a router. Most home boxes from ISPs combine a modem, a router and an access point, and people loosely call the whole box the modem or the router. On fibre lines the device that ends the line is called an ONT.
Examples
Restart the modem first and wait until the DSL light stays green.
The ISP sent a new modem because the old one didn't support the faster line.
Usage note
Turkish speakers call the whole home internet box 'modem'. In English, 'router' or 'Wi-Fi router' is often the more accurate word for that box.
The hardware in a computer or server that connects it to a network, either as a separate card or built into the motherboard, with its own MAC address.
Where you use it
Usually shortened to NIC, said 'nick'. Server engineers talk about dual NICs, 10 Gb NICs and NIC teaming, which combines two NICs for speed or redundancy. In everyday English people also say 'network card' or 'network adapter'.
Examples
The server has two network interface cards, one for production traffic and one for backups.
Device Manager shows a warning on the network interface card, so try updating the driver.
Common phrases
NIC teaming · network card · dual NICs · NIC driver · network adapter
A device or service that spreads incoming traffic across several servers, so that no single server is overloaded and the service stays available if one server fails.
Where you use it
Used by network, server and cloud teams. Servers are put behind a load balancer, which runs health checks and removes unhealthy servers from the pool. Engineers talk about layer 4 and layer 7 load balancers and about methods such as round robin.
Examples
The load balancer marked two web servers as down after their health checks failed.
We'll add a third server behind the load balancer before the campaign starts.
Common phrases
behind a load balancer · load balancer pool · health check · layer 7 load balancer · load-balancing method
A small plug-in module, such as an SFP, that both sends and receives signals, usually converting electrical signals in a switch or router into light for a fibre link.
Where you use it
Engineers order, insert, replace and check transceivers, which are often called 'optics' or named by their form factor: SFP, SFP+, QSFP. A module must match the speed, the fibre type and the distance, and many vendors only fully support their own branded optics.
Examples
The link stays down because the transceiver on the far end is the wrong type.
Check the receive power on the transceiver; the connector may just be dirty.
Common phrases
SFP transceiver · optical transceiver · replace a transceiver · transceiver module · receive power
Short for Power over Ethernet: a technology that sends electrical power and data over the same Ethernet cable, so devices such as access points, IP phones and cameras need no separate power supply.
Where you use it
Spelled out letter by letter. Engineers check the PoE budget of a switch (the total power it can supply), the PoE standard a device needs (802.3af, at or bt) and whether a port is actually delivering power. A switch that runs out of PoE budget will not power new devices.
Examples
The new access points need more power than the old PoE switch can provide.
Check whether port 6 is supplying PoE; the camera has no lights at all.
A set of agreed rules that defines how devices format, send, receive and check data, so that equipment from different vendors can talk to each other.
Where you use it
Used everywhere: routing protocols, network protocols, a protocol stack. Protocols are defined in standards such as RFCs and IEEE documents, and devices support, run or implement them. Many protocol names are acronyms ending in P: TCP, UDP, BGP, DHCP.
Examples
Both sites must run the same routing protocol, otherwise they won't exchange routes.
This old camera only supports outdated protocols, so we're keeping it on an isolated VLAN.
Common phrases
routing protocol · network protocol · protocol stack · support a protocol · run a protocol
Short for Domain Name System: the service that translates names such as example.com into the IP addresses that computers use to find each other.
Where you use it
Spelled out letter by letter. Engineers talk about DNS servers, DNS records, DNS lookups and name resolution. When a website doesn't open by name but works by IP address, DNS is the usual suspect, which is why engineers joke that 'it's always DNS'.
Examples
Users can reach the portal by IP address but not by name, so let's check DNS.
We changed the DNS record last night, but some offices are still seeing the old address.
Common phrases
DNS server · DNS record · DNS lookup · DNS resolution · DNS propagation
Short for Dynamic Host Configuration Protocol: a protocol that automatically gives devices an IP address, subnet mask, default gateway and DNS servers when they join a network.
Where you use it
Spelled out letter by letter. Engineers talk about the DHCP server, a DHCP pool or scope, DHCP leases and DHCP reservations. A typical problem is a pool that runs out of addresses, so new devices get no IP.
Examples
The guest Wi-Fi DHCP pool is full, so new phones aren't getting an address.
Set up a DHCP reservation for the printer so its address never changes.
Common phrases
DHCP server · DHCP pool · DHCP lease · DHCP reservation · DHCP relay
The family of protocols that the internet and almost all modern networks are built on, named after its two best-known members, TCP and IP.
Where you use it
Used when talking about networking in general: the TCP/IP model, the TCP/IP stack, TCP/IP settings on a computer. The TCP/IP model is usually described with four layers and is the practical counterpart of the seven-layer OSI model.
Examples
Every device on the network needs correct TCP/IP settings: an address, a mask, a gateway and DNS.
The course starts with the TCP/IP model before moving on to routing.
Common phrases
TCP/IP model · TCP/IP stack · TCP/IP settings · TCP/IP suite
Short for Transmission Control Protocol: a protocol that sets up a connection and makes sure data arrives complete and in the right order, resending anything that is lost.
Where you use it
Spelled out letter by letter. Web browsing, email and file transfers run over TCP. Engineers talk about TCP ports, TCP sessions, the three-way handshake (SYN, SYN-ACK, ACK) and TCP retransmissions when they analyse slow connections.
Examples
The capture shows a lot of TCP retransmissions, so packets are being lost somewhere.
SSH uses TCP port 22.
Usage note
TCP versus UDP is a classic interview question: TCP is reliable and connection-based; UDP is lighter and faster but does not check delivery.
Short for User Datagram Protocol: a simple, fast protocol that sends data without setting up a connection and without checking whether it arrived; used for voice, video, DNS and gaming.
Where you use it
Spelled out letter by letter. Used when speed matters more than perfect delivery: a late voice packet is useless, so it is better to skip it than to resend it. Firewall rules must say whether a port is TCP or UDP.
Examples
DNS normally uses UDP port 53.
The firewall only allowed TCP, so the UDP traffic for the video calls was blocked.
Short for Address Resolution Protocol: the protocol a device uses on a local network to find the MAC address that belongs to a known IPv4 address.
Where you use it
Usually said as a word, 'arp'. Devices send ARP requests and keep the answers in an ARP table, also called the ARP cache. Engineers check the ARP table to see which IP address belongs to which MAC address. IPv6 uses a different mechanism, Neighbor Discovery, instead of ARP.
Examples
The router's ARP table shows two devices using the same IP address.
