Communications networks are ubiquitous.  The Internet is everywhere and carriers are attempting to provide more and more services over it to their customers. 
Reference is now made to FIG.  1, which illustrates how a signal from a source 10 is distributed to customers 12 over the Internet 14.  Source 10 might be, for example, a broadcast news station or a movie channel.  The Internet 14, or any other wide area network (WAN), is typically organized into different levels of networks.  There typically is a national backbone network 16 and multiple metro edge networks 18.  Small metropolitan areas may have a single edge network, as shown, while larger metropolitan areas may have a central edge network with smaller sub-networks.  Finally, each customer 12 may be connected to the Internet 14 via access networks 20.  The latter are typically low bandwidth, copper connections, while national backbone 16 and edge networks 18 may be formed from high bandwidth, optical fibers. 
Networks 16 and 18 are typically formed of multiple points of presence (POPs) 22 connected, with “bus” connectivity, in a ring 23 of optical fibers.  Due to the bus connection, each POP 22 can transmit directly to any other POP 22 in the ring.  This minimizes the number of POPs through which any piece of data has to travel. 
POPs 22 may be formed of multiple routers, each typically having I/O ports residing on line cards and a switching fabric connecting the line cards to each other.  The routers use multiple mechanisms, such as shaping, queuing, backpressure, etc.,  to switch large amounts of traffic with few errors. 
The routers may also have other mechanisms to handle network conditions between the routers, such as routing protocols, DiffServ (classification at the edge of the network and class of service (CoS) control in the core of the network) and IntServ (end to end resource reservation and enforcement of priorities and rates). 
The bandwidth capacity between POPs 22 is very high.  However, if the traffic is higher than the capacity, the network becomes congested.  Links between routers in the core of a network typically become clogged due to aggregate traffic flow and this congestion typically affects the service: packets may be delayed or dropped. 
When the network is not congested, a packet will move without delay through POPs 22A and 22B and towards its final destination 12.  However, when the network is congested, the traffic management mechanisms of the routers in POPs 22 will delay a packet, due to other packets being handled or transmitted before it at each hop on its path, or they will drop it.  The latter may occur when a queue within one of the routers of a POP 22 is filled or when a stream has limited latency constraints (which may define when a packet is no longer of use—e.g. a packet in an audio stream which is part of a phone call may no longer be usable if it comes too late compared to the other packets in the stream).