Uplink vs. Downlink
A downlink is a connection made in the opposite direction of an uplink, either from a satellite to the ground or from an outside network into a local network. Internet downloads, for example, travel over a downlink to the downloading device, while internet uploads travel over uplink connections. Uplinks are commonly used in satellite telecommunications to broadcast satellite radio and television. Broadcasters transmit signal feeds from ground stations to the orbiting satellite, a process known as satellite uplink. Cellular and other wireless broadband service providers sometimes refer to the upstream communication path of a network as uplink transmission. These uplinks may carry text messages, internet file uploads, and other data sent through the provider network.
Uplink Ports on Computer Networks
Some computer network hardware feature uplink ports designed for plugging in network cables. These ports allow a network to communicate with other outside networks. Uplink ports on home routers, for example, allow a connection to broadband modems and the internet. Ethernet hubs, switches, and routers traditionally designate one Ethernet port as the uplink connection. That port is marked on the unit by name or color. Home broadband routers usually label this port as WAN or “Internet” instead of uplink, but the concept and function are the same.
When to Use an Uplink Connection
Uplink connections can be used to:
Connect a broadband modem to a home router for internet access. Connect one uplink device (a router, switch, or hub) to another. Plug the uplink port of one switch, for example, into the standard port of another switch to expand the network size.
When Not to Use an Uplink Connection
Conversely, uplink connections should generally not be used to:
Connect two uplink ports to each other.Connect a computer to an uplink port.
Bi-directional Connections
In modern computer networks, connections are bi-directional. For connections to an uplink port, the same cable or wireless link can transfer data from and to devices on either end, rather than only up or down. The terms uplink and downlink here apply to which end of the connection initiates a data transfer. Networking professionals may point out that an Ethernet crossover cable can be used to connect a computer to an uplink port or connect two uplink ports to each other. While technically correct, the usefulness of this type of connection is limited.
Dual-Purpose and Shared Uplink Ports
The traditional hardware logic of an uplink port supports only network uplink devices. However, many modern home broadband routers offer a dual-purpose port instead, one that functions either as an uplink or as a standard port depending on the type of device connected to it. Before dual-purpose ports became popular, some older network equipment configured a standard port next to the uplink one and linked the two together as a pair. The hardware logic of these products supported connections to either the uplink port or to the standard shared port, but not both. Connecting devices to both ports of a shared port device stops the unit from functioning properly.