Clear the ARP cache on the firewall after you replace the server.
Short for Internet Control Message Protocol: a protocol that network devices use to send error and status messages, such as 'destination unreachable'; ping and traceroute rely on it.
Where you use it
Spelled out letter by letter. Firewalls often block ICMP for security reasons, which makes ping fail even when a host is working. Blocking all ICMP can also break functions such as path MTU discovery, so most teams allow the important message types.
Examples
The server is up, but it doesn't answer ping because ICMP is blocked on its firewall.
The router sent back an ICMP 'destination unreachable' message.
A unique numerical label given to every device on an IP network so that data can be sent to it, for example 192.168.1.20 in IPv4.
Where you use it
One of the first things checked in any troubleshooting. Devices get, release and renew IP addresses, and engineers assign them; they also distinguish public and private, static and dynamic addresses. People often just say 'IP': 'What's the IP of the printer?'
Examples
The laptop has an IP address from the wrong subnet, so it can't reach the file server.
Can you send me the IP address of the camera? I'll add it to the firewall rule.
Common phrases
assign an IP address · public IP address · IP address conflict · get an IP address · renew an IP address
A smaller network created by dividing a larger IP address range, so that groups of devices such as offices, departments or servers can be kept separate and managed more easily.
Where you use it
Used both as a noun and as a verb ('to subnet a network'). Engineers plan, allocate and assign subnets, often written in CIDR form such as 10.20.30.0/24. Devices in different subnets need a router to talk to each other.
Examples
We gave the security cameras their own subnet, 10.20.50.0/24.
The new server is in a different subnet, so traffic has to go through the router.
Common phrases
allocate a subnet · same subnet · subnet calculator · management subnet · subnet a network
The router address that a device sends traffic to when the destination is outside its own subnet; without it, a device can only talk to its local network.
Where you use it
Checked early in almost every connectivity problem: 'Can you ping the default gateway?' Often shortened to 'gateway'. It is usually the first or last usable address of a subnet, and DHCP hands it out together with the IP address.
Examples
The PC has the wrong default gateway, so it can reach local printers but not the internet.
First ping the default gateway, then try an external address like 8.8.8.8.
Common phrases
set the default gateway · ping the default gateway · default gateway address · gateway of last resort
Version 4 of the Internet Protocol, which uses 32-bit addresses written as four numbers from 0 to 255 separated by dots, such as 192.168.10.5; it allows about 4.3 billion addresses.
Where you use it
Said 'eye-pee-vee-four'. It is still the most common version in offices and homes. Because the supply of public IPv4 addresses has run out, operators rely on NAT and private address ranges, and companies buy or lease IPv4 blocks.
Examples
We only have eight public IPv4 addresses, so most services sit behind NAT.
The old devices support IPv4 only, so we can't switch it off yet.
Version 6 of the Internet Protocol, which uses 128-bit addresses written as groups of hexadecimal digits separated by colons, such as 2001:db8::1, giving an almost unlimited number of addresses.
Where you use it
Said 'eye-pee-vee-six'. Mobile operators and large content providers use it widely; many companies run IPv4 and IPv6 side by side, which is called dual stack. Engineers enable, deploy, roll out and troubleshoot IPv6.
Examples
Our mobile customers mostly reach the website over IPv6.
Before we roll out IPv6, we need to update the firewall rules as well.
A number such as 255.255.255.0 that shows which part of an IPv4 address identifies the network and which part identifies the device; it can also be written as a prefix such as /24.
Where you use it
Entered together with the IP address and gateway, or handed out by DHCP. A wrong subnet mask is a classic configuration mistake: the device thinks local hosts are remote, or remote hosts are local. Engineers often just say 'the mask'.
Examples
The server was set up with a /16 subnet mask instead of /24, so it couldn't reach the other offices.
Check the subnet mask: 255.255.255.0 gives you 254 usable addresses.
Common phrases
wrong subnet mask · enter the subnet mask · /24 mask · mask and gateway
Short for network address translation: a method in which a router or firewall rewrites the addresses in packets, typically so that many devices with private addresses can share one public IP address.
Where you use it
Said like the word 'nat'. Engineers configure NAT rules, put servers behind NAT and troubleshoot applications that break behind NAT, such as some VoIP and VPN setups. Operators also use carrier-grade NAT (CGNAT) to share public addresses among many customers.
Examples
All 300 office PCs go out to the internet through NAT on a single public address.
The camera works locally but not from outside because there's no NAT rule for it.
An IP address that is set by hand or permanently reserved for one device, so that it does not change, unlike a dynamic address handed out by DHCP.
Where you use it
Used for servers, printers, network devices and anything that other systems must always find at the same address. Businesses also buy a static IP address from their ISP to host a VPN or a server. Often shortened to 'static IP'.
Examples
Give the new NAS a static IP address outside the DHCP range.
We pay the ISP extra for a static IP address so the branch VPN can always find us.
Common phrases
assign a static IP address · static IP from the ISP · static vs dynamic IP · outside the DHCP range
A NAT rule that sends traffic arriving on a public IP address and port to a specific device and port inside a private network, so that an internal service can be reached from outside.
Where you use it
Common in small offices and home setups: engineers set up, add or remove port forwarding on the router or firewall for cameras, game servers or remote access. Opening ports to the internet carries security risks, so many companies prefer a VPN.
Examples
We set up port forwarding so that port 8443 on the public address goes to the camera recorder.
Remove the old port forwarding rule for RDP; it's a security risk.
Common phrases
set up port forwarding · port forwarding rule · forward a port · open a port
Short for Classless Inter-Domain Routing: the system of writing an IP network as an address plus a prefix length, such as 192.168.0.0/22, which replaced the old fixed address classes.
Where you use it
Usually said like the drink 'cider'. Engineers use CIDR notation everywhere: in firewall rules, routing tables and cloud network settings. The number after the slash shows how many bits belong to the network: a /24 has 256 addresses, a /30 has four.
Examples
Write the subnet in CIDR notation, for example 10.10.0.0/16, not with the full mask.
The cloud team asked for a /20 CIDR block for the new environment.
An IP address from the ranges reserved for internal networks, such as 10.0.0.0/8, 172.16.0.0/12 and 192.168.0.0/16, which cannot be routed on the public internet.
Where you use it
Used every day in office and home networks. Devices with private IP addresses reach the internet through NAT. Problems appear when two companies, or a home and an office, use the same private range and are joined by a VPN, because the addresses overlap.
Examples
The printer has a private IP address, so you can't reach it from outside without the VPN.
