Overview Overview • VoIP Introduction • Basic PSTN Concepts and SS7 • Old Private Telephony Solutions • Internet Telephony and Services Voice- -over over- -IP (VoIP) IP (VoIP) Voice • VoIP-PSTN Interoperability • IP PBX ENUM ENUM • Network Convergence • Technology Comparison • VoIP Signaling Protocols • SIP • ENUM Voice-over-IP 2 Basic concepts and directions in telecommunications C. Courcoubetis VoIP Introduction (1/2) VoIP Introduction (2/2) VoIP Introduction (1/2) VoIP Introduction (2/2) • Voice becomes another Internet application • VoIP is relevant to both the wide and local area � Toll bypass and IP PBX/Centrex • The VoIP model is similar to the Web (and email) model • VoIP can offer novel telephony services in addition to voice • VoIP signaling is a value-added service • It coexists with legacy telephony � VoIP signaling supports both centralized and distributed architectures � Can signaling be kept inside the carriers’ networks? • It is based on open standards � Where can carriers benefit? � Numerous vendors of services and equipment: competition, choice, and faster development of new services • Important economic issues with VoIP � Low cost of entry • VoIP ultimate goal: global, low-cost, unified communications � How can carriers maintain competitive position? Voice-over-IP 3 Voice-over-IP 4 Basic concepts and directions in telecommunications C. Courcoubetis Basic concepts and directions in telecommunications C. Courcoubetis
PSTN / SS7 Operation PSTN / SS7 Operation The Old Approach The Old Approach Voice-over-IP 6 Basic concepts and directions in telecommunications C. Courcoubetis Internet Telephony Internet Telephony • IP as the transport protocol for both media and signaling � Media: Packetized voice instead of TDM virtual circuits � Signaling: Internet protocols instead of SS7 and proprietary PBX protocols • Programmable servers, open APIs, third-party services � Instead of “closed” switches and PBXs The New Approach The New Approach Signaling Requests Location Service Signaling Responses Media Signaling Server Signaling Server 3 Domain A 2 4 Domain B 1 5 7 8 6 9 Multimedia terminal Multimedia terminal or IP phone or IP phone Voice-over-IP 8 Basic concepts and directions in telecommunications C. Courcoubetis
Why IP- -Based Communications? Based Communications? PSTN Interoperability (1/2) Why IP PSTN Interoperability (1/2) • Efficient use of link bandwidth • Interoperability remains a key issue � Statistical multiplexing � The PSTN and SS7 will not go away soon • Introduce PSTN-VoIP gateways • Fault tolerance � Devices that translate both media and signaling traffic between the � Per-packet routing PSTN / SS7 and IP networks � Gateways are connected to both the PSTN and to an IP network • Wide-area infrastructure available � Gateways are critical resources � Optical core, currently over-provisioned • Limited number of PSTN lines per gateway � limited concurrent PSTN sessions • PSTN access � PSTN billing � Cost for the gateway’s owner • Potential targets for Internet hackers • Economic reasons � Easier to manage, uniform technology Voice-over-IP 9 Voice-over-IP 10 Basic concepts and directions in telecommunications C. Courcoubetis Basic concepts and directions in telecommunications C. Courcoubetis PSTN Interoperability (2/2) The IP PBX PSTN Interoperability (2/2) The IP PBX • The IP telephony equivalent of the PBX � An example of voice/data network convergence � Uses IP over Ethernet to provide local telephony services Voice-over-IP 11 Voice-over-IP 12 Basic concepts and directions in telecommunications C. Courcoubetis Basic concepts and directions in telecommunications C. Courcoubetis
IP PBX Components Network Convergence IP PBX Components Network Convergence 2 Interoffice Communications: Before and After Convergence 1. A VoIP-aware Ethernet switch 2. A Signaling Server � Can be a standard PC, but more specialized devices also exist � Cheaper, easier to configure, maintain and upgrade compared to a PBX box 3. Terminals � Connect to the Ethernet network � Multimedia PCs can also be used as terminals 4. A PSTN gateway 3 1 4 … and a signaling protocol to manage the sessions Voice-over-IP 13 Voice-over-IP 14 Basic concepts and directions in telecommunications C. Courcoubetis Basic concepts and directions in telecommunications C. Courcoubetis Internet Telephony: signaling VoIP Signaling