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CMPE 150: Introduction to Computer Networks J.J. Garcia-Luna-Aceves Email: [email protected] Phone: 94153 Office: E2, Room 317 CCRG Lab: E2, Room 315 http://www.cse.ucsc.edu/research/ccrg/CMPE150/FALL2004 May 17 UCSC CMPE150 1 CMPE 150: Introduction to Computer Networks LECTURE 1: Introduction and Background May 17 UCSC CMPE150 2 Outline What is a computer network? Brief history and outlook of the Internet. What are communication protocols and how do we go about studying them? Architectural structure of the Internet. Issues of interest with transmission media as a black box. More about networks and links. May 17 UCSC CMPE150 3 What Is a Computer Network? A communication network is a set of nodes connected by links and able to communicate with one another. A computer network is a communication network in which nodes are computers. The purpose of the network is to serve users, which can be humans or processes. Network links can be point-to-point or multipoint and implemented with several transmission media. Information exchanged can be represented in multiple media (audio, text, video, images, etc.) Services provided to users can vary widely. May 17 UCSC CMPE150 4 Why Learn about Computer Networks? Computer networks started as a means for The “web” and affordable hardware have changed this! Distributed processing Communicating among people (electronic mail, conferencing) Increasing system reliability We are evolving into Internet-based enterprises, Internet-based home services, and an Internet society The network will be everywhere… Computers will be used in almost everything we build (including sensors, appliances, books, newspapers) These computers need to be interconnected NETWORKING = COMPUTING May 17 UCSC CMPE150 5 Why Learn about Computer Networks? Industry and research are wide open to innovation! Today’s protocols are oriented to support “host-to-host” communication and assume a client-server model for services and an “open door” policy for the Internet community. The continuing success of the Internet requires: Person-to-person communication (voice and other media over the Internet) Client-to-content services. Security in the services, the infrastructure, and the clients of the Internet Innovation required includes: Mechanisms to “look-up” content, rather than addresses. Protocols aimed at the new types of communication and services Protocols that adhere to new principles of design. Protocol stacks for nomadic users. May 17 UCSC CMPE150 6 Evolution of Computer Networks 1876: 1890s: 1897: 1940s: 1960: 1960s: 1961: 1962: 1965: 1968: 1969: 1970s: May 17 Telephone by A. Graham Bell Electromagnetic telephone switches Cathode Ray Tube by K.F. Braun Computers, error detection and retransmission RS-232 physical layer interface (the “serial port”) and modems T-1 carrier system for telephone transmission (1.5Mbps) The Compatible Time Sharing System Paul Baran at RAND proposes packet switching Automatic equalization by Bob Lucky and others Carterfone FCC decision that led to AT&T divestiture in 1984. DARPA funds project on packet switching Computerized switches; work on ISDN starts UCSC CMPE150 7 Evolution of Computer Networks 1970s: ARPANET starts (UCLA, Utah, SRI, UCSB); its technology evolved into today’s Internet 1970s: ALOHA system at U. of Hawaii; first protocol for multiple access channels; leads to Ethernet 1970s: GUI, mouse, hypertext by Doug Engelbart at SRI 1974: “A Protocol for Packet Network Interconnection,” V. Cerf and R. Kahn, IEEE Trans. Comm (May). 1980s: OSI (open system interconnection) reference model 1982: TCP/IP is deployed in ARPANET/MILNET 1984: Host table evolves into DNS in ARPANET 1984: AT&T breaks up 1986: NSFNET is created; becomes Internet backbone 1992: WWW by Tim Berners-Lee (CERN) is released; gives a GUI to the Internet 1990s: Caches and proxies helping clients access content May 17 UCSC CMPE150 8 Evolution of Computer Networks 1970s: CCITT publishes standards for public data networks (X.25 standards) 1980s: Token ring LANs, FDDI emerge; do not replace Ethernet 1990s: ATM evolves; does not replace IP 1990s: Internet: From 4 to 30M+ wired, published nodes in two decades 1990s: SONET (synchronous optical network) and SDH (synchronous digital hierarchy) evolve 1990s: Cellular phones, laptops, palmtops become popular 1999: Gigabit Ethernet starts, simplicity wins again. May 17 UCSC CMPE150 9 Evolution of Computer Networks What will happen in the 2000s?: Ad-hoc wireless networks; self-configuring nets Networked sensors and appliances System-area networks (“the