Instructor’s Guide for Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design Edn. 4 © Pearson Education 2005 Network principles (16) zCongestion control yhigh traffic load, packets dropped due to limited resources yreducing transmission rate: "choke packets" from sender to receiver

Instructor’s Guide for Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design Edn. 4 © Pearson Education 2005 Networking principles (17) zNetwork connecting devices yHubs: extending a segment of LAN ySwitches: routing traffic at data-link level (could be different segments of a LAN) yRouters: routing traffic at IP level yBridges: link networks of different types, could be router as well yMobile IP using IP

Instructor’s Guide for Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design Edn. 4 © Pearson Education 2005 Networking principles (18) zTunneling ycommunicate through an "alien" protocol y“Hide” in the payload yIPv6 traffic using IPv4 protocols AB IPv6 IPv6 encapsulated in IPv4 packets Encapsulators IPv4 network

Instructor’s Guide for Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design Edn. 4 © Pearson Education 2005 Internet protocols (1) zIP (Internet Protocol) y"network" layer protocol yIP addresses z TCP (Transmission Control Protocol) ytransport layer yconnection-oriented z UDP (User Datagram Protocol) ytransport layer y connection-less

Instructor’s Guide for Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design Edn. 4 © Pearson Education 2005 Internet protocols (2): TCP/IP layers Messages (UDP) or Streams (TCP) Application Transport Internet UDP or TCP packets IP datagrams Network-specific frames Message Layers Underlying network Network interface

Instructor’s Guide for Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design Edn. 4 © Pearson Education 2005 Internet protocols (3): layer encapsulation Application message TCP header IP header Ethernet header Ethernet frame port TCP IP

Instructor’s Guide for Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design Edn. 4 © Pearson Education 2005 Internet protocols (4): Programmer’s view

Instructor’s Guide for Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design Edn. 4 © Pearson Education 2005 Internet protocols (5): Internet address structure z32-bit

Instructor’s Guide for Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design Edn. 4 © Pearson Education 2005 Internet protocols (6): Decimal representation z ( octet 1octet 2octet 3 Class A: 1 to to to 254 Class B: 128 to 191 Class C: 192 to to 239 Class D (multicast): Network ID Host ID Multicast address 0 to to to 255 Multicast address 0 to to to 255 Class E (reserved): to to to to to Range of addresses

Instructor’s Guide for Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design Edn. 4 © Pearson Education 2005 Internet protocols (7) zClassless interdomain routing (CIDR) yshortage of Class B networks yadd a mask field to indicate bits for network portion y /22 [subnet: first 22 bits; host: 10 bits]

Instructor’s Guide for Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design Edn. 4 © Pearson Education 2005 Internet protocols (8)

Instructor’s Guide for Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design Edn. 4 © Pearson Education 2005 Internet protocols (9): Network Address Translation zSharing one “global” IP address at home zRouters with NAT yRouter has a “global” IP address from ISP yEach machine has a “local” IP address via DHCP yMachine -> router xRouter stores the local IP addr and source port # xTable entry indexed by a virtual port # yRouter -> outside xput the router IP addr and virtual port # in the packet yOutside -> router xReply to the router IP addr and virtual port # yRouter -> machine xUse the virtual port # to find table entry xForward to the local IP address and port # zWhat happens if we want the device to be a server, not a client?

Instructor’s Guide for Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design Edn. 4 © Pearson Education 2005 Internet protocols (10)

Instructor’s Guide for Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design Edn. 4 © Pearson Education 2005 Internet protocols (11) zServer with NAT yFixed internal addr and port # yFixed entry in the table yAll packets to the port on the router are forwarded to the internal addr and port # in the entry zWhat if more than one internal machines want to offer the same service (port)?

Instructor’s Guide for Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design Edn. 4 © Pearson Education 2005 Internet protocols (12) zIP Protocol yunreliable or best-effort y lost, duplicated, delayed, out of order y header checksum, no data checksum y IP packet longer than MTU of the underlying network, break into fragments y before sending and reassemble after receiving y Address resolution (on LANs) xmapping IP address to lower level address xARP: address resolution protocol xethernet: cache; not in cache, broadcast IP addr, receive Ethernet addr y IP spoofing: address can be stolen (not authenticated)

