Chapter 1: Introduction Internet Structure & Protocols IT 424 Networks2 Chapter 1: Introduction Internet Structure & Protocols Ack.: Slides are adapted from the slides of the book: “Computer Networking” – J. Kurose, K. Ross

Overview What’s the Internet? Internet Hardware Internet Software (Protocols) Overview Internet Performance Internet History

Learning Outcomes 1 Define the structure of the Internet in terms of software and hardware 2 Identify the roles of end systems and the network core 3 Differentiate between circuit switching and packet switching 4 Explain the Internet structure as a network of networks 5 Describe the protocol stack in the Internet and the role of each layer 6 Evaluate the performance of the network in terms of end-to-end delay, packet loss and throughput

Overview What’s the Internet? Internet Hardware Internet Software (Protocols) Overview Internet Performance Internet History

What’s The Internet? Service View mobile network global ISP regional ISP home network institutional Infrastructure that provides services to applications: Web, VoIP, email, games, e-commerce, social nets, … Provides programming interface to applications Hooks that allow sending and receiving app programs to “connect” to Internet Provides service options, analogous to postal service

What’s The Internet? Component View Internet: “network of networks” mobile network global ISP regional ISP home network institutional Internet: “network of networks” Interconnected ISPs (Internet Service Providers) Protocols control sending, receiving of messages E.g., TCP, IP, HTTP, Skype, 802.11 Components: hardware + software Internet standards RFC: Request For Comments IETF: Internet Engineering Task Force

Overview What’s the Internet? Internet Hardware Internet Software (Protocols) Overview Internet Performance Internet History

Internet Hardware Millions of connected computing devices: mobile network global ISP regional ISP home network institutional smartphone PC server wireless laptop Millions of connected computing devices: hosts = end systems running network applications Communication links Fiber, copper, radio, satellite Transmission rate: bandwidth wired links wireless Packet switches: forward packets (chunks of data) Routers and switches router

A Closer Look at Network Structure Internet Hardware – Network Structure A Closer Look at Network Structure mobile network global ISP regional ISP home network institutional 1-Network edge: Hosts: clients and servers Servers often in data centers 2- Network core: Interconnected routers Network of networks 3-Access networks, physical media: Wired, wireless communication links

1. The Network Edge “Fun” internet appliances End systems (hosts): Hardware - 1. The Network Edge 1. The Network Edge End systems (hosts): Run application programs e.g., WWW, email at “edge of network” IP picture frame http://www.ceiva.com/ Web-enabled toaster + weather forecaster Slingbox: watch, control cable TV remotely Tweet-a-watt: Monitor energy use Internet refrigerator Internet phones “Fun” internet appliances

Host: Sends Packets of Data Hardware - 1. The Network Edge Host: Sends Packets of Data Host sending function: Takes application message Breaks into smaller chunks, known as packets, of length L bits Transmits packet into access network at transmission rate R Link transmission rate, aka link capacity, aka link bandwidth R: link transmission rate host 1 2 two packets, L bits each

2. The Network Core Mesh of interconnected routers Packet-switching: Hardware - 2. The Network Core 2. The Network Core Mesh of interconnected routers Packet-switching: Hosts break application-layer messages into packets Forward packets from one router to the next, across links on path from source to destination Each packet transmitted at full link capacity

Packet Switching Station breaks long message into packets Hardware - 2. The Network Core Packet Switching application transport network data link physical Station breaks long message into packets Packets sent one at a time to the network Packets from separate messages interleaved with other packets for transmission. network data link physical application transport network data link physical

Packet-Switching: Store-and-Forward Hardware - 2. The Network Core Packet-Switching: Store-and-Forward source R bps destination 1 2 3 L bits per packet Takes time to transmit (push out) L-bit packet into link at R bps Store and forward: entire packet must arrive at router before it can be transmitted on next link

Packet Switching: Queuing Delay, Loss Hardware - 2. The Network Core Packet Switching: Queuing Delay, Loss A B C R = 100 Mb/s R = 1.5 Mb/s D E queue of packets waiting for output link Queuing and loss: If arrival rate (in bits) to link exceeds transmission rate of link for a period of time: packets will queue, wait to be transmitted on link packets can be dropped (lost) if memory (buffer) fills up

