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CISC 370 - Class TodayCISC 370 - Class Today

• GradingGrading• ExamExam• Recap on ProxiesRecap on Proxies• Internet PhonesInternet Phones• RoutingRouting• Quality of ServiceQuality of Service

Assignment 6Assignment 6

• Missing plans from people?Missing plans from people?

• Grading – looking for ‘substance’Grading – looking for ‘substance’– Architectural plan and assessment of impactArchitectural plan and assessment of impact

• If you didn’t get it back, hand it in againIf you didn’t get it back, hand it in again

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GradingGrading

• Current class median 88%Current class median 88%

• Options on weighting the examOptions on weighting the exam– I chose to spread the weight – class avg = 83.6I chose to spread the weight – class avg = 83.6

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Exam AnswersExam Answers

• 1. All pretty obvious – do it with powers of 21. All pretty obvious – do it with powers of 2– Errors: not using powers of 2Errors: not using powers of 2

• Specifying a fractional number of channelsSpecifying a fractional number of channels

• 2. Change something in 1 – calculate difference2. Change something in 1 – calculate difference– Errors: increased image size does NOT increase channels!Errors: increased image size does NOT increase channels!

• 3. No problem3. No problem

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More AnswersMore Answers

• 4. Looked for ‘parallel’ layers 4. Looked for ‘parallel’ layers • 5. Looked for different ones:5. Looked for different ones:

– TCP/IP application = session/pres/app ISOTCP/IP application = session/pres/app ISO– TCP network does ROUTINGTCP network does ROUTING– TCP transport has UDPTCP transport has UDP

• 6. Swapped pres/app layers6. Swapped pres/app layers– Errors: choosing the wrong stackErrors: choosing the wrong stack

• 7. Partitioned7. Partitioned• 8. a: rerouted queries; b) more traffic8. a: rerouted queries; b) more traffic• 9. Replicated9. Replicated

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04/19/23 6R. Smith - University of St Thomas - Minnesota

Recap: Proxies and the InternetRecap: Proxies and the Internet

• DNS query forwarding and proxyingDNS query forwarding and proxying

• Proxies for Web TrafficProxies for Web Traffic– Proxy protocolsProxy protocols– ““Transparent” redirected proxiesTransparent” redirected proxies

• Proxies for general trafficProxies for general traffic– Purely transparent proxies/Firewall applicationPurely transparent proxies/Firewall application

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Session Initiation Protocol/PhonesSession Initiation Protocol/Phones

• The problem: how do we deal with mobility?The problem: how do we deal with mobility?

• Let’s come up with some ideas.Let’s come up with some ideas.

• Constraints:Constraints:– Fits into existing Internet architecture and securityFits into existing Internet architecture and security– More or less fits the existing cel phone business modelMore or less fits the existing cel phone business model

• Charge periodic fee for phone useCharge periodic fee for phone use• Track individual usage and charge for extra useTrack individual usage and charge for extra use

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Problems to solveProblems to solve

• Do phones have names or numbers?Do phones have names or numbers?

• Do phones have IP addresses? Permanent?Do phones have IP addresses? Permanent?

• How do we avoid single-point failures?How do we avoid single-point failures?

• How do we locate a phone “right now”?How do we locate a phone “right now”?

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SIP ComponentsSIP Components

– User agent Client, User Agent Server – elements that send User agent Client, User Agent Server – elements that send requests (clients) or respond to requests (servers)requests (clients) or respond to requests (servers)

– Redirect Server – Find the address of a called deviceRedirect Server – Find the address of a called device– Proxy Server – routes requests to the right server to process Proxy Server – routes requests to the right server to process

them. Provides a ‘local’ place to make queriesthem. Provides a ‘local’ place to make queries– Location Service – provides information about a callee’s Location Service – provides information about a callee’s

possible locations: SIP address->IP mappingspossible locations: SIP address->IP mappings– Registrar – registers a SIP address as having an IP addressRegistrar – registers a SIP address as having an IP address

• SIP URI – looks like an e-mail addressSIP URI – looks like an e-mail address

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SIP DiagramSIP Diagram

Call setup Call setup between between two two phones phones requires requires two two servers servers and two and two proxiesproxies

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Internet AddressingInternet Addressing

• Review from last timeReview from last time• Class A? B? C?Class A? B? C?• Subnet masks?Subnet masks?

