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Timing over packet
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What is Timing over Packet (ToP): To put it in simple terms “It’s a method to transport timing information over PSN (packet switched network)”. It’s all known that Packet switched networks are very cost effective and widely used in data communication. But due asynchronous nature of PSN’s they are not reliable for cellular backhaul networks. Timing over Packet enables time-sensitive services to be supported over packet-switched networks. About ToP: ToP is not dependent on physical layer technologies. It just uses a stream of packets to encode the clock information and transfer it across the packet switched network. It may use a variety of protocols to achieve timing distribution e.g. RTP, NTP, PTP(IEEE1588). The clock from the packet stream will be recovered by using adaptive clock recovery algorithm. Impairments during Timing distribution: Packet Transfer Delay Packet Delay Variation (PDV) Random delay variation (e.g., queuing delays) Low frequency delay variation (e.g., day/night patterns) Systematic delay variation (e.g., store and forward mechanisms in the underlying transport layer) Routing changes Congestion effects Packet Loss Packet Error Extended Packet Loss (Network Outages) All of the above impairments are addressed by adaptive clock recovery algorithm. 
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