Chapter 1 Introduction Computer Networking: A Top Down Approach 6th edition Jim Kurose, Keith Ross Addison-Wesley March 2012 A note on the use of these ppt slides: We’re making these slides freely available to all (faculty, students, readers). They’re in PowerPoint form so you see the animations; and can add, modify, and delete slides (including this one) and slide content to suit your needs. They obviously represent a lot of work on our part. In return for use, we only ask the following: If you use these slides (e.g., in a class) that you mention their source (after all, we’d like people to use our book!) If you post any slides on a www site, that you note that they are adapted from (or perhaps identical to) our slides, and note our copyright of this material. Thanks and enjoy! JFK/KWR All material copyright 1996-2012 J.F Kurose and K.W. Ross, All Rights Reserved Introduction

Lecture 2 CPE 400 / 600 Computer Communication Networks University of Nevada – Reno Computer Science & Engineering Department Fall 2015 CPE 400 / 600 Computer Communication Networks Lecture 2 Prof. Shamik Sengupta Office SEM 204 ssengupta@unr.edu http://www.cse.unr.edu/~shamik/ Introduction

Intro to Computer Networking

What is computer network: “nuts and bolts” view PC server wireless laptop cellular handheld Numerous connected computing devices: hosts = end systems running network apps Home network Institutional network Mobile network Global ISP Regional ISP communication links fiber, copper, radio, satellite transmission rate = bandwidth wired links access points routers: forward packets (chunks of data) router

Uses of Computer Networks Business Networks Home Networks Mobile Networks

Example Network Applications (1) A network with two clients and one server (typical client-server connection)

Example Network Applications (2) The client-server model involves requests and replies over the public/private network

Example Network Applications (3) Peer-to-peer networking: no fixed clients and servers

Example wireless network (4) wireless hosts laptop, PDA, IP phone run applications may be stationary (non-mobile) or mobile wireless does not always mean mobility network infrastructure

Categorization of networks by coverage scale Personal area networks (PAN) Local area networks (LAN) Metropolitan area networks (MAN) Wide are networks (WAN) The Internet (Global network)

Personal Area Network (PAN) Bluetooth PAN configuration

Local Area Networks (LAN) Wireless and wired LANs. (a) 802.11. (b) Switched Ethernet.

Metropolitan Area Networks (MAN) A metropolitan area network

Wide Area Networks (WAN) WAN that connects three branch offices in Australia

Coverage scale (contd.) Classification of interconnected processors by scale

A different categorization of networks In terms of communication technology Unicasting Broadcasting Multicasting

What is computer networking: an operational view Any communication is all about protocol Hi Connection req. Hi Connection reply. Got the time? Get http://www.cnn.com/slide.ppt 2:00 <file> time human protocol networking protocol

What is computer networking: an operational view human protocols: … specific msgs sent … specific actions taken when msgs received, or other events network protocols: machines rather than humans all communication activity governed by protocols protocols define format, order of msgs sent and received among network entities, and actions taken on msg transmission, receipt

Protocol “Layers” Question: Networks are complex! It is not just two machines communicating! Millions of components: hosts routers Access networks Physical links Numerous functionalities Question: How to manage such vast amount of components? Soln: Divide functionalities among multiple layers.

Layering of airline functionality ticket (purchase) baggage (check) gates (load) runway (takeoff) airplane routing departure airport arrival intermediate air-traffic control centers ticket (complain) baggage (claim gates (unload) runway (land) ticket baggage gate takeoff/landing Layers: each layer implements a service via its own internal-layer actions relying on services provided by layer below and above Another example: Postal Service!

What are the adv. of layering? Network is a huge complex system. Reduce the design complexity Ease of updating the system change of implementation of layer’s service transparent to rest of system e.g., Postal service (overnight flight or overnight ground)

Internet protocol stack application support host/network applications Email, FTP, HTTP (HTML) transport process-process data transfer TCP, UDP network routing of datagrams from src. to destn. IP address, routing protocols link data transfer between neighboring network elements Ethernet physical bits “on the wire” application transport network link physical (Compare with the Postal System!)

