1. How Circuit-Switched Digital
Networks Work
About ISDN
About LAN
About TCP/IP 1
TCP/TP 2
About Circuit Switching
Group F
How Circuit-Switched Digital Networks Work – p.1/7

2. About ISDN
• ISDN is a set of CCITT/ITU standards for digital
transmission over ordinary telephone copper
wire. ISDN requires adapters at both ends to
handle a digital call, so users must dial into an
ISDN-capable PoP. There are two levels of
service: the BRI, intended for the home and small
enterprise, and the Primary Rate Interface, for
larger users. Our customers get a BRI line to
connect to us. We have a PRI to the PoPs to
handle the incoming calls. The BRI consists of
two B channels for carrying data at 64Kbps.
Hence, a quot;2Bquot; connection is at 128K. On top of
that is one D channel, which carries control and
signaling information at 16K. A PRI consists of
23 B channels and 1 64K D channel.
How Circuit-Switched Digital Networks Work – p.2/7

3. About LAN
• ˘ ˘
LAN 2013 Local Area Network 2013 usually a
small network, within a small geographic area.
An example of this would be a small office, with
2 or more computers connected to the same
printer. Another example would be a school,
where several computers are connected to shared
resources (pronters, faxes, etc) and are then
connected to the internet or some other kind of
WAN.
How Circuit-Switched Digital Networks Work – p.3/7

4. About TCP/IP 1
• TCP and IP were developed by a DOD research
project to connect a number different networks
designed by different vendors into a network of
networks . It was initially successful because it
delivered a few basic services that everyone needs
across a very large number of client and server
systems. Several computers in a small department
can use TCP/IP on a single LAN. The IP
component provides routing from the department
to the enterprise network, then to regional
networks, and finally to the global Internet.
How Circuit-Switched Digital Networks Work – p.4/7

5. About TCP/IP 2
• On the battlefield a communications network will
sustain damage, so the DOD designed TCP/IP to
be robust and automatically recover from any
node or phone line failure. This design allows the
construction of very large networks with less
central management. However, because of the
automatic recovery, network problems can go
undiagnosed and uncorrected for lon! g periods
of time.
How Circuit-Switched Digital Networks Work – p.5/7

6. About Circuit Switching
• In telecommunications, a circuit switching
network is one that establishes a fixed bandwidth
circuit (or channel) between nodes and terminals
before the users may communicate, as if the
nodes were physically connected with an
electrical circuit. The bit delay is constant during
a connection, as opposed to packet switching,
where packet queues may cause varying delay.
Each circuit cannot be used by other callers until
the circuit is released and a new connection is set
up. Even if no actual communication is taking
place in a dedicated circuit that channel remains
unavailable to other users. Channels that are
available for new calls to be set up are said to be
idle. How Circuit-Switched Digital Networks Work – p.6/7

7. Reference
• http://ja.wikipedia.org/wiki/Wiki
• http://chiebukuro.yahoo.co.jp/
• http://jobsearchtech.about.com/od/
historyoftechindustry/g/LAN.htlm
How Circuit-Switched Digital Networks Work – p.7/7