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Optical Communications

Networks

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Virtual Session

End-to-End Messages

Physical

Presentation Presentation

Session Session

Network Network

Data Link

Control

Data Link

Control

PhysicalPhysical

Physical Link, e.g. electrical

signals

Physical

portion of code

Logical

portion of

code

Virtual Network ServiceApplicationApplication

End-to-End PacketsTransport Transport

DLC DLC DLC DLC

NetworkNetwork

Bits

Packets

Frames

Physical Physical Physical

Originating

site

Terminatin

g siteSubnet

node

Subnet

node

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Opto-electronic systems and networks

LAN protocols

Fiber distributed data interface (FDDI)

Fiber channel

Gigabit/10 Gigabit Ethernet

SONET/SDH

Ethernet over optical networks

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LAN protocols

Layers 1 and 2

Map into OSI reference model

Souce: Cisco

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FDDI

Developed by American National Standards Institute (ANSI)

Originally proposed as internal fiber optic I/O channel forcomputers

Later became generalized to high-speed LAN running at 100Mbps

Can run on copper as well as fiber

Dual-ring is usual configuration

Can go up to 200 Mbps with single ring

Token ring architecture

Advantage of token-passing networks: deterministic Possible to calculate maximum time before station can

transmit

Popular in real-time environments

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Characteristics of FDDI

Token ring architecture

Two countercirculating rings

Only one used for data; other for backup

Ring size

Up to 200 km (on multimode fiber, single ring)

Dual ring size up to 100 km

Maximum of 500 stations

Max distance between stations is 2 km

Packet switched: utilizes variable length frames Max frame size is 4500 bytes

Frame header contains destination address

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Characteristics of FDDI (continued)

Guaranteed bandwidth availability

Equality of access as in all token-ring systems

Guaranteed bandwidth for synchronous traffic

Token-ring protocol

Similar to IEEE 802.5 token-ring LAN

Differs in that it is dependent on timers Ring stations

Each may connect to both rings or only primary ring

Ring monitor

Performed cooperatively by all stations rather than by

single active monitor All look for errors; if found any station can request

reinitialization of ring

Each station does not have to have ring monitorfunction

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FDDI ring structure, with/without break

Source: Dutton

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FDDI ring configuration

Source: Dutton

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FDDI token ring protocol operation

Ring access controlled by special frame called a token

Only one token present at any time

When a station receives the token it has permission to

send

When station finishes sending it must place token backon ring

Each station on the ring receives and retransmits frames

Ring is not a node

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Timing on FDDI

3 timers required due to need to handle synchronous traffic

Token rotation timer (TRT)

Elapsed time since last token received

Target token rotation timer (TTRT)

Target maximum time between tokens time for

token to traverse ring

4 msec < TTRT < 165 msec

Optimal value often around 8 msec

Token holding timer (THT) Governs max amount of data station may send

Max time allocated for station to send

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Operation

When station receives token it compares time since lasttoken (TRT) with target time (TTRT)

Normal operation: TRT < TTRT

Station can send multiple frames until TTRT reached

TTRT-TRT = THT

Overload: 2xTTRT> TRT > TTRT

Synchronous data only permitted

Error: TRT > TTRT

Must be conveyed to LAN manager

Delays may occur

Stations must be capable of buffering data Stations must remove data they send when it returns to

them

May be many frames on ring, but only one token

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Operation (continued)

When ring initialized, stations cooperate to determine TTRT

value

Minimum of all requested TTRT values

Changed only if new station enters ring

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Physical media for FDDI

Multimode fiber

Originally defined mode of operation

Single mode fiber

Included in standard but little used

Twisted pair copper wire

STP = shielded twisted pair

Not as good as fiber, but cheaper

UTP-5 (=cat 5) unshielded twisted pair standard in 1994

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Media specifications

Medium Fiber Light

source

Detecto r Transm it power Receiver

sensi t iv i ty

Multimode 62.5/125

50/125

85/125

100/140

LED PIN diode (1) -20 to -14 dBm

(2) -4 to 0 dBm

(1) -31 to -14 dBm

(2) -37 to -15 dBm

Single

mode

9 micron LED PIN diode (1)-20 to -14 dBm

(2)-4 to 0 dBm

(1)-31 to -14 dBm

(2)-37 to -15 dBm

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Data encoding and clocking

Four data bits encoded as five bit group 100 Mbps actually 125 Mbaud on ring

Allows adding of more transitions into bit stream to allowfor problem of too many 1s or 0s

