ECE 4436 - Chapter 1.pdf

ECE 4436 Networking Chapter 1: Introduction to Computer Networks and the Internet Fadi AlMahamid, Ph.D.  Learning Outcomes 01 Demonstrate an understanding of the Internet. 02 Demonstrate knowledge of the Network Edge. 03 Demonstrate knowledge of the Network Core. Demonstrate...

ECE 4436 Networking Chapter 1: Introduction to Computer Networks and the Internet Fadi AlMahamid, Ph.D.  Learning Outcomes 01 Demonstrate an understanding of the Internet. 02 Demonstrate knowledge of the Network Edge. 03 Demonstrate knowledge of the Network Core. Demonstrate knowledge of the Network Access and 04 Physical Media. 2  Learning Outcomes Demonstrate an understanding of ISPs and Internet 05 Backbones. Demonstrate an understanding of Delay and Loss in 06 Packet-Switched Networks. Demonstrate an understanding of Protocol Layers and 07 Their Service Models. 3 Roadmap What is the Internet? Internet What is the protocol? Host Network Access Edge Network Physical Media Circuit Switching Roadmap Network Core Packet Switching Loss Performance Delay Protocol Throughput Layers Service Model 4 01 The Internet Connected Devices Tweet-a-watt: monitor energy use bikes Pacemaker & Monitor Amazon Echo Web-enabled toaster + IP picture frame weather forecaster Internet refrigerator Slingbox: remote cars AR devices Security Camera control cable TV sensorized, bed scooters mattress Fitbit Internet phones Gaming devices diapers Others? 6 What is the Internet? Billions of connected mobile network computing devices: national or global ISP § hosts = end systems § running network apps at Internet’s “edge” Packet switches: forward packets (chunks of data) local or Internet regional ISP § routers, switches Communication links home network content provider § fiber, copper, radio, satellite network datacenter network § transmission rate: bandwidth Networks § collection of devices, routers, enterprise links: managed by an network organization 7 What is the Internet? mobile network 4G national or global ISP Internet: “network of networks” – Interconnected ISPs protocols are everywhere IP Streaming Skype video – control sending, receiving of messages local or – e.g., HTTP (Web), streaming video, regional ISP Skype, TCP, IP, WiFi, 4/5G, Ethernet home network Internet standards content provider – RFC: Request for Comments HTTP network datacenter network – IETF: Internet Engineering Task Ethernet Force TCP enterprise network WiFi 8 The Internet: a “services” view mobile network Infrastructure that provides national or global ISP services to applications: – Web, streaming video, multimedia teleconferencing, email, games, e-commerce, Streaming social media, inter-connected appliances, … Skype video provides programming interface to local or regional distributed applications: ISP – “hooks” allowing sending/receiving home network content provider apps to “connect” to, use Internet HTTP network datacenter transport service network – provides service options, analogous to postal service enterprise network 9 What is a protocol? Human protocols: “what’s the time?” “I have a question.” introductions Rules for: Specific messages are sent. Specific actions are taken when a message is received or other events. 10 What is a protocol? A human protocol and a computer network protocol: Hi TCP connection request Hi TCP connection response Got the time? GET http://gaia.cs.umass.edu/kurose_ross 2:00 time Q: other human protocols? 11 What is a protocol? Human protocols: Network protocols: § “what’s the time?” § computers (devices) rather than humans § “I have a question” § all communication activity in Internet § introductions governed by protocols Rules for: Protocols define the format, … specific messages sent order of messages sent and … specific actions taken when message received, received among network or other events entities, and actions taken on message transmission, receipt 12 02 Network Edge A closer look at Internet structure Network edge: hosts: clients and servers servers often in data centers 14 03 Network Core 15 A closer look at Internet structure Network core: national or global ISP § interconnected routers § network of networks local or regional ISP home network content provider network datacenter network enterprise network 16  Network Access and Physical 04 Media. 17  A closer look at Internet structure mobile network Access networks, physical media: national or global ISP wired, wireless communication links local or regional ISP home network content provider network datacenter network enterprise network 18  Access networks and physical media mobile network Q: How to connect end systems to edge national or global ISP router? residential access nets institutional access networks (school, company) mobile access networks (WiFi, 4G/5G) local or regional ISP Q: What to look for: home network content provider What is the transmission rate (bits per second) network datacenter network of access networks? Shared or dedicated access among users? enterprise network 19 Access networks: cable-based access cable headend … cable splitter modem C O V V V V V V N I I I I I I D D T D D D D D D A A R E E E E E E T T O O O O O O O A A L 1 2 3 4 5 6 7 8 9 Channels frequency division multiplexing (FDM): different channels transmitted in different frequency bands 20 Access networks: cable-based access cable headend … cable