The Internet Engineering Task Force (IETF) is in the process of adopting standards for IP-layer encryption and authentication (IPSEC). We describe how "probable plaintext" can be used to aid in cryptanalytic attacks, and analyze the protocol to show how much probable plaintext is available. We also show how traffic analysis is a powerful aid to the cryptanalyst. We conclude by outlining some likely changes to the underlying protocols that may strengthen them against these attacks.

The unslotted Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) with backoff is a fully distributed, asynchronous Media Access Control (MAC) protocol for multiple-access Wavelength Division Multiplexing (WDM) ring networks with simplicity and robustness comparable to those of Ethernet [1,2]. In this paper we present the results of performance evaluation of four scheduling algorithms --- Random Select (RS), Destination Priority Queueing (DPQ), Longest Queue First (LQF), and Shortest Packet First (SPF) --- designed for the unslotted CSMA/CA with backoff MAC protocol to address the issues of fairness and bandwidth effciency. Through extensive network-level simulations for a multiple-access WDM ring with 10 nodes and 10 wavelengths on a 100 km ring, we have verified that under uniform traffc condition, the LQF with optical buffer size of 13 and 78 octets shows the best performance in terms of fairness, guaranteeing full fairness (fairness index#1) for arrival rates up to 9.5 Gbps/node, while for throughput and packet delay, the DPQ with the maximum optical buffer size of 1538 octets gives the best results. We have also identified that the optical buffer size greatly affects the performance of nonrandom scheduling algorithms.

Priority queueing models have been commonly used in telecommunication systems. The development of analytically tractable models to determine their performance is vitally important. The discrete time batch Markovian arrival process (DBMAP) has been widely used to model the source behavior of data traffic, while phase-type (PH)distribution has been extensively applied to model the service time. This paper focuses on the computation of the DBMAP/PH/1 queueing system with priorities, in which the arrival process is considered to be a DBMAP with two priority levels and the service time obeys a discrete PH distribution. Such a queueing model has potential in performance evaluation of computer networks such as video transmission over wireless networks and priority scheduling in ATM or TDMA networks. Based on matrix-analytic methods, we develop computation algorithms for obtaining the stationary distribution of the system numbers and further deriving the key performance indices of the DBMAP/PH/1 priority queue.

We propose a new EPON MAC protocol guaranteeing fairness among users by allocating excess bandwidth proportional to their subscription rates. The novelty of the protocol is in the use of scalable per-subscription-rate-queuing with round-robin scheduling and packet reclassification at ONU.

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