Introduction to SIP and Open Source VoIP Implementations by aof19662

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									       Introduction to SIP
       Open Source VoIP
     Ruwan Lakmal Silva
Lanka Communication Services
    (Subsidiary Of Singtel)
          Sri Lanka
          Topics for the day
 Introduction to SIP Architecture
  – SIP components
  – Message Headers and Message flows
  – NAT issues with SIP
 SIP Open source Implementations (LAB)
  – SIP Express Router

  Session Initiation Protocol (SIP) is a
   Requests For Comments (RFC) of the
   Internet Engineering Task Force (IETF)
  First standardized in March 1999 in RFC
   2543 (Obsolete)
  A second version in 2002 in RFC 3261
What is SIP anyway?

 “Session Initiation Protocol (SIP),
   an application-layer control (signaling)
   protocol for creating, modifying, and
   terminating sessions with one or more
   participants” (RFC 3261)

  Internet telephone calls
  multimedia conferences
  Instant Messaging and Presence
  How ever it’s not limited to the above
Another VoIP Protocol? (1)

  Simplifies access, interfaces, and applications
   allowing powerful new service combinations
  Facilitating a platform which is of vendor
  Critical enabler for Circuit to Packet
   convergence, delivering on the Service
   Intelligent Architecture vision
Another VoIP Protocol ? (2)

    Growing interest in the industry
      Microsoft adopted SIP as primary
       communications protocol in Windows XP
      Various standard bodies have incorporated
       SIP into their plans:
         SIP will be used as the official 3G
          Wireless multimedia protocol (by 3GPP)
Another VoIP Protocol (3)

    Most competitors are incorporating SIP into
     product plans
    Some are operating or planning
     commercially available SIP offerings for end
Another VoIP Protocol (4)

    Another SIP based IETF draft SIMPLE (SIP
     for Instant Messaging and Presence
     Leveraging Extensions) – a SIP based
     protocol for Instant Messaging
    MSN / AOL already implemented (MSN 4.7)

    Yahoo to follow
SIP Vendors
SIP Overview (1)

  ASCII based, signalling protocol
  Analogous to HTTP messages
  Works independent of the underlying network
   transmission protocol and indifferent to media
  It provides mechanisms to:
     Establish a session

     Maintain a session

     Modify and Terminate a session
SIP Overview (2)

    Strength is it’s simplicity and basic
        Component reuse
          A child of SMTP and HTTP
          SIP also uses MIME to carry extra information

          Uses URI Eg:
SIP Overview (3)

    Scalability
             Functionality such as proxying, redirection, location, or
              registration can reside in different physical servers.
             Distributed functionality allows new processes to be added
              without affecting other components.

    Interoperability
        An open standard
        Can implement to communicate with other SIP
         based products
SIP Overview (4)

    Mobility
        Supports user mobility by proxying and redirecting
         requests to a user’s current location.
        The user can be using a PC at work, PC at home,
         wireless phone, IP phone, or regular phone.
        Users must register their current location.
        Proxy servers will forward calls to the user’s current
        Example mobility applications include presence and
         call forking.
Integration with IETF Protocols

 SIP   forms only part of an overall IP telephony
 Other IETF protocol standards are used to build
 a fully functioning VoIP system.
   RSVP - to reserve network resources.

   RTP (Real Time Transport Protocol) -to
    transport real time data
Integration with IETF Protocols…

    RTSP (Real Time Streaming Protocol) - for
     controlling delivery of streaming media.
    SAP (Session Advertisement Protocol) - for
     advertising multimedia session via
Related Protocols

Signalling   Gateway control                         QoS


    SIP          MGCP           RTSP    RTCP   RTP    RSVP

     TCP                                UDP

                               IPv4 / IPv6
SIP Capabilities (1)

  Determine location of target points –
   Support address resolution, name
   mapping, call redirection
  Determine media capabilities – SIP uses
   Session Description Protocol (SDP) for
  Determine availability – returns a
   message why the remote party cannot
   be contacted
SIP Capabilities (2)

  Establish a session between end points
   – also support mid call changes,
   changes of media characteristics or
  Handles termination of calls – transfer of
  Permits interaction between devices via
   signalling messages
SIP Capabilities (3)

    SIP messages can:
      Register a user with a system
      Invite a users to join an interactive session

      Negotiating the terms and conditions of a
      Establish a media stream between 2 or
       more end points
      Terminate a session
SIP Architecture

