TLEN 5470 Tue 4/11/06 /share/handouts/20.lecture
topics:
1 - restart VOCAL processes
2 - VoIP news item
3 - INVITE through SIP-based system
4 - basic call setup through SIP-based system (continued).
1 - restart VOCAL processes
The following restarts the VOCAL processes.
$ . /share/mkALL # makes env variable ALL as ../allinoneconfigure
$ /share/vlls # lists what the vl?? scripts do
$ /share/vlsp # stop all VOCAL processes
$ sudo /share/RS # restart web server (user = `whoami`)
$ $ALL # run ../allinoneconfigure
$ /share/vlss # verify VOCAL status as running, for example
fs 5080 18351
fs 5085 18352
fs 5090 18353
fs 5095 18354
fs 5100 18355
fs 5105 18356
fsvm 5110 18357
ms 5060 18358
ms 5065 18359
rs 5070 18360
vmserver 18361
Also note that executing /share/csls yields
csin - initialize cscope file list
csdb - (re)builds cscope data base
csst - starts cscope
csls - this file, list cs?? scripts
for another set of short scripts, these are for using 'cscope'
2 - VoIP news item
Story from BBC NEWS:
http://news.bbc.co.uk/go/pr/fr/-/2/hi/technology/4401136.stm
Published: 2005/11/03 01:28:51 GMT
** Internet phone calls on the rise
A third of people in the US and Europe will abandon phone lines
in favour of wireless and broadband telephony come 2009, a report
from Gartner has found.
Broadband telephony is gaining ground among consumers as people
become more confident users of their high-speed net connections.
It offers a cheap alternative to fixed-line voice calls.
By 2009, 70% of voice connections around the world will be wireless,
the report found.
This is due to falling mobile costs and greater penetration in
countries such as China and India.
Market research group Gartner predicted that handsets would be
available for as little as 14 British pounds by 2010.
Skype, which provides software for broadband telephony via the
PC, has proved immensely popular with consumers, although Gartner
predicts that VoIP-enabled telephones will eventually win out.
"With Skype lots of people have downloaded it but not that many
people use it. It requires a computer and a headset and it is
more likely that telephone services such as that offered by Vonage
will be what catches on," said David Neil, research vice president
at Gartner.
** Wireless strategy
The growing popularity of broadband telephony is both good and
bad for traditional telephone companies, the report said.
Most are embracing the technology and will therefore gain some
revenue from it but the fact that the prices for VoIP are much
lower means it will not be a cash cow in the same way as fixed
telephone services have been in the past.
There will be three billion mobile subscribers in the world by 2010,
according to Gartner.
Mr Neil thinks it is vital that telcos put wireless at the top of
their agenda if they are be successful in the future.
"They will have to have a very clear wireless strategy or they
are going to be dead," he said.
Many fixed line operators are integrating wireless with their
traditional phone services, selling the service to consumers with
the convenience of having one device and one bill for both mobile
and fixed line calls.
But if mobile voice pricing continues to fall this might not be
enough to convince people that they still need a phone line in
their home.
It will also be crucial for telcos to upgrade their networks so
they can provide the backbone to the much talked-about digital
home of the future, where appliances such as ovens can be switched
on remotely.
In this, British Telecom, alongside firms such as South Korea
Telecom, is one the leaders, according Mr Neil.
Its rollout of the so-called 21st century network is well underway
and will broadband telephony, TV as well as applications for the
digital home.
3 - INVITE through SIP-based system
// If you take two SIP phones and connect them to a distributed
// network, the more realistic scenario, the basic call setup and
// teardown involves a lot more messages than those shown earlier.
// The following figure shows an INVITE going through a SIP-based
// network and arriving at the called party's phone. In this call,
// Proxy server A is the 'ingress' proxy because it is receiving the
// INVITE message from outside the call control system. This proxy
// then forwards the INVITE to its Redirect server. Proxy server
// B is the 'egress' proxy because it is forwarding the INVITE to
// an endpoint that is outside the call control system. For a local
// call, both servers might be running on the same host, and even be
// the same proxy server code. In general, however, the two proxies
// are on different, geographically-separated hosts.
Redirect server
___
|----- 3 -->| |<-10 ------|
| | | |
| |--- 4 ---| |-- 9 ----| |
| | | | | |
| | |- 5 -->|___|<- 8 --| | |
| | | | | |
_|_+_|_ _|_+_|_
|----- 1 -->| |------- 6 ------>| |--- 11 -----|
| | | | | |
| |--- 2 ---| |<------ 7 -------| |<-- 12 ---| |
| | |_____| |_____| | |
__|_+__ __|_+__
| | Proxy server A Proxy server B | |
| | | |
|_____| |_____|
SIP phone A SIP phone B
// The following is a description of the dozen messages in the
// above figure.
// 1. INVITE
// Phone A sends an 'INVITE' into the call control system with the
// 'phone number' inserted by caller A for called party B.
