PPPmux-a new protocol for transporting small IP packets

We introduce a new protocol to improve the capacity of communication links to carry real-time applications that generate a large number of small packets. The key issue in the transport of such applications is the relatively large protocol overhead for each packet. For example, the overhead for RTP/UDP/IP/PPP/HDLC is 12/8/20/7 bytes respectively resulting in a total of 47 bytes. This is considerable for applications with a small payload (10-20 bytes). RTP/UDP/IP header compression (cRTP) mitigates the problem partially by reducing the corresponding protocol overhead from 40 bytes to a best case of 2 bytes. PPPmux provides a further improvement by multiplexing multiple application-level packets into a single PPP frame thereby reducing the PPP overhead per packet. One potential deployment of PPPmux is in cellular networks (IS-95A and UMTS) on links connecting base stations to the radio access network controllers (RNC). The paper provides numerical results listing capacity improvements over existing schemes. Since, multiplexing concatenates multiple IP packets into a single PPP frame, a frame loss would result in loss of multiple IP packets. We provide guidelines on the choosing the optimal multiplexing size that gives the best trade-off between increase in link capacity and increase in packet loss. Specifically, the multiplexing size of 200 bytes gives the best compromise between capacity and packet loss for typical cellular applications.