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Networking Technology

Layer 1 Standards

Dan Ionescu

Fall 2012

ELG 5369IP-Based Internetworking Technologies

Chapter 2

1. Physical Layer: Responsible for the transmission of

unstructured bit streams over a physical medium. This covers the mechanical, electrical and procedural characteristics required to establish, maintain and deactivate physical links.

Signals and Systems

Signal and “Measures”

Modulation Rate: 1/Duration of the smallest element=Baud rate

Data Rate: Bits per second

Data Rate = Fn(Bandwidth, signal/noise ratio,encoding)

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The Seven Layers of CommunicationsThe Seven Layers of Communications

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Systems and “Measures” 2

Communication Channels, Bandwith, Capacity...

Channel

H(ω)

ω

+ ωc- ωc

Bw

Shannon's Theorem and Channel Capacity

Bandwidth = H Hz � sampling rate ωs � 2ωc

Capacity = Maximum data rate for a channel

Nyquist Theorem:

Bilevel Encoding: Data rate = 2 × Bandwidth

Multilevel coding: Data rate = 2 × Bandwidth × log 2 M

LAN – Layer 1 StandardsLAN – Layer 1 Standards

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Hub (a collision domain)

• A hub is a L1 (physical layer) multi-port repeater.

– It receives a signal on one port, regenerates it, and transmits it out all ports.

– All devices connected to a hub receive any transmission on that hub,

regardless of the intended recipient.

– Note: Simple hubs have a single bus that is capable of operating at either 10Mbps or

100Mbps, but not both. These are pure L1 devices, no “smarter” than the original coax

Ethernet bus they replaced. The very common 10/100 hubs actually have two buses, a

10M bus and a 100M bus, which are bridged. This bridging function is a L2 function, so

technically speaking 10/100 hubs are not pure L1 devices.

• Two or more devices on a hub cannot transmit at the same time.

– When two or more devices simultaneously transmit, there is a collision.

– The devices must back off and re-transmit at dispersed intervals, so that only

one device is transmitting at any given time.

• Because of these characteristics, a hub (or a group of hubs connected

together) is known as a collision domain.

• Hubs operate only at half duplex; attached devices cannot transmit and

receive at the same time.

• Generally speaking, only four 10M hubs or two 100M hubs can be

connected together.

LAN Architectures � Topologies

LAN TopologiesLAN Topologies

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10BASE5: 10 Mb/s over coaxial cable (ThickWire)

10BROAD36: 10 Mb/s over broadband cable, 3600 m max segments

1BASE5: 1 Mb/s over 2 pairs of UTP

10BASE2: 10 Mb/s over thin RG58 coaxial cable (ThinWire), 185 m max segments

10BASE-T: 10 Mb/s over 2 pairs of UTP

10BASE-FL: 10 Mb/s fiber optic point-to-point link

10BASE-FB: 10 Mb/s fiber optic backbone (between repeaters). Also, known as

synchronous Ethernet.

10BASE-FP: 10 Mb/s fiber optic passive star + segments

10BASE-F: 10BASE-FL, 10BASE-FB, or 10BASE-FP

100BASE-T4: 100 Mb/s over 4 pairs of CAT-3, 4, 5 UTP

100BASE-TX: 100 Mb/s over 2 pairs of CAT-5 UTP or STP

100BASE-FX: 100 Mbps CSMA/CD over 2 optical fiber

Ethernet Layer 1 StandardsEthernet Layer 1 Standards

Ehternet/Fast EthernetEhternet/Fast Ethernet

MAC – Media Access Control

CSMA/CD- Carrier Sense Multiple Access With Collision Detection a network

control protocol in which:

•a carrier sensing scheme is used.

•a transmitting data station that detects another signal while transmitting a

frame, stops transmitting that frame, transmits a jam signal, and then waitsfor a random time interval (known as "backoff delay" and determined using

the truncated binary exponential backoff algorithm) before trying to send that

frame again.

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Uses point-to-point links between TWO nodes

Full-duplex bi-directional transmission

Transmit any time

Many vendors are shipping switch/bridge/NICs with full duplex

No collisions ⇒⇒⇒⇒ 50+ Km on fiber.

Between servers and switches or between switches

Full Duplex EthernetFull Duplex Ethernet

Switch (a broadcast domain)

• A switch is more than just a repeater. It is a L2 (data link layer)

bridge, which means that it is “aware” of L2 MAC addresses.

– MAC addresses and Ethernet frames will be discussed in

more detail later.

• A switch keeps track of which devices are connected to which

ports by maintaining a table of the MAC-address-to-switch-port

mapping.

– We’ll simply call this the MAC table. It is populated by

recording the source MAC addresses of incoming Ethernet

frames on each port.

– MAC table entries are designed to time out, typically after a

few minutes, if no other frame from the same source is not

received on that port.

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• Transmissions on a switch are sent only to the intended

recipients, determined by the destination MAC address.

– The exception to this is if the destination MAC address is not

already in the MAC table, in which case the Ethernet frame is

transmitted out to all ports.

• Broadcasts are sent to all recipients, as they are intended to

be.

• For this reason, a switch (or a group of switches connected

together) is known as a broadcast domain.

• Switches can operate at full duplex; multiple attached devices

can transmit and receive at the same time.

• Synchronous Optical NETwork (SONET) Standard for digital optical

transmission(bit pipe)

Developed originally by Bellcore. Standardized by ANSI T1X1

Synchronous Digital Hierarchy (SDH): STS-n, STM-n (ITU-T)

Standardized by CCITT

– STS-n = n x STS-1 (51,8Mbit/s) - STM-n = n x STM-1 (155.52Mbit/s) = STS-3n

• Plesiochronous Digital Hierarchy (PDH): DS-1, DS-3, etc.

