What types of network technologies are there

Network Technologies II


1 Network Technologies II 1. Ethernet Switching 1.1 Spanning Tree 1.2 Virtual LANs 1.3 Prioritization 2. Wireless networks 2.1 WLAN media access methods 2.3 Bluetooth WIMAX 1 Prof. Dr. Thomas Schmidt

2 About the content In this chapter we address two advanced, widespread areas of network technologies: Ethernet switching and wireless LANs. You will get to know the most important features of switch processing such as redundancy and segmentation, as well as the core problems and technologies of WLANs. The corresponding chapter in Tanenbaum is 4. We also recommend Jochen Schiller: Mobilkommunikation. 2nd edition, Pearson Studies, Prof. Dr. Thomas Schmidt

3 1. Ethernet switching switches convey which intelligence is required on L2? Ethernet is based on redundancy-free topologies, failover functionalities to increase operational reliability. Switching is faster than routing, but it is broadcast-transparent. Segmentation to ward off broadcast storms. Physical separation of participants is expensive. Virtual segmentation on a cable / in a domain. Real-time traffic requests / QoS. Prioritization on Layer 2. 3 Prof. Dr. Thomas Schmidt

4 1.1 Redundancy paths: Spanning Tree (802.1D) Problem: Redundantly interconnected switches generate forwarder loops. Solution: Dynamic spanning trees 1. Root finding: Smallest switch serial number 2. Path structure: From every network on the shortest route to the root. Bridges stand by. 3. Loop: Find paths to discover changes. o Spanning Tree very slowly improvement: Fast Spanning Tree 4 Prof. Dr. Thomas Schmidt

5 1.2 Virtual LANs (VLAN) VLANs define virtual network boundaries that are routed against each other. Three approaches are obvious: o Port Based VLAN: A unicast or broadcast packet is received on a port with ID = x and only forwarded to ports with the same ID. o MAC Address Based VLAN: The VLAN membership of a packet is identified by the source or destination address. Switches keep a membership table. o Protocol (L3) Based VLAN: The membership of a packet in a VLAN is determined by the Layer 3 protocol (IP, IPX, Netbios) and the L3 network affiliation. 5 Prof. Dr. Thomas Schmidt

6 Q Port Based VLAN Each host group (VLAN) receives an ID Packets are only forwarded within a VLAN. Each switch port belongs to at least one ID. Each host belongs to exactly one VLAN. Frames are tagged for cross-switch validity. Tagging by NIC or Ingress Port Default VLAN (ID = 1) 1D Trunk: Forward all tag-free frames 1Q Trunk: Forward all tag-bearing frames Filtering database for higher-order functions 6 Prof. Dr. Thomas Schmidt

7 Q / p - Tagging Tag Protocol Identifier = 0x8100 Canonical Format Identifier Priority Tagging for 802.1p VLAN ID: 802.1Q assignment 7 Prof. Dr. Thomas Schmidt

8 Practical example: VLAN topology 8 Prof. Dr. Thomas Schmidt

9 1.2 VLAN configuration VLANs must be configured separately on each switch and ports must be assigned. This can be done manually (CLI, Web) or with the manufacturer's VLAN management tools. Automatic distribution of VLAN information through Generic Attribute Registration Protocol (GARP) / the VLAN extension GARP VLAN Registration Protocol (GVRP). Likewise: Proprietary manufacturer protocols such as Cisco Virtual Trunking Protocol (VTP). 9 Prof. Dr. Thomas Schmidt

10 p Prioritization Priority classes are mapped to switching queues. Port-based priority: Packets received through a high-priority port are treated as a high priority frame p / Q VLAN Priority tag: If tagging is used, the priority bit is extracted and compared with threshold value 3. The priority values ​​0 3 count as low, the values ​​4 7 as high priority. 10 Prof. Dr. Thomas Schmidt

