Session I5 Creating Secure Services for Internet Telephony

1
Session I5Creating Secure Services for Internet
Telephony

• Henning Schulzrinne
• Columbia University
• hgs_at_cs.columbia.edu

2
Overview

• What are IP telephony services?
• Where do services reside?
• How to create services?
• basic fixed services (call forwarding, follow
  me, ...)
• registration-based services caller preferences
• sip-cgi model
• Call Processing Language (CPL)
• sip servlets JAIN
• Event notification and presence
• Example of an enterprise IP telephony platform
• Billing in IP telephony

3
Overview

• Security in IP telephony
• dealing with NATs and firewalls
• differences to classical PSTN networks
• threats
• theft of service
• registration impersonation
• denial of service
• privacy
• current SIP approaches
• Summary and conclusion

4
Aside evolution of SIP

• Not quite what we had in mind
• initially, SIP for initiating multicast
  conferencing
• in progress since 1992
• still small niche
• even the IAB and IESG meet by POTS conference
• then VoIP
• written-off equipment (circuit-switched) vs. new
  equipment (VoIP)
• bandwidth is (mostly) not the problem
• cant get new services if other end is POTS ??
  why use VoIP if I cant get new services

5
Evolution of SIP

• VoIP avoiding the installed base issue
• cable modems lifeline service
• 3GPP vaporware?
• Finally, IM/presence and events
• probably, first major application
• offers real advantage interoperable IM
• also, new service

6
VoIP at Home

• Lifeline (power)
• Multiple phones per household
• expensive to do over PNA or 802.11
• BlueTooth range too short
• need wireless SIP base station handsets
• PDAs with 802.11 and GSM? (Treo)
• Incentives
• SMS IM services

7
SIP phones

• Hard to build really basic phones
• need real multitasking OS
• need large set of protocols
• IP, DNS, DHCP, maybe IPsec, SNTP and SNMP
• UDP, TCP, maybe TLS
• HTTP (configuration), RTP, SIP
• user-interface for entering URLs is a pain
• see success of Internet appliances
• PCs with handset cost 500 and still have a
  Palm-size display
• thus, offer services
• Java-programmable
• XML forms input

8
Example SIP phones
9
What are IP telephony services?

• Services (features) modify basic call behavior
• Can be
• invoked by user
• pre-programmed into network elements (e.g., SIP
  proxies)
• programmable feature logic
• PSTN CLASS (Custom local area signaling
  services) features
• call waiting
• call forwarding
• caller ID (calling number delivery)
• distinctive ringing
• selective call rejection
• three-way calling, ...
• PSTN pre-subscribed for feature access codes
  (e.g., 66)

10
IP telephony services

• Call routing services pre-call, one party
• speed dial
• click-to-dial
• call forwarding
• follow me
• call filtering/blocking (in/out)
• do not disturb
• distinctive ringing
• call prioritization
• feature-based agent selection
• call return
• Call handling features
• hotline
• autoanswer
• intercom

• Multi-party features
• call waiting
• whispered call waiting
• blind transfer no confirmation of success
• attended transfer
• consultative transfer three-party conference ?
  transfer
• conference call
• call park
• call pickup
• music on hold
• call monitoring
• barge-in
• speakerphone paging
• single-line extension

11
IP telephony features Internet-specific

• Presence-enabled calls
• place call only if callee is available
• Presence-enabled conferencing
• call conference participants when all are online
  and not busy
• IM conference alerts
• receive IM when someone joins a conference
• Unified messaging
• receive email with new voice message
• IM alert for voicemails

12
Voice-enabled features

• Interactive Voice Response (IVR)
• VoiceXML
• voice browser

13
Voice-enabled features VoiceXML

• lt?xml version"1.0"?gt
• ltvxml version"2.0"gt
• ltform id"basic"gt
• ltfield name"acctnum" type"digits"gt
• ltpromptgt What is your account number? lt/promptgt
• lt/fieldgt
• ltfield name"acctphone" type"phone"gt
• ltpromptgt What is your home telephone number?
• lt/promptgt
• ltfilledgt
• lt!-- The values obtained by the two fields
  are supplied to the calling dialog by the
  "return" element. --gt
• ltreturn namelist"acctnum acctphone"/gt
  lt/filledgt
• lt/fieldgt
• lt/formgt
• lt/vxmlgt

