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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