Signaling
Fifth Meeting
Sunday Monday Tuesday
Sixth meeting Sixth meeting Seventh meeting
Telephone Network
transport data The data supplied by
customers signaling data.
supervisory and management data
signaling channels channels carrying signaling
transport channels channels carrying transport
data
Source: http://www.windowsfordevices.com/files/misc/3cx_ippbx_diag.jpg
Channel-Signaling
Channel-Associated signaling data is always associated with a specific
transport channel Two means of data signaling
The signaling data and the transport data share a single communication channel
The signaling data and transport data use different channels
Common-Channel A single channel carries signaling data of several transport channels. The transmission capacity is shared by statistical multiplexing The signaling data is sent in the form of messages ach message must carry an identification of the transport channel to which it refer
Channel-Signaling
Protocol Reference Models
Source: http://www.cs.wustl.edu/~jain/cis788-97/ftp/atm_security/figure1.gif
Dual-tone Multi-frequency Signaling,
16 possible tone combinations
The minimum signal duration 68 ms,
Total duration at least 136 to be sent by a telephone
Features of Communication Networks
Capable of evolution. Evolve to include new requirements without any major
disruptions. Flexible.
It should be possible to change one part of a network without affecting other parts.
Able to support a range of applications. There may be problems of quality of service.
Robust. A network should be able to tolerate a certain degree of
failure of its components,
Different Views of Telephone Network
Signaling System 7 (SS7)
1. Physical, electrical and functional characteristics of a signaling link.
2. Transfer of signaling messages
3. Routing signaling messages through the signaling network
4. Has several user parts, each of which provides the services required by a particular application of SS7.
SS7 With Respect to OSI
Application Entity breaks down into smallerfunctions, called application service elements (ASEs).
application entities (AEs) which represent the functions needed by
applications (such as the operations, maintenance and administration part)
The transaction capabilities application part (TCAP): One system request another system to perform an operation; remote procedure call RPC.
Message Transfer Part
Each message must contain addressing information It is the forwarded to
signaling point. It is located in a routing
label It is contained in each
signaling message signaling message
Routing Label
point codes 14-bit numbers signaling network has a
maximum of 214 = 16384 signaling points.
signaling link selection 4-bit It distribute the traffic over the
available routes between two signaling points.
Hi momHimom
MTP Message
MTP messages have variable lengths.
A complete MTP message (user data + routing label) is placed in the signaling information field
MTP Flag
The pattern chosen is the octet ‘01111110’. A receiver examines all the bits it receives,
Five consecutive bits with the value ‘1’ followed by a bit with the value ‘0’ it removes the ‘0’, thereby restoring the bit-sequence to its original value.
Exactly six consecutive bits with the value ‘1’, A boundary flag is received
Seven consecutive bits with the value ‘1’ An error has occurred.
111110111110111111011111110
SS7
signaling connection control part (SCCP)
The SCCP provides four general classes of service to the level above: 0 Connectionless service
sequence of messages is not guaranteed, 1 Basic connectionless service
sequence of messages is guaranteed. (under normal conditions)
2 Basic connection-oriented service a virtual connection is set up, no flow control nor out-of-sequence detection is provided.
3 connection-oriented service virtual connection is set up, flow control and message sequence are guaranteed.
SCCP messages format
Example of a ‘Connection request’ message
Example of a ‘Connection request’ message
Parameters for ‘Connection Request’
Flow Control for SCCP Service Class 3 ‘Data form 2’ message type
‘Data acknowledgement’ message (piggybacking)
Integrated Services Digital Network User Part (ISDN)
control the signaling of any circuit-switched network setting up 64 kbit/s circuit clearing of a 64 kbit/s
circuit, calling line identification, and call forwarding
It employs the services provided by the MTP (message transfer part) and the SCCP (signaling connection control part).
Public Land Mobile Networks (PLMNs)
Mobile Application Part (MAP)
Support transactions that occur in mobile telephony. Supports ground-based mobile networks, which are
commonly referred to as public land mobile networks (plmns).
Customers are linked dynamically to the switching center nearest to their current location.
Therefore, distributed databases are used in a plmn