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Chapter Intro to Data-Link Layer → intro internet networks glued together a packet passes network to go from a host to another LLC 2.1.) Logical Link Control MAC Phy framing 2.2.) Medium Access Control L control accessability of devices Lif many devices access to at the same time collision signal interference. -Hop = packet is passed from one interconnecting device to onother Nodes & Links L Communication at data-link layer = node-to-node + Hops! Services Point-to-point a. A small part of the Internet Link Point-point Link router network separator L data-link layer provides services for network layer 2 categories of data-link -point-to-point LLE broadcast LLE - 99 b Mat - tv. แบ่งสาย Link-layer addressing -in internet MAC IP DS S D Packet SW -E Frame final destination. router also has N,L L2 L2 Da T₂ H2 frame If cant find dest. in the same network route (change MINT) S= start, D=dest. MAC address (permanent from factory IP address (network) 3 types of addresses send datagram to default gateway devices) unicast 1:1 Laddress destination - multicast 1: some Lo self duplicate to each branch broadcast 1: All Link-layer addresses 2 digit i even multicast odd - unicast 1's every bit -broadcast (F) ex. 43:34:45:11: 92: F1 MAC add. (2) 4 bit 192.168.1.0 IP address (3) 32 bit 3 Hop W -3 network
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LARP protocol used to acquire Layer 2 MAC if already know IP address Process (Request - Response) •broadcast: which node has this IP address, please tell MAC address replu unicast to the node broadcasting know 3.30 2s, find 2p (All as at first) Layer 2 address hardware address Layer address protocol address 0x0001 0x06 0x04 0x0800 0x0001 0x0001 0x0800 0x06 0x04 0x0002 are LD L2 swrce 12source har NI address N2 know L₂ dest. of Request in ARP Dest All Os Dest LI N2 Lo N2 Request Response ARP only in the local network. If no match, router forwards to default gate was to other networks
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Chapter 10 Error Detection & Correction -less found due to the waste of time (mostly found at Layer 4) introduction - types of error L bit errorbit changed. burst error > bit changed -redundancy add extra bits to detect error. L added ky sender & removed by receiver block coding -k-date words -r-redundant bits n-codewords-k+r error detection - just defect! ·ex. if k=2 n-3 so Code words 000 data words-00 dmin minimum hamming distance (between cide words) Hamming distance of ₫ (000,011) = 2 Datawords 00 01 Codewords 000 011 Compare each codewords pair d=s+1 + s = capability of bit MSB Sender Dataword BICIDIO LEB Encoder (000011) Datawords 10 11 Codewords 101 110 →dmin = 2 error detection Generator Unreliable Parity bit transmission 84444 Codeword redundancy Receiver Decoder Dataword XOR XOR 0 0 0 = 0 0 0 1 = 1 100 = 1 18 | - 0 Accept 111 So 0; no error transform back to data word. Syndrome Checker -cyclic codes (type of preferred block code) = codeword is rotated ex. 10110 Cyclic redundancy check used to correct errors Layerz trailer ex. C(7,4) codeword (CRC) r-3 dotoword h = 7 left rotate, 01101 date 0000000 Code Sender Dalawood Receiver Decoder Divison Generator d, d, d, d Checker AAAAAAA Codeword Umeliable transmission bb bbq Codeword for LANS, WANG Codeword O error discard
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checksum error detecting techniques Layer 3,4 not 2 (every hop slow) Concept Lex. a message is a list of five & -bit numbers total must be 16-bit words wrapped sum checksum sum (7, 11, 12,0, 6, 5) → (7,11,12,0,6,9) ↳ (7,11,12, 0,6) + (7,11,12,0,6,36) 36 (100100) but we need 4-bit number 50, (10) + (0100) 2 = (0110) 2 = (6) 10 find the complement of (0110) → (1001) 2-9 Forward Error Correction (FEC) -retransmission of corrupted / lost packets is not useful for real-time multimedia transmission 4 correct error reproduce immediately Use Hemming Distance To detect + errors, we need dmin = 2++1 dmin-2t+1 - 3+1 ++= Correction capability know where the error is & correct it detection capability. = know if there is error ex. If we want to correct to bits in a packet, we need to make the dmin 21 bits d=2+1=2/10)+1=21 bits ไม้ ก น น ZILIZ
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Chapter 11 Data Link Control (DLC) DLC services - DLC = Data Link Control *framing and flow & error Framing date-link laver needs to pack bits into frame stuffins unstuffing bate stuffins and unstuffing Flag Data from upper layer ESC Stuffed Header ESC Flag ESC ESC Trailer Flag Two extra bytes Frame received Fl Header ESC Flag ESC ESC Unstuffed Flag Some bytes has the same pattern Flag t edd ESC in front of that bute count Flag as date for ESC that is date, add ESC in front of ESC the back ESC is date bit stuffing (bit-by-bit instead of byte) Data from upper layer 0001111111001111101000 Stuffed 000111110110011111001000 Frame sent Flag Header Frame received Flag Header 000111110110011111001000 Trailer Flag Two extra Trailer Flag Unstuffed 0001111111001111101000 Data to upper layer flag pattern = 01111110. data: WIN I Manu >5 m² 6th insert o (bit stuffing) Flow and Error control at Data-link layer Hop-to-hop (may also at Layer 4) · Assume 1 buffer slot if the one slot is empty, it sends note to network laver connection Connection less to send the next frame Connection-oriented Date-link Layer Protocols L& protocols for data - link laver to deal w/ flow and error control. L -Simple, Stop-and-wait Simple Protocol no flow & error control Go-back N Selective-repeat the receiver can immediately handle any frame it receives : "ideal" sends frames continuously w/o thinking about the receiver Stop-and-Wait Protocol "sliding windows" wait for an Ack before sending the next one has CRC to detect corrupted frames Packet came from network layer. Make a frame and send it. Frame arrived. Deliver the packet to network layer. Ready Start Ready Sending node Receiving node
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Sending node in case sent frame is error Packet came from network layer. Make a frame, save a copy, and send the frame. Start the timer ACK before timer expired Time-out. Resend the saved frame. Restart the timer. Receiving node Ready Blocking Corrupted frame arrived. Discard the frame. Start Error-free ACK arrived. Stop the timer. Discard the saved frame. Corrupted ACK arrived. Discard the ACK. Ready Start Error-free frame arrived. Extract and deliver the packet to network layer. Send ACK. get frame w/ bit loss discard ACKlet time timeout + sender resend Chapter 12 Media Access Control (MAC) Random access ALOHA medium is shared between stations. Pure ALOHA send whenever want to →hish collision K: Number of attempts T: Maximum propagation time T: Average transmission time T: (Back-off time): RT, or Rx T can be 0,2,4,6 ms R: (Random number): 0 to 2-1 ex. ALOHA network; Lex R +0-2² = (0,1,2,3} = if K-2 -max 600 km apart, propagate rate 3×10 m/6 600 10 - 201 wait 4ms for ACK = 2Tp vulnerable time for pure ALOHA = 2x Tfr hish worse Transmission frame · = period of time u likely to be collided. Station 2 Station3 NAK = frame มีป ACK = can send next frame (sequencely) Corrupt all - in form 0, send +ACK 1 back send ACK back duration ion time xT, or Rx T : 0 to 2K-1 Wait TB Station has a frame to send K-0 Send the frame Choose R random avoid collision Wait (2x T₂) ไป. บ K>K |false] next transmission (K-K+1) ACK received? attempts attempt(true] or not [false] [true] Abort Success if other stations start send its message | Ter before / during the current one collide ex. ALOHA network; transmits 200-bit frames on a shared channel of 200 kbps Find throughput it system produces 1000/500/250 frames/sec Sol unit, conversion B-How many frames are generated during 1 Ter Ter = frame transmission time = 200/200 kbps = 1ms - during 1 ms, have I frame 2000; If system creates 1000 frames/s frame/ms frame -26 46-1 S-throughput of pure ALOHA = 6xe = 0.135 13.5% Throughput = 0.135 (1000) = 135 510; If system creates 500 frames/s = 1.5 frames/ms ↳ G = 0.5 +5 = x -2 = 18.4% → Throughput = 0.184 × 500 - 92 frames survive slotted ALOHA CSMA - send only at the start of timeslot vulnerable time for slotted ALOHA = Ter. ex. ALOHA network; transmits 200-bit frames on a shared channel of 200 kbps. Find throughput if system produces. 1000/500/250 frames/sec Sol" Ter=200/200 kbps - 1ms 1000; S- Gxe = 0.368 - 0.368 7000 368 bits survive listen if busy back off collide when B starts transmit but before B reaches C, C starts transmit too since line is not busy at that time Tp Vulnerable time -
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3 persistence methods = behaviors in listening to channels 1-persistent transmit immediately once silent Transmit Continuously sense Busy Time Nonpersitent =transmit immediately if randomly sense silent P-persistent transmit if RCP. types A start sending B here ONLY C senses bere D senses here - Time Sandif R Sendif R&P p = certain prob. value R = random # + ·CSMA/CD collision detection. if collision is detected back off immediately listen again. CD is enabled only the time u transmit B Frame propagation Time Transmission Fint bit of A First bit of C Transmission # of bite C transmit = (t₂-t₂) = R time A's collision detection C's collision detection and bortion of C ration of message - ↓ and abortion Time Collision occurs frame length Time when 1st bit of A is here, C just know that line is busy find min size of frame = ? → stop sending ·ex. bandwidth = 10 Mbps max propagation time 25.6 MS, Sol" Tex = 2xTp AD LA sends 1. -51.2 MS min size frame 10 Mbps 51.2 MS = 512 bits ☐ B Baches T collide happens but 4 & 8 doesn't know since it does not collide in front of A/B station A detects collision A is still sending until at to to be able to delect collision detect collision rend jamming signal to all in the same collision domain all stop & listen again CSMA/CA : avoid collision before it happens · for wireless network (cont listen) RTS - send CTS to al→ some NAV, source send date to dest→ dest. ACK → cancel NAV Controlled Access = stations consult nu in which station will send Reservation method reserve before send date. # time slot # users Polling method stations/secondary devices has primary station, asking who wants to send / ready to receive Select and poll functions -select: SEL dest. station → dest. ACK in ready to receive send date → ACK back Poll: Poll A if A wants to transmit NAK ( doesn't want to) Token Passing Poll BB sends data 1° ACK L = assign sequence of sending by arab token → the station wants to send or not release token Vulnerable time propagation time