14
PSTN vs. Internet Telephony
Internet Telephony end system
PSTN
Number of lines or pending calls is virtually
unlimited
More intelligence, PCs can be considered to be
end-user devices
Single line, 12 buttons and hook flash to signal
15
PSTN vs. Internet Telephony
PSTN
Signaling Media
Signaling Media
Internet telephony
Signaling
Signaling
Media
16
Service provider architectures

• Models of providing services
• IP PBX
• IP Centrex (and cable/DSL)
• Carrier / 3G
• Similar equipment (logically), but
• different trust models
• sharing of resources (SIP proxies, gateways)

17
IP PBX
18
IP Centrex
19
IP Carrier
20
3G Architecture (Registration)
mobility management
signaling
serving
interrogating
interrogating
CSCF
proxy
home IM domain
registration signaling (SIP)_
visited IM domain
21
Service models protocols

• Master-slave protocols (MGCP, Megaco)
• feature logic in media gateway controller (MGC)
• send detailed behavioral commands to MG
• send ring tone
• expect dialed digit string
• play announcement
• MG can only guess what is meant
• assembly-language instructions
• Peer-to-peer protocols (SIP, H.323)
• more like function calls
• methods (SIP method, H.323 request) and
  parameters (SIP headers, H.323 ASN.1 variables)
• H.323 per-feature specification (H.450.x)
• SIP building blocks (Headers, REFER, JOIN, ...)

22
Combining peer-to-peer and master-slave
23
CLASS services Caller-ID

• SIP To/From headers ( Organization)
• Also Call-Info
• Call-Info http//alice.com/photo.jpg
  purposeicon,
• lthttp//alice.com/gt purposeinfo
• Can be anonymous
• Cannot necessarily be trusted, since inserted by
  user
• Remote-Party-ID "John Doe" ltsipjdoe_at_foo.comgt
  partycalling idtypesubscriberprivacyfull
  screenyes

24
CLASS services call forwarding, follow-me

• Built into core SIP
• Call forwarding
• either at proxy or at end system
• 302 Contact temporary forwarding
• 301 Contact permanent forwarding
• Follow me
• REGISTER using single identifier
• with different temporary IP addresses
• adopt different hardware via (e.g.,) i-button

25
SIP personal mobility
26
Call filtering (in/out)

• Outbound call filtering done by outbound proxy
• Often, outbound proxy controls firewall
• Inbound call filtering at any of the stages
• e.g., sipalice_at_bigcorp.com ? sipalice_at_paris.eng.
  bigcorp.com
• proxies can do filtering at
• bigcorp.com
• eng.bigcorp.com
• paris.eng.bigcorp.com
• Fixed or programmable rules (later)

27
Call routing -- forking
28
Call routing -- ENUM

• Translation between E.164 telephone numbers and
  URIs (e.g., SIP URIs)
• RFC 2916
• 46-8-9761234 becomes 4.3.2.1.6.7.9.8.6.4.e164.arp
  a
• Look up using (new) NAPTR DNS record
• Example ? contact 1st using SIP, 2nd using email
• ORIGIN 4.3.2.1.6.7.9.8.6.4.e164.arpa.
• IN NAPTR 100 10 "u" "sipE2U" "!.!sipinfo_at_te
  le2.se!" .
• IN NAPTR 102 10 "u" "mailtoE2U"
  "!.!mailtoinfo_at_tele2.se!" .

