Definition

Multicast virtual scheduling is a traffic scheduling mechanism for subscribers who demand multicast programs. After a subscriber joins a multicast group, if multicast traffic needs to be copied based on the multicast VLAN or if the replication point is a downstream device, the bandwidth for the unicast traffic of the subscriber is adjusted accordingly. As a result, bandwidths for the unicast traffic and multicast traffic of the subscriber are adjusted in a coordinated manner.

Purpose

Multicast virtual scheduling is a subscriber-level traffic scheduling. It adjusts the bandwidths for the unicast traffic and multicast traffic of a subscriber in a coordinated manner without changing the total bandwidth of the subscriber, thus ensuring the quality of BTV services of the subscriber.

Multicast Virtual Scheduling Overview

With the development of the broadband TV (BTV) service, the quality of video services on TVs is now a key issue that has a direct impact on the experiences and feelings of users. Therefore, carriers must ensure that users can view TV programs smoothly by managing the available bandwidth subtle.

Figure 11-1 Schematic view of the background of multicast virtual scheduling

As shown in Figure 11-1, a family views multicast programs (multicast data) through a Set Top Box (STB) and browses the Internet (unicast data) through a PC. For example, the maximum bandwidth for the family is 3 Mbit/s. The Internet service occupies all the 3 Mbit/s bandwidth, and then the user demands a multicast program requiring a bandwidth of 2 Mbit/s through the STB.

As the multicast data and unicast data require the bandwidth of 5 Mbit/s in total, data congestion will occur in the access network, and some packets will be discarded. Therefore, the quality of the multicast program cannot be ensured.

Multicast Virtual Scheduling Solutions

The multicast virtual scheduling technology is developed to solve this problem. The multicast virtual scheduling technology is the user-class scheduling. When the total bandwidth of a user is limited, this technology realizes the dynamic adjustment of the unicast bandwidth and the multicast bandwidth for the user. Therefore, the quality of the BTV service is ensured.

The multicast virtual scheduling can solve the problem shown in Figure 11-1. The router is configured with the multicast virtual scheduling feature. When the sum of the multicast traffic and unicast traffic received by a user is greater than the bandwidth assigned to the user, the router reduces the bandwidth for unicast traffic of the user to 1 Mbit/s to meet the requirement of bandwidth for multicast traffic. Therefore, the multicast program can be played normally.

Multicast Shaping Overview

After the IPTV multicast service is deployed, the multicast source may jitter when the multicast traffic is huge. The NE20E can shape the multicast traffic so that the jitter of the multicast source can be limited in an acceptable degree. If the NE20E is configured with the function of multicast shaping, the NE20E can control the multicast traffic of users in the domain when users use multicast services. This prevents the multicast traffic from bursting and can help to send multicast packets smoothly and control the jitter of the multicast source in an acceptable degree.