Part IV: Carriers, Traffic Mgt, and Trends

© 2000 B. Stiller, B. Plattner ETHZ-TIK, D. Bauer IBM Research CM IV – 1 ETH Zürich

Part IV: Carriers, Traffic Mgt, and Trends

• Carrier Technologies– SDH/SONET– WDM– xDSL

• Traffic Management– Definitions and Traffic Models– ATM Services

• Trends


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.

STS-1STS-3STS-9STS-12STS-24STS-36STS-48STS-192

STM-1STM-3STM-4STM-8STM12STM-16STM-64

51,84155,52466,56622,08

1244,161866,242488,32

9953.28

50,12150,336451,008601,344

1202,6881804,0322405,376

9621.504

SONET SDHTransmissionRate in Mbit/s

User DataRate in Mbit/s

Synchronous Digital Hierarchy – SDH

STS-x: Synchronous Transfer Signal level xSTM-y: Synchronous Transport Modul level y


SONET – Architecture

Section: Fiber-optical cable between sender/receiver. Line: Sequence of sections.

• Unchanged internal signal and channel structure.

Path: Interconnection of two devices.

Repeater(STE)

SONETMultiplexer

(PTE + LTE)

Add-DropMultiplexer

(LTE)

SONETMultiplexer

(PTE + LTE)

Repeater(STE)

Terminals Terminals

Section Section Section Section

Line Line

Path


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.

Sectionoverhead(3 rows)

Lineoverhead(6 rows)

Transportoverhead

(3 columns)

STS - Frame:

(3+6) * (3+87) Octett

810 Octett

Brutto data:

810 Octett / 125 s

51,84 Mbit/s

User data:

810 - [3*(3+6) + 1*(3+6)] Octett

49,536 Mbit/s

Synchronous PayloadEnvironment

(87-1 columns)

Path overhead (1 column) 125 s

0 s


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)

Sectionoverhead(3 rows)

Lineoverhead(6 rows)

Transportoverhead

(3*3 columns)

Synchronous PayloadEnvironment

((87-1) * 3 columns)

Path overhead (1*3 columns) 125 s

0 s

Payload150.336 Mbit/s

Overhead5.184 Mbit/s


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.

FrameN

(9 rows)

FrameN+1

(9 rows)Path overhead

(1 column)

H1H2

H1H2

(9 rows)

H3 is used as padding byte.


SDH Network Topologies

Point-to-PointTerminal




Point-to-point configurationwith 1:4 protection channel sharing





Linear Add/Drop Route

Add/DropMultiplexer

Add/DropMultiplexer


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.


Wavelength-Division Multiplexing

Dense* Wavelength-Division Multiplexing (DWDM):

Optical Fiber

Array of LasersArray of Photodetectors

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 > 1 Tbit/s (=1.000.000.000.000 bits/s)

* „Dense“ WDM: More than 10 lasers used simultaneously. Today: WDM usually means dense WDM.

1 2 3 4


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.


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).

ADSLModem

ADSLModem

ExistingCopperCore Network

Internet

Server 16 … 640 kbit/s

1.5 … 9 Mbit/s *) depending on the implementationarchitecture

*)

144 kbit/s (POTS)


ADSL Technology – Overview (2)

ADSL Forum Reference Model:

ATU-C

ATU-C

ATU-C

ATU-RATM-SM

Splitter Splitter

Vc Va UC-2 U-C U-R U-R2 T-SM T-P T

POTS-C POTS-R

AccessNode

PSTN PhonesetsPremises

Distribution Network

T.E.

DigitalBroadcast

BroadbandNetwork

NarrowbandNetwork

NetworkManagement


DSL Comparison

1441,000

160 – 1,1682,048

1,500 – 8,0001,500 – 25,000

Downstream[kbit/s]

DSLScheme

IDSLUDSLSDSLHDSLADSLVDSL

Upstream[kbit/s]

VoiceSupport

144300

160 – 1,1682,048

64 – 8001,600

ActiveSplitterless

NoNo

PassivePassive

ADSL: Asymmetric DSlHDSL: High bit-rate DSLIDSL: ISDN DSLSDSL: Symmetric DSLUDSL: Universal DSLVDSL: Very high bit-rate DSL


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.

