Byte

Summary

The byte is a unit of digital information that most commonly consists of eight bits. Historically, the byte was the number of bits used to encode a single character of text in a computer and for this reason it is the smallest addressable unit of memory in many computer architectures. To disambiguate arbitrarily sized bytes from the common 8-bit definition, network protocol documents such as the Internet Protocol () refer to an 8-bit byte as an octet. Those bits in an octet are usually counted with numbering from 0 to 7 or 7 to 0 depending on the bit endianness. The first bit is number 0, making the eighth bit number 7. The size of the byte has historically been hardware-dependent and no definitive standards existed that mandated the size. Sizes from 1 to 48 bits have been used. The six-bit character code was an often-used impl

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A 2.78 mm2 65 nm CMOS Gigabit MIMO Iterative Detection and Decoding Receiver

Andreas Peter Burg

Iterative detection and decoding (IDD), combined with spatial-multiplexing multiple-input multiple-output (MIMO) transmission, is a key technique to improve spectral efﬁciency in wireless communications. In this paper we present the—to the best of our knowledge—ﬁrst complete silicon implementation of a MIMO IDD receiver. MIMO detection is performed by a multi-core sphere decoder supporting up to 4×4 as antenna conﬁguration and 64-QAM modulation. A ﬂexible low-density parity check decoder is used for forward error correction. The 65 nm CMOS ASIC has a core area of 2.78 mm2 . Its maximum throughput exceeds 1 Gbit/s, at less than 1 nJ/bit. The MIMO IDD ASIC enables more than 2 dB performance gains with respect to non-iterative receivers.

2012

Optimizing TCP Receive Performance

Aravind Menon, Willy Zwaenepoel

The performance of the networking stack in an operating system depends on the overhead incurred by two of its components: the per-byte overhead incurred in data-touching operations, and the per-packet overhead of protocol processing and other operating system routines. While many mechanisms exist for reducing the per-byte and per-packet overheads for packet transmission in TCP, little progress has been made for addressing these issues for the performance of TCP receive. Conventionally, it has been shown that the performance of TCP receive is dominated by the cost of the per-byte data touching operations. However, in this paper we show that the per-packet cost of TCP processing dominates the TCP receive performance in modern operating systems. We show that the high per-packet overhead is caused by the forced one-to-one correspondence between the host packet unit and the network packet unit. We propose a restructuring of the TCP stack which allows the operating system to amortize the cost of per-packet operations over multiple network packets. By restructuring the TCP stack in this manner, we demonstrate performance improvements of 45-67% for TCP receive workloads involving bulk data transfers in native Linux, and of 86% for similar workloads running in a virtualized Linux guest OS running on Xen.

2008

This paper presents an evaluation of three software implementations of release consistency. Release consistent protocols allow data communication to be aggregated, and multiple writers to simultaneously modify a single page. We evaluated an eager invalidate protocol that enforces consistency when synchronization variables are released, a lazy invalidate protocol that enforces consistency when synchronization variables are acquired, and a lazy hybrid protocol that selectively uses update to reduce access misses. Our evaluation is based on implementations running on DECstation-5000/240s connected by an ATM LAN, and an execution driven simulator that allows us to vary network parameters. Our results show that the lazy protocols consistently outperform the eager protocol for all but one application, and that the lazy hybrid performs the best overall. However, the relative performance of the implementations is highly dependent on the relative speeds of the network, processor, and communication software. Lower bandwidths and high per byte software communication costs favor the lazy invalidate protocol, while high bandwidths and low per byte costs favor the hybrid. Performance of the eager protocol approaches that of the lazy protocols only when communication becomes essentially free.

1995