Internet Technology Voice over IP

(1)

(2)

www.gradwell.com |01225 800 800 |info@gradwell.com

BT Advert from 1980s

http://www.youtube.com/v/o0H65_pag04

(3)

Welcome to Gradwell

(4)

The TCP/IP Stack

Page |4

(5)

Different Types of VoIP

(6)

Voice Protocols



All systems use some kind of application protocol to communicate

-

SIP

-

H323

-

IAX (Inter Asterisk eXchange)‏

-

Skinny (Cisco Protocol)‏

(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

(8)

Good book:



If you're interested in more details

(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

(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

(11)

SIP – Session Initiation Protocol



SIP is the dominant VoIP protocol

(12)

SIP Addressing



SIP is very similar to Email and HTTP



URI Address format:

-

sip:

peter@gradwell.com

-

sip:

100@sip.gradwell.net

:5060

-

sip:441225800800@sip.gradwell.net

(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.

(14)

SIP Registration



Phone registers periodically to tell the SIP server where it is

(15)

(16)

A Complete Call

16 Often we'll draw

SIP call path

(17)

(18)

You can also do redirects

(19)

Codecs



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



Narrow Band (8k) or Wide Band (16k)‏



We waste loads of Bandwidth on packet

overhead



Audio transmitted as RTP

Codec

BR

NEB

G.711 64 Kbps

87.2 Kbps

G.729 8 Kbps

31.2 Kbps

G.723.1 6.4 Kbps

21.9 Kbps

G.723.1 5.3 Kbps

20.8 Kbps

G.726 32 Kbps

55.2 Kbps

G.726 24 Kbps

47.2 Kbps

G.728 16 Kbps

31.5 Kbps

iLBC

15 Kbps

27.7 Kbps

BR = Bit rate

NEB = Nominal Ethernet

(20)

Jitter & Packet Loss



―Jitter‏is‏the‏variation‏of‏packet‏interarrival time‖



Jitter is a major problem

-

The internet is asymmetrical

(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?

(22)

Page |22

Shift Change in the handset industry

What about Mobile Handsets?



SIP over WiFi has a very bad user

experience – Still difficult to setup



GSM‏Calls‏“Just‏work”



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

(23)

(24)

Google Voice Video

(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)



Needs‏a‏new‏‗root‘

-

.e164.arpa

-

Managed by RIPE

(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)

-

Email

-

Tel(ephone)

-

Fax



NAPTR records can be very sophisticated

-

Can contain time of day and other information

(27)

What is ENUM



This is a record for +1 770 555 1212



100 / 102 is priority

-

Lowest number, highest priority



10 is a preference level

-

Can be ignored here as both records 10



―u‖‏is‏a‏user‏record‏i.e.‏stop‏processing

$ORIGIN 2.1.2.1.5.5.5.0.7.7.1.e164.arpa.

(28)

(29)

(30)

ENUM in production



Asterisk‏supports‏ENUM‏―out‏the‏box‖



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

(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

(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

(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

(35)

ENUM Conclusions

Story so far



ENUM allows interoperability between

carriers



More than just voice

(36)

Page |36

Voice Over IP?



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

(37)

Peter Gradwell

T:

01225 800 810

E:

peter@gradwell.com