Internet Technology Voice over IP

Transcription

1 Internet Technology Voice over IP Peter Gradwell

2 BT Advert from 1980s Page 2

3 Welcome to Gradwell Gradwell provides technology for every line on your business card Every product we sell solves a problem we had Page 3

4 The TCP/IP Stack Where does VoIP fit in? Page 4

5 Different Types of VoIP VoIP Comes in Many Flavours Page 5

6 Voice Protocols All systems use some kind of application protocol to communicate - SIP - H323 ( exchange - IAX (Inter Asterisk ( Protocol - Skinny (Cisco Audio is transported as RTP

7 TCP/UDP/Ports Traffic is either TCP or UDP MTU on Ethernet typically 1500 bytes 100 bytes of headers, 1400 bytes of data Lots of packet overhead Socket = IP Address + Port MTU = Max Transfer Unit/A Packet

8 Good book: If you're interested in more details You can read most of it on amazon

9 H.323 Point to Point Protocol H.323 is actually a family of protocols H.323 is used a lot on trunk routes, as it's signalling reflects ISDN, but is becoming obsolete Modem over IP Conferencing Fax 9

10 Inter-Asterisk exchange Asterisk is a major OpenSource phone system IAX was invented by Mark Spencer/Digium Single UDP stream port 4569 Handles the Media inband on the same socket - Can support multiple RTP streams - Single signalling link - Far more bandwidth efficient - Also much friendlier for firewalls - Pronounced eeks 10

11 SIP Session Initiation Protocol SIP is the dominant VoIP protocol It's a peer to peer protocol, unlike H

12 SIP Addressing SIP is very similar to and HTTP URI Address format: - sip:[email protected] - sip:[email protected]: sip: @sip.gradwell.net 12

13 Types of SIP Message INVITE An INVITE method indicates that the recipient user or service is invited to participate in a session. ACK - An ACK request confirms that the UAC has received the final response to an INVITE request. - ACK is used only with INVITE requests. ACK is sent end to end for a 200 OK response. OPTIONS A UA uses the OPTIONS request to query a UAS about its capabilities BYE A UA uses BYE to request the termination of a previously established session. CANCEL The CANCEL request enables UACs and network servers to cancel an in-progress request, such as INVITE. This does not affect completed requests in which the UAS had already sent final responses. REGISTER A client uses a REGISTER request to register its current location information corresponding to the AOR of the user with SIP servers. 13

14 SIP Registration Phone registers periodically to tell the SIP server where it is 14

15 SIP Call Flow 15

16 A Complete Call Often we'll draw SIP call path diagrams out like this for debugging 16

17 Debug using wireshark 17

18 You can also do redirects 18

19 Codecs Nyquist theorem states that if you sample an analog signal at twice the rate of the highest frequency of interest, you can accurately reconstruct that signal back into its analog form Audio is sampled at 8k or 16k times per second (Hertz) Pulse Code Modulation Codecs trade off quality, bandwidth and CPU to produce an RTP data packet ( 16k ) Narrow Band (8k) or Wide Band We waste loads of Bandwidth on packet overhead Audio transmitted as RTP Codec BR NEB G Kbps 87.2 Kbps G Kbps 31.2 Kbps G Kbps 21.9 Kbps G Kbps 20.8 Kbps G Kbps 55.2 Kbps G Kbps 47.2 Kbps G Kbps 31.5 Kbps ilbc 15 Kbps 27.7 Kbps BR = Bit rate NEB = Nominal Ethernet ( direction Bandwidth (one Skype uses ilbc and ISAC

20 Jitter & Packet Loss Jitter is the variation of packet interarrival time Jitter is a major problem - The internet is asymmetrical - Manage the problem with a Jitter buffer ~ 20ms

21 Quality of Service QoS is needed if a network link is congested Routers need to enforce traffic prioritisation across their links How do they decide? - Trust the user? - DiffServ, Expedited Forwarding and Low Delay bits in IP header - Trust the network all traffic on port X or from IP address Y is special 21

