ISO IEC 14476-6 pdf download – Information technology — Enhanced communications transport protocol: Specification of QoS management for n-plex multicast transport

ISO IEC 14476-6 pdf download – Information technology — Enhanced communications transport protocol: Specification of QoS management for n-plex multicast transport
5
Conventions
None.
6
Overview
This Recommendation / International Standard provides a specification of QoS management for n-plex multicasttransport connections.This Specification describes the following QoS management operations:
a)Qos negotiation, including reservation of network resources:
For QoS negotiation, this Specification assumes that a desired QoS level for multicast application servicecan be expressed in terms of a set of QoS parameters. Qos negotiation is performed via an exchange ofcontrol packets between the TCN (TC-owner) and TS-users for the multicast data channel. The TCNproposes the target values of QoS parameters obtained from the application’s requirements in order forTS-users to send or receive multicast data,and each TS-user can propose modified values based on itssystem and/or network capacity and the application’s requirements. The TCN arbitrates the modifiedvalues proposed by TS-users. Target values for Qos parameters can be used as input parameters forreservation of network resources.
b)QoS monitoring:
QoS control in ECTP-6 is based on feedback of control packets from TS-users. The feedback messagesfrom TS-users enable the TCN to keep track of the number of TS-users and also to monitor theconnection status for the multicast data channel.QoS monitoring is designed to allow TS-users and theTCN to diagnose the connection status in terms of QoS parameter values, and thus to take the necessaryactions for maintaining the connection status at a desired QoS level. The monitored connection statuswill be reported to the application on the TCN side. The information conveyed could provide statisticsuseful for billing purposes, for example.
c)QoS maintenance:
Based on feedback information from TS-users, the TCN and SUs (Sending TS-users) take one or moreactions so as to maintain the connection status at a desired QoS level. These QoS maintenance actionsinclude adjustment of the data transmission rate,connection pause and resume,troublemaker ejectionand connection termination operations. These Qos monitoring and maintenance functions, based onmonitored parameter status, provide rate-based congestion control.
In the connection creation phase, theTCN informs TS-users whether Qos management is enabled. lf Qos managementis enabled,the TCN must also specify whether or not Qos negotiation will be performed in the connection.QoSmonitoring and maintenance operations are performed only if QoS management is enabled.
Figure l illustrates these QoS management operations for the n-plex multicast connection.In the figure, the protocoloperations marked as dotted lines are specified in Rec.ITU-T X.608|ISO/IEC 14476-5(ECTP-5).
In this figure, it is noted that the basic control operations of the n-plex multicast connection are described in ECTP-5,such as control tree creation，tree-based reliability control,control tree maintenance and token control. In thisSpecification, the QoS negotiation, monitoring and maintenance operations for the n-plex multicast connection will beintroduced.
From the requirements of the applications, the TCN will determine the target values for each QoS parameter. Theprocedures for mapping the requirements of an application to these target parameter values are outside the scope of thisSpecification. Application programs could be used to carry out such mappings.
QoS negotiation is performed in the connection creation phase. The TCN proposes the desired target values for eachQoS parameter, used when sending multicast data to TS-users and receiving multicast data from SUs by multicast, viathe CR packet. For the throughput parameter,three target values are specified: Controlled Highest Quality (CHQ),Operating Target (OT) and Lowest Quality Allowed (LQA).For the other parameters,such as transit delay, transitdelay jitter and data loss rate, only two target values are specified: OT and LQA.
lf QoS negotiation is enabled, each TS-user can propose modifications to the TCN’s proposed parameter values. Thesemodified values will be determined by considering the system capacity at the TS-user side and network environment.The following restrictions are imposed for modification of the parameter values by TS-users:
a)OT values must not be modified by TS-users;
b) the values modified by TS-users must be within the LQA and CHQ values proposed by the TCN.
The parameter values modified by TS-users are delivered to the TCN via CC messages. The TCN arbitrates differentparameter values for various TS-users by taking a default range of values.
Figure 2 shows an abstract sketch of QoS negotiation that can occur in ECTP-6. From the requirements of theapplication, a set of target Qos parameter values for the multicast data channel will be configured at the TCN. The TCNinforms TS-users about the target values for sending multicast data to TS-users and receiving multicast data from an SU(step 1).Based on these target values, each TS-user begins to make resource reservations with the help of RSVP [4][5]or Diffserv [6] (step 2). If QoS negotiation is enabled in the connection, each TS-user may propose modified values forQoS parameters based on its system andor network capacity and the requirements of the application for the multicastdata channel (step 3). From these modified parameter values, the TCN determines the arbitrated values for sendingmulticast data to other TS-users and receiving multicast data from other TS-users (step 4). These arbitrated values aredelivered to TS-users via subsequent TSR or JC packets and will be used for QoS monitoring and maintenance.