Both offices use 192.168.1.0/24 as their private IP address range, so the VPN between them can't route properly.
Common phrases
private IP range · private vs public IP · RFC 1918 address · overlapping address ranges
A hardware address, usually set in a network card at the factory, that identifies a device on a local network; it has 48 bits and is written as six pairs of hexadecimal digits.
Where you use it
'MAC' is said like the word 'mack'. Switches learn MAC addresses and store them in a MAC address table; engineers look up a MAC address to find which port a device is plugged into. Unlike an IP address, it only matters inside the local network.
Examples
Send me the MAC address of the new printer and I'll add a DHCP reservation.
The MAC address table shows the camera on port 17 of the second switch.
Common phrases
MAC address table · look up a MAC address · MAC filtering · learn a MAC address
The process of choosing the path that traffic takes from one network to another, carried out by routers using routes that are either entered by hand or learned from other routers.
Where you use it
Used in phrases like static routing, dynamic routing, routing protocols and routing issues. When traffic goes the wrong way or nowhere at all, engineers say it's a routing problem. Routing and switching together form the core of most networking jobs and certifications.
Examples
Routing between the two data centres is handled by BGP.
The VPN is up, but there's a routing issue: the remote side doesn't know how to reach our subnet.
A list stored in a router or host that shows which networks it knows about and where to send packets for each one, such as the next router or an outgoing interface.
Where you use it
Engineers check or display the routing table when traffic doesn't arrive: 'Is the route in the routing table?' A route can be missing from, added to or removed from the table. The default route is used when no more specific route matches.
Examples
The 10.30.0.0/16 network isn't in the routing table, so the router drops that traffic.
After the OSPF change, the routing table on the core router has twice as many entries.
Common phrases
check the routing table · routing table entry · full routing table · default route
Short for virtual LAN: a separate logical network created on a switch, so that devices plugged into the same hardware, for example staff PCs, guests and cameras, can be kept apart.
Where you use it
Said 'vee-lan'. Engineers create VLANs, assign ports to a VLAN, tag VLANs on trunk links and route between VLANs. VLANs are identified by numbers (1 to 4094 in the 802.1Q standard): 'Put this port in VLAN 20.'
Examples
Cameras are in VLAN 50, so they can't talk to staff laptops directly.
Can you move port 14 to the voice VLAN? A new IP phone is going there.
Common phrases
create a VLAN · voice VLAN · VLAN ID · assign a port to a VLAN · inter-VLAN routing
Short for Border Gateway Protocol: the routing protocol that networks on the internet use to exchange routes with each other, so that traffic can find its way between different operators and companies.
Where you use it
Spelled out letter by letter. Engineers set up BGP sessions with ISPs, advertise prefixes, filter routes and watch for BGP sessions going down. Each network is identified by an autonomous system number (ASN). Mistakes in BGP can make large parts of the internet unreachable.
Examples
We have BGP sessions with two ISPs, so if one fails, traffic moves to the other.
A wrong BGP announcement sent our traffic through another country for an hour.
Short for Open Shortest Path First: a routing protocol used inside one organisation's network, where routers share information about their links and each one calculates the best path itself.
Where you use it
Spelled out letter by letter. Engineers enable OSPF on interfaces, form neighbour relationships (adjacencies), design areas (area 0 is the backbone) and troubleshoot neighbours that get stuck. It is a link-state protocol and chooses paths by cost.
Examples
OSPF picked the slower path because nobody had adjusted the link costs.
The two routers aren't forming an OSPF adjacency; check that the area IDs match.
A route that an engineer enters into a router by hand, telling it exactly where to send traffic for a particular network, instead of letting a routing protocol learn it.
Where you use it
Engineers add, remove and redistribute static routes. They are simple and predictable, so small sites often use only a static default route pointing to the ISP. Their weakness is that they don't adapt automatically when a link fails.
Examples
Add a static route to 10.50.0.0/16 via the VPN firewall.
Someone left an old static route in place, so traffic kept going to the closed office.
Common phrases
add a static route · static default route · floating static route · remove a static route
A switch port that carries traffic for several VLANs over one link, adding a tag to each frame so the device at the other end knows which VLAN it belongs to.
Where you use it
Used for links between switches and to routers, firewalls and virtualisation hosts. The opposite is an access port, which carries a single VLAN for an end device. 'Trunk' is mostly Cisco wording; other vendors often say 'tagged port'. Tagging follows the IEEE 802.1Q standard.
Examples
VLAN 30 isn't allowed on the trunk port to the second floor, so those phones can't register.
Configure the uplink as a trunk port and allow VLANs 10, 20 and 30.
Common phrases
configure a trunk port · trunk link · allowed VLANs · access port · native VLAN
A protocol that stops switches from forming loops by blocking extra paths between them, and opens a blocked path again if an active link fails.
Where you use it
Usually called STP; faster versions are RSTP and MSTP. Engineers set the root bridge, check port states (forwarding, blocking) and investigate spanning tree events after a network slowdown. Without it, a single loop can cause a broadcast storm that brings down a whole LAN.
Examples
Someone plugged both ends of a cable into the same switch, but spanning tree protocol blocked the loop.
We moved from classic spanning tree protocol to RSTP to recover faster after link failures.
Common phrases
spanning tree · root bridge · blocking port · rapid spanning tree · spanning tree loop
Short for software-defined wide area network: an approach that manages a company's WAN links centrally through software and sends each application over the best available link, such as internet, 4G or MPLS.
Where you use it
Said 'S-D-wan'. Companies deploy, migrate to and roll out SD-WAN; engineers set application policies, for example sending video calls over the link with the lowest latency. Branch devices are often installed with zero-touch provisioning: someone plugs them in and they download their own configuration.
Examples
Since we moved to SD-WAN, a single broken line no longer stops sales at a branch.
The SD-WAN policy sends voice traffic over the fibre line and backups over 4G.
One step in the path of a packet, from one router to the next; the number of hops shows how many routers a packet passes through to reach its destination.
Where you use it
Used when reading traceroute output and configuring routing: hop count, next hop, 'the third hop is slow'. Each hop reduces the packet's TTL (time to live) by one, and the packet is discarded when it reaches zero, which stops packets from looping forever.
Examples
Latency jumps at the fifth hop, which is inside the ISP's network.
Set the next hop for this static route to 10.0.0.1.
The common name for wireless local networks based on the IEEE 802.11 standards, which connect devices to a network by radio, mainly in the 2.4, 5 and 6 GHz bands.
