| To make remote connections,
remote-node users should have the application software (for example,
File Transfer Protocol [FTP], Telnet), protocol stacks (for example,
TCP/IP), and link-layer drivers (for example, PPP, Serial Line
Internet Protocol [SLIP]) installed on their own remote devices, as
shown in the Figure. The
higher-layer protocols are encapsulated in the link-layer protocols
(such as SLIP and PPP) when they are transmitted across the dialup
line.
Point-to-point links between LANs,
hosts, terminals, and routers can provide sufficient physical
connectivity in many application environments. Many regional and
commercial network services provide access to the Internet, and
point-to-point links provide an efficient way to access the service
provider locally.
The Internet community adopted two
schemes for the transmission of IP datagrams over serial
point-to-point lines:
- SLIP -- SLIP is a standard
protocol for point-to-point serial connections, using a
variation of TCP/IP. SLIP was a predecessor of PPP.
- PPP -- PPP provides
router-to-router and host-to-network connections over
synchronous and asynchronous circuits.
PPP and SLIP are data link layer
protocols (Layer 2 of the Open System Interconnection [OSI] model).
Although both SLIP and PPP were designed with IP in mind, SLIP is
pretty much limited for use with IP, whereas PPP can be used for
other network-layer protocols. Unlike SLIP, PPP supports multilink,
which allows hosts to load balance over multiple channels. Multilink
is especially useful with ISDN when both B channels can be used to
achieve 128-kilobit-per-second (Kbps) throughput.
Note: ARAP and SLIP are not used very
frequently in current network configurations, so they are not
covered in the course. For additional configuration information,
refer to Cisco Connection Online (CCO) at www.cisco.com.
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