Transcript Signaling - Weber State University

TBE 2710
Chapter 12
Signaling
Signaling Functions
• Switch to switch communication
• Switch to station communication
– Supervising
– Addressing
– Alerting
– Call Progress
Signaling Methods: In Band...
• Loop-Start Signaling
• Ground-Start Signaling
• Wink Start
General Call-State Model: In-Band
Caller A
LEC CO
Off
Hook
Call
Setup
B
C
IXC Tandem
IXC Tandem
Send dial tone
Receive digits
Translate digits
Translate digits
Seize trunk
Seize trunk
Outpulse digits
Outpulse digits
Translate digits
Seize trunk
Callee D
LEC CO
Receive digits
Outpulse digits
Ring telephone
Call
Answering
Begin call
timing
Send answer
signal
Send answer
signal
Send answer
signal
Talking
State
Call
Termination
Disconnect
Trunk
Stop call timing
Disconnect
Trunk
Disconnect
Trunk
Off
Hook
Disconnect
Trunk
Hang up
Signaling Methods: Out-of-Band or
Clear Channel...
• ISDN – Primary Rate Interface (PRI)
– Used for PBX and Business customers
– Added features (CLID, RLT, etc.)
– Quicker call setup than in-band
• System Signaling No. 7 (SS7)
– Used for PSTN Carrier Networks
– Enables multiple network services
Signaling System 7
• Standard Method for Linking Central Offices
• Supports CLASS Services
• Required for:
–
–
–
–
Local Number Portability (LNP)
E800 services
Calling Name/Number Delivery (CNAM)
Advanced Intelligent Networking (AIN)
Architecture of SS-7
SCP
SP
SP
User
STP
STP
SP
SP
STP
STP
SP
User
SP
SP=Signal Point
STP=Signal Transfer Point
SCP=Service Control Point
Purposes of SS7
•
•
•
•
•
•
•
Improves Call Management
Enhances Network Management
Separates Network Control From Hardware
Supports User Database
Handles Addressing And Supervision
Supports 800 Number Portability
Supports Local Number Portability
SS7 Vs OSI
OSI
Layer
SS7
Layer
Application
Network Applications
7
TCAP
Presentation
6
Session
5
Transport
4
Network
3
Datalink
2
Physical
1
ISDN
service
user
part
(ISUP)
Presentation
Telephone
User
Part
Session
OAM&P
4
Transport
Signaling connection
control point (SCCP)
Message
Transfer
Part
Signaling
Network
Signaling Link
Signaling Data Link
3
Network
Service
Part
2
1
SS7 Messaging
• ISDN User Part – (ISUP)
– Call Setup Messages
• IAM, ACK, DIS, etc…
• Transaction Capability User Part (TCAP)
– Transports INAP messages
• SCP Database queries
– E800, LNP, CNAM, etc.
SS7 Signaling Examples
• Call Setup
– Global Title Translation
– Point Code
• CNUM/CNAM
• E800
• LNP
IP Signaling
• IP traffic and PSTN traffic merging
• Gateways required for conversion
• Protocols
– H.323
– Media Gateway Control (Megaco)
– SIP
H.323
• Large, open, flexible protocol with many options
(good/bad), somewhat proprietary though
• H.225 – call control
– Session master/slave
• H.245 – multimedia control
– Negotiates capabilities of endpoints (intelligent or dumb).
• Gatekeeper
– RAS – registration, admission, status
• Uses Q.931 messages (PSTN) over TCP/IP
• Can be setup as peer to peer with intelligent endpoints
Media Gateway Control
• Megaco and H.248
• Controls interaction between Media
Gateway and Media Gateway Controller
(softswitch, ie. Gatekeeper in H.323)
• Call Control in central controller
SIP
•
•
•
•
•
Simple protocol for multimedia applications over IP
Text messaging between endpoints
Addresses are a URL
Decentralized – intelligent endpoints
Presence
– Servers keep track of users status and availability, and
where to be reached (Instant Messaging uses SIP)
• Proxy server – routes information, locates users and
stores their preferences
• Uses other protocols
– SAP, SDP, TRIP, RSVP, AAA
SIP Advantages
• Operates over Any Network
• Provides Expanded User Choices
• Enables Developers to Create New
Applications
• Supports Multimedia
• Allows User to Specify Best Way to
Communicate
SIP Architecture
IP
Network
Ethernet
SIP Proxy
Ethernet
SIP Proxy
Location
Server
SIP Client
SIP Client
Redirect
Server
SIP Call Setup
User Agent A
Proxy Server
User Agent B
Invite
Invite
Trying
Ringing
Ringing
OK
OK
ACK
ACK
Bye
Bye
OK
OK