Innehåll, föreläsning 2 (fredag) Innehåll, föreläsning 1 (idag) Innehåll, föreläsning 3 (måndag) TDDC22

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1 Innehåll, föreläsning 1 (idag) introduktion till datornät trådlös kommunikation kommunikationsnät atm-nät switchade nät protokoll tcp/ip Innehåll, föreläsning 2 (fredag) trådlösa lokala nät ad hoc-nät WLAN (IEEE ) arkitektur, MAC-lager/DCF, säkerhet WPAN (Bluetooth) Glomosim-labben Innehåll, föreläsning 3 (måndag) gsm-nät satelliter TDDC22 Mobila trådlösa nätverk, föreläsning 1 av Juha Takkinen Avdelningen för databas- och informationsteknik (ADIT), IDA/LiU Ljusbilder baserade på boken Wireless communications and networks, William Stallings, 2002, Prentice Hall Wireless Communication Background [1] Wireless Communication Background [2] Wireless telegraph (Marconi) encoding alphanumeric characters in analog signal sent telegraphic signals across the Atlantic Ocean Satellite communication - first 1960 Wireless networks: WAN, MAN, LAN, MANET, HAN, PAN Radio, television Mobile telephony Convenient and often less expensive than fixed networks 3 Cellular Communication by billion users! since 1996 exceed new fixed subscribers new services, e.g. mobile different standards (AMPS, GSM, PCS ) => need for unification IMT 2000 Broadband wireless communication WLAN to Home s high data rate from 2 Mbps to over 100 Mbps 4 1

2 Wireless Communication Background [3] Wireless communication problems Communication s WAN - Wide Area s MAN - Metropolitan Area s LAN - Local Area s lack of industry-wide standards and thus interoperability technical limitations, e.g transmission problems political limitations, e.g. frequency spectrum devices limitations 5 6 Wide Area s Metropolitan Area s Local Area s WAN - Wide Area s large geographic areas may rely on circuits provided by a common carrier, e.g telephone network traditional data rates up to 64 Kbps for regular subscribers and 1.544Mbps for business subscribers high-speed WAN - possible data rates over 100 Mbps MAN - Metropolitan Area s traditional techniques in WAN not appropriate for organizations need for private and public networks with high capacity smaller geographical area than WAN 7 LAN - Local Area s smaller geographic area in comparison with previous networks, e.g. a building usually owned by an organization internal data much higher than for previous networks traditional data rates up from 1 to 20 Mbps high-speed LAN data rate from 100 Mbps to 10 Gbps 8 Stations Switched s Switching nodes Communication Frågor Stations-to-nodes Nodes-to-nodes Not fully connected 9 2

3 Circuit Switching Switching Techniques dedicated communication path between two stations Packet Switching data transmitted in blocks and may be send on separate paths Circuit Switching [1] Dominant technology for voice/data communication today (e.g. PSTN-public switched telephone network) Communication phases Circuit establishment -> end-to-end circuit between stations Information transfer -> data exchanged between end stations Circuit disconnect -> circuit release A Switching node 1 Switching node M B 10 Switching node N 11 Circuit Switching [2] Packet Switching Some benefits network transparent to user delay at each node negligible fixed data rate to be sent divided in packets typical packet size bytes control information added to original data as headers each node receiving a packet will forwards it to the next node until it reaches the destination Efficiency problem unused channel capacity, e.g. idle time introduced delay due to call establishment Application Heade r Heade r Heade r Packet Switching vs. Circuit Switching Packet Switching - gram Approach Advantages greater line efficiency data-rate conversion call block for heavy traffic may be avoided on the cost of delay can use priorities Disadvantages each node forwarding operation introduce delay overall packet delay may experience extensive variations overhead data have to be included in packets nodes need to have more processing capabilities 14 gram each packet treated independently each node choose the next node based on neighbors information packets not need to follow same route exit or destination nodes reconstruct the data by ordering received packets exit or destination nodes determine lost packets and may employ recovery techniques call setup avoided flexible reliable 15 3