Protocols Internet Telephony: signaling VoIP Signaling Protocols Signaling Requests • H.323: the ITU’s IP-based signaling protocol Signaling Responses � Initially designed to be carrier-friendly: centralized intelligence Media Redirect Server Redirect Server � Assumed dumb terminals Domain A � Modeled after existing PSTN / ISDN signaling protocols Domain B 1 3 � Carrier-centric, enables carriers to have greater control 2 4 5 • SIP: the IETF’s IP-based signaling protocol 6 Caller 7 Callee � Initially designed to be user-friendly: edge intelligence Proxy Server � Assumed smart terminals Proxy Server � Modeled after existing Internet protocols (HTTP, SMTP) Domain A 2 Domain B � User-centric, leverages other Internet protocols (lightweight protocol) 1 3 5 6 4 Caller Callee 7 Voice-over-IP 15 Voice-over-IP 16 Basic concepts and directions in telecommunications C. Courcoubetis Basic concepts and directions in telecommunications C. Courcoubetis
SIP - - General General SIP – – Typical Call Setup Typical Call Setup SIP SIP • IETF’s Session Initiation Protocol � Used to initiate, modify, and terminate multimedia sessions The Location Server is being • Sessions can be two-party or multiparty DNS Server queried to check the (current) DNS Query for the • Sessions may include advanced services destination IP address of the IP Address of the callee’s User Agent � A text-based, client-server protocol similar to HTTP and SMTP SIP Proxy of the Destination Location Server The INVITE is Domain 2 4 forwarded 3 • Main SIP entities A request is sent (Inbound) Proxy (SIP INVITE) to � User agents (the software that runs on a client device) 5 INITIATE a The request is forwarded to the session � Proxy and redirect servers End-Device ( Outbound) Proxy � Registrars 1 6 User Agent: Callee � Location servers Media Transport � Feature servers (supporting voice-mail, presence, gaming, etc.) Destination device returns its IP Address to the originating device and a “direct” media User Agent: Caller connection is opened (SIP IP Phone) Voice-over-IP 17 Voice-over-IP 18 Basic concepts and directions in telecommunications C. Courcoubetis Basic concepts and directions in telecommunications C. Courcoubetis SIP – – Calling a Roaming User Calling a Roaming User SIP – – Presence and Instant Messaging Presence and Instant Messaging SIP SIP Voice-over-IP 19 Voice-over-IP 20 Basic concepts and directions in telecommunications C. Courcoubetis Basic concepts and directions in telecommunications C. Courcoubetis
Advanced Services with SIP Advanced Services with SIP • Device independence example � A user binds his SIP URL to his home phone, his office phone, and his mobile phone (or his hotel room phone when traveling) � Incoming calls ring all devices and user picks up the one that is closest • Voice-mail notification example � Callers can be redirected to voice-mail after a user-specific timeout ENUM ENUM � The inbound proxy can send an SMS or e-mail notification to the callee • Smart screening example � User agents (or proxy servers) can be configured to screen incoming calls � Calendar integration can enable smart, time-of-day call routing • Text-to-speech example � Proxies can use text-to-speech to read to users their urgent e-mail • Forking example � Proxies can “fork” a call addressed to a virtual endpoint (e.g. to sip:sales@company.com ) to all the devices used by sales staff � The first one to answer “wins” Voice-over-IP 21 Basic concepts and directions in telecommunications C. Courcoubetis ENUM (1/5) ENUM (2/5) ENUM (1/5) ENUM (2/5) • IETF’s E.164 Number Mapping Protocol • ENUM: one number for all services � Given a E.164 number, find additional contact information for this number (such as email addresses, web URLs, fax numbers, SIP URIs) � “Only one number printed on business cards” • If the user changes Internet providers he can keep the same number and only inform an ENUM registrar of his new email address and web URL � Companies with “unfortunate” domain names can potentially rely only on a well-known 800 number • ENUM assumptions � People are used to phone numbers � 12-key communication devices are still common Voice-over-IP 23 Voice-over-IP 24 Basic concepts and directions in telecommunications C. Courcoubetis Basic concepts and directions in telecommunications C. Courcoubetis
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