From a basic point of view, a leased line WAN works a lot like an Ethernet crossover cable connecting two routers, but with few distance limitations. Each router can send at any time (full-duplex) over the leased line, for tens, hundreds, or even thousands of miles.

leased line
Nowadays the term service provider is rather used



Leased Line Service

Used 2 pairs of wires (full-duplex)


Channel Service Unit / Data Service Unit Can be integrated into the router (serial interface) Or external
Customer Premises Equipment

Connected using .

A leased line provides a service. The most popular data link protocols for leased lines between 2 routers are:

HDLC Encapsulation

Service Provider

Inside the SP’s network , the SP uses any technology that it wants to create the specific Ethernet WAN service.

Ethernet WAN Service

Goes by 2 names

**** provides:

2 routers R1 and R2 connect with an service instead of a serial link. The routers use Ethernet interfaces, and they can send data in both directions at the same time. Physically, each router connects to some SP **** but logically the 2 routers cand send Ethernet frames to each other over the link.

Packet routing

Atention: Although each router is using 802.3 encapsulation, each router discards the old data link header/trailer and add its own ones