29
Call routing TRIP and SLP

• TRIP (RFC 3219) allows routing of SIP requests to
  the best IP telephony gateway
• Based on BGP model of route propagation

30
Do not disturb distinctive ringing

• End system or proxy features
• Distinctive ringing inserted by proxy
• Alert-Info http//www.example.com/sounds/moo.wav
  
• Do not disturb
• 600 (Busy)
• 603 (Decline)
• with Retry-After

31
Call prioritization

• SIP Priority header
• Subject A tornado is heading our way!
• Priority emergency
• Can be inserted or removed by proxy
• Useful for call routing

32
Caller preferences

• One SIP address ? many destinations
• home vs. office
• cell phone vs. landline
• PC video phone vs. black phone
• Callees proxy decides, but caller preferences
  mechanism allows caller to influence choices
• Can influence
• whether to proxy or redirect
• which URI to proxy or redirect to
• whether to fork or not
• whether to search recursively or not
• whether to search in parallel or sequentially

33
Caller preferences

• Adds parameters to Contact headers describing
  properties of location
• Carol speaks English, Spanish and German and can
  send/receive audio video, but only wants this
  address to be used for urgent calls
• Contact Carol ltsipcarol_at_example.comgt
  language"en,es,de"
• media"audio/,video/,application/chat"
• duplex"full"
• priority"urgent
• INVITE request then contains headers
• Accept-Contact sipuser_at_hostfeature"voicemail
  attendant"
• Accept-Contact sipuser_at_foo.edumobility"!fixe
  d"

34
Using URIs for SIP Service Control

• RFC 3087
• User part is left to local configuration
• Voice mail services
• siprjs_at_vm.wcom.commodedeposit
• sip670002_at_vm.wcom.com
• Ad-hoc conferences
• Invoke VoiceXML scripts
• sipdialog.vxml.http3a//dialogs.server.com/scrip
  t32.vxml_at_vxmlservers.com

35
Using SIP events for services

• Many telecom services generate asynchronous
  events
• participant joined or left conference
• message waiting
• call leg completed or terminated
• SIP defines event notification requests
  SUBSCRIBE and NOTIFY
• Event packages for call legs, conferences,
  message waiting, IM, DTMF, ...
• NOTIFY siprohan_at_rmahy-phone.cisco.com SIP/2.0
• To ltsiprohan_at_cisco.comgttag78923
• From ltsiprohan_at_cisco.comgttag4442
• Event message-summary
• Content-Type application/simple-message-summary
• Messages-Waiting yes
• Voicemail 4/8 (1/2)

36
Call waiting
no notion of lines ? unlimited number of line
presences
A
B
C
37
Call waiting
A
Hold on line 1
C
B
38
Call transfer (unsupervised)
39
Multi-party features

• Permanently or temporarily mixing multiple media
  streams
• Generally, combinations of
• adding conference servers (ad-hoc conferences)
• transfer use REFER to ask other party to do
  something
• combinations of who asks whom to do what ?
  recipient just follows instructions

40
Third-party call control

• Separate signaling and media endpoints
• Also sometimes called back-to-back UA (B2BUA)
• but some B2BUAs handle media, too

41
End system vs. Network server
End system Temporary IP address Powered off so
often (Users address always changed and can not
be reached sometime) Limited computational
capacity Low bandwidth (One to one or small size
conf.) Direct user interaction Signal and media
converge (easier to deal with human interaction,
easier to deal with interaction with media)
Network server Permanent IP address Always
on (User can have unique address and can always
be reached) Ample computational capacity High
bandwidth (Conference) Indirect user
interaction Usually only deals with
signaling (Based on predefined mechanisms, or
indirect user interaction, like through web page)
42
End system vs. Network server
Network server Information hiding Logical call
distribution Gateway
End system Busy handling Call
transfer Distinctive ringing
43
Service location examples
Service End system Network (proxy) Network with Media (UA)
Distinctive ringing Yes Can assist Can assist
Visual call id Yes Can assist Can assist
Call waiting Yes No Yes()
CF busy Yes Yes() Yes()
CF no answer Yes Yes Yes
CF no device No Yes Yes
Location hiding No Yes Yes
Transfer Yes No No
Conference bridge Yes No Yes
Gateway to PSTN No No Yes
Firewall control No No Yes
Voicemail Yes No Yes
() with information provided by end system
 
