4VoIP Summary of knowledge points

 

 

After SharePoint Class , I make a summary about the knowledge points ,which will help you review the SharePoint.

1.Voip : provide voice transmission throught an IP network
Toip : IPBX functions : Call routing ,Voice mail , Conference rooms ,IVR
2.For Toip : IPBX –> IP Private branch exchange
Asterisk,Cisco Call Manager
Link tranditional telephony with Voip:
–FXO: Foreign eXchange Office –> Phone line to PSTN(Public Switched Telephone Network)
–FXS: Foreign eXchange Station –> Telephone interface for end-user devices
PSTN:Public Switched Telephone Network
3.Voip Protocols(H323): Call Control(Signaling)
Gateway Control (Signaling)
Media
Call Control and Gateway Control we use TCP
For phone call we use UDP
Make a phone call, find the number on server ,and bingding use TCP(most use SIP Protocol)
4.SIP Protocol(Session Initiation Protocol): use connect users connect Protocol
not use RTP ,so can not transport voice
use UDP( Standard port :5060) and TCP
SIP Components: A user Agent (client part)
Sip server /Register
SIp trunk(connect to a SIP provider to recieve/placecalls on PSTN)
5.CODECS
Coder/Decoder 编码/解码
Covert human voice in digital packets
G.711 coders : 8kHZ sampling
G.722 coders : 16kHZ sampling voice is better than G.711
6.Asterisk is a Open Source PBX system
Supports serveral codecs : G711 ,G722,G729,Speex,LPC-10
Provides transcoding between codecs
7.DAHDI
commucation between Asterisk and hardware cards

8.Asterisk Administrating
–Asterisk console
–Configuration files

9.Core restart now –> Force Asterisk to restart Asterisk as the command is entered
core restart gracefully –> Restart Asterisk but allow active calls to continue. All new calls are rejected
core restart when convenient –> Restart Asterisk but allow active calls to continue. All new calls are accepted.

10.Standard extensions: s –> start
t –> timeout
i –> incalid
o –> operator
h –> hangup
11.Asterisk 3 SIP types:
Peer we usually use for trunk
User
Friend we usually use for user

11.Ring group
Ring All (同时全部拨打)
Round Robin (轮流)

12.Call Detail Records(CDR)
Track all calls made through Asterisk including details on them

13.MUSIC ON HOLD
Plays music to callers who have been placed on hold.
we use Exten => s,1,Set(CHANNEL(musicclass)=musicWeWant)

14.IVR
Allows administrator to offer to callers an automated voice response system(very useful to guide automatically users in the right service).

15.VOICE PROMPTS AND TEXT-TO-SPEECH
Text-To-Speech is a technique of converting string of characters to voice element
Google Text-To-Speech

16.CONFERENCES WITH Asterisk ( 电话会议)
exten => 810,1,ConfBridge(bender_room,bridge1,user1,menu1)

we need create elements
the conference bridge in ConfBridge.conf
the extension
in ConfBridge.conf file 3 Configuration
–User profile
–bridge profile
–Bridge menu

17.Call PARKING
Call parking is a feature that can put on hold callers and allow callees to retake the call from every phone

18.INTERCONNECTING ASTERISK SERVERS
Allows the administrator to interconnect Asterisk servers to
Form trunk between Asterisk server
Allow communication between users of differents sites with IP connectivity
On AST-PAR1
In iax.conf file
[AST-LIL-1]
username=AST-PAR-1
type=friend
host=192.168.123.3
trunk=yes
secret=Th1si5SpArtA!
context=my_context
qualify=yes
In extensions.conf file in [my_context]
_61XX,1,Dial(IAX2/AST-LIL-1/${EXTEN})
_61XX,2,Answer()
_61XX,3,Playtones(congestion)
_61XX,4,Congestion()

19.ASTERISK SECURITY THREATS
(1) Phreaking盗用电话线路
攻击者可以盗用,窃取点服务商的服务。
Mitigation options: Strong user password
automatic bans too many authentication failures

(2)VIshing 钓鱼
伪造信赖组织,获取关键信息,密码
Mitigation options: training employees
block the calls from outside (阻拦未知电话)

(3)Call tampering 呼叫篡改/DoS
阻止合法用户发出维持呼叫
Mitigation options: FireWalling
Fail2Ban — a framework to avoid DoS

(4)Spamming over Internet Telephony(SPIT)垃圾邮件互联网电话(SPIT)

(5)Eavesdropping窃听/Man-in-the-middle 中间人
Listening of the calls by sniffing VoIP packets/modifying call content
Mitigation options: Encryption of call signaling and voice payload with Asterisk