The IP Connectivity Access Network (IP-CAN) session is a concept that has roots in mobile applications. A policy rule via the Gx interface can be applied/modified to an entity that is identified as an IP-CAN session (in addition to individual bearers within the IP-CAN session, the bearer concept is currently not applicable to the BNG). For example, a UE (user interface or simply a mobile phone) can host several services, each of which appears as a separate IP-CAN session associated with the same IP address. For example, in mobile technologies, an IP-CAN session can be defined as <IP_address, APN, IMSI>, where:
APN (Access Point Name) is the service identifier
IMSI (International Mobile Subscriber Identification) is the UE identifier (SIM Card)
In wireline environment (ESM deployments), an IP-CAN session identifies an entity to which the policy can be applied or modified. In SR OS, this can be a single or dual stack IPoE host, IPoE session, or PPPoE session.
For the purpose of identifying the subscriber host or session in the SR OS node in all Gx-related transactions, the SR OS node generates a unique Gx session-id AVP (RFC 6733, §8.8) per single or dual stack IPoE host, IPoE session, or PPPoE session. Note that the Gx Session-Id AVP is not the same as the Acct-Session-Id attribute used in RADIUS accounting.
If the IPoE session is enabled, the Gx session key can be based on one of the following combinations (configuration dependent):
{SAP,MAC}
{SAP,MAC,Circuit-Id}; the Circuit-Id must be present in the packet
{SAP,MAC,Remote-Id}; the Remote-Id must be present in the packet
If the IPoE session is disabled, the Gx session key for IPoE hosts (dual or single stack) is, by default, based on the {SAP,MAC} combination.
In an environment where a Layer 3 node is in front of the BNG, the MAC address of arriving packets are that of the Layer 3 node. Then, it is not possible to differentiate between IPoE hosts on the same SAP unless the IPoE session concept is enabled in SR OS. Each IPoE session must have a Circuit-id or Remote-id as a differentiator.
A session concept is native to PPPoE where the Gx session equates to a single or dual stack PPPoE session. This means that the Gx session key is based on a {MAC,SAP, PPPoE session-id} combination.