44
Service architectureProgramming language model
45
Programmable service creation

• Cant win by (just) recreating PSTN services
• Programmable services
• equipment vendors, operators JAIN
• local sysadmin, vertical markets sip-cgi
• proxy-based call routing CPL
• voice-based control VoiceXML

46
Programmable service creation
API servlets sip-cgi CPL
language-independent no Java only yes own
secure no mostly can be yes
end user service creation no yes power users yes
GUI tools no no no yes
Multimedia some yes yes yes
call creation yes no no no
47
APIs (e.g., JAIN)

• Tradition of TAPI, JTAPI, ...
• Typically, call model
• Treat calls as objects to be manipulated
• e.g., JAIN
• bearer independent (PSTN, IP, ATM)
• protocol-independent (ISUP, SIP, H.323, BICC,
  ...)
• protocol APIs and application APIs

48
SIP servlets

• Servlet runs in SIP server
• Receives SIP objects and processes them
• Example call rejection application
• import org.ietf.sip.
• public class RejectServlet extends
  SipServletAdapter
• protected int statusCode
• protected String reasonPhrase
• public void init(ServletConfig config)
• super.init(config)
• try
• statusCode Integer.parseInt(getInitParam
  eter("status-code"))
• reasonPhrase getInitParameter("reason-ph
  rase")
• catch (Exception _) ...
• public boolean doInvite(SipRequest req)
• SipResponse res req.createResponse()
• res.setStatus(statusCode, reasonPhrase)
• res.send()
• return true

49
sip-cgi

• web common gateway interface (cgi)
• oldest (and still most commonly used) interface
  for dynamic content generation
• web server invokes process and passes HTTP
  request via
• stdin (POST body)
• environment variables ? HTTP headers, URL
• arguments as POST body or GET headers
  (?arg1var1arg2var2)
• new process for each request ? not very efficient
• but easy to learn, robust (no state)
• support from just about any programming language
  (C, Perl, Tcl, Python, VisualBasic, ...)
• Adapt cgi model to SIP ? sip-cgi
• RFC 3050

50
sip-cgi

• Designed for SIP proxies and end systems
• call routing
• controlling forking
• call rejection
• call modification (Priority, Call-Info,
  Alert-Info)
• cgi once per HTTP request
• sip-cgi maintain state via an opaque token
• script gets body of request on stdin
• script gets SIP headers via environment variables
• initiates actions via stdout
• proxy request
• return response
• generate request
• generate response

51
sip-cgi examples

• Block _at_vinylsiding.com
• if (defined ENVSIP_FROM ENVSIP_FROM
  "sip_at_vinylsiding.com")
• print "SIP/2.0 600 I can't talk right
  now\n\n"
• Make calls from boss urgent
• if (defined ENVSIP_FROM ENVSIP_FROM
  /sipboss_at_mycompany.com/)
• foreach reg (get_regs())
• print "CGI-PROXY-REQUEST reg SIP/2.0\n"
• print "Priority urgent\n\n"

52
Call Processing Language (CPL)

• XML-based language for processing requests
• intentionally restricted to branching and
  subroutines
• no variables, no loops
• thus, easily represented graphically
• mostly used for SIP, but protocol-independent
• integrates notion of calendaring (time ranges)
• structured tree describing actions performed on
  call setup event
• top-level events incoming and outgoing

53
CPL

• Location set stored as implicit global variable
• operations can add, filter and delete entries
• Switches
• address
• language
• time, using CALSCH notation (e.g., exported from
  Outlook)
• priority
• Proxy node proxies request and then branches on
  response (busy, redirection, noanswer, ...)
• Reject and redirect perform corresponding
  protocol actions
• Supports abstract logging and email operation

