Packet Optical Networks for High Speed TCP-IP Backbones

                      F. Callegati, M. Casoni
  DEIS University of Bologna, Viale Risorgimento 2, 40136 Bologna
                               ITALY

	A new proposal for the implementation of TCP-IP backbones
based on optical packet switching technology is here described.  The
proposed network architecture merges the flexibility in resource
management of packet switching with the high capacity offered by full
optical technology.
	We consider a network scenario in which TCP-IP are the
communication protocols. In LANs we believe that IP over ATM will
hardly be competitive with Gigabit Ethernet. At the same time this
emerging technology will warrant the development of high speed optical
backbones, to carry the increased capacity. In WANs the debate of IP
versus ATM is still an open issue.
	As regards ATM, a large infrastructure has not succeeded in
long distance networks yet and the complete support of voice over ATM
does not seem to have been definitely solved. IP over ATM is getting
also complicated and costly.
	As regards IP, still the problem of QoS guarantees for real
time applications (for instance Internet telephony) is on stage and
the proposed reservation protocols such as RSVP are difficult to
evaluate in terms of cost-efficiency.
	Meanwhile, another fundamental player has come on the stage:
optical networks.  Optical fibers offer huge bandwidth at a reasonable
cost and optical devices for multiplexing and switching in simple
configurations are now available. These facts are making optical
networks a very appealing solution for development of
telecommunication networks, changing some of the optimization and
cost-effectiveness evaluation made by network engineers.
	One of the main issues investigated in ATM networks has been
the bandwidth optimization because bandwidth was an important limited
resource for services.  Today, optical fibers provide almost unlimited
bandwidth and this means that most of the implementation complexity
and cost typical of ATM can be remarkably reduced.
	Our  focus will  then be  on  fast WAN  connections for TCP-IP
remote LANs by means of an Optical Transparent Packet Network (OTP-N),
as a possible   future scenario. In  particular,  we will describe  an
optical packet WAN studied in the framework of the European ACTS KEOPS
(KEys to Optical Packet Switching) Project.
	In Internet routers are interconnected through a meshed
network topology based on point to point links that carry flows of
aggregated IP traffic potentially reaching several Gbit/s.  This
solution shows drawbacks on a wide area as complexity increases.
Therefore a solution, for router interconnection, flexible in term of
bandwidth management, scalability and paths reconfiguration is
recommended.
	Current approaches to face this issue are based on the
implementation of high performance routers, using existing high speed
switching technology and links for packets delivery; for instance
gigabit IP routers with output ports towards SDH or ATM.  These
solutions, though based on fairly mature technologies, lack of
flexibility and/or scalability. In particular ATM, due to the very
short cell, does not seem to be able to follow up with the huge
increase of bandwidth made available by the optical technology.  This
means that for link speeds up to 40 Gbit/s and beyond, the cell
duration is so short that cell processing in the switches becomes a
hard task, even with very advanced electronics.  On the other hand SDH
is well suited for high speeds, but since it is based on a circuit
transfer mode, lacks in flexibility of bandwidth management and the
same holds also for pure WDM circuits.  Thus, our proposal aims at
providing interconnection among remote IP islands by means of the
OTP-N whose core network relies on photonic packet switches.
	Our presentation will address the network reference models
used inside the project to provide a basis for the OTP-N within the
framework of WDM access to the fibre bandwidth. The functionality of
the interfacing units with other networks, both electronic (IP) and
optical (WDM transport), and their principles of operation will be
shown.