Cable Modem Termination System
The CMTS takes the
traffic coming in from a group of customers on a single channel and routes it
to an Internet service provider (ISP) for connection to the Internet. At the
head-end, the cable providers will have, or lease space for a third-party ISP
to have, servers for accounting and logging, Dynamic Host Configuration
Protocol (DHCP) for assigning and administering the IP addresses of all the
cable system's users, and control servers for a protocol called CableLabs
Certified Cable Modems -- formerly Data Over Cable Service Interface
Specifications (DOCSIS), the major standard used by U.S. cable systems in
providing Internet access to users.
Another benefit of the
cable modem for Internet access is that, its performance doesn't depend on
distance from the central cable office. A digital CATV system is designed to
provide digital signals at a particular quality to customer households. On the
upstream side, the burst modulator in cable modems is programmed with the
distance from the head-end, and provides the proper signal strength for
accurate transmission.
XGCM
This module is responsible for providing MGCP embedded
client functionality. It parses and processes each message received from an
MGCP call agent. It reports detected events to the call agent, generates
signals requested by the call agent, reports detected DTMF digits, and sets up
connections requested by the call agent. This module is also responsible for
forwarding audio packets received from the DSP to packet network interface and
forwarding audio packets received from the packet network interface to the DSP.
Introduction
Voice (and fax) service over cable networks is
known as cable-based Internet Protocol (IP) telephony. Cable based IP telephony
holds the promise of simplified and consolidated communication services
provided by a single carrier at a lower cost than consumers currently to pay to
separate Internet, television and telephony service providers. Cable operators
have already worked through the technical challenges of providing Internet
service and optimizing the existing bandwidth in their cable plants to deliver
high speed Internet access. Now, cable operators have turned their efforts to
the delivery of integrated Internet and voice service using that same cable
spectrum.
Putting both upstream
and downstream data on the cable television system requires two types of
equipment: a cable modem on the customer end and a cable modem termination
system (CMTS) at the cable provider's end. Between these two types of
equipment, all the computer networking, security and management of Internet
access over cable television is put into place.
Tuner
The tuner connects to the cable outlet, sometimes with the
addition of a splitter that separates the Internet data channel from normal
CATV programming. Since the Internet data comes through an otherwise unused
cable channel, the tuner simply receives the modulated digital signal and
passes it to the demodulator.
Fax
Software
This software performs a fax relay function by demodulating
PCM data, extracting the relevant information, and packing the fax-line scan
data into frames for transmission.
Unsolicited Grant Service(UGS)
Cable networks are asymmetric, i.e., the downstream data
received is streaming while the upstream data transmitted is either transmitted
on a collision time fragment or must get a time slot or grant. Because
requesting a grant can cause significant delay, UGS ensures that cable modems
will be contacted at regular intervals without having to make separate
requests. The concatenation process mentioned earlier can lighten UGS
requirements and increase the efficient bandwidth.
Abstract
Voice (and fax) service over cable networks is known as
cable-based Internet Protocol (IP) telephony. Cable based IP telephony holds
the promise of simplified and consolidated communication services provided by a
single carrier at a lower cost than consumers currently to pay to separate
Internet, television and telephony service providers.
Conclusion
With the merging of telecom carriers, cable operators, and
Internet service providers (ISPs), most experts agree that convergence is not
merely a trend but an inevitability. The potential cost savings, consolidated
billing, streamlined network management, and overall convenience are too
compelling for service providers and customers to ignore.
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