Outlines Received due 13 March 2000

OutlinesReceiveddue13 March 2000 6%

MID-TERM • Wednesday, 1 March • Start studying NOW! • Work 4 of 5 pages • 1-2 pages of the previous midterm will be on the upcoming exam • Anything in the notes and reading assignment is fair game • Equations are provided

Ethernet Performance • Heard that Ethernet Throughput = 4 Mbps?Take it with a grain of salt.Simulations show Heavy Load throughput is a lot larger. • Simulations also show that Average Delay to move a packet at head of queue is small, even under heavy load conditions.

Token Ring Performance • Token Ring Efficiency No Load = 1/(1 + 2*NPD + TranTK/TranPK)Heavy Load = 1/(1 + (N+1)*NPD/N + TranTK/TranPK) = 1/(1 + NPD) (under certain conditions)

Ethernet & Token Ring Efficiency 1.0 0.5 0.0 .01 .10 1.0 10.0 100 NPD

Performance Issues • Slow Speed Network? Both Ethernet & Token Ring work well • Borderline Network? Token Ring offers clearly superior performance • High Speed Network? Both stink. • Token Ring and Ethernet MAC’s don’t scale well to long distances or high speeds

ANSI FDDI • Covers OSI Layers 1 & 2 • 100 Mbps Line Speed • Originally Dual Counter-Rotating Rings • MAC is Timed Token Ring using RAT • Data traffic can only be passed ifTRT < TTRT, and then only for TTRT-TRT seconds • Has Priorities. • MMAT = 2*TTRT

FDDI Performance • FDDI Efficiency No Load = TranPK/(1 + NPD + TranTK/TranPK) Heavy Load = (TTRT - Prop - N*TranTK)/TTRT

FDDI Status • ‘Looked down upon’ in trade pubs • Still an important protocol • Sees more use than is commonly acknowledged • Used mostly as a backbone • Roughly 50-60% corporate networks • Internet NAP’s & MAE’s • Bell Atlantic • New use declining - Glory days are over

Hi Speed LAN’s & MAN’s (Jan 1994) • FDDI

Hi Speed LAN’s & MAN’s (January 2000) • FDDI • ATM • 100 Mbps Ethernet • 100 Mbps Token Ring • 1 Gbps Ethernet Medium Distance Connectivity Short Distance Connectivity

Multiplexing • Splitting a chunk of Bandwidth up into channels • Channel can carry one conversation • FDM, TDM, & StatMux

Different channels use some of the frequency all of the time. FDM frequency 1 2 3 4 5 time

Different channels use all of the frequency some of the time. TDM frequency 1 2 3 time 1 etc.

Different channels use all of the frequency some of the time, at random, as needed. StatMux frequency 1 3 1 time 2

StatMux vs. TDM & FDM • uses bandwidth more efficiently for bursty traffic • requires more overhead • has more variable deliveries • requires more complex & expensive hardware

Switching: How Long will a user get to use a channel? • For the duration of the conversation? Circuit Switching • For a tiny, variable length, portion of the conversation? Packet Switching • Circuit vs. Packet SwitchingCircuit has less end-to-end delayCircuit is less complex & cheaper Packet is more efficient for Bursty Traffic

MULTIPLEXING StatMux TDM FDM common for voice Circuit common for data SWITCHING Packet Cell

Repeater or Hub • Operates at OSI Level 1 • ‘Electric Cable’Traffic arriving at an input is immediately copied to all outputs.

Outlines Received due 13 March 2000

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