Synchronization of VoDSL of DSLAM connected only to ethernet
AssigneeTelefonaktiebolaget L M Ericsson (publ)
InventorsTore Andre, Anders Lindblad, Kenneth Johansson
Life of this patent
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Abstract
A packet forwarding unit such as a Digital Subscriber Line Access Multiplexer (DSLAM) receives Ethernet packets carrying real-time information and forwards the information therein on output lines such as Asymmetric Digital Subscriber Lines (ADSLs). The DSLAM includes a clock device having an extraction unit and an adaptive clock. The extraction unit analyzes received packets to select streams of received packets from one destination to one user, and the adaptive clock generates a reference clock signal according to the arrival times of packets in the selected streams. The clock signal is sent to time reference units in DSL modems for the output lines.
Claims12
A forwarding unit for receiving Ethernet packets and forwarding information therein on a digital subscriber line, said forwarding unit comprising:
- a device for producing a clock signal, said device including:
- a selection unit for selecting at least one stream of received Ethernet packets, wherein the selection unit includes a general analyzing unit for analyzing received Ethernet packets to find a stream of packets from one destination to one user, the packets carrying real time information belonging to a real time service;
- and
- a clock signal generating unit for generating a reference clock signal according to arrival times of packets in the selected at least one stream, wherein the clock signal generating unit includes a delay determining unit for determining the delays of arrived packets in relation to the reference clock signal, wherein the delay determining unit includes:
- a signal generator providing a first clock signal having a frequency;
- a delay measuring counter configured to receive a signal obtained by dividing the first clock signal by a set number and to count the pulses of the received signal modulo a first number of times;
- and
- a measuring unit connected to the counter for determining, as a measure of the delays of the packets in relation to the reference clock signal, the counter value for the arrival time of each of the packets of the selected stream delays;
- and
- a modem connected to the digital subscriber line and to the clock signal generating unit, said modem including a Network Timing Reference (NTR) unit for receiving the reference clock signal for use in transmission of voice information to the digital subscriber line.
A method of producing a reference clock signal in a unit receiving Ethernet packets and forwarding them on a digital subscriber line, said method comprising the steps of:
- analyzing received Ethernet packets to select a stream of packets from one destination to one user, the packets carrying real time information belonging to a real time service;
- determining from arrival times of packets of said selected stream, delays in relation to a clock signal having a frequency, said step of determining the delays including:
- generating the clock signal by a signal generator;
- receiving by a delay measuring counter, a signal obtained by dividing the clock signal by a set number and counting the pulses of the received signal modulo a first number of times;
- and
- determining by a measuring unit connected to the counter, as a measure of the delays of the packets in relation to the reference clock signal, the counter value for the arrival time of each of the packets of the selected stream delays;
- calculating from the determined delays, a correction of the frequency of the clock signal;
- and
- adjusting the frequency of the reference clock signal according to the calculated correction.
Dependencies are inferred from the claim text.