Alternative Core: Circuit Switching Hardware - 2. The Network Core Alternative Core: Circuit Switching End-end resources allocated to, reserved for “call” between source & destination: In diagram, each link has four circuits. call gets 2nd circuit in top link and 1st circuit in right link. Dedicated resources: no sharing circuit-like (guaranteed) performance Circuit segment idle if not used by call (no sharing) Commonly used in traditional telephone networks

Circuit Switching: FDM versus TDM Hardware - 2. The Network Core Circuit Switching: FDM versus TDM 4 users Example: Frequency Division Multiplexing (FDM) Frequency Time Time Division Multiplexing (TDM) Frequency Time

Packet Switching versus Circuit Switching Hardware - 2. The Network Core Packet Switching versus Circuit Switching Packet switching allows more users to use network! Example: 1 Mb/s link Each user: 100 kb/s when “active” Active 10% of time Circuit-switching: 10 users Packet switching: With 35 users, probability > 10 active at same time is less than .0004 N users 1 Mbps link ….. Q: What happens if > 35 users ?

Packet Switching versus Circuit Switching Hardware - 2. The Network Core Packet Switching versus Circuit Switching Packet Switching Circuit Switching Advantages Flexibility, high throughput, cheap, simple connection Disadvantages Complex routing, performance? Advantages Simple, correct ordering, low delay Disadvantages Expensive, wasteful, slow connection setup VS.

Packet Switching versus Circuit Switching Hardware - 2. The Network Core Packet Switching versus Circuit Switching Is packet switching a “winner?” Great for bursty data Resource sharing Simpler, no call setup Excessive congestion possible: packet delay and loss Protocols needed for reliable data transfer, congestion control Q: How to provide circuit-like behavior? Bandwidth guarantees needed for audio/video apps Still an unsolved problem Q: Human analogies of reserved resources (circuit switching) versus on-demand allocation (packet-switching)?

3. Access Networks Q: How to connect end systems to edge router? Hardware - 3. Access Networks 3. Access Networks Q: How to connect end systems to edge router? Residential access nets Institutional access networks (school, company) Mobile access networks Keep in mind: Bandwidth (bits per second) of access network? Shared or dedicated?

to/from headend or central office Hardware - 3. Access Networks Access Network: Home Network wireless devices to/from headend or central office often combined in single box wireless access point (54 Mbps) router, firewall, NAT cable or DSL modem wired Ethernet (100 Mbps)

Enterprise Access Networks (Ethernet) Hardware - 3. Access Networks Enterprise Access Networks (Ethernet) Ethernet switch institutional mail, web servers institutional router institutional link to ISP (Internet) Typically used in companies, universities, etc 10 Mbps, 100Mbps, 1Gbps, 10Gbps transmission rates Today, end systems typically connect into Ethernet switch

Wireless Access Networks Hardware - 3. Access Networks Wireless Access Networks Shared wireless access network connects end system to router - via base station aka “access point” to Internet to Internet Wireless LANs: within building (100 ft) 802.11b/g (WiFi): 11, 54 Mbps transmission rate Wide-area wireless access provided by telco (cellular) operator, 10’s km between 1 and 10 Mbps 3G, 4G: LTE

Internet Structure: Network of Networks Hardware – Internet Structure Internet Structure: Network of Networks End systems connect to Internet via access ISPs (Internet Service Providers) Residential, company and university ISPs Access ISPs in turn must be interconnected. So that any two hosts can send packets to each other Resulting network of networks is very complex Evolution was driven by economics and national policies Let’s take a stepwise approach to describe current Internet structure

Internet Structure: Network of Networks Hardware - Internet Structure Internet Structure: Network of Networks access net … Question: given millions of access ISPs, how to connect them together?

Internet Structure: Network of Networks Hardware - Internet Structure Internet Structure: Network of Networks access net … connecting each access ISP to each other directly doesn’t scale: O(N2) connections. Option: connect each access ISP to every other access ISP?

Internet Structure: Network of Networks Hardware - Internet Structure Internet Structure: Network of Networks access net … global ISP Option: connect each access ISP to a global transit ISP? Customer and provider ISPs have economic agreement.