Data Rate[Mbit/s]

1.5 or 21.5 or 2

6.16.1

Wire Gauge[mm]

0.5 (26 AWG)0.4 (24 AWG)0.5 (26 AWG)0.4 (24 AWG)

Distance[km]

5.54.63.72.7

C Channels 1664

Optional 160 Channels 384

544576

DuplexBearer Channels

[kbit/s]

DownstreamBearer Channels

[Mbit/s]

n*1.536 1.5363.0724.6086.144

n*2.048 2.0484.096


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.

Data rate = No of channels * no of bits/channel * modulation rateTheoretical max upstream: 25*25*4k = 1.5 Mbit/sTheoretical max downstream: 249*15*4k = 14.9 Mbit/s

Discrete Multitone (DMT) Modulation

POTS each 4 kHz (32 QAM) 1.4 MHz


ADSL Network Architectures (1)

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

DSLAM: Digital Subscriber Line Access Multiplexor


ADSL Network Architectures (2)

ADSL-ATM including L2TP:

LAC: Local Access CarrierLAC: Local Access Carrier




• Traffic Management– Definitions and Traffic Models– ATM Services

• Trends


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.


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.


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!


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:

t

P(T>t)

0.010.00010.000001

10 20 30

Exponential

Heavy-tailed


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.


Time Scales of Traffic Management

Scheduling, buffer managementRegulation, policingRouting (connection less)Error detection and correctionFeedback flow-controlRetransmissionRenegotiationSignallingAdmission-controlService pricingRouting (connection-oriented)Peak-load pricingCapacity Planning

Less than oneRTT(Cell level)

One or moreRTTs(Burst level)Session(Call level)

DayWeeks and more

Time Scale Mechanism Net Endsystem


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.


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.

T T T

marked or dropped

T


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

marked or dropped

T = 1/PCRTS = 1/SCR

t T with mean value TS

t t t t


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 the

Allowed Cell Rate (ACR).

reserved

dynamic

Link Rate

PCR (Peak Cell Rate)

MCR (Minimum Cell Rate),may be 0.

ACR(Allowed Cell Rate)

Dynamically changedby the flow control.


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

OKOK Not OKOK OK


Peak Cell Rate Conformance

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

network interfaces.

Shaping

Physical PrivateATM

PublicATM

UPCUPC

PrivateUNI

PublicUNI

GCRA(T,0)

GCRA(T, *)GCRA(T, )

Sha-ping




• Traffic Management– Definitions and Traffic Models– ATM Services– IP Services

• Trends


Use of Network Protocols

0

10

20

30

40

50

60

70

80

1994 1996 1998 2000 2002

IP

SNA

IPX

RFC 1490

Others

IP is the only protocol that matters anymore!

Source: Gartner Group


Data Traffic is Overtaking Voice

Voice

Data

Time

Volume

Source: CIENA Corp.

POTS

Data

DATA

POTS

Voice-Centric Data-Centric

Today


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!


Technology Trends

Chip performance doubles every 18 months (Moore‘s 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


DWDMDWDM

Layer upon Layer...

Sonet

ATM

IP

DWDM

ATM

IP

Sonet

IP

DWDM

IP


Traffic Multiplexing in the Backbone

SonetADM

OC-48OC-48

DWDM Ring

OC-48

DWDMADM

DWDM

Sonet

ATM

IP

N x OC-48

Multiplexing of IP traffic over ATM or Sonet no longer required.

Segmentation of IP packets into ATM cells not possible at OC-48.


Optical Internet Backbones (1)

OC-48DWDM

IPDWDMADM

DWDM Ring

N x OC-48

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


Optical Internet Backbones (2)

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.

Router network Optical network

Optical Crossconnects

IP routers


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.


References (1)

• M.-C. Chow: Understanding SONET/SDH; 1995, Andan Publisher, Holmdel, New Jersey, U.S.A.,ISBN 0–9650448–2–3.

• 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 0–13–342171–6.


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.

Part IV: Carriers, Traffic Mgt, and Trends

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