Packet switching with common time reference over links with dynamically varying delays

DETAILED DESCRIPTION The invention describes a method for transmitting and forwarding packets over a packet switching network where the delay between two switches increases, decreases, or changes arbitrarily over time.
Packets are being forwarded over each link inside the network in predefined periodic time intervals.
The switches of the network maintain a common time reference, which is obtained either from an external source (such as GPS--Global Positioning System) or is generated and distributed internally.
The time intervals are arranged with simple periodicity and complex periodicity (like seconds and minutes of a clock).
The common time reference is used to determine in advance the periodic time intervals a packet will be forwarded by each switch on its route from source to destination.
The time interval duration can be longer than the time duration required for transmitting a packet, in which case the exact position of a packet in the time interval is not predetermined.
A packet that arrives to an input port is switched to an output port based on specific routing information in the packet's header (e.
g.
, IPv4 destination address in the Internet, VCI/VPI labels in ATM) and the time interval of its arrival.
Packets that are forwarded inside the network over the same route and in the same time intervals constitute a virtual pipe and share the same pipe-ID.
Pipe-ID can be either explicit, such as a tag or a label that is generated inside the network, or implicit such as a group of IP addresses.
Virtual pipe provides deterministic quality of service guarantees.
The time interval in which a switch forwards a specific packet is determined by the packet's pipe-ID, the time it reaches the switch, and the current value of the common time reference.
The invention provides methods for maintaining timely forwarding within predefined time interval over two types of link delay variations: (i) increasing delay and (ii) decreasing delay.
When the delay increases at some point of time a packet may be late for its predefined forwarding time interval