In a time when convergence is be coming increasingly important, Internet Protocol Television (IPTV), a new service provided over a broadband network, brings the protocol of the Internet that is being applied in fixed and mobile networks to enable video-on-demand and broadcast multimedia services. With the roll out of IPTV trials and intensified competition, the IPTV market is gaining momentum and evolving from its infancy into a large worldwide market.
The IPTV deployment is a systematic project involving multiple aspects such as business models, network structures, bearer modes, quality assurance, etc. Since the provision of IPTV streaming media, especially live broadcasting services, requires a reliable and robust bearer, its deployment over telecom networks has become an industry focus.
IPTV services and network
The characteristics of the IPTV services and network structure will be described before a comparative analysis of the live IPTV bearer network solutions is given. The IPTV network provides video-on-demand, live TV and gaming services. When compared to other emerging services such as NGN and 3G, it has the following characteristics:
- The service flow has a clear direction in a tree or a star typology, with point-to-multipoint transmission in downstream and multipoint-to-point transmission in upstream;
- It requires high bandwidth as advanced video services such as SD require a bit rate of 2Mbps per stream;
- Asymmetric upstream and downstream bandwidth rates are required–low rates upstream and high rates downstream;
- QoS guarantees in terms of delay, jitter, and bit errors are required;
- The bearer network should have multicast transport capabilities.
As illustrated in Fig.1, the IPTV bearer network consists of a core/convergence layer, service access control nodes and an access layer network. The core/convergence layer carries IPTV traffic from the service layer to the service access control layer built by the broadband access server (BRAS) or the service router (SR). Depending on the network where the service layer nodes are located, the convergence layer can be a two-tiered architecture, which includes both the MAN and backbone network, or an architecture with only the MAN. Either the BRAS or SR is in charge of the access control and authentication of IPTV subscribers.
Fig. 1 Structure of the IPTV bearer network
The IPTV access layer network includes the portion of the network from the terminals to the service access control nodes. As the user terminal is connected with the DSLAM via copper cables, the network access layer mentioned here usually refers to the portion of the network from the access control nodes to DSLAMs.
Network solutions for live IPTV services
When providing live broadcasts, the bearer network is responsible for sending live streaming media contents from the programme source centre to the subscriber terminals. First, the program contents are pushed from the broadcasting server to the MAN, then sent to the edge router/BRAS for distribution of multicast content, which would finally reach subscribers through the access layer.
From a wider perspective, both core/convergence and access layers are based on two technologies: IP/Ethernet and MSTP/SDH. The MSTP-based bearer solution is demonstrated here and the core convergence layer, which transports live streaming from the server to the BRAS/SR, is given as an example.
Solution 1: Point-to-point bidirectional transparent transmission
The first solution is a point-to-point bidirectional transparent transmission, as illustrated in Fig. 2. In Fig. 2, A, B, C, D, E, and F represent the transport nodes connecting the live server with the BRAS/SR. Assuming the interface between all these nodes is GE, the live service is required to push from Node A to the other nodes. This solution has the following characteristics:
Fig. 2 Point-to-point bidirectional transparent transmission
- Transports live streaming video utilising GE transparent transmission provided by the MSTP solution.
- It uses a traditional point-to-point bidirectional configuration, offering five GE circuits with point-to-point bidirectional connections from Node A to B-F respectively which occupy about 35-40 VC-4 channels;
- As IPTV service equipment has limited GE ports, it is necessary to converge the five GEs into one through an aggregation switch before connecting Node A to the IPTV equipment.
This solution enables live IPTV services with QoS assurance through a traditional MSTP configuration. However, it is obvious that this solution can not adapt properly to IPTV live broadcasting services, resulting in high costs.
Advantages: Mature technology, simple configuration;
Based on the existing MSTP network;
Applicable in multiple network topologies;
Disadvantages: Occupies large amounts of bandwidth with low utilisation ratio; bandwidth used will be increased with the increase of the BRAS/SR nodes.
Much pressure is piled on the Node A port and an extra aggregation equipment is required, raising costs.
This solution is suitable for an initial deployment or a field trial of an IPTV service. During the initial phase of the IPTV deployment the customer base is expected to be small and the bandwidth requirement low, thus the IPTV traffic bearing problem could be solved by utilising the existing MSTP transport network or modifying the network so that more efforts can be spent on the design of the service layer.
