Synchronizing upstream signals in distributed cable systems

Abstract

A distributed CATV system capable of removing jitter of upstream IP packets from distribution nodes over a packet distribution network is described. The headend of the CATV system has a jitter buffer that temporarily stores each upstream packet until a scheduled time that is computed to equalize the delays among the different distribution nodes. Each packet is associated with a timestamp, and the scheduled time to remove the packet from the jitter buffer is computed based on the packet's timestamp and the equalized delay. The distribution node that sends the packet upstream to the headened also inserts the timestamp into the packet.

What is claimed is: 
     
         1 . A distributed Cable Television (CATV) system comprising:
 a headend; and   a set of distribution nodes that are communicatively coupled with the headend through a digital communications medium supporting packet traffic, each distribution node further communicatively coupled with a corresponding set of information consuming devices through a Radio Frequency (RF) communications medium,   wherein the headend receives upstream packets from the set of information consuming devices via the set of distribution nodes, wherein each received packet is stored in a buffer and is retrieved at a time that is scheduled according to an equalized delay values and a timestamp of the packet,   wherein the equalized delay value is identified based on latencies between the set of distribution nodes and the headend.   
     
     
         2 . The system of  claim 1 , wherein the RF communications medium coupling a distribution node with its corresponding set of information consuming devices comprises a set of CATV cables, and the digital communications medium supporting packet traffic comprises optical fiber. 
     
     
         3 . The system of  claim 1 , wherein the scheduled time for retrieval is further based on an expected maximum jitter for packet traffic across the digital communications medium. 
     
     
         4 . The system of  claim 1 , wherein the scheduled time for retrieval and the timestamps of the packets are based on a time that is synchronized across the headend and the set of distribution nodes. 
     
     
         5 . The system of  claim 1 , wherein the timestamp of the packet indicates a time when the distribution node composed the packet. 
     
     
         6 . The system of  claim 1 , wherein two of the received packets come from two different distribution nodes are scheduled to be retrieved from the buffer at the same time, wherein one of the two received packet is retrieved from the buffer and transmitted. 
     
     
         7 . The system of  claim 1 , wherein the received upstream packets comprises data from upstream out-of-band signals transmitted by at least one of the set of information consuming devices. 
     
     
         8 . The system of  claim 1 , wherein the headend comprises a video engine for providing media content and for relaying upstream out-of-band RF signals from the distribution nodes to an out-of-band demodulator, wherein the upstream packets stored at the buffer are for carrying the upstream out-of-band RF signals and for retrieval by the video engine. 
     
     
         9 . The system of  claim 8 , wherein the upstream out-of-band RF signals are for carrying control data that are supplementary to the provided media content. 
     
     
         10 . A method for coordinating the transmission of upstream signals in a distributed CATV system, the CATV system comprising a cable headend, a set of distribution nodes, and a set of information consuming devices, wherein cable headend and the set of distribution nodes are communicatively coupled by a digital communications medium supporting packet traffic, wherein each distribution node is communicatively coupled with a corresponding set of information consuming devices through a Radio Frequency (RF) communications medium, the method comprising:
 identifying an equalized delay value based on latencies between the set of distribution nodes and the headend;   receiving upstream packets from the set of information consuming devices via the set of distribution nodes; and   for each received packet:
 storing the packet in a buffer; 
 scheduling a time for retrieval of the stored packet based on the equalized delay values and a timestamp of the packet; and 
 retrieving the stored packet at its scheduled time from the buffer for retrieval and transmission to an out-of-band demodulator. 
   
     
     
         11 . The method of  claim 10 , wherein the RF communications medium coupling a distribution node with its corresponding set of information consuming devices comprises a set of CATV cables, and the digital communications medium supporting packet traffic comprises optical fiber. 
     
     
         12 . The method of  claim 10 , wherein the scheduled time for retrieval is further based on an expected maximum jitter for packet traffic across the digital communications medium. 
     
     
         13 . The method of  claim 10 , wherein the scheduled time for retrieval and the timestamps of the packets are based on a time that is synchronized across the headend and the set of distribution nodes. 
     
     
         14 . The method of  claim 10 , wherein the timestamp of the packet indicates a time when the distribution node composed the packet. 
     
     
         15 . The method of  claim 10 , wherein two of the received packets come from two different distribution nodes are scheduled to be retrieved from the buffer at the same time, wherein one of the two received packet is retrieved from the buffer and transmitted. 
     
     
         16 . The method of  claim 10 , wherein the received upstream packets comprises data from upstream out-of-band signals transmitted by at least one of the set of information consuming devices. 
     
     
         17 . The method of  claim 10 , wherein the headend comprises a video engine for providing media content and for relaying upstream out-of-band RF signals from the distribution nodes to an out-of-band demodulator, wherein the upstream packets stored at the buffer are for carrying the upstream out-of-band RF signals and for retrieval by the video engine. 
     
     
         18 . The method of  claim 17 , wherein the upstream out-of-band RF signals are for carrying control data that are supplementary to the provided media content. 
     
     
         19 . A computing device for coordinating the transmission of upstream signals in a distributed CATV system, the CATV system comprising a cable headend, a set of distribution nodes, and a set of information consuming devices, wherein cable headend and the set of distribution nodes are communicatively coupled by a digital communications medium supporting packet traffic, wherein each distribution node is communicatively coupled with a corresponding set of information consuming devices through a Radio Frequency (RF) communications medium, the computing comprising:
 a set of processing units for executing instructions; and   a computer readable storage medium storing sets of instructions for execution by the set of processing units, the sets of instructions for:
 identifying an equalized delay value based on latencies between the set of distribution nodes and the headend; 
 receiving upstream packets from the set of information consuming devices via the set of distribution nodes; and 
 for each received packet:
 storing the packet in a buffer; 
 scheduling a time for retrieval of the stored packet based on the equalized delay values and a timestamp of the packet; and 
 retrieving the stored packet at its scheduled time from the buffer for retrieval and transmission to an out-of-band demodulator. 
 
   
     
     
         20 . The computing device of  claim 19 , wherein the scheduled time for retrieval is further based on an expected maximum jitter for packet traffic across the digital communications medium.