Slides for Chapter 3: Networking and Internetworking

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Slides for hapter 3: Networking and Internetworking From oulouris, ollimore and Kindberg istributed Systems: oncepts and esign dition 4, Networking Issues () Performance: Latency (time between send

1 Slides for hapter 3: Networking and Internetworking From oulouris, ollimore and Kindberg istributed Systems: oncepts and esign dition 4, Networking Issues () Performance: Latency (time between send and start to receive) ata transfer rate (bits per second) [max] Transmission time = latency + length / transfer rate System bandwidth, throughput [actual]: total volume of traffic in a given amount of time Using different channels concurrently can make bandwidth > data transfer rate traffic load can make bandwidth < data transfer rate network speed < memory speed (about 000 times) ccess to local disk is usually faster than remote disk Fast (expensive) remote disk + fast network can beat slow (cheap) local disks Networking Issues () Types of Networks () scalability reliability corruption is rare mechanisms in higher-layers to recover errors errors are usually timing failures, the receiver doesn't have resources to handle the messages security firewall on gateways (entry point to org's intranet) encryption is usually in higher-layers mobility--communication is more challenging: locating, routing,... quality of service--real-time services multicasting--one-to-many communication Local rea Networks (LN) floor/building-wide single communication medium no routing, broadcast segments connected by switches or hubs high bandwidth, low latency thernet - 0Mbps, 00Mbps, Gbps no latency guarantees (what could be the consequences?) Personal area networks (PN) [ad-hoc networks]: blue tooth, infra-red for Ps, cell phones, Types of Networks () Metropolitan rea Networks (MN) city-wide, up to 50 km igital Subscriber Line (SL):.5-8 Mbps, 5.5km from switch ellsouth:.8 to 6 Mbps able modem:.5 Mbps, longer range than SL right house w/ Road Runner:.5 to 0Mbps Types of Networks (3) Wide rea Networks (WN) world-wide ifferent organizations Large distances routed, latency. -.5 seconds -0 Mbps (upto 600 Mbps)

2 Types of Networks (4) Wireless local area networks (WLN) I 80. (WiFi) 0-00 Mbps,.5km 80. (997): upto Mbps,.4 GHz 80.a (999): upto 54 Mbps, 5 GHz, ~75 feet outdoor 80.b (999): upto Mbps,.4 GHz, ~50 feet [most popular] 80.g (003): upto 54 Mbps,.4 GHz, ~50 feet [backward compatible with 80.b, becoming more popular] Wireless metropolitan area networks (WMN) I 80.6 (WiMax).5-0 Mbps, 5-50km Types of Networks (5) Wireless wide area networks (WWN) worldwide GSM (Global System for Mobile communications) kbps 3G ( third generation ): kbps to Mbps Types of Networks (6) Network performance Internetworks connecting different kinds of networks routers, gateways Wired: xample Range andwidth Latency (Mbps) (ms) LN thernet - km MN TM 50 km WN IP routing worldwide Internetwork Internet worldwide Wireless: WPN luetooth (80.5.) 0-30m WLN WiFi (I 80.) km WMN WiMX (80.6) 550 km WWN GSM, 3G phone nets worldwide Network principles () Packet transmission message: logical unit of informatio packet: transmission unit restricted length: sufficient buffer storage, reduce hogging Network principles () ata Streaming audio/video Need 0 Mbps (.5 Mbps compressed) play time: the time when a frame need to be displayed for example, 4 frames per second, frame 48 must be display after two seconds IP protocol provides no guaranteesipv6 (new) includes features for real-time streams, stream data are treated separately Resource Reservation Protocol (RSVP), Real-time Transport Protocol (RTP)

3 Network principles (3) Switching schemes (transmission between aribitrary nodes) roadcast: ethernet, token ring, wireless ircuit switching: wires are connected Packet switching: store-and-forward different routes store-and-forward needs to buffer the entire packet before forwarding Frame relay Small packets Looks only at the first few bits on t buffer/store the entire frame Network principles (4) Protocols Key components Sequence of messages Format of messages Network principles (5) Network principles (6) Protocol layers, why? Layer n Message sent Message received ncapsulation in layered protocols Presentation header pplication-layer message Session header Layer Layer Sender ommunication medium Recipient Network header Transport header Network principles (7) Network principles (8) ISO Open Systems Interconnection (OSI) model Layers pplication Presentation Session Transport Network ata link Physical Sender Message sent ommunication medium Message received Recipient Internet layers pplication = application + presentation Transport = transport + session Layers pplication Transport Internetwork Network interface Message Internetwork packets Network-specific packets Underlying Instructor s network Guide for oulouris, ollimore and Kindberg istributed Systems: oncepts and esign dn. 4 Internetwork protocols Underlying network protocols 3