Where you use it
Used by everyone, from users to engineers. People connect to and drop off Wi-Fi; engineers plan Wi-Fi coverage, upgrade to Wi-Fi 6 or Wi-Fi 7 and fix weak Wi-Fi in meeting rooms. Engineers often write WLAN in documentation and say 'wireless' in speech.
Examples
The Wi-Fi in the large meeting room drops whenever more than thirty people join.
Guests can use the Wi-Fi, but they can't reach any internal systems.
Usage note
Wi-Fi is a brand name, not an abbreviation; it does not officially stand for 'wireless fidelity'.
Common phrases
connect to Wi-Fi · Wi-Fi coverage · guest Wi-Fi · Wi-Fi signal · Wi-Fi password
A device, usually mounted on a ceiling or wall, that sends and receives Wi-Fi signals and connects wireless devices to the wired network.
Where you use it
Often shortened to AP, said 'ay-pee'. Engineers install, mount, power and manage access points, often from a central wireless controller or a cloud dashboard. A home 'Wi-Fi router' combines a router and an access point in one box.
Examples
We need two more access points to cover the warehouse properly.
The access point in room 204 is offline; it has probably lost PoE power.
Common phrases
install an access point · wireless access point · ceiling-mounted access point · access point placement · wireless controller
Short for service set identifier: the name of a Wi-Fi network, up to 32 characters long, that devices see in their list of available networks.
Where you use it
Spelled out letter by letter. Engineers create, broadcast, hide and rename SSIDs, and usually map each SSID to a VLAN: one for staff, one for guests, one for IoT devices. Too many SSIDs on the same access points waste airtime.
Examples
Visitors should join the 'Guest' SSID, not the corporate one.
We hid the SSID for the barcode scanners so it doesn't appear in people's Wi-Fi lists.
Common phrases
broadcast an SSID · hidden SSID · guest SSID · map an SSID to a VLAN
The fifth generation of mobile network technology, designed to offer much higher speeds, lower latency and support for far more connected devices than 4G.
Where you use it
Said 'five-gee'. Operators roll out, launch and expand 5G, and talk about 5G coverage, 5G spectrum and standalone (SA) versus non-standalone (NSA) 5G. The earlier generations are 4G (LTE), 3G and 2G.
Examples
5G coverage is good in the city centre but drops off quickly near the industrial zone.
The factory is testing a private 5G network for its robots.
The radio equipment and antennas, usually on a mast or rooftop, that connect mobile phones and other devices in a particular area to an operator's mobile network.
Where you use it
Used by radio and mobile network engineers, regulators and the public. In 4G a base station is called an eNodeB, in 5G a gNodeB. People also say 'cell site' or, in everyday American English, 'cell tower'.
Examples
A new base station on the hospital roof should improve coverage in the area.
The power cut took three base stations offline in the north of the city.
Common phrases
base station site · install a base station · mobile base station · base station antenna · cell site
Using a mobile network other than your own operator's, usually abroad; in Wi-Fi, moving from one access point to another without losing the connection.
Where you use it
Mobile operators sign roaming agreements and charge roaming fees, and customers turn data roaming on or off. Wi-Fi engineers tune roaming so that phones and laptops switch smoothly to a closer access point as people walk around a building.
Examples
Turn off data roaming before you land, or the bill could be very high.
Calls drop when people walk to the warehouse, so we need to look at Wi-Fi roaming.
Common phrases
data roaming · roaming agreement · roaming charges · international roaming · seamless roaming
How strong a received Wi-Fi or mobile signal is, usually measured in dBm; values closer to zero are stronger, so -55 dBm is better than -80 dBm.
Where you use it
Used by engineers and users alike: weak signal strength, full bars. Engineers measure signal strength in site surveys and check RSSI values in logs. Strong signal alone isn't enough; interference and noise also affect quality.
Examples
Signal strength in the basement is around -85 dBm, which is too weak for video calls.
The site survey showed good signal strength everywhere except the stairwells.
Common phrases
weak signal strength · measure signal strength · signal strength in dBm · improve signal strength · site survey
Unwanted radio signals that disturb a wireless connection, coming from other access points, neighbouring networks, microwave ovens or other devices that use the same frequencies.
Where you use it
Wi-Fi and radio engineers detect, reduce and avoid interference by changing channels, lowering transmit power or moving clients to the 5 or 6 GHz bands. Co-channel interference happens when nearby access points use the same channel.
Examples
There's heavy interference on channel 6 from the offices next door.
Moving the clients to 5 GHz reduced the interference a lot.
Common phrases
radio interference · co-channel interference · reduce interference · source of interference
The process of moving an active call or data session from one cell or base station to another as the user moves, without the connection dropping.
Where you use it
A key term in mobile network engineering. Engineers analyse handover success rates, failed handovers and handover parameters. American documents often say 'handoff'. In general business English, 'handover' also means passing work to a colleague, for example a shift handover.
Examples
Calls are dropping on the motorway because the handover between the two sites is failing.
The handover success rate improved after we adjusted the neighbour lists.
The standard technology (IEEE 802.3) for wired local networks, which defines how devices send frames over copper or fibre cables at speeds from 10 Mbps up to hundreds of gigabits per second.
Where you use it
Used for wired connections in general: an Ethernet cable, an Ethernet port, Gigabit Ethernet. Copper Ethernet cables (Cat5e, Cat6) use RJ45 connectors and are normally limited to 100 metres per run.
Examples
For the video conference room, use Ethernet instead of Wi-Fi.
The new access points need Gigabit Ethernet ports with PoE.
Usage note
Ethernet is written with a capital E, and in English the first syllable has a long 'ee' sound: /ˈiːθənet/.
A cable that carries data as pulses of light through very thin strands of glass, allowing much higher speeds and much longer distances than copper.
Where you use it
Used across data centres, campuses and operator networks. Fibre optic cables are laid, pulled, terminated, spliced and tested. In speech people mostly say 'fibre': 'Is the building on fibre yet?' A fibre cut during roadworks is one of the most common causes of operator outages.
Examples
A construction crew cut the fibre optic cable between the two sites this morning.
We'll run a fibre optic cable to the warehouse because it is 400 metres away.
Usage note
British English writes 'fibre'; American English writes 'fiber'. Both spellings appear in vendor documents.
Common phrases
lay fibre optic cable · fibre optic link · fibre cut · fibre connection · terminate a fibre
A panel, usually mounted in a rack, where the permanent cables from offices or other rooms end in rows of numbered ports, so that short cables can connect them to switches.
