Photonic Network Communications, 1, 89±103 (1999)
# 1999 Kluwer Academic Publishers, Boston. Manufactured in The Netherlands.
A Comparison of Bit-Parallel and Bit-Serial Architectures
for WDM Networks
Krishna M. Sivalingam*
School of Electrical Engg. & Computer Science, Washington State University, Pullman, WA 99164-2752, E-mail: firstname.lastname@example.org
Received May 22, 1998; Revised November 30, 1998
Abstract. Wavelength division multiplexing (WDM) is emerging as a viable solution to reduce the electronic processing bottleneck in very
high-speed optical networks. A set of parallel and independent channels are created on a single ®ber using this technique. Parallel
communication utilizing the WDM channels may be accomplished in two ways: (i) bit serial, where each source-destination pair communicates
using one wavelength and data are sent serially on this wavelength; and (ii) bit parallel, where each source-destination pair communicates using
a subset of channels and data are sent in multiple-bit words. Three architectures are studied in the paper: single-hop bit-serial star, single-hop bit-
parallel star, and multi-hop bit-parallel shuf¯enet. The objective of this paper is to evaluate these architectures with respect to average packet
delay, network utilization, and link throughput. It is shown that the Shuf¯enet offers the lowest latency but suffers from high cost and low link
throughput. The star topology with bit-parallel access offers lower latency than the bit-serial star, but is more expensive to implement.
Keywords: optical wavelength division multiplexing (WDM) Networks, bit parallel, bit serial, star architecture, shuf¯enet architecture
All-optical networks based on Wavelength Division
Multiplexing (WDM) technology appear to hold
enormous promise for a post-ATM network genera-
tion . Optical networks have characteristics that
enable signi®cant advancement beyond the current
state-of-the-art in network architecture. A major
obstacle faced in building photonic systems is the
speed mismatch between the high-speed optical
components and the interface electronics. This is
particularly true in a packet switched environment.
Wavelength division multiplexing is a technique that
reduces the impact of the speed mismatch by
partitioning the enormous bandwidth into multiple,
multi-access channels that operate at speeds compa-
tible with the electronic interface . Research pro-
jects are under development at universities and labs to
build systems based on these WDM techniques [3±7].
The objective of this paper is to examine the
performance of WDM based network architectures for
large scale communication networks. The main
objective is low-latency, low-cost communication
that is suf®ciently scalable to support thousands of
nodes. A primary design constraint, needed to achieve
the low-cost and scalability objectives, is the assump-
tion that there will be only a few WDM channels
(many less than the number of processors) .
The C parallel channels offered by WDM can be
utilized in two ways: (i) bit-serial transmission (BST)
where data is transmitted bitwise serially on a
channel, and each source-destination pair uses a
single wavelength. Up to C simultaneous source-
destination pairs may exist in this case; (ii) bit-per-
wavelength (BPW) or bit-parallel format where a
subset of the C channels is allocated to a source
destination pair . Information is sent as multiple-bit
words. The number of simultaneous source-destina-
tion pairs is not C: if each pair is allocated K of the C
such pairs exist.
Typically, BPW reduces the packet transmission
time for a packet potentially reducing packet latency.
*This work was supported in part by the Research Grants Committee of the University of North Carolina at Greensboro, where part of the
research was conducted. Part of the research utilized computing facilities at the North Carolina Supercomputing Center.
Prof. Krishna Sivalingam, Assistant Professor, Computer Science, School of Elect. Engg. & Computer Science, EME 102 Bldg, Mail Stop
642752, Washington State University, Pullman, WA 99164-2752, Email: email@example.com, URL:www.eecs.wsu.edu/Krishna, Phone: 509
335 3220, Fax: 509 335 3818