Media and ISUP Signaling Transition
for IMS and Next-Gen Networks
James Rafferty, Cantata Technology
[email protected]
Agenda
• Introduction: Networks in Transition
• Needs for Translation
– Signaling
– Media
•
•
•
•
3
How Does it Work Now?
How will it Work in the IMS?
The Way Forward
Summary
Introduction: Networks in Transition
• IP has excellent momentum in both carriers and
enterprises
• Voice and other services will run over IP in the future
• The transition is underway…
– But it will take many years
• SIP has won the IP standards war
– But it needs to interwork with the current networks
– Traditional circuit based signaling is still prevalent for both
landline and wireless networks
• IP Multimedia Subsystem has won mind share as a
next-gen service architecture
– But implementations are still at the trial stage
4
Network Evolution for Service Delivery
Network
Architecture
Signaling/Functions
Media/Functions
Applications
5
Traditional
Transition
Next-Gen
TDM
Hybrid
IP
Centralized
• Integrated Design
Open & distributed
• TDM-IP Migration
Open & distributed
• Pure IP (IMS)
SS7, ISDN, CAS
SS7-SIP
ISDN-SIP
CAS-SIP
SIP-SIP
H.323-SIP
TDM – TDM
“circuit to circuit”
TDM - IP conversion
“circuit to packet”
IP - IP
“packet to packet”
• TDM enhanced
services
• Discrete applications
•
•
•
•
IP-based transport
SS7 services over IP
IP services over TDM
IP-enable/extend TDM
services
• Multimedia services on
common service platform
(IMS)
• Blended SIP services
Needs for Translation
Signaling:
• SIP is likely to be the protocol of choice for next generation IP
communications
• It will need to interwork with other signaling methods
– Circuit:
• SS7 network overlays for Intelligent Network services
– ISDN User Part (ISUP) for call control
– TCAP for Database Services like Caller ID
• ISDN PRI
• Channel Associated Signaling (tonal)
– IP
• H.323 was rolled out starting in 1998
– Still found in many carriers and enterprises
• MGCP is the gateway protocol of choice for Cable networks
• H.248 is used for gateway control in the IP Multimedia Subsystem
6
Needs for Translation (2)
Media:
• Next generation IP architectures envision end-to-end
trancoding-free voice operations
– This is the ideal
/ Reality is messier
• Why?
– Most common VoIP voice codecs:
• G.711, G.729A, G.723.1
– Up and coming
• iLBC
– Most common Wireless codecs:
• CDMA, GSM-FR, GSM-EFR, AMR
– Fax
• Both T.38 and G.711 IP coding are common
• Result:
– Need to translate media across network boundaries
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Needs for Translation (3)
• Situation is not much better for video
• H.324-3G translates media between IP and first gen
3G phones
– Special gateways needed to multiplex the media for
transmission to the handset
• A variety of different video codecs in use
–
–
–
–
8
H.263 (2000), H.263++
MPEG-4 Advanced Simple Profile
H.264 (aka MPEG-4 Advanced Video Coding)
And more are being produced all the time…
How Does it Work Now?
• VoIP relies strongly on a variety of network elements
– Media Gateways
• Translate media and typically some signaling
– Signaling Gateways
• Usually translate from circuit signaling to IP signaling
– Session Border Controllers
• May translate between IP signaling protocols
– For example, H.323 to SIP
– Softswitches
• Provide control over media and signaling gateways in a
distributed architecture
• Sometimes these elements are combined
– For example, media + signaling ->
• Integrated Media Gateway
9
Typical VoIP Architecture
IMG 1010
Media Gateway
SIP / H.323
SIP / H.323
IMG 1010
Media Gateway
IP Network
SS7
Class 5
Switch
End Users
10
ISDN / CAS
SS7
ISDN / CAS
Class 5
Switch
Media Gateway
Functions:
PSTN-to-IP Connection
>Media
>Signaling
>Routing
End Users
VoIP Using Softswitch Architecture
Softswitch
SIP - T
Softswitch
IP Network
SS7 / M3UA
Signaling
GW
SIP - T
H.248 / MGCP
H.248 / MGCP
Class 5
Switch
Media
GW
TDM / IMT
End User
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Media
GW
RTP
SS7
SS7
IP Network
Media Gateway
Functions:
PSTN-to-IP Connection
>Media
RTP
Signaling GW
Functions:
TDM-to-IP
connection
>SS7 to SS7 over
SIGTRAN
TDM / IMT
End Users
Voice over Broadband
SIP
RTP
IP
Backbone
SIP
RTP
IP Phone
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Telco
Class 5
Switch
Media Gateway
Functions:
PSTN-to-IP Connection
>Media
>Signaling
>Routing
TDM Phone
VoIP Peering
Session Border
Controller
SIP / H.323
SIP
SS7 + TDM
SIP
SIP / H.323
TDM Carrier
ISDN / CAS
IMG 1010
Media Gateway
Media Gateway
Functions:
PSTN-to-IP Connection
>Media
>Signaling
>Routing
IP to IP Connection
>Transcoding
> ENUM address
translation
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RTP
Peering
Fabric
SIP
SBC Functions:
IP-to-IP connection
>Firewall and NAT
traversal
>Policy enforcement
>Security
>Signaling Interwork
(SIP, H.323)
IP Carrier
1
Peering Fabric
offers simpler
connections among
carriers
IP Carrier
2
What’s Next: IMS
• Wireless Vendors worked to produce standards for
Multimedia Services over SIP
• Design Criteria:
–
–
–
–
Provide common architecture for multiple services
IP at the core
Offer access to users on existing networks
Need to interwork between IP and circuit switched at the
edges
• Result: IP Multimedia Subsytem (IMS)
– Developed by Third Generation Partnership Project (3GPP)
