The Hacker's Encyclopedia 1998/hackers_encyclopedia.iso/zines/n_z/phun3.007

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=                  P/HUN Issue #3, Volume 2: Phile #7 of 11                   =
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              Common Channel (InterOffice) Signalling: An overview
              ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
                               By Tubular Phreak


 References:
 o - BTJ!
 o - AT&T comunications
 o - Tel-Network planing

This article will inform you of the stages CCS has gone through over the past
years.
CSC known originally as Common Channel Interoffice Signalling was introduced
back in 1976. Since its introduction it has added datagram direct signalling
and has been modernized  by new digital and proccesor technology
and by delvelopments in software enginerring techniques.
This prevents Blue Boxing due to the fact that signals are carried over a
different link than voice.
CCIS net improved its the old trunk signalling bettween SPC (Stored Control
Program) toll switches thereby increasing speed and its economical.
The CCIS network was composed of what know as STPs(Singal Trasfer Points)


       CCIS Network
       ------------

 Region #1      + Region #2
 **             +         **
  |             +          |
  |             +          |
  |             +          |
(SPC)------**      **----(SPC)
  |________________________|

** - STP mated pair
__ - Voice Trunks
|  - Links
+ - Divider


The Datalinks use 2.4 kb/s(kilobytes per second).In 1979 they used 1A switch
was added.

Later in 80 they added a special feature of direct signalling (datagram)
which operate at 4.8 kb/s. This capability provided the SPC machines with
the neccesary information through the CCIS Net.The allowed NCP (Network Control
Points). The NCPs connect directly to CCIS at certain STPs.
The SPC machines quired the NCPs and receives the instructions for the action
in response.Therefore they became known as ACPs(Action Control Points).
This status if the CCIS provided 800 services and calling cards.

In 1985 the siganlling network added 2STPs and 56kb/s.This new network was
called CCS7. This new method of signalling used CCITT No.7 Protocol and with
it new more efficient feature came like ISDN.

                          Archaic CCIS in 76'
                          ~~~~~~~~~~~~~~~~~~
Before the introduction of CCIS, SF/MF signalling method was in use.
The SF was responsible in determining the idle/busy side state of a trunk.
2600 Hz the idle trunk was removed when a call was to be placed on the trunk.
Then MF signaling was used to determine  routing information to the distant
end and when the party answered the SF was removed from there side.

Tandem switching was not economical and was slow.

As the introduction of SPC came about in which common control equipment was
based on electronic procedures, the overhead associated with the call setup
became a more dominant factor. MF/SF signaling was used until a toll switch
ESS4 was introduced in 76'. Therefore AT&T produced CCIS in assocation with
the ESS4 toll switch. Signalling used a different link than voice.
As mentioned above CCIS used 2.4/kb signalling links to transmit the signal.
Due to the fact that one 2.4/kb could could provide for more than 2000 trunks,
therfore the a regional STP was put in place.
Each STP was connected to several toll switches.Each regional STP was connected
to each of the distant STPs.Each STP was connected to its parner which provided
a path for connections between switches if there was a failure of distant STPs
The STPs in the network were provided by a portion of the processor associated
with the 4A-ETS(Electronic Translator Systems). Message routine within the
STPs was performed by a band and lable scheme that defined a virtual signalling
circuit where 512 bands of 16 trunks coule be accomodated. This allows 8192
voice trunks to be uniquely identified on a specific signaling link.

                     Direct Dialing Signalling(1980)
                     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
In 1980, a direct signalling capability was added to the CCIS Network. This
capability allwed messages to be sent from a signalling point to any other
signalling point in the network and supported a new network architechture in
which a portion if the switched network routing instruction could be placed an
a database shared by multiple SPC switches.
These common databases became known as network control points (NCPs). The SPC
switches became known as action points (ACPs). because they performed actions
based on instructions from NCPs. This required an inquiry-response in the
Common Channel Interoffice Network.

This communication between ACPs and NCPs was performed by a new feature called
Datagram Direct Signalling. Unlike banded(trunk) signalling. This method of
signalling directed messages on a destination-routing basis through all the
Singal Tranfer Points. Therefore the direct signalling messages included a
unique destination address that was used by the STPs to route the message based
on a table that associated destination addresses with physical points in the
network. With this, the CCIS network could direct messages to individual
functions allowing the introduction of unique services such as advanced 800
with features like time of day routing call prompter and customer-controlled
routing of traffic based on information stored at central databases.

