MTU UP! Marek Hajduczenia, PhD.

Transcription

1 MTU UP! Marek Hajduczenia, PhD

2 MTU in EPON (1) When 1G-EPON standard was first published, supprted MTU up t 1500B. Life was simple added differentiatin fr basic frames, Q-tagged frames, and envelpe frames. Operatrs mved t require supprt f envelpe frames in EPON. Excerpt frm ,

3 MTU in EPON (2) A large share f existing 1G-EPON implementatins supprt up t 2kB MTU tday, allwing t transprt Ethernet frames with paylad larger than 1500 bytes. Similarly, all existing 10G-EPON implementatins supprt 2kB MTU. All f 10G (and abve) P2P interfaces n ruters, switches, etc. deplyed tday supprt at least 9kB MTU. A grwing class f applicatins puts increased MTU requirements n peratrs, demanding 4kB and 9kB MTU supprt in the access space. Transitin t larger MTU in P2P links is relatively simple, given that nly tw link peers are invlved. In EPON, situatin is nt that simple, especially in burst-mde upstream directin. 2

4 MTU Drivers Tday, there are three majr applicatins driving MTU demand twards 4/9kB: cellular backhaul (driven by prtcls, such as CPRI, etc), business custmers running distributed strage / clud applicatins between remte sites (driven by end applicatin), custmer demand (n specific technical reasn, apart frm the perceived need fr larger MTU and better link efficiency) In these cases, mving twards larger frames imprves link utilizatin and minimizes Ethernet tax (framing verhead). 3 Tday, an peratr typically sets ff the Ethernet tax by increasing the prvisined service rate by certain fixed amunt. This wrks fr mst applicatins, especially when IP hsts are invlved and surce data can be fragmented withut any prblems. In cellular backhaul r distributed strage, surce hsts may require specific frame size abve 2kB and fragmentatin wuld require additinal NIDs t be placed befre access equipment, driving cst and cmplexity

5 MTU Slutin The MTU quandary has tw pssible slutins: a) Supprt fragmentatin between the ONU and the OLT; OR b) Increase the MTU size, supprting larger Ethernet frame sizes. Individual ptins are discussed in the fllwing tw slides In the scpe f NG-EPON effrt, it is recmmended that the supprt fr MTU >2kB becmes ne f the fficial requirements t supprt existing and future applicatins, driving MTU size up. Withut ability t carry larger MTU ver NG-EPON, sme applicatins will have t be migrated int CWDM P2P links, taking away a large share f ptential NG-EPON market. 4

6 MTU Slutin (a): Fragmentatin P802.3br (IET) Task Frce is currently wrking t define extended MAC architecture t supprt interspersing express traffic. It will als add framewrk fr MAC frame fragmentatin. The same framewrk culd be reused in NG-EPON fr packet fragmentatin: large incming frames wuld be fragmented int 2kB chunks, transmitted t OLT and reassembled. The drawback f this slutin is the increased jitter, delay, and increased cst f resulting equipment due t fragmentatin / reassembly at high data rates. Further analysis f this slutin, its impact n jitter budget in NG-EPON, limitatins, transmissin verhead, etc. wuld be required when NG-EPON becmes a Task Frce. 5

7 MTU Slutin (b): increase MTU Alternatively, the size f Ethernet frame culd be again increased beynd 2kB envelpe frames. Since the last time this tpic was discussed, line rates increased frm 10 Gb/s t 100 Gb/s and beynd (400 Gb/s is under active develpment). With a fixed maximum frame size, frame rates increase linearly with the increase in the data rate. If MTU is increased t 9kB, the peratr is respnsible fr making sure that all devices supprt this MTU and then cnfigure them accrdingly. Legacy devices wuld nt be expected t supprt such frames (n need t slve the legacy-equipment-in-the-middle type f prblems that IEEE usually has t deal with) 6

8 7 THANKS!