Datasheet

Book VII
Chapter 1
Wide-Area
Networking Basics
815
Introducing Cable Connections
persistent nature of PVC connections allows for a permanent mode of
communications where call setup and termination is not required.
A PVC connection guarantees an “always on” communications availabil-
ity using a manual static setup method.
✦ Switched virtual circuits (SVCs): SVCs dynamically generate connections
and terminate them after data has been completely transferred, function-
ing similarly to a telephone call. A signaling protocol is used between the
ATM endpoint and the ATM switch to dynamically control the connection.
SVCs provide flexibility and call setup to networking devices, but require
additional time and overhead to set up the connection.
Both PPP and ATM WAN encapsulation types support asynchronous
communications.
X.25
This is an international WAN protocol family standardized by the ITU’s
Telecommunication Standardization Sector (ITU-T) that defines how
connections are established and maintained between end user devices and
networking equipment.
X.25 network devices are categorized into three types:
✦ Data terminal equipment (DTE): DTE devices are customer-owned com-
puters, terminals, and routers that communicate across the X.25 network.
✦ Data circuit-terminating equipment (DCE): DCE devices are modems
and packet switches that reside between DTE devices and PSEs.
✦ Packet-switching exchange (PSE): PSEs transfer data between DTE devices
over the X.25 network. X.25 was designed before the conception of the OSI
layer and has been generally replaced by the more efficient Frame Relay
technology, although X.25 is still used in some ISDN scenarios.
Introducing Cable Connections
Cisco routers use either RJ-45 or DB-25 connectors for DCE/DTE console and
AUX ports. A terminal DTE device or DCE modem may be connected to these
ports using an RJ-45 cable and an RJ-45–to–DB-25 or RJ-45–to–DB-9 connector.
RJ-45 cabling
Unshielded twisted-pair (UTP) cable uses four pairs of eight individual wires
twisted together to eliminate electrical interference known as crosstalk. UTP
cables feature RJ-45 connectors that contain eight connector pins per con-
nector. RJ-45 cables are categorized into these main types:
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