Thought For The Week
No Question Is A Bad Question!
In Telephone Circuits, Signals Can Be Sent In Two
Different Ways:
In-Band
Out-of-Band
Signals Include:
Digits That You Dial
Dial Tone
Ringing
Disconnect Signals
etc.
In-Band Signaling
In-Band Signaling Signaling Made Up Of Tones Which
Pass Within The Voice Frequency Band And Are Carried
Along The Same Circuit As The Talk Path.
Out-of-Band Signaling Signaling That Is Separated From
The Channel That Is Carrying The Information, e.g.
Voice.
Class 5 Office
For Example
Lucent 5ESS
Nortel DMS
Local Loop
Local Loop
If Endpoints In Same CO
95% Of Local Loop Circuits Are In-Band Signaling
Class 5 Office
Class 5 Office
Local
Loop
For Example
Lucent 4ESS
Local Loop
Class 4 Office
(W/ Tandem Switch)
If Endpoints Connect To Different CO’s (One-Hop)
Interoffice Signaling Via In-Band Signaling
Out-Of-Band-Band Signaling
Common Channel Signaling Is The Most Prominent Outof-Band Signaling System.
Common Channel Interoffice Signaling A Way Of
Transmitting All Signaling Information For A Group Of
Trunks In A Separate Channel.
Class 5 CO
Class 5 CO
Voice Path
Separate Signaling
Network
Common Channel Signaling System No. 7 (i.e.
SS7)
A Global Standard For Telecommunications Defined
By The International Telecommunication Union (ITU)
Telecommunication Standards Sector (ITU-T).
The ITU Definition Of SS7 Allows For National
Variants Such As The American National Standards
Institute (ANSI) Standards Used In North America
And The European Telecommunications Standards
Institute (ETSI) Standard Used In Europe.
The SS7 Network And Protocol Are Used For:
Basic Call Setup, Management, And Tear Down.
Wireless Services Such As Personal Communications
Services (PCS), Wireless Roaming, And Mobile
Subscriber Authentication.
Local Number Portability (LNP).
Toll-free (800/888) And Toll (900) Wireline Services.
Enhanced Call Features Such As Call Forwarding,
Calling Party Name/Number Display, And Three-way
Calling
Efficient And Secure Worldwide Telecommunications.
SCP
SCP
STP
STP
STP
STP
Voice Path
SSP
Residential PRI
BRI
PBX
SSP
Residential
PRI
BRI
PBX
There Are Three Kinds Of Elements In The SS7
Network.
SSP - A Service Switching Point (Class 5 CO
Switch).
SSPs Are Switches That Originate, Terminate, Or Tandem
Calls.
An SSP Sends Signaling Messages To Other SSPs To Setup,
Manage, And Release Voice Circuits Required To Complete
A Call.
An SSP May Also Send A Query Message To A Centralized
Database (An SCP) To Determine How To Route A Call
(E.G., A Toll-free 1-800/888 Call In North America).
SCP – Service Control Point, Various Data
Bases.
An SCP Sends A Response To The Originating SSP
Containing The Routing Number(s) Associated With The
Dialed Number.
An Alternate Routing Number May Be Used By The SSP If
The Primary Number Is Busy Or The Call Is Unanswered
Within A Specified Time.
Actual Call Features Vary From Network To Network And
From Service To Service.
The SSP Is The Local Exchange To The Subscriber And
The Subscribers Interface To The Network.
The SSP Creates SS7 Signaling Units At The Sending SSP
And Translates Them At The Receiving SSP.
The SSP Supports Database Access Queries For 800/900
Numbers.
The STP Is A Router For The SS7 Network.
It Relays Messages Through The Network, But Does Not
And Translates Them At The Receiving Originate Them.
STPs Are Installed As
A national STP.
An International STP.
A Gateway STP.
SS7 Is An International Standard, Nevertheless, There Are
“Some” Differences Between The Way That Countries
Implement SS7.
In The United States, SS7 Is Implemented To ANSI
Standards.
In Many Other Countries SS7 Is Implemented To ITU-T
Standards.
In The United States, STPs Provides Conversions Between
ANSI SS7 And ITU-T SS7.
Collect And Store Traffic And Usage Statistics For OAM.
Collects Billing Information.
Acts As The Interface Into The Telephone Company
Databases.
Business Services Database (BSDB)
Depends On RBOC and Subscriber
SCP
Call Management Services Database
(CMSDB)
Routing Information, Some Billing
Information
Reaction To Congestion
Acts As The Interface Into The Telephone Company
Databases.
Line Information Database (LIDB)
Calling Card, Billing, Third Party
Billing.
PINs, Custom Calling Features.
SCP
Home Location Register (HLR)
Used In Cellular Networks.
Visitor Location Register (VLR)
Used In Cellular Networks.
A Link Is Another Name For A Communications Channel
Or Circuit.
A Link Known Also As Access Links. Used To Connect
SSPs And SCPs To STPs.
B Link Known Also As Bridge Links. Used To Connect
Mated STP Pairs To Other Mated STP Pairs.
C Link Known Also As Cross Links. Used To Connect
STPs Together To Form Mated Pairs.
STPs Are Deployed As Mated Pairs.
Uses A Fully Meshed Topology Which Provides 100
Percent Redundancy.
Any Single Point Of Failure Does Not Bring Down The
System.
C Link Known Also As Cross Links. Used To Connect
STPs Together To Form Mated Pairs.
The Telephone User Should Not Have To Worry About
SS7 Addresses.
A Customer Should Only have To Enter A Called Party
Telephone Number – Even Non-Conventional Telephone
Numbers Such As 911, A Mobile Phone Number, Or An
800/900 Number.
SS7 Accepts These Logical Addresses And Translates
Them To Routable Numbers.
C Link Known Also As Cross Links. Used To Connect
STPs Together To Form Mated Pairs.
Signaling Is The Exchange Of Information Between The
Components Of A Telephony For The Purposes Of
Establishing, Monitoring, Or Releasing Phone Circuits.
The Four Main Functions Of Switch Signaling Are:
Alerting
Transmitting Address Information
Supervising
Transmitting Information.
Common Channel Signaling Was Developed By AT&T
In The 1970s After They Had Lost Significant Revenue To
Fraudulent Use Of In-Band Signaling.
Signaling System No.7 (SS7) Is A Particular Type Of CCS
Employed By Modern Telephone Networks.
SS7 Is A Standard Developed And Published By The ITU.
In SS7, Any Central Office Or Other Telecommunications
Switching Facility Is Called A Service Switching Point
(SSP).
SCPs Supply Customer Information To STPs.
STPs Act As Intermediaries For Signals Moving Between
SCPs And SSPs.
Class 1
Regional Center
Norway, IL
Class 2
Section Center
Eau Claire, WI
Class 1
Regional Center
Rockdale, GA
Toll Call Using AT&Ts FiveLevel Network
Class 2
Section Center
Greensboro, NC
Class 3
Primary Center
Stevens Point, WI
Class 3
Primary Center
Fayetteville, NC
Class 4
Toll Center
WaUsau, WI
Class 4
Toll Center
Fayetteville, NC
Digital Line Card
Analog Line
Card
Intra-Office
Call
Digital T1
Local Loop
Analog
Local Loop
Class 5
Local Office Digital T1
Analog
Local Loop
Local Loop (Wausau, WI)
Residence
Office
Digital Line Card
Analog Line
Card
Residence
Class 5
Local Office
(Raeford, NC)
Office