Part IV: Carriers, Traffic Mgt, and Trends

1
Part IV Carriers, Traffic Mgt, and Trends

• Carrier Technologies
• SDH/SONET
• WDM
• xDSL
• Traffic Management
• Definitions and Traffic Models
• ATM Services
• Trends

2
Synchronous Digital Hierarchy SDH

• SONET Synchronous Optical Network.
• ANSI-SONET (U.S.A.) and ETSI-SONET (Europe).
• SDH Synchronous Digital Hierarchy
  (international)
• Synchronous frames 125 ?s
• Integration of ATM-and STM-baseddata.
• Compatibility withexisting equipmentand
  signaling.
• Support of varioustransmission rates.

Transmission Rate in Mbit/s
User Data Rate in Mbit/s
SONET
SDH
STS-1 STS-3 STS-9 STS-12 STS-24 STS-36 STS-48 STS-
192
STM-1 STM-3 STM-4 STM-8 STM12 STM-16 STM-64
51,84 155,52 466,56 622,08 1244,16 1866,24 2488,32
9953.28
50,12 150,336 451,008 601,344 1202,688 1804,032 24
05,376 9621.504
STS-x Synchronous Transfer Signal level
x STM-y Synchronous Transport Modul level y
3
SONET Architecture

• Section Fiber-optical cable between
  sender/receiver.
• Line Sequence of sections.
• Unchanged internal signal and channel structure.
• Path Interconnection of two devices.

Path
Terminals
Terminals
Line
Line
Section
Section
Section
Section
SONET Multiplexer (PTE LTE)
Add-Drop Multiplexer (LTE)
SONET Multiplexer (PTE LTE)
Repeater (STE)
Repeater (STE)
4
SONET Frame (STS-1)

• The frame length is 125 ?s.
• Rows and columns are used.
• Transmission from left to right by rows.
• Frames contain user data and additional control
  data as well as timing information.

STS - Frame (36) (387) Octett ? 810
Octett Brutto data 810 Octett / 125 ?s ? 51,84
Mbit/s User data 810 - 3(36) 1(36)
Octett ? 49,536 Mbit/s
Transport overhead (3 columns)
Synchronous Payload Environment (87-1 columns)
0 ?s
Section overhead (3 rows)
Line overhead (6 rows)
125 ?s
Path overhead (1 column)
5
SONET Frame (STS-N)

• Basic frame STS-1 with 810 octets.
• Higher rate SONET channels formed by
  octet-interleaving of multiple STS-1 inputs
• STS-N rate is formed from N STS-1 inputs.
• Advantage STS-1 line cards remain operable in an
  STS-1-to-STS-N multiplexor.
• STS-N frame 90 N columns per row, including
  4 N columns of interface overhead.
• Example STS-3 STM-1 (155.52 Mbit/s)

Transport overhead (33 columns)
Synchronous Payload Environment ((87-1) 3
columns)
0 ?s
Section overhead (3 rows)
Payload 150.336 Mbit/s
Overhead 5.184 Mbit/s
Line overhead (6 rows)
Path overhead (13 columns)
125 ?s
6
SONET Localization of Payload

• Pointer H1 and H2 contain values for number of
  payload bytes inbetween H3 and J1.? Direct
  access to single channels.? No (de-)multiplexing
  necessary.
• Payload may be located in two STS-1 frames.

Frame N (9 rows)
H1
H2
(9 rows)
Frame N1 (9 rows)
H1
H2
Path overhead (1 column)
H3 is used as padding byte.
7
SDH Network Topologies
Point-to-point configuration with 14 protection
channel sharing
Linear Add/Drop Route
8
Fiber Optic Networks Revisited

• Traditional use of fibers

Optical Fiber
Laser
Receiver

• Current transmission capacities
• 2.5 Gbit/s (OC-48)
• 10 Gbit/s (OC-192)
• Lasers available for 850 nm, 1310 nm and 1550 nm
  wavelength.

9
Wavelength-Division Multiplexing

• Dense Wavelength-Division Multiplexing (DWDM)

Optical Fiber
Array of Photodetectors
Array of Lasers
l1 l2 l3 l4

• Current available transmission capacities
• 96 lasers at 2.5 Gbit/s 240 Gbit/s (OC-4608)
• 32 lasers at 10 Gbit/s 320 Gbit/s (OC-6144)
• Soon 128 lasers at 10 Gbit/s gt 1 Tbit/s
  (1.000.000.000.000 bits/s)
• Dense WDM More than 10 lasers used
  simultaneously. Today WDM usually means dense
  WDM.

