We consider the definition of the expedited forwarding per-hop behavior (EF PHB) as given in RFC 2598 and its impact on worst case end-to-end delay jitter. On the one hand, the definition in RFC 2598 can be used to predict extremely low end-to-end delay jitter, independent of the network scale. On the other hand, the worst case delay jitter can be made arbitrarily large, while each flow traverses at most a specified number of hops, if we allow networks to become arbitrarily large; this is in contradiction with the previous statement. We analyze where the contradiction originates and find the explanation. It resides in the fact that the definition in RFC 2598 is not easily implementable in known schedulers, mainly because it is not formal enough and also because it does not contain an error term. We propose a new definition for the EF PHB, called "packet scale rate guarantee" (PSRG) that preserves the spirit of RFC 2598 while allowing a number of reasonable implementations and has very useful properties for per-node and end-to-end network engineering. We show that this definition implies a rate-latency service curve property. We also show that it is equivalent, in some sense, to the stronger concept of "adaptive service guarantee". Then we propose some proven bounds on delay jitter for networks implementing this new definition in cases without loss and with loss.

We consider the definition of the expedited forwarding per-hop behaviour (EF PHB) as given in RFC 2598 (Jacobsen et al. 1999), and its impact on worst case end-to-end delay jitter. On one hand, the definition in RFC 2598 can be used to predict extremely low end-to-end delay jitter, independent of the network scale. On the other hand, we find that the worst case delay jitter can be made arbitrarily large, while each flow traverses at most a specified number of hops, if we allow networks to become arbitrarily large; this is in contradiction with the previous statement. We analyze where the contradiction originates, and find the explanation. It resides in the fact that the definition in RFC 2598 is not easily implementable in schedulers we know of, mainly because it is not formal enough, and also because it does not contain an error term. We propose a new definition for the EF PHB, called "packet scale rate guarantee", which preserves the spirit of RFC 2598, while allowing a number of reasonable implementations, and has very useful properties for per-node and end-to-end network engineering. We show that this definition implies the rate-latency service curve guarantee. Then we propose some proven bounds on delay jitter for networks implementing this new definition, both in cases without loss and with loss.

Packet switching devices that rely on input buffering to prevent cell loss in the switch fabric must regulate the arrival pattern of data packets to the input links of the switch fabric. Frame-based bandwidth allocation can be used in cell-based switch fabrics to regulate the number of cells from a flow entering the fabric during a fixed-length frame of cell slots. We present a simple cell slot assignment algorithm for distributing each flow's cell slot allocations within a frame. The algorithm controls the inter-cell spacing for each flow and bounds fabric queues to a small number independent of the frame length. The simplicity of the algorithm supports per-frame changes in the allocated rates.