Uses Non Return to Zero Inverted (NRZI) encoding

Each station has own clock Specification is accuracy of 0.005%

Max difference between stations 0.01%

10 bit buffer inside each station to allow for differences inclocks between stations

Gives average of 4.5 bit times to smooth out timingdifferences

Determines max frame size

4.5 bits/0.01% = 45,000 bits = 9,000 symbols = 4,500 bytes

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Physical layer operation

Source: Dutton

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Comparison with standard token ringnetworks

Standard TRN uses Manchester encoding

Allows exact recovery of clock, but at cost of doubling

frequency

FDDI uses optical signals at higher speed than TRN

Does not have exact clock recovery, substitutes buffer

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FDDI layers

Source: Dutton

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FDDI layers (continued)

Physical Medium Dependent layer (PMD)

Optical link parameters

Cables and connectors

Optical bypass switch

Power levels

Physical Layer Protocol (PHY)

Access to ring

Clocking, synchronization, buffering

Code conversion

Ring continuity

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FDDI layers (continued)

Media Access Control (MAC)

Tokens and timers

Frame check sequence

Station Management (SMT)

Ring Management (RMT)

Ensures valid token circulating

Connection Management (CMT)

Physical connections and topology

Operational Management

Monitors timers and parameters

Interfaces to external network management software

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SONET overview

SONET = Synchronous Optical Network

Should have been called Synchonous Opto-electronic

network (SOENET)

Technology developed in 1980s for long-haul trunks

needed by Telcos

Formulated by Exchange Carriers Standards

Association (ECSA)

Industry group which sets standards for telecoms

1984 work began

Expected to serve as basis for Telcos for 20-30 years Designed from ground up based on 64kbps channels

(DS0voice channels)

Everything a multiple of this

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SONET (continued)

Emphasis on qualities important to Telcos

Reliability

Availability

Millisecond recovery from outages

Optimal use of bandwidth of secondary concern

Not originally intended as bulk data carrier or carrier for

asychronous packets

Serves as transport only

Does not do switching Utilizes optical components only because copper not fast

enough

Otherwise copper or fiber could transmit SONET

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Advantages of SONET

Reduction in equipment

Standardization of equipment to allow for plug and play

Increased network reliability

Provision of overhead and payload bytes

Synchronous multiplexing format

Allows carrying of different loads

Simplifies interfacing to switching equipment

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Basic structure of SONET

Utilizes time division multiplexing to combine large number

of individual signals

Structured in fixed-length frames

Entire network operates synchronously

Synchronous operation requires extremely precise clockingthroughout network

Utilizes Stratum atomic clock

Known as Primary Reference Clock (PRC)

Accurate to 1 part in 1011

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Basic structure of optical part ofSONET

ModulatorInput signal Connector Optional optical

amplifier

Amplifier DecoderOutput signal

Optical fiberOptical fiber

Light

Wavelength = 800-1600 nmElectricityElectricity

Lightsource

Detector

Input

SONET

signal

(time

multiplexed

individual

signals)

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Evolving SONET networkarchitecture

Source Encoder

(TimeDivision

Multiplexer)

Modulator/

transmitter

(Wavelength

multiplexer)

ReceiverDecoder

(Demux)

Receiver/

demodulator

(Demux)

Link

end user

services

end userservices

SONET

SONET

D

W

D

M

D

W

D

M

SONET

SONET

end user

services

end user

services

1

n

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SONET structure

First step in SONET multiplexing process: generation of

lowest level or base signal

Referred to as Synchronous Transport Signal level-1, or

STS-1

51.84 Mbits/second

Higher level signals are multiples of this, giving rise to

STS-N

N is not arbitrary, but restricted to certain values

STS-N signals composed of N byte-interleaved STS-1

signals

Optical counterpart known as Optical Carrier level-1 or

OC-1

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SONET hierarchy

Source: Tektronix

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SONET frame format

810 bytes

Logically a 90 column by 9 rows

Order of transmission: row by row, L to R within rows,

most significant byte first

9 rows

90 columns

Source: Tektronix

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SONET frame format (continued)

One frame per 125 sec = 8,000 frames/sec

8,000 frames/sec x 810 bytes/frame x 8 bits/byte = 51,840,000

bits/sec

Column = 9 bytes x 8000 per second x 8 bits/byte = 576K bits

SONET frame

Transport

Overhead

Synchronous Payload

Envelope (SPE)783 bytes

STS Path

Overhead

(POH)9 bytes

Payload

756 bytes

(84 cols.)

