Dasar Telekomunikasi Pensinyalan
Definition • The IEEE defines signaling as the exchange of information specifically concerned with the establishment and control of connections and the transfer of user-to-user and management information in a telecommunication network • Conventional signaling has evolved with the telephone network
• With telephony, signaling is broken down in three functional areas: • Supervisory • Address • Call progress: audible-visual
• Another signaling breakdown is • Subscriber signaling • Interswitch (interregister) signaling
Supervisory Signaling • Supervisory signaling provides information on line or circuit condition • It informs a switch whether a circuit (internal to the switch) or a trunk (external to the switch) is busy or idle, when a called party is off-hook or on-hook, and when a calling party is on-hook or off-hook
Address Signaling • Address signaling directs and routes a telephone call to the called subscriber
• It originates as dialed digits or activated push-buttons from a calling subscriber • The local switch accepts these digits and, by using the information contained in the digits, directs the call to the called subscriber • If more than one switch is involved in the call setup, signaling is required between switches (both address and supervisory)
• Address signaling between switches is called interregister signaling
Call Progress: Audible-Visual • This type of signaling we categorize in the forward direction and in the backward direction • In the forward direction there is alerting • This provides some sort of audible-visual means of informing the called subscriber that there is a telephone call waiting • This is often done by ringing a telephone’s bell • A buzzer, chime, or light may also be used for alerting.
• In the backward direction, among these are audible tones or voice announcements that will inform the calling subscriber the following: • Ringback
• This tells the calling subscriber that the distant telephone is ringing.
• Busyback
• This tells the calling subscriber that the called line is busy
• ATB-All Trunks Busy
• There is congestion on the routing. Sometimes a recorded voice announcement is used here.
• Loud Warble on Telephone Instrument—Timeout • This occurs when a telephone instrument has been left off-hook unintentionally
Klasifikasi Signaling Signalling
Subscriber - exchange
Exchange - exchange
Channel associated
Common channel
Areas of Signaling • There are mainly three areas of signaling during a telephone call : • between subscribers and exchanges. • within exchanges. between • between exchanges. exchanges
Exchange A
within exchange
Exchange B
between Subscriber and exchange
Subscriber – Exchange Signaling •
Dari pelanggan ke sentral
– Informasi kondisi off-hook – Informasi nomor B (nomor tujuan) – Informasi jumlah uang yang dimasukkan (khusus untuk payphone) – Informasi kondisi on-hook ketika panggilan usai •
Dari sentral ke pelanggan A (nomor pemanggil)
– – – – •
Informasi bahwa sentral siap menerima nomor B Informasi mengenai status B (busy atau tidak) Informasi kongesti atau interception Sinyal charging (khusus untuk payphone)
Dari sentral ke pelanggan B
– Sinyal ringing untuk menarik perhatian pelanggan B
sentral
A •
Pelanggan A mengangkat telepon, hal ini dapat berarti – A ingin menghubungi seseorang – Pesawat A berbunyi lalu menjawab
• • •
•
• •
B
Sentral dapat mendeteksi keadaan telepon apakah merupakan panggilan atau jawaban Sentral menanggapi panggilan dengan mengirimkan dial tone A mengirimkan digit nomor B (B number) Sentral menganalisa digit lalu mencek apakah B ada dan tidak busy. Ringing tone dikirimkan ke A sedangkan sinyal ringing ke B B mengangkat handset, sentral mendeteksinya sebagai jawaban Ketika A dan B menyimpan handset, sentral mendeteksi sebagai sinyal clear lalu koneksi diputuskan
Off-hook
Dialling tone N O M O R
Ringing tone
Ringing signal
~425Hz
~90V, 20-25 Hz
answer conversation Clear forward Clear back
Off-Hook Signaling (Analog) • Loop Start (almost all telephones) • Seizure is detected when current flows through local loop, due to off-hook
• Ground Start (antar PBX (Private Branch Exchange) atau antara PBX dengan Sentral Lokal) • Seizure (upaya pendudukan kanal komunikasi) is detected when one wire is grounded • Seizure can be initiated in both directions • Untuk mengindikasikan status on/off-hook ke sentral lokal
Ground Start
Source: Cisco Interactive Mentor
Ground Start
Loop Start
Switch
Switch
Exchange – exchange Signaling • Channel Associated Signalling (CAS) • Common Channel Signalling (CCS)
Common Channel Signaling
Signaling dilakukan menggunakan kanal yang juga digunakan untuk mentransfer informasi
Common Channel Signalling • Informasi speech dan informasi signalling mengalir melalui jalur yang sama • Beberapa macam CAS – Signalling dilakukan secara bersama pada kanal untuk speech (DC signalling, inband) – Signalling dilakukan pada kanal yang sama dengan speech tetapi menggunakan frekuensi yang berbeda (out-band) • Contoh: Signalling dilakukan melalui timeslot 16 (PCM signalling)
Pelanggan B
Pelanggan A
sentral
sentral seizure Seizure acknowledgment B number answer
conversation Clear back A- hangs up
Clear forward
B- hangs up
Forward and Reverse direction • Forward signal mengalir dari sentral telepon tempat A berada menuju sentral telepon tempat B berada • Backward signal mengalir pada arah yang berlawanan dengan forward signal
Channel Associated Signaling
Signaling menggunakan kanal yang terpisah dari kanal untuk mentransfer informasi Terdapat jaringan signaling tersendiri
Signaling System NO. 7 Signaling System Number 7 (SS #7)
• Signaling System No. 7 (SS No. 7) was developed to meet the stringent signaling requirements of the all-digital network based on the 64-kbps channel • It is a data network entirely dedicated to interswitch signaling • defined by Telecommunication Standardization Sector (ITU-T). • defines the procedures and protocol by which network elements in the PSTN exchange information over a digital signaling network to effect wireless (cellular) and wireline call setup,routing and control.
