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School of Computing Science Simon Fraser University CMPT 880: Internet Architectures and Protocols Instructor: Dr. Mohamed Hefeeda 1 Course Objectives Understand principles of designing and operating computer networks structure and protocols of the Internet services that can/cannot be offered by the Internet Know how to analytically analyze performance of a system/protocol implement network protocols and applications And, more importantly, … Have fun! 2 Course Info Most of the course will be lectures given by the instructor Last three weeks, each student presents at most one chapter/paper Course web page http://nsl.cs.surrey.sfu.ca/teaching/06/880/ Or access it from my web page: http://www.cs.sfu.ca/~mhefeeda 3 Course Info: Textbooks and References All are on reserve in SFU Surrey Library Kurose and Rose, Computer Networking: A topdown Approach Featuring the Internet, 2005 Background materials Ch 7: Multimedia Networking and QoS Hassan and Jain, High Performance TCP/IP Networking, 2004 Several chapters on analyzing TCP/IP in different environments Stallings, High-speed Networks and Internets: Performance and Quality of Service, 2002 Three chapters on (basics of) probability and queuing Papers: will be posted on the course web page 4 Course Info: Grading Homework: 20% 3 – 4 problem sets Projects: 30% 3 projects; later two of them are group projects Class participation: 15% Ask and answer questions Present one chapter/paper Final exam: 35% Comprehensive 5 Course Info: Schedule Schedule is posted on the course web page Let us quickly review it 6 Review of Basic Networking Concepts 7 Review of Basic Networking Concepts Internet structure Protocol layering and encapsulation Internet services and socket programming Network Layer Network types: Circuit switching, Packet switching Addressing, Forwarding, Routing Transport layer Reliability and congestion control TCP, UDP Link Layer Multiple Access Protocols Ethernet 8 The Internet Millions of hosts (end systems) Inter-connected, running network apps Diverse communication links router server workstation mobile local ISP fiber, copper, radio, satellite regional ISP Routers forward packets Internet: “network of networks” loosely hierarchical Public, versus private intranet company network 9 “Cool” Internet appliances Web-enabled toaster + weather forecaster IP picture frame http://www.ceiva.com/ World’s smallest web server http://www-ccs.cs.umass.edu/~shri/iPic.html Internet phones 10 Internet structure: network of networks roughly hierarchical at center: “tier-1” ISPs (e.g., MCI, Sprint, AT&T, Cable and Wireless), national/international coverage treat each other as equals Tier-1 providers interconnect (peer) privately Tier 1 ISP Tier 1 ISP NAP Tier-1 providers also interconnect at public network access points (NAPs) Tier 1 ISP 11 Tier-1 ISP: e.g., Sprint Sprint US backbone network Seattle Tacoma DS3 (45 Mbps) OC3 (155 Mbps) OC12 (622 Mbps) OC48 (2.4 Gbps) POP: point-of-presence to/from backbone Stockton … … Kansas City . … Anaheim peering … … San Jose Cheyenne New York Pennsauken Relay Wash. DC Chicago Roachdale Atlanta to/from customers Fort Worth Orlando 12 Internet structure: Tier-2 ISPs “Tier-2” ISPs: smaller (often regional) ISPs Connect to one or more tier-1 ISPs, possibly other tier-2 ISPs Tier-2 ISP pays tier-1 ISP for connectivity to rest of Internet Tier-2 ISP is customer of tier-1 provider Tier-2 ISP Tier-2 ISP Tier 1 ISP Tier 1 ISP Tier-2 ISP NAP Tier 1 ISP Tier-2 ISPs also peer privately with each other, interconnect at NAP Tier-2 ISP Tier-2 ISP 13 Internet structure: Tier-3 ISPs “Tier-3” ISPs and local ISPs last hop (“access”) network (closest to end systems) local ISP Local and tier3 ISPs are customers of higher tier ISPs connecting them to rest of Internet 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 NAP Tier 1 ISP Tier-2 ISP local ISP Tier-2 ISP local ISP 14 Internet structure: packet journey a packet passes through many networks! 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 NAP Tier 1 ISP Tier-2 ISP local ISP Tier-2 ISP local ISP 15 A snapshot of the Internet in 1999 showing major ISPs 16 Review of Basic Networking Concepts Internet structure Protocol layering and encapsulation Internet services and socket programming Network Layer Network types: Circuit switching, Packet switching Addressing, Forwarding, Routing Transport layer Reliability and congestion control TCP, UDP Link Layer Multiple Access Protocols Ethernet 17 Protocol Layers Networks are complex! many “pieces”: hosts routers links of various media applications protocols hardware, software Question: Is there any hope of organizing structure of network? Or at least our discussion of networks? 18 Layering of Airline Functionality ticket (purchase) ticket (complain) ticket baggage (check) baggage (claim baggage gates (load) gates (unload) gate runway (takeoff) runway (land) takeoff/landing airplane routing airplane routing airplane routing departure airport airplane routing airplane routing intermediate air-traffic control centers arrival airport Layers: each layer implements a service via its own internal-layer actions relying on services provided by layer below 19 Why layering? Dealing with complex systems: explicit structure allows identification, relationship of complex system’s pieces 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 What is the downside of layering? 