splitter cable modem modem CMTS termination system data, TV transmitted at different frequencies over shared cable ISP distribution network § HFC: hybrid fiber coax asymmetric: up to 40 Mbps – 1.2 Gbps downstream transmission rate, 30-100 Mbps upstream transmission rate § network of cable, fiber attaches homes to ISP router homes share access network to cable headend 21 Access networks: digital subscriber line (DSL) central office telephone network DSL splitter modem DSLAM voice, data transmitted ISP at different frequencies over DSL access dedicated line to central office multiplexer § use existing telephone line to central office DSLAM data over DSL phone line goes to Internet voice over DSL phone line goes to telephone net § 24-52 Mbps dedicated downstream transmission rate § 3.5-16 Mbps dedicated upstream transmission rate 22 Access networks: home networks Wireless and wired devices to/from headend or central office often combined in single box cable or DSL modem WiFi wireless access router, firewall, NAT point (54, 450 Mbps) wired Ethernet (1 Gbps) 23  Wireless access networks Shared wireless access network connects end system to router § via base station aka “access point” Wireless local area networks Wide-area cellular access networks (WLANs) § provided by mobile, cellular network § typically within or around operator (10’s km) building (~100 ft) § 10’s Mbps § 802.11b/g/n (WiFi): 11, 54, 450 § 4G/5G cellular networks Mbps transmission rate to Internet to Internet 24 Access networks: enterprise networks Enterprise link to ISP (Internet) institutional router Ethernet institutional mail, switch web servers § Companies, universities, etc. § Mix of wired, wireless link technologies, connecting a mix of switches and routers (we’ll cover differences shortly) § Ethernet: wired access at 100Mbps, 1Gbps, 10Gbps § WiFi: wireless access points at 11, 54, 450 Mbps 25  Access networks: data center networks mobile network § high-bandwidth links (10s to 100s national or global ISP Gbps) connect hundreds to thousands of servers together, and to Internet local or regional ISP home network content provider network datacenter network Courtesy: Massachusetts Green High Performance Computing enterprise Center (mghpcc.org) network 26  Host: sends packets of data host sending function: § takes application message § breaks into smaller chunks, two packets, known as packets, of length L bits L bits each § transmits packet into access network at transmission rate R 2 1 link transmission rate, aka link host capacity, aka link bandwidth R: link transmission rate packet time needed to L (bits) transmission = transmit L-bit = delay packet into link R (bits/sec) 27  Links: physical media § bit: propagates between Twisted pair (TP) transmitter/receiver pairs § two insulated copper wires § physical link: what lies Category 5: 100 Mbps, 1 Gbps Ethernet between transmitter & Category 6: 10Gbps Ethernet receiver § guided media: signals propagate in solid media: copper, fiber, coax § unguided media: signals propagate freely, e.g., radio 28  Links: physical media Coaxial cable: Fiber optic cable: § two concentric copper conductors § glass fiber carrying light pulses, each pulse a bit § bidirectional § high-speed operation: § broadband: high-speed point-to-point multiple frequency channels on cable transmission (10’s-100’s Gbps) 100’s Mbps per channel § low error rate: repeaters spaced far apart immune to electromagnetic noise 29  Delay and Loss in Packet- 05 Switched Networks 30  The network core mesh of interconnected mobile network national or global ISP routers packet-switching: hosts break application-layer local or messages into packets regional ISP – network forwards packets from home network content provider one router to the next, across network datacenter network links on path from source to destination enterprise network 31 The network core routing algorithm Routing: Forwarding: local local forwarding forwarding table table § global action: aka “switching” header value output link determine source- local action: 0100 0101 3 2 destination paths move arriving 0111 2 taken by packets packets from 1001 1 router’s input link § routing algorithms to appropriate 1 router output link 3 2 11 01 destination address in arriving packet’s header 32  Links: physical media Wireless radio Radio link types: § signal carried in various § Wireless LAN (WiFi) “bands” in electromagnetic 10-100’s Mbps; 10’s of meters spectrum § wide-area (e.g., 4G/5G cellular) § no physical “wire” 10’s Mbps (4G) over ~10 Km § broadcast, “half-duplex” § Bluetooth: cable replacement (sender to receiver) short distances, limited rates § propagation environment effects: § terrestrial microwave reflection point-to-point; 45 Mbps channels obstruction by objects § satellite Interference/noise up to < 100 Mbps (Starlink) downlink 270 msec end-end delay (geostationary) 33 34  forwarding forwarding 35 Packet-switching: store-and-forward L bits per packet 3 2 1 source destination R bps R bps packet transmission delay: takes L/R One-hop numerical example: seconds to transmit (push out) L-bit § L = 10 Kbits packet into link at R bps § R = 100 Mbps store and forward: entire packet must § one-hop transmission delay = 0.1 msec arrive at router before it can be transmitted on next link 36 Packet-switching: queueing R = 100 Mb/s A C D B R = 1.5 Mb/s E queue