598 8.4 Integrated Services (IS)
rienced quality of service may vary widely from vendor to vendor and from
one traffic environment to another. There will have to be agreements made
on what constitutes acceptable service for the various classes of ATM and
how that service will be provided. Developing mechanisms to ensure quality
of service in ATM is one of the most important topics that the ATM Forum
is currently investigating.
8.4 Integrated Services (IS)
The fundamental service model of the Internet, exemplified in the best-
effort delivery service of IP, has remained essentially unchanged for over 20
years. This model has serviced legacy applications such as file transfer and
terminal access well, but routing delays and congestion mean that real-time
applications do not work so well on a best-effort Internet. The Integrated
Services (IS) model is intended to solve these problems by becoming a key
component of future Internet architecture. This new Internet architecture
includes support for both the current best-effort services and emerging real-
time services. IS is designed to optimize network resources for real-time
applications such as videoconferencing, video broadcast, and audioconfer-
encing. These applications all require guaranteed QoS in order to offer
acceptable quality. IS enables Internet traffic to be separated into legacy best-
effort traffic and real-time data flows requiring guaranteed QoS. IS defines
two service classes specifically designed for real-time traffic, as follows:
Guaranteed service—intended for applications requiring a fixed delay
Predictive service—intended for applications requiring prognosticate
delay [32].
IS integrates (hence the name) all of these services over a common link,
using a scheme called controlled link sharing. IS is also designed to work
equally well with multicast as well as unicast traffic. The IS model is speci-
fied by the IETF in [11].
8.4.1 Implementation model
There are four main components required in an implementation of IS;
these comprise the packet scheduler, the admission control routine, the clas-
sifier, and the reservation setup protocol. These are discussed briefly below.
Reservation setup protocol. IS use the reservation protocol (RSVP)
for the signaling of the reservation messages. The IS instances com-
8.4 Integrated Services (IS) 599
Chapter 8
municate via RSVP to create and maintain flow-specific states in the
end-point hosts and in routers along the path of a flow. An applica-
tion that wants to send data packets in a reserved flow communicates
with the reservation instance RSVP. The RSVP protocol tries to set
up a flow reservation with the requested QoS, which will be accepted
if the application fulfilled the policy restrictions and the routers can
handle the requested QoS. RSVP advises the packet classifier and
packet scheduler in each node to process the packets for this flow ade-
quately. If the application now delivers the data packets to the classi-
fier in the first node, which has mapped this flow into a specific
service class complying to the requested QoS, the flow is recognized
with the sender IP address and is transmitted to the packet scheduler.
The packet scheduler forwards the packets, depending on their ser-
vice class, to the next router or, finally, to the receiving host. Because
RSVP is a simplex protocol, QoS reservations are made only in one
direction: from the sending node to the receiving node. If the applica-
tion in our example wants to cancel the reservation for the data flow,
it sends a message to the reservation instance, which frees the reserved
QoS resources in all routers along the path, so the resources can be
used for other flows.
Admission control. The admission control contains the decision algo-
rithm that a router uses to determine if there are enough routing
resources to accept the requested QoS for a new flow. If there are not
enough free routing resources, accepting a new flow would impact
earlier guarantees and the new flow must be rejected. If the new flow
is accepted, the reservation instance in the router assigns the packet
classifier and the packet scheduler to reserve the requested QoS for
this flow. Admission control is invoked at each router along a reserva-
tion path to make a local accept/reject decision at the time a host
requests a real-time service. The admission control algorithm must be
consistent with the service model. Admission control should not be
confused with policy control, which is a packet-by-packet function
processed by the packet scheduler. It ensures that a host does not vio-
late its promised traffic characteristics. Nevertheless, to ensure that
QoS guarantees are honored, the admission control will be concerned
with enforcing administrative policies on resource reservations. Some
policies will be used to check the user authentication for a requested
reservation. Unauthorized reservation requests can be rejected.
Admission control will play an important role in accounting costs for
Internet resources in the future.

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