LDP Bit Error Detection

Background

As mobile services evolve from narrowband voice services to integrated broadband services, providing rich voice, streaming media, and high speed downlink packet access (HSDPA) services, the demand for network bandwidth is rapidly increasing. Meeting the bandwidth demand on traditional bearer networks requires huge investments. Therefore, carriers are in urgent need of an access mode that is low cost, flexible, and highly efficient, which can help them meet the challenges brought by the growth in wideband services. In this context, the all-IP mobile bearer networks are an effective means of dealing with these issues. IP radio access networks (RANs), a type of IP-based mobile bearer network, are increasingly widely used.

IP RANs, however, have more complex reliability requirements than traditional bearer networks when carrying broadband services. Traditional fault detection mechanisms cannot trigger protection switching based on random bit errors. Therefore, bit errors may degrade or even interrupt services on an IP RAN in extreme cases. Bit-error-triggered protection switching can solve this problem.

Benefits

Bit-error-triggered LDP protection switching has the following benefits:

• Protects traffic from random bit errors, improving service quality.

• Enables devices to record bit error events, enabling carriers to quickly locate the nodes or lines with bit errors and take corrective measures.

Related Concepts

LDP interface bit error rate

LDP interface bit error rate is the bit error rate detected by LDP on an interface. A node uses a Link Hello message to report its LDP interface bit error rate to an upstream LDP peer.

LSP bit error rate

LSP bit error rate on a node = LSP bit error rate reported by the downstream LDP peer + the LDP interface bit error rate reported by the downstream LDP peer.

Implementation

The NetEngine 8000 F supports single-node and multi-node LDP bit error detection and calculation. When LDP detects an interface bit error on a node along an LSP, the node sends a Link Hello message to notify its upstream LDP peer of the interface bit error rate and a Label Mapping message to notify its upstream LDP peer of the LSP bit error rate. Upon receipt of the notifications, the upstream LDP peer uses the received interface bit error rate as the local LDP interface bit error rate, adds the LDP interface bit error rate to the received LSP bit error rate to obtain the local LSP bit error rate, and sends the interface bit error rate and local LSP bit error rate to its upstream LDP peer. This process repeats until the ingress of the LSP calculates its local LSP bit error rate. Figure 1 illustrates the networking for bit-error-triggered LDP protection switching.

Figure 1 LDP bit error detection

In Figure 1, an LSP is established between PE1 and PE2. If if1 and if3 interfaces both detect bit errors, the bit errors along the LSP to the ingress are advertised and calculated as described by the text in Figure 1.

LDP only detects and transmits bit errors, and service switching such as in PW switching or L3VPN route switching occurs on paths carried over LDP.