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Explore the structure of communication networks, edge computing, network protocols, and data transfer mechanisms. Learn about TCP, UDP, packet switching, and different network types. Dive into circuit-switched vs. packet-switched networks.
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Overview • Course administrative trivia • Internet Architecture • Network Protocols • Network Edge • A taxonomy of communication networks
network edge: applications and hosts A closer look at network structure: • access networks, physical media: wired, wireless communication links • network core: • interconnected routers • network of networks
end systems (hosts): run application programs e.g. Web, email at “edge of network” peer-peer client/server The network edge: • client/server model • client host requests, receives service from always-on server • e.g. Web browser/server; email client/server • peer-peer model: • minimal (or no) use of dedicated servers • e.g. Skype, BitTorrent
Goal: data transfer between end systems handshaking: setup (prepare for) data transfer ahead of time Hello, hello back human protocol set up “state” in two communicating hosts TCP - Transmission Control Protocol Internet’s connection-oriented service TCP service[RFC 793] reliable, in-order byte-stream data transfer loss: acknowledgements and retransmissions flow control: sender won’t overwhelm receiver congestion control: senders “slow down sending rate” when network congested Network Edge: Connection-oriented Service
Goal: data transfer between end systems same as before! UDP - User Datagram Protocol [RFC 768]: Internet’s connectionless service unreliable data transfer no flow control no congestion control App’s using TCP: HTTP (Web), FTP (file transfer), Telnet (remote login), SMTP (email) App’s using UDP: streaming media, teleconferencing, DNS, Internet telephony Network Edge: Connectionless Service
A Taxonomy of Communication Networks • The fundamental question: how is data transferred through net (including edge & core)? • Communication networks can be classified based on how the nodes exchange information: Communication Networks SwitchedCommunication Network BroadcastCommunication Network Packet-SwitchedCommunication Network Circuit-SwitchedCommunication Network TDM FDM Datagram Network Virtual Circuit Network
Broadcast vs. Switched Communication Networks • Broadcast communication networks • Information transmitted by any node is received by every other node in the network • Examples: usually in LANs (Ethernet) • Problem: coordinate the access of all nodes to the shared communication medium (Multiple Access Problem) • Switched communication networks • Information is transmitted to a sub-set of designated nodes • Examples: WANs (Telephony Network, Internet) • Problem: how to forward information to intended node(s) • This is done by special nodes (e.g., routers, switches) running routing protocols
A Taxonomy of Communication Networks • The fundamental question: how is data transferred through net (including edge & core)? • Communication networks can be classified based on how the nodes exchange information: Communication Networks SwitchedCommunication Network BroadcastCommunication Network Packet-SwitchedCommunication Network Circuit-SwitchedCommunication Network TDM FDM Datagram Network Virtual Circuit Network
End-end resources reserved for “call” Link bandwidth, switch capacity Three phases circuit establishment data transfer circuit termination Dedicated resources + Guaranteed performance - no sharing Circuit-Switched Network
Examples Telephone networks ISDN (Integrated Services Digital Networks) network resources (e.g., bandwidth) divided into “pieces” Pieces allocated to calls Resource piece idle if not used by owning call (no sharing) Dividing link bandwidth into “pieces” frequency division time division Circuit Switching
Example: 4 users FDM frequency time TDM frequency time Circuit Switching: FDM and TDM
A Taxonomy of Communication Networks • The fundamental question: how is data transferred through net (including edge & core)? • Communication networks can be classified based on how the nodes exchange information: Communication Networks SwitchedCommunication Network BroadcastCommunication Network Packet-SwitchedCommunication Network Circuit-SwitchedCommunication Network TDM FDM Datagram Network Virtual Circuit Network
Packet Switching • Data is sent as formatted bit-sequences (Packets) • Packets have the following structure: • Header and Trailer carry control information (e.g., destination address, check sum) • Each packet traverses the network from node to node along some path (Routing) • At each node the entire packet is received, stored briefly, and then forwarded to the next node (Store-and-Forward Networks) • No dedicated allocation or resource reservation – no guarantees! Header Data Trailer
Sequence of A & B packets does not have fixed pattern statistical multiplexing. In TDM each host gets same slot in revolving TDM frame. D E Packet Switching: Statistical Multiplexing 10 Mbs Ethernet C A statistical multiplexing 1.5 Mbs B queue of packets waiting for output link
1 Mbit link Each user: 100 kbps when “active” active 10% of time Circuit-switching: 10 users Packet switching: with 35 users, probability > 10 active less than .0004 Packet switching allows more users to use network! Packet Switching versus Circuit Switching N users 1 Mbps link