Fixed

stuff

18 bytes

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SONET frame structure: SPE

Source: Tektronix

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SONET frame structure (continued)

SPE does not have to be aligned with STS frame

Can begin anywhere in STS frame

Starting location designated by STS payload pointer in

transport overhead

Source: Tektronix

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Overhead structure

Two types

Transport (27 bytes)

Section (9 bytes)

Line (18 bytes)

Path (9 bytes, embedded in SPE)

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Overhead structure (continued)

Source: Tektronix

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Detailed structure of overhead

Source: Tektronix

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Function of overhead

Section (9 bytes)

Performance monitoring (STS-N signal)

Local orderwire

Datacomm channels to carry info for OAM&P

Framing

Line overhead (18 bytes)

Locating SPE in frame

Multiplexing or concatenating signals

Performance monitoring Automatic protection switching

Line maintenance

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Function of overhead (continued)

Path overhead (9 bytes)

Performance monitoring (STS SPE)

Signal label (contents of STS SPE)

Path status

Path trace

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SONET alarms

Three levels to allow close monitoring of deteriorating

conditions

Anomaly: discrepancy between observed and expected

Does not constitute interruption in service

Defect: density of anomalies reached level whereservice is interrupted

May be correctable

Failure: Inability of function to perform required action

(defect) persisted beyond allowable time span

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SONET alarms

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SONET Alarms (continued)

Source: Tektronix

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Tributaries and Virtual Tributaries(VTs)

Need exists to transmit channels slower than full STS

Called tributaries or virtual tributaries

Only certain channel speeds allowed

Tributaries may occupy a number of consecutive columns

within payload or be interleaved (time multiplexed) (usual) US T-1 (1.544 Mbps) uses 3 columns

Only requires 24 slots, given 27 = 3 slots wasted

Recall that each slot is 64 kbits, x 24 = 1.544 Mbps

European E-1 (2.048 Mbps) uses 4 columns

Only requires 32, given 36 = 4 slots wasted

Benefit is that single tributary can be demultiplexed

without need to demultiplex entire stream

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VT sizes

Used for T1

Used for E1

Source: Tektronix

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Tributaries (continued)

An SPE carrying VTs is divided into 7 VT groups Each group consists of 12 columns

12 x 7 = 84 columns = payload capacity

Columns for each VT type are all factors of 12

Each VT group can carry only one VT type

Cannot mix VT1.5 and VT3, even though they would fit Separate VT groups within frame can carry different VT

types

Allowed combinations within a VT group

4 VT1.5

3 VT2 2 VT3

1 VT6

Within group, VTs are interleaved (time multiplexed)

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Multiplexing of VTs within group

Source: Tektronix

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Multiplexing of VT groups

Source: Tektronix

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Pointers

Used to compensate for frequency and phase variation

Allow transport of synchronous payloads across

plesiosynchronous (almost synchronous) network

boundaries

Avoid delays and losses of having to use 125 sec slipbuffers

Dynamically and flexibly aligning payloads

Dropping

Inserting

Cross-connecting

Effects of jitter can also minimized

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Pointers (continued)

Byte stuffing used to fix alignment dynamically

Positive: byte added

Negative: byte deleted

Does not affect data

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Pointers (continued)

Source: Tektronix

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Layers of multiplexing in SONET

Time division

(1) Data prior to sending to SONET

E.g., several slow-speed channels multiplexed to

make T1

(2) Within VT group E.g., several T1s

(3) Among VT groups in STS frame

(4) Among STS frames for speeds greater than OC-1

May be done multiple times, e.g., 4 OC-3 to OC-12, 4

OC-12 to OC-48, 4 OC-48 to OC-192

If WDM used, (5) wavelength multiplexing of SONET signals

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SONET multiplexing (continued)

