Chi-Cheng Lin, Winona State University CS 313 Introduction to Computer Networking & Telecommunication Local Area Networks

2 Topics l Ethernet l Data Link Layer Switching

and Ethernet l  1-Persistent CSMA/CD LAN, Mbps l Ethernet  A specific product that almost implements 802.3

Classic Ethernet Physical Layer Architecture of classic Ethernet

Classic MAC Sublayer Protocol l Frame formats.  (a) DIX Ethernet, (b) IEEE l Preamble: for synchronization l Start of frame:

6 Ethernet MAC Sublayer Protocol l Addresses  Ethernet uses 6 bytes  Support  Unicast: address begins with 0  Multicasting: 1 + group number  Broadcasting: all 1’s

Classic MAC Sublayer Protocol Collision detection can take as long as 2 .

8 Ethernet MAC Sublayer Protocol l Minimum frame size: 64 bytes  Why? frame_size bits/channel_capacity bps > 2  s In 10-Mbps Ethernet, 2  = 50  s, therefore frame_size > 50  s x 10 Mbps = 500 bits, rounded up to 512 bits = 64 bytes

9 Binary Exponential Backoff Algorithm l Wait time t time slots after a collision  t = a random number between 0 and 2 i - 1 after i collisions  t = 1023, for i = 10,...,16  when i > 16, reset i = 0 l Low delay for light load l Reasonable delay for high load

Switched Ethernet (a) Hub. (b) Switch. Collision Domain?

Switched Ethernet An Ethernet switch. Switch Twisted pair Switch ports Hub

Fast Ethernet The original fast Ethernet cabling. Xbase-Y Channel capacity Cable type

Gigabit Ethernet A two-station Ethernet

Gigabit Ethernet A multistation Ethernet

Gigabit Ethernet Gigabit Ethernet cabling.

10 Gigabit Ethernet 10-Gigabit Ethernet cabling

17 Retrospective on Ethernet l Has been 20+ years l Simple and flexible  Reliable  Cheap  Easy to maintain l Works easily with TCP/IP  Both IP and Ethernet are connectionless l Evolution – no software change required  Speed: higher and higher  Hubs, switches

Data Link Layer Switching Uses of bridges Learning bridges Spanning tree bridges Repeaters, hubs, bridges, switches, routers, and gateways

Learning Bridges Bridge connecting two multidrop LANs

Learning Bridges Bridges (and a hub) connecting seven point-to- point stations.

21 Learning Bridges l Transparency  Plug and play l Operates in Promiscuous Mode  Accepting every frame transmitted on all LANs to which it is attached l Decides  Discard or forward  If forward, to which LAN?  Look up a huge destination address hash table

22 Learning Bridges l Hash Table  Initially empty  Flooding algorithm  Backward learning algorithm  Arrival time noted for dynamic topology  Scanned periodically to remove old entries l Routing procedure for an incoming frame  If dest LAN = src LAN then discard  If dest LAN != src LAN then forward  If dest LAN unknown then use flooding

Learning Bridges Protocol processing at a bridge.

Spanning Tree Bridges l To increase reliability  Two or more bridges between 2 LANs l Problem: looping Bridges with two parallel links

Spanning Tree Bridges (2) A spanning tree connecting five bridges. The dotted lines are links that are not part of the spanning tree.

Repeaters, Hubs, Bridges, Switches, Routers, and Gateways (a) Which device is in which layer. (b) Frames, packets, and headers. Discussions: Collision domain? Plug-and-play?