In 2006, "All IP" is becoming true in the network construction of the operator. The operator has basically stopped further construction of traditional voice switching networks, and the existing services are being adapted to IP bearer. For both new construction and reconstruction, the first issue to be solved by the NGN bearer network is availability. However, in the traditional IP network, fault detection and protection response are in the magnitude of seconds, which cannot meet the basic requirement of the NGN bearer network for 50~200ms protection switching. Before building an IP bearer network, it is necessary to eliminate the bottleneck of availability and protection switching technology.

Huawei is one of the few suppliers in the industry which provide entire-network products and solutions covering data communication, fixed network, optical network, and mobile communication. By virtue of the in-depth understanding to the telecom operation network services and technical features along many years, Huawei has gained insight to the high availability technology of IP bearer network, and has applied it to its own data communication products and solutions maturely. The following text will briefly introduce the high availability technology and networking solution of Huawei in building NGN bearer network.

The preceding figure shows a typical topology of the NGN bearer network. As shown in the figure, the NGN devices connected to the bearer network include:

According to the network layer, routers can be categorized into the access-layer
router (AR) and the core-layer router (CR).

Note:

Huawei uses the names such as AG, UMG, and SoftX instead of TMG, MGW and MSC Server.

The IP bearer network generally uses the MPLS VPN to distinguish between different services and traffic. For example, the signaling traffic and voice media traffic of the NGN service are included into different VPNs carried by different TEs. This practice ensures the end-to-end availability and QoS and realizes the secure isolation between different services. In the MPLS VPN, the AG/UMG/SoftX serves as a CE device, the AR serves as a PE device, and the CR serves as a P device.

The following table shows the availability requirements of NGN bearer network.

Recovery time	Impact on the voice service
<50ms	No impact.
50–200ms	The connection loss probability is less than 5% and has no impact on signaling.
>2s (Connection loss threshold)	Voice session and dedicated line connection are interrupted.

The precondition for availability is fast fault detection. The fault detection technologies can be divided into the link detection technologies and network detection technologies.

The link fault detection technologies supported by Huawei routers include:
The network fault detection technologies supported by Huawei routers include:
Huawei routers support correlation between BFD, MPLS LDP and multiple routing protocols. They can perform fast fault detection in multiple connection statuses, including:
The shortest detection duration is 30ms.

When multiple fault detection technologies are applied concurrently, the principle of detection is: First perform the detection with the lower-layer link fault detection technology, and, if the lower-layer fault detection is not applicable, resort to the upper-layer network fault detection technology. Combination of multiple fault detection technologies can discover faults quickly and provide conditions required for fast protection switching.

Huawei routers support diversified protection switching solutions.

For single-point equipment protection, Huawei

In the part where the NGN equipment is connected to the bearer network, the general solution is dual-homing of CE to PE. At present, all Huawei routers support layer 2 features. All Huawei routers support fast fault detection (BFD) and the correlation between BFD and routing protocols. Thus, E-VRRP and IP FRR technologies can be used to carry out fast protection switching between CE and dual PE.

VPN FRR is a proprietary technology of Huawei. It aims to realize the fast convergence of service when the PE device fails in the CE dual-homed network. It can shorten the time of protection switching between PE peers to milliseconds.

In the IP core network, Huawei adopts TE FRR or IGP/LDP FC technology to ensure the high availability of the core network.

TE FRR is one of the technologies for realizing fast protection switching of network in the MPLS backbone area. In real practice, TE FRR can realize fast protection switching on the basis of fast fault detection in collaboration with BFD technology.

Tunnel Backup builds up a standby tunnel along the active TE tunnel PE—P—P—PE. When the active tunnel fails, the data flow immediately switches to the standby tunnel to ensure quick recovery of the service. By integrating tunnel backup technology with MPLS OAM or BFD, Huawei shortens the time of protection switching of PE to PE Tunnel Backup to milliseconds. This practice greatly improves the availability of MPLS TE backbone network.

Routing information is the most important basic information in the IP bearer network. The IGP FC (fast convergence of route) technology is a precondition for ensuring end-to-end fast protection switching of the IP bearer network. In addition, Huawei routers also support LDP FC to ensure that the MPLS LSP is carried out synchronously with the route convergence. This practice lays a solid foundation for realizing the high availability of backbone network.

By integrating high-availability technologies such as FC, TE FRR and Tunnel Backup together, we can shorten the end-to-end typical protection switching time of the overall network to 200ms–1000ms.

At present, Huawei NGN high availability solution has been widely applied in the commercial networks of China Netcom, China Telecom, Thailand True, and Etisalat of the United Arab Emirates. The practical application is very successful.