  A distributed client server architecture
  Different servers to handle
  Hence load balancing
  Redundancy
SIP Components

    SIP User Agents
      User Agent Clients (UAC)
      User Agent Servers (UAS)

    SIP Servers
      Proxy server
      Location server

      Redirect server

      Registrar server
User Agents (1)

 Consists of UAC part and a UAS part
  UAC - An entity that initiates a call
  UAS – An entity that receives a call
  UAC is the only SIP component that can
   create an original request
  Phones – acts as UAC or UAS
  Implemented in Hardware or Software
  Includes softphones, sip ip phones, gateways
User Agents (2)

    Gateways – provide call control, mainly
     translation function between SIP
     conferencing end points and other
     terminal types
         Includes   a translation between translation
         Translation between codecs
User Agents (3)

Examples of user SIP user agents:

                               Cisco 7960 SIP IP Phone
         Komodo ATA 182/186

         Pingtel xpressa
                              PC with softphone application

User Agents (4)
SIP Distributed Architecture
                SIP Components

              Location   Redirect       Registrar
               Server     Server         Server


 User Agent                                         Gateway
                Proxy               Proxy
                Server              Server
Proxy Server
    Acts Both as a Server and a Client
    Receives SIP messages, forwards to next SIP
    Can perform functions such as Authentication,
     Autherisation, network access control, routing
    Requests are serviced internally or by passing
     them on, possibly after translation, to other
    Interprets, rewrites or translates a request
     message before forwarding it.
Redirect server

  Provides information about next hop to the
  Maps address to zero or more real
  Does not accept or terminate calls
  Does not initiate its own SIP request
  Generates SIP responses to locate other
Registrar server

  Accept registration requests from users
  Maintains user’s whereabouts at a
   Location Server
  Typically co-located with a proxy server
   or a redirect server and may offer
   location services
  May also support authentication
Location Server

  Used by a SIP redirect or proxy
  server to obtain information about a
  called party’s possible location (s)
Similar Domain Communication

                                        (4) Proxied call

                                              (5) Response

                (3) SIP URL of “B”

                                                                         (7) RTP
                    (2) User B?
  SIP Registrar &                 SIP Proxy
  Location Server
                                              (6) Response

                                        (1) Call user B

                                                             SIP Phone
                    Domain A
Dissimilar Domains
                        (2) How to reach
                                  B?                           (5) Where’s B?

SIP Registrar &
                              (3) Address
                                             Redirect Server           (6) SIP URL of “B”
Location Server                                                                             SIP Registrar &
                              of                                                            Location Server
                              Dom B Proxy
  (1) Call user B
                                      (4) Proxied call

      (10) Response                        (9) Response
                    Domain A’s SIP Proxy                   Domain B’s SIP Proxy
                                                                                      (7) Proxied Call
                                                                       (8) Response
                                             (11) RTP

 User Agent A              Domain A                                     Domain B
Registering process

  Registration links a user to their service
  First a REGISTER message is sent
   looking for a registrar server
  Registrar finds user ID with IP
  These registrations are not permenant
  Registrations expires within minutes but
   continuously renewed
Inviting users

  Need to be a registered user
  Send INVITE message to one or more
   devices / users
  INVITE has many forms of addressing :
      E.164 phone numbers
      Direct dialed IP addresses

      SIP URLs
Negotiating terms and conditions

    Need to pass type of session
    Carries this information as attachment
    Concern only with the delivery of message and
     not the content
    To carry this information, SIP uses SDP
     (Session Description Protocol)
    Upon receiving an INVITE message, a party
     can either accept or reject the invitation
Establishing a media stream

  After accepting invitation, inviting party see or
   hear an indication to indicate the called party
   has been located
  This may be a ring tone or a graphical
  Generally generated by the end users device
  In voice calls media stream uses RTP (Real
   time Transmission Protocol RFC 1889)

