CS 417: Operating Systems Design 9/10/2012 © 2012 Paul Krzyzanowski 1 Distributed Systems 2a. Networking Terminology [background information] Paul Krzyzanowski [email protected] 1 Local Area Network (LAN) Communications network – small area (building, set of buildings) – same, sometimes shared, transmission medium – high data rate (often): 1 Mbps – 1 Gbps – Low latency – devices are peers • any device can initiate a data transfer with any other device Most elements on a LAN are workstations – endpoints on a LAN are called nodes 2 Connecting nodes to LANs ? network computer 3 Connecting nodes to LANs network computer Adapter – expansion slot (PCI, PC Card, USB dongle) – usually integrated onto main board Network adapters are referred to as Network Interface Cards (NICs) or adapters or Network Interface Component (since they’re often not cards anymore) 4 Hubs, routers, bridges Hub – Device that acts as a central point for LAN cables – Take incoming data from one port & send to all other ports Switch – Moves data from input to output port. – Analyzes packet to determine destination port and makes a virtual connection between the ports. Concentrator or repeater – Regenerates data passing through it Bridge – Connects two LANs or two segments of a LAN – Connection at data link layer (layer 2) Router – Determines the next network point to which a packet should be forwarded – Connects different types of local and wide area networks at network layer (layer 3) 5 How do nodes share a network? • Dedicated connection – no sharing: physical circuit • Talk on different frequencies: broadband – Data uses segment of medium (channels, frequency bands) • Take turns (baseband) – A node can use the entire bandwidth of medium 1. Short fixed time slots: TDMA (Time Division Multiple Access) • Circuit switching: performance equivalent to an isolated connection 2. Variable size time slots: Packets • Statistical multiplexing for network access • Permits many-to-many communication • Packet switching is the dominant means of data communication 6CS 417: Operating Systems Design 9/10/2012 © 2012 Paul Krzyzanowski 2 Broadband: RF broadcasts http://www.ntia.doc.gov/osmhome/allochrt.pdf 7 Broadband/Baseband: Cable TV 55-552 MHz: analog channels 2-78 553-865 MHz: digital channels 79-136 DOCSIS: Data Over Cable Service Interface Specification (approved by ITU in 1998; DOCSIS 2.0 in 2001; DOCSIS 3.0 in 2006) Downstream: 50-750 MHz range, 6 MHz bandwidth - up to 38 Mbps - received by all modems Upstream: 5-42 MHz range - 30.72 Mbps (10 Mbps in DOCSIS 1.0, 1.1) - data delivered in timeslots (TDM) DOCSIS 3.0 features channel bonding for greater bandwidth +1.25 MHz video +5.75 MHz audio 6 MHz Broadband Baseband within Broadband 8 DOCSIS Modem modulator demodulator tuner MAC CPU network interface Restrictions on upload/download rates set by transferring a configuration file to the modem via TFTP when it connects to the provider. ethernet interface (to PC) cable 9 Baseband: Ethernet • Packet-based network – Data sent as a series of frames (packets) • Speeds: 1 Gbps most common interface today – Ethernet: 10 Mbps • Fast Ethernet: 100 Mbps • Gigabit Ethernet: 1 Gbps – Also 10 Gbps and 100 Gbps • Ethernet network access method on a shared channel is Carrier Sense Multiple Access with Collision Detection (CSMA/CD) – Node first listens to network to see if busy – Send – Sense if collision occurred – Retransmit if collision • Ethernet switches don’t use shared channels – no need for CSMA/CD 10 802.11 Family (Wi-Fi) Network access via Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) – Cannot use CSMA/CD on wireless networks – can’t listen while sending – Node first listens on the desired channel to see if idle – Send a packet if idle – If busy, wait until transmission stops + random contention period – Transmit if still idle – Receive ACK from receiver 11 ethernet Wireless Ethernet media Wireless (star topology) – 802.11 (1-2 Mbps) – 802.11b (11 Mbps - 4-5 Mbps realized) – 802.11a (54 Mbps - 22-28 Mbps realized) – 802.11g (54 Mbps - 32 Mbps realized) – 802.11n (108 Mbps - 30-47 Mbps realized) Access Point 12CS 417: Operating Systems Design 9/10/2012 © 2012 Paul Krzyzanowski 3 Connecting to the Internet • DOCSIS modem via cable TV service • DSL router – Ethernet converted to ATM data stream – Up to 20 Mbps up to ~ 2 km. – POTS limited to 300-3400 Hz – DSL operates > 3500 Hz • Modem – Data modulated over voice spectrum (300-3400 Hz) – Serial interface to endpoint – V.92: 48 kbps downstream, near 56 kbps up – Use PPP or SLIP to bridge IP protocol 13 Connecting to the Internet • Dedicated T1 or T3 line – T1 line: 1.544 Mbps (this used to be fast!) (24 PCM TDMA speech lines @ 64 kbps) – T3 line: 44.736 Mbps (672 channels) – CSU/DSU at router presents serial interface • Channel Service Unit / Data Service Unit CSU/DSU T1 line RS-232C, RS-449, V.xx serial line router LAN Phone network 14 Connecting to the Internet • Fiber to the Home, Fiber to the Curb – Ethernet interface – E.g., Verizon’s FiOS – up to 100 Mbps to the home • Long Reach Ethernet (LRE) – Ethernet performance up to 5,000 feet • Wireless: – WiMax – LTE (Long Term Evolution, known as 4G) • Peak downstream rate: 326.5 Mbps; Peak upstream: 86.4 Mbps • Support from Verizon, AT&T, T-Mobile, France Télécom, … – HSPA (3G: 14 Mbps downlink, 5.8 Mbps uplink) – HSPA+ (AT&T calls it 4G now: up to 84 Mbps downlink, 22 Mbps uplink) – EDGE (2G: 70-135 Kbps) – GPRS (<32 Kbps) 15 The End