SCTP, part of the Signaling Transport (SIGTRAN) suite of protocols, is an IP transport protocol that allows carriers to use IP infrastructure to transport SS7 telephony traffic over an IP network. This protocol functions at an equivalent level and replaces the Transmission Control Protocol (TCP). SCTP has been approved by the International Engineering Task Force (IETF) as specified in RFC 2960 and RFC 4960.

Multihoming, one of the key features of SCTP, is the ability of an association (that is a connection) to support multiple IP addresses or interfaces at a given end point in your network. In case of a network failure, use of more than one IP address allows rerouting of packets and provides an alternate path for retransmission. Therefore, the network address redundancy provides a certain level of network-level fault tolerance. Within an SCTP association, one of the IP addresses assigned to receive data is the primary address of the peer endpoint. During normal operation, the traffic is sent on this (primary) IP path (see the following figure).

Note

Remote Node in the following figure may be one endpoint if this endpoint supports multiple connections to the same Diameter ID or if end DSC node has a different Diameter ID.

DSC 8000 Multihomed Configuration Control Shelf (Example)

If one of the routes fails, SCTP manages the lost packets according to SCTP specifications. SCTP recognizes that the IP path is unavailable, and all traffic is transmitted using the other (secondary) IP path. SCTP sends a message to the Management layer, but the link typically does not fail. This process is not visible using the Menu UI, but can be detected by reviewing the log records.

Caution

When using a multihomed SCTP association, each endpoint must use exactly two IP addresses. Other configurations (n addresses on one endpoint and m addresses on the other endpoint) are supported by the SCTP RFC, but are not supported for this product.

IP aliases are not supported.

Some advanced planning is necessary. You should determine how many SS7-over-IP links you are going to have between the DSC and the remote node, and which Ethernet interface on the DSC each link uses. Plan to have at two IP paths for each remote device, ensuring that each IP path is routed through a different Ethernet interface for failover.

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