20 Internet protocol stack application: supporting network applications FTP, SMTP, HTTP transport: host-host data transfer TCP, UDP network: routing of datagrams from source to destination IP, routing protocols link: data transfer between neighboring network elements PPP, Ethernet application transport network link physical physical: bits “on the wire” 21 source message segment Ht datagram Hn Ht frame Hl Hn Ht M M M M Encapsulation application transport network link physical Hl Hn Ht M link physical Hl Hn Ht M switch destination M Ht M Hn Ht Hl Hn Ht M M application transport network link physical Hn Ht Hl Hn Ht M M network link physical Hn Ht Hl Hn Ht M M router 22 Review of Basic Networking Concepts Internet structure Protocol layering and encapsulation Internet services and socket programming Network Layer Network types: Circuit switching, Packet switching Addressing, Forwarding, Routing Transport layer Reliability and congestion control TCP, UDP Link Layer Multiple Access Protocols Ethernet 23 Internet Services View the Internet as a communication infrastructure that provides services to apps Web, email, games, e-commerce, file sharing, … Two communication services Connectionless unreliable Connection-oriented reliable 24 Internet Services Connection-oriented Prepare for data transfer ahead of time establish connection set up state in the two communicating hosts Usually comes with reliability, flow and congestion control TCP: Transmission Control Protocol Connectionless No connection set up, simply send Faster, less overhead No reliability, flow control, or congestion control UDP: User Datagram Protocol How can we access these services? 25 Network (Socket) Programming Process sends/receives messages to/from its socket Socket analogous to door sending process shoves message out door sending process relies on transport infrastructure on other side of door which brings message to socket at receiving process host or server host or server process controlled by app developer process socket socket TCP with buffers, variables Internet TCP with buffers, variables controlled by OS Socket is the interface (API) between application and transport layer 26 Addressing Processes For a process to receive messages, it must have an identifier A host has a unique32-bit IP address Q: does the IP address of the host on which the process runs suffice for identifying the process? A: No, many processes can be running on same host We use ports Process is identified by: IP address, Transport protocol, and Port number Example port numbers: HTTP server: 80 (TCP) Mail server: 25 (TCP) 27 Socket Programming Socket API introduced in BSD 4.1 UNIX, 1981 explicitly created, used, released by apps client/server paradigm provides two services • reliable, byte stream-oriented • unreliable datagram 28 Socket Programming using TCP TCP service: reliable transfer of bytes from one process to another virtual pipe between sender and receiver controlled by application developer controlled by operating system process process socket TCP with buffers, variables host or server internet socket TCP with buffers, variables controlled by application developer controlled by operating system host or server 29 Socket Programming using TCP Server (running on hostid) Client create socket, port=x, for incoming request: welcomeSocket = ServerSocket() TCP wait for incoming connection request connection connectionSocket = welcomeSocket.accept() read request from connectionSocket write reply to connectionSocket close connectionSocket setup create socket, connect to hostid, port=x clientSocket = Socket() send request using clientSocket read reply from clientSocket close clientSocket 30 Socket Programming using TCP Server process must first be running, and creates a socket (door) that welcomes client’s contact, then wait Client contacts server by creating local TCP socket using IP address, port number of server process When client creates socket client TCP establishes connection to server TCP When contacted by client server TCP creates new socket for server process to communicate with client • allows server to talk with multiple clients • source port numbers and IPs used to distinguish clients 31 Socket programming using UDP UDP Service: unreliable transfer of groups of bytes (datagrams) between client and server no connection between client and server no handshaking sender explicitly attaches IP address and port of destination to each packet server must extract IP address, port of sender from received packet transmitted data may be received out of order, or lost 32 Socket Programming using UDP Server (running on hostid) create socket, port=x, for incoming request: serverSocket = DatagramSocket() read request from serverSocket write reply to serverSocket specifying client host address, port number Client create socket, clientSocket = DatagramSocket() Create