  Device hangs up first issues a BYE
   message to the other device
  Tear down the media stream and make
   way both ends to create or receive future
    SIP Messages – Methods and
SIP   Methods:                             SIP     Responses:
   INVITE – Initiates a call by inviting      1xx - Informational Messages
    user to participate in session.                  180 ringing
   ACK - Confirms that the client has         2xx - Successful Responses
    received a final response to an                  200 OK
    INVITE request.                            3xx - Redirection Responses
   BYE - Indicates termination of the               302 Moved Temporarily
    call.                                      4xx - Request Failure Responses.
   CANCEL - Cancels a pending                       404 Not Found
                                               5xx - Server Failure Responses.
   REGISTER – Registers the user                    503 Service Unavailable
                                               6xx - Global Failures Responses.
   OPTIONS – Used to query the                      600 Busy Everwhere
    capabilities of a server.
   INFO – Used to carry out-of-bound
    information, such as DTMF digits.
SIP Responses (1)
 Informational           Redirection
  100 Trying             300 Multiple Choices
  180 Ringing            301 Moved Perm.
  181 Call forwarded     302 Moved Temp.
  182 Queued             380 Alternative Serv.
  183 Session Progres

  200 OK
SIP Responses (2)
 Request Failure         Server Failure
  400 Bad Request        504 Timeout
  401 Unauthorized       503 Unavailable
  403 Forbidden          501 Not Implemented
  404 Not Found          500 Server Error
  405 Bad Method
  415 Unsupp. Content
  420 Bad Extensions
  486 Busy Here
SIP Responses (3)

 Global Failure
  600 Busy Everwhere
  603 Decline
  604 Doesn’t Exist
  606 Not Acceptable
SIP Addressing
      A SIP address is identified by a SIP URL
      These are globally accessible addresses
      Examples of SIP URLs:
        Fully-Qualified Domain Names
        SMTP-style Domain Names [RFC 2368]
        E.164 style addresses [RFC 2806]
      ; user=phone
        user=phone means this is a gateway
        Mixed addresses
                sip:14085551234@; user=phone
DNS SRV (RFC 2782) Resource
  SIP clients need to reach SIP servers for
   purposes of registration and call control
  Redundant servers to handle calls if
   primary SIP server is unavailable
  Can meet these requirements by using
   DNS SRV Resource Records
  Available in BIND 8.X and up releases
SRV Resource Records

    Format
     _service._protocol SRV Priority Weight Port hostname
    Example :
     _sip._udp        SRV 0 0 5060
     _sip._tcp        SRV 0 0 5060
                      SRV 1 0 5060
     _sip._udp        SRV 0 0 5060
                      SRV 1 0 5060
     allows priority (for back-up) and weight (for load
Zone file configuration
 ; zone '' last serial 2004071308
 $ORIGIN com.
 mydomain 86400     IN         SOA       (
                                                                     2004111908 ; Serial
                                                                     36000 ; Refresh
                                                                     900 ; Retry
                                                                     36000 ; Expire
                                                                     28800 ); Minimum
             IN         NS                                 
             IN         NS                                 
             IN         MX                                           1
             IN         A                                  
 ;If we place the SRV record above the next line it fails to load
 _sip._udp              SRV        00           5060       
  gateway IN            A                                  
 www         IN         CNAME                              
DNS Quarrying
 dig -t SRV
 Example SRVrecords
       #dig -t srv
       #host –v –t   srv
       #host -v -t   srv
       #host -v -t   srv
SIP Headers (1)

    Much  of the syntax and semantics
     are borrowed from HTTP.
    Looks more like HTTP message –
     message formatting, header and
     MIME support
SIP Headers (2)

      Example SIP INVITE header:
          INVITE sip:5120@ SIP/2.0
          Via: SIP/2.0/UDP
          From: sip:5121@
          To: <sip:5120@>
          Call-ID: c2943000-e0563-2a1ce-2e323931@
          CSeq: 1 INVITE
          Expires: 180
          User-Agent: Cisco IP Phone/ Rev. 1/ SIP enabled
          Accept: application/sdp
          Contact: sip:5121@
          Content-Type: application/sdp
Breakdown of header (1)

    INVITE :
      message type
      Address of called party

      SIP version used by caller

      Semicolon indicates start of URI parameters

      Eg:- user=phone indicates call is for a
       phone number and not a SIP IP address
        INVITE sip:5120@ SIP/2.0
Breakdown of header (2)

    Via:
      History of message’s path through
      Helps to prevent looping and ensures
       replies route back to originator
      Indicates the used transport protocol, ip
       address and port of sender
        Via: SIP/2.0/UDP
Breakdown of header (3)

    From:
      A field required in all requests and response
      Provides identity of request’s initiator
        From: sip:5121@
Breakdown of header (4)

    To:
        Provides identity of the intended
         recipient of the request
        To: <sip:5120@>
Breakdown of header (5)