// 2. 100 Trying
// Proxy A receives the 'INVITE' and immediately sends a '100
// Trying' response to the caller's phone.
// 3. INVITE
// Proxy A, having authenticated the 'INVITE' as coming from a
// legitimate user, forwards it to its Redirect server for routing.
// 4. 302 Moved Temporarily
// The Redirect server generates a '302 Moved Temporarily'
// message from the data provided by the 'INVITE' and the routing
// information provided by the Location server (not shown).
// 5. ACK
// Proxy A sends and 'ACK' back to the Redirect server as soon
// as it receives the '302 Moved Temporarily' message to complete
// the triple handshake.
// 6. INVITE
// Proxy server A takes the new routing information from the '302
// Moved Temporarily' message, generates a new 'INVITE' with more
// complete routing information, and sends it to Proxy server B.
// 7. 100 Trying
// Proxy server B, perhaps far away physically, receives the
// 'INVITE' and immediately returns a '100 Trying' response.
// 8. INVITE
// Proxy B forwards the 'INVITE' to a (probably different) Redirect
// server for final routing.
// 9. 302 Moved Temporarily
// The Redirect server generates a '302 Moved Temporarily' message
// and sends it to Proxy B.
// 10. ACK
// Proxy B sends an 'ACK' response back to the Redirect server
// as soon as it receives the '302 Moved Temporarily' message to
// again complete a triple handshake.
// 11. INVITE
// Proxy server B takes the routing information it received from the
// '302 Moved Temporarily' message, generates the (last) 'INVITE',
// and sends it to phone B.
// 12. 100 Trying
// Phone B receives the 'INVITE' and immediately returns a '100
// Trying' response.
// We are only half done in setting up a basic call through a
// SIP-based phone system. Note that errors could occur at any
// point making a complete description of the procedure much more
// complicated. Programming the finite state machines in the servers
// is also non-trivial as now not only errors but also timing delays,
// retransmissions, and race conditions must also be addressed.
4 - basic call setup through SIP-based system (continued).
// The last half of the SIP call setup is shown below.
Redirect server
___
| |
| |
| |
| |
|___|
_______ _______
|----- 15 --| |<----- 14 -------| |<- 13 ------|
| |--- 18 --| |<----- 17 -------| |<- 16 ----| |
| | |- 19 ->| |------ 20 ------>| |-- 21 --| | |
| | | |_____| |_____| | | |
__+_+_|__ __+_|_|__
| | Proxy server A Proxy server B | |
| |<- - - - - - - - - 22 - - - - - - - - - ->| |
|_______| |_______|
SIP phone A SIP phone B
// 13. 180 Ringing
// Phone B starts ringing and sends a '180 Ringing' back through
// the network, first to Proxy server B,
// 14. 180 Ringing
// which forwards the '180 Ringing' message to Proxy server A,
// 15. 180 Ringing
// which finally forwards the '180 Ringing' message to Phone A.
// The user listening at Phone A then "hears" ringing tones.
// 16. 200 OK
// The user at Phone B picks up the phone. Phone B generates a
// '200 OK' message and send it back though the network towards
// Phone A, first to Proxy server B,
// 17. 200 OK
// which forwards the '200 OK' message to Proxy server A,
// 18. 200 OK
// which finally forwards the '200 OK' message to Phone A.
// 19. ACK
// Yet again, a message is forwarded from one endpoint to the other,
// this final time Proxy server A launches an 'ACK' towards phone
// B first to Proxy server A,
// 20. ACK
// which forwards the 'ACK' message to Proxy server B,
// 21. ACK
// finally arriving at SIP Phone B completing the triple handshake.
// 22. RTP Voice Channel
// At this point, the final voice channel is set up (early media
// may have been used earlier), and the calling and called parties
// can talk to each other.
// Finally, one or the other party hangs up which triggers the messages
// depicted and explained below.
Redirect server
___
| |
| |
| |
| |
|___|
_______ _______
|----- 27 --| |<----- 25 -------| |<- 23 ------|
| |--- 28 ->| |------ 26 ------>| |-- 24 ----| |
| | |- 29 ->| |------ 30 ------>| |-- 31 --| | |
| | | |_____| |_____| | | |
__+_|_|__ __+_+_|__
| | Proxy server A Proxy server B | |
| |<- - - - - / terminated / - - - - ->| |
|_______| |_______|
SIP phone A SIP phone B
// 23-28. BYE and 100 Trying
// Starting at the user that hangs up first, in this case the
// user at B, pairs of 'BYE'/'100 Trying' messages propagate from
// Phone B to/from Phone A. Each intermediate 'BYE' causes an
// immediate '100 Trying' return response and a forwarded 'BYE'
// ending at Phone A.
// 29-31. 200 OK
// Phone A, after receiving the 'BYE', launches a '200 OK' towards
// Phone B. The call and voice channel are torn down, and both users
// get themselves ready to send or receive an initial 'INVITE'.
// Next time we will look at the internal structure of some of the
// messages, especially 'INVITE'.