Towards applications: communication with a changing network protocol
We finally return to our original technical motivations for studying semantic communication, outlined in Section 1.1. Specifically, we will present a first attempt at designing end-user network protocols that can adapt to “simple” modifications of the protocol used on the network without third-party intervention. In practice, the network protocols we wish to modify serve the purpose of forwarding messages from one user to another – in effect, realizing a channel across the network. Thus, our task seems like an insurmountable challenge a priori, since we stressed earlier (at the outset of Chapter 2) that this goal is not verifiable in general. Therefore, in service of the design of a protocol, we will need to first develop a verifiable goal of communication for the network’s users, and then exhibit a user protocol that achieves our goal. Perhaps surprisingly, a pair of users can arrange for a scheme that allows them to verify that they receive the correct messages after a (bounded) adversarial modification of the protocol, under the assumption that the encoding of the data under the protocol is computable in a single pass by a small-space program (and given that the modification is computed by a short program with similar restrictions). In particular, our scheme is ultimately capable of coping with networks that drop and reorder the packets.
KeywordsHash Function Sequence Number Signature Scheme Input Word Active Message
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