ZTE's IP over WDM Solution

Development Trend of IP Network
Since the global information industry transitioned from peak growth to stable growth, the market competition got fiercer than ever. Faced with the changing competition patterns, operators need to adjust their strategies in a timely manner to achieve successful transformation. Service transformation is vital to operators' transformation, whereas developing new services is a key driver of service growth. Service transformation will drive network transformation since networks are required to implement more competitive intelligent services. Therefore, new network models (3G, NGN, IPTV, and etc.) have become the focal points that guide operators' research and investment.
Currently, 3G, NGN and IPTV services can be carried by the IP-based multi-service platform. As there is an increasing trend towards IP technologies, the present IP network has played a role that is totally different from what it was several years ago. The earlier stage IP network was mainly used to bear Internet services and was characterized by small scale, low QoS and security requirements, and the best-effort transport.
With the move towards IP-based services and transport, the IP network has to accommodate the increased volume of Internet usage as well as to bear advanced services like 3G, NGN, IPTV and VPN. More and more challenges for IP network come forth accordingly, such as how to bear high quality services, how to transform itself into a telecom-level integrated service platform, and etc. The requirements for the IP network are listed as follows:

As telecoms infrastructure is entering the new era of IP, more emphasis will be placed on constructing an IP bearer network that can carry carrier-class services.

IP Bearer Network for Carrier-Class Services

Defects of IP over Fiber
Regarding the current network transformation and service demands, an IP over Fiber network cannot take the role of a carrier-class multi-service IP bearer network due to the following reasons:

• The routing convergence time, which totally depends on core router recovery, may be in the order of several hundred milliseconds, so that it can't meet carrier-class protection demand of less than 50 ms.
• Network QoS can't be planned from end to end; thus, QoS-sensitive services (e.g., VoIP, VOD and VPN) can hardly be implemented.
• There is a lack of effective mapping between the requirements of QoS and the resources.

To be a carrier-class IP bearer network, the IP over transmission network should reposition itself and take the following situations into consideration: bandwidth-intensive applications put high requirement on network capacity; services interfaces are switched to Gigabit (GE) and 2.5G Packet over SONET (POS), as the granularity of services increases; facilitated by the data network, there are decreasing requirements on the network's service dispatching capability; and the networking requirement is not high as the network structure is flatter.

Comparison Between IP over WDM and IP over ASON/MSTP
There has been a bit of controversy over which technology should be applied in the IP over transmission network. Tab. 1 shows the comparison between IP over MSTP/ASON and IP over WDM.

From Tab. 1, it can be seen that interfacing IP directly over WDM has irreplaceable advantages in terms of available bandwidth, service granularity and bearing efficiency. Today, 10GE (providing speeds of 10 GE per second) services are widely used, and the advantages of IP over WDM will become more apparent when applied in the metro core layer.
The networking and capacity expansion schemes of IP over WDM technology will also be demonstrated. Tab. 2 illustrates the traffic distribution in a network built on a dual-homing six-node data service model (A and F are core nodes in the expansion scheme).

There can be three approaches to build the network based on the traffic distribution in Tab. 2: using data equipment, WDM, or ASON/MSTP. The comparisons between these three approaches are shown in Tab. 3.

On condition that the same service demands should be met, the IP over WDM networking has evident comparative advantages.
If the network adds a GE service and the network capacity needs to be expanded, there will be three possible expansion schemes as shown in Tab. 4.

In the WDM networking mode (IP over WDM technology), the network capacity can be expanded by adding more boards without having to use additional fiber resource. As services multiply and the network construction scale increases, the advantages of IP over WDM, with respect to capacity expansion, will become more pronounced.
Therefore, IP over WDM technology is the first choice to construct an IP bearer network for bearing telecom-level service.

ZTE's IP over WDM Solution
ZTE's IP over WDM solution has the following advantages and characteristics:

• Highly-efficient bearing capability: multi-service convergence and access
  ZTE's IP over WDM solution supports full-service access, and SDH or low-rate data traffic aggregation.
• Flexible dispatching: ZTE's WDM dispatching scheme
• ZTE's ROADM system allows operators to implement a variety of network topologies like chain, ring, mesh and multi-ring, thus satisfying their varying demands.
• The DWDM General Service Switch Platform (GSS) is composed of customer-side aggregation, line-side aggregation, and clock/cross-connect units. The client-side aggregation unit can offer eight simultaneous tributary channels with each channel supporting a variety of client-side signals including GE, FC, DVB and FICON. The line-side aggregation unit has four STM-16 signals with each signal having one working and one protection channel (1+1). These signals are connected to the clock/cross-connect unit after transmission through the backplane, realizing the eight-channel traffic access, convergence and cross-connection.
• GSS, which supports subwavelength dispatching, when coupled with the ROADM, which supports wavelength dispatching, enables the WDM equipment to implement X-ADM functionality.
• Reliability: leading optical layer protection schemes
  Since 2001, ZTE has installed long-haul backbone, regional backbone and metropolitan networks, transporting IP services with various service interfaces such as FE, GE, 10GE, 2.5G POS and 10GE POS. Since 2002, its industry-leading optical channel shared protection technology has found wide application in regional backbone and metro networks, providing mature and stable protection functions at the optical layer.
  ZTE's WDM transmission equipment allows 1+1/1:1 multiplex section protection, optical channel protection schemes of 1+1 and 1: N, 2-fiber bidirectional multiplex section shared protection ring, 2-fiber bidirectional channel shared protection ring. Among them, 2-fiber bidirectional channel shared protection ring is ZTE's patented technology and has been accepted as an international standard.

ZTE's IP over WDM Application Models
ZTE's IP over WDM solution has found many applications. It has two main application models as demonstrated below:
Application model 1 is a dual-homing architecture with two adjacent core nodes (Fig. 1).

Application model 2 is a dual-homing architecture with two non-adjacent core nodes (Fig. 2).

Widely deployed in current metro networks, ring typologies are proven to have inherent survivability. Meanwhile, the ring-based network ensures a high level of reliability with mature protection technologies at the optical layer. The IP over WDM network planning solution should try to locate these two core nodes away from each other to enable even distribution of traffic. When the traffic load on the network tends to get evenly distributed, a channel shared protection ring will give fuller play to its wavelength saving advantage.