The TCP/IP Reference Model

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 application presentation session transport network link physical Introduction

Messages, Segments, Datagrams and Frames source message M application transport network link physical segment Ht M Ht datagram Ht Hn M Hn frame Ht Hn Hl M link physical Encapsulation switch destination network link physical Ht Hn M message Ht Hn Hl M M application transport network link physical Ht Hn M Ht M Ht Hn M router Ht Hn Hl M

Lecture 3 CPE 400 / 600 Computer Communication Networks University of Nevada – Reno Computer Science & Engineering Department Fall 2015 CPE 400 / 600 Computer Communication Networks Lecture 3 Prof. Shamik Sengupta Office SEM 204 ssengupta@unr.edu http://www.cse.unr.edu/~shamik/ Introduction

Network core Network structure packet switching, circuit switching, 27 Introduction 27

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 Introduction

Packet-switching: store-and-forward L bits per packet 3 2 1 source destination R bps R bps takes L/R seconds 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 one-hop numerical example: L = 7.5 Mbits R = 1.5 Mbps one-hop transmission delay = 5 sec end-end delay = 2L/R (assuming zero propagation delay) more on delay shortly … Introduction

Packet Switching: queueing delay, loss R = 100 Mb/s D R = 1.5 Mb/s B 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 Introduction

Alternative core: circuit switching end-end resources allocated to, reserved for “call” between source & dest: 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 Introduction

Circuit switching: FDM versus TDM 4 users Example: FDM frequency time TDM frequency time Two simple multiple access control techniques. Each mobile’s share of the bandwidth is divided into portions for the uplink and the downlink. Also, possibly, out of band signaling. As we will see, used in AMPS, GSM, IS-54/136 Introduction

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 ….. N users 1 Mbps link Introduction

Packet switching versus circuit switching is packet switching a “clear 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… Introduction

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 Question: given millions of access ISPs, how to connect them together? access net …

Internet structure: network of networks Option: connect each access ISP to every other access ISP? access net … … connecting each access ISP to each other directly doesn’t scale: O(N2) connections.

Internet structure: network of networks Option: connect each access ISP to a global transit ISP? Customer and provider ISPs have economic agreement. access net … global ISP

Internet structure: network of networks But if one global ISP is viable business, there will be competitors …. access net … ISP A ISP B ISP C

Internet structure: network of networks But if one global ISP is viable business, there will be competitors …. which must be interconnected Internet exchange point access net … ISP A IXP IXP ISP B ISP C peering link

Internet structure: network of networks … and regional networks may arise to connect access nets to ISPS access net … ISP A IXP IXP ISP B ISP C regional net

Internet structure: network of networks roughly hierarchical at center: “tier-1” ISPs (e.g., Verizon, Sprint, AT&T, Cable and Wireless), national/international coverage treat each other as equals Tier 1 ISP Tier 1 ISP Tier 1 ISP

Tier-1 ISP: e.g., Sprint

Internet structure: network of networks “Tier-2” ISPs: smaller (often regional) ISPs Connect to one or more tier-1 ISPs, possibly other tier-2 ISPs Tier-2 ISPs also peer privately with each other. Tier-2 ISP Tier-2 ISP pays tier-1 ISP for connectivity to rest of Internet tier-2 ISP is customer of tier-1 provider Tier 1 ISP Tier 1 ISP Tier 1 ISP

Internet structure: network of networks “Tier-3” ISPs and local ISPs last hop (“access”) network (closest to end systems) local ISP Tier 3 Local and tier- 3 ISPs are customers of higher tier ISPs connecting them to rest of Internet Tier-2 ISP Tier 1 ISP Tier 1 ISP Tier 1 ISP

Internet structure: network of networks a packet passes through many networks! local ISP Tier 3 ISP local ISP local ISP local ISP Tier-2 ISP Tier 1 ISP Tier 1 ISP Tier 1 ISP local ISP local ISP local ISP local ISP

Delay, loss, throughput in networks Introduction 47

How do loss and delay occur? packets queue in router buffers packet arrival rate to link (temporarily) exceeds output link capacity packets queue, wait for turn packet being transmitted (delay) A free (available) buffers: arriving packets dropped (loss) if no free buffers B packets queueing (delay) Introduction

Four sources of packet delay transmission A propagation B 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 Introduction

Four sources of packet delay transmission A propagation B 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 Introduction 50

Packet loss 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 buffer (waiting area) packet being transmitted A B packet arriving to full buffer is lost Introduction

Throughput 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 server, with file of F bits to send to client link capacity Rs bits/sec server sends bits (fluid) into pipe pipe that can carry fluid at rate Rs bits/sec) Rc bits/sec) link capacity Rc bits/sec Introduction

Throughput: Internet scenario per-connection end-end throughput: min(Rc,Rs,R/10) in practice: Rc or Rs is often bottleneck Rs Rs Rs R Rc Rc Rc 10 connections (fairly) share backbone bottleneck link R bits/sec Introduction

The principal metric prefixes Metric Units (1) The principal metric prefixes

The principal metric prefixes Metric Units (2) The principal metric prefixes