Handling of ATM flows in the demonstratorby means of localized
measurements and decisions
Nicola Blefari-Melazzi
3/7/01, CNR, Sede Centrale– Roma
University of Perugia
No admission control
best effort performance
RSVP: explicit resource reservation along the signaling path
“hard” QoS guarantees
Per-flow management->complexity, limited scalability (ex. ADPCM
coding requires 32 kb/s for a voice channel. A single OC-12 link
(622 Mb/s) can support up to 20000 flows)
Differentiated Services approach (DiffServ)
Edge-only state implies that the service indication must be carried
in the packet->establishing different “priority levels”
simplicity and scalability but no QoS guarantees
the lack of an admission control scheme means that, upon overload
in a given service class, all flows in that class suffer a
degradation of service
# *
RFC 2998 and RFC2990 (Nov. 2000) recognize that:
“both the IntServ architecture and the DiffServ architecture have
some critical elements in terms of their current definition which
appear to be acting as deterrents to widespread deployment
there appears to be no single comprehensive service environment
that possesses both service accuracy and scaling properties
further refinement of the QoS architecture is required to integrate
DiffServ network services into an end-to-end service delivery model
with the associated task of resource reservation
# *
Measurement-based Admission Control
MBAC: each router takes admission control decision based on
run-time measures of aggregate traffic handled (necessity of
signaling)
Source
Destination
Signalling
Measur.&
Decision
Measur.&
Decision
Measur.&
Decision
Data
Data
Signalling
Signalling
Signalling
Endpoint Admission Control
EAC: admission control managed by pure end-to-end operation, by
means of a probing phase (long set-up time or imprecise
measurements)
Probing
Probing
1
2
Ack
Measur.
3
Source
Destination
Rin
Rout
injection of a “probe” packet (tagged as such)
activation of a timer (DECISION_WAITING state)
if an ACK is received from the destination before timeout
expiration, it can start emitting “data” packets (tagged as
such)
DESTINATION NODE:starts a DECISION_ACTION procedure, after
receiving a probe packet; if it is willing to accept the
connection, it replies with an ack packet
ROUTERS: drop probes (GATE closed) when congestion is estimated
(Gauge)
Measur.&Decision
GRIP: Internal Router Decision Criterion
The MBAC module measures the aggregate traffic and implements a
Decision Criterion
The Decision Criterion acts as a switch on the probe queue
ACCEPT state: probe packets served
REJECT state: probe packets discarded
# *
Probing and data packets marked by different DSCPs
The decision criterion (DC) must not be necessarily based on
traffic measurements but could be independently defined by network
operators (i.e., by implementing a separate probing queue with
given capacity and buffer space, to suitably limit accepted probe
packets, or by relying on lower layers capabilities, e.g., ATM,
MAC)
The notion of internal router congestion is not standardized, and
it is up to each specific router DC implementation to locally
determine if, and when, congestion arises
The internal (arbitrarily sophisticated and performing) router
decision is summarized in the router state (ACCEPT vs.
REJECT)
# *
GRIP: end-to-end operation
The router state is not notified to the end points by means of
explicit signaling information transmission
end points rely on probing packet losses (i.e. dropped by routers
in the REJECT state) as an implicit signaling pipe, of which the
network remains unaware
when the router is in the ACCEPT state, it advertises that it can
admit new connections by allowing probing packets to be served.