22 Shift Change in the handset industry What about Mobile Handsets? SIP over WiFi has a very bad user experience Still difficult to setup GSM Calls Just work Costs of calling can be fixed commercially e.g. All inclusive call plans Operators are not keen on offloading voice minutes onto their data networks iphone & Google Voice are changing things Page 22

23 Which Mobile App Should I run? Page 23

24 Google Voice Video Page 24

25 What is ENUM User ENUM - Allows users to define how calls should be routed to their numbers - Stores telephone numbers in DNS and routing records ENUM = E.164 NUmber Mapping (E164 is an ITU standard) Needs a new root -.e164.arpa - Managed by RIPE Numbers stored in reverse becomes e164.arpa

26 What is ENUM DNS uses a special form of record - Name Authority Pointer (NAPTR) - RFC2915 NAPTR contains a URI - Information on how to route call - Can specify multiple ways to call - VoIP (SIP/H323) - - Tel(ephone) - Fax NAPTR records can be very sophisticated - Can contain time of day and other information - Can contain regular expressions so say a SIP record relates to the ENUM data - (Generic ENUM records for a telco)

27 What is ENUM $ORIGIN e164.arpa. IN NAPTR "u" "E2U+sip" IN NAPTR "u" "E2U+ " This is a record for / 102 is priority - Lowest number, highest priority 10 is a preference level - Can be ignored here as both records 10 u is a user record i.e. stop processing E2U+sip is the way of writing it s a SIP record Regular expression and the final destination

28 ENUM call Company A Dials PSTN Company B SIP:[email protected] No ENUM Internet SIP:[email protected]

29 ENUM call Company A Dials PSTN Company B SIP:[email protected] arpa ENUM Internet D N S SIP:[email protected] SIP:[email protected]

30 ENUM in production Asterisk supports ENUM out the box OpenSIPS has an ENUM module Various PBX suppliers can support ENUM though may require special configuration Nominet have developed an Android application Enumdroid - Integrated into dialer ENUM in the UK is currently looking for users -

31 Enumdroid real life app Developed by Nominet s Ray Bellis published as open source. Available on the Android Marketplace Dial the number of your contact Application performs an ENUM query and Presents the user the options available Caller make decision of call method and places the call. Presents a number of options Has flexibility to turn off GSM if necessary

32 Enumdroid real life app Developed by Nominet s Ray Bellis published as open source. Available on the Android Marketplace Dial the number of your contact Application performs an ENUM query and Presents the user the options available Caller make decision of call method and places the call. Presents a number of options Has flexibility to turn off GSM if necessary

33 Enumdroid real life app Developed by Nominet s Ray Bellis published as open source. Available on the Android Marketplace Dial the number of your contact Application performs an ENUM query and Presents the user the options available Caller make decision of call method and places the call. Presents a number of options Has flexibility to turn off GSM if necessary

34 Enumdroid real life app Developed by Nominet s Ray Bellis published as open source. Available on the Android Marketplace Dial the number of your contact Application performs an ENUM query and Presents the user the options available Caller make decision of call method and places the call. Presents a number of options Has flexibility to turn off GSM if necessary

35 ENUM Conclusions Story so far ENUM allows interoperability between carriers More than just voice Most applications can be completed thecontrolyouif, ENUM without network & devices It needs a lot of end user applications Page 35

36 Voice Over IP? Where are we at with VoIP? Protocols and services are well established & here to stay Lines (no pun intended) are bluring Network convergence is actually happening No one wants a desk phone Some of the mobile problems will be fixed commercially Some problems by changes in end user behaviour and open access to networks The desktop environment is quickly unifying Telcos still like building islands of subscribers Regulator is looking at mobile number portability ENUM gives end-user control, but no applications or drive for it Page 36

37 Any Questions? Peter Gradwell T: E: Page 37