Where you use it
Used by cabling installers and network technicians in comms rooms. Cables are terminated on, labelled on and patched from the patch panel. A messy patch panel full of unlabelled cables makes troubleshooting much slower.
Examples
Desk 3B is on port 24 of the patch panel in the second-floor cabinet.
The installers will terminate all the new Cat6 runs on a 48-port patch panel.
Common phrases
patch panel port · label the patch panel · fibre patch panel · 48-port patch panel · terminate on a patch panel
A short cable with a connector at each end, used to connect devices to each other or to a patch panel, for example a switch port to a patch panel port.
Where you use it
Also called a patch cord or, in speech, just a patch. It comes in copper (RJ45) and fibre versions, in many lengths and colours, and teams often use colours to show the purpose, such as red for firewall links. Faulty patch cables are a surprisingly common cause of errors.
Examples
Swap the patch cable first; the port errors might just be a bad cable.
We need twenty one-metre blue patch cables for the new switch.
A type of optical fibre with a very thin core, about 9 micrometres across, that carries light along a single path and can send data over many kilometres; used by operators and between buildings.
Where you use it
Often written SMF or SM. Engineers must match the fibre type to the optics: single-mode transceivers will not work properly on multimode fibre. Single-mode patch cables are usually yellow, while multimode ones are often orange or aqua.
Examples
The link between the two campuses is 12 km long, so it has to be single-mode fibre.
We ordered the wrong optics: they're multimode, but the building has single-mode fibre.
Usage note
Also spelled 'single-mode fiber' (US) and 'singlemode'. Its partner term is 'multimode fibre' (MMF), used for shorter distances, mostly inside buildings.
To join two optical fibres end to end so that light passes from one to the other with as little loss as possible, usually by melting them together with a fusion splicer.
Where you use it
Used by fibre technicians, as a verb and a noun: splice a fibre, a splice closure, a bad splice. After a cable cut, crews splice the broken fibres back together. Each splice adds a small loss, typically well under 0.1 dB for a good fusion splice.
Examples
The crew has found the cut and will splice the 96 fibres one by one.
The OTDR trace shows a bad splice about 3 km from the exchange.
Common phrases
splice a fibre · fusion splice · splice closure · splice loss · fusion splicer
Short for fibre to the home: a broadband setup in which optical fibre runs all the way to the customer's home, instead of ending at a street cabinet and continuing over copper.
Where you use it
Spelled out letter by letter. Operators roll out, deploy and sell FTTH. Related terms are FTTB (fibre to the building) and FTTC (fibre to the cabinet), where the last part is still copper; the whole group is often written FTTx.
Examples
With FTTH, every flat in the new building can get gigabit speeds.
This street only has FTTC, so speeds drop the further you are from the cabinet; FTTH is planned for next year.
The gradual loss of signal strength as a signal travels along a cable or through the air, measured in decibels (dB), often per kilometre for fibre.
Where you use it
Used in fibre and radio engineering. Engineers calculate a loss budget, measure attenuation with a light source and power meter or an OTDR, and look for high attenuation caused by dirty connectors, tight bends or bad splices.
Examples
Attenuation on the new link is 6 dB higher than expected, so check the connectors.
Single-mode fibre has low attenuation, which is why it works over long distances.
Common phrases
fibre attenuation · high attenuation · measure attenuation · loss budget · attenuation per kilometre
The maximum amount of data a connection can carry in a given time, usually measured in megabits or gigabits per second (Mbps, Gbps).
Where you use it
Used in capacity planning, sales and complaints alike. People buy, upgrade, use up and run out of bandwidth; a link may be short of bandwidth during backups. Bandwidth is the capacity of the pipe; throughput is how much data actually gets through.
Examples
Video calls are using most of the bandwidth on the branch link.
We upgraded the internet line from 100 Mbps to 1 Gbps because we kept running out of bandwidth.
Usage note
Mbps (megabits) and MBps (megabytes) are not the same: a byte is 8 bits, so 100 Mbps is about 12.5 megabytes per second.
Common phrases
increase bandwidth · bandwidth usage · high bandwidth · run out of bandwidth · bandwidth upgrade
The time it takes for data to travel from one point of a network to another, usually measured in milliseconds; lower latency means a faster response.
Where you use it
Very common when talking about voice, video, gaming, trading and cloud applications. Latency is high or low, it increases or spikes, and engineers measure, monitor and reduce it. Users usually say 'lag'; engineers say 'latency'.
Examples
Latency to the Frankfurt data centre jumped from 30 ms to 180 ms this morning.
Satellite links have high latency because the signal travels a very long distance.
The amount of data that actually gets through a connection in a given time, which is usually lower than the bandwidth because of overhead, errors and congestion.
Where you use it
Used in performance tests and capacity reports. Engineers measure, test and improve throughput, often with tools like iperf. A user on a 1 Gbps link may see a throughput of only 300 Mbps because of a slow server or weak Wi-Fi.
Examples
The link is 1 Gbps, but throughput drops to 200 Mbps during backups.
We ran a throughput test between the two sites before accepting the new circuit.
Common phrases
measure throughput · throughput test · maximum throughput · low throughput · throughput drops
A situation in which some packets sent across a network never reach their destination, usually shown as a percentage; it causes slow downloads, choppy calls and frozen video.
Where you use it
Reported in ping results and monitoring tools: '2% packet loss'. Engineers see, measure and investigate packet loss; typical causes are congestion, faulty cables, bad optics and wireless interference. Even 1% loss can make voice calls hard to follow.
Examples
We're seeing 5% packet loss on the link to Ankara, mostly in the evening.
The packet loss disappeared after we replaced the faulty patch cable.
Common phrases
packet loss rate · high packet loss · see packet loss · cause packet loss · intermittent packet loss
Variation in the delay of packets arriving over a network; when packets arrive at uneven intervals, voice and video calls become choppy or robotic.
Where you use it
Measured in milliseconds and watched closely for VoIP and video. Engineers measure, reduce and smooth out jitter, often with QoS and jitter buffers. As a rough guide, many voice systems aim to keep jitter below about 30 ms.
Examples
Latency is fine, but jitter on the branch link is making the audio sound robotic.
After we enabled QoS, jitter dropped from 45 ms to under 10 ms.
Common phrases
high jitter · jitter buffer · measure jitter · latency and jitter
Short for quality of service: a set of techniques that give important traffic, such as voice and video, priority over less urgent traffic when a link is busy.
Where you use it
Spelled out as 'Q-O-S' or said 'kwoss'. Engineers configure QoS policies, mark and classify traffic (for example with DSCP values) and apply QoS on WAN links. QoS cannot create bandwidth; it only decides who goes first when there isn't enough.