                         CCIS Network Growth
                         ~~~~~~~~~~~~~~~~~~~
As the AT&T network grew both in terms of SPC swicthes and volume of traffic,
it became necessary to augment the initial CCIS network capability. First the
number of STP pairs was increased from the initial 10 pairs to 16 pairs.
Three of the additional -airs were used as area STPs, which served the trunking
needs of the portion of the network. The remaining 3 STP pairs were associated
directly with NCP pairs and performed a direct signal funtion. In addition
the message handling capacity of the network was increased by deploying 4-8kb/s
signalling links in place of the original 2.4kb/s links.STP processing capacity
was also increased as the original shared use of the ETS processor was removed
when the switch function at each STP location was transfered to a new 4 Elect-
ronics Switching System machines.

               The Impact of AT&T Divestiture on CCIS Network
               ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
On January 1, 1984 the court-ordered AT&T divestiture became effective.
Divestiture establishment local access and transport areas (LATAs), which
defined local markets areas. AT&T became an inter-LATA carrier providing
communication services between these LATAs. Under the divestiture agreements,
the STPs,NCPs,and interconnecting data links were assigned to AT&T. The minor
use of these facilities by the divestiture BOCs(Bell Operating Companies) was
provided under contract.Equal access to the inter-LATA carriers under
divestiture was provided mostly by MF/SF signalling. However a new multi-stage
MF outpulsing arrangement was added to forward the orginating number to inter-
LATA carrier for billing and other purposes.

                     Common Channel Signalling 7 (1985)
                     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
During 1985, the STP capability was enhanced by the introduction of 2STP based
on the AT&T 3B20 duplex (3B20D) processor and an associated processor inter-
connect capability (PIC).In addition , 56-kb/s digital facilities were provided
between the STPs. The 2STP uses the CCITT Signalling System 7 protocol and
provides message transfer part (MTP) function. The MTP can route a message
reliably and qucikly from one point in the signalling network to any other
point. The resulting network has been named the CCS7 network. Initially, the
CCS7 network was used to augment the trunk signalling capabilities of the 1STP
network using the embedded CCIS6 (ECIS6) protocol. ECIS6 interacts with CCS7
and allows switching systems connected to the 1STP network to communicate with
other switches connected to the 2STP network.However during this transitional
period, all switching systems are connected to either the 1STP or 2STP
locations via 2.4 or 4.8 kb/s signalling links.

                       CCS7 Destination CCIS (1986)
                       ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
In 1986 the CCS7 network was expanded to include direct signalling. This was
done by adding new capabilities in the NCPs to allow 56-kb/s connecting links
and the ability to route direct-signalling messages within the 2STPs. For
transitional compatibility, a new destination CCIS6 (DCIS6) interworking
protocol was deployed. The 4ESS and 5ESS switches in the network will use the
Integrated Services Digital Network User Part (ISDN-UP) to control call setip
and will have the capability to support ISDN services. The ISDN-UP will use the
services of the already deployed MTP and provide a broad set of switched
digital services.

           Evolution of NCP Serices to a Distibuted Architecture
           ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The increasingly demanding requirements of call processing services such as the
AT&T card service, advanced 800 and software defined network (ISDN) have led to
a steady evolution of the NCP architecture toward more distribution. This is to
increase versatility of the usage, flexibity of growth and performance. At the
same time we will be able to introduce more new services. The orgianl NCPs
introduced in 1980 consisted of AT&T 3B20 duplex processors and multiple disk
drives. The 3B20D handled all the fucntions including query processing database
admnistration and updates and signaling. The first step toward a distriuted
NCP architecture was in the signalling architecture. In 1985 the NCP
incorporated a highly reliable processor interconnect capability(PIC) with the
same technology used in the 2STPs. It provides communication between the CCS
network and the NCP application databases in the 3B20D host Signalling links
from the STPs to an NCP terminate through link nodes(LNs) on the PIC.The CCS
query messages could access an NCP through the LNs and travel to the
appropriate database application in the 3B20D. Similarly query responses
destined to the CCS network could exit from the NCP through the PIC and the LNs
The future NCP architecture will continue to serve host to the NCP distributed
enviroment and the PIC will remain the vehical for the interprocess
communication and signaling-link termination. To attain distributed query
processing, the NCP database architecture will feature the intergration of
multiple transaction-processing components.

                        CCS7 Network Interconnection
                        ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
With the potential for end to end signalling services and the adoption of CCS7
standards, there is a growing effort to connect networks of different carriers
and different countries as well as various privately owned networks. It is
expected that in the future all North American networks will have CCS7.
Therefore AT&T is  currently involved in defining standard CCS7 interface for
use between netwroks. Initially, the new interface will consist of 2STPs
deployed in pairs.This network configuration assumes that interconnecting will
use designated STPs as gateways. The gateway STPs will be required to screen
all incoming message to prevent unauthorized use of network resources and
services :-)

Interconnecting networks using designated STPs as gateways.


