Introduction to LAN/WAN
Medium Access Sublayer (Part II)
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Medium Access Sublayer Two - Local and Wide Area Networks - Lecture Slides, Slides of Social Work
Main points of Local and Wide Area Networks are: Medium Access Sublayer Two, Multiple Access Protocols, Ieee, Standard, Ethernet, Wireless, Protocols, Misc, Channel Efficiency, Complicated Stuff Skipped
Typology: Slides
2012/2013
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Introduction to LAN/WAN
Medium Access Sublayer (Part II)
Now,Where Were We?
)
Introduction
)
Multiple Access Protocols
)
IEEE 802 Standard
- Ethernet (802.3)
)
Wireless LAN Protocols
)
Misc
Ethernet Performance (cont.)
)
Convert previous formula to:
- Frame length
F
- Network bandwidth B– Cable len
L
- Cable propagation speed
c
- (complicated stuff skipped)
)
Channel Efficiency = _____1_____
BL
e/
cF
)
Increasing
B
x
L
reduces efficiency
)
But everyone wants high-bandwidth, WAN!
- Then they better not use Ethernet
Ethernet Performance and Frame Size
Saturated LAN
)
Net saturated? Add bandwidth … good idea?
- Expensive to replace cards– Efficiency– Instead
Switched LANs
)
Switch with high-speed
backplane
with
connected
cards
(typically, 1 Gbps)
)
4 to 32 plug-in cards
)
Each plug in card can support 1 to 8connectors (computers)
)
Can reduce or eliminate contention
Switched LANs
)
When receives frame, sees if destined for anotheron same line, forwards as needed
- different than hub or repeater– Run classic ethernet on same card– Proprietary protocol between cards
Fast Ethernet
)
FDDI, Fibre channel too complicated, didn’tbecome LAN )
Used as backbones, no widespread success )
Made 802.3 committee think tank (in 1992)
- keep Ethernet, make faster (winner, 802.3u)– make new LAN, call Ethernet (802.12) (loser:flopped!!)
)
Reasons 802.3 won:
- Backwards compatible– New protocol = new unforseen problems– Quicker deployment
Fast Ethernet
)
Change bit time from 100 nsec to 10 nsec
- all must use hubs– shorter “wire-length” to hub– Wiring changes– Mostly copper (10BaseT) (successful)
The original fast Ethernet cabling.
Gigabit Ethernet
(a) A two-station Ethernet. (b) A multistation Ethernet.
)
Two modes:
- Full-duplex– Half-duplex
)
Full duplex used when a switch is used (b) )
No contention since line is FD, so no CSMA/CD
Gigabit Ethernet
)
Half-duplex used when a hub is used instead of aswitch )
Hub cannot buffer packets, switch can )
Collisions are possible so CSMA/CD )
Higher bandwidth means shorter longest distance )
Solutions:
- Carrier extention: stations pad min. frames to 512 bytes– Frame bursting: concatenate multiple outgoing streams
)
Result: extends network radius to 200 meters
IEEE 802.2: Logical Link Control(a) Position of LLC. (b) Protocol formats.
)
So far Ethernet and MAC protocols offer no reliableservice (e.g. stop-and-wait, etc) )
IEEE defined LLC to run above MAC to providethese services )
Closely based on HDLC
Ethernet Retrospective
)
Been around for over 20 years
)
Few technologies make it that long (operatingsystem, architecture, etc)
)
Ethernet
- pros: popular, simple, reliable, flexible, cheap– cons: non-deterministic, no priorities, min frame size