Leased line – a pre-established WAN communications path from the CPE, through the DCE switch, to the CPE of the remote site, allowing DTE networks to communicate at any time with no setup procedures before transmitting data.
Circuit switching – uses dial-up modems or ISDN and is used for low-bandwidth data transfers. Think phone call.
It uses a Network Control Protocol field in the Data Link header to identify the Network layer protocol. It allows authentication and multilink connections and can be run over asynchronous and synchronous links.
In byte-oriented protocols, control information is encoded using entire bytes.
On the other hand, bit-oriented protocols may use single bits to represent control information.
Bit-oriented protocols include SDLC, LLC, HDLC, TCP, IP, and others.
Point-to-Point Protocol (PPP) (Lammle, p. 484)
Point-to-Point Protocol (PPP) is a Data Link layer protocol that can be used over either asynchronous serial (dial-up) or synchronous serial (ISDN) media.
It uses the LCP (Link Control Protocol) to build and maintain data-link connections.
The basic purpose of PPP is to transport layer 3 packets across a Data Link layer point-to-point link.
PPP Protocol stack compared to OSI Reference Model (Lammle, p. 485) Physical layer (such as EIA/TIA-232, V.24, V.35, ISDN) 1 Network Control Protocol (NCP) Link Control Protocol (LCP) High-Level Data Link Control Protocol (HDLC) 2 Upper-layer Protocols (such as IP, IPX, AppleTalk) 3 PPP Protocol Stack OSI Layer
PPP contains four main components: (Lammle, p.485)
1) EIA/TIA-232-C, V.24, V.35, and ISDN – a Physical layer international standard for serial communication.
2) HDLC – a method for encapsulating datagrams over serial links.
3) LCP – a method of encapsulating, configuring, maintaining, and terminating the point-to-point connection.
4) NCP – a method of establishing and configuring different Network layer protocols. NCP is designed to allow the simultaneous use of multiple Network layer protocols.