    Call-ID:
      Provides a globally unique identifier to
       distinguish specific invitations or multiple
       registrations of the same user
      Typically uses a 32-bit cryptographically
       random numbers
        Call-ID: c2943000-e0563-2a1ce-2e323931@
Breakdown of header (6)

    CSeq or command sequence:
      Needed in both request messages as well
       as response messages
      Need to increment this when a user with the
       same Call-ID wants to send different SIP
       methods or content
      When sending responses to requests, CSeq
       should be the same
        CSeq: 1 INVITE
Breakdown of header (7)

    Content-Type :
        Provides information about media type of
         message body
        Content-Type: application/sdp
SDP (RFC 3550) Messages
    Describes components of communication channel
     under negotiation
    Includes information about :
        Codecs
        Ports
        Streaming protocols
    Usually sent with INVITE and 200 OK in SIP based
    Describes how data stream is going to be support via
     Real Time Transport Protocol (RTP, RFC 1889)
SDP Header
 INVITE sip:2000@;user=phone SIP/2.0
 Content-Type: application/sdp
 Content-Length: 168

 o= - 123467777 123467777 IN IPV4
 s=VOVIDA Session
 c=IN IPV4
 t=1253886592 0
 m=audio 23456 RTP/AVP 0
 a=rtpmap:0 PCMU/8000
Breakdown of header (1)
    v: Vesrion number
        Also indicates start of SDP content
    o: Session origin and owner’s name
    Format:
     o=<username><session ID><version><net type><address type><address>

    If user is unknown, session ID is set to Network Time
     Protocol (NTP, RFC 1305) time stamp of start time
    <address> - the address of the machine of the user
     initiating the session
        o= - 123467777 123467777 IN IPV4
Breakdown of header (2)

    s:Session Name
        Just an identifier
    c:connection information
      ip address of the session
      Very critical when communicating with
       clients behind NATs
    Example of an IPV4 address session
        c=IN IPV4
Breakdown of header (3)
    m: media name and transport address
    Describe type of media
    Format :
     <media><port><no. of ports><transport><fmt list>
        m=audio 23456 RTP/AVP 0

    When RTP/AVP is used for port, fmt list is list of
     integers that specify the codec that can be used
CODECS, the bandwidth manager

        Identifier     Codec                 Bandwidth
          0             G.711ULaw             64 Kbps
          2             G.726-32              32 Kbps
           3               GSM                13 Kbps
           4               G.723.1            5.3 / 6.3 Kbps
           8               G.711aLaw          64 Kbps
           9               CD-quality audio
         15                G.728              16 Kbps
          Full list is in RFC 3551
Simplified SIP Call Setup and

        User Agent                Proxy Server    Location/Redirect Server            Proxy Server            User Agent
                      INVITE                   INVITE
                     100 Trying                 302
                                         (Moved Temporarily)
Call                                                                     100 Trying
Setup                                                                                            INVITE

                 180 (Ringing)                           180 (Ringing)                        180 (Ringing)

                     200 (OK)                              200 (OK)                             200 (OK)
                       ACK                                   ACK                                     ACK
                                                       RTP MEDIA PATH
Call                   BYE                                   BYE                                     BYE
Teardown             200 (OK)                              200 (OK)                             200 (OK)
Feature Creation

  A SIP based system supports rapid feature
   and service creations
  Tools
        Call Processing Language (CPL) – XML based
        Common Gateway Interface (CGI)
        SIP-CGI
        Servlets and Applets
        JAIN API
             Enable rapid development of telecommunication products
              and services for the Java platform.
Call Processing Language

  Allow users to create simple Internet
   telephony services
  Features:
      Creatable and editable by simple graphical
      Independent of signalling protocol

      Safe to run in servers

      XML like tags
CPL Example
           <address-switch field="origin" subfield="host">
                <address subdomain-of=“">
                     <location url="">
                                   <busy> <sub ref="voicemail" /> </busy>
                                   <noanswer> <sub ref="voicemail" /> </noanswer>
                                   <failure> <sub ref="voicemail" /> </failure>
                     <sub ref="voicemail" />
NAT issues with SIP
Types of NATs

 1.   Full Cone
 2.   Restricted Cone
 3.   Port Restricted Cone
 4.   Symmetric
Full Cone

                                            Computer A
                     NAT Gateway            IP :
                                            Port : 10000

