Translational cross-connect (TCC) is a switching concept that allows you to establish interconnections between a variety of Layer 2 protocols or circuits. It is similar to CCC. However, while CCC requires the same Layer 2 encapsulations on each side of a Juniper Networks router (such as PPP-to-PPP or Frame Relay-to-Frame Relay), TCC lets you connect different types of Layer 2 protocols interchangeably. Using TCC, combinations such as PPP-to-ATM (see Figure 25) and Ethernet-to-Frame Relay connections are possible.
Figure 25: TCC Example
The Layer 2 circuits and encapsulation types that can be interconnected by TCC are:
TCC works by removing the Layer 2 header when frames enter the router and adding a different Layer 2 header on the frames before they leave the router. In Figure 25, the PPP encapsulation is stripped from the frames arriving at Router B, and the ATM encapsulation is added before the frames are sent to Router C.
Note that all control traffic is terminated at the interconnecting router (Router B). Examples of traffic controllers include the Link Control Protocol (LCP) and the Network Control Protocol (NCP) for PPP, keepalives for HDLC, and Local Management Interface (LMI) for Frame Relay.
TCC functionality is different from standard Layer 2 switching. TCC only swaps Layer 2 headers. No other processing, such as header checksums, TTL decrementing, or protocol handling is performed. TCC is supported for IPv4 only.
You can configure TCC for interface switching and for Layer 2 VPNs. For more information about using TCC for virtual private networks (VPNs), see the JUNOS VPNs Configuration Guide.
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