Challenges to IPTV Bearer

IPTV, also interactive network TV, uses common TV sets as terminals and delivers Video On Demand (VOD), Broadcast TV (BTV) and other services to residents over the IP bearer. As a program meant for entertainment, IPTV must ensure good user experience and high image quality. The implementation of IPTV is a complex system project, involving operation support, operation management, content service, bearer transport, and home network. It needs the collaboration of all levels. As for the bearer network, the large bandwidth and streaming characteristics of IPTV must be considered for building efficient, controllable, secure and reliable transport channels, so as to ensure the perfect realization of IPTV services.

IPTV services mainly include BTV and VoD. When an operator builds an IPTV bearer network, these two types of service are regarded as prototypes. The main challenge to BTV is multicast distribution, which needs considering bandwidth consumption, path between source and receiver, load balance between multicast sources and the complex degree of implementation. VoD is point to point and the bandwidth it uses is in proportion to number of user. This makes VoD a network bandwidth killer. It is, therefore, a necessary consideration of the operator to apply reasonable VoD service control. In addition, IPTV is a high value added service, which requires strict planning of QoS, security and reliability. Only when all these are realized can entertainment programs of high quality and assured experience be presented to end users.

Build Efficient and Controllable IPTV Bearer Network

BTV Service Solution



A s shown in the above picture, above the Metro Ethernet（ME）aggregation node, PIM-SSM is deployed; below the aggregation node, Multicast VLAN（MVLAN）is used. The packets of user registration enter into MVLAN on the DSLAM and is terminated at the ME aggregation node along the MVLAN. At the terminating aggregation node, the user is registered and added to the multicast service. Then, according to the multicast group and source address, an end-to-end multicast distribution tree is built using PIM-SSM.

User registration requests can be carried in IGMP V1/2/3 messages. The IGMP V3 registration message directly incorporates the multicast group and the multicast source. The IGMP V1/2 registration message only includes the multicast group. In this case, SSM-MAPPING need be configured at the aggregation node for adaptation with PIM-SSM.

PIM-SSM is a multicast technology for given multicast sources. It is a subset of the currently most mature multicast protocol, PIM-SM. Compared with PIM-SM, PIM-SSM is simpler and more efficient. It spares the switching from RPT to SPT. When a user joins, a shortest path tree (SPT) is built between the specified multicast source and the receiver. PIM-SSM does not rely on the lower layer network to build the multicast distribution tree. For either a ring network or a tree network, different receivers can always construct their shortest paths to the multicast source based on the unicast route. Multicast streams of a same muticast address are forwarded along different multicast distribution trees, thus assuring the balance of network load. Besides, PIM-SSM supports the ANYCAST of a multicast source by nature, which can realize the load sharing of multicast sources. Multicast streams are carried directly over IP, which is simpler than multicast over MPLS and reduces the complexity of network maintenance.

When a network node or link fails, IGP fast convergence and PIM-SSM refinement can restore the multicast distribution tree in a quick manner, thus ensuring the reliability of multicast services.

In addition, the multicast technology with given sources can prevent the join and spoofing of illegal sources and avoid the play of illegal programs and the waste of bandwidth resources.

To enhance user experience, in the case of large numbers of users, static multicast join is used directly to route multicast streams to the ME aggregation node and even the DSLAM. This can largely cut the time for channel switching.

In the above solution, PIM-SSM is deployed as far as the ME network edge to minimize the coverage of other layer 2 multicast technologies. The solution also enhances network security and reliable protection as required by carrier-class operation. All these add to the eventual construction of a simple, efficient BTV bearer network that offers high user experience.

VOD Service Solution

The above picture depicts a VoD service solution, wherein VPN technology is adopted to isolate VoD from other services. This means a L3 VPN is deployed over the whole network. The aggregation node, ES, CS, and VoD related components all join this VPN. VoD user requests are terminated by the aggregation node at network edge where the user accesses the L3 VPN. If the demanded program is stored in ES, the program is transferred over the L3 VPN from ES to the user directly. If the demanded program is stored in CS, it is transferred over the L3 VPN from the CS to the user.

