Signaling i protocolul SS7

ISDN Integrated Services Digital Network

Signaling

Signaling schimbul de informatii specific pentru stabilirea si controlul conexiunilor, precum si pentru transferul datelor user user, gestionarii retelelor de telecomunicatii

Funcii:Conexiuni

StabilireControl

Transferul informaiilor ntre utilizatoriDe management

Signaling Arii de funcionare

Signaling de supervizare Informaii despre starea liniilor i a circuitelor Abonatul on/off hook Ocuparea circuitelor de legtur

Signaling de adrese Routarea apelului spre cel apelat ntre switchuri interregister signaling

Starea apelului audible-visual Sunarea aparatului chemat Ringback, Busyback, AllTrunksBusy

Signaling

Tehnici de signaling Transferul informaiei de signaling prin:

Durata pulsurilor Combinaia de pulsuri Frecvena semnalului Combinaia de frecvene Prezena ori absena unui semnal Cod binar Tensiune i direcie de curent continuu

Signaling

Tipuri de Signaling de supervizare In-band

Semnalizarea este facut n intervalul de voce(300-3400 Hz) pe o frecven ntre 2000 i 3000Hz(avem semnal vocal slab) Tipuri

SF Single Frequency 2VF Two Frequency (line signaling si address signaling)

Problema: talk-down: activare/dezactivare incorecta a echipament supervizare prin secventa de tonuri de voce (pentru SF mai ales)

Signaling

Out-of-band Semnalizarea se face peste 3400Hz la sistemele

vechi: 3700 sau 3825Hz La sistemele digitale se folosete un canal

separat de 56 ori 64 kbps doar pentru semnalizare

Reprezinta un sistem SF

Signaling

Non-Compelled signaling Durata fiecrei uniti de signaling este

important (call set-up, proceed to send, end-of-pulsing)

Compelled signaling Se folosete obligatoriu ACK ca raspuns;

simplitate si adaptabilitate Link-by-link

Toate informaiile de conectare sunt trimise pentru fiecare link, de catre fiecare nod tranzit

End-to-end Switchul celui care transmite comunic cu

fiecare hop n parte, trimite doar informaia minim necesar

Signaling

Associate Liniile de semnalizare merg mpreun cu liniile de voce

Quasi-asociate Liniile sunt separate dar totui merg paralel

Neasociate Linii total separate pt. voce i pt. switching

Signaling System #7 (SS7)

SS7 SS7 este standard pentru transfer de date

digital dedicat pentru inter-switch signaling Forma de Common Channel Sgnaling (out of

band) Standard independent de echipamente (switch)

sau tehnologii transmisie Optimizat pentru

sisteme digitale Transferul informaiilor de tranzacii

interprocesor n ordine corect, fr pierderi

SS7

Ofer Supervizarea circuitelor Signaling de adrese Signaling de starea/progresul apelului Notificarea de alerte

Folosit pentru ISDN dar i pentru PSTN-urile digitale

SS7SS7 ca functionalitate:

Setting up, gestionare, terminare apeluri; Apeluri cu valoare adaugata: inaintare apel,

apel bazat pe trei faze handshaking , identificare apelant

Local Number Portability (LNP); Servicii Wireless: Personal Communications

Services (PCS), wireless roaming, autentificare abonat mobil

SS7

Componente de reea SS7

SSP Signal Switching Point Acestea sunt switchuri de telefon aflate la

captul reelei de SS7, conectate direct la liniile de telefoane

Ofer pornirea, switchingul i terminarea apelurilor

SS7

Componente de reea SS7

STP Signal Transfer Point Acestea sunt switchurile de pachet ale

reelei SS7 Acestea primesc i trimit mai departe

mesajele de signaling Au i capacitai de rutare

SS7

Componente de reea SS7

SCP Signaling Control Point Acestea sunt baze de date care ofer

informaii suplimentare pentru servicii avansate de procesare ale apelurilor(taxare, informatii clienti ..)