Instructor’s Guide for Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design Edn. 4 © Pearson Education 2005 Internet protocols (13) zRIP-1: discussed previously zRIP-2: CIDR, better multicast routing, authentication of RIP packets zlink-state algorithms: e.g., open shortest path first (OSPF) zaverage latency of IP packets peaks at 30-seconds intervals [RIP updates are processed before IP] y because 30-second RIP update intervals, locked steps y random interval between seconds for RIP update z large table size y all destinations!! y map ip to geographical location y default route: store a subset, default to a single link for unlisted destinations

Instructor’s Guide for Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design Edn. 4 © Pearson Education 2005 Internet Protocols (14): IPv6 zIP addresses:128 bits (16 bytes) y 3 x addresses (7 x addresses per square meter!) zrouting speed y no data checksum as before y no fragmentation (need to know what?) zreal-time and special services y priority field: importance/reliability y flow label: timing requirements z“next” header field y extension header types for IPv6 y routing information, authentication, encryption... zAnycast: at least one nodes gets it zsecurity ycurrently handled above the IP layer yextension header types zMigration from IPv4 ybackward compatibility: IPv6 addresses include IPv4 addresses yIslands of IPv6 networks, traffic tunnels though other IPv4 networks

Instructor’s Guide for Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design Edn. 4 © Pearson Education 2005 Internet protocols (15): Source address (128 bits) Destination address (128 bits) Version (4 bits)Traffic class (8 bits)Flow label (20 bits) Payload length (16 bits)Hop limit (8 bits)Next header (8 bits)

Instructor’s Guide for Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design Edn. 4 © Pearson Education 2005 Internet Protocols (10): Mobile IP zDynamic Host Configuration Protocol (DHCP) y assign temporary IP address y provide addresses of local resources like DNS zRouting y IP routing is subnet-based, fixed relative locations y Home agent (HA) and Foreign agent (FA) y HA - current location (IP addr) of the mobile host x is informed by the mobile host when it moves x proxy for the host after it moves x inform local routers to remove cached records of the host xresponds to ARP requests yFA - informed by the host when if arrives x new temp IP addr x contacts HA what the new IP address is y HA - receives the new IP address and may tell the sender the new IP addr

Instructor’s Guide for Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design Edn. 4 © Pearson Education 2005 Internet protocols (11): MobileIP routing mechanism Sender Home Mobile host MH Foreign agent FA Internet agent First IP packet addressed to MH Address of FA returned to sender First IP packet tunnelled to FA Subsequent IP packets tunnelled to FA

Instructor’s Guide for Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design Edn. 4 © Pearson Education 2005 Internet protocols (12) zTransport protocols: TCP and UDP ynetwork protocol: host to host ytransport protocol: process to process yPort #’s to indicate processes zUDP yno guarantee of delivery ychecksum is optional ymax of 64 bytes, same as IP yno setup costs, no segments

Instructor’s Guide for Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design Edn. 4 © Pearson Education 2005 Internet protocols (13) zTCP yarbitrarily long sequence yconnection-oriented ysequencing of segments yflow control: acknowledgement includes "window size" (amount of data) for sender to send yinteractive service: higher frequency of buffer flush, send when deadline reached or buffer reaches MTU yretransmission of lost packets ybuffering of incoming packets to preserve order and flow ychecksum on header and data

Instructor’s Guide for Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design Edn. 4 © Pearson Education 2005 Internet protocols (14) zDomain names zDNS y distributed data y each DNS server keeps track of part of the hierarchy y unresolved requests are sent to servers higher in the hierarchy

Instructor’s Guide for Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design Edn. 4 © Pearson Education 2005 Internet protocols (15) zFirewalls y monitor and filter communication y controlling what services are available to the outside y controlling the use of services y controlling internal users access to the outside z Filtering at different protocol levels y IP packet filtering: addresses, ports.. y TCP gateway: check for correctness in TCP connections x e.g., are they partially opened and never used (why?) y Application-level gateway: proxy for applications x no direct communication between the inside and outside x e.g., smtp proxy can check addresses, content...

