Networking Bin Li Assistant Professor Dept. of Electrical, Computer and Biomedical Engineering University of Rhode Island
Why is Networking Needed? To enhance many devices Cars communicating to reduce traffic On-line game play Access media libraries To access data or computational power outside of the device
Client-Server Transactions Request Handle request Client Server Resource Response Client-server model is very common Single server, one or more clients Server provides a service for clients Server manages a resource Server responds to requests from the client
Computer Networks: LAN Hierarchical system of computer-based devices which communicate Local Area Network (LAN) spans a building or campus (Ethernet is most common)
Computer Networks: WAN Wide Area Network (WAN) Internet is best example
Computer Networks: MANET Mobile Ad Hoc Network (MANET) Continually changing network built from wireless, mobile devices Typically short-range Most common for IoT devices
Network Structure
Statistical Multiplexing Consider a link with bandwidth 10 Mbps, which is shared by multiple data sources. At any given time, a source is active with a probability of 0.1, and transmits at a rate of 100 kbps when active. If the link bandwidth is allocated according to the peak rate, the link needs to reserve 100kbps for each source. The maximum number of sources that can be allowed 10 Mbps 10 MMMMMMMM 100 kkkkkkkk = 100
Statistical Multiplexing Let XX ii be a random variable such that XX ii = 1 if source ii is active and XX ii = 0 otherwise. The probability that the aggregated rate of active sources exceeds the link capacity is nn Pr XX ii 100 ii=1 Observation: the link can accommodate up to 650 sources if the overflow probability is allowed to be 0.01%. We can increase the number of sources to 750 if the overflow probability is allowed to be 1%.
A Small LAN Switch 100 Mb/s Host 1 Host 2 Host 3 Ethernet is a common LAN protocol Ethernet switch sends messages to the right input or output
A Larger LAN Switch Bridge Switch Host 1 Host 2 Host 3 Host 1 Host 2 Host 3 Spans a building or campus Small LANs connected by bridges which speak both LAN protocols
A Wide Area Network LAN LAN Router LAN Router Router LAN LAN LAN Multiple LANs connected by routers
Internet Structure Ad hoc interconnection of networks Unpredictable structure Can be changed by anyone at any time Messages travel from source to destination by hopping through networks
Internet Protocol How is it possible to send bits across incompatible networks Solution: Protocol software running on each host and router Common communication rules for all networks
Internet Protocol: Solution Implement protocol (set of rules) Governs how hosts and routers should cooperate when they transfer data from network to network TCP/IP is the protocol for the global IP Internet
What does an Internet Protocol Do? Provides a naming scheme An internet protocol defines a uniform format for host addresses Each host (and router) is assigned at least one of these unique internet address Rules that determine how computers will communicate CB radio protocol Over I am done talking Roger Data received Rules enable efficient communication
Network Protocols Many networking tasks to transmit and receive data Routing, flow control, congestion control Flow control: techniques to match the source sending rate with the destination receiving rate Congestion control: techniques to regulate sources sending rate to prevent network overload faucet = Source water = data bucket = buffer Flow control pipe = path destination Congestion control destination
Network Protocols OSI divides these tasks between network abstraction layers Each layer has its own responsibilities Each layer uses different data Routing requires network topology
OSI Layer Concept Message is received at each layer and decisions are made Assume layer R performs routing, Message M is received by layer R Layer R identifies a route for message M Layer R adds routing information, creating M Layer R passes message M to the next lower layer M Layer R M
The Postal Analogy Application Presentation Session Transport Network Data - Link Physical A Write a 20 page letter to a foreign country P Translate the letter so the receiver can read it S Insure the intended recipient can receive letter T Separate and number pages. Like registered mail, tracks delivery and requests another package if one is lost or damaged in the mail N Postal center sorting letters by zip code to route them closer to destination D Local Post Office determining which vehicles to deliver letters P Physical trucks, planes, rail, autos, etc., which carry letters between stations.
Encapsulation Communication tasks are confined to one protocol layer Protocol stack is the implementation (usually software) of each protocol layer
Encapsulation: Transmission Messages start at top layer and go down Message decisions are made at each layer Relevant information is added to the message at each layer (header or footer)
Encapsulation: Reception Messages start at bottom layer and go up Relevant information is stripped at each layer New decisions are made, if necessary
TCP/IP Transmission Control Protocol (TCP) Internet Protocol (IP) Protocol stack used in the Internet TCP/UDP used at Transport layer App-to-App IP used at network layer Host-to-Host 5 layers total, Unlike OSI s 7 Application TCP/UDP IP Data - Link Physical TCP/IP Application Presentation Session Transport Network Data - Link Physical OSI
Application Layer Protocols that directly support applications Information is application-specific Simple Mail Transfer Protocol (SMTP): email Hypertext Transfer Protocol (HTTP): web Line Printer Daemon (LPD): printing
Application Layer Example HTTP response message transmitted in response to a request for a web page (GET)
Mobile Ad Hoc Network (MANET) Self-configuring network of mobile hosts/routers Connected by wireless links Often connected to a wired LAN via an Access Point Common for IoT devices
MANET Issues: Power Budget Power budget Mobile devices are power constrained Standard LAN protocols must be modified Battery is often the heaviest component
MANET Issues: Data Rate and Security Data rate Wireless bandwidth is lower than wired Bandwidth costs power Security Power is not available for complex security No encryption, antivirus, etc.