VoIP. Overview. Jakob Aleksander Libak Introduction Pros and cons Protocols Services Conclusion

Transcription

1 VoIP Jakob Aleksander Libak 1 Overview Introduction Pros and cons Protocols Services Conclusion 2 1

2 Introduction Voice over IP is routing of voice conversations over the internet or other IP-based networks Voice flows over a packet switched network instead of a circuit switched network Can be a LAN, WAN or other IP based networks, Internet 3 Pros and Cons (I) Advantages Cost VoIP to VoIP is typically free, VoIP to PSTN costs the VoIP user Functionality Calls automaticly routed to your phone, regardless of where you are connected in the network Can integrate with other services, e.g. video conversations Mobility Allows users to travel anywhere and still make and recieve phone calls 4 2

3 Pros and Cons (II) Disadvantages QoS Routing in the internet is best effort Reliability Broadband routers need electrical power Emergency calls Difficult or impossible to locate callers Technical workaround is beeing implemented Security Zfone by Philip Zimmermann, secure VoIP used together with SIP 5 VoIP protocols Protocols used to carry voice signals refered to as VoIP protocols Two popular protocols H.323 Session Initiation Protocol (SIP) Other protocols Megaco (H.248) and MGCP Media gateway control protocols IAX Inter-Asterisk exchange protocol Skinny Client Control Protocol (SCCP) Proprietary protocol by Cisco

4 H.323 Zone Terminal Internet Telephone Network Defined by ITU More an architectural overview of internet telephony than a specific protocol References specific protocols for speech coding, call setup, signaling e.g. Speech encoding protocols G.711, 64kbps PCM G.723.1, 6.4/5.3kbps predictive coding Others Speech G.7xx RTP Gatekeeper Gateway H.323 architectural model Control RTCP H.225 Q.931 H.245 UDP TCP IP Data link protocol Physical layer protocol H.323 protocol stack 7 SIP Designed by IETF, described in RFC 3261 Describes how to set up phone calls and other multimedia connections Single module Supports a variety of services Method INVITE ACK BYE OPTIONS CANCEL REGISTER Description Request initiation of a session Confirm that a session has been initiated Request termination of a session Query a host about its capabilities Cancel a pending request Inform a redirection server about the user s current location Defined SIP methods 8 4

5 SIP Location server Caller 2 LOOKUP 3 REPLY Proxy Callee 1 INVITE 6 OK 4 INVITE 5 OK 7 ACK 8 ACK 9 Data SIP signaling 9 H.323 vs SIP Item H.323 Designed by ITU Compability with PSTN Compability with internet No Architecture Monolithic Compliteness Full protocol stack Parameter negotiation Call signaling Q.931 over TCP Message format Binary Media transport RTP/RTCP Multiparty calls Multimedia conferences Addressing Host or telephone number Call termination Explicit or TCP release Instant messaging No Encryption Size of standards 1400 pages Implementation Large and complex Status Widely deployed SIP IETF Laregely Modular SIP just handles setup SIP over TCP or UDP ASCII RTP/RTCP No URL Explicit or timeout 250 pages Moderate Up and coming 10 5

6 Services Skype SkypeIn SkypeOut Yahoo MSN Many broadband companies provides VoIP services e.g. Telenor Nextgentel Tele2 Typical VoIP setup 11 Systems Cisco unified IP phone 7970G SCCP UTStarcom F1000 SIP Skype 12 6

7 Office setup with IP-PBX 13 The Future Mobile VoIP Hybrid mobile phones, supports both VoIP and cellular networks Automatic switch between and cellular networks Nokia 14 7

8 Conclusion VoIP is routing of phone calls over IP based networks Competitor to PSTN Most used VoIP protocols are H.323 and SIP SIP is the protocol of choice VoIP and the future? 15 References Andrew S. Tannenbaum: Computer Networks fourth edition,