56K

128K

384K

x1001 Tbps

TDM

Level 1

TDM

Level 2

TDM

Level 3TDM

Level 4

WDM

Level 5

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SONET network elements

Terminal multiplexers

Level 3 or 4

Regenerator (repeater)

Digital loop carrier (DLC)

Concentrator at level 1

Add/drop multiplexer (ADM) Picks off multiplexed signals

Adds new signals

Source: Tektronix

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SONET network elements (continued)

Digital cross-connects (DCS or DCX)

Accesses signals at STS-1 level and switches them

SONET equivalent of DS3 cross connect

Allows overhead to be maintained because network is

synchronous

Can make 2-way connections at DS3, STS-1, STS-Nclevels

STS-Nc requires contiguous, not interleaved bytes

Source: Tektronix

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SONET network configurations

Point-to-point

Point-to-multipoint

Hub

Ring

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Point-to-point

Two terminal multiplexers connected by optical link

May or may not use repeaters

Simplest SONET application

Source: Tektronix

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Point-to-multipoint

Linear add/drop architecture

Circuits added, dropped along the path

SONET ADM designed for this task

Avoids need to completely demux signal, cross-connect

channels, remux Typically placed along path to allow adding, dropping

channels where needed

Source: Tektronix

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H b

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Hub

Concentrates traffic at one or more sites

Allows for easy reprovisioning

Two implementations

Cross-connecting tributary services

Requires 2 or more ADMs, cross-connect switch

Cross-connecting at tributary and SONET level

Requires cross-connect switch

Source: Tektronix

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Ri hit t

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Ring architecture

Most popular architecture

Used by all major carriers Basic building block is ADM

Bi-directional or uni-directional traffic

Main advantage: survivability

If fiber cut, multiplexers can

reroute in milliseconds

Source: Tektronix

After cut

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Ring architecture (continued)

Source: Tektronix

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Limitations of SONET ring

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Limitations of SONET ringarchitecture

SONET ring architecture very complex

Main problem is scalability

To increase capacity or add new locations requires

building a new set of rings, which is very expensive

Mitigated to some extent by DWDM

But hardware is standardized and available from multiple

sources

SONET does its job well

Is established and low-risk technology

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SONET and SDH

SDH=Synchronous Digital Hierarchy

Used widely outside of US, Japan

Same 125sec frames Developed to accommodate different world standards

T1-based E1-based

Original SONET standard changed from bit interleaving

to byte interleaving

SONET is subset of SDH

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SONET/SDH hierarchies

Source: Tektronix

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Non-synchronous hierarchies

Source: Tektronix

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Address for following slides:

http://www.cisco.com/networkers/nw00/pres/pdf2000.htm

Presentation # 3003

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http://www.cisco.com/networkers/nw00/pres/pdf2000.htmhttp://www.cisco.com/networkers/nw00/pres/pdf2000.htm

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Eth t

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Ethernet

Primarily of interest because of newer, high-speed versions

Gigabit Ethernet (GBE)

10 Gigabit Ethernet

Fast Ethernet (100 Mbps) can run on fiber, but normally

implemented with Cat-5 UTP

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B i f i f Eth t ti

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Brief review of Ethernet operation

All stations connected to bus, which is in effect a node

Ethernet uses Carrier Sense Multiple Access with Collision

Detection (CSMA/CD) to control bus traffic

Stations transmit independently and asychronously

If a frame is received, all stations check to see if it isaddressed to them

If two stations transmit simultaneously or closely in

time, a collision occurs

No guarantee that data will get through without error

Requires higher level protocol to monitor and indicatedneed for retransmission

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Cl ifi ti ( ti d)

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Clarification (continued)

Most modern Ethernet network interface cards (NICs) can

operate either half duplex (with bus or hub) or full duplex

(with switch)

Switches are sold by all major vendors

Improve throughput on slower speed LANs

Not much more expensive than hubs

Allow more devices to be connected to LAN

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Source: Luxpath/IEC

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Operation of Ethernet (continued)

