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
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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
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Measurement-based Admission Control
MBAC: each router takes admission control decision based on run-time measures of aggregate traffic handled (necessity of signaling)
Source
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Signalling
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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
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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
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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)
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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
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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
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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
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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)
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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
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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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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)
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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
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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