LAN Evolution - 1
New Generation LAN and MAN
Gruppo Reti TLC [email protected]
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 - 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 - 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 - 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 - 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