This API provides the functions that the application can use
to exchange signaling information with the SS7 stack.
The guidelines given in this chapter will ensure that the
application correctly uses the services of the Level 3 (MTP3/M3UA)
API.
The same API is used for both MTP3 and M3UA. Consequently,
the API behavior is the same whether the level 3 layer is MTP3 or
M3UA.
In this guide, this Level 3 API is referred to as the MTP3
API.
As the basis of SS7, MTP provides its applications (such as
SCCP, TUP and ISUP) with reliable transfer of messages between signaling
points, and error correction and detection. MTP provides all the
functions of layers one, two and three in the OSI model. These functions
can be categorized according to MTP levels.
MTP
Level 1 |
 |
This level supports the physical transfer of signaling information
over the SS7 network.
MTP
Level 2 |
|
Level 2 provides the functions and procedures for the error
detection and correction of signaling information between two signaling
points. This level is maintained at the signaling link level.
MTP
Level 3 |
|
This level provides signaling functions to SS7 Level 4. These
functions include signaling message handling and signaling network
management.
MTP3 User
Adaptation (M3UA) Layer |
|
HP OpenCall SS7 uses the services of M3UA on top of SCTP to exchange signaling
messages over IP networks (a SIGTRAN solution). The connection to
the IP network is provided by LAN cards accommodated in the host
server(s) of the platform. No special signaling hardware is required.
HP OpenCall SS7 uses M3UA to transfer MTP3 signaling information between
the upper layers of the protocol stack (SCCP, ISUP, and TUP) and
remote network entities via SCTP services. Since M3UA and MTP3 provide
identical interfaces (Service Access Points) to the upper stack layers,
it is transparent to these upper layers whether M3UA or MTP3 is being
used.
Stream
Control Transport Protocol (SCTP) Layer |
|
SCTP interacts directly with the Internet Protocol (IP) to
connect entities in an IP network, in the same way as TCP. SCTP
also provides the following facilities:
Multi-homing which provides the high
availability of IP connectivity. An SCTP end-point supports multiple
IP addresses, allowing an alternative address to be used if the
main one becomes unavailable. This improves the tolerance of an
SCTP connection to network faults.
Multi-streaming which allows an SCTP connection
that contains several independent parallel streams. A failure in
one stream does not affect message delivery in the other streams.
Order-of-arrival option for the delivery of individual
user messages within the streams.
Acknowledged, error-free, non-duplicated transfers
of user data.
Data fragmentation to conform with MTU size.
Optional bundling of multiple user messages into
a single SCTP packet.
Cookie mechanism during initialization to protect
against security attacks.
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