TRƯỜNG ĐẠI HỌC ĐIỆN LỰC KHOA ĐIỆN TỬ - VIỄN THÔNG TỔNG ĐÀI & KỸ THUẬT CHUYỂN MẠCH Chương 1: Lý thuyết tổng quan và sơ VI Thoại qua IP (VoiceOverIP) Giảng viên: Phan Thị Thanh Ngọc EPU - 2012 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 J.Tiberghien - VUB The Multi-media challenge Traffic characteristics Throughput: Correctness: Delay: Data Voice & Images Bursty Essential Unimportant Stable Non-essential Small & Stable Conclusion: Data and multi-media traffic have totally different requirements Mixing them on a single network is technically and economically challenging J.Tiberghien - VUB 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 J.Tiberghien - VUB Real Time Voice over the Internet The initial goal : free international calls Internet Sound enabled PC (full duplex) Sound enabled PC (full duplex) - To communicate, precise appointments need to be made, by phone ?!? - IP addresses on both sides need to be known - Voice quality dependent on network delays - Acceptable if network not overloaded J.Tiberghien - VUB Internet Telephony Low cost POTS emulation Local PSTN Internet Telephone Gateways Local PSTN Internet + Access through local PSTN - Quality dependant from network load J.Tiberghien - VUB Internal Communications • Internal communications in many organizations : – voice : PABX – data : intranet • If geographically separated sites : – voice : PABX’s interconnected via » leased lines » public telephone network – data : Intranets interconnected via » leased lines » Virtual Private Networks J.Tiberghien - VUB Traditional Communications in multi-site organizations WAN Intranet PABX PSTN PABX J.Tiberghien - VUB PABX & Intranet Integration Transport POTS costs lower for traditional and data for data than for telephony ! PSTN PABX WAN Intranet PABX PSTN PABX needs to be IP compatible J.Tiberghien - VUB Full voice-data Infrastructure Integration savings + Productivity gains WAN or LAN Intranet What about the 109 pots users ??? 10 J.Tiberghien - VUB Full voice-data Integration Infrastructure savings + Productivity gains WAN or LAN Intranet PSTN 11 H231 Gateway J.Tiberghien - VUB • 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 12 J.Tiberghien - VUB Addresses & Directories • Addresses are hard to memorize numbers – Tel : +32 (0) 673 64 76 – Gsm : +32 (0) 475 81 27 93 – ip : 134.184.1.25 – ipV6: 64.0.0.0.0.0.0.0.0.0.0.0.134.184.1.25 • Need of directories, but hard to maintain consistency • Internet solution : – DNS = distributed directory – Local addresses maintained by local authority 13 J.Tiberghien - VUB Internet Root Domains uk ibm be edu mtv ac vrt ulb tiberghien tiberghien@ulb.ac.be com org ieee vub info tiberghien tiberghien@info.vub.ac.be 14 J.Tiberghien - VUB Domain Name • In Each domain, there is at least one DNS Servers – 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 15 J.Tiberghien - VUB Names vs • A name identifies a service Addresses – 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 16 J.Tiberghien - VUB Beyond • For some applications DNS is insufficient DNS – 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 multimedia communicating applications 17 J.Tiberghien - VUB Session Initiation Protocol Cathy@info.vub.ac.be The SIP server can handle both diversity in terminals and mobility of terminals 18 J.Tiberghien - VUB SIP functionality • Call forwarding, unconditional, on busy, … • • • • • • • • • • 19 Call transfer Caller ID Call hold Multiparty conferences Call return Follow me Find me Call queuing Do not disturb …… J.Tiberghien - VUB SIP in Redirection mode SIP Redirection server Callers network Home network Actual Data transfer Session set-up • Most efficient data transfer • Caller has access to actual called address 20 Mobility management Visited network J.Tiberghien - VUB SIP in Proxy Session mode set-up Callers network SIP Proxy server Home network Actual Data transfer • Longer transmission delays • SIP server can be bottleneck • Caller has no access to the actually called address 21 Mobility management Visited network J.Tiberghien - VUB 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 22 J.Tiberghien - VUB SIP Requests Invite user to a session The session • INVITE 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 23 J.Tiberghien - VUB SIP references • The initial designers: www.cs.columbia.edu/sip/ • SIP Forum : www.sipforum.org • SIP Charter : www.ietf.org/html.charters/sip-charter.html 24 J.Tiberghien - VUB The Universal IP Network ? 25 J.Tiberghien - VUB ... Visited network J.Tiberghien - VUB 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... with a SIP server Each SIP transaction has a unique identifier, which identifies the session 23 J.Tiberghien - VUB SIP references • The initial designers: www.cs.columbia.edu/sip/ • SIP Forum... www.cs.columbia.edu/sip/ • SIP Forum : www.sipforum.org • SIP Charter : www.ietf.org/html.charters/sip-charter.html 24 J.Tiberghien - VUB The Universal IP Network ? 25 J.Tiberghien - VUB