Điện tử viễn thông c1 6 thoại qua IP (VoiceOverIP) khotailieu

• Infrastructure savings – PABX and separate telephone wiring replaced by additional capacity requirements on data network – Reduced external telecommunication costs – Maintenance and m

TỔNG ĐÀI &

KỸ THUẬT CHUYỂN MẠCH

Chương 1: Lý thuyết tổng quan và cơ sở

TRƯỜNG ĐẠI HỌC ĐIỆN LỰC KHOA ĐIỆN TỬ - VIỄN THÔNG

Giảng viên: Phan Thị Thanh Ngọc

VI Thoại qua IP (VoiceOverIP)

Multi-media & Data Integration

Benefits

• Productivity increases

– Voice and even multi-media communications become part of

office automation and web environment (“click to talk”).

• Infrastructure savings

– PABX and separate telephone wiring replaced by additional

capacity requirements on data network

– Reduced external telecommunication costs

– Maintenance and management reduced to one single network

• Increased reliability

– PABX single point of failure could be replaced by distributed

software

The Multi-media challenge

Traffic characteristics

Conclusion:

Data and multi-media traffic have totally different requirements Mixing them on a single network is technically and economically challenging

Voice & Images Data

Delay: Unimportant Small & Stable

Multi-media & Data Integration

Challenges

• Control over delays in IP networks

? Enough network capacity

? GMPLS

? IP V6

? New transport protocols

• Reliability and availability culture in data networks

• Power via data cables for IP phones

• Organizational and cultural changes

• Addressing and Directory management

Real Time Voice over the Internet

The initial goal : free international calls

- IP addresses on both sides need to be known

- Voice quality dependent on network delays

- Acceptable if network not overloaded

Sound enabled PC

(full duplex)

Internet Telephony

Internet

+ Access through local PSTN

- Quality dependant from network load

Local PSTN

Local PSTN

Internet Telephone

Gateways

Low cost POTS emulation

Internal Communications

• Internal communications in many organizations :

– voice : PABX – data : intranet

• If geographically separated sites :

– voice : PABX’s interconnected via

Traditional Communications

in multi-site organizations

PABX PABX

WAN Intranet

PSTN

PABX & Intranet Integration

for traditional POTS and data

Full voice-data Integration

WAN or LAN Intranet

Infrastructure savings

+ Productivity gains

What about the 10 9 pots users ???

Full voice-data Integration

WAN or LAN Intranet

Infrastructure savings

+ Productivity gains

PSTN H231 Gateway

The role of SIP

• Voice or multimedia (= voice, images, streaming music and

video, streaming computer data, …) communication implies a

“connection” between two or several people.

• The host addresses and the port numbers of the appropriate

applications that need to be connected to enable these people

to communicate need to be identified.

• The nature and the characteristics of the communication

between these applications needs to be negotiated

• The connection needs to be established

• The connection needs to be maintained, even when the address

of some partners change (mobility)

• Mobility might imply renegotiation of the communication

characteristics

• When no longer needed, the connection needs to be closed

Addresses & Directories

• Addresses are hard to memorize numbers

Domain Name Servers

• In Each domain, there is at least one DNS

– Name & DNS Address of all subdomains – Name & address of all hosts in the domain – DNS address of, at least, root of DNS system – Names & DNS addresses of frequently used domains

• Each host must know the address of one DNS

• Address resolution can be done recursively or by

successive calls to different DNS

• Local DNS is locally maintained

• Caching greatly improves performance of DNS by

keeping the translations of most recently accessed domains and hosts

Names vs Addresses

• A name identifies a service

– The mail service of a specific person (mailbox)

– The web service of a specific company

• An address specifies a host on which services are available

• Several names can be linked with a single address

– jacques.tiberghien@ulb.ac.be

– tiberghien@info.vub.ac.be

• Several addresses can be linked with a single name

– Redundant web servers

• DNS assumes stable links between names and addresses

– Machines offering services have stable addresses

Beyond DNS

• For some applications DNS is insufficient

– Internet telephony = person to person service

– At different times, people are at different locations

– Personal computers seldom have unique address

– One person can be reached through different devices, with

different service levels.

• Session Initiation Protocol (SIP, RFC 3261)

– A SIP server is an agent that handles multi-media services

for one or several people:

» As any server, it has a stable address

» It knows the present address of the people it works for

» It establishes and manages connections between

multi-media communicating applications.

Session Initiation Protocol

Cathy@info.vub.ac.be

The SIP server can handle both diversity

in terminals and mobility of terminals

Home network

Visited network

SIP in Redirection mode

Callers network SIP Redirection

server

Mobility management

Session set-up

Actual Data transfer

• Most efficient data transfer

• Caller has access to actual

called address

Home network

Visited network

SIP in Proxy mode

Callers network SIP Proxy

server

Mobility management

Session set-up

Actual Data transfer

• Longer transmission delays

• SIP server can be bottleneck

• Caller has no access to the

actually called address

SIP properties

• SIP is user friendly

– People accessed through their URLs

» Jacques.tiberghien @sip.vub.ac.be

» 2905 @sip.vub.ac.be

• SIP is well in line with Internet technology

– Commands in clear text (html) – Few different commands

– Readable answers to commands – Details of desired session described with SDP.

SIP Requests

• INVITE Invite user to a session The session

description is contained in the body of the message,

using SDP The session description contains the

address where the host wants to receive media streams.

• ACK Acknowledgment of an INVITE request

• BYE Sent when a call is to be released

• OPTIONS Query server about capabilities

• CANCEL Cancel a pending request

• REGISTER Register with a SIP server

Each SIP transaction has a unique identifier, which identifies the session.

The Universal IP Network ?