4 gram Approach- example Packet Switching - Virtual Circuit Approach Virtual Circuit preplanned route before sending packets the route is used by all packets from source to destination information similar with a circuit for a logical connection original packets order at the receiver packets arrive correctly minimal delay at nodes Virtual Circuit Approach- example 18 Asynchronous Transfer Mode (ATM) [1] Similar with packet switching Transfer data chunks in fixed size packets called cells Minimal error and flow control capabilities Multiple logical connections called virtual channel connections (VCC) multiplexed over a single physical interface VCC analogue with a virtual circuit in packet-switching VCC used for: user-user: data and signaling between users user-network: control signaling network-network: traffic management and routing a group of VCC -> a virtual path connection (VPC) 19 Asynchronous Transfer Mode (ATM) [2] Asynchronous Transfer Mode (ATM) [3] Virtual channel connection characteristics Quality of Service (QoS): use parameters such as cell loss and cell delay Switched and semipermanent VCC: switched and dedicated connections Cell sequence integrity Traffic parameters negotiation (e.g. average data rate, peak duration) and usage monitoring (e.g. congestion management) Virtual path connection characteristics Same first four characteristics as for VCC Virtual channel identifier restriction within VCC: several virtual channel may be reserved for network management 20 ATM Service Categories Real-time Services: constant bit rate (CBR) and real-time variable bit rate (rt-vbr) Non-real-time Services: non-real-time variable bit rate (nrt-vbr), available bit rate (ABR) and unspecified bit rate (UBR) ATM Application Examples videoconferencing (CBR) distance learning (CBR) banking transaction (nrt-vbr) remote terminal (UBR) LAN interconnection (ABR) 100 % ABR, UBR VBR CBR Tid 21 4

5 Protocols Frågor Protocol: A set of rules used for two or more peers to communicate Needed for the successful data transfer! e.g. sender must connect to network and indicate the destination e.g. sender want to know if receivers can receive data e.g. data format translation needed Protocol features: Syntax: data format Semantics: control data for data management and error handling Timing: speed matching and sequencing 22 TCP/IP Protocols Reference Model [1] Started from ARPANET (1970) Based on layers of services concept: Application Transport access 23 TCP/IP Protocols Reference Model [2] Layer between transmission device and transmission medium handle hardware details (e.g. data rate) Access Layer: between an end system and the network functions dependent of network type such as LAN (e.g. Ethernet) or packet switching (e.g X25) handle packet movement across the network Layer provide routing functions for data relay over interconnected networks use Protocol (IP) implemented in end systems and routers (i.e. entities that connect networks and relay data between them) 24 TCP/IP Protocols Reference Model [3] Transport Layer send data between applications running on computers implemented usually by using Transmission Control Protocol (TCP) or User gram Protocol (UDP) use secondary address named port for identifying the sending and receiving process TCP: connection-oriented, two-way connection, reliable (e.g. use checksum), fragmentation, order received data UDP: datagram-oriented (e.g. send one chunk of data), connectionless, unreliable Application Layer manage details of applications build upon TCP or UDP example: Telnet, FTP, SMTP (e.g. mail), HTTP 25 TCP/IP - How Does It Works? [1] Communication example End System A Application Transport access Networ k access Router N access Networ k End System B Application Transport access 26 5

6 TCP/IP - How Does It Works? [2] OSI Reference Model [1] processing flow example TCP Segment IP gram header IP header IP header TCP header TCP header TCP header frame End System Application Transport access Developed by International Organization for Standardization (ISO) Model for computer architecture Seven Layers Application Presentation Session Transport Link OSI Reference Model [2] TCP/IP and OSI Reference Models OSI does not replaced TCP TCP-based protocols were already mature when OSI was developed OSI is more complex than TCP Summary Frågor Wireless Communication Wireless s Switched s Circuit Switching Packet Switching Protocols TCP/IP Reference Model OSI Reference Model 31 6

7 Additional References Communication Frequency Spectrum Electromagnetic spectrum and applications (Tanenbaum 2003) Tanenbaum A. (2003), Computer s. Fourth Edition. Prentice Hall. Toh, C-K (2002), Ad-Hoc Mobile Wireless s. Prentice Hall. William Stallings, (2004), and computer communication. Seventh Edition. Prentice Hall. Geier J. (2002), Wireless LANs. SAMS Publishing. 32 Wireless s Background Aspects of Wireless s mobility and convenient deployment scarce frequency spectrum wireless implications such as transmission problems (e.g. interference, path loss, fading), security, battery, installation, health Wireless networks Cellular: GSM, PCS, IMT 2000 Satellite: IRIDIUM, Globalstar WLAN: IEEE , HiperLAN Ad-Hoc, PAN, HAN 7