    Client                                  Computer B
    IP:                          IP :
    Port : 9000                             Port : 20000

                        IP :
                        Port : 4567
Restricted Cone

  External IP:port pair is only opened,
   once the internal computer sends out a
   packet to a specific destination IP(Eg.
   From client to Computer A)
  Then the external computer can sends
   packets back (From Computer A to
   client, but packets from Computer B are
Port Restricted Cone

  Almost identical to restricted cone
  Blocks packets from outside, unless the
   client had not sent a packet to the
   particular IP and port, where the packets
   are coming from
  If client has sent a packet to ip and port 20000, NAT will
   only allow packets from that ip and port

                                     Port: 1234
                                                        Computer A
                       NAT Gateway
                                                        Port: 10000

     Port: 9000                                         Computer B
                                                        Port: 20000
                                     Port: 4567
NAT issues with SIP
    Two parts in a SIP based call
       Signalling
       Media stream
    Signalling
       SIP signaling messages can easily traverse NAT
    SIP proxy needs to return SIP packets on the same
     port it received from the client
    Special tags in SIP message header to achieve this (
     the received tag and rport)
Example header
 INVITE sip:1000@ SIP/2.0
 Via: SIP/2.0/UDP;branch-a43u4h42-507c77f2
 Via: SIP/2.0/UDP;reveived=;rport=10000
 From: <sip: 1001@>tag=108bcd14
 To: sip: 1000@
 o=123467777 123467777 IN IPV4
 s=VOVIDA Session
 c=IN IPV4
 t=1253886592 0
 m=audio 23456 RTP/AVP 4
 a=rtpmap:0 PCMU/8000
Solutions to NAT

     2 main methods for determining
      mapping information
     1.   Ask from the NAT device
     2.   Ask someone outside the NAT device

  UPnP (Universal Plug and Play)
  Mainly pushed by Microsoft
  Client queries the NAT device via UPnP
  NAT device responds with the IP:port on
   the public internet
  Cannot use with cascading NATs
External Query
         Used when it’s not possible to communicate with
          NAT device
         Ask a server, outside the NAT on the internet how it
          sees the source packets
         A server is listening (NAT probing)
         Server replies from the same port of the received
          packet, containing IP:port as the server sees
         Then client can determine
     1.     If it’s behind the NAT
     2.     Public IP:port that should be used in SDP message
External Query
                               End point

    IP:                Public Internet

                                  NAT probe

                     Port: 5642
  Simple Traversal of UDP Through NAT
  A protocol which helps in determining the
   type of NAT
  Clients need to be developed with STUN
   awareness so that they can set their SDP
  Clients can determine if it is:
     1.   On the open internet
     2.   Behind a firewall that blocks UDP
     3.   Behind a NAT, and the type of NAT
RTP relay

  STUN and UPnP works only with the first
   3 types of NATs
  If connection oriented media is used in
   Symmetric NAT, the problem is solved
  One possible solution is to have :
      an RTP relay between the RTP flow
      A NAT proxy between the SIP flow
Solution for Symmetric NAT
               1 INVITE                     Proxy                4 SDP modified INVITE

               8 forwarded response

               With modified SDP                             5 OK with own SDP

                                      2   3 Assigns
 UA    NAT Gateway                        Ports          7 Upstream RTP port             V

                                          6 IP:PORT of gateway
      9 RTP
                                                                                Voice Gateway
                                                           10 forwards RTP

                                                                       11 RTP
                 12 RTP                     RTP
  Open Source VoIP
(SIP) Implementations
SIP Express Router
  is another SIP deployment organization
    Unique open-source SIP server with premium service
     creation flexibility and performance
  spun off from Germany’s national research
     labs,Fraunhofer, home of MP3 and very first
     implementations ever of mobile IP and IPv6
  provides software, consultancy and technical
     support to both operators and vendors in the SIP area.
SIP Express Router (1)

  The server is built for operation in huge
  Already powering large public SIP
   networks such as FWD.
  Server supports cryptographic standard
   protocols (TLS, OSP) to achieve secure
   multi- domain peering and granular
   service access control mechanisms
SIP Express Router (2)

  Can  handle any SIP client devices
   behind NAT routers
  Feature flexibility that allows
   operators to attract customers with a
   variety of charging plans
SER Features (1)