datagram (hostid,port=x,data) send datagram request using clientSocket read reply from clientSocket close clientSocket 33 Review of Basic Networking Concepts Internet structure Protocol layering and encapsulation Internet services and socket programming Network Layer Network types: Circuit switching, Packet switching Addressing, Forwarding, Routing Transport layer Reliability and congestion control TCP, UDP Link Layer Multiple Access Protocols Ethernet 34 The Network Core Mesh of interconnected routers The fundamental question: how is data transferred through net? circuit switching: dedicated circuit per call: telephone net packet-switching: data sent thru net in discrete “chunks” 35 Network Core: Circuit Switching Network resources (e.g., bandwidth) divided into “pieces” using Frequency division multiplexing (FDM) Time division multiplexing (TDM) Pieces allocated to “calls” (connections) guaranteed performance Resource piece idle if not used by owning call no sharing Connection setup is required Examples (Traditional) Telephone network 36 Circuit Switching: Dedicated Circuits 37 Network Core: Packet Switching each end-end data stream divided into packets resource contention: packets from different users share network resources aggregate resource demand can exceed amount available each packet uses full link bandwidth congestion: packets queue, wait for link use resources used as needed store and forward: packets move one hop at a time Node receives complete packet before forwarding Bandwidth division into “pieces” Dedicated allocation Resource reservation 38 Packet Switching: Statistical Multiplexing 10 Mb/s Ethernet A B statistical multiplexing C 1.5 Mb/s queue of packets waiting for output link D E Sequence of A & B packets does not have fixed pattern, shared on demand statistical multiplexing In contrast, in TDM each host gets same slot in revolving TDM frame 39 Packet Switching: Efficiency Packet switching allows more users to use network! 1 Mb/s link each user: 100 kb/s when “active” active 10% of time circuit-switching: 10 users N users 1 Mbps link packet switching: with 35 users, probability > 10 active less than 0 .0004 Q: how did we get value 0.0004? 40 Packet Switching Advantages no call setup simpler resource sharing (statistical multiplexing) • better resource utilization • more users or faster transfer (a single user can use entire bw) • Well suited for bursty traffic (typical) Disadvantages Congestion may occur • packet delay and loss • need protocols to control congestion and ensure reliable data transfer 41 Packet Switching: Two Classes Datagram network Example: The Internet Virtual-circuit network Examples: ATM (Asynchronous Transfer Mode), frame relay, X.25 42 Packet-switched Datagram Networks no call setup at network layer routers: no state about end-to-end connections no network-level concept of “connection” packets forwarded using destination host address packets between same source-dest pair may take different paths application transport network data link 1. Send data physical application transport 2. Receive data network data link physical 43 Packet-switched VC Networks Source-to-dest path behaves much like telephone circuit” performance-wise connection setup, teardown for each call before data can flow each packet carries VC identifier (not destination address) every router on source-dest path maintains state for each passing connection link, router resources (bandwidth, buffers) may be allocated to VC Examples: ATM (Asynchronous Transfer Mode), frame relay, X.25 44 VC Networks: Connection Setup Signaling protocols are used to setup, maintain, and teardown VCs Note: not used in the current Internet application transport 5. Data flow begins network 4. Call connected data link 1. Initiate call physical 6. Receive data application 3. Accept call transport 2. incoming call network data link physical 45 VC Networks: VC Implementation A VC consists of: 1. Path from source to destination 2. VC numbers, one number for each link along path 3. Entries in forwarding tables in routers along path Packet belonging to VC carries same VC number VC number must be changed on each link New VC number comes from forwarding table 46 VC Networks: Forwarding table VC number 22 12 1 Forwarding table in northwest router: Incoming interface 1 2 3 1 … 2 32 3 interface number Incoming VC # 12 63 7 97 … Outgoing interface 3 1 2 3 … Outgoing VC # 22 18 17 87 … Each routers maintains connection state information! 