10
Breaking the Internet Gridlock

• Utilizing publically available infrastructure
• How to serve private users with sufficient
  bandwidth?
• How to interconnect two enterprise sites with an
  at least medium bandwidth solution?
• Solution possibilities
• Hybrid fiber/coax (HFC) technology any
  configuration of fiber-optic and coaxial cable
  that is used to distribute local broadband
  communications
• Shared downstream bandwidth, up to 30 Mbit/s.
• Wireless cable.
• xDSL (Digital Subscriber Lines).
• Deployment 650 M customers on twisted pair.

11
ADSL Technology Overview (1)

• Twisted pair access to the information highway
• Delivering video und multimedia data.
• Avoids the replacement of existing cabling.
• Transformation of existing telephone network into
  a multi-service network by applying modulation.
• Use of full copper frequency spectrum (app. 1.1
  MHz).

144 kbit/s (POTS)
Server
16 640 kbit/s
)
Existing Copper
ADSL Modem
ADSL Modem
Core Network
Internet
1.5 9 Mbit/s
) depending on the implementation architecture
12
ADSL Technology Overview (2)

• ADSL Forum Reference Model

Vc
Va
UC-2
U-C
U-R
U-R2
T-SM
T-P
T
Digital Broadcast
T.E.
ATU-C
Broadband Network
ATU-R ATM-SM
ATU-C
Splitter
Splitter
Narrowband Network
POTS-C
POTS-R
Network Management
ATU-C
Access Node
Premises Distribution Network
PSTN
Phonesets
13
DSL Comparison
Downstream kbit/s
DSL Scheme
Upstream kbit/s
Voice Support
144 1,000 160 1,168 2,048 1,500 8,000 1,500
25,000
IDSL UDSL SDSL HDSL ADSL VDSL
144 300 160 1,168 2,048 64 800 1,600
Active Splitterless No No Passive Passive
ADSL Asymmetric DSl HDSL High bit-rate
DSL IDSL ISDN DSL SDSL Symmetric
DSL UDSL Universal DSL VDSL Very high bit-rate
DSL
14
ADSL Technology Capabilities

• Data rates depend on
• Length of copper line,
• Wire gauge,
• Presence of bridged taps, and
• Cross-coupled interference.
• 95 of todays loop plantsmeet these measures.
• Requires advanced digitalsignal processing and
  advanced coding schemes to deal with varying
  noise figures.

15
ADSL Technology DMT Modulation

• To work simultaneously withPOTS on copper line.
• Lower 4 kHz are used by POTS.
• Discrete Multi Tone (DMT)256 separate
  sub-frequenciesfrom 64 kHz.
• Amplifica-tion varies dependenton frequency.

Discrete Multitone (DMT) Modulation
POTS each 4 kHz (32 QAM) 1.4 MHz
Data rate No of channels no of bits/channel
modulation rate Theoretical max upstream
25254k 1.5 Mbit/s Theoretical max downstream
249154k 14.9 Mbit/s
16
ADSL Network Architectures (1)

• ADSL-ATM network architecture, point-to-point

DSLAM Digital Subscriber Line Access Multiplexor
17
ADSL Network Architectures (2)

• ADSL-ATM including L2TP

LAC Local Access Carrier
LAC Local Access Carrier
18
Part IV Carriers, Traffic Mgt, and Trends

• Carrier Technologies
• SDH/SONET
• WDM
• xDSL
• Traffic Management
• Definitions and Traffic Models
• ATM Services
• Trends

19
Traffic Engineering Definition

• Traffic Engineering is the task of mapping
  traffic flows onto an existing physical topology.
• The goals of traffic engineering are
• Minimization of packet loss and packet delay.
• Optimization of network resources (avoiding
  overload situations through load balancing).
• Traffic engineering applications allow for a
  precise control of how traffic flows are placed
  within a routing domain.

