TRANSPORT LAYER

Part II: LAN Technologies and Internetworking

• LAN Technologies
– Switching
– Ethernet
– Token Ring and Fiber Channel
• Multi Protocol Label Switching
– Evolution
– Architecture
– Impacts on Network Management




© 2000 B. Stiller, B. Plattner ETHZ-TIK, D. Bauer IBM Research CM II – 1 ETH Zürich




LAN Technologies

IEEE 802.3 Carrier Sense Multiple Access with
Collision Detection (CSMA/CD), also known as the
Ethernet:
• 10 Mbit/s transmission speed and
• Bus topology (shared medium).

IEEE 802.5 Token Ring:
• 4 Mbit/s and 16 Mbit/s versions and
• Ring topology (shared medium).

Distributed Medium Access Control Algorithm.

Universal cabling systems with star topology are
suitable for both LANs (unshielded and shielded
twisted pair).
© 2000 B. Stiller, B. Plattner ETHZ-TIK, D. Bauer IBM Research CM II – 2 ETH Zürich

, IEEE 802 LAN Standards

802.1: LAN/MAN Bridging & 802.9 Integrated Services /
Management (.1p, .1q) Isochronous LAN*
802.2 Logical Link Control* 802.10: LAN/MAN Security*
802.3 CSMA/CD Access Method 802.11: Wireless LAN
(.3z, .3ab) 802.12: Demand Priority Access
Method*
802.4 Token-Passing Bus* Access
802.13 n/a (!)
Method
802.14: Cable Modems

802.5 Token Ring Access
802.15: Wireless Personal Area
Method*
Networks
802.6 DQDB Access Method* 802.16: Broadband Wireless
802.7 Broadband* Access
802.8 Fiber Optic
802.17: Resilient Packet Rings
(study group)

*: inactive;
:disbanded
© 2000 B. Stiller, B. Plattner ETHZ-TIK, D. Bauer IBM Research CM II – 3 ETH Zürich




CSMA/CD Medium Access Algorithm

A B location
Ort
Maximum throughput is
A’s frame B’s frame
Frame
roughly indirectly Frame
von A von B
proportional to β: A detects BBdetektiert
detects
A detektiert
collision. Kollision
collision.
Kollision
β = τ /m = (τ ∗ C) / L A sendet Kollision ist allen
All stations
Stationen
B sendet
BSperrsignal
sents
A sents
Sperrsignal know about the
jam signal.
bekannt.
collision. A and jam signal.
A und B warten je
τ: Propagation delay [s] B back-up for
eine zufällige
a randomized
Dauer
m: Frame length [s] period of time.

L: Frame length [bit] B wiederholt
B retransmits
Frame
C: Transmission rate [bit/s] A recognizes
A sieht the frame.
besetztes
busy medium.
Medium
For good performance, β
should be <= 0.01.
time

© 2000 B. Stiller, B. Plattner ETHZ-TIK, D. Bauer IBM Research CM II – 4 ETH Zürich

, CSMA/CD Frame Format

7 1 2 (6) 2 (6) 2 0...1500 ≤46 4 Byte
Preamble SFD DA SA Length Payload PAD FCS




Preamble: Bit synchronization
SFD: Byte synchronization
DA: Destination address
SA: Source address
Length: Length of payload
Payload: Upper layer frame
PAD: To fill up a short frame
FCS: 32-Bit CRC for error detection


© 2000 B. Stiller, B. Plattner ETHZ-TIK, D. Bauer IBM Research CM II – 5 ETH Zürich




Switching (1)


Hubs vs. Switches:
• Similar locations in networks.
• Hubs repeat all packets while switches examine all of them.
• Switches require address examination and forwarding.
– Store-and-forward: Analyze the entire packet.
– Cut-through: Only examine destination and forward.
– Blocking vs. non-blocking architectures.
– Buffering: backpressure or large buffers.
BCDE BCDE


A Hub F A Switch F
to E to E
© 2000 B. Stiller, B. Plattner ETHZ-TIK, D. Bauer IBM Research CM II – 6 ETH Zürich