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Operation of Ethernet (continued)

Operation of CSMA/CD

If a station wishes to send, it must listen to see if anotherstation is transmitting

If so, must wait until bus is free

If not, it can begin to transmit

Because of signal propagation delays down the bus, a station

may be unaware that another has begun to transmit

If this occurs, called collision, garbage is result

Transmitting station must listen to bus to monitor for

collisions

If collision detected, transmitting station sends jamming

signal to improve chance that other station detects

collision, then stops transmitting

If collision occurs, all transmitting stations must cease

transmission and wait for (different) random periods before

retransmitting

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Eth t d OSI f d l

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Ethernet and OSI reference model

Application

Presentation

Session

Transport

Network

Data Link

Physical

TCP

IP

Applications:

Telnet

FTP

SMTP

HTTP

Ethernet

(802.3)

LLC SublayerMAC Sublayer

Physical signaling

Media attachment

TCP/IP

Application

Protocols

OSI Reference Model

TCP/IP Implementation

Using Ethernet

Source: IBM

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B d h b hit t

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Bus and hub architectures

Source: Dutton

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Half d ple and f ll d ple

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Half-duplex and full-duplex

Meaning of half duplex (HDX) and full duplex (FDX)

Terms going back to teletype days

Half-duplex = same physical line (or bus) used for both

transmit and receive

Requires special protocol to prevent simultaneoustransmission and reception

Full-duplex = different physical line used for both

transmit and receive

Does not require special protocol, but does require

dedicated (at least temporarily) connection

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Half-duplex and full-duplex

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p p(continued)

Original Ethernet: half-duplex because all transmitting and

receiving on same bus

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Implementation of Ethernet

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Physical bus rarely used anymore

Too difficult to manage and repair

Unwieldy to add or change workstations

Requires coax cable in most cases

Implementations done with hub and Cat-5 UTP Logically looks like bus

Manchester encoding always used

Signal always has transition with every bit

Logic 0: 0 to 1 transition at bit center

Logic 1: 1 to 0 transition at bit center

Effectively doubles frequency

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p(continued)

Example of Manchester encoding

Manchester encoding important for collision detection

Because a 0 level and a 1 level occur for each bit, codeis balanced

Average DC level is of logic 1 level

If collision occurs, signals are ORed, which raisesaverage DC level

Detected and interpreted as collision by transceivers

1 1 10 0 0

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Implementation on fiber

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Implementation on fiber

Collision detection

Light pulses converted to electricity in transceivers

Average DC value will also change when light pulses

collide on fiber

Uses LEDs at 850 nm

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CSMA/CD performance and

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ppropagation delay

Propagation delay is main factor limiting performance of

Ethernet

Delay means station may begin transmitting when bus

not free

Also means stations will learn that bus is free at

different times

Collisions reduce utilization of Ethernet LAN because they

force two or more retransmissions

Maximum utilization (maximum throughput) given by

1/(1+6.44)where

= end-to-end delay/transmission time

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Ethernet throughput vs offered load

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Ethernet throughput vs. offered load

Source: Dutton

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CSMA/CD performance and

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ppropagation delay (continued)

On copper wire, transmission speed about 5.2 sec/km

For 10 mbps Ethernet, with 1000 bit frame size, utilization

estimated as

= 2 x 5.2 sec/100 sec = 0.104

Max utilization = 1/(1+6.44x0.104) = 0.60 = 60% For 100 mbps Ethernet, same frame size,

= 2 x 5.2 sec/10 sec = 1.04

Max utilization = 1/(1+6.44x1.04) = 0.13 = 13%

For 1 Gbps Ethernet, same frame size,

r = 2 x 5.2 sec/1 sec = 10.4

Max utilization = 1/(1+6.44x10.4) = .0147 = 1.5%

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Ways to fix speed problem (continued)

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Gigabit Ethernet: would be ~ 20 m, but 200 was kept as

spec

Other changes need to be made

Switches used instead of hubs

Minimum frame size 512 bytes, max same as before,1524 bytes

Switch is layer 2 device

Reads addresses of frames and sends frame only to

destination

Reduces chances of collision significantly Increases utilization seen by stations