Examples
Without QoS, a large file upload can ruin every video call in the office.
We mark voice packets so the QoS policy on the WAN router puts them first.
The point in a network or system where capacity is lowest, so it limits the speed of everything that passes through it, like the narrow neck of a bottle.
Where you use it
Used in performance analysis and capacity planning. Engineers identify, find and remove bottlenecks; once one is fixed, the next slowest part becomes the new bottleneck. Common bottlenecks are WAN links, firewalls and old switches.
Examples
The firewall is the bottleneck: its CPU hits 100% whenever traffic goes above 2 Gbps.
Upgrading the server links won't help if the WAN is the real bottleneck.
Common phrases
performance bottleneck · identify a bottleneck · network bottleneck · remove a bottleneck
A situation in which more traffic is trying to cross a link or device than it can handle, so packets are queued or dropped and everything slows down.
Where you use it
Used in performance discussions, capacity planning and operator reports. Congestion builds up at peak hours, causes latency and packet loss, and is managed with QoS and capacity upgrades. Operators talk about evening congestion, when everyone is streaming video.
Examples
Congestion on the uplink between 8 and 11 p.m. is causing the packet loss.
We added a second 10G link to relieve congestion between the data centres.
Common phrases
network congestion · peak-hour congestion · relieve congestion · congestion control · link congestion
The time it takes for a packet to travel from a source to a destination and for the reply to come back, usually shown in milliseconds; ping reports this value.
Where you use it
Often shortened to RTT. Used in performance tests, SLA reports and application tuning. Engineers compare average, minimum and maximum round-trip times. Distance matters: light in fibre needs about 5 ms to travel 1,000 km one way.
Examples
The round-trip time from Istanbul to London is usually around 50 to 60 ms.
The round-trip time jumps to 300 ms every time the backup runs.
Common phrases
average round-trip time · measure the round-trip time · high round-trip time · RTT
Having extra devices, links or power supplies in place so that the network keeps working if one of them fails.
Where you use it
A key design word: engineers build in, add and test redundancy, and talk about redundant links, redundant power supplies and having no single point of failure. Redundancy only helps if failover actually works, so it should be tested regularly.
Examples
The site has full redundancy: two routers, two firewalls and two ISPs.
We lost the whole branch because the redundant link ran through the same duct as the main one.
Usage note
In general British English, 'redundancy' also means losing your job because your position is no longer needed. In networking it is a positive word: backup capacity.
Common phrases
build in redundancy · redundant link · redundant power supply · full redundancy · single point of failure
Automatic switching to a backup device, link or system when the main one fails, so that the service continues with little or no interruption.
Where you use it
'Failover' is the noun and 'fail over' the verb: 'The firewall failed over to the secondary.' Engineers configure, test and trigger failover; returning to the primary afterwards is called failback. A failover test in a maintenance window shows whether redundancy really works.
Examples
Failover to the backup line took about 30 seconds, and most users didn't notice.
We'll run a failover test on the firewall cluster on Saturday night.
Common phrases
automatic failover · failover test · fail over to the backup · failover time · failback
To send a small test message to another device and wait for a reply, in order to check whether it can be reached and how long the round trip takes.
Where you use it
Used as a verb and a noun: you ping a server, run a ping, or say 'the ping is 40 ms'. Ping uses ICMP echo messages, so a device may be up even if it doesn't answer because ICMP is blocked. In offices, 'ping me' also means 'send me a quick message'.
Examples
I can ping the gateway, but not the DNS server.
The switch replies to ping, so the management interface is up.
Common phrases
ping a server · run a ping · ping test · ping response · continuous ping
To find the cause of a technical problem step by step, usually by testing one possible cause at a time, and then fix it.
Where you use it
A core word in network operations, job adverts and interviews. Engineers troubleshoot a connection, a link or a slow application; the noun is 'troubleshooting'. A common approach is to work up through the OSI layers, starting with the cable.
Examples
We spent two hours troubleshooting the VPN before we found an expired certificate.
Can you help me troubleshoot why the printer keeps dropping off the network?
Common phrases
troubleshoot a problem · troubleshoot connectivity · troubleshooting steps · basic troubleshooting
A period during which a network, a link or a service is not working or cannot be reached by its users.
Where you use it
Used in operations, customer communication and incident reports. Outages are planned or unplanned, partial or total; they are reported, investigated and resolved. Operators publish outage notices, and engineers write a report after a major outage. An outage is the event; downtime is how long the service was unavailable.
Examples
The outage affected about 3,000 customers in the eastern districts for two hours.
We have a planned outage on Sunday night to replace the core switch.
Usage note
Turkish speakers often translate 'kesinti' as 'interruption', but in network operations the usual word is 'outage'.
Common phrases
planned outage · network outage · major outage · power outage · outage report
A diagnostic tool that lists every router a packet passes through on its way to a destination, with the delay to each one, so you can see where traffic slows down or stops.
Where you use it
Used as a noun and a verb: run a traceroute, traceroute to a server. On Windows the command is 'tracert'. It works by sending packets with increasing TTL values, so each hop reports back in turn. Engineers attach traceroute output to tickets they open with ISPs.
Examples
The traceroute stops at the ISP's second hop, so the problem isn't inside our network.
Please run a traceroute to the payment provider's server and paste the output into the ticket.
Common phrases
run a traceroute · traceroute output · traceroute to a host · tracert
To stop working or become unreachable; used for links, servers, services and whole networks. The opposite is 'come back up' or 'be back up'.
Where you use it
Extremely common in spoken and written operations English: 'The link went down at 3 a.m.', 'Is the site down?' Status is often given simply as 'up' or 'down'. A link that keeps going down and coming back up is said to be 'flapping'.
Examples
The main internet link went down at 3 a.m. and the backup took over.
If the core switch goes down, the whole building loses connectivity.
Common phrases
the link went down · go down unexpectedly · be down for maintenance · come back up · the site is down
The total time during which a system, link or service is not available, whether because of a fault or because of planned work.
Where you use it
Used in SLAs, reports and change planning. Teams try to minimise, avoid or schedule downtime; a change may need zero downtime or ten minutes of downtime. Its opposite is uptime, often given as a percentage such as 99.9%.
Examples
The firmware upgrade will cause about 15 minutes of downtime on the branch routers.
Last year's total downtime was only 40 minutes, well within our SLA.
Common phrases
planned downtime · unplanned downtime · minimise downtime · zero downtime · cause downtime
An agreed period, usually at night or at the weekend, when engineers are allowed to make changes that may interrupt service, such as software upgrades and hardware swaps.
