LAN Evolution - 1

New Generation LAN and MAN

Gruppo Reti TLC nome.cognome@polito.it

http://www.telematica.polito.it/

LAN Evolution - 2

What is today scenario• LAN must be

– Reliable– Fast– Cheap

• Collapsed backbone topology: from shared BUS to start topology

• The star could be– hub (shared bandwidth)– switch (dedicated bandwidth)

• Redundancy for fault management at the star• Today LANs are Ethernet (but the same happened for

Token Ring, FDDI, ...)

LAN Evolution - 3

Ethernet Switching• Ethernet technology in which only switches

are used• Forwarding (simple routing)

– cut-through (smaller delay, but no FCS check)• Only available if the all ports have the same MAC,

same speed, unicast is adopted, and destination port is free

– store-and-forward – fragment free (avoid the transmission of collided

frames)

LAN Evolution - 4

Half or Full duplex?• LAN were designed as half duplex• Switches makes the physical link

– A point-to-point link– Can then be full duplex

• with two separate channels (TX and RX)

• If transceiver are full duplex, no collision can occur

• The collision domain constraints is then ineffective

LAN Evolution - 5

100Mb/s Ethernet• Transmission speed (V), minimum frame size (Dmin )

and RTT are subject to Dmin /V>RTT/2

• Increasing V from 10Mb/s to 100Mb/s possible if– RTT is 10 times smaller– Dmin is 10 times bigger– The MAC protocol is modified

• Two solutions:– Fast Ethernet (100Base-T) CSMA/CD– 100VG AnyLAN (based on a polling MAC)

LAN Evolution - 6

Fast Ethernet• Keep the same Dmin and CSMA-CD MAC of

10Base-xx • Different physical layers (twisted pair with 2

pairs, 4 pairs or optical fibers)• Encoding 8B6T or 4B5B (not Manchester

encoding anymore)• RTT must be 10 times smaller

– Maximum distance between two stations is 200m• Backward compatible with 10Base-xx

LAN Evolution - 7

Gigabit Ethernet• Same 802.3 frame format• Same CSMA-CD MAC protocol• Support half duplex and full duplex

– If full duplex is enables, no constraint on the collision domain

– CSMA/CD has no impact• Flow control to avoid packet loss• Backward compatible with same UTP-5 cables• Dmin is 10 times larger (512B) if half duplex• Encoding 8B10B (from fibre channel)

LAN Evolution - 8

Line Encoding

• It is based on the correspondence between blocks of k bits at input to n bits at output, n>k

• Goals:– 100% D.C. voltage balance– Clock recovery (large transition density)– Error identification– Extra symbols can be adopted for signalling (Start/End of

Frame)• Line speed increases by a factor n/k

Encoder(k,n) Channel

Decoder(k,n)

k bits n bits n bits k bits

LAN Evolution - 9

Gigabit Ethernet• IEEE 802.3z defines three different physical interfaces:

– 1000Base LX: mono and multimode fiber in the second window– 1000Base SX: multimode fiber in the first window– 1000Base CX: STP cable (2 shielded pairs)– 1000Base T: STP or UTP (4 pairs, shielded or twisted)

• The physical encoder is the same as Fiber Channel

standard fiber Diameter (µm)

BW(MHz×km)

Distance(m)

1000BASE-SX(850 nm)

MMMMMMMM

62.562.55050

160200400500

2 to 2202 to 2752 to 5002 to 550

1000BASE-LX(1300 nm)

MMMMMMSM

62.550509

500400500NA

2 to 5502 to 5502 to 5502 to 5000

SXshort-wavelength

(850 nm)

LXlong-wavelength

(1300 nm)

LAN Evolution - 10

Gigabit Ethernet layers

1000BASE-LXLWL

Fiber Optic

1000BASE-SXSWL

Fiber Optic

1000BASE-TUTP

Category 5

MAC Layer

Physical Layer 1000BASE-TEncoder/decoder

Media Access Control (MAC)

Gigabit Media Independent Interface (GMII) (optional)

1000BASE-CXShielded

Balanced Copper

FibreChannel

Encoder/Decoder (8B10B)

SMF -

5km50µ MMF -

550m62.5µ MMF -

500m

50µ MMF -

550m62.5µ MMF -

220-275m25 m 100 m

802.3z physical layer 802.3ab physical layer

Several different physical interfaces have been standardized, including special short reach cables (both fiber or copper based)

LAN Evolution - 11

What changes• Dmin from 64 to 512 bytes (huge degradation

in case of small frames)• Collision domain of 210 m• Only star topologies• ”frame bursting” is allowed to keep

transmitting up to 8192 bytes (limits the impact of Dmin since only the first frame must be larger than 512 bytes)

• Introduction of “Jumbo Frames” (9000B)

LAN Evolution - 12

Some 1 Gigabit Optical transceivers

1x9 GBIC

SFF

SFPPluggable

Pin in Hole

LAN Evolution - 13

10 Gigabit Ethernet• Standard from 2005 (fiber transmission) and 2006 (

802.3an twisted pair)• Full duplex only, no CSMA-CD• Physical layer:

– Serial transmission, up to 40 Km• 650 m on new MMF• 300 m on legacy MMF• 2 km SMF• 10 km SMF • 40 km SMF

– Over SONET if >40Mk

LAN Evolution - 14

Goal of IEEE 802.3ae

• Same framing of 802.3• Same frame size 802.3• Only full duplex support• Only fiber transmission (but…)• 10.0 Gbps at the MAC-PHY interface• LAN PHY capacity = 10 Gbps• WAN PHY capacity ~9.29 Gbps (OC-192

from SONET)