Internet Structure: Network of Networks Hardware - Internet Structure Internet Structure: Network of Networks access net … ISP B ISP A ISP C But if one global ISP is viable business, there will be competitors …

Internet Structure: Network of Networks Hardware - Internet Structure Internet Structure: Network of Networks access net … ISP B ISP A ISP C IXP peering link Internet exchange point But if one global ISP is viable business, there will be competitors …. which must be interconnected

Internet Structure: Network of Networks Hardware - Internet Structure Internet Structure: Network of Networks access net … ISP B ISP A ISP C IXP regional net … and regional networks may arise to connect access nets to ISPS

Internet Structure: Network of Networks Hardware - Internet Structure Internet Structure: Network of Networks access net … ISP B ISP A IXP regional net Content provider network … and content provider networks (e.g., Google, Microsoft, Akamai ) may run their own network, to bring services, content close to end users

Internet Structure: Network of Networks Hardware - Internet Structure Internet Structure: Network of Networks 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 network (e.g, Google): private network that connects it data centers to Internet, often bypassing tier-1, regional ISPs

Tier-1 ISP: e.g., Sprint … to/from backbone peering to/from customers Hardware - Internet Structure Tier-1 ISP: e.g., Sprint … to/from customers peering to/from backbone POP: point-of-presence

Overview What’s the Internet? Internet Hardware Internet Software (Protocols) Overview Internet Performance Internet History

Protocol “Layers” Networks are complex, with many “pieces”: hosts Internet Software Protocol “Layers” Networks are complex, with many “pieces”: hosts routers links of various media applications protocols hardware, software

Why Layering? Dealing with complex systems: Internet Software Why Layering? Dealing with complex systems: Explicit structure allows identification, relationship of complex system’s pieces layered reference model for discussion Modularization eases maintenance, updating of system change of implementation of layer’s service transparent to rest of system e.g., change in gate procedure doesn’t affect rest of system Layering considered harmful?

ISO/OSI Reference Model Internet Software ISO/OSI Reference Model Presentation: allow applications to interpret meaning of data, e.g., encryption, compression, machine-specific conventions Session: synchronization, checkpointing, recovery of data exchange Internet stack “missing” these layers! these services, if needed, must be implemented in application needed? application presentation session transport network link physical

Internet Protocol Stack Internet Software Internet Protocol Stack Application: supporting network applications Ftp, smtp, http Transport: process-process data transfer Tcp, udp Network: routing of datagrams from source to destination IP, routing protocols Link: data transfer between neighboring network elements Ethernet, 802.111 (wifi), PPP Physical: bits “on the wire” application transport network link physical

Encapsulation destination source application transport network link Internet Software Encapsulation source message M application transport network link physical segment Ht Ht M datagram Ht Hn M Hn frame Ht Hn Hl M link physical switch destination network link physical Ht Hn M Ht Hn Hl M M application transport network link physical Ht Hn M Ht M Ht Hn M router Ht Hn Hl M

Overview What’s the Internet? Internet Hardware Internet Software (Protocols) Overview Internet Performance Internet History

How Do Loss and Delay Occur? Network Performance How Do Loss and Delay Occur? Packet being transmitted (delay) A Free (available) buffers: arriving packets dropped (loss) if no free buffers B Packets queueing (delay) Packets queue in router buffers Packet arrival rate to link (temporarily) exceeds output link capacity Packets queue, wait for turn

Packet Loss buffer (waiting area) packet being transmitted A B Network Performance - Packet Loss Packet Loss A B packet being transmitted packet arriving to full buffer is lost buffer (waiting area) Queue (aka buffer) preceding link in buffer has finite capacity Packet arriving to full queue dropped (aka lost) Lost packet may be retransmitted by previous node, by source end system, or not at all

Four sources of packet delay Network Performance - Delay Four sources of packet delay A B propagation transmission nodal processing queueing dnodal = dproc + dqueue + dtrans + dprop dproc: nodal processing check bit errors determine output link typically < msec dqueue: queueing delay time waiting at output link for transmission depends on congestion level of router

Four sources of packet delay Network Performance - Delay Four sources of packet delay A B propagation transmission nodal processing queueing dnodal = dproc + dqueue + dtrans + dprop dtrans: transmission delay: L: packet length (bits) R: link bandwidth (bps) dtrans = L/R dprop: propagation delay: d: length of physical link s: propagation speed in medium (~2x108 m/sec) dprop = d/s dtrans and dprop very different