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Baseband (digital) Changes in Standard Sharing Bandwidth take turn to transmit dato bridging he bridging -collision domain lo Mbps share BW w/ 12 users collision domain 6+1 share 10 Mbps Bridge Fusers for 10 Mbps b. With bridging +1i/p of bridae (in case crossing bridge to the other user) Bridge 2-port switch. Switched Ethernet Domain 3 pairs of 10 Mbps Fast Ethernet (100 Mbps) MAC sublayer unchanged, but features changed Access Method Lex. If min frame size = 512 bits + transmit Gigabit Ethernet (1000 Mbps) MAC sublayer unchanged, full-duplex 10-Gigabit Ethernet All fiber 100 = commin = 30 Mbps Backplane capacity - Total capability. = better ! of switch Chapter 15 Wireless LANS LAN owned by s.o. ex. company (only private area) MAN, WAN - owned by telecom operator can be placed in public area BAND Licensed band : คลื่นประมูล Unlicensed band: ec microwave Introduction wireless LANG Architectural Comparison L Wired LAN Access point Infrastructure network router gateway to other places Wired wireless that can connect to other networks Infrastructur ค 8 8 8 8 bus (share airspace medium) Access Control L CSMA/CD not work since wireless hosts do not have enough power to full-duplex (antenna) hidden station Pb. prevents collision detection Range of B Range of C Great distance between stations IEEE 102.11 Project Ad hoc network Host Host Host Wireless No access point communicate directly to others. =Ad hoc wired: CD (Collision detection) B&C not in each other's range solved by ATS, CTS! wireless: CA (collision avoidance) 4 สางลง พร้อม - A confused IEEE 802.11 project
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must also be certified by Wifi alliance wireless Ethernet - Wifi = organization define standards in Laver 1 & 2 for wireless LAN Architecture 2 kinds of services BSS (basic service set) -Infrastructure BSS Ad hoc BSS No AP : 1 Access Point connect to users All users that can communicate among them - same BSS ESS (extended) L router connects BSSs together (+AP) - MAC sublayer 2 MAC sublayers Distributed coordination function (DCF) L CSMA/CA and NAV interframe space L CA by if small pause after channel before next sending -SIFS short ifs before every sending Source DIFS Destination Argot to and det RTS Clear To send CTS DIFS Time SIFS CTS Data NAV idle mode SIFS ACK ACK end session Time Time Time LLC 802.1 (wired & wireless) Date-link PCF MAC DCF Physical 802.11 CTS Clear to send = broadcasted by destination but others addressed (not specified in CTG header) becomes idle (NAV) ACK broadcasted by dest. to stop NAV ·Pointed coordination function (PCF) ex. repetition interval Polled station Others API PIES SIFS B Poll Repetition interval PCF DCF PCF is optional mode Contention-free SIS, repeat (send time sensitive date) only infrastructure mode (AP) SIFS Time Legend want to send ACK answer data B: Beacon frame CF: Contention-free Time AP: Access point NAV: No carrier sensing NAV 6-start contention- free period Poll broadcast to users if any user wants to send -Addressing Mechanism 00 01 Host Host AP destination (Ad Hoc) AP wired Host Host Host 10 source + AP 11 AP. - AP₂ Exposed station Problem Lex. A wants to talk to B A sends RTS (want to send to 8) I BAC D
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C wants to talk to D B sends CT6 C becomes NAV 1 B.C in the distance of A I cant send date to D bluetooth (802.11 in general purposes) = connect between devices (Ad hoc) Architecture Piconet mobile earbuds -2° scatternet both in device ✓ Chapter 17 Connecting Devices and Virtual LANS Connecting devices Hubs (Cayer 1) Discarded Maintained Discarded LAN for hub/switch t If dest. matches maintain Application Transport Network Data-link Physical Application Transport Network Link-layer switches Data-link Hub Physical A sent data to Hub + broadcast date to All others discard it physically star operationally bus -Link-layer switches (Laver 2) forward data to dest. only address 71: 28: 13:45: 61:1 L₁ num4bits bin ARP Protocol -broadcast to ask whose IP address it this send me MAC address (unicast) Store MAC address + its port in switching table Next time, look on the table to send data correctly. Loop Problem Lex. LANI AM P LAN 2 Switches D A sends frame to D A broadcasts to connected devices switches create table: A ports ARP protocol find D's port from its IP address ↳ got reply MAC address from port 2 + D1 port 2 Next time, if A sends data to D, D will get 2 frames. from 2 switches Loop Pb. To solve Loop problem: Minimum Spanning Tree protocol (MST) - choose active/inactive LAN |
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