54
CPL example
55
CPL example

• lt?xml version"1.0" ?gt
• lt!DOCTYPE call SYSTEM "cpl.dtd"gt
• ltcplgt
• ltincominggt
• ltlookup source"http//www.example.com/cgi-bin
  /locate.cgi?userjones"
• timeout"8"gt
• ltsuccessgt
• ltproxy /gt
• lt/successgt
• ltfailuregt
• ltmail url"mailtojones_at_example.comSubjec
  tlookup20failed" /gt
• lt/failuregt
• lt/lookupgt
• lt/incominggt
• lt/cplgt

56
CPL example anonymous call screening

• ltcplgt
• ltincominggt
• ltaddress-switch field"origin" subfield"user"gt
• ltaddress is"anonymous"gt
• ltreject status"reject"
• reason"I don't accept anonymous calls" /gt
• lt/addressgt
• lt/address-switchgt
• lt/incominggt
• lt/cplgt

57
Billing

• PSTN evolution from distance/time-sensitive
  per-minute billing
• bucket of minutes
• flat-rate plans (all you can eat) Canada, ATT
• Per-minute billing doesnt fit well
• SIP sessions can remain open for months, without
  sending a single packet
• voice silence suppression ? unfair to charge for
  both directions for large conferences
• incremental value is
• non-linear
• thus, video unlikely

utility
bit rate
58
Billing and charging

• What are we billing for?
• infrastructure
• services
• unlikely to be able to charge for call forwarding
  for corporate users
• but Yahoo might for residential users
• traffic
• but network cost depends on peak usage, not
  average usage
• treat all traffic the same?
• 3G charge more for data traffic than voice
  traffic?
• escalation of traffic cloaking and detection
• A simple billing model
• bill per-minute for calls gatewayed into the PSTN
• bill for services on a subscription basis (e.g.,
  as part of ISP service)
• bill for traffic
• independent of traffic type
• by volume, 95th percentile, congestion pricing

59
Open Settlement Protocol (OSP)

• clearing-house model

60
AAA Authentication, Authorization, Accounting

• separate SIP protocol elements from making
  authentication/authorization decisions
• allow visited proxy to ask home proxy of visitor
  whether visitor is legit
• accounting
• resource dimensioning
• apportionment of charges
• commercial billing
• three primary protocols
• RADIUS used for dial-up servers, popular with
  ISPs
• can lose data (UDP)
• DIAMETER successor of RADIUS
• will be used in 3G for AAA

61
Challenges Security

• Classical model of restricted access systems ?
  cryptographic security
• Objectives
• identification for access control billing
• phone/IM spam control (black/white lists)
• call routing
• privacy

62
SIP security

• Bar is higher than for email telephone
  expectations (albeit wrong)
• SIP carries media encryption keys
• Potential for nuisance phone spam at 2 am
• Safety prevent emergency calls

63
System model
outbound proxy
SIP trapezoid
a_at_foo.com 128.59.16.1
registrar
64
Threats

• Bogus requests (e.g., fake From)
• Modification of content
• REGISTER Contact
• SDP to redirect media
• Insertion of requests into existing dialogs BYE,
  re-INVITE
• Bid-down attacks attacker gets to pick algorithm
• Denial of service (DoS) attacks
• Privacy SDP may include media session keys
• Inside vs. outside threats
• Trust domains can proxies be trusted?

65
Threats

• third-party
• not on path
• can generate requests
• passive man-in-middle (MIM)
• listen, but not modify
• active man-in-middle
• replay
• cut-and-paste

66
L3/L4 security options

• IPsec
• Provides keying mechanism
• but IKE is complex and has interop problems
• works for all transport protocol (TCP, SCTP, UDP,
  )
• no credential-fetching API
• TLS
• provides keying mechanism
• good credential binding mechanism
• no support for UDP SCTP in progress

67
Hop-by-hop security TLS

• Server certificates well-established for web
  servers
• Per-user certificates less so
• email return-address (class 1) certificate not
  difficult (Thawte, Verisign)
• Server can challenge client for certificate ?
  last-hop challenge

68
HTTP Digest authentication

• Allows user-to-user (registrar) authentication
• mostly client-to-server
• but also server-to-client (Authentication-Info)
• Also, Proxy-Authenticate and Proxy-Authorization
• May be stacked for multiple proxies on path

