Connection Admission Control


Connection Admission Control

Admission control, in the most primitive sense, is the simple practice of discriminating which traffic is admitted into a network in the first place [#REF| [1] . Admission control in ATM networks is known as "Connection Admission Control" (CAC).

Connection admission control is defined as ‘the set of actions taken by the network during the call set-up phase (or during the call renegotiation phase) to establish whether a VC/VP connection can be accepted’ [#REF| [2] [#REF| [3] .

Where is Connection Admission Control (CAC) used?

By definition, CAC can only exist in a connection oriented network. Connectionless networks such as the Internet and SMDS networks have no CAC role. However, in any connection-oriented network, CAC is a major part of the strategy for controlling congestion (see congestion control), and in the case of circuit switching and CBR services (see Traffic Contract), it is the only mechanism [#REF| [2] .

What is the Role of Connection Admission Control?

In principle, in a connection-oriented network, the role of CAC is to decide whether there are sufficient free resources on the requested link to allow a new connection [#REF| [4] . A connection can only be accepted if sufficient resources are available to establish the connection end-to-end with its required quality of service. The agreed quality of service of existing connections in the network must not be affected by the new connection [#REF| [2] .

If the network has the required resources, the CAC may allow a connection request to proceed; if not, the CAC will indicate this and notify the originator of the request that the request has been refused [#REF| [4] .

What criteria are used to make the decision?

When a connection is requested by an application, the application indicates to the network (in the form of a traffic descriptor-see traffic contract) [#REF| [1] the:

* type of service required
* traffic parameters of each data flow in both directions (a set of parameters describing the source traffic characteristics)
* quality of service parameters requested in each direction

The CAC uses this information to determine the required quality of service of the connection, and determines whether it has sufficient resources to accept the requested connection based on the current network status.

Strategy and Policy of Connection Admission Control for different services

The strategy employed by CAC varies according to the type of service (see traffic contract), and in the case of VBR, ABR, and UBR services, becomes a complex issue and is still the subject of intensive research.

The policy for each connection type depends on the stochastic nature of the service. The following gives a brief indication of policies for each connection type [#REF| [4] .

Circuit-Switched connection

In this case, the request for a connection, if granted, results in a link connection being allocated to the connection. In principle, a resource manager can be completely non-discriminatory in its allocation of free capacity to connection requests as they will all have the same effect on the state of the resource. There may, however, be some circumstances where CAC may refuse a new connection even when there is sufficient capacity for the connection. For example, circuits could be designated as low priority or high priority, and the CAC may choose to accept a high-priority connection while refusing a lower priority. In refusing the lower priority connection, it is effectively reserving the remaining capacity on the resource for high-priority connections. Prioritisation becomes important in service restoration after a failure where the resources become scarce and some connections must be dropped. Higher priority services can reasonably attract a premium tariff [#REF| [1] [#REF| [4] [#REF| [5] .

CBR Connections

While the principles of CAC are basically similar to those for circuit-switched connections, CAC is more likely to be discriminatory in CBR connections (see traffic contract). As the connections can have different bandwidths, they will have different impacts on the remaining capacity within the link. For example, CAC for CBR connections could employ a strategy of only accepting connections that take less than half of the remaining capacity. With such a strategy, some connections will be refused even if there is capacity available to resource the connection. This makes good commercial sense if several smaller connections are worth more than one large connection of the same capacity [#REF| [4] [#REF| [5] .

VBR Connections

With VBR connections (see traffic contract), the CAC is not only making judgment about the nature of future connection requests, but is also having to make a judgment on the future behavior of the connections it has already accepted onto the link based on the VBR parameters. This is based on statistical assessment as to whether accepting the new connection will take the likelihood of cell loss for the current traffic beyond acceptable limits [#REF| [1] [#REF| [4] .

