1. CSS 4321 CSS432 Shared Access Networks Textbook Ch2.6, 2.7, and 2.1.1 Professor: Munehiro Fukuda

2. CSS 4322 Ethernet Overview History  Developed by Xerox PARC in mid-1970s  Similar to IEEE 802.3 standard CSMA/CD  Carrier sense multiple access with collision detection Frame Format MAC (Media Access Control) Addresses  unique, 48-bit unicast address assigned to each adapter  example: 8:0:e4:b1:2  broadcast: all 1 s  multicast: first bit is 1 Bandwidth: 10Mbps (10Base2=Thin Coax 200m, 10B5=Yellow Thick Coax 500m, 10BT=Twisted pair 100m), 100Mbps(10BaseT), 1Gbps Length: 2500m (500m segments with 4 repeaters) Dest addr 644832 CRCPreamble Src addr TypeBody 1648

3. CSS 4323 Ethernet Transmit Algorithm If line is idle…  Send immediately  Upper bound message size of 1500 bytes: MTU (Maximum Transmission Unit)  Must wait 9.6us between back-to-back frames Why? (See the next slide.) If line is busy…  Wait until idle and transmit immediately  Called 1-persistent Transmit a packet with probability 1. (special case of p-persistent: transmitting a packet with P percent, where 0 < p ≤ 1)

4. CSS 4324 Transmit Algorithm (cont) If collision…  Send a 32-bit jamming sequent, and then stop transmitting frame (64bit preamble + 32bit jam = 96bit)  Minimum frame is 64 bytes (header + 46 bytes of data) Why? (See the next slide.)  Delay and try again 1st time: 0 or 51.2us 2nd time: 0, 51.2, or 102.4us 3rd time51.2, 102.4, or 153.6us nth time: k x 51.2us, for randomly selected k=0..2 n - 1 give up after several tries (usually 16) exponential backoff

5. CSS 4325 Collisions AB AB AB AB 500m x 5 = 2500m (with 4 repeaters) A collision occurred Time t Time t + d (d = 25.6us) Time t + 2d (2d = 51.2us) Jam seq 10Mbps x 51.2us = 10 x 10 6 x 51.2 x 10 -6 = 512bits = (64bytes)

6. CSS 4326 Token Ring Overview Examples  16Mbps IEEE 802.5 (based on earlier IBM ring)  100Mbps Fiber Distributed Data Interface (FDDI) Idea  Frames flow in one direction: upstream to downstream  Special bit pattern (token) rotates around ring  Must capture token before transmitting  Release token after done transmitting Immediate release: FDDI Delayed release (after a sent frame came back) IEE802.5  Remove your frame when it comes back around  Stations get round-robin service Frame Format Control 888 24 CRC Start of frame End of frame Dest addr Body 48 Src addr Status 32 Priority bits

7. CSS 4327 Timed Token Algorithm: IEEE802.5 Token Holding Time (THT)  Upper limit on how long a station can hold the token: 10ms Token Rotation Time (TRT)  How long it takes the token to traverse the ring.  TRT <= ActiveNodes x THT + RingLatency Target Token Rotation Time (TTRT)  Agreed-upon upper bound on TRT Each node measures TRT between successive tokens  if measured-TRT > TTRT: token is late so don’t send  if measured-TRT < TTRT: token is early so OK to send Worse case: 2xTTRT between seeing token

8. CSS 4328 Timed Token Algorithm: FDDI Two transfer modes  Synchronous traffic Real time traffic: voice data Can always send must be bounded by TTRT Time to send: Ts = (TTRT – RingLatency)/Nodes  Asynchronous traffic High throughput: bulk data Can send only if token is early TRT = time since last token If TRT > TTRT  Token is late  Send synchronous data for Ts  Don’t send asynchronous data If TRT < TTRT  Token is early  Send synchronous data for Ts  THT = TTRT - TRT  Send asynchronous data for THT

9. CSS 4329 Token Maintenance Lost Token  No node emits a token when initializing ring.  A bit error corrupts token pattern.  A node holding token crashes. Lost Token Detection  IBM Token Ring: No more presence message from a monitor station  FDDI: No more message for more than 2.5ms

10. CSS 43210 Monitor Station Election Procedure  A station transmits a claim token with its MAC address if doubting the existence of a monitor station.  The highest address wins.  FDDI: the largest TTRT wins. Token Generation  Wait for NumStations x THT + RingLatency  Generate a new token Corrupted/orphaned frame removal  Frame status A bit: the destination station started to receive it C bit: the frame was accepted.

11. CSS 43211 Network Adapters CPU Memory I/O bus Controller Bus Interface Link Interface FIFO DMA Network Processor memory Interrupt System Bus PCI Bus Network Link Host Computer Network Interface Card (NIC) Programmed I/O 32bit, 33MHz = 1056Mbps 633Mbps STS-12 1000Mbps Ehternet

12. CSS 43212 Network Adapters (Cont’d) Network Processor  Intel IXP series Intel IXP series  Myrinet Lanai series Myrinet Lanai series  FPGA FPGA Scatter-read/Gather write  writev( ) and readv( ) system calls ssize_t readv( int fd, const struct iovec *iov, int iovcnt ) ssize_t writev( int fd, const struct iovec *iov, int iovcnt ) struct iovec {  void *iov_base;  Size_t iov_len; }; 100 1400 1500 Memory buffersBuffer descriptor list

13. CSS 43213 Memory Bottleneck PCI(33bit, 33MHz) = 1056Mbps System Bus = 235MBps = 1880Mbps (Text example) > real throughput  Memory Bus Controller Arbitration among CPU and DMA DRAM setup time  Data copy: Application memory space to OS OS memory space to NIC DMA-manageable space Zero copy/pin-downed communication  Bypassing OS Reducing memory-copying overhead Reducing interrupts Application DMA-manageable memory OS

14. CSS 43214 Reviews  Ethernet: k-persistent, exponential back off, and the relationship between the minimum frame size and collisions.  Token ring network: immediate/delayed release, THT, TRT, and TTRT  Network adapters: writev/readv and memory bottleneck Exercises in Chapter 2  Ex. 43 (Ethernet)  Ex. 47 (Ethernet)  Ex. 57 (Token ring)  Ex. 59-(a) only (Token ring). Instead, solve p15.

15. CSS 43215 Consider FDDI’s timed token algorithm with the following parameters: Token: immediate release #hosts = 3 Ring latency = 6μs (i.e, 2μs to pass a token from one to another host) Ts (Time for sending synchronous data) = 20μs TTRT (Target token rotation time) = 100μs Let’s assume that none of those three hosts sends any data in the first token rotation, however all of them maximize their opportunity of sending data from the second rotation. In other words, each host sends its synchronous data per every token rotation as well as asynchronous data “if allowed”. Fill out the following blanks by keeping track of the first three token rotations. RotationHost 1Host 2Host 3 1stArrival time 024 TRT000 Sync000 Async000 2ndArrival time 6122124 TRT6100120 Sync20 Async9400 3rdArrival time 146168224 TRT14066100 Sync20 Async0340