network is [in] the computer”) Network-based computing: grid computing (“the computer--processing and storage--is in the network”) Internet-to-go; deeply networked systems IP voice, IP devices Content routing: ISPs start to be CDNs, allow clients to obtain content based on its name from the best location …. Networking May 17 UCSC = Computing CMPE150 10 What Do We Study? We will use the Internet as our running example. The Internet has computer hardware, software, operating systems, transmission technology, services defined over it... What is its glue? Communication protocols implemented in software or hardware transform otherwise isolated machines into a society of computers. Protocols specify how processes in different machines can interact to provide a given service. Distributed algorithms are the essence of what we study. May 17 UCSC CMPE150 11 Communication Protocols A set of rules governing the interaction of concurrent processes in a system. A protocol has five parts: The service it provides. The assumptions about the environment where it executes, including the services it enjoys. The vocabulary of messages used to implement it The format of each message in the vocabulary. The procedure rules (algorithms) guarding the consistency of message exchanges and the integrity of the service provided. May 17 UCSC CMPE150 12 What Do We Study Regarding Protocols? What is a good protocol design? What are good and bad aspects in a protocol? Judging by their survival, Ethernet and IP are good; token ring protocols are not very good TCP adapts to congestion, but it inherently assumes that the Internet sends packets in order. Use representative protocols to go over these issues. Discuss new directions in computer communication. May 17 UCSC CMPE150 13 What Do We Study Regarding Protocols? We will take a quick look at the principles of computer communication. Our principles are: May 17 The description of a protocol has no ambiguity. A protocol does what it is supposed to do, all the time. A protocol does not leave any communicating party waiting forever for something to happen. A protocol makes efficient use of available resources. A protocol enables the use of resources fairly or according to a predefined contract. As with most engineering topics, simplicity is important. UCSC CMPE150 14 Principles of Computer Communication Protocol specification: The description of the protocol is complete and accurate. Safety: A protocol does what it is supposed to do, all the time. Liveness: A protocol does not leave any deadlocks. Efficiency: A protocol makes efficient use of available resources. Fairness: Fair or contractual use of resources Simplicity is desirable, but not necessary. May 17 UCSC CMPE150 15 In The Beginning There Was ARPANET SRI UTAH IMP IMP UCSB IMP IMP UCLA 12/1/69 May 17 UCSC CMPE150 16 The Beginnings of Protocol Layering Host-Host HOST IMP HOST IMP IMP IMP-IMP application Host-IMP application IMP Routing within ARPANET is transparent to hosts attaching to the ARPANET May 17 UCSC CMPE150 17 Characteristics of ARPANET Architecture Backbone-based: A finite number of identifiers suffices to name the IMPs that constitute the backbone. The backbone provides a common packet-delivery service to the backbone users. Host-centric: May 17 The users of the backbone are host computers. The identifiers used to route packets to destinations are the names of the attachment points of the hosts; these are unique identifiers throughout the network. A centralized host table can be used to map text-based host names to the numeric names. UCSC CMPE150 18 Internet Model Problem: Need to maintain the details of how packets are forwarded within and across heterogeneous networks transparent to the users (hosts) of the interconnect. Approach: May 17 Use a common end-to-end protocol spoken by all gateways interconnecting networks, and also by the hosts talking to gateways. UCSC CMPE150 19 Internet Model 3 A A@3 NET NET G IP G IP G G B NET NET Users of the interconnect are hosts. A single address space is used to draw numeric names for networks (“3”) and hosts (“A@3”). An end-to-end protocol (the Internet Protocol or IP) is used for delivering all user and control data, with a common definition of services. A table is used to map people-friendly names to numeric names. May 17 UCSC CMPE150 20 Internet Model R R G R R R G G G How data are forwarded within each network is transparent to IP, and IP is transparent to each network May 17 UCSC CMPE150 21 Internet R R R R R R R R R R NSFNET: Routers inside networks also use IP. IP in every router; no need for network gateways. Names of