11 2. Wireless networks We experience wireless communication networks everywhere: lighthouses, Morse codes, bush drums, opt. Telegraphs, remote controls on home devices Satellite communication Cell phones: A / B / C / D / E networks, Dect, 3G (UMTS) Radio networks: Directional radio, WLAN, Hiperlan, Bluetooth Optical transmissions: Infrared (links, IrDA), laser links The technologies of wireless networks are particularly pronounced by the medium of air regulation the mobility paradigm The presentations in this chapter follow in part the materials from J. Schiller, FU Berlin 11 Prof. Dr. Thomas Schmidt

12 2. Wireless access points 12 Prof. Dr. Thomas Schmidt

13 2. Reference model Application Application Transport Transport network network network network backup backup backup backup bit transfer bit transfer bit transfer bit transfer radio medium 13 Prof. Dr. Thomas Schmidt

14 2. Modulation and demodulation analog baseband signal digital data digital analog modulation modulation transmitter carrier frequency analog demodulation analog baseband signal synchronization decision digital data receiver carrier frequency Sinusoidal carrier oscillation as a special periodic signal: s (t) = A t sin (2 π ftt + ϕ t) 14 Prof. Dr. Thomas Schmidt

15 2. Signal propagation Propagation in free space basically straight-line (like light) Received power decreases with 1 / d² (d = distance transmitter: receiver) Received power is also influenced by free space attenuation (depending on frequency) Shadowing by obstacles Reflection on large areas Refraction depending on the Density of a medium Scattering on small obstacles Diffraction on sharp edges Shadowing Reflection Refraction Scattering Diffraction 15 Prof. Dr. Thomas Schmidt

16 2. Signal propagation areas Transmission area communication possible Low error rate Detection area Signal detection No communication possible Interference area Signal cannot be detected Signal contributes to background noise at transmitter Transmission Detection of interference distance 16 Prof. Dr. Thomas Schmidt

17 2. Practical examples 17 Prof. Dr. Thomas Schmidt

18 2.1 Media access methods Restricted frequency bands result in a split medium air But: The signal propagation in the air is not homogeneous (in contrast to the cable): Signal strength decreases quadratically with the distance Transmitters can drown out each other Collisions happen at the receiver, CS & CD at the transmitter Other access methods are used required, e.g. Multiplexing: SDMA (Space Division Multiple Access) FDMA (Frequency Division Multiple Access) TDMA (Time Division Multiple Access) CDMA (Code Division Multiple Access) 18 Prof. Dr. Thomas Schmidt

19 2.1 Space Division Multiplexing: Frequency arrangement Frequencies can only be reused if the distance between the cells or the base stations is sufficiently large k3 Model with 7 frequency ranges: Fixed channel allocation: certain number of channels permanently allocated to certain cells Problem: change in cell load Dynamic channel allocation: channels a cell is selected according to the already assigned channels of the neighboring cells more capacity in areas with higher demand also assignment possible based on interference measurements k4 k3 k5 k1 k2 k6 k7 k2 k4 k5 k1 19 Prof. Dr. Thomas Schmidt

20 2.1 Hidden and delivered end devices Hidden end device A sends to B, C no longer receives A, C wants to send to B, medium is free for C (CS fails) Collision at B, A does not see this (CD fails) A is hidden for C Delivered end device B sends to A, C wants to send to some device (not A or B) C has to wait, as CS signals an occupied medium but since A is out of range of C, this is unnecessary C is B delivered 20 Prof. Dr . Thomas Schmidt A B C

21 2.1 MA / CA - Collision Avoidance MACA (Multiple Access with Collision Avoidance) uses short signaling packets to avoid collisions RTS (request to send): Request from a sender to a recipient before a packet can be sent CTS (clear to send): Confirmation from the recipient as soon as it is ready to receive signaling packets contain: sender address receiver address packet size Variants of this procedure are used in IEEE as DFWMAC (Distributed Foundation Wireless MAC) Thomas Schmidt