                        Network
                        boundary
 Network 1 (AT&T)          |     Network 2
 _____           ______    |   _______
 |\  |          |\   | |   |  |\   | |
 | \ |----------| \  | |___|__| \  | |
 |__\|          |__\_|_|   |  |__\_|_|\
   |  \            |       |      |    \
   |   \           |       |      |   SPC Switch
   |    \        __|___    |      |    /
   |     \______|\   | |   |   ___|___/
   |       _____| \  | |___|__|\   | |
   |______|     |__\_|_|   |  | \  | |
                Gateway    |  |__\_|_|
         2STP mated pair   |  Gateway STP
                           |   mated pair
                           |

The figure below shows interconnection of a small network that does not have
STP gateway.
                  Network
                  boundary
Small network 3      |     AT&T CCS7 netowrk
                     |
               ______|_________%%%%
              /      |         %%%%
             /       |
  +++++++++ /        |
  +  SPC  +/         |
  +switch +\         |
  +++++++++ \        |
             \       |         2STP mated pair
              \______|_________%%%%
                     |         %%%%

The same arrangement that is being used domestically is currenlty being inves-
tigated for application to the CCITT No. 7 message transfer part/telephone
user part (MTP/TUP) international network interconnection. However because of
differences between national networks, international interconnection is more
complex. With the implementation of ISDN-UP for international signalling in
early 1990s, it is expected that many of the existing domestic services will
be extended to embrace the international networks as well.

                     CCS7 Support for ISDN Services
                     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Common Channel Signalling was designed for signalling between network entities.
ISDN protocols are designed for out of band signalling all the way to the end
user.Much of the current effort in ISDN is in defining protocols and
architectures for providing the out of band signalling from the end user
premises to the network.However to provide end to end service the network has
to transport the end user's out of band signalling, using CCS or other means.
An important benifit of CCS7 is its inherent ability to support feature
transperancy i.e., allowing of passing of information that can only be
interpreted and used by end users.This capability can be attained by
interworking the ISDN Q.931 protocol with the CCS7 ISDN-UP and extending ISDN
to switched access users through network interconnection.
Methods of supporting CCS7 features transparency include:

o Message-associated user to user information
o Temporary and permanent signalling connections.Message associated user to
  user information could pass along with regualar CCS7 call control messages
  as opposed to using signaling connections specifically established for that
  purpose. The transfer of transparent inoformation would generally be done
  after the signalling connection (temporary or permanant) is established but
  message associted transparent information could be transfered during the
  establishment and/or termination phases of the signaling connection.

Both AT&T and the regional BOCs are deploying ISDN signalling in their networks
Once in place, ISDN offers capabilities such as

o Per-cali selsction of services and bandwidth
o Combined voice,data and even video on a single call
o Calling-number identification at the terminating end (for example, a digital
  display for the calling number during ringing)
o Sophisticated multimedia teleconferencing capabilities

Futhermore ISDN will be able to make it possible to add new features and
improve the implementation of the exsisting services such as support packet
transmission and separation of the call/control from user control information
in ISDN.

                   Potential CCS7 Network Enhancements
                   ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The future CCS network will probably be configured as follows:

1) The ISDN-UP will be used throughout North America.As local carriers adopt
   CCS7 network interconnect will provide for end to end digital services. The
   signalling connection control part (SCCP) will be used to provide data
   capability for ISDN user to user information.
2) The CCITT No. 7 protocol will be used internationally.First the telephone
   user part (TUP) will provide basic call setup to countries that chose to use
   this protocol initially. However because of its increased flexibility and
   support for digital services, the ISDN-UP will be used to extend domestic
   ISDN services worldwide.
3) The interconnection with local exchnage carriers as they expand their own
   CCS systems will enhance LATA access services and allow new inter-LATA
   service.
4) AT&T services will evolve as the flexibility and capacity of the CCS7 of the
   protocol is utilized.The transaction capability and part (TCAP) will provide
   an effecient protocol for direct-signalling query and responses, to support
   new databases and switch-based services.
   The interworking of CCS7 with the Q.931 ISDN access protocol will allow end
   to end services that are not possible with in-band signalling and will
   provide more effective and innovative use of work.

                                  Conclusion
                                  ~~~~~~~~~~
The evolution os the AT&T common channel signalling system has been shown to be
a critical part of the AT&T network and services. It has provided a cost
effective means of providing flexibility in the marketplace. The system
is expected to evolve as new capabilities and need are indentified.

Tubular Phreak NUA!