25-08-2017, 09:32 PM
Internet working connectionless and connection-oriented networks
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ABSTRACT:
This paper proposes a scheme for taking advantage of the
properties of both connectionless (CL) and connection-oriented
(CO) networks to carry traffic from existing applications.
Specifically, it proposes a solution for allowing data generated by
endpoints on a CL (IP) network to be redirected to CO networks
if there is an advantage from the user or service provider
perspective. The advantage to a user is that the user can ask for
and receive a guaranteed quality of service for a specific flow. The
advantage to a service provider is that bandwidth utilization in a
packet-switched CO network is better than in a CL network with
precomputed routes since bandwidth can be dynamically
allocated to flows on an as-needed basis. These advantages only
exist when the CO network is operated in a switched mode (i.e.,
some connection “setup” actions are performed for each arriving
flow) rather than in a provisioned mode (where all these actions
are performed a priori).
Introduction
Connectionless (CL) networks and connection-oriented (CO)
networks have some fundamental distinguishing features. CO
networks are those in which connection setup is performed prior
to information transfer. In CL networks, no explicit connection
setup actions are executed prior to transmitting data; instead, data
packets are routed to their destinations based on information in
their headers. CL networks do not suffer the delay and processing
overhead associated with connection setup. In contrast,
information about the connections in CO networks helps in
providing service guarantees and, furthermore, makes it possible
to most efficiently use network resources (e.g., bandwidth) by
“switching” them to appropriate connections as they are set up.
Prior work
Prior work on this specific problem of internetworking a CL
IP network with a CO network operated in the switched mode
include MPOA (MultiProtocol Over ATM [6]) and MPLS
(MultiProtocol Label Switching [3]). In this section, we compare
our solution with these two prior solutions.
Though MPOA was defined for ATM networks, it is easily
extendible to any CO network operated in the switched mode. In
MPOA, gateways (nodes with connectivity to both the CL and CO
network) perform the following actions:
• make decisions of whether to route flows through the CO
network or CL network (details of how this is done are not
part of the MPOA specification),
• for those flows for which a decision is made to use the CO
network:
— an address resolution is first performed through the
IP network to obtain the address of the farthest
gateway possible on the CO network, and
— a connection is set up through the CO network to
this gateway.
Routing related actions
Our solution is to broadcast information about the available
resources of the CO network to the routers of the CL network.
This would result in IP routers computing “shortest path” routes
to some destinations that traverse the CO network. While this
concept is applicable to any IP routing protocol, we explain how
it is realized if the routing protocol used in the IP network is the
OSPF (Open Shortest Path First) routing protocol [8].
In the most common configurations, routers running OSPF are
connected via point-to-point links or broadcast networks, such as
ethernet. However, OSPF also allows routers to be interconnected
via non-broadcast networks. A common interpretation of the term
“non-broadcast network” is a switched CO network, such as an
X.25 network or ATM network. Thus, OSPF allows routers to be
interconnected via a CO network without provisioned
connections; provisioned connections are treated merely as pointto-
point links by OSPF. To handle non-broadcast networks, two
modes of operation are recommended in the OSPF specification
[8]: (i) NBMA (Non-Broadcast Multi-Access) and (ii) point-tomultipoint.
In the NBMA mode, the non-broadcast network
emulates a broadcast network and assigns designated routers (and
backup designated routers) to generate network state
advertisements, while in the point-to-multipoint mode, the nonbroadcast
network is advertised as a set of point-to-point links
between some of the routers on the non-broadcast network.
User-plane actions
Having addressed in Section 3.1 the routing related actions
that enable data flow from the IP network to the CO network, in
this section we focus on user-plane actions to handle IP packets
that arrive at CL-CO gateways. Connections are set up through the
CO network for some, but not necessarily all, of the arriving TCP
and UDP flows. Thus, CL-CO gateways need to handle traffic
from both (1) flows for which connections are set up, and (2) flows
for which connections are not set up. The decision to set up
connections is made at the CL-CO gateways based on the userspecified
service requirements and the traffic situation in the CL
and CO networks; specific algorithms are beyond the scope of this
paper.
Summary and conclusions
We conclude that there are advantages both from the user
perspective and the service provider perspective to carry some of
the data generated by Internet applications on CO (Connection-
Oriented) networks. Applications on Internet endpoints continue
generating traffic assuming the CL (Connectionless) mode, but
special nodes called CL-CO gateways determine whether or not to
redirect traffic from the CL network to the CO network.