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, andthree-way calling • efficient and secure worldwide telecommunications
• SS No. 7 is described as an international standardized general-purpose common-channel signaling system that:
• Is optimized for operation with digital networks where switches used stored-program control (SPC) • Can meet present and future requirements of information transfer for interprocessor transactions with digital communications networks for call control, remote control, network database access and management, and maintenance signaling • Provides a reliable means of information transfer in correct sequence without loss or duplication
SS7 Signaling Points Diagram
Signaling Architecture Components Component
Function SSP's are telephone switches (end offices or tandems) equipped Signal Switching Points with SS7-capable software and terminating signaling links. They (SSP's) generally originate, terminate, or switch calls. STP's are the packet switches of the SS7 network. The receive Signal Transfer Points (STP's) and route incoming signaling messages towards the proper destination. They also perform specialized routing functions. SCP's are databases that provide information necessary for Signal Control Points (SCP's) advanced call-processing capabilities
Basic SS7 Signalling Architecture
SS7 Signaling Links
SS7 Link Types • “A” Link: An access link connects a SSP or SCP to an STP. • “B” Link: A bridge link connects an STP to another STP. • “C” Link: A cross link connects two “mated pair” STP. This is done to improve reliability • “D” Link: A diagonal links similarly to a B link • “E” Link: An extended link connects an SSP to an extra STP in the event that the A link cannot reach one. • “F” Link: A fully associated link connects SSP’s
CCS7 Network Components • The CCS7 Network consists of the following Components : • SP – Signaling Point : The SP is the source or originating entity of the signaling message. • STP – Signaling Transit Point : These entities transfer the signaling message to another SP or STP without processing the signaling message. • SRP – Signaling Relay Point : These are STPs with ability to process the signaling message. • SEP – Signaling End Point : The SEP is defined to be the terminating point of the signaling message
SS7 Network Architecture • A typical SS7 network is a mixture of various SPs STPs SRPs and SEPs, As shown below : STP (SPC=200)
SRP (SPC=400)
SP (SPC=100)
STP (SPC=300)
SEP (SPC=500)
CCS7 Terminologies • SPC : SPC is defined as signaling point code which uniquely identifies each element within the SS7 network. • Signaling Links : The signaling links transmit signaling messages between the communicating entities.
• Signaling Link Set : A signaling link set is a collection of signaling links between two signaling entities. • Signaling Route : A signaling route is defined to be the path through which signaling messages are exchanged between two entities. There can be multiple signaling routes between two SPCs, wherein there will be one primary route and several alternate routes.
SS7 Routing Modes • Associated Mode :
In the associated mode, the signaling link is routed together with the circuit group belonging to the link. In other words, the signaling link is directly connected to signaling points which are also the terminal points of the circuit group. This mode of signaling is recommended when the capacity of the traffic relation between the signaling points A and B is heavily utilized.
Associated Mode of Signaling
SS7 Routing Modes • Quasi associated mode :
In the quasi-associated mode of signaling, the signaling link and the circuit group run along different routes, the circuit group connecting the signaling point. A is directly connected with the signaling point B. For this mode the signaling, the circuit group is carried out via one or more defined signaling transfer points. This signaling mode is favorable for traffic relations with low capacity utilization, as the various signaling links can be used for several destinations.
SS7 Network Structure SPC=100 NAT 1 SPC=200
SPC=700 NAT 1
SPC=300 SPC=800 SPC=100
SPC=900
SPC=800
NAT 0 SPC=100 SPC=400
SPC=400
SPC=100 SPC=600 NAT 1 SPC=500
INAT 0
SPC=200
SPC=300
SS7 Protocol Structure • SS7 protocol stack can be broadly divided into two main categories : • A ) MTP – Message Transfer Part : The message transfer part has three levels , namely MTP Layer 1, Layer 2 and Layer 3. The message transfer part (MTP) represents a user-neutral means of transport for messages between the users. • B ) User Parts (UP) : Each user part (UP) encompasses the functions, protocols and coding for the signaling via SS7 for a specific user type (e.g. data service, ISDN). In this way, the user parts control the set-up and release of circuit connections, the processing of facilities as well as administration and maintenance functions for the circuits.
SS7 Protocol Structure SS7 Users B S
TCAP Users
S A
P
I S U
TCAP
P
M U P
SCCP
MTP Layer 3 (Network Management) MTP Layer 2 (Signaling Link)
MTP Layer 1 (Signaling Data Link)
Other User Parts
Contoh signaling CCS#7 IAM: Paket pertama yang membawa informasi nomor B Sisa nomor berikutnya dibawa oleh SAM
ACM: Paket yang berisi konfirmasi dari sentral B bahwa seluruh digit sudah diterima; selain itu paket ini berisi pula informasi apakah panggilan dapat di-charge atau tidak juga apakah pelanggan tujuan sibuk atau tidak Ketika pelanggan B offhook, sentral B mengirimkan sinyal ACN untuk mengaktifkan charging