This is only a basic VoD implementation procedure. As VoD is a network bandwidth killer, the solution must offer reasonable means to plan and control bandwidth usage. In the core network, the common practice is to deploy the mature CDN technology and assure 70% programs for demand are stored in the ES. The real bandwidth usage in the core network is normally acceptable.

In the ME network, because all VoD requests consume bandwidth, without control, the danger of bandwidth exhaustion will be at sight and other services will be severely affected. Based on many years of experience in telecom network construction, Huawei uses Connetion Adminission Control （CAC） technology to achieve reasonable control of VoD accesses. In the CAC solution, some network resources are first reserved for VoD use. Then a policy server is there to determine the allowable VoD sessions according to the amount of reserved resources and determines whether to admit a VoD access according to the number of sessions in progress. Resource reservation is performed in two sections. One section is from ES to the aggregation node at the ME edge, where all VoD resources under a aggregation node are reserved. The reservation can be implemented by the adoption of RSVP-TE technology. For instance, when 500Mbps bandwidth is reserved, if one VoD session consumes 2Mbps, 250 VoD requests can be admitted. The other section is from the aggregation node at the ME edge to the home gateway. This reservation can be implemented by adopting H-QOS at the aggregation node. It can reserve all VoD resources under a DSLAM or VoD resources for a user. Suppose 50Mbps bandwidth is reserved for a DSLAM (H-QOS according to the outer layer label) and 25 VoD requests can then be accessed. Suppose 4Mbps bandwidth is reserved for a user (H-QOS according to the inner layer label), and then 2 VoD sessions can be guaranteed. The policy server judges the position of the VoD request. If the session limit is already reached, it rejects the VoD request. When the VoD Server gets aware of the end or failure of an active VoD session, it notifies the policy server to release the occupied resource. Then the number of allowed sessions increases by one automatically. This solution avoids over consumption of bandwidth by VoD sessions while assuring the quality of VoD programs.

Other Guarantees for IPTV Bearer Network

IPTV is a high value added service. It requires high network security and reliability. Besides the above technologies, some other technologies are applied to assure this purpose. Regarding security, DHCP+ authentication is enabled on the aggregation node. OPTION82 is inserted to the packets of DHCP,and user port, IP address and VLAN information are bound at the aggregation node. This can prevent MAC attacks and IP address spoofing. In addition, controllable multicast technology can be enabled on DSLAM to prevent the access of illegal users, thus reducing the loss of operator revenue. As for reliability, TE FRR or active-standby TE can be used to assure the fast recovery of services in the event of a network fault. For a ring network, RPR can be applied in the lower layer to realize fast recovery.

Huawei IPTV Bearer Products

Huawei can provide high performance equipment to address the above networking requirements. In the core network, Huawei offer NE40E/NE80E; in the ME network, Huawei offers CX600 as the aggregation node equipment, and NE40E/NE80E/CX600 as distribution node equipment. Huawei also supplies high performance RM9000 to serve as the policy server of CAC. All the equipment supports the refined PIM-SSM, SSM-MAPPING, IGP fast convergence, RSVP-TE and TE FRR. CX600 also supports H-QOS. A configuration at CX can assure the resource reservation per DSLAM and per user under the CX. CX also supports DHCP+ authentication to guarantee network security. Huawei is also able to provide the whole set of IPTV system equipment, from home sets to operation, management, and content service.

Reasons for Choice

For operators, this solution assures simple multicast deployment, easy maintenance and effective cut of OPEX.

PIM-SSM makes full use of network resources to efficiently forward multicast traffic. Operators need not constantly add bandwidth so that the network CAPEX is low.

Built on rich experience in telecom network operation, the VOD service solution employs the CAC technology and brings service development under operator control. It satisfies all quality requirements of the service and avoids cost increase due to repetitive capacity expansion. The investment is rational and the risk is reduced.

In addition, the solution also considers some requirements from telecommunications services. It engages a number of technologies concerning security, reliability and QoS to guarantee quality offering of IPTV services, thus enhancing user loyalty and adding to the number of users. Operator revenue and ARPU can both be increased.

Throuth multicast deployment based PIM-SSM and CAC technology based telecom network, can provide operators a simple, efficient and highly controllable IPTV bearer network. and a good foundation for IPTV service development.