Use of switches and routers also allows conventional

Ethernet networks to span large areas

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10 Gigabit Ethernet uses only full duplex to avoid timing

problems associated with CSMA/CD protocol Lower speed versions can use it as well

Requires switch which physically connects two devices

which are communicating

No collisions because both connected devices can

transmit and receive at same time

Terminal 1

Terminal 2 Terminal 3

Terminal 4

SwitchT

R

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Gigabit Ethernet standard

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Gigabit Ethernet standard

Shielded twisted pair up to 500 m

UTP cat-5 available

Requires 5-level encoding

100 m max length

Cat-7 standard under development Shielded twisted pairs

Single mode fiber at 1310 nm, up to 2 km

Multimode fiber at 780 nm (CD-ROM lasers) or VCSELs at

850 nm

On 62.5/100 MM fiber up to 200m

May be extended to 1 or 2 km

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Cabling standards

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Source: 10 Gigabit Ethernet Alliance

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10 Gbit Ethernet

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Fiber only

Full duplex only, in combination with switches, will notneed CSMA/CD protocol required for half-duplex slower

Ethernet

Standard called IEEE 802.3ae; see

http://grouper.ieee.org/groups/802/3/ae/for info on the spec


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10 Gbit Ethernet
http://grouper.ieee.org/groups/802/3/ae/http://grouper.ieee.org/groups/802/3/ae/

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For further info,

www.10gea.org


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Growth rate anticipated for Ethernet
http://www.10gea.org/http://www.10gea.org/

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Growth rate anticipated for Ethernet

Source: Luxpath/IEC

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Ethernet over SONET

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Ethernet over SONET

Ethernet over SONET inefficiencies

Source: Cisco

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Other trends in Ethernet

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Other trends in Ethernet

All-optical Ethernet switches

Eliminate need for conversion back to electronic form

Useful in 10 Gbit WAN applications

Source: Luxpath/IEC

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Fiber Channel

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Fiber Channel

Developed by ANSI to address problems of existingcomputer channel interfaces

Main thrust: connecting disk drives or arrays of disk driveswith computer systems

Allows systems managers to combine data warehouses

spread over a campus orwith repeatersametropolitan area

Primarily within computer, but can also be used as LAN

Allows interconnection of computers and peripheraldevices

Point-to-point Crosspoint switch

Arbitrated loop

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Fiber Channel (continued)

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Fiber Channel (continued)

Architecture is neither a channel nor a real networktopology

An active intelligent interconnection scheme, called aFabric, to connect devices

High performance serial link supporting its own, as well as

higher level protocols such as the FDDI, SCSI, HIPPI and IPI Speeds up to 4 Gbit/s (higher speeds planned for future)

8 Gbit standard ratified

10 Gbit used now but only to interconnect switches

Can be converted for Local Area Network technology by

adding a switch Primary application is in storage area networks

Can also run on copper twisted-pair

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Fiber channel topologies

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Fiber channel topologies

Point-to-Point

Crosspoint switch

Arbitrated loop

Source: Dutton

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Characteristics of FDDI topologies

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Characteristics of FDDI topologies

Source: Wikipedia

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Fiber Channel Speeds

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Fiber Channel Speeds

133 Mbit/sec

266 Mbit/sec

530 Mbit/sec

1 Gbit/sec

2 Gbit/sec

4 Gbit/sec

Highest performance: 10 km at 1 Gbit/sec

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Terminology

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e o ogy

N_Port: connection for device to fiber channel

F_Port: special connection to crosspoint switch fabric

NL_Port: N_port in arbitrated loop

FL_Port: F_Port connected to arbitrated loop

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Media for Fiber Channel

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Uses single mode or multimode fiber

Single mode

Lasers at 1300 nm, 1550 nm

Data rates up to 1 Gbps

Distance up to 10 km at 1300, >50 km at 1550 Multimode

Laser at 780 nm, 850 nm

Distance up to 2 km

LED at 1300 nm

Distance up to 1.5 km

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Classes of service

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Class 1: Dedicated (connection oriented)

2 N_Ports

Maximum bandwidth guaranteed

Class 2: Multiplex

Connectionless Acknowledgement of successful delivery

Class 3: Datagram

Connectionless

Best effort

No acknowledgement

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