Where you use it
Used in change management and customer notices. Teams schedule, request, announce and extend maintenance windows; work must finish, or be rolled back, before the window closes. Operators notify customers about the maintenance window in advance.
Examples
The core router upgrade is scheduled for Saturday's maintenance window, 01:00 to 05:00.
We ran out of time in the maintenance window, so we rolled back the change.
Common phrases
schedule a maintenance window · overnight maintenance window · within the maintenance window · extend the maintenance window
A recording of the actual packets passing through a network interface, saved to a file so that engineers can analyse exactly what was sent and received.
Where you use it
Used when other troubleshooting has not found the cause. Engineers take, open and analyse a packet capture, usually with tools such as Wireshark or tcpdump, and the file is often a .pcap. In speech people say 'grab a capture' or 'take a pcap'.
Examples
Can you take a packet capture on the firewall while the user tries to log in?
The packet capture showed the server was resetting the connections, so it wasn't a network problem.
Common phrases
take a packet capture · analyse a packet capture · pcap file · capture filter
Short for Simple Network Management Protocol: a protocol that lets monitoring systems collect information such as traffic, errors and temperature from network devices, and lets devices send alerts.
Where you use it
Spelled out letter by letter. Monitoring tools poll devices with SNMP, and devices send SNMP traps when something happens, such as a link going down. Versions 1 and 2c use a shared 'community string'; SNMPv3 adds authentication and encryption and is the safer choice.
Examples
The new switches aren't in the monitoring system yet because SNMP isn't configured.
We received an SNMP trap saying the fan in rack 4 has failed.
Continuously checking the health and performance of network devices and links, such as availability, traffic, errors and latency, and alerting engineers when something goes wrong.
Where you use it
Used for both the activity and the tools. Engineers set up network monitoring, add devices to it, set thresholds and respond to alerts. Good monitoring means the NOC notices an outage before the customers call.
Examples
Network monitoring flagged high CPU on the core router twenty minutes before the outage.
Every new device has to be added to network monitoring before it goes live.
Common phrases
network monitoring tool · monitoring dashboard · set up monitoring · monitoring alert · proactive monitoring
Short for internet service provider: a company that sells internet access to homes and businesses, usually over fibre, DSL, cable or mobile networks.
Where you use it
Spelled out letter by letter. Engineers call the ISP, open a ticket with the ISP and check whether a problem is on their own side or the ISP's side. Large companies often use two ISPs for redundancy.
Examples
Traffic stops at the ISP's first router, so the problem is on their side.
We opened a ticket with the ISP about the packet loss on the main line.
Common phrases
call the ISP · local ISP · ISP outage · open a ticket with the ISP · backup ISP
Short for service level agreement: the part of a contract in which a provider promises measurable service levels, such as uptime, repair time and latency, often with penalties if it fails.
Where you use it
Spelled out letter by letter. Customers check whether the provider met or breached the SLA; operators track SLAs for every circuit. An SLA of 99.9% availability still allows almost nine hours of downtime a year; 99.99% allows less than an hour.
Examples
The fibre was cut for six hours, which breaches the four-hour repair time in our SLA.
Before signing, check what the SLA says about latency, not just uptime.
Common phrases
meet the SLA · breach the SLA · SLA penalty · 99.9% SLA · SLA report
The range of radio frequencies that can be used for wireless communication; mobile operators need licences from the national regulator to use particular parts of it.
Where you use it
Used in telecom business, regulation and radio planning. Regulators allocate and auction spectrum; operators acquire it, hold it and refarm it, which means moving it from an older technology to a newer one. Spectrum is described in bands, such as the 700 MHz or 3.5 GHz band.
Examples
The operator bought extra spectrum in the 3.5 GHz band for its 5G network.
Spectrum is expensive, so we have to use every megahertz efficiently.
A telecommunications company that owns or operates a network and carries voice and data traffic for customers or for other operators.
Where you use it
Common in American and industry English: a wireless carrier, a long-haul carrier, carrier-grade equipment. Large companies often buy links from two different carriers for diversity. In radio engineering, 'carrier' can also mean a carrier wave or a block of spectrum, such as a 20 MHz carrier.
Examples
We use two different carriers so that one fibre cut can't take both links down.
The carrier confirmed a fault on their side and sent a field team.
Usage note
In everyday British English, 'operator' or 'telco' is more common than 'carrier'.
The final part of a telecom network that connects the operator's local exchange or street cabinet to the customer's building; it is often the slowest and most expensive part to build.
Where you use it
Used in telecom strategy, regulation and network planning. Operators talk about last-mile access, last-mile technologies (copper, fibre, cable, wireless) and last-mile bottlenecks. The phrase is used even though the distance is rarely exactly one mile.
Examples
The backbone has plenty of capacity; the problem is the old copper in the last mile.
Fixed wireless can be a cheaper last-mile option for rural villages.
The high-capacity core part of a network that connects smaller networks, sites or cities and carries most of the traffic between them.
Where you use it
Used for operator networks (an internet backbone, a national fibre backbone) and for company networks (the campus backbone between buildings). Backbone links are usually the fastest in the network and are built with redundancy.
Examples
The operator is upgrading its national backbone to 400G links.
All buildings on the campus connect to the backbone over two separate fibre paths.
Common phrases
internet backbone · fibre backbone · backbone network · campus backbone · backbone link
High-speed internet access that is always on, delivered over fibre, cable, DSL, mobile or satellite networks, as opposed to old dial-up connections.
Where you use it
Used by operators, regulators and customers: broadband packages, fixed broadband, mobile broadband, broadband speeds. In the UK, 'broadband' is the everyday word for a home internet connection. Regulators publish statistics on broadband subscribers and coverage.
Examples
Fixed broadband subscriptions grew by 8% last year, mostly thanks to fibre.
Most of our customers in the region still get their broadband over copper lines.
Short for Multiprotocol Label Switching: a technique used in operator networks that forwards traffic using short labels instead of full IP lookups; it is widely sold to companies as a private WAN service.
Where you use it
Spelled out letter by letter. Companies buy MPLS circuits or an MPLS VPN from a carrier to connect their branches privately, with QoS and an SLA. Many are now moving part of that traffic to SD-WAN over cheaper internet links.
Examples
All 60 branches connect to the data centre over the carrier's MPLS network.
The MPLS contract ends next year, so we're evaluating SD-WAN.
To set up and make ready a service, line, device or account for a customer, including the equipment, configuration and capacity it needs.