22 2.1 MACA - Effect Avoiding the problem of hidden end devices A and C want to send to B A first sends RTS RTS C waits because it hears CTS CTS from B CTS ABC Avoiding the problem of delivered end devices B wants to send to A, C somewhere C is waiting RTS is no longer unnecessary as it does not receive the CTS from CTS A 22 Prof. Dr. Thomas Schmidt RTS A B C

23 2.1 MACA variant: DFWMAC in IEEE sender receiver idle idle ACK RxBusy time-out NAK; RTS packet ready to send; RTS wait for right to send time-out; RTS data; ACK time-out data; NAK RTS; CTS wait for acknowledgment CTS; Data waiting for data RTS; RxBusy ACK: positive acknowledgment of receipt NAK: negative acknowledgment of receipt 23 Prof. Dr. Thomas Schmidt RxBusy: Receiver busy

24: Ad Hoc Network Base Service Set 24 Prof. Dr. Thomas Schmidt

25 infrastructure networks connection using the Extended Service Set 25 Prof. Dr. Thomas Schmidt

26 layers and functions MAC access mechanism, fragmentation, encryption MAC management synchronization, roaming, MIB, Power PHY MAC LLC Logical Link Control MAC Medium Access Control PLCP Physical Layer Convergence Protocol PMD Physical Medium Dependent MAC Management PHY Management Station Management PLCP Clear Channel Assessment Signal ( Carrier Sense) PMD modulation, coding PHY management channel selection, MIB station management Coordination of management functions 26 Prof. Dr. Thomas Schmidt

27 Physical layer 3 variants: 2 radio (primarily in the 2.4 GHz band), 1 IR data rate 1 or 2 Mbit / s FHSS (Frequency Hopping Spread Spectrum) spread, despread, signal strength, only 1 Mbit / s DSSS (Direct Sequence Spread spectrum) Infrared DBPSK modulation for 1 Mbit / s (Differential Binary Phase Shift Keying), DQPSK for 2 Mbit / s (Differential Quadrature PSK) Preamble of a frame always with 1 Mbit / s, then it may be switched to 11 Mbit / s HR -DSSS in b, 54 Mbit / s OFDM in a max. Transmission power 1 W (USA), 100 mw (EU), min. 1 mw nm, diffuse light, typ. 10 m range carrier detection, energy detection, synchronization 27 Prof. Dr . Thomas Schmidt

28 MAC layer: Distributed Foundation Wireless MAC (DFWMAC) Types of traffic: Asynchronous data service (standard) Exchange of data packets on a best-effort basis Support of broadcast and multicast Time-limited services (optional) implemented via PCF (Point Coordination Function) Access types: DFWMAC- DCF CSMA / CA (standard) Collision avoidance through random backoff mechanism Minimum distance between successive packets Acknowledgment of receipt by ACK (not for broadcast) DFWMAC-DCF with RTS / CTS (optional) Distributed Foundation Wireless MAC Avoiding the problem of hidden end devices DFWMAC-PCF (optional) Polling procedure with a list in the access point 28 Prof. Dr. Thomas Schmidt

29 CSMA / CA procedure DIFS Occupied according to Network Allocation Vector NAV Medium occupies DIFS PIFS SIFS Competition window (random backoff mechanism) Next frame Waiting time time slot (20 µs) t Station wishing to transmit listens to the medium (Carrier Sense based on CCA, Clear Channel Assessment) If the medium is free for the duration of an Inter-Frame Space (IFS), transmission is carried out (IFS selected depending on the type of transmission) If the medium is occupied, a free IFS is waited for and then additionally delayed by a random back-off time (collision avoidance , in multiples of a slot time) If the medium is occupied by another station during the back-off time, the back-off timer remains in place for as long (fair competition). Thomas Schmidt