SS7

De multe ori STP-urile i SCP-urile se instaleaz n perechi din motive de redundan

Plane de operare

SS7 Arhitectura de baz

a unei reele SS7

STP W i X au funcii redundante, n astfel de conexiune se numesc mated

SSP-urile au cte un link spre fiecare STP STP-urile din reele diferite sunt interconectate n acest fel

(vezi poza), care se numete quad

SS7 Tipuri de linkuri

A link (access link) este interconectarea STP-urilor cu SSP-uri sau SCP-uri(signaling end-ponts). Folosit doar pt. transfer de signaling

B link (bridge) interconectare STP-uri

C link (cross link) pentru a interconecta STP-uri care indeplinesc functii identice; sunt pereche (mated)

D link (diagonal) pentru interconectarea STP-urilor in quad (intre perechi STP primare si secundare)

SS7

E link (extended link) pentru a conecta un SSP i la alte STP-uri (cele legate prin A link)

F link (fully associated) pentru a crea o conexiune direct ntre doua SSP-urisau SCP-uri (signaling end points)

Arhitectura protocolului

Arhitectura protocoluluiPatru nivele arhitecturale:- Message Transfer Part (MTP) ocupa primele 3 nivele- Nivelul 4 are componentele:

-signaling connection control part (SCCP); impreuna cu MTP formeaza network service part (NSP)

-ISDN user part (ISUP)

Operations, maintenance and administration pat (OMAP)

Application Service elements (ASE)

-transaction capabilities application part (TCAP), divizat in:

SS7 Layer-ele protocolului

Physical Layer Definete caracteristicile fizice i electronice ale legturilor de

signaling Se folosete un canal digital de 56 sau 64 kbps

Message Transfer Part Level 2 Acesta este de fapt Link Layer, asigur c dou SP-uri

(Signaling Point) pot schimba mesaje unul cu cellalt. Funcionaliti: error checking, flow control, sequence

checking, Message Transfer Part Level 3

Extinde funcionalitile oferite de MTP level 2 pentru a oferi servicii de reea. Asigur transferul mesajelor de signaling ntre oricare dou SP-uri, indiferent dac ele sunt conectate direct sau nu.

Capabiliti: Node addressing, routing, alternate routing, congestion control,

SS7 Layer-ele protocolului cont.

Signaling Connection Control Part (SCCP) Ofer funcii de adresare si rutare care nu sunt prezente n

MTP

ISDN User Part (ISUP) Aceasta definete mesajele i protocolul folosit pentru a realiza

i a ntrerupe apeluri de voce sau de date n cadrul PSTN-ului i managementul reelei de trunk-uri prin care se realizeaz apelul respectiv

Cu toate c numele conine ISDN, acest ISUP este folosit chiar i pentru apelurile non-ISDN n momentul de fa

SS7 Informaiile de signaling sunt transmise n

pachete numite Signaling Unit (SU) Tipuri:

Message Signal Unit (MSU) Acesta conine toate mesajele de signaling

pentru serviciile oferite de SS7 Link Status Signal Unit (LSSU)

Informaii legate de starea celor dou SP-uri de la captul unui link

Fill-in Signal Unit (FISU) Acestea sunt n continuu transmise n

perioadele n care nici MSU-uri nici LSSU-uri nu sunt de transmis

SS7

Adresarea SP-urilor Adresarea este de trei nivele

Network Cluster

Member

Fiecare este un numr ntre 0 i 255 Acestea mpreun se numesc: the three

point address

Concluzii SS7 este un protocol dezvoltat n

exclusivitate pentru signaling El folosete out-of-band signaling i

associated+quasi-associated mode Este structurat similar cu OSI n mai multe

layere Viitorul lui SS7

Deja au aprut aplicaiile IMS (IP Multimedia Subsystem), pe care le putem ntlni i sub denumirile de VoIP i SIP.

Acestea vor fi succesorii lui SS7, dar pentru acest lucru este nevoie nc de mult vreme pn cnd operatorii i amortizeaz costurile i echipamentele curente.

Integrated Services Digital Network

(ISDN)

ISDN?

Simultaneous transmission of digitized voice and data on the same digital transmission link and by the same digital exchanges

ISDN Benefits

Carries a variety of user traffic, such as digital video, data, and telephone network services, using the normal phone circuit-switched network

Offers much faster call setup than modems by using out-of-band signaling (D channel) Often less than one second

Provides a faster data transfer rate than modems by using the 64-kbps bearer channel (B channel) Can combine multiple B channels to bandwidth of

128 kbps

Can negotiate PPP links

ISDN Devices

Terminal Adapter (TA) - Converter device that converts standard electrical signals into the form used by ISDN -allows non-ISDN devices to operate on an ISDN network.

Terminal Equipment Type 1 (TE1) - Compatible with the ISDN network. Example: Telephones, personal computers, fax machine or videoconferencing machine.