– Endorsed by both wireless and wireline industry groups
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IMS Architecture
IP Multimedia Networks
Legacy mobile
signalling Networks
CS Network
Mm
Mb
Mb
CS
BGCF
I-CSCF
AS
Mm
CS
Mk
Mk
ISC
Mw
Mj
Sh
Cx
C, D,
Gc, Gr
BGCF
Mi
Cx
IMMGW
MGCF
Mc
MRFP
MRFC
Mp
Mb
Mb
Mg
Mr
Mb
Mb
HSS
S-CSCF
Dx
SLF
Mw
Dx
P-CSCF
UE
Gm
Ut
IMS Subsystem
3GPP TS 23.228 V7.2.0 (2005-12)
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IMS for the Rest of US
Application
Servers
Key Elements:
 AS – Application Server
 SCIM - Service Capability Interaction Manager
SCIM
 MRFC - Multimedia Resource Function Controller
 MRFP - Multimedia Resource Function Processor
 MRF – Media Resource Function
S-CSCF
SIP
HSS/HLR
 BGCF - Breakout Gateway Control Function
I-CSCF
BGCF
P-CSCF
MGCF
MRFC
 CSCF- Call Session Control Function
CSCF
 MGCF - Media Gateway Control Function
 MGW - Media Gateway
 HSS - Home Subscription Server
 HLR - Home Location Register
MRFP
MGW
RTP
MRF
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IMS and Signaling Translation
• All signaling converted from circuit to IP at the edges
– Integrated Approach:
• Convert SS7 ISUP, PRI, CAS directly to SIP
– Follows TS 29.163 which is based on ITU-T Q.1912.5
– Distributed Approach
• Signaling GW: Convert SS7 ISUP and PRI to run over IP
– Use the SIGTRAN suite of adaption layers that run over SCTP
» For example, ISUP runs over M3UA
• Media Gateway Control Function
– Terminates SS7 over IP and converts to SIP
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IMS and Media Translation
• Ideally, media is NOT converted from end to end
– For example, use AMR codec for voice over entire 3G UTMS
network from end to end
• Conversions needed to connect to existing networks
– Media Gateways
• Landline Connection - Will convert G.711 to AMR or EVRC
• 2G to 3G Wireless– Will convert GSM series to AMR
• Voice over Broadband to Wireless IP
– May need conversions such as G.729A, iLBC, or G.723.1 to AMR
or EVRC
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State of the Standards
• SIP is a many splendored thing…
– Core 3261 specification and many, many others
• Hitchhiker’s Guide to SIP outlines the “Core SIP” (draft)
• IMS is standardized on SIP, But:
– Several different versions, each offering its own profile of
SIP and other related specifications
• Release 5: First real specs for IMS in 2003; introduces the
architecture
• Release 6: More complete IMS specs in late 2004, but still
incomplete
• Release 7: Just being standardized now; Rollout probably 2
years away
– More complete, but some areas are very immature
» For example, no standard for media control between
application servers and Media Resource Functions
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State of the Marketplace
• VoIP Rollout is not waiting for IMS
• SIP has overtaken H.323 for new VoIP deployments
– SIP enabled Media Gateways very popular
– H.323 mainly needed to tie into legacy deployments
• Distributed Gateway model
– Many of the large gateways use the distributed approach
• Media Gateway controlled by Softswitch
• Softswitch Protocols of choice are MGCP and H.248
• Usually have separate signaling gateways to terminate SS7
and convert to IP signaling
• Integrated Media Gateway Model
– Incorporate both signaling and media translation in GW
– Include SS7 termination and conversion to SIP or SIP-T in
one box for better economics
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The Way Forward
• IMS will continue to mature and is well regarded by
Tier 1 carriers
– Pressures on Landline vendors such as BT will be the early
IMS implementors
– Wireless vendors have less incentive to make the
investment except for new applications
• Voice over Cable vendors start transition to IMS as
well, but currently using SIP and MGCP
• Tier 2 and below vendors will continue to use SIP and
only convert to IMS if obvious advantages
• Peer to Peer models will also compete with the IMS
Client – Server approach
– Skype is the 1st big success story
– SIP PTP is being standardized
• Slow transition from hybrid to all-IP networks
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Resources
• Internet Engineering Task Force: www.ietf.org
– Provides RFCs for SIP, RTP and some aspects of SS7 / IP
interworking
– Hitchhiker’s Guide to SIP:
• http://www.ietf.org/internet-drafts/draft-ietf-sip-hitchhikersguide-02.txt
• International Telecommunications Union: www.itu.int
– Develops H.248 / Megaco and SS7 series of
recommendations
• Third Generation Partnership Program (3GPP):
www.3GPP.org
– Develops IP Multimedia Subsystem and related standards
• Cablelabs: www.cablelabs.org
– Develops standards for Cable use of IMS and MGCP
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Summary
• Transition underway from Circuit to IP
communications networks
• SIP is the IP Communications protocol of choice
• Both Signaling and Media Conversion needed today
and for years to come
• IMS has good mind share, but still at early stage of
deployments
• In the meantime, a variety of network elements will
fuel the transition to IP
• Both distributed and integrated models popular
methods for signaling and media translation
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Thank You!
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