Transcript Andy Valdar - NICC Standards

The Demise of
Circuit
Voice Switching
Andy Valdar
President of FITCE
& Visiting Professor at UCL
4th November 2016
So, is TDM digital circuit switching in demise?
Leased Lines
• Shift from TDM circuits to packet based alternative – Ethernet
Voice Switching
• ‘Over-the-Top’ services like Skype are IP based
• Move to NGN
– PSTN replacement by IP-based network
» Delay in introducing
– 4G/LTE is an all-IP architecture
» requires the addition of IMS
Circuit Switching Today
Digital circuit switching is used today to provide voice calls on:
• The fixed line telephone networks (Public Switched Telephone Networks)
• Mobile networks
– 2G (GSM, CDMA, etc)
– 3G
– 4G (LTE) even!! [although the LTE architecture allows for VOIP solution VoLTE]
• Cable TV networks
• Specialised business services networks (Centrex, VPN)
GSM and GPRS
Voice
& data
(GPRS)
BC
2G, 2½G
BSC
Node B
Voice
Voice
& data
MSC
Voice
RNC
eUTRAN
4G/LTE
eNode B
data
SGSN
data
GGSN
data
Internet
MGW
Data & VoLTE
S-GW
data &
VoLTE
eNode B
Voice
VoLTE
interworking
4G/LTE
Data &
VoLTE
G/MSC
Data (GPRS)
Voice
UTRAN
Circuitswitch
fallback
voice
Voice
PSTN
3G
3G
Other CS
networks
Data &
VoLTE
P-GW
Data
&
VoLTE
data
Other IP
networks
EPC
Key
= Circuit switched
= Packet switched
Why Put Voice Calls Over (IP) Packet Networks?
The main arguments made:
1.
2.
3.
4.
It’s cheaper!
Better quality
Circuit-switching is yesterday’s ‘analogue’ technology
Everything is moving to IP anyway
Let’s briefly examine these fom an economic perspective........
Cost Comparison: Circuit & Packet Switching
1.
Cost rather than price
Most people’s perception is influenced by the association of VoIP with free
or very cheap calls.
• Skype: using broadband access already paid for by subscriber; the
Skype company makes almost no profit.
•
Cheap international calls with specialist service providers. This is
price advantage due to by-passing normal voice call interconnect
charges between network operators.
Cost Comparison: Circuit & Packet Switching
2. No inherent cost difference between the two technologies
– Digital.
• Both are digital, using a form of PCM encoding of voice
–
Efficient use of network capacity
• Circuit switching uses TDM, channels identified by their timeslot
• Packet switching uses interleaving, packets identified by address or
label in the header
–
Technology
• Both use high speed VSLI chip technology
Digital circuit switches and IP routers look just the same inside
the box....
A TDM T-S-T Switch-Block
TS124
A1
Time
Switch
C1
Time
switch
A1
TS45
C1
B1
TS10
Time
switch
A2
A2
Time
Switch
C2
b2
C2
Space switch B
A3
Time
switch
A3
Time switch (in)
Time
Switch
C3
Space switch
C3
Time switch (out)
TDM circuit established between A2/TS10 and C1/TS45 via b2:B1/TS124
A Packet Router
Packet i at t2
A1
Packet i at t3
Buffer
#C1
Buffer
#A1
C1
B1
Packet i at t1
Buffer
#A2
A2
Buffer
#C2
b2
C2
Space switch B
A3
Buffer
#A3
Input Buffers
Buffer
#C3
Space switch
C3
Output Buffers
Packet routed from Port A2 (at t1) to Port C2 (at t3) via Space Switch at t2
CONCLUSION 1
So, there is no inherent cost difference between
circuit and
packet switches
However, there are 2 architectural features that can
give an economic advantage to an (IP) packet switching
solution for voice………
3. First Architectural Advantage:
Shift of User-Termination Costs
Shift of User-Interface Costs
• The major costs of voice switching are in the interface cost in terminating
the subscribers line(or channel):
– 70% of total capital cost of any switching or multiplexing
system terminating subscribers’ lines are due to the line cards
» True for PSTN subscriber concentrator switches
» True for ADSL DSLAMS (IP/ATM)
» True for Edge IP routers
•
Therefore, cost savings can be made by shifting the line terminating
functions to the users equipment – customers then pay for it (usually
unwittingly)
The Components of a Subscriber Line Card
BORSCHT functions:
Test
Ringing
current
Hybrid
Overload
Battery
Supervision
64kbit/s
Codec
Line Card
Test
Relay
test
bus
Ring
relay
& trip
detector
OverVoltage
protection
Linepower
feed
signalling
extractor
linefeed
bus
Ring bus
encoder
decoder
8kHz
line unit
controller
timing
Shift of User-Interface Costs
Sub’s premises
Fixed access network
Exchange
UNI
Operator’s network costs
User’s costs
MDF
Cu
LTE
Conc
Optical fibre to the home
CircuitSwitched
Network
LTU
IP phone
or
Computer with
audio mike &
speaker
DSLAM
Conc
Broadband/fibre
A
Subs line card
MDF
Broadband ADSL/Cu
B
C
Transmission line termination
PacketSwitched
Network
Similarly for Mobile
Mobile
Circuit-switched
network
Battery,
Ringing, &
Codec
No per-sub
equipment
55th FITCE Congress - Athens 2016
4. Second Architectural Advantage:
Multi-Service Platform
Multi-Service Platform Concept
(a) n separate dedicated
platforms
(b) single multi-service
platform equivalent
#1
#2
#n
MSP
aggregation
& serviceinterface
Multi-Service Platform Concept
Multi-Service Platform (MSP) concept offers several advantages compared to
the use of separate platforms to support each service., namely:
1. Total capacity savings, due to combining several services with differing
volume distribution throughout the day (i.e. non-co-incident peaks).