LAN Evolution - 15

Layer Model

ApplicationPresentation

SessionTransportNetworkData linkPhysical

PMDPMA

64B/66B PCS

PMDPMA

8B/10B PCS

Reconciliation Sublayer (RS)MAC

MAC ControlLLC

Higher LayersOSi reference

layer

MEDIUM MEDIUM

Layers 802.3ae

XGMII XGMII

MDI MDI

MDI = Medium Dependent InterfaceXGMII = 10 Gigabit Media Independent InterfacePCS = Physical Coding SublayerPMA = Physical Medium AttachmentPMD = Physical Medium DependentWIS = WAN Interface Sublayer

10GBASE-R: Point to point fiber links10GBASE-W: compatible with SONET standard10GBASE-X: uses WDM, 4 λ

at 2.5G

10GBASE-R 10GBASE-X

PMDPMAWIS

64B/66B PCS

MEDIUM

XGMII

MDI

10GBASE-W

LAN Evolution - 16

Copper at 10Gb/s• 10GBASE-CX4 - IEEE 802.3ak - transmits

over 4-lanes similar to InfiniBand• 10GBASE-Kx - Backplane Ethernet – IEEE

802.3ap - is used in backplane applications such as blade servers and routers/switches

• 10GBASE-T - IEEE 802.3an-2006 - provides 10 gb/s over STP or UTP, up to 100m (Cat6 cable)

LAN Evolution - 17

10 Gigabit Optical transceivers

XGXSFTRX

XENPACK

LAN Evolution - 18

100Gb/s Ethernet• Presently under early development from

IEEE 802.3ba• Goal

– 100GbE optical fiber Ethernet– at least 100 meters (MMF)– at least 10 kilometers (SMF)– full-duplex operation only– uses current frame format and size standards

LAN Evolution - 19

Ethernet Evolution• Ethernet is the winner in the LAN arena• Born at 10Mb/s on a shared medium

– Real throughput is smaller• Then it was adapted to cope with

– different transmission cabling (coaxial, Twisted pair, fibre) – up to a 10 Gbit/s

• The goal has always been to have cheap interconnection, no QoS, for PCs– Still true at 10Gb/s?

LAN Evolution - 20

Ethernet from 10, 100, 1000, …Mb/s

• Bandwidth of the same order of PC capacity

• Shared Coaxial cable• Distance up to (~ 1 km) – due to

physical and MAC constraints• Cheap

– Simple– Exploit the economy of scale

• Hub (switch): bandwidth is shared (dedicated) among terminals

LAN Evolution - 21

Robert M. Metcalfe

LAN Evolution - 22

50% 25% 25%

Ethernet at 10, 100, 1000, … Mb/s• Both optical fiber and copper wires.• Switches improves capacity, but uncontrolled

switching.• Spanning tree protocol to cope with faults

LAN Evolution - 23

Dedicated

Shared

Hierarchic view of a LAN

LAN Evolution - 24

10 Gigabit Ethernet

Wide AreaTDM

Connection

WAN Level

Wide AreaCore

Connectivity

WANAccess

Services

MAN Level

Metro Network

Metro Network

Gigabit Ethernet

Desktop Level

Workgroup Level

DesktopSwitch

WorkgroupSwitch Servers

BackboneLevel

BackboneSwitch

Enterprise Router

Gigabit Ethernet

10/100 MbpsEthernet

2001/2002

1999/2000

1998/1999

1970’s/1980’s

Ethernet Evolution

LAN Evolution - 25

Ethernet Evolution

0.1 1 10 100 1000 Distance [km]

Cap

acity

[Mb/

s]1

10 1

00

1,

000

1

0,00

0

Ethernet

Fast Ethernet

Gigabit Ethernet

10 Gigabit Ethernet

LAN Evolution - 26

Cost Comparison - Ethernet vs. SDH

$100

$1,000

$10,000

$100,000

2000 2001 2002 2003 2004

OC-3

OC-12OC-48

OC-192

10G Eth

$ P

er G

igab

it of

Ban

dwid

th$

Per

Gig

abit

of B

andw

idth

Source: Dell’Oro Group

1G Eth

LAN Evolution - 27

RPR IEEE 802.17 Resilient Packet Ring

• Layer-2 technology for MAN• Exploit ring topology with spatial reuse• Carrier class protection (based on rings)• QoS support thanks to complex MAC algorithms• Simple management cost• High capacity• MAC is independent from physical layer: supports

both SONET and Ethernet physical layer

LAN Evolution - 28

Converging technology

Optical Transmission Choice(Ethernet, SONET,…new ones)

Ring Operations(Forwarding, Topology, Fairness, Protection)

Service Intelligence(Adaptation, QoS, protocols)

Vendor Specific

802.17 Specific

PHY Specific

Keep simple standards, and let manufacturer free to add extra functionalities

Layer-2 MAC independent fromPhysical layer

Data TDM Video

Bound Scope

LAN Evolution - 29

Resilient Packet Ring• Based on bidirectional ring• Both rings are operational during normal

operation• Topology Discovery algorithm to simplify

network management• Explicit support for three types of packets:

– Data (variable length, up to 9218 byte)– Control (Topology Discovery and Protection)– Fairness (to enable resource allocation)

LAN Evolution - 30

Resilient Packet Ring• Three classes of service:

– Class A: bandwidth and delay guaranteed traffic– Class B: bandwidth guaranteed traffic, no delay

constraint– Class C: best-effort

• Failure recovery within 50 ms (as SDH):– Steering: the source changes the routing– Wrapping: the entire ring is reconfigured by the

two nodes involved

LAN Evolution - 31

Resilient Packet Ring• MAC: buffer insertion with multiclass support

RXPTQ

STQ

local trafficA B C

TXlogic

PTQ: primary transmission queueSTQ: secondary transmission queue

LAN Evolution - 32

RPR Alliance Members