Solution 2: Unidirectional broadcast transparent transmission
The second solution (Fig. 3) transports live streaming traffic by utilising the broadcast cross-connect function at the VC-4 level, saving bandwidth significantly:
Fig. 3 Unidirectional broadcast transparent transmission
- Delivers live IPTV services through the GE transparent transmission mode provided by MSTP;
- Configures one GE circuit with an unidirectional point-to-multipoint connection from Node A to B-F through VC broadcasting, occupying 7-8 VC-4 channels, to transport live broadcast services; .
Advantages: High bandwidth utilisation ratio, suitable for living streaming;
Applicable in multiple network topologies;
No need for extra aggregation equipment, lowering costs.
Disadvantages: The maintenance of the network as well as locating eventual faults are more complicated with a unidirectional VC connection;
The deployment of this solution is not feasible when different types of services exist in the same GE port as bidirectional services such as VoD and gaming are not supported.
This solution can be used partially and temporarily in the initial phase of the IPTV deployment or when there is a lack of network bandwidth. It is problematic for large-scale and long-term applications as there are risks connected to adopting unidirectional connections for transport.
Solution 3: Utilising RPR multicasting function
The third solution transports live IPTV services through video multicast over resilient packet ring (RPR) as shown in Fig. 4:
Fig. 4 RPR is used to transport live IPTV services
- Configures 1.25G RPR ring in the network (the RPR bandwidth can be configured on demand);
- Adds live server and service control nodes to the RPR ring, enabling efficient multicast over ring topologies;
- Eight VC-4 channel bandwidth is required for transport;
Advantages: RPR, which provides support for multicast traffic, is suitable for live service transport;
High bandwidth utilisation ratio;
Extra aggregation equipment is not necessary;
Simple configuration with no need for unidirectional configuration.
Disadvantages: RPR as a ring network technology is usually used in ring topology and cannot support complex network typology.
This solution is comparatively better as the RPR technology offers powerful multicast capabilities and a superior QoS mechanism, ensuring a quality bearing service and efficient utilisation of bandwidth. Furthermore, the RPR technology is adaptable to a wide range of applications, which are suitable for transporting both live service and other data services such as VoD. Therefore, this solution should be taken into account when planning and designing an IPTV service bearer network.
The actual bearer transport has diversified network topologies and different network scales and the application of the MSTP with embedded RPR has been very limited as the RPR ring is only applicable to single ring networking. How to handle cross-ring traffic has therefore been the major challenge for RPR.
ZTE is a big supplier of global MSTP equipment with wide application of embedded RPR products. The company has brought forward several strategies based on extensive research on transport in cross-ring scenarios and communications with telecom operators.
A. Cross-ring transport via GE user port
As shown in Fig. 4, transporting live IPTV services from Node A to E and F has to transverse two RPR rings (Ring 1 and 2). The cross-ring transport can be realised by connecting Node G and D through adding the GE user port. The IPTV live services are transported around Ring 1 from Node A to G where it will be stripped from Ring 1. Then the live services are transferred to Ring 2 through the GE user port, and multicasted to Node E and F around Ring 2. The interconnection nodes between adjacent rings can be selected according to practical networking scenarios, for example, two nodes at the same location could be selected.
B. Cross-ring transport via network-side interface
In Fig. 4, there already exists fibre connection between Node C in Ring 1 and Node H in Ring 2. The live IPTV services can be stripped from Ring 1 when it is transported around Ring 1 from Node A to C. The live services will then transfer to Ring 2 through the line interfaces of Node C and H, and multicast to Node E and F in Ring 2. The bandwidth between Node C and H should be sufficient for practical applications.
C. Cross-ring transport via logic RPR ring
We can assume that there are two physical links connecting Ring 1 and 2 (Fig. 5), forming a logic RPR ring linking Node A-H where multicast flows will be naturally transmitted from Node A to the other nodes.
Fig. 5 Ring 1 and Ring 2 are connected by two physical links
IPTV is an emerging technology in a time when telecom networks are tending towards convergence and its commercial prospects are vast. However, success in IPTV space is masked by many difficulties and uncertainties, an important issue being the deployment of IPTV service bearer solutions, which requires serious research and analysis regarding practical network planning. The deployment of IPTV service bearer solutions is a key component to ensure end-to-end service and the long-term development of IPTV services.