of packets waiting for transmission over output link Queueing occurs when work arrives faster than it can be serviced: 37 Packet-switching: queueing R = 100 Mb/s A C D B R = 1.5 Mb/s E queue of packets waiting for transmission over output link Packet queuing and loss: if arrival rate (in bps) to link exceeds transmission rate (bps) of link for some period of time: packets will queue, waiting to be transmitted on output link. packets can be dropped (lost) if memory (buffer) in router fills up. 38 Alternative to packet switching: circuit switching end-end resources allocated to, reserved for “call” between source and destination q in diagram, each link has four circuits. q call gets 2nd circuit in top link and 1st circuit in right link. q dedicated resources: no sharing q circuit-like (guaranteed) performance q circuit segment idle if not used by call (no sharing) q commonly used in traditional telephone networks 39  Circuit switching: FDM and TDM Frequency Division Multiplexing (FDM) 4 users frequency § optical, electromagnetic frequencies divided into (narrow) frequency bands § each call allocated its own band, can transmit at max rate of that narrow time band Time Division Multiplexing (TDM) frequency § time divided into slots time 40  Packet switching versus circuit switching example: § 1 Gb/s link N ….. § each user: users 100 Mb/s when “active” 1 Gbps link active 10% of time Q: how many users can use this network under circuit-switching and packet switching? § circuit-switching: 10 users § packet switching: with 35 users, probability > 10 active at same time is less than.0004 * Q: how did we get value 0.0004? 41 Packet switching versus circuit switching Is packet switching a “slam dunk winner”? It's great for handling bursty data (data is sent when needed, but at other times, there's no data to send). Resource sharing: The network dynamically allocates bandwidth to users as needed. It's simpler than circuit-switching, as there's no need for call setup. Challenges: Excessive congestion can lead to packet delay and loss (due to buffer overflow). Protocols are required for reliable data transfer and congestion control. 42 06 ISPs and Internet Backbones 43 Internet structure: a “network of networks” § hosts connect to Internet via access Internet mobile network Service Providers (ISPs) national or global ISP § access ISPs in turn must be interconnected so that any two hosts (anywhere!) can send packets to each other § resulting network of networks is very complex evolution driven by economics, national local or regional ISP policies home network content provider network datacenter network enterprise network Let’s take a stepwise approach to describe current Internet structure 44 Internet structure: a “network of networks” Question: given millions of access ISPs, how to connect them together? … access net access net … access net access access net net access access net net … … access access net net access net access net access net access net … access access … net access net net 45 Internet structure: a “network of networks” Question: given millions of access ISPs, how to connect them together? … access net access net … access net access access net … … net access access net net connecting each access ISP to … … each other directly doesn’t scale: … access O(N2) connections. access … net net access net access net access net access … net … access access … net access net net 46 Internet structure: a “network of networks” Option: connect each access ISP to one global transit ISP? Customer and provider ISPs have economic agreement. … access net access net … access net access access net net access access net net … … global access net ISP access net access net access net access net access net … access access … net access net net 47 Internet structure: a “network of networks” But if one global ISP is viable business, there will be competitors …. … access net access net … access net access access net net access ISP A access net net … … access net ISP B access net access ISP C net access net access net access net … access access … net access net net 48 Internet structure: a “network of networks” But if one global ISP is viable business, there will be competitors …. who will want to be connected Internet exchange point … access net access net … access net access access net net IXP access access ISP A net net … … access net IXP ISP B access net access ISP C net access net access net peering link access net … access access … net access net net 49 Internet structure: a “network of networks” … and regional networks may arise to connect access nets to ISPs … access net access net … access net access access net net IXP access access ISP A net net … … access net IXP ISP B access net access ISP C net access net access net regional ISP access net … access access … net access net net 50  Internet structure: a “network of networks” … and content provider networks (e.g., Google, Microsoft, Akamai) may run their own network, to bring services, content close to end users … … access net access net access net access access net net IXP access access ISP A net net … … Content provider network access net IXP ISP B access net access ISP C net access net access net regional ISP access net … access access … net access net net 51  Internet structure: a “network of networks” Tier 1 ISP Tier 1 ISP Google IXP IXP IXP Regional ISP Regional ISP access access access access access access access access ISP ISP ISP ISP ISP ISP ISP ISP At “center”: small # of well-connected large networks § “tier-1” commercial ISPs (e.g., Level 3, Sprint, AT&T, NTT), national & international coverage § content provider networks (e.g., Google, Facebook): private network that connects its data centers to Internet, often bypassing tier-1, regional ISPs 52 Tier-1 ISP Network map 53 Tier-1 ISP Network map 54  Protocol Layers and Service 07 Models 55 Protocol layers and reference models Networks are complex with many components: hosts routers links of various media applications protocols hardware, software Question: is there any hope of organizing the structure of the network? and/or our discussion of networks? 