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Why
ATM?
•All digital
telephone network
•Need for data
applications like computer communications and facsimile
•Nonvoice
applications like videoconferencing need to be included in the future networks
•Circuit switching
not suitable but packet switching would accommodate this
•ISDN were the first
effort to address this
ISDN Overview
•There are many types
of WAN technologies that can be used to solve the problems of users who need
network access from remote locations.
•ISDN has been
specifically designed to solve the low bandwidth problems
that small offices or dial-in users have with traditional telephone dial-in
services.
•Telephone companies
developed ISDN with the intention of creating a totally digital
network whilst making use of the existing telephone wiring system.
•ISDN works very much
like a telephone - When you make a data call with ISDN, the WAN link is brought
up for the duration of the call and is taken down when the call is completed
•ISDN allows digital
signals to be transmitted over existing telephone wiring.
••This became
possible when the telephone company switches were
upgraded to handle digital signals.
••ISDN is generally
viewed as an alternative to leased lines,
which can be used for telecommuting and networking small and remote offices into
LANs.
•ISDN's ability to
bring digital connectivity to local sites has many benefits, including the following:
••ISDN can carry a variety
of user traffic signals including:
–digital video,
packet-switched data, and telephone network services.
•ISDN offers much faster
call setup than modem connections because it uses out-ofband (D, or
delta, channel) signaling.
–For example, some
ISDN calls can be setup in less than one second.
•ISDN provides a faster
data transfer rate than modems by using the bearer channel (B channel of
64kbps).
–With multiple B
channels, ISDN offers users more bandwidth on WANs than some leased lines.
–For example, if you
were to use two B channels, the bandwidth capability is 128Kbps because each B
channel handles 64Kbps.
–•ISDN can provide a clear
data path over which to negotiate PPP links.
BRI
(Basic Rate Interface)
Connection from the
ISDN office to the user location provides for access to three
channels. The channels are two 64Kb B-channels and one 16Kb D-channel
The B-channels and
the D-channel provide the user with access to the circuit switched network
PRI
(Primary Rate Interface)
ISDN Primary Rate
Interface service provides digital access via a T1 line. A T1 line provides a
1.544 bandwidth. This bandwidth is divided into 24 64Kb channels. The ISDN PRI
service uses 23 B channel access and uses the 24th
(D) channel for signaling purposes
BSDN
Reference Model
•There are three
planes
•User Plane
•Control Plane
•Management Plane
User Plane
•ATM is specified via
a three-layer reference model:
•Physical layer (OSIs
physical layer)
•ATM layer (generally
OSIs data link layer)
•ATM adaptation layer
(AAL) (generally OSIs higher-level layers (transport, session, and application)
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