ZyXEL Communications Prestige 724, User Manual

Page: 16 / 87

Prestige 724 G.SHDSL CSU/DSU
xvi CSU/DSU and DSL Basics
CSU/DSU and DSL Basics
What is a CSU/DSU?
A CSU/DSU (Channel Service Unit/Data Service Unit) is a hardware device that converts a digital data
frame, the communications technology used on a local area network (LAN), into a frame appropriate to a
wide-area network (WAN) and vice versa. It sits between the DTE (Data Terminal Equipment) and a
transmission circuit such as a phone line and converts signals from the DTE (routers, bridges and
multiplexors) into the bipolar digital signals used by digital lines.
What is DSL?
A DSL (Digital Subscriber Line) enhances the data capacity of the existing telephone wire running between
the local telephone company switching offices and most homes and offices. While the wire itself can handle
higher frequencies, the telephone switching equipment is designed to cut off signals above 4,000Hz to filter
noise from the voice line. DSL services make use of signals above the 4,000Hz for data transfer. Several
DSL services offer speeds of up to 52 Mbits/sec. DSL services are symmetrical (traffic flows at the same
speed in both directions) or asymmetrical (the downstream capacity is higher than the upstream capacity).
As carrying distances decrease, data rates increase. This means that users who are beyond a certain distance
from the telephone company’s central office may not be able to obtain the higher speeds for DSL maximum
transmission distances.
What is G.SHDSL?
G.SHDSL (Single-pair High-speed Digital Subscriber Line) is a symmetrical, bi-directional DSL service
that operates on one twisted-pair wire and provides data rates up to 2.3 Mbits/sec. (The “G.” in “G.SHDSL”
is defined by the G.991.2 ITU (International Telecommunication Union) state-of-the-art industry standard).
A G.SHDSL connection is a point-to-point dedicated circuit, meaning that the link is always up and there is
no dialing required.
The Benefits of G.SHDSL
•
Continuous Connection
You are always online.
•
Dedicated Bandwidth
Line speed is “symmetric,” i.e., the same bandwidth in both directions.
•
Investment Protection
Scalability. Offers a flexible upgrade path. You can choose a higher
access speed yourself - no site visit is necessary.
• Low Maintenance
Connectivity requires no complex manual configuration; G.SHDSL
equipment is Plug and Play.
•
Distance Capabilities
G.SHDSL achieves 20% better loop-reach than older versions of
symmetric DSL. (Loop reach defines speed that can be attained at
various distances).