56 Example: organization of air travel end-to-end transfer of person plus baggage ticket (purchase) ticket (complain) baggage (check) baggage (claim) gates (load) gates (unload) runway takeoff runway landing airplane routing airplane routing airplane routing How would you define/discuss the system of airline travel? § a series of steps, involving many services 57 Example: organization of air travel ticket (purchase) ticketing service ticket (complain) baggage (check) baggage service baggage (claim) gates (load) gate service gates (unload) runway takeoff runway service runway landing airplane routing routing service airplane routing airplane routing layers: each layer implements a service § via its own internal-layer actions § relying on services provided by layer below 58 Why layering? Approach to designing/discussing complex systems: explicit structure allows identification, relationship of system’s pieces layered reference model for discussion modularization eases maintenance, updating of system change in layer's service implementation: transparent to rest of system e.g., change in gate procedure doesn’t affect rest of system 59 Layered Internet Protocol Stack Application: supporting network applications HTTP, IMAP, SMTP, DNS application application Transport: process-process data transfer TCP, UDP transport transport Network: routing of datagrams from network source to destination IP, routing protocols link Link: data transfer between neighboring network elements physical Ethernet, 802.11 (WiFi), PPP Physical: bits “on the wire” 60  Services, Layering and Encapsulation M application Application exchanges messages to implement some application application service using services of transport layer Ht M transport Transport-layer protocol transfers M (e.g., reliably) from transport one process to another, using services of network layer network § transport-layer protocol encapsulates network application-layer message, M, with link transport layer-layer header Ht to create a link transport-layer segment Ht used by transport layer protocol to physical implement its service physical source destination 61  Services, Layering and Encapsulation M application application Ht M transport Transport-layer protocol transfers M (e.g., reliably) from transport one process to another, using services of network layer network Hn Ht M network Network-layer protocol transfers transport-layer segment [Ht | M] from one host to another, using link layer services link link § network-layer protocol encapsulates transport-layer segment [Ht | M] with physical network layer-layer header Hn to create a physical network-layer datagram source Hn used by network layer protocol to destination implement its service 62  Services, Layering and Encapsulation M application application Ht M transport transport network Hn Ht M network Network-layer protocol transfers transport-layer segment [Ht | M] from one host to another, using link layer services link Hl Hn Ht M link Link-layer protocol transfers datagram [Hn| [Ht |M] from host to neighboring host, using network-layer services physical physical § link-layer protocol encapsulates network datagram [Hn| [Ht |M], with link-layer header source Hl to create a link-layer frame destination 63 Encapsulation Matryoshka dolls (stacking dolls) message segment datagram frame 64  Services, Layering and Encapsulation application message M M application transport segment Ht M Ht M transport network datagram Hn Ht M Hn Ht M network link frame Hl Hn Ht M Hl Hn Ht M link physical physical source destination 65 Encapsulation: an end-end view source message M application segment Ht M transport datagram Hn Ht M network frame Hl Hn Ht M link physical link physical switch destination Hn Ht M network M application Hl Hn Ht M link Hn Ht M Ht M transport physical Hn Ht M network Hl Hn Ht M link router 66 physical Two layers not found in the Internet protocol stack! Presentation: allow applications to interpret application the meaning of data, e.g., encryption, compression, machine-specific conventions presentation Session: synchronization, checkpointing, session recovery of data exchange transport The Internet stack is “missing” these network layers! these services, if needed, must be link implemented in application physical needed? The seven layer OSI/ISO reference model 67 Wireshark application (www browser, packet email client) analyzer application OS packet Transport (TCP/UDP) capture copy of all Network (IP) Ethernet frames Link (Ethernet) (pcap) sent/received Physical 68 Thank You A bit more on unit 1 in the following lecture