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Cisco's ISDN Implementation
Cisco implements BRI using a BRI RJ45 interface on a router enabled as a TE1 device.
HDLC
The High Level Data Link Control Protocol is a link layer protocol that is the standard encapsulation
type for Cisco Serial interfaces. It is a bit-oriented synchronous data link layer protocol developed by
ISO. Derived from SDLC, HDLC specifies a data encapsulation method on synchronous serial links
using frame characters and checksums.
PPP
Point-to-Point Protocol. A successor to SLIP, PPP provides router-to-router and host-to-network con-
nections over synchronous and asynchronous circuits. This data link protocol can be used over either
asynchronous (dial-up) or synchronous (ISDN) media. It uses the Link Control protocol (LCP) to
maintain the data link. It has a number of features, including Authentication using either PAP or CHAP
and compression. PPP can actually use the 4 physical interfaces:
·
Asynchronous Serial
·
Synchronous Serial
·
HSSI
·
ISDN
PPP is enabled at the Interface configuration mode by typing:
Router(config-if)# encapsulation ppp
There are then several sub PPP commands such as authentication, multilink, compression, and callback.
The Show Interface command lists the encapsulation method on an interface. Also Show Running-Config displays the PPP commands allocated to an interface.
*Keypoints:PPP compression is handled by the Link Control Protocol (LCP).Network Control Program (NCP) is the PPP service that supports multiple network layer protocols.LAPD protocol is based on the HDLC protocol.PPP can be used over DDR or ISDN interfaces.Know that HDLC and PPP support multiple upper layer protocols and are the most commonly usedISDN encapsulation methods.To display the encapsulation type used on an interface, you would use the "show interface" com-mand.PPP provides router-to-router and host-to-network connections over synchronous and asynchro-nous interfaces.Network ProtocolsNetwork Addresses
There are two parts to every Network address. These are the Network ID and the Host ID. In TCP/IP,
this is decided by the address class and the subnet mask. In IPX/SPX, the first 8 hex digits represent
the network ID and the remaining 12 hex digits represent the host ID (the MAC address).
Routers and other internetworking devices require one network layer address per physical network
connection for each network layer protocol supported. For example, a router with three interfaces, each