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Policies and Mechanisms

• Traffic engineering consists of
• Traffic management (short-term) and
• Network planning (long-term).
• Traffic management
• Set of policies and mechanisms for satisfying a
  range of diverse application service requests.
• Acting across diversity and efficiency.
• Subsumes traditional ideas of congestion control
• An overloaded resource suffers from service
  degradation.
• Policies scale back demand or restrict access.

21
Traffic Models

• Goal of effectively managing traffic requires
• Requirements of individual applications and
  organizations.
• Their typical behavior.
• Traffic Models
• Summarize expected behavior.
• Obtained by detailed traffic measurements or
  amenable to mathematical analysis.
• State of the art in traffic modelling
• Telephone traffic model and
• Internet traffic model.
• Change of applications make these models to
  change!

22
Telephone Traffic Model

• Call arrival model
• How are calls placed?
• Interarrival times drawn from an exponential
  distribution (poisson process models all
  arrivals).
• Memoryless (certain time elapse does not tell the
  future).
• Call holding-time model
• Call holding-times drawn from an exponential
  distribution
• Call longer than x decreases exponentially with
  x.
• Heavy-tailed distribution in recent studies

23
Internet Traffic Model

• Parameters to characterize applications
• Distributions of interarrival times between app.
  invocations.
• Duration of a connection.
• Number of bytes transferred during a connection.
• Interarrival times of packets within a
  connection.
• Note There is little consensus on models!
• E.g., interarrival times Exponential or Weibull.
• Effective means Measurements to fit to
  statistical model.
• LAN traffic differs heavily from WAN traffic.
• More local bandwidth, tendency for longer holding
  times, higher peak data rates.
• Expensive wide area bandwidth, less volume.

24
Time Scales of Traffic Management
Time Scale
Mechanism
Net Endsystem
Scheduling, buffer management Regulation,
policing Routing (connection less) Error
detection and correction Feedback
flow-control Retransmission Renegotiation Signalli
ng Admission-control Service pricing Routing
(connection-oriented) Peak-load pricing Capacity
Planning
Less than one RTT (Cell level) One or
more RTTs (Burst level) Session (Call
level) Day Weeks and more
? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?
? ?
25
Service Categories

• ATM offers six service categories
• Real-time services using resource reservation.
• Non-real-time services without resource
  reservation.
• Non-real-time services with partial resource
  reservation.
• Sources have to comply to a previously negotiated
  traffic characteristic (traffic contract).
• Conforming traffic is transported with the
  negotiated quality of service guarantees.

26
Real-Time Services (1)

• CBR (Constant Bit Rate)
• Traffic constant, Peak Cell Rate (PCR).
• QoS parameter max. Cell Transfer Delay (maxCTD),
  Cell Delay Variation (CDV), Cell Loss Ratio
  (CLR).
• Example uncompressed video/audio data.

Peak Cell Rate defines a temporal distance T
1/PCR. Cells have to be evenly spaced in time.
marked or dropped
T
T
T
T
27
Real-Time Services (2)

• rt-VBR (Real-Time Variable Bit Rate)
• Traffic Peak Cell Rate (PCR), Sustainable Cell
  Rate (SCR), Maximum Burst Size (MBS).
• QoS parameter maxCTD, CDV, CLR.
• Example compressed video / audio data

T 1/PCRTS 1/SCR
t ? T with mean value ? TS
marked or dropped
t
t
t
t
28
Non-Real-Time Services (2)

• ABR (Available Bit Rate)
• Traffic Peak Cell Rate (PCR) and Minimum Cell
  Rate (MCR), flow control mechanism mandatory.
• "QoS parameter" minimum cell loss.
• Flow control mechanism determines theAllowed
  Cell Rate (ACR).

Link Rate

PCR (Peak Cell Rate)
dynamic
ACR (Allowed Cell Rate) Dynamically changedby
the flow control.
MCR (Minimum Cell Rate), may be 0.
reserved
29
Usage Parameter Control

• Test, whether a cell stream conforms to a given
  traffic characteristics.
• Generic Cell Rate Algorithm GCRA(T, ?).
• Virtual Scheduling Algorithm or
• Continuous-State Leaky Bucket.
• Input parameters T 1/PCR, ? CDVT.

?
?
?
T
T
T
OK
OK
OK
OK
Not OK
30
Peak Cell Rate Conformance

• For CBR traffic, it is sufficient to test peak
  cell rate.
• Usage Parameter Control takes places at the
  network interfaces.