    SIP: Registrar, proxy, redirect
    Web- based provisioning with SERweb
     (missed calls, voicemail, IM paging)
     Application builder: user provisioning, click-
     to- dial
     Gateways: SMS, Jabber
     Accounting, Authorization, Authentication
     (syslog, RADIUS, SQL, LDAP)
     Voicemail2Email, Announcements
SER Features (2)

 RADIUS/ CLID integration
  Presence Agent
  NAT- Traversal Helper
  Multidomain Hosting
  DB integration: MySQL, LDAP,
  TLS security
SER Features (3)
    Extensibility: new plug- ins can extend feature set.
    Standard compliancy: Interoperability tested and
     proven in SIPITs.
    Flexibility through routing language
    Small footprint (a few hundreds of Kilobytes)
    Application building through Application Scripting
    Support for both IPv4 and IPv6
    Written in Plain C
    Superior performance
Effectiveness of Application

     Development overhead for SER-
      based applications claims to be fairly
         Click- to- dial: ~ 150 lines of code (LOC) in shell
         T- storm alerts (experimental application for a
         Web phonebook (part of SER’s web front- end): ~
          230 LOC
         + 120 for click- to- dial in PHP
          SIP- layer Ping utilitity: ~ 10 LOC (Perl)
Example: Web Integration, Missed
Calls/Click Calls/Click-to to-Dial
More Examples: FWD on-line
    Pulver’s Free World
     Dialup site allows to
     display online status
     in users’ webpages
     and email
     Overhead: 30 lines
     in PHP
Application Agent (AA)
    SIP server for rapid service creation
    Minimize Time To Market
        Hide signaling complexity by high call-level abstraction
        Reduce Lines Of Code by using AA’s built in functions
        Bet on effective programming environment: Python
    Improve Quality Of Service
        Underlying libraries take care of proper call state processing
         and protocol communication transparently
        AA leverages proven SER’s features, performance,
    stability and interoperability
Interoperability Matters
    SER has been extensively tested in SIP
     Interoperability Tests (SIPIT) in past years.

    iptel.Org has set up an interoperability lab in which
     SER has been tested against existing SIP devices
     (3Com, Ahead Software, Avaya, AudioCodes, Allied
     Telesyn, Cisco, GrandStream, HotSIP, Intertex,
     Microsoft, Mitel, net. com, Pingtel, Siemens, Snom,
     Vegastream, XTen, etc.)
SER Installation Guide
Supported architectures

  Linux/i386 (RedHat, Mandrake etc..)
  Linux/armv4l
  FreeBSD/i386
  OpenBSD/i386
  Solaris/sparc64
  NetBSD/sparc64
Requirements (1)

    gcc or icc : gcc >= 2.9x; >=3.1 recommended
    bison or yacc (Berkley yacc)
    flex
    GNU make (on Linux the standard "make", on
     FreeBSD and Solaris, "gmake")
    sed and tr (used in the make files)
    GNU tar ("gtar" on Solaris) and gzip
Requirements (2)

  GNU install or BSD install (on Solaris
  Mysql if MySQL support is needed
  Apache (httpd) for serweb support
  PHP, MySQL-PHP for serweb support
  libmysqlclient & libz (zlib) want mysql
   support is needed (the mysql module)
Install the package
    Latest Stable as of this date is ser-0.9.4
    From source
    #make all
      builds everything
    #make install
        Installs the compiled binaries in /usr/local/sbin
        Configuration files in /usr/local/etc/ser
Controlling SER (1)

    Start the server
        #/usr/local/sbin/ser
        #/usr/local/sbin/ser start
        #/usr/local/sbin/ser restart
    watch server's health with serctl utility
        first set the environment variable SIP_DOMAIN
        Eg :#exportSIP_DOMAIN="”
Controlling SER (2)

    Run the serctl utility
      #/usr/sbin/serctl monitor
      #/usr/local/sbin/serctl monitor
MySQL setup
    Once you have MySQL installed and started,
        #/usr/sbin/
    Verify that the database has been created
        Mysql> select * from user;
        mysql> connect ser;
         Connection id: 294
         Current database: ser
        mysql> show tables;
    Configure SER
        /usr/local/etc/ser/ser.cfg

    SIP is gaining acceptance in the industry
    Open Source projects are taking the lead in
     SIP implementations
    New generation of services are already being
    SIP based VoIP services can even be more
     attractive if the NAT issues are addressed
    As ISPs in the region, how are you going to
     take advantage of this new protocol??

That’s it!!!
Thank you
      Lakmal Silva

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