Layer 1 Networking 5/21/2015 Warner Link on last slide

1. Layer 1 Networking 5/21/2015 Warner Link on last slide

3. Example – 56K modem

4. Telephone system • Central office digitizes voice w 8 bit codec • 2⁸ = 256 discrete amplitude values • Quantization leads to power S/N = 65536:1 • ln(S/N) = 16

5. Modem speed • CODEC sample rate 8000/sec • Filter limits frequency response to 3.5 KHz • So C = 3500 * 16 = 56K

7. We want to use cheap media along with fancy electronics to get the best performance possible. Communications integrated circuits are ultimately printed at low incremental cost while expensive wire has a cost per foot. Overall theme

8. ADSL • Asymmetrical Digital Subscriber Loop • Works like dial-up, except... • BW is greater – 2 Mb/s versus 3.5 Kb/s • BW falls with CO distance • Performance is noise-limited by crosstalk rather than quantization

9. Crosstalk • Each signal path is a pair of wires twisted together • Many pairs are bundled together into a cable • Individual pairs act like transformers and couple energy into each other • Higher frequencies have more crosstalk

10. ADSL distance

11. Yet higher speeds . . . • ADSL2 is not the end of the road • VDSL up to 52 Mb/s but distance 300 M • At that scale, useful for large buildings

12. 10base5 Yellow cable Ethernet

13. 10 and 100 Mb/s Ethernet permits repeaters subject to a rule that information about collisions needs to propagate to all stations in the time required to send a minimum length packet. This is required to guarantee that all stations will detect a collision while the sender is still transmitting. Four repeaters in the longest path across the network are permitted in 10 Mb/s systems. Repeaters

14. Repeaters • Regenerate the amplitude of signals that may have attenuated over distance • Re-time signal transitions to remove accumulated jitter • Replace lost preamble bits at the front of each packet

15. 10base2 Thinnet

16. Structured cabling • 10base5 and 10base2 have a daisy chain architecture • Generally, this leads to a mess • To be supportable, all communications paths should connect radially to a serving cable closet. • 100 meter link distance was selected as a workable but somewhat arbitrary standard.

17. Thin repeater

18. 10 base T • 802.3i-1990 • Uses 8P8C connector a.k.a. RJ-45 • 100 meter cat 3 cable • Uses two pairs: one transmit, one receive

19. Line code: a digression • This code is called NRZ • A “1” is a positive voltage • A “0” is a negative voltage

20. NRZ = Non Return to Zero • How does the receiver find the bit cell boundaries? • Long runs of all 0s or 1s have no transitions • Early answer: send bit clock on a spare wire pair • Not a great answer. . .

21. Manchester coding • Direction of transition determines value • Lots of transitions for clock recovery • No DC content

22. Twisted pair Ethernet • Signals are driven differentially over their respective pairs. • Because each pair is twisted together external fields excite the same noise in both of the pair conductors. • Receivers reject common mode signals, providing low cost noise immunity. • 10 Mb/s tw-pr uses manchester code

23. Category 3 & 5e

24. Category. . . • Anixter, an electrical distributor, cooked up the category classification to solve what they saw as major marketplace confusion among customers who just wanted to know what to buy. • The EIA/TIA fell into line behind Anixter and helped with the classification. • The IEEE generally does not bother with things like this.

25. 100 Mb/s tw-pr Ethernet • 802.3u-1995 • 100 meters over category 5 wire • 4B/5B encoding • MLT-3 line code results in 31.25 Khz • Max one repeater in a collision domain • Uses two pairs, same as 10 base T

26. There are 32 different codes that are five bits long. The 16 values that can be taken on by 4-bit nibbles are selected from the 32 5-bit possibilities so that codes are rich in 1's content. This coding guarantees a transition density sufficient for the clock to be extracted from the data stream. The cost to make the stream self-clocking is 25 percent. 4B/5B, what is that??

27. Category 3 vs 5 • Category 5 wire has tighter twisting so to rejects noise to higher frequencies. • Each pair has a different pitch to its twist. This reduces pair-to-pair coupling. • Category 3 wire can have PVC insulation. PVC has poor frequency characteristics caused by dielectric loss. Cat 5 wire uses better insulation that gives lower loss.

28. Category 5 vs 5e ?? • The “e” stands for enhanced. • Not much difference. It is the same stuff made the same way. • Category 5e has some additional tests to assure it can be used bi-directionally. • Category 5 has disappeared from the market.

29. Gigabit over fiber • 802.3z 1998 • There are no repeaters. • All links are point-to-point • Short range (SR) to 100 meters uses multimode fiber at 850 nM (deep red) • Long range (LR) uses single mode fiber at 1300 nM. Distance limit is 0-10 KM.

30. Multimode – Single mode

31. Why did they do that ? • The 9 micron core in SM fiber requires a very intense light source. Lasers are needed. $$$$ • A larger core diameter permits a cheaper light source. $$$$ Favors multimode. • Graded index MM fiber shapes the refractive index profile so that the rays that travel farther go faster. This partially compensates for the effect on speed.

32. Fiber bandwidth • Single mode: 10's of terabit/sec per core. Limitation is non-linear effects like heating that are hard to quantify. • Multimode: OM3 – a type of 50 micron multimode – has 2000 MHz-km • At 1 KM, the BW is 2 GHz • At 100 M, the BW is 20 GHz

33. Gigabit over twisted pair • 1000baseT IEEE802.3ab 1999 • Designed for same wire as 100 Mb/s • Uses all 4 pairs in both directions • 4x improvement in capacity • Each byte sprays across all four pairs • 5 level PAM5 code replaces 3 level code • Symbol rate is the same as 100 Mb/s, but cleaner transmission is required for PAM5

34. What happened to Cat 6 ? • Category 6 tests the wire to 250 MHz and has tighter parameters than 5e. It is not sufficient for 10 Gig-E. • All dressed up with no place to go – Cat 6 wire was designed for a 2-pair Gig-E standard that was a commercial failure. The incremental cost of Category 6 wire has earned it some popularity since it is better than 5e and backward compatible.

35. OPTICAL TRANSPORT

36. Glass

37. MSA Modules

38. 10 Gigabit/s over twisted pair • 10GbaseT IEEE 802.3an 2006 • Requires category 6a cable to reach 100 m • Uses PAM16 for more bits per symbol • Full duplex operation only • Uses BW to 450 MHz • Thruput: 4 pr x 833 Mbaud x 3 bits/symbol

39. 10G Warts • Alien crosstalk – signals from nearby cables induce noise too complex to be compensated electronically • Aliens require shielding that makes the cable bigger and heavier • Power consumption is high, making for high operating costs. This will come down. • Direct connect is cheaper and faster.

40. 10 Gb/s applications • Data center, when power consumption improves • Wave 2 802.11ac WiFi access points

41. What about WiFi?

42. 20, 40, 80 MHz 20 dB = 100:1 OFDM From 1 bit per Hz to 8 bits per Hz MIMO WiFi • Channel Bandwidth • Signal to Noise • Modulation • Line codes • Stream count

43. Http://noc.ucsc.edu/docs/Layer-1.pdf