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
Naming
Examples
Leased Line Service
Used 2 pairs of wires (full-duplex)
- sending
- receiving
Components
- CSU/DSU
- Channel Service Unit / Data Service Unit Can be integrated into the router (serial interface) Or external
- CPE
- Customer Premises Equipment
Connected using .
Data Link Details
A leased line provides a service. The most popular data link protocols for leased lines between 2 routers are:
- Point-to-Point Protocol (PPP)
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
-
Ethernet emulation
-
Ethernet over MPLS
-
service acts like one Ethernet link
-
Multi Protocol Label Switching
Point of Presence
**** provides:
- a point-to-point connection between 2 customer devices
- behaviour as if a fiber Ethernet link existed between the 2 devices
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