4 Network principles (9) Packet assembly header and data maximum transfer unit (MTU): 500 for thernet 64K for IP (8K is common because of node storage) ports: destination abstraction (application/service protocol) addressing: transport address = network address + port Well-known ports (below 03) Registered ports (04-495) Private (up to 65535) Network principles (0) Packet delivery (at the network layer) atagram packet one-shot, no initial set up different routes, out of order thernet, IP Virtual circuit packet initial set up for resources virtual circuit # for addressing TM Similar but different pairs of protocols at the transport layer (connection-oriented and connectionless) Network principles () Network principles () Routing LN? Routing lgorithm decide which out-going link to forward the packet for circuit switching, the route is determined during the circuit setup time for packet switching, each packet is routed independently update state of the out-going links Routing Table a record for each destination fields: outgoing link, cost (e.g. hop count) Router example Hosts or local networks 3 Links Routers Network principles (3): Routing tables Network principles (4) Routings from Routings from Routings from To Link ost To Link ost To Link ost local 3 0 local 4 0 local Routings from Routings from To Link ost To Link ost local local 0 Router information protocol (RIP) "ellman-ford distance vector" algorithm Sender: send table summary periodically (30s) or changes to neighbors Receiver: onsider receives a table from, updates. -> -> -> X: updates-- has more up-to-date (authoritative) info. -> not -> -> X: oes routing via have a lower cost? 3. -> -> X: does not know X 4. [ -> -> -> X]: doesn t update-- has more up-to-date info 5. Faulty link, cost is infinity RIP- (RF 058) More recent algorithms more information, not just neighbors link-state algorithms, each node responsible for finding the optimum routes 4

5 Network principles (5): Pseudocode for RIP routing algorithm Network principles (6) Tl is the table local table; Tr is the received remote table Send: ach t seconds or when Tl changes, send Tl on each non-faulty outgoing link. Receive: Whenever a routing table Tr is received on link n: for all rows Rr in Tr { if (Rr.link!= n) { // destination not routed via the receiver Rr.cost = Rr.cost + ; Rr.link = n; if (Rr.destination is not in Tl) add Rr to Tl; // add new destination to Tl else for all rows Rl in Tl { if (Rr.destination = Rl.destination and (Rr.cost < Rl.cost or Rl.link = n)) Rl = Rr; // Rr.cost < Rl.cost : remote node has better route // Rl.link = n : remote node is more authoritative } } ongestion control high traffic load, packets dropped due to limited resources reducing transmission rate: "choke packets" from sender to receiver } Networking principles (7) Networking principles (8) Network connecting devices Hubs: extending a segment of LN (broadcast) Switches: switching traffic at data-link level (different segments of a LN), making temporary hardware connections between two ports (or store and forward) [switches do not exchange info with each other] Routers: routing traffic at IP level ridges: linking networks of different types, could be routers as well Tunneling communicate through an "alien" protocol Hide in the payload IPv6 traffic using IPv4 protocols IPv6 encapsulated in IPv4 packets IPv6 IPv4 network IPv6 ncapsulators Internet protocols () Internet protocols (): TP/IP layers IP (Internet Protocol) "network" layer protocol IP addresses TP (Transmission ontrol Protocol) transport layer connection-oriented UP (User atagram Protocol) transport layer connection-less Layers pplication Transport Internet Network interface Underlying network Message Messages (UP) or Streams (TP) UP or TP packets IP datagrams Network-specific frames 5

6 Internet protocols (3): layer encapsulation Internet protocols (4): Programmer s view pplication message TP header port pplication pplication IP header TP TP UP thernet header IP IP thernet frame Internet protocols (5): Internet address structure Internet protocols (6): ecimal representation 3-bit 7 4 lass : 0 Network I Host I 4 6 lass : 0 Network I Host I 8 lass : 0 Network I Host I lass (multicast): 0 Multicast address lass (reserved): 0 unused ( octet octet octet 3 Network I Host I to 7 0 to 55 0 to 55 lass : 0 to 55 Network I Host I lass : 8 to 9 0 to 55 0 to 55 0 to 55 Network I Host I 0 to 55 0 to 55 to 54 lass : 9 to 3 Multicast address lass (multicast): 4 to 39 0 to 55 0 to 55 to 54 lass (reserved): 40 to 55 0 to 55 0 to 55 to 54 Range of addresses to to to to to Internet protocols (7) Internet protocols (8) lassless interdomain routing (IR) shortage of lass networks add a mask field to indicate bits for network portion / [subnet: first bits; host: 0 bits] header IP address of source IP address of destination up to 64 kilobytes data 6