Terminal Equipment Type 2 (TE2) - Not compatible with the ISDN network. Example: Analog phone or modem, requires a TA (TE2 connects to TA).

Network termination type 1 & 2 (NT1 and NT2) - A small connection box that physically connects the customer site to the telco local loop, provides a four-wire connection to the customer site and a two-wire connection to the network (PRI CSU/DSU).

ISDN Components and Reference Points

ISDN Components and Reference Points

NT-1 (Network Terminator-1) An NT-1 is an interface box that converts ISDN

data into something a PC can understand (and vice versa). It works a little like a cable TV descrambler for ISDN signals, and is often built into ISDN adapters.

TA (Terminal Adapter) This chunk of hardware converts the data it

receives over ISDN to a form your computer can understand. Sometimes mistakenly called an ISDN modem or a digital modem, a terminal adapter handles data digitally and does not need to modulate or demodulate an analog signal. Terminal adapters can be an internal board or an external board that connects to the computer through the serial port.

ISDN Reference Points

U - Two wire cable that connects the customers equipment to the telecommunications provider

R - Point between non-ISDN equipment (TE2) and the TA

S - Four-wire cable from TE1 or TA to the NT1 or NT2

T - Point between NT1 and NT2

ISDN Reference Points

ISDN Protocols

E-series protocolsTelephone network standards for ISDN.

I-series protocolsSpecify ISDN concepts and interfaces.

Q-series protocolsStandards for ISDN switching and signaling.

Operate at the physical, data link, and network layers of the OSI reference model

ISDN Protocols

Physical layer ISDN protocols BRI (ITU-T I.430) / PRI (ITU-T I.431)

Defines two ISDN physical layer frame formats Inbound (local exchange to ISDN customer) Outbound (ISDN customer to local exchange )

Data link layer ISDN protocols LAPD signaling protocol (ITU-T Q.920 for BRI and Q.921 for

PRI) for transmitting control and signaling information over the D channel LAPD frame format similar to ISO HDLC frame format

Network layer ISDN protocols ITU-T I.930 and ITU-T Q.931 defines switching and signaling

methods using the D channel.

ISDN Physical Layer

ISDN physical-layer frame formats are 48 bits long, of which 36 bits represent data

ISDN Data Link Layer

Frame format is very similar to that of HDLC

ISDN Network Layer

Two Layer 3 specifications are used for ISDN signaling: ITU-T I.450 (also known as ITU-T Q.930) ITU-T I.451 (also known as ITU-T Q.931) Together, these protocols support:

User-to-user circuit-switched connections User-to-user packet-switched connections A variety of standards for:

Call establishment Call termination

ISDN Encapsulation

The two most common encapsulations: PPP HDLC

ISDN defaults to HDLC. PPP is much more robust.

Open standard specified by RFC 1661 Supported by most vendors

ISDN Services BRI

Basic Rate Interface (BRI)

Two 64 Kbps B channels, one 16 Kbps D channel, and 48 Kbps worth of framing and synchronization. Available data bandwidth: 128 Kbps (2 x 64 Kbps) User bandwidth: 144 Kbps (128 Kbps + a 16 Kbps D

channel) Total line capacity: 192 Kbps (144 Kbps + 48 Kbps

framing) Each B channel can be used for separate applications

Such as Internet and Voice

Allows individual B channels to be aggregated together into a Multilink channel

ISDN Services PRI

Primary Rate Interface (PRI) A PRI connection can assign various 64 Kbps channels to both

ISDN and analog modem connections North America and Japan PRI service has 23 * 64 Kbps B

channels, one 64 Kbps D channel, and 8 Kbps of synchronization and framing for a total bit rate of up to 1.544 Mbps (same as T1)

Europe, Australia, and other parts of the world PRI service has 30 * 64 Kbps B channels, one 64 Kbps D channel, and 64 Kbps of framing and synchronization for a total bit rate of up to 2.048 Mbps (same as E1)

Each B channel to be used for separate applications including voice, data and Internet

Multiple B channels can be Multilinked together

Referine

Roger L. Freeman: Fundamentals of Telecommunication Capitolul 7 i 14

Wikipedia:Signaling System #7 http://en.wikipedia.org/wiki/SS7

International Engineering ConsortiumWeb ProForums: Signaling System 7 http://www.iec.org/online/tutorials/ss7

Guerrero Ibez ISDN lecture notes