Where you use it
Very common at operators and in cloud work. Teams provision circuits, SIM cards, IP addresses and new customer services; the noun is 'provisioning', as in the provisioning team or provisioning time. A new business fibre line can take weeks to provision.
Examples
The carrier needs ten working days to provision the new 1 Gbps circuit.
Once the order is approved, the system provisions the customer's line automatically.
Common phrases
provision a circuit · provision a service · provisioning team · automated provisioning · provisioning time
Short for network operations centre: the team and room, often staffed 24/7, that monitors a network, responds to alarms and coordinates the repair of faults and outages.
Where you use it
Said like the word 'knock'. Operators, ISPs and large companies run a NOC; engineers call the NOC, escalate issues to it or get paged by it. NOC staff open tickets, contact field teams and post status updates. Its security counterpart is the SOC.
Examples
The NOC noticed the fibre cut within two minutes and sent a field team.
If the link is still down after 30 minutes, escalate to the NOC.
Common phrases
NOC engineer · 24/7 NOC · escalate to the NOC · NOC dashboard · call the NOC
A hardware device or software that checks network traffic against a set of rules and allows or blocks it, protecting a network from unwanted access.
Where you use it
A daily word for network and security teams. Engineers add, change and remove firewall rules, open or close a port on the firewall, and ask whether the firewall is blocking something when an application can't connect.
Examples
The application can't reach the database because the firewall is blocking port 5432.
Please raise a change request before adding a new firewall rule.
Common phrases
firewall rule · open a port on the firewall · next-generation firewall · firewall policy · blocked by the firewall
Short for virtual private network: an encrypted connection over a public network such as the internet, used to link sites securely or to let remote staff reach internal systems.
Where you use it
Spelled out letter by letter. Staff connect to the VPN or are 'on VPN'; engineers set up site-to-site VPNs between offices and remote-access VPNs for users. A VPN tunnel can go down, keep dropping or fail to come up because the settings on the two sides don't match.
Examples
You need to be on the VPN to open the internal dashboard from home.
The site-to-site VPN to the Izmir office has been down since midnight.
Common phrases
connect to the VPN · VPN tunnel · site-to-site VPN · remote-access VPN · VPN client
Short for access control list: an ordered list of rules on a router, switch or firewall that permits or denies traffic based on things like source, destination, protocol and port.
Where you use it
Spelled out letter by letter. Engineers write ACLs, apply them to interfaces in the inbound or outbound direction and keep them up to date. Rules are checked from top to bottom and the first match wins; on many devices an invisible 'deny all' rule sits at the end, so anything not explicitly allowed is dropped.
Examples
The new ACL blocks traffic from the guest VLAN to the server subnet.
Monitoring stopped working after the change because the ACL didn't permit SNMP.
Common phrases
apply an ACL · inbound ACL · ACL entry · permit and deny rules · implicit deny
Short for demilitarised zone: a separate network segment between the internet and the internal network, where public-facing servers such as web or mail servers are placed.
Where you use it
Spelled out letter by letter. Servers are placed in or moved to the DMZ, so that if one is compromised, an attacker still has to get past the firewall to reach internal systems. Firewall rules usually allow traffic from the internet into the DMZ but strictly limit traffic from the DMZ inwards.
Examples
The new web server will sit in the DMZ, not on the internal network.
Only port 443 is open from the internet to the DMZ.
Common phrases
DMZ network · place a server in the DMZ · DMZ segment · DMZ firewall rules
An attack in which huge amounts of traffic from many compromised devices are sent to a target at the same time, so that its links or servers are overwhelmed and real users cannot get through.
Where you use it
DDoS stands for distributed denial of service and is said 'dee-doss'. Operators and companies detect, absorb and mitigate DDoS attacks, often with scrubbing services that clean the traffic before it reaches the customer. Attacks are described by their size in Gbps or in packets per second.
Examples
A DDoS attack filled our internet links for 40 minutes before mitigation kicked in.
The ISP offers DDoS protection that filters attack traffic inside their network.
Ten questions from this glossary. Pick the right meaning for each term and see your score.
How to learn networking & telecommunications vocabulary
Read real texts from the field regularly: vendor configuration guides, release notes, RFC summaries, operator status pages and the outage reports that large providers publish.
Learn verbs together with the nouns engineers combine them with: configure an interface, bring up a link, run a traceroute, open a ticket, provision a circuit.
Keep apart the pairs that look similar: bandwidth and throughput, latency and jitter, router and switch, outage and downtime. Interviews and certification exams often test exactly these.
Say acronyms the way teams do: LAN, WAN, VLAN and NAT are said as words, while DNS, DHCP, BGP and VPN are spelled out letter by letter.
Practise writing short status updates in English: what is affected, since when, what you have checked and when the next update will come.
Frequently asked questions
How can I learn English vocabulary for networking and telecoms?
Read real texts from the field and notice how the words are used: vendor configuration guides, release notes, RFCs, certification study material and operator status pages. Learn each term with its usual partners (configure an interface, run a traceroute, open a ticket with the carrier) and use the new words in your own tickets, change requests and status updates.
Which networking terms should I learn first?
Start with the words you will hear every day: network, router, switch, IP address, subnet, bandwidth, latency, DNS, DHCP, firewall and outage. Then move on to routing and switching (VLAN, routing table, BGP, OSPF), wireless and fibre vocabulary, and finally operator terms such as SLA, backbone and provisioning. The terms in this glossary follow the same order, from most to least essential.
What is the difference between bandwidth, throughput and latency?
Bandwidth is the maximum capacity of a link, for example 1 Gbps. Throughput is how much data actually gets through, which is usually lower. Latency is how long data takes to travel from one point to another, measured in milliseconds. A link can have plenty of bandwidth and still feel slow if its latency is high.
Do network engineers in Turkey use English or Turkish terms?
Mostly a mix. Device names, commands and protocols usually stay in English in daily speech: router, switch, VLAN, trunk, ping, BGP and config. Other words have well-established Turkish equivalents, such as bant genişliği, gecikme, alt ağ, güvenlik duvarı, kesinti and baz istasyonu. Contracts, tenders and regulatory documents prefer the Turkish terms, so it pays to know both.
Is 'router' pronounced 'rooter' or 'rowter'?
Both are correct. Most Americans say 'rowter' /ˈraʊtər/, rhyming with 'outer', while many British and Australian speakers say 'rooter' /ˈruːtə/. The same variation is heard with 'route' and 'routing'. Choose one and use it consistently; nobody in the field will misunderstand you.