7 Internet protocols (9): Network ddress Translation Sharing one global IP address at home Routers with NT Router has a global IP address from ISP ach machine has a local IP address via HP Machine -> router Router stores the local IP addr and source port # Table entry indexed by a virtual port # Router -> outside put the router IP addr and virtual port # in the packet Outside -> router Reply to the router IP addr and virtual port # Router -> machine Use the virtual port # to find table entry Forward to the local IP address and port # What happens if we want the device to be a server, not a client? Internet protocols (0) SL or able connection to ISP xx subnet thernet switch WiFi base station/ access point Laptop Game box Media hub TV monitor Modem / firewall / router (NT enabled) printer P P luetooth adapter luetooth printer amera Internet protocols () Internet protocols () Server with NT Fixed internal addr and port # Fixed entry in the table ll packets to the port on the router are forwarded to the internal addr and port # in the entry What if more than one internal machines want to offer the same service (port)? IP Protocol unreliable or best-effort lost, duplicated, delayed, out of order header checksum, no data checksum IP packet longer than MTU of the underlying network, break into fragments before sending and reassemble after receiving ddress resolution (on LNs) mapping IP address to lower level address RP: address resolution protocol ethernet: cache; not in cache, broadcast IP addr, receive thernet addr IP spoofing: address can be stolen (not authenticated) Internet protocols (3) Internet Protocols (4): IPv6 RIP-: discussed previously RIP-: IR, better multicast routing, authentication of RIP packets link-state algorithms: e.g., open shortest path first (OSPF) Observed: average latency of IP packets peaks at 30- seconds intervals [RIP updates are processed before IP] because 30-second RIP update intervals, locked steps random interval between 5-45 seconds for RIP update large table size all destinations!! map ip to geographical location default route: store a subset, default to a single link for unlisted destinations IP addresses:8 bits (6 bytes) 3 x 0 38 addresses (7 x 0 3 addresses per square meter!) routing speed no data checksum as before no fragmentation need to know the smallest MTU in data-link layer real-time and special services traffic class: priority, time-dependent (expired data are useless) flow label: timing requirements for streams (reserving resources in advance) next header field extension header types for IPv6 routing information, authentication, encryption... nycast: at least one nodes gets it security currently handled above the IP layer extension header types Migration from IPv4 backward compatibility: IPv6 addresses include IPv4 addresses Islands of IPv6 networks, traffic tunnels though other IPv4 networks 7

8 Internet protocols (5): Internet Protocols (0): Mobile IP Version (4 bits) Traffic class (8 bits) Payload length (6 bits) Source address (8 bits) Flow label (0 bits) Next header (8 bits) Hop limit (8 bits) estination address (8 bits) ynamic Host onfiguration Protocol (HP) assign temporary IP address provide addresses of local resources like NS Routing to maintain continuous access IP routing is subnet-based, fixed relative locations Home agent (H) and Foreign agent (F) H - current location (IP addr) of the mobile host is informed by the mobile host when it moves proxy for the host after it moves inform local routers to remove cached records of the host responds to RP requests F - informed by the host when it arrives new temp IP addr contacts H what the new IP address is H - receives the new IP address and may tell the sender the new IP addr Internet protocols (): MobileIP routing mechanism Internet protocols () ddress of F returned to sender First IP packet addressed to MH Sender Home agent Subsequent IP packets tunnelled to F Internet First IP packet tunnelled to F Mobile host MH Foreign agent F Transport protocols: TP and UP network protocol: host to host transport protocol: process to process Port # s to indicate processes UP no guarantee of delivery checksum is optional max of 64 bytes, same as IP no setup costs, no segments Internet protocols (3) Internet protocols (4) TP arbitrarily long sequence connection-oriented sequencing of segments flow control: acknowledgement includes "window size" (amount of data) for sender to send before next ack interactive service: higher frequency of buffer flush, send when deadline reached or buffer reaches MTU retransmission of lost packets buffering of incoming packets to preserve order and flow checksum on header and data omain names NS distributed data each NS server keeps track of part of the hierarchy unresolved requests are sent to servers higher in the hierarchy 8