69
HTTP Digest authentication
REGISTER To sipalice_at_example.com
401 Unauthorized WWW-Authenticate Digest
realm"alice_at_example.com", qopauth,
nonce"dcd9"
REGISTER To sipalice_at_example.com Authorization
Digest username"alice", nc00000001,
cnonce"defg", response"9f01"
REGISTER To sipalice_at_example.com Authorization
Digest username"alice", nc00000002,
cnonce"abcd", response"6629"
70
End-to-end authentication

• What do we need to prove?
• Person sending BYE is same as sending INVITE
• Person calling today is same as yesterday
• Person is indeed "Alice Wonder, working for
  Deutsche Bank"
• Person is somebody with account at MCI Worldcom

71
End-to-end authentication

• Why end-to-end authentication?
• prevent phone/IM spam
• nuisance callers
• trust is this really somebody from my company
  asking about the new widget?
• Problem generic identities are cheap
• filtering bozo_at_aol.com doesn't prevent calls from
  jerk_at_yahoo.com (new day, sam person)

72
End-to-end authentication and confidentiality

• Shared secrets
• only scales (N2) to very small groups
• OpenPGP chain of trust
• S/MIME-like encapsulation
• CA-signed (Verisign, Thawte)
• every end point needs to have list of Cas
• need CRL checking
• ssh-style

73
Ssh-style authentication

• Self-signed (or unsigned) certificate
• Allows active man-in-middle to replace with own
  certificate
• always need secure (against modification) way to
  convey public key
• However, safe once established

74
DOS attacks

• CPU complexity get SIP entity to perform work
• Memory exhaustion SIP entity keeps state (TCP
  SYN flood)
• Amplification single message triggers group of
  message to target
• even easier in SIP, since Via not subject to
  address filtering

75
DOS attacks amplification

• Normal SIP UDP operation
• one INVITE with fake Via
• retransmit 401/407 (to target) 8 times
• Modified procedure
• only send one 401/407 for each INVITE
• Suggestion have null authentication
• prevents amplification of other responses
• E.g., user "anonymous", password empty

76
DOS attacks memory

• SIP vulnerable if state kept after INVITE
• Same solution challenge with 401
• Server does not need to keep challenge nonce, but
  needs to check nonce freshness

77
Challenges NATs and firewalls

• NATs and firewalls reduce Internet to web and
  email service
• firewall, NAT no inbound connections
• NAT no externally usable address
• NAT many different versions -gt binding duration
• lack of permanent address (e.g., DHCP) not a
  problem -gt SIP address binding
• misperception NAT security

78
Challenges NAT and firewalls

• Solutions
• longer term IPv6
• longer term MIDCOM for firewall control?
• control by border proxy?
• short term
• NAT STUN and SHIPWORM
• send packet to external server
• server returns external address, port
• use that address for inbound UDP packets

79
Emergency calls

• Opportunity for enhanced services
• video, biometrics, IM
• Finding the right emergency call center (PSAP)
• VoIP admin domain may span multiple 911 calling
  areas
• Common emergency address
• User location
• GPS doesnt work indoors
• phones can move easily IP address does not help

80
Emergency calls
common emergency identifier sos_at_domain
EPAD
REGISTER sipsos Location 07605
302 Moved Contact sipsos_at_psap.leonia.nj.us Conta
ct tel[phone]
SIP proxy
INVITE sipsos Location 07605
INVITE sipsos_at_psap.leonia.nj.us Location 07605
81
Scaling and redundancy

• Single host can handle ?10-100 calls
  registrations/second ? 18,000-180,000 users
• 1 call, 1 registration/hour
• Conference server about 50 small conferences or
  large conference with 100 users
• For larger system and redundancy, replicate proxy
  server

82
Scaling and redundancy

• DNS SRV records allow static load balancing and
  fail-over
• but failed systems increase call setup delay
• can also use IP address stealing to mask failed
  systems, as long as load lt 50
• Still need common database
• can separate REGISTER
• make rest read-only