routers are “router@net” May 17 UCSC CMPE150 22 ARPANET Growth (a) December 1969, (b) July 1970, (c) March 1971, (d) April 1972, (e) September 1972. May 17 UCSC CMPE150 23 NSFNET Topology May 17 The NSFNET backbone in 1988. UCSC CMPE150 24 Internet Elements R R R R R R R R R Hosts: The computers running user applications (clients, servers, proxies). Routers/bridges/switches: Devices used to interconnect hosts and to forward data from source to destination host. Networks: Aggregations of hosts and routers. Links between devices. May 17 UCSC CMPE150 25 What Is The Internet protocols Internet: “network of networks” router server workstation mobile local ISP loosely hierarchical public Internet versus private intranet regional ISP Internet standards May 17 RFC: Request for comments IETF: Internet Engineering Task Force UCSC company network CMPE150 26 Internet Example What does it take to get a page from the web? Your client computer (client) and attached router have to be configured. Host and router communicate with each other through a LAN or point-to-point link (PPP, CSMA/CD, 802.11, etc.). Data is broken into “packets,” which are to be routed from client to server and from server to client over a large number of links, computers dedicated to routing, and networks (IP, ARP, ICMP, OSPF, RIP, BGP). Host obtains the IP address of remote server from a name resolver (UDP, DNS) . Client starts an end-to-end reliable connection with remote server (TCP). Client and server start exchanging messages (HTTP). May 17 UCSC CMPE150 27 Internet Example P P R R R R R R R R R R One of many processes at one of many hosts in one of many networks communicates with another process, which is one of many processes at one of many hosts attached to one of many networks. May 17 UCSC CMPE150 28 Layering Model Purpose is to divide and conquer complex software and hardware needed to implement services Partition services and functions needed in system into layers Each layer of service is provided by peer protocol entities Communication can be point-to-point or multipoint Layer N packets NODE A Layer-N Protocol Entity (virtual communication) interface NODE B protocol Layer-(N - 1) Protocol Entity May 17 Layer-N Protocol Entity Layer-(N - 1) Protocol Entity UCSC CMPE150 29 The OSI Architecture Proposed by the International Standards Organization Specifies the functions at each layer, not the protocols that implement them APPLICATION PRESENTATION SESSION TRANSPORT NETWORK LINK PHYSICAL May 17 End-user services (e.g., mail, file transfer) Web access Formatting, encryption, compression of data Setup and management of end-to-end dialogue End-to-end delivery of messages to processes TCP End-to-end transmissions of packets in net IP Transmissions of packets over a link PPP, CSMA/CD Transmission of bits over physical media SONET UCSC CMPE150 30 Protocol Description Specify the service to be provided by the protocol Specify assumptions about environment Specify vocabulary (messages) needed in the protocol Specify the algorithms used to process and exchange information in the protocol Specify format of messages in vocabulary We do this only in some cases Our specifications are informal! May 17 UCSC CMPE150 31 Protocol Correctness A protocol must be safe and live Safety: Liveness: Protocol provides the desired service all the time Protocol has no deadlocks (no process waits forever for an event to occur) Proving one may depend on the other May 17 UCSC CMPE150 32 Protocol Performance Average delay Throughput or capacity Time between transmission of an information bit and reception of the bit at the receiver Number of information bits sent divided by the time between transmission of first bit and delivery of the last bit Bottlenecks Computations will make strong assumptions; in most cases, results of analytical model provide only a rough approximation Most effective for comparative analysis May 17 UCSC CMPE150 33 Basic Network Services S 1,2 1,2 D All data flow along same path Shared network resources Connection-oriented service: May 17 Reliable data transfer: In-order delivery, no duplicates or missing data. Flow control: Do not congest the receiver(s). Congestion control: Do not congest the network(s). UCSC CMPE150 34 Basic Network Services S 1,2 2 2 2 1 1,2 1 1 D Data may take different paths to destination 1 Shared network resources Connection-oriented service: May 17 Reliable data transfer: In-order delivery, no duplicates or missing data. Flow control: Do not congest the receiver(s). Congestion control: Do not congest the network(s). UCSC CMPE150 35 Basic Network Services S 1,2,3 