“IP over SONET” allows IP datagram transfers over high-speed carrier links

using PPP

SONET is appearing as a competition to ATM

SONETSONET

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SONET provides for Automatic Protection Switching

100 ms or more is “loss of signal”

2.3 ms or less is not “loss of signal”

In-between is up to implementations

Most implementations use 13-27 ms

⇒ Higher speed lines ⇒ maintain sync for more bits

APS allows switching circuits on fault

May take up to 50 ms to complete

SONET does not provide QoS, Dynamic bandwidth

(SVCs), QoS multiplexing, traffic management

Payload scrambling is a hot issue

Sonet Physical Layers Functions

HEC Header Error Control B-ISDNBroadband ISDN

(Integrated Service

Digital Networks).

Based on ATM.

Can run up to

several hundred

Mbps.

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SMDS (Switched Multimegabit Data Service) is a public, packet-switched service aimed at

enterprises that need to exchange large amounts of data with other enterprises over the wide-area

network on a nonconstant or "bursty" basis. SMDS provides an architecture for this kind of data

exchange and a set of services. In general, SMDS extends the performance and efficiencies of a

company's local area network (LANs) over a wide area on a switched, as-needed basis.

PLCP -- Physical Layer

Convergence Procedure

STM- Synchronous

Transfer Mode

SDH-Synchronous

Digital Hierarchy

SMDS Layer 1 StandardsSMDS Layer 1 Standards

Physical Layer:

transports ATM cells between two adjacent ATM Layers

The ATM Layer is independent of the Physical Layer

Comprises two sub-layers :

– Transmission Convergence (TC) Sub-Layer

– Physical Medium Dependant (PMD) Sub-Layer

Various Physical Layer Implementations

– Defined by ANSI, ITU-T (ex CCITT) and ATM Forum

Based on DS 1 - DS 3, Sonet

ATM TechnologiesATM Technologies

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ATM StandardsATM Standards

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1994: IBM 9729. 10 full-duplex channels in one fiber up to 50 kms. to avoid

amplifiers.

Designed to connect large mainframe datacenters.

Channel spacing is 1 nm

Lucents's WaveStar product -- 400 Gbps over a single fiber using 80 channel

DWDM (January 1998)

Lucent's LazrSPEED a- 10 Gb/s up to 300 on LazrSPEED multimode fibers

using low cast short-wavelength (850nm) vertical cavity surface-emitting laser

(VCSEL) transceivers.

Monterey made wavelength routers that allow mesh architecture and use OSPF

or PNNI like routing.

Optical NetworksOptical Networks

Tunable Lasers

Fast tuning receivers

Frequency converters

Amplifiers

Splitters, Combiners

FIBER:

Multimode Fiber: Core Diameter 50 or 62.5 mm

Wide core ⇒⇒⇒⇒ Several rays (mode) enter the fiber

Each mode travels a different distance

Single Mode Fiber: 10-mm core. Lower dispersion.

Optical Network TechnologiesOptical Network Technologies

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Wave Division Multiplexing(WDM)

Dense Wave Division Multiplexing (DWDM)

WANs: Fiber links ⇒⇒⇒⇒ WDM ⇒⇒⇒⇒ DWDM Links

Undersea Links: Amplifiers ⇒⇒⇒⇒ High maintenance cost ⇒⇒⇒⇒ Can't put too many

fibers

DWDM highly successful in long-haul market.

Bandwidth demand is low and more dynamic.

Dark Fiber –very successful for cheep optical network cabling.

WDMWDM

Results with WDM

40 Gbps over a single wavelength up to 65 km, Alcatel in Summer of 1998.

Modulation gave 20 GHz at 3-dB point. The distance limitation was due to PMD.

2.64 Tbps to 120km (NEC'96): 132 λ λ λ λ × 20 Gbps

1.4 Tbps 600 km (NTT'97): 70 λ λ λ λ × 20 Gbps

1 Tbps 400 km (Lucent 97): 100 λ λ λ λ × 10 Gbps using TrueWave Fiber

320 Gbps 7200 km (Lucent 97): 64 λ λ λ λ × 5 Gbps

WDMWDM

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Hybrid Optical Network

Optical Network TopologiesOptical Network Topologies

Tunable components moved to a central switch

Each station has a preassigned receiver wavelength

Switch converts the signal to receiver wavelength

Optical Router

A crossconnect with

wavelength conversion

Centralized WDM SwitchCentralized WDM Switch

Wavelength RouterWavelength Router

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Either transmitters, receivers, or both tunable.

Switches are programmable.

Signaling channel could be electronic or optical

Wavelength collisions ⇒⇒⇒⇒ Suitable for medium size

networks.

Wavelength converters help avoid wavelength

collisions

Wavelength Routed NetworksWavelength Routed Networks

Committee FO-6 develops standards:

•Fiber Optic Test Procedure (FOTPs),

•Informative Test Methods (ITMs),

•Fiber Optic Connector Intermatability Standards (FOCISs)

and

•Specifications for the individual components of a fiber optic system.

International Electrotechnical Commission (IEC)

•Technical Committee (TC) 86, Fibre Optics.

TIA, Bellcore, Telcordia,... all work towards promoting a set of standards which

will regulate the way that the Physical Link shall work.

TIA:

Standards for Optical NetworksStandards for Optical Networks

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ISDN (Integrated Services Digital Network):

PPP - Point to Point Protocol

Frame Relay

CDPD (Cellular Digital Packet Data)

Other Technologies for Layer 1Other Technologies for Layer 1