ABR Connections

The role of CAC in ABR services (see traffic contract) depends on the ABR strategy employed. The use of the resource management protocol allows for the use of CAC; however, it is quite possible to use a policy of accepting all connections and simply regulating the rate of all the connections on the resource to ensure the resource does not become overloaded [#REF| [4] [#REF| [5] .

UBR Connections

The role of CAC in basic UBR (see traffic contract) connections is similar to that in VBR connections in that it must decide according to the requested peak cell rate (see traffic contract) on whether to admit the connection [#REF| [1] [#REF| [4] .

ee also

* Admission control
* Traffic Contract
* Teletraffic engineering in broadband networks
* Broadband Networks


=

References
=

[1] Ferguson P., Huston G., “Quality of Service: Delivering QoS on the Internet and in Corporate Networks”, John Wiley & Sons, Inc., 1998. ISBN 0-471-24358-2.

[2] Handel R., Manfred H., Schroder S., “ATM Networks: Concepts, Protocols, Applications“, Addison-Wesley Publishing company Inc., 1994. ISBN 0-201-42274-3.

[3] ITU-T: Recommendation I.371. ‘Traffic Control and Congestion Control in B-ISDN’. Geneva, 1993.

[4] Sexton M., Reid A., “Broadband Networking: ATM, SDH and SONET”, Artech House Inc., Boston, London, 1997. ISBN 0-89006-578-0.

[5] Hiroshi Saito, Teletraffic Technologies in ATM Networks, Artech House, 1993. ISBN 0-89006-622-1.


Wikimedia Foundation. 2010.

Look at other dictionaries:

  • Connection Admission Control —    Abbreviated CAC. An Asynchronous Transfer Mode (ATM) function that determines whether a virtual circuit connection request will be accepted.    See also Asynchronous Transfer Mode …   Dictionary of networking

  • Admission control — is a network Quality of Service (QoS) procedurecite book | author = Ferguson P., Huston G. | title = Quality of Service: Delivering QoS on the Internet and in Corporate Networks | publisher = John Wiley Sons, Inc. | date = 1998 | id = ISBN 0 471… …   Wikipedia

  • Network Admission Control — (NAC) refers to Cisco s version of Network Access Control, which restricts access to the network based on identity or security posture. When a network device (switch, router, wireless access point, DHCP server, etc.) is configured for NAC, it can …   Wikipedia

  • Call Admission Control — prevents oversubscription of VoIP networks, CAC is a concept that applies only to real time media traffic and not to data traffic. CAC mechanisms complements the capabilities of QoS tools to protect voice traffic from the negative effects of… …   Wikipedia

  • Flow control — distinguish|control flowIn computer networking, flow control is the process of managing the rate of data transmission between two nodes to prevent a fast sender from over running a slow receiver. This should be distinguished from congestion… …   Wikipedia

  • Network Access Control — (NAC) is an approach to computer network security that attempts to unify endpoint security technology (such as antivirus, host intrusion prevention, and vulnerability assessment), user or system authentication and network security… …   Wikipedia

  • CAC — Connection Admission Control (Computing » Telecom) **** Common Access Card (Governmental » Military) * College And Career (Academic & Science » Universities) * Citizen s Advisory Committee (Community) * Climate Analysis Center (Academic & Science …   Abbreviations dictionary

  • MUSE QoS solution — MUSE advocates the introduction of QoS into IP networks as this allows better resource utilization while at the same time it allows to serve multiple and different applications with the transport quality they actually need.The solution needs to… …   Wikipedia

  • Teletraffic engineering in broadband networks — Teletraffic engineering is a well understood discipline in the traditional voice network, where traffic patterns are established, growth rates can be predicted, and vast amounts of detailed historical data are available for analysis. However, for …   Wikipedia

  • UPC and NPC — The main purpose of UPC (Usage Parameter Control) and NPC (Network Parameter Control) is to protect the ATM (see Asynchronous Transfer Mode) network resources from malicious connections and to enforce the compliance of every connection to its… …   Wikipedia