2,1,2 D Shared network resources Connectionless service: No delivery guarantees needed from the network. Any connection-oriented service to application is provided by end-to-end protocol. May 17 UCSC CMPE150 36 Switching Methods S D Shared network resources Allocation of shared network resources to the transport of user data. Circuit switching and packet switching are the two main types we will consider. May 17 UCSC CMPE150 37 Circuit Switching S D call request call accept DATA call termination termination ack Portion of physical resource is assigned to a single connection. Delay and signaling overhead in establishing and ending connections. May 17 UCSC CMPE150 38 Multiplexing in Circuit Switching Share a given communication channel among multiple connections. Frequency division multiplexing (FDM): Frequency spectrum of a link is partitioned into multiple bands, and each band is assigned to zero or one connection at any given time. Time division multiplexing (TDM): May 17 Time is divided into frames of fixed duration, and each frame is divided into a fixed number of time slots. A connection is assigned to a time slot, and occupies the same time slot for multiple frames. UCSC CMPE150 39 FDM and TDM Example: FDM 4 users frequency time TDM frequency May 17 UCSC time CMPE150 40 Message Switching S D message Message from sender is sent on a store-and-forward basis. Message has a header used for forwarding. Resources shared among different calls. May 17 UCSC CMPE150 41 Statistical Multiplexing Share the same communication channel among multiple connections without fixed allocations of the resource to those connections. S1 S2 m2 m1 m2 m2 m1 m1 m2 D1 m1 Link is shared based on the statistics of each connection or flow. D2 Limitation: Entire message must be received at a switch before it can be forwarded May 17 UCSC CMPE150 42 S Packet Switching D packet 1 packet 2 packet 3 packet 4 Message from sender is broken into packets. Each packet consists of a header and a payload. Header information is used to forward packet to destination. May 17 UCSC CMPE150 43 S Packet Switching D forward store A packet switch stores each packet it receives and determines how to forward it based on the header information in the packet. May 17 UCSC CMPE150 44 S Packet Switching D packet 1 packet 2 packet 3 packet 4 Resources are shared among connections Packets from the same connection can be processed concurrently Connection setup delay can be avoided using datagrams May 17 UCSC CMPE150 45 Packet Switching vs Message Switching D S Processing message as packets in store-and-forward mode saves time if propagation delays are small! May 17 UCSC CMPE150 46 Packet Switching Information is organized into packets A packet consists of a header and a payload Header specifies the control information needed to transport the packet from origin to destination Packets are forwarded from source to destination using routing tables There are two basic approaches to packet switching: datagrams virtual circuits May 17 UCSC CMPE150 47 Datagrams 2 e 6 a 7 5 1 b c 3 4 c->d To b To d To e To 4 …. go to 2 go to 3 go to 2 go to 3 d next next next next Routing table specifies next hop to each destination Packets are forwarded based on the routing table Each packet is routed independently May 17 UCSC CMPE150 48 Virtual Circuits VC1 2 a e 6 VC3 1 7 5 b c 3 VC2 4 d Virtual circuits are established and terminated much like circuits in circuit switching. Statistical multiplexing using packets, rather than FDM or TDM is used to share links among connections. May 17 UCSC CMPE150 49 Virtual Circuits VC1 2 a e 6 7 5 1 b c 3 4 d VC2 For VC1 use 2 For VC2 use 3 For VC3 use 3 ... Routing table specifies the next hop of an established VC. Packet header specifies VC to be used for the packet. All packets of the same VC are routed the same way. May 17 UCSC CMPE150 50 Virtual Circuits VC1 2 a e 6 7 5 1 b c VC5 3 4 d VC2 VC4 For VC5 in, use 4 and label as VC2 For VC4 in, use 5 and label as VC3 ... Relative or global VC names can be used. Relative VC names require “label swapping.” May 17 UCSC CMPE150 51 Packet Switching versus Circuit Switching Packet switching allows more users to use network! 