GCRA(T,0)
GCRA(T, ?)
GCRA(T, ?)
Shaping
Sha- ping
Physical
UPC
UPC
Private UNI
Public UNI
31
Part IV Carriers, Traffic Mgt, and Trends

• Carrier Technologies
• SDH/SONET
• WDM
• xDSL
• Traffic Management
• Definitions and Traffic Models
• ATM Services
• IP Services
• Trends

32
Use of Network Protocols
IP is the only protocol that matters anymore!
Source Gartner Group
33
Data Traffic is Overtaking Voice
Data
Volume
Voice
Source CIENA Corp.
Time
Today
POTS
Voice-Centric Data-Centric
34
Effect on (Carrier) Networks

• Everything will be data, soon.
• The only protocol that matters is IP.
• Networks have to accomodate for the exponential
  traffic growth.
• It makes sense to design networks for IP only!

35
Technology Trends

• Chip performance doubles every 18 months (Moores
  Law).
• Modern chips can switch packets as fast as ATM
  cells.
• New router architectures have appeared
• Routing at Gigabit/s speed
• Routers support traffic management with thousands
  of queues per interface
• Routers interface directly to DWDM

36
Layer upon Layer...
IP
ATM
IP
IP
Sonet
ATM
Sonet
IP
DWDM
DWDM
DWDM
DWDM
37
Traffic Multiplexing in the Backbone
IP
ATM
DWDMADM
N x OC-48
SonetADM
Sonet
OC-48
OC-48
OC-48
DWDM
DWDM Ring

• Multiplexing of IP traffic over ATM or Sonet no
  longer required.
• Segmentation of IP packets into ATM cells not
  possible at OC-48.

38
Optical Internet Backbones (1)
N x OC-48
DWDMADM
OC-48
DWDM Ring

• Most important objective high bandwidth.
• No Quality of Service, but Classes of Service
• IP-centric Control (no SONET, no ATM).
• Traffic engineering using MPLS.

39
Optical Internet Backbones (2)
Optical Crossconnects
IP routers
Router network
Optical network

• Optical network Provides point-to-point
  connectivity between routers (lightpaths).
• Lightpaths have fixed bandwidth (e.g. OC-48).
• Lightpaths define virtual topology, which may
  be static by design.

40
Conclusions

• Transporting data using IP will be the key task
  of the New Public Network.
• IP over ATM can not keep up with the very
  high-speed backbones (SAR!).
• IP over DWDM or IP over Sonet needs to solve the
  traffic engineering problem.
• IP over ATM will remain for small ISPs or large
  enterprise networks due to its proven reliability
  and traffic management capabilities.

41
References (1)

• M.-C. Chow Understanding SONET/SDH 1995, Andan
  Publisher, Holmdel, New Jersey, U.S.A.,ISBN
  0965044823.
• The Sonet Home Page URL http//www.sonet.com,
  1999.
• CIENA Inc. Fundamentals of DWDM URL
  http//www.ciena.com, 1999.
• D. Ginsburg Implementing ADSL Addison-Wesley,
  Reading, Massachusetts, U.S.A., July, 1999,ISBN
  0-201-65760-0.
• M. de Prycker Asynchronous Transfer Mode
  Solution for Broadband ISDN, 3rd Edition, 1995,
  Prentice Hall, Englewood Cliffs, New Jersey,
  U.S.A., ISBN 0133421716.

42
References (2)

• X. Xiao, L. M. Ni Internet QoS A Big Picture
  IEEE Network Magazine, Vol. 13, March/April 1999,
  pp 8 18.
• C. Schmidt, M. Zitterbart Reservierung von
  Netzwerkres-sourcen Ein Überblick über
  Protokolle und Mechanismen Praxis der
  Informationsverarbeitung und Kommunikation, Vol.
  18, No. 3, 1995, pp 140 147.
• L. Zhang, S. Deering, D. Estrin, S. Shenker, D.
  Zappala RSVP A New Resource ReSerVation
  Protocol IEEE Network, Vol. 7, No. 5, September
  1993, pp 8 18.
• The SWITCHlan backbone network available at the
  URL http//www.switch.ch/lan, 1999.
• C. Metz IP Routers New Tool for Gigabit
  Networking IEEE Internet Computing
  November/December 1998, pp. 14-18.