47 ATM vs. Internet: QoS Network Architecture Internet Service Model Guarantees ? Congestion Bandwidth Loss Order Timing feedback best effort none ATM CBR ATM VBR ATM ABR ATM UBR constant rate guaranteed rate guaranteed minimum none no no no yes yes yes yes yes yes no yes no no (inferred via loss) no congestion no congestion yes no yes no no 48 Network Taxonomy Telecommunication networks Circuit-switched networks FDM TDM Packet-switched networks Networks with VCs Datagram Networks 49 Review of Basic Networking Concepts Internet structure Protocol layering and encapsulation Internet services and socket programming Network Layer Network types: Circuit switching, Packet switching Addressing, Forwarding, Routing Transport layer Reliability and congestion control TCP, UDP Link Layer Multiple Access Protocols Ethernet 50 Network Layer Network layer protocols in every host and router Network layer’s goal transport data from sending host to receiving host application transport network data link physical network data link physical network data link physical network data link physical We focus on datagram networks (Internet) network data link physical network data link physical network data link physical network data link physical network data link physical application transport network data link physical 51 Network Layer in the Internet Host, router network layer functions: Transport layer: TCP, UDP Network layer IP protocol •addressing conventions •datagram format •packet handling conventions Routing protocols •path selection •RIP, OSPF, BGP forwarding table ICMP protocol •error reporting •router “signaling” Link layer physical layer 52 Routing vs. Forwarding Routing determine route taken by packets from source to destination Routing algorithms, e.g., RIP, OSPF, BGP Forwarding move packets from router’s input to appropriate output use forwarding table populated by routing algorithm routing algorithm local forwarding table header value output link 0100 0101 0111 1001 3 2 2 1 value in arriving packet’s header 0111 1 3 2 E.g., IP forwarding function 53 IP Datagram Format IP protocol version number header length (bytes) Provides some QoS max number remaining hops (decremented at each router) upper layer protocol to deliver payload to how much overhead with TCP? 20 bytes of TCP 20 bytes of IP 32 bits type of ver head. len service length fragment 16-bit identifier flgs offset upper time to Internet layer live checksum total datagram length (bytes) for fragmentation/ reassembly 32 bit source IP address 32 bit destination IP address Options (if any) data (variable length, typically a TCP or UDP segment) E.g. timestamp, record route taken, specify list of routers to visit. = 40 bytes + app layer overhead IP ver 4.0 54 IP Addressing: Introduction IP address: 32-bit identifier for each host, router network interface Represented in Dotted-decimal notation 11011111 00000001 00000001 00000001 223 1 1 1 223.1.1.1 55 IP Addressing Network interface: connection between host/router and physical link routers typically have multiple interfaces host typically has one interface Unique IP addresses associated with each interface 223.1.1.1 223.1.2.1 How do we assign IPs? 223.1.1.2 223.1.1.4 223.1.1.3 223.1.2.9 223.1.3.27 223.1.2.2 Divide network into subnets, each has a common ID 223.1.3.1 223.1.3.2 56 223.1.1.0/24 Subnets 223.1.2.0/24 Subnet is: a group of devices that can reach each other without intervening router identified by high order bits of IP addresses 11011111 00000001 00000001 00000001 223.1.3.0/24 Subnet ID Host ID 223.1.1.0/24 /24: # bits in subnet portion of address, subnet mask 57 Subnets How many subnets? 223.1.1.1 223.1.9.2 Recipe: Each isolated network is a subnet 223.1.1.4 223.1.1.3 6 subnets detach each interface from its host or router, creating isolated networks 223.1.1.2 223.1.7.0 223.1.9.1 223.1.7.1 223.1.8.1 223.1.8.0 223.1.3.27 223.1.2.6 223.1.2.1 223.1.2.2 223.1.3.1 223.1.3.2 58 IP Addressing: CIDR CIDR: Classless InterDomain Routing subnet portion of address of arbitrary length address format: a.b.c.d/x, where x is # bits in subnet portion of address Old Classful Addressing: Subnet length had to be /8 (class A), /16 (class B), /24 (class C) Why CIDR? Finer control over address allocation reduce waste of addresses Ex: company with 2000 machines would have to get class B, wasting 63,000+ addresses subnet part host part 11001000 00010111 00010000 00000000 200.23.16.0/23 59 IP Addresses: How to Get One? Q: How does host get IP address? hard-coded by system admin in a file WIN: control-panel->network->configuration->tcp/ip>properties UNIX: /etc/rc.config DHCP: Dynamic Host Configuration Protocol: dynamically get address from as server “plug-and-play” 60 IP Addresses: How to Get One? Q: How does network get subnet part of IP addr? A: gets allocated portion of its provider ISP’s address space ISP's block 11001000 00010111 00010000 00000000 200.23.16.0/20 Organization 0 Organization 1 Organization 2 ... 11001000 00010111 00010000 00000000 11001000 00010111 00010010 00000000 11001000 00010111 00010100 00000000 ….. …. 200.23.16.0/23 200.23.18.0/23 200.23.20.0/23 …. Organization 7 11001000 00010111 00011110 00000000 200.23.30.0/23 61 Hierarchical Addressing: Route Aggregation Hierarchical addressing allows efficient advertisement of routing information: Organization 0 200.23.16.0/23 Organization 1 200.23.18.0/23 Organization 2 200.23.20.0/23 Organization 7 . . . . . . Fly-By-Night-ISP “Send me anything with addresses beginning 200.23.16.0/20” Internet 200.23.30.0/23 ISPs-R-Us “Send me anything with addresses beginning 199.31.0.0/16” 62 IP Addressing: the last word... Q: How does an ISP get block of addresses? A: ICANN: Internet Corporation for Assigned Names and Numbers allocates addresses manages DNS assigns domain names, resolves disputes 63