Conversely, when the router is in the REJECT state, no probing
packets are forwarded
# *
no explicit agreement among entities (e.g., probing packet format,
probing/feedback packets payload contents) is necessary to run
GRIP
this principle can be the way to provide a smooth migration path,
consisting in distributed admission control schemes of increasing
complexity and effectiveness, which can indeed operate over a
multi-provider and multi-vendor Internet
# *
The Migration Path
GRIP can seamlessly operate, at the expense of perceived
performance, even in the legacy Internet and in a DiffServ
network
(failed reception of probing packets means that a congestion
condition occurs in the network, as in TCP)
in these conditions, GRIP provides at least a form of stability
that impedes persistent link congestion and allows a receiver
capability negotiation
The performance of GRIP are related to the capability of routers to
locally take decisions
Thus, GRIP opens up a future smooth migration path toward gradually
improved QoS, as routers in different domain will be enhanced,
without losing inter-operability with installed devices
# *
Smooth migration path
toward a QoS capable infrastructure by means of independent
upgrades
Scalability:
the exchange of signaling is implicit
inter-working among different sub-networks is simplified
Performance calibration:
Compatibility with AF PHB (RFC2597)
# *
We consider a full-fledged QoS GRIP domain
The traffic is regulated at the network edge by means of DLB
devices
the sources are greedy (they use all the emitting opportunity they
have)
rS
BTS
PS
1
Source
In(t)
Out(t)
DLB
Estimation of Admitted Sources
Conservative estimation of the number of active sources, N, based
on the worst case behavior of the DLB output processes
Maximum number of admissible sources, K, determined off-line by
means of acceptance rules based on loss/delay constraints
New requests are accepted as long as N≤K
K is a “tunable knob” and can be chosen by the network operator by
trading network utilization with user-perceived performance (e.g.
loss, delay, etc)
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Transient Management
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0
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600
0
10
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Micromobility support
Mobility is handled hierarchically, to reduce traffic generated by
handovers and the relevant latency (a local “anchor” node handles
mobility, without involving Home Agent and Correspondent
Node)
Integration between Mobility and QoS
QoS during and after the handover (QoS-Aware Handover)
# *
Extensions needed to support QoS-Aware handovers:
Perform a test of the availability of the resources on the new path
before switching the QoS-sessions of the Mobile Node on that
path
Maintaining the current path active while testing resources
availability on the new path
Avoid to reserve resources both for the new and the current path
along the entire end-to-end path
# *
QoS aware Handover in micromobility
The SHA can be introduced in IP Micromobility Architectures such
as
Hierarchical Mobile IP
RSVP has not been designed to handle two contemporary routes
intra-domain user migration cannot be managed in a localized manner
(as micromobility management suggests), but requires RSVP signaling
to travel back and forth to the destination node
Local SHA
References
G. Bianchi, N. Blefari-Melazzi: "GRIP: QoS support over Stateless
DiffServ Networks by means of localized measurements and
decisions", Lecture Notes on Computer Science, Springer-Verlag,
volume 1989 (a more detailed technical report can be found at
http://drake.diei.unipg.it/netweb/GRIP_tech_rep.pdf)
G. Bianchi, N. Blefari-Melazzi, M. Femminella, F. Pugini:
"Performance Evaluation of a Measurement-Based Algorithm for
Distributed Admission Control in a DiffServ Framework", to appear
on 2001 Tyrrhenian International Workshop on Digital
Communications, 17-20 Settembre, 2001, Taormina, Italy (in Lecture
Notes on Computer Science, Springer-Verlag, Sergio Palazzo,
Ed.).
G. Bianchi, N. Blefari-Melazzi, M. Femminella: “A Migration Path to
provide End-to-End QoS over Stateless Networks by Means of a
Probing-driven Admission Control”, Internet Draft,
draft-bianchi_blefari-end-to-end-QoS-00.txt, work in progress,
http://www.ietf.org/ID.html
G. Bianchi, N. Blefari-Melazzi: " Per Flow Admission Control over
AF PHB Classes”, Internet Draft,
draft-bianchi_blefari-Adm-Contr-over-AF-PHB-00.txt , work in
progress, http://www.ietf.org/ID.html
G. Bianchi, N. Blefari-Melazzi, M. Femminella, F. Pugini:
“Stateless Per-flow Admission Control in a Mobile IP Environment”,
http://drake.diei.unipg.it/netweb/GRIP_mobile.pdf