Throughput server sends bits (fluid) into pipe pipe that can carry Network Performance - Throughput Throughput server sends bits (fluid) into pipe pipe that can carry fluid at rate Rs bits/sec) Rc bits/sec) Throughput: rate (bits/time unit) at which bits transferred between sender/receiver Instantaneous: rate at given point in time Average: rate over longer period of time

Throughput bottleneck link Rs bits/sec Rc bits/sec Rs bits/sec Network Performance - Throughput Throughput Rs < Rc What is average end-end throughput? Rc bits/sec Rs bits/sec Rs > Rc What is average end-end throughput? Rs bits/sec Rc bits/sec Link on end-end path that constrains end-end throughput bottleneck link

10 connections (fairly) share backbone bottleneck link R bits/sec Network Performance - Throughput Throughput: Internet Scenario Rs Rc R Per-connection end-end throughput: min(Rc,Rs,R/10) In practice: Rc or Rs is often bottleneck 10 connections (fairly) share backbone bottleneck link R bits/sec

Overview What’s the Internet? Internet Hardware Internet Software (Protocols) Overview Internet Performance Internet History

Internet History 1961-1972: Early packet-switching principles 1972: ARPAnet public demo NCP (Network Control Protocol) first host-host protocol first e-mail program ARPAnet has 15 nodes 1961: Kleinrock - queueing theory shows effectiveness of packet-switching 1964: Baran - packet-switching in military nets 1967: ARPAnet conceived by Advanced Research Projects Agency 1969: first ARPAnet node operational

Internet History 1972-1980: Internetworking, new and proprietary nets 1970: ALOHAnet satellite network in Hawaii 1974: Cerf and Kahn - architecture for interconnecting networks 1976: Ethernet at Xerox PARC late70’s: proprietary architectures: DECnet, SNA, XNA late 70’s: switching fixed length packets (ATM precursor) 1979: ARPAnet has 200 nodes Cerf and Kahn’s internetworking principles: minimalism, autonomy - no internal changes required to interconnect networks best effort service model stateless routers decentralized control define today’s Internet architecture

Internet History 1980-1990: new protocols, a proliferation of networks New national networks: Csnet, BITnet, NSFnet, Minitel 100,000 hosts connected to confederation of networks 1983: deployment of TCP/IP 1982: smtp e-mail protocol defined 1983: DNS defined for name-to-IP- address translation 1985: ftp protocol defined 1988: TCP congestion control

Internet History 1990, 2000’s: commercialization, the Web, new apps late 1990’s – 2000’s: more killer apps: instant messaging, P2P file sharing network security to forefront est. 50 million host, 100 million+ users backbone links running at Gbps early 1990’s: ARPAnet decommissioned 1991: NSF lifts restrictions on commercial use of NSFnet (decommissioned, 1995) early 1990s: Web hypertext [Bush 1945, Nelson 1960’s] HTML, HTTP: Berners-Lee 1994: Mosaic, later Netscape late 1990’s: commercialization of the Web

Internet History 2005-present ~750 million hosts Smartphones and tablets Aggressive deployment of broadband access Increasing ubiquity of high-speed wireless access Emergence of online social networks: Facebook: soon one billion users Service providers (Google, Microsoft) create their own networks Bypass Internet, providing “instantaneous” access to search, emai, etc. E-commerce, universities, enterprises running their services in “cloud” (eg, Amazon EC2)

Conclusion Conclusion The Internet consists of network edge, network core and access Packet switching is more suitable for the transmission of bursty data in the Internet Layering architecture is very useful to isolate layers. Updating and changing one layer will not affect the others. The performance of the network is measured by packet loss, throughput and delay Delay is caused by four components: processing delay, transmission delay, propagation delay and queuing delay. Processing, transmission, and propagation delay can be calculated. Queuing delay can’t be predicted

References References Computer Networking: A Top-Down Approach Featuring the Internet by James Kurose and Keith Ross, Addison Wesley, 2012 (chapter 1 ) Internet Protocol (RFC791) A Brief History of the Internet, S. Segaller, TV Books, New York, 1998