Networks for Distributed Systems

1. Networks for Distributed Systems • network types • Connection-oriented and connectionless communication • switching technologies • circuit • packet

2. Local Area Network • Local area network (LAN) — connectsnodes in a small geographic area(e.g., single building, single campus) • nodes connected to single communication medium • media — twisted-pair, coaxialcable, fiber optic cable • Topologies • tree/bus (used in Ethernet) • ring (used in Token Ring) • generally faster (lower latency) thanWAN’s and have lower error rates

3. Wide Area Network • Wide area network (WAN) — connects nodes in a wide geographic area (e.g., across the country) • media – set of communication circuits linking dedicated computers - routers • lines - leasedtelephone lines(T1 & T3 service), satellite channels, optical links (OC-1, OC-3 …) • Router (Switch) – special purpose computer primarily responsible for routing data from one point to another through an appropriate path while avoiding network congestion. • Arbitrary topology • Data loss due to size and unpredictable environment, routing introduces delays

4. Other Network Types • metropolitan area network (MAN) – connects nodes within a city (distance under 50km), uses either copper or fiber cables, variety of technologies – Ethernet, ATM, etc. • wireless networks – uses wireless technology to connect devices • variety of different technologies, usually restricted bandwidth and small (handheld devices) • infrared • low-power radio: BlueTooth • wireless phone networks: digital – GSM (Global System of Mobile Communication), analogue – AMPS (Cellular Radio Network)

5. Network Comparison

6. network switched broadcast circuit- packet- satellite local packet switched switched radio datagram virtual circuit Network communication • Connection-oriented communication • Information delivered as a stream of bytes, in correct order • Connect, exchange data, release • Connectionless communication • Information delivered as a set of packets • Packets may be delivered out of sequence, must be reassembled

7. Switching technologies • In a broadcast (or multiaccess) network, all hosts directly connect to a single shared communication medium • Each host checks the destination address on every message to decide whether or not to read that message • In a switched network, there is a partially-connected topology, and there may be multiple paths between two hosts • Messages may have to pass through intermediate nodes to reach destination • Circuit switching — a dedicated communication path is reserved, and then used to send the entire message • Connection occupies a fixed capacity (not necessarily entire capacity) of each link for the entire lifetime of the connection • Connection-oriented communication

8. Switching technologies (cont.) • Packet switching — data is broken upinto a sequence of fixed-size packets • Each packet is passed through the network from source to destination along some (possibly different) route (path) • At each node, the entire packet is received, stored briefly, and then forwarded to the next node • Datagram package switching • Packets are called datagrams • Each packet is routed independently • A sequence of packets can be receivedout of order • Connectionless communication • Virtual circuit package (message) switching • All packets from one packet stream aresent along the same path (= virtual circuit) • Guarantees packets are received in sequence • Connection-oriented communication