Mobile Cloud Networking and Mobility Control 129
sent along that path, and has no impact on the other flows. Each SCTP
flow independently numbers its chunks, using the sequence numbers
StreamID and Stream Sequence Number (SSN).
Thanks to multistreaming, transport capacity is greatly improved.
One of the most important services provided by SCTP is multihoming
support. In this case, each SCTP terminal has a list of IP addresses
linked to its interfaces.
When the connection is established, the SCTP terminals exchange
their address lists. Of the IP addresses on that list, the terminal
chooses one as a primary address, with the others being secondary
addresses. In accordance with this principle, each SCTP
connection has one primary path and multiple secondary paths. The
primary path is used for data transmission. In case the primary path
breaks down, SCTP uses one of those secondary paths to continue
communication.
SCTP uses the Heartbeat mechanism to check whether a path is
active. The Heartbeat message is periodically sent to each
address advertised by the other terminal. The consecutive absence of
an acknowledgement, Heartbeat-Ack, from the addressee indicates
that a path is unavailable. Figure 5.21 illustrates the Heartbeat
mechanism.
Terminal A periodically sends the Heartbeat message (every THB
seconds) to check the availability of the path between two IP
addresses (IP1a and IP1b). After n tests without acknowledgement,
the path (IP1a, IP1b) is deemed to be inactive. If the primary path
becomes inactive, a secondary path is used to send data until the
primary path becomes active once more.
In each SCTP connection, a single path may be used for the data
transmission, with the others being considered as backup paths.
Multihoming stems from the possibility of using several paths
simultaneously. Extensions of SCTP are needed in order for SCTP to
be able to completely support multihoming.
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sent along that path, and has no impact on the other flows. Each SCTP
flow independently numbers its chunks, using the sequence numbers
StreamID and Stream Sequence Number (SSN).
Thanks to multistreaming, transport capacity is greatly improved.
One of the most important services provided by SCTP is multihoming
support. In this case, each SCTP terminal has a list of IP addresses
linked to its interfaces.
When the connection is established, the SCTP terminals exchange
their address lists. Of the IP addresses on that list, the terminal
chooses one as a primary address, with the others being secondary
addresses. In accordance with this principle, each SCTP
connection has one primary path and multiple secondary paths. The
primary path is used for data transmission. In case the primary path
breaks down, SCTP uses one of those secondary paths to continue
communication.
SCTP uses the Heartbeat mechanism to check whether a path is
active. The Heartbeat message is periodically sent to each
address advertised by the other terminal. The consecutive absence of
an acknowledgement, Heartbeat-Ack, from the addressee indicates
that a path is unavailable. Figure 5.21 illustrates the Heartbeat
mechanism.
Terminal A periodically sends the Heartbeat message (every THB
seconds) to check the availability of the path between two IP
addresses (IP1a and IP1b). After n tests without acknowledgement,
the path (IP1a, IP1b) is deemed to be inactive. If the primary path
becomes inactive, a secondary path is used to send data until the
primary path becomes active once more.
In each SCTP connection, a single path may be used for the data
transmission, with the others being considered as backup paths.
Multihoming stems from the possibility of using several paths
simultaneously. Extensions of SCTP are needed in order for SCTP to
be able to completely support multihoming.
www.it-ebooks.info