1 Mbit link Each user: 250 kbps when “active” active 10% of time Circuit-switching: N users 4 users Packet switching: 1 Mbps link With 10 users, the probability of having more than 4 active users is 0.0016! The average number of users active on the link is one. May 17 UCSC Look at the probability of having up to 10 active users. Look at the arithmetic average. CMPE150 52 Packet Switching versus Circuit Switching Works great in the average! However, more than 4 users may be active at the same time. In that case, packets are queued at the switch, and congestion occurs. Queuing delays are important. May 17 UCSC N users 1 Mbps link CMPE150 53 By Contrast: FDM and TDM Example: FDM 2 active users frequency time TDM frequency May 17 UCSC time CMPE150 54 Packet Switching versus Circuit Switching Great for bursty data Resource sharing Simpler, no call setup (with datagrams!) Excessive congestion: packet delay and loss Protocols needed for reliable data transfer, congestion control, etc. Q: How to provide circuit-like behavior? Bandwidth guarantees needed for audio/video applications. Answer: Still a research problem. May 17 UCSC CMPE150 55 Transmission Media We consider the physical layer as a “black box” We are interested in the characteristics and services provided by the transmission media that impact the link layer and higher layers. Parameters: May 17 Bandwidth Delay or latency: average and variance Storage capacity (bandwidth-delay product) Reliability and security Order of delivery Type of sharing or access UCSC CMPE150 56 Bandwidth We can communicate information over transmission media using energy, by varying some physical property (e.g., voltage or current). Problem: What the sender transmits is not exactly what the receiver obtains from the communication link. Reasons: Link incurs some energy loss and delays, and there are other interfering sources. receiver sender May 17 UCSC CMPE150 57 Bandwidth We think of the bandwidth of a network or link as the number of information bits that can be transmitted over it in a certain period of time (e.g., bits per second). The bandwidth of a link is really the frequency range tolerated by the channel without major attenuation. Telephone line is 3000 Hz (300Hz to 3300 Hz) Available bandwidth depends on the rate at which channel can change stored energy. We can model waveforms as sums of sine waves of different frequencies. Channel attenuates and delays each frequency component differently, causing distortion. May 17 UCSC CMPE150 58 Bandwidth Signals are run through a low-pass filter, and a signal can have V discrete levels. Maximum data rate of a noiseless channel of bandwidth B when V discrete levels are used is Data Rate = 2B log2 V bps (Nyquist, 1924). Keep increasing V to achieve higher data rates with same B ? Regardless of V, the maximum data rate (capacity) of a noisy channel with bandwidth B and signal-to-noise ratio S/N is C = B log2 (1+S/N) bps (Shannon, 1948) S is the average signal power and N is the average noise power Example: For a telephone line, B is 3000 Hz, with a typical S/N ratio of 1000, so C is 30Kbps or so We can achieve higher capacity only by increasing S/N! May 17 UCSC CMPE150 59 Sources of Packet Delay A B t1 t2 What contributes to the delay from the time the first information bit is sent by the source (t1) to the time when the last information bit is obtained by the receiver? May 17 UCSC CMPE150 60 Sources of Packet Delay A transmission time of packet over each link B queueing nodal processing delay nodal queueing processing delay propagation delay of each link May 17 UCSC CMPE150 61 Sources of Packet Delay Nodal processing: Queueing delay: Time waiting at output link for transmission. Depends on congestion level of router. Transmission delay: Checking for bit errors. Determining output link. Time to send bits into link: L/R, where R = link bandwidth (bps) and L = packet length (bits) Propagation delay: May 17 Time for each bit to traverse a link: d/s, where d = length of physical link and s = propagation speed in medium (~2x108 m/sec) UCSC CMPE150 62 Packet Delay Packet delay is the time elapsed between the instant when the sender transmits the first bit of a obtains the last bit of the packet. Packet delay = Processing delay + Propagation delay + Transmission delay + Queuing delay Propagation delay = Distance / Speed of light Speed of light = 3x108 meters/sec in the vacuum ~ 2x108 meters/sec in fiber We can reduce processing, transmit, and queue components using higher link speeds and faster processors, but we cannot reduce the speed of light! Long distances mean long latency! May 17 UCSC CMPE150 63 Nodal Delay d nodal d proc d queue d trans d prop dproc = processing delay dqueue = queuing delay depends on congestion dtrans = transmission delay typically a few microsecs or less = L/R, significant for low-speed links dprop = propagation delay May 17 a few microsecs to hundreds of msecs UCSC CMPE150 64 Queueing delay (revisited) R=link bandwidth (bps) L=packet length (bits) a=average packet arrival