30: Roaming No connection or bad connection? - Then: Scanning the environment (listening to the medium after beacon from APs or sending a sample into the medium and waiting for a response) Reassociation Request Station sends request to AP (s) Reassociation Response if successful, i.e. an AP has answered, station now participates if it is unsuccessful Scanning AP continues to accept reassociation request Display of the new station to the distribution system Distribution system updates database (ie who is where) normally the old AP is informed by the distribution system. Thomas Schmidt

31 2.2 Handoff 31 Prof. Dr. Thomas Schmidt

32 2.2 Ethernet Wireless Standards 1997 max. 2 Mbit / s 2.4 GHz max. 11 Mbit / s 2.4 GHz b 2000 max. 54 Mbit / s 5 GHz a 2003 max. 54 Mbit / s 2.4 GHz g 2003 max. 54 Mbit / s 5 GHz h 2005 QoS e 2009? MIMO, Mbit / s 2.4 & 5 GHz n * 2009? Vehicular Environment 5 GHz p * * In draft status: standardization not completed 32 Prof. Dr. Thomas Schmidt

33 2.3 Bluetooth universal radio system for wireless ad-hoc connections Linking computers with peripherals, portable devices, PDAs, cell phones essentially a more powerful IrDA replacement Defines 13 service profiles (e.g. fax, phone, file transfer,) embedded in other devices, Goal: 5 / device (2002: 50 / USB Bluetooth) Short range (10 m), low power consumption, license-free in the 2.45 GHz ISM band (risk of interference with), approx. 1 Mbit / s gross data rate SIG (Ericson et al ), since 1999 V1.0, physical layer now part of IEEE WPAN One of the first modules (Ericsson). 33 Prof. Dr. Thomas Schmidt

34 2.3 Piconet & Scatternet Connection of several nearby devices to an ad hoc piconet A master gives frequency hopping sequence and timing before connection of several nearby piconets by common master or slave devices Devices can be slaves in one piconet, masters in another Communication between piconet devices, which jump back and forth between the piconets PSS piconets (each with max. 720 kbit / s capacity) SMPMM = Master S = Slave P = Parked SB = Standby SB P SB 34 Prof. Dr. Thomas Schmidt S S SB P

35 Wireless MAN (WIMAX) Originally Fixed Wireless Broadband Access Network IEEE d 2004: Rigid access technology IEEE e 2005: Mobile access with handoff MAN infrastructure technology: Range <45 km Umbrella standard: Various frequency ranges: 2 66 GHz, free in the 5 GHz band Various media access methods : TDMA, OFDM (with Fast Fourier Transform), MIMO bandwidths depending on frequency ranges, MAC, distance typical today: Mbit / s without MIMO,> 100 Mbit / s with MIMO 35 Prof. Dr. Thomas Schmidt

36 2.4 Classification of WIMAX 36 Prof. Dr. Thomas Schmidt

37 Properties Connection-oriented radio technology Channel management: Base Station (BS) assigns Subscriber Station (SS) Channel IDs (CIDs) within Service Flows (SFIDs) No autonomous packet addressing Separate uplink and downlink channels Downlink controlled by BS Uplink with admission control from BS Automatic Repeat Request (ARQ) optionally via Service Flow Various convergence layers Point-to-Point (IP) and Ethernet 37 Prof. Dr. Thomas Schmidt

38 e Mobile WIMAX 4 GPP technology Soft, Hard and Fast Basestation Switching Handover Hard: Initiated by the Base Station (similar) Soft: Downlink data is sent synchronously over several base stations Fast Switching: All BSs in the environment keep the same MAC context before frequency reuse through radially directed antennas Integrated All IP network architecture 38 Prof. Dr. Thomas Schmidt

39 e Architecture Network 39 Prof. Dr. Thomas Schmidt

40 self-assessment questions 1. What special problems arise from the inhomogeneous medium air? 2. How does the competing media access procedure work in CSMA / CA? 3. Why can't mere Ethernet switches be interconnected redundantly? What does Spanning Tree do? 4. What is the advantage of segmentation according to Q in large switched networks? At what level does it happen? 40 Prof. Dr. Thomas Schmidt