83
Large system
stateless proxies
a1.example.com
sip1.example.com
a2.example.com
sip2.example.com
sipbob_at_example.com
b1.example.com
sipbob_at_b.example.com
sip3.example.com
b2.example.com
_sip._udp SRV 0 0 b1.example.com 0
0 b2.example.com
_sip._udp SRV 0 0 sip1.example.com
0 0 sip2.example.com 0 0
sip3.example.com
84
Enterprise VoIP

• Allow migration of enterprises to IP multimedia
  communication
• Add capacity to existing PBX, without upgrade
• Allow both
• IP centrex hosted by carrier
• PBX-style locally hosted
• Unlike classical centrex, transition can be done
  transparently

85
Motivation

• Not cheaper phone calls
• Single number, follow-me even for analog phone
  users
• Integration of presence
• person already busy better than callback
• physical environment (IR sensors)
• Integration of IM
• no need to look up IM address
• missed calls become IMs
• move immediately to voice if IM too tedious

86
Migration strategy

• Add IP phones to existing PBX or Centrex system
  PBX as gateway
• Initial investment ?2k for gateway
• Add multimedia capabilities PCs, dedicated video
  servers
• Reverse PBX replace PSTN connection with
  SIP/IP connection to carrier
• Retire PSTN phones

87
Example Columbia Dept. of CS

• About 100 analog phones on small PBX
• DID
• no voicemail
• T1 to local carrier
• Added small gateway and T1 trunk
• Call to 7134 becomes sip7134_at_cs
• Ethernet phones, soft phones and conference room
• CINEMA set of servers, running on 1U rackmount
  server

88
CINEMA components
Cisco 7960
MySQL
rtspd
sipconf
user database
LDAP server
plug'n'sip
RTSP
conferencing
media
server
server
(MCU)
wireless
sipd
802.11b
RTSP
proxy/redirect server
unified
messaging
server
Pingtel
sipum
Cisco
Nortel
2600
Meridian
VoiceXML
PBX
server
T1
T1
SIP
sipvxml
PhoneJack interface
sipc
SIP-H.323
converter
sip-h323
89
Experiences

• Need flexible name mapping
• Alice.Cueba_at_cs ? alice_at_cs
• sources database, LDAP, sendmail aliases,
• Automatic import of user accounts
• In university, thousands each September
• /etc/passwd
• LDAP, ActiveDirectory,
• much easier than most closed PBXs
• Integrate with Ethernet phone configuration
• often, bunch of tftp files
• Integrate with RADIUS accounting

90
Experiences

• Password integration difficult
• Digest needs plain-text, not hashed
• Different user classes students, faculty, admin,
  guests,
• Who pays if call is forwarded/proxied?
• authentication and billing behavior of PBX and
  SIP system may differ
• but much better real-time rating

91
SIP doesnt have to be in a phone
92
Event notification

• Missing new service in the Internet
• Existing services
• get put data, remote procedure call HTTP/SOAP
  (ftp)
• asynchronous delivery with delayed pick-up SMTP
  ( POP, IMAP)
• Do not address asynchronous (triggered)
  immediate

93
Event notification

• Very common
• operating systems (interrupts, signals, event
  loop)
• SNMP trap
• some research prototypes (e.g., Siena)
• attempted, but ugly
• periodic web-page reload
• reverse HTTP

94
SIP event notification

• Uses beyond SIP and IM/presence
• Alarms (fire on Elm Street)
• Web page has changed
• cooperative web browsing
• state update without Java applets
• Network management
• Distributed games

95
Conclusion

• Service creation as central reason for IP
  telephony
• Beyond replication of PSTN services
• modularity
• easy interface to external databases
• user-created services
• interface to web services (SOAP)
• event model as versatile service component
• Security as core component
• protect users against impersonation, phone/IM
  spam
• user privacy
• operator protection often secondary
• unless SIP is used in billing
• Deploying SIP services
• example of a PBX-like service