9 Internet protocols (5) Internet protocols (6) Firewalls monitor and filter communication controlling what services are available to the outside controlling the use of services controlling internal users access to the outside Filtering at different protocol levels IP packet filtering: addresses, ports.. TP gateway: check for correctness in TP connections e.g., are they partially opened and never used (why?) pplication-level gateway: proxy for applications no direct communication between the inside and outside e.g., smtp proxy can check addresses, content... astion (tcp/ application filter) ): two router filters ccess to web/ftp server, but not LN Hide internal IP addresses astion has the mapping Second router is the second IP filter (invisible to the outside) a) Filtering router Internet b) Filtering router and bastion Internet Internet Router/ filter web/ftp server R/filter web/ftp server astion c) Screened subnet for bastion R/filter astion web/ftp server Protected intranet R/filter Internet protocols (7) Network ase Studies (): thernet and WiFi Virtual Private Network (VPN) extending a secured internal network to an external unsecured host e.g. IPSec tunneling through IP I No. Name Title Reference 80.3 thernet SM/ Networks (thernet) [I 985a] 80.4 Token us Networks [I 985b] 80.5 Token Ring Networks [I 985c] 80.6 Metropolitan rea Networks [I 994] 80. WiFi Wireless Local rea Networks [I 999] luetooth Wireless Personal rea Networks [I 00] Zigee Wireless Sensor Networks [I 003] 80.6 WiMX Wireless Metropolitan rea Networks[I 004a] Network ase Studies (): thernet Network ase Studies (3) thernet, SM/, I 80.3 Xerox Palo lto Research enter (PR), 973, 3Mbps 0,00,000 Mbps extending a segment: hubs and repeaters connecting segments: switches and bridges ontention bus Packet/frame format preamble (7 bytes): hardware timing start frame delimiter () dest addr (6) src addr (6) length () data (46-500): min total becomes 64 bytes, max total is 58 checksum (4): dropped if incorrect arrier Sensing Multiple ccess / ollision etection (SM/) S: listen before transmitting, transmit only when no traffic M: more than one can transmit : collision detected when signals transmitted are not the same as those received (listen to its own transmission) fter detection of a collision send jamming signal wait for a random period before retransmitting T (Tau): time to reach the farthest station When is the collision detected? and send at the same time sends, sends within T seconds sends, sends between T and T seconds sends, sends after T seconds Minimum length of packet for collision detection: packet length > T, between T and T, and < T? 9

10 Network ase Studies (4) Network ase Studies (5): Ranges and speeds Physical implementation: <R><><L> R: data rate in Mbps : medium signaling type: baseband [one channel] or broadband [multiple channels] L: max segment length in 00meters or T (twisted pair cable, hierarchy of hubs) 0ase5 0aseT 00aseT 000aseT ata rate 0 Mbps 0 Mbps 00 Mbps 000 Mbps Max. segment lengths: Twisted wire (UTP) 00 m 00 m 00 m 5 m oaxial cable (STP) 500 m 500 m 500 m 5 m Multi-mode fibre 000 m 000 m 500 m 500 m Mono-mode fibre 5000 m 5000 m 0000 m 000 m Network ase Studies (6): WiFi I 80. wireless LN up to 50m and 54Mbps access point (base station) to land wires d hoc network--no specific access points, "on the fly" network among machines in the neighborhood Radio Frequency (.4, 5GHz band) or infra-red Network ase Studies (7): Problems with wireless SM/ Hidden station: not able to detect another station is transmitting can t see, or vice versa Fading: signals weaken, out of range and are out of range from each other ollision masking: stronger signals could hide others and are out of range from each other, both transmits, collide, can't detect collision, ccess point gets garbage Laptops radio obstruction Server Palmtop Wireless LN ase station/ access point LN Network ase Studies (8) Network ase Studies (9) arrier sensing multiple access with collision avoidance (SM/) reserving slots to transmit if no carrier signal medium is available, out-of-range station requesting a slot, or out-of-range station using a slot Steps. Request to send (RTS) from sender to receiver, specify duration. lear to send (TS) in reply 3. in-range stations see the RTS and/or TS and its duration 4. in-range stations stop transmitting 5. acknowledgement from the receiver Hidden station & Fading: TS, need permission to transmit RTS and TS are short, don't usually collide; random back off if collision detected Should have no collisions, send only when a slot is reserved 0

Recap. Requirements of Networks. Overview of the lecture LAN. Types of Networks. Lecture 03: Networking

Recap. Requirements of Networks. Overview of the lecture LAN. Types of Networks. Lecture 03: Networking Lecture : Networking istributed Systems ehzad ordbar School of omputer Science, University of irmingham, UK Recap rchitecture, what? and why? Tiered rchitecture Various software layer: middleware client/server