Datasheet

Book VII
Chapter 1
Wide-Area
Networking Basics
813
Encapsulation Types
dialup and ISDN links. PPP features include connection authentication,
encryption, and compression.
Two basic PPP sublayers are as follows:
✦ Network Control Protocol (NCP): Encapsulates heterogeneous network
layer protocols over PPP. This allows multiple, dissimilar protocols to
be transmitted by NCP over the PPP link.
✦ Link Control Protocol (LCP): Manages initial link setup, handshake
negotiations, and ongoing connections during PPP communications. LCP
also manages the termination of point-to-point links.
SLIP (Serial Line Internet Protocol)
SLIP is a very simplistic, nonstandard protocol used to frame and transmit IP
datagrams over serial connections.
Due to its inflexible design, SLIP does not provide additional features such as
encryption, authentication, or error detection and has been widely replaced
by PPP.
Frame Relay
Frame Relay is a high-performance packet-switching WAN protocol originally
designed for use with ISDN, which has superseded X.25. Frame Relay uses HDLC
encapsulation between connected devices at T-1 (1.544-Mbps) and T-3 (45-Mbps)
speeds, but is relatively inexpensive compared to ATM or dedicated leased lines.
Frame Relay is an OSI Layer 2 protocol that relies on the upper-layer protocols
to handle flow control and error correction responsibilities. Frame Relay uses
virtual circuits to multiplex multiple connections over a single transmission
link between DTE and DCE devices. Service providers assign connection i
dentifiers to customer DTE devices and map them to outgoing ports.
ATM (Asynchronous Transfer Mode)
ATM is packet-switching digital transmission technology that sends voice,
video, and data signals using 53-byte, fixed-length cell relay between end
points over a virtual circuit. An ATM cell contains a 5-byte header and a
48-byte payload (user data), which is processed individually (asynchro-
nously). ATM cells are queued before being multiplexed over the
connection-oriented transmission path.
Packaging data into smaller fixed-size cell units allows jitter reduction and
prevents data-queuing delays known as contention. By preventing contention
in applications where timely delivery of data is crucial — such as voice and
video applications — jitter is reduced and overall performance is improved.
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