Instructor’s Guide for Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design Edn. 4 © Pearson Education 2005 Internet protocols (16) zBastion (tcp/ application filter) zC): two router filters yHide internal IP addresses yBastion has the mapping ySecond router is the second IP filter (invisible to the outside)

Instructor’s Guide for Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design Edn. 4 © Pearson Education 2005 Internet protocols (17) zVirtual Private Network (VPN) y secure connections from the outside y IPSec tunneling through IP

Instructor’s Guide for Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design Edn. 4 © Pearson Education 2005 Network Case Studies (1) zEthernet zWiFi

Instructor’s Guide for Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design Edn. 4 © Pearson Education 2005 Network Case Studies (2): IEEE 802 standards IEEE No.NameTitleReference 802.3EthernetCSMA/CD Networks (Ethernet)[IEEE 1985a] 802.4Token Bus Networks[IEEE 1985b] 802.5Token Ring Networks[IEEE 1985c] 802.6Metropolitan Area Networks[IEEE 1994] WiFiWireless Local Area Networks[IEEE 1999] BluetoothWireless Personal Area Networks[IEEE 2002] ZigBeeWireless Sensor Networks[IEEE 2003] WiMAXWireless Metropolitan Area Networks[IEEE 2004a]

Instructor’s Guide for Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design Edn. 4 © Pearson Education 2005 Network Case Studies (3): Ethernet zEthernet, CSMA/CD, IEEE y Xerox Palo Alto Research Center (PARC), 1973, 3Mbps y 10,100,1000 Mbps y extending a segment: hubs and repeaters y connecting segments: switches and bridges y Contention bus y Packet/frame format x preamble (7 bytes): hardware timing x start frame delimiter (1) x dest addr (6) x src addr (6) x length (2) x data ( ): min total becomes 64 bytes, max total is 1518 x checksum (4): dropped if incorrect

Instructor’s Guide for Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design Edn. 4 © Pearson Education 2005 Network Case Studies (4) zCarrier Sensing Multiple Access / Collision Detection (CSMA/CD) y CS: listen before transmitting, transmit only when no traffic y MA: more than one can transmit y CD: collision occurs when signals transmitted are not the same as those received y After detection a collision xsend jamming signal x wait for a random period before retransmitting z T (Tau): time to reach the farthest station z Scenarios: y A and B send at the same time y A sends, B sends before T seconds y A sends, B sends between T and 2T seconds y A sends, B sends after 2T seconds y packet length > 2T, between T and 2T, and < T

Instructor’s Guide for Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design Edn. 4 © Pearson Education 2005 Network Case Studies (5) zPhysical implementation: y y R: data rate in Mbps y B: medium signaling type: baseband [one channel] or broadband [multiple channels] y L: max segment length in 100meters or T (twisted pair cable, hierarchy of hubs)

Instructor’s Guide for Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design Edn. 4 © Pearson Education 2005 Network Case Studies (6): Ranges and speeds 10Base510BaseT100BaseT1000BaseT Data rate10 Mbps 100 Mbps1000 Mbps Max. segment lengths: Twisted wire (UTP)100 m 25 m Coaxial cable (STP)500 m 25 m Multi-mode fibre2000 m 500 m Mono-mode fibre25000 m m2000 m

Instructor’s Guide for Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design Edn. 4 © Pearson Education 2005 Network Case Studies (7): WiFi zIEEE wireless LAN y up to 150m and 54Mbps y access point (base station) to land wires y Ad hoc network--no specific access points, "on the fly" network among machines in the neighborhood y Radio Frequency (2.4, 5GHz band) or infra-red

Instructor’s Guide for Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design Edn. 4 © Pearson Education 2005 Network Case Studies (8): Problems with wireless CSMA/CD yHidden station: not able to detect another station is transmitting xA can’t see D, or vice versa y Fading: signals weaken, out of range xA and C are out of range from each other y Collision masking: stronger signals could hide others x A and C are out of range from each other, both transmits, collide, can't detect collision, Access point gets garbage

Instructor’s Guide for Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design Edn. 4 © Pearson Education 2005 Network Case Studies (9) z Carrier sensing multiple access with collision avoidance (CSMA/CA) y reserving slots to transmit y if no carrier signal x medium is available, x out-of-range station requesting a slot, or x out-of-range station using a slot

Instructor’s Guide for Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design Edn. 4 © Pearson Education 2005 Network Case Studies (10) zSteps 1.Request to send (RTS) from sender to receiver, specify duration 2.Clear to send (CTS) in reply 3.in-range stations see the RTS and/or CTS and its duration 4.in-range stations stop transmitting 5.acknowledgement from the receiver zHidden station & Fading: CTS, need permission to transmit zRTS and CTS are short, don't usually collide; random back off if collision detected zShould have no collisions, send only when a slot is reserved