Outlines Received due 13 March %

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

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

Token Ring Performance n 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 NPD

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

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

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

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

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

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

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

FDM frequency time Different channels use some of the frequency all of the time

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

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

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

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

StatMuxTDMFDM Circuit Packet Cell MULTIPLEXING SWITCHING common for voice common for data

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