Laura B. James

Error Behaviour In Optical Networks

The UK Engineering and Physical Sciences Research Council and Marconi Corporation supported my work financially through an Industrial CASE studentship.

Optical network packet error rate due to physical layer coding

A physical layer coding scheme is designed to make optimal use of the available physical link, providing functionality to higher components in the network stack. This paper presents results of an exploration of the errors observed when an optical gigabit Ethernet link is subject to attenuation. The results show that some data symbols suffer from a far higher probability of error than others. This effect is caused by an interaction between the physical layer and the 8B/10B block coding scheme. The authors illustrate how the application of a scrambler, performing data whitening, restores content-independent uniformity of packet loss. They also note the implications of their work for other (N, K) block-coded systems and discuss how this effect will manifest itself in a scrambler-based system. A conjecture is made that there is a need to build converged systems with the combinations of physical, data link, and network layers optimized to interact correctly. In the meantime, what will become increasingly necessary is both an identification of the potential for failure and the need to plan around it.

Chasing errors through the network stack: a testbed for investigating errors in real traffic on optical networks

A testbed is described that allows both physical layer errors to be observed and analyzed, as well as monitoring network performance via frame loss. Real network traffic loads can be used for testing so that all measurements taken are representative of what would be seen in a deployed system. We illustrate our testbed with an examination of the behavior of a well-known networking standard, Gigabit Ethernet, in conditions of reduced receiver power on optical fiber. Our testbed results show that the line codes used to represent the data in the network affect the bit error rate for that data. Along with the previously reported result that bit error rate and packet error rate have only a weakly deterministic relationship, this highlights the need for testing of all network layers within a complete system carrying real-world traffic.

Structured Errors in Optical Gigabit Ethernet Packets

This paper presents a study of the errors observed when an optical Gigabit Ethernet link is subject to attenuation. We use a set of purpose-built tools which allows us to examine the errors observed on a per-octet basis. We find that some octets suffer from far higher probability of error than others, and that the distribution of errors varies depending on the type of packet transmitted.

TCP Sending Rate Control at Terabits Per Second

An analysis of the sending rate of TCP control over Terabit per second rate links illustrates how future optical network characteristics, such as higher bitrates, network congestion, and larger data loads, would affect performance. We have implemented a model to allow increased sending rate for TCP. It is shown that even if the network bitrate is higher and the sending rate of TCP is scaled up, the throughput does not grow considerably, and latency remains one of the key parameters which must be reduced to improve performance.

Packet error rate and bit error rate non-deterministic relationship in optical network applications

The non-deterministic relationship between bit error rate and packet error rate is demonstrated for an optical media access layer in common use. We show that frequency components of coded, non-random data can cause this relationship.