2. Forecasting errors in each of the services create less of a penalty, due to
‘swings and roundabouts’ – i.e. any over-forecasting in some services is
compensated by under forecasting in the other services.
3. Time to market for new services is reduced, since there is already a widescale deployment of the platform – so new service is accessible across all of
MSP immediately.
4. Capital cost savings due to single high-volume platform
5. Operational cost savings due to only one set of technologies to maintain
These advantages apply whatever the technology
Hence:
There are cost savings due to Integration of Voice & Data Traffic onto one
platform:
• The use of an IP common-services platform (e.g. in Internet or NGN) leads
to economies of scale and high utilisation of capacity
– High level of capital cost saving is possible due to integration
– Early time-to-revenue possible with new product launch (with positive
impact on current account income)
•
Service integrations gives opportunities for new converged features and
services – so potential new revenue sources
•
However, there are difficulties in managing services with a range of QoS
– Hard to run differential QoS on same IP platform (without partitioning)
–
Need to run network at lower than optimum occupancy in order to
manage the QoS, especially latency and jitter.
Utilisation versus Queueing Delay on IP Platform
Source: Capacity Planning for Carrier-Scale IP Networks; Ch 9 of Telecommunications Performance Engineering, The IEE, 2003
5. Other Reasons for VOIP
a) New converged services
b). New features that exploit the IMS capability
– Presence
– Location
– Multimedia
– Machine-machine
c). Terminal developments
– Screen display capability
– Improvements in portable battery life
– Integration with other devices (head-up displays, etc)
d. There is a general adoption of IP technology, which increases the costvolume characteristics and so reduces the price of IP equipment (self-fulfilling
prophecy!)
The Rationale for Next Generation Networks (NGN)
e) Cost Savings Due to Reduction in the number of Existing Network Platforms
• The cost savings resulting from the replacement of network platforms by
a single NGN platform form the logic for the NGN business case.
– Substantial savings in capital costs in equipment to build and expand
the NGN platform
– Substantial current account savings in running fewer platforms.
•
Current account savings will only accrue if the old legacy platforms are
withdrawn.
– In practice it is difficult to completely withdraw network platforms
•
Difficult business case to construct
– Given the practical difficulties in rapid replacement of platforms,
particularly when there are reducing revenue streams means the breakeven time for the business case can be unacceptably long
Conclusions
What should one conclude from this analysis?
1. On a like-for-like basis there is no inherent cost difference between the
circuit-switching and packet-switching technology.
2. However, packet switching (IP) can benefit from two architectural
advantages:
a) Shift of the user-network interface
b) Use of a multi-service IP network (e.g: NGN)
Hence
3. When the existing subs line/telephone is kept the NGN business case is
impossible because the first architectural advantage cannot be exploited!
Conclusions-2
4.
All mobile systems inherently take advantage of the First architectural
advantage (UNI boundary).
– The 4G (LTE) architecture is based on a single IP multi-service platform,
so once IMS is adopted the ‘Circuit-switch fall back’ will cease and the
MSC will be withdrawn.
Final Thoughts
A Philosophical View:
The original concept of an IP network (particularly the Internet) was its
simplicity and best-effort performance.
However, progressive enhancements over the last few years have made the
networks more complicated (protocol stacks) and costly. Much of the
enhancement is to impose order and structure on the IP routings by providing
virtual paths (e.g. ATM, MPLS, Ethernet) – i.e. making the packet network
behave like a circuit-switched network!
Perhaps one can foresee a time in the future when…..
- the additional costs and complexity to manage the quality of service, plus
- the elaborate measures to ensure cyber security
…….make circuit switching a more economical choice!
Thank you.