rate traffic intensity = La/R La/R ~ 0: average queueing delay small La/R -> 1: delays become large La/R > 1: more “work” arriving than can be serviced, average delay infinite! May 17 UCSC CMPE150 65 Packet Loss Queue (i.e., the buffer) of each outgoing link has finite capacity. When packet arrives to a full queue, packet is dropped (lost). Lost packet may be retransmitted by previous node, by source end system, or not retransmitted at all. May 17 UCSC CMPE150 66 Bandwidth-Delay Product The amount of data “stored” in the link. Think of a link as a pipe; the latency is the length of the pipe and the bandwidth is its diameter. The BD product gives the volume of the pipe. Example: A channel of 50 ms latency and just 45 Mbps bandwidth can hold 2.25 million bits (the same as the memory of a PC of early 80s!). We are moving to Gigabit networks... Big bandwidth and big distances require: May 17 Big aggregation and big memories at hosts New reliable transmission algorithms Migration from client-server to client-content models. UCSC CMPE150 67 Bandwidth-Delay Product Low-speed link S R high-speed link Links stretching long distances have large storage capacity. Problem: How do we provide feedback to senders? TCP was originally designed for such applications as telnet and ftp over paths with small BDP. May 17 UCSC CMPE150 68 Other Parameters Reliability: We will assume that information is transmitted correctly across a link or network with a given likelihood. Security: We will likely not cover this aspect in much detail :( Order of delivery: We will assume FIFO and nonFIFO delivery of packets or messages, depending on the protocol and transmission media. Access: We will consider point-to-point and broadcast links. May 17 UCSC CMPE150 69 Internet Structure: Network of Networks Roughly hierarchical At its center: “tier-1” ISPs (e.g., UUNet, BBN/Genuity, Sprint, AT&T), national/international coverage Treat each other as equals Tier-1 providers interconnect (peer) privately May 17 Tier 1 ISP Tier 1 ISP UCSC NAP Tier-1 providers also interconnect at public network access points (NAPs) Tier 1 ISP CMPE150 70 Tier-1 ISP Example: Sprint US Backbone Network May 17 UCSC CMPE150 71 Internet Structure Each packet passes through many networks! Limiting factor: Speed of light! local ISP Tier 3 ISP Tier-2 ISP local ISP local ISP local ISP Tier-2 ISP Tier 1 ISP Tier 1 ISP Tier-2 ISP local local ISP ISP May 17 NAP Tier 1 ISP Tier-2 ISP local ISP UCSC CMPE150 Tier-2 ISP local ISP 72 Internet Structure Why we need user-to-content rather than client-server approach. local ISP Tier 3 ISP Tier-2 ISP local ISP local ISP local ISP Tier-2 ISP Tier 1 ISP Tier 1 ISP Tier-2 ISP local local ISP ISP May 17 NAP Tier 1 ISP Tier-2 ISP local ISP UCSC CMPE150 Content comes from nearest outlet to client. Content needs to be routed to nearest outlets. Tier-2 ISP local ISP proxy 73 END May 17 UCSC CMPE150 74 Internet Delays and Routes What do “real” Internet delay and loss look like? Traceroute program: provides delay measurement from source to router along end-end Internet path towards destination. For all i: sends three packets that will reach router i on path towards destination router i will return packets to sender sender times interval between transmission and reply. 3 probes 3 probes 3 probes May 17 UCSC CMPE150 75 Internet Delays and Routes traceroute: gaia.cs.umass.edu to www.eurecom.fr Three delay measements from gaia.cs.umass.edu to cs-gw.cs.umass.edu 1 cs-gw (128.119.240.254) 1 ms 1 ms 2 ms 2 border1-rt-fa5-1-0.gw.umass.edu (128.119.3.145) 1 ms 1 ms 2 ms 3 cht-vbns.gw.umass.edu (128.119.3.130) 6 ms 5 ms 5 ms 4 jn1-at1-0-0-19.wor.vbns.net (204.147.132.129) 16 ms 11 ms 13 ms 5 jn1-so7-0-0-0.wae.vbns.net (204.147.136.136) 21 ms 18 ms 18 ms 6 abilene-vbns.abilene.ucaid.edu (198.32.11.9) 22 ms 18 ms 22 ms 7 nycm-wash.abilene.ucaid.edu (198.32.8.46) 22 ms 22 ms 22 ms trans-oceanic 8 62.40.103.253 (62.40.103.253) 104 ms 109 ms 106 ms link 9 de2-1.de1.de.geant.net (62.40.96.129) 109 ms 102 ms 104 ms 10 de.fr1.fr.geant.net (62.40.96.50) 113 ms 121 ms 114 ms 11 renater-gw.fr1.fr.geant.net (62.40.103.54) 112 ms 114 ms 112 ms 12 nio-n2.cssi.renater.fr (193.51.206.13) 111 ms 114 ms 116 ms 13 nice.cssi.renater.fr (195.220.98.102) 123 ms 125 ms 124 ms 14 r3t2-nice.cssi.renater.fr (195.220.98.110) 126 ms 126 ms 124 ms 15 eurecom-valbonne.r3t2.ft.net (193.48.50.54) 135 ms 128 ms 133 ms 16 194.214.211.25 (194.214.211.25) 126 ms 128 ms 126 ms 17 * * * * means no reponse (probe lost, router not replying) 18 * * * 19 fantasia.eurecom.fr (193.55.113.142) 132 ms 128 ms 136 ms May 17 UCSC CMPE150 76