• Difference between “network address”Difference between “network address”– and “host address”and “host address”

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Autonomous Systems (AS)Autonomous Systems (AS)

• Networks managed by different entitiesNetworks managed by different entities– Each network is its own “AS”Each network is its own “AS”

• Each AS handles its own internal routingEach AS handles its own internal routing• ““Global” Internet routing is between ASesGlobal” Internet routing is between ASes

• This makes the Internet a hierarchyThis makes the Internet a hierarchy– Chaos of the olden days of the ‘flat’ InternetChaos of the olden days of the ‘flat’ Internet

• Special router protocolsSpecial router protocols– ERP – exterior routing, usually BGP (Border Gateway Protocol)ERP – exterior routing, usually BGP (Border Gateway Protocol)– IRP – interior routingIRP – interior routing

The Routing ProblemThe Routing Problem

• You have a bunch of nodesYou have a bunch of nodes– They are interconnected with linksThey are interconnected with links

• You have messagesYou have messages– They arrive on one node, destined for anotherThey arrive on one node, destined for another

• The Network Problem: find the shortest routeThe Network Problem: find the shortest route

• The Node problem: pick which link to useThe Node problem: pick which link to use

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04/19/23 14R. Smith - University of St Thomas - Minnesota

Routing ProtocolsRouting Protocols

• Distance vector protocolsDistance vector protocols– Oldest approach, ARPANET in 1969Oldest approach, ARPANET in 1969– RIP – Routing Improvement ProtocolRIP – Routing Improvement Protocol

• Internet protocol that uses distance vectorsInternet protocol that uses distance vectors– The “Tell your neighbor everything” protocolThe “Tell your neighbor everything” protocol

• Link state protocolsLink state protocols– Developed in late 1970s on the ARPANETDeveloped in late 1970s on the ARPANET– OSPF protocol – Open Shortest Path FirstOSPF protocol – Open Shortest Path First

• Internet protocol that uses link stateInternet protocol that uses link state– The “Tell everyone about your neighbors” protocolThe “Tell everyone about your neighbors” protocol

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Distance Vector ProtocolsDistance Vector Protocols

• What it doesWhat it does– Figures out how far “this node” is from everyone else.Figures out how far “this node” is from everyone else.

• Save in a huge tableSave in a huge table• Share the table with your neighborsShare the table with your neighbors

• How it worksHow it works– Keep a list of all hosts in the network. For each host:Keep a list of all hosts in the network. For each host:• Which interface gives the shortest path to that Which interface gives the shortest path to that

hosthost• Delay (number of hops) to reach that hostDelay (number of hops) to reach that host

– Exchange the (big) list of delays with your neighborExchange the (big) list of delays with your neighbor

Updating your routesUpdating your routes

• The stepsThe steps– Get the list from your neighborGet the list from your neighbor

– For each non-neighbor, add a hop (delay) to get to themFor each non-neighbor, add a hop (delay) to get to them

– If that count is less than what’s already in your table,If that count is less than what’s already in your table,

• Update your table with the new delayUpdate your table with the new delay

• The link to that neighbor yields the best path to that host.The link to that neighbor yields the best path to that host.

• The node doesn’t care WHO its neighbors are!The node doesn’t care WHO its neighbors are!

• ““Tell your neighbor everything”Tell your neighbor everything”– Big messages sent to neighbors onlyBig messages sent to neighbors only

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Let’s do an exampleLet’s do an example

• Six nodesSix nodes

• Two west, two middle, two eastTwo west, two middle, two east

• Parallel connections north-south on all 3 pairParallel connections north-south on all 3 pair

• Parallel connections acrossParallel connections across– Three westwardThree westward– Two eastwardTwo eastward

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ARPANET Distance Vector ProtocolARPANET Distance Vector Protocol

• Address: 6 bits of ‘node’ and 2 bits of ‘host’Address: 6 bits of ‘node’ and 2 bits of ‘host’– 1 entry per node1 entry per node– So, how big was the distance vector table?So, how big was the distance vector table?

• New Address: 24 bits: 16 bits node, 8 bits hostNew Address: 24 bits: 16 bits node, 8 bits host– So, how big was a distance vector table?So, how big was a distance vector table?– Was this practical?Was this practical?

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Link State ProtocolsLink State Protocols

• What it doesWhat it does– Tell everyone who your neighbors areTell everyone who your neighbors are– Use those messages to incrementally build a network mapUse those messages to incrementally build a network map

• How it worksHow it works– Measure the delay to reach your neighborsMeasure the delay to reach your neighbors– Broadcast a list of your neighbors to everyone on the networkBroadcast a list of your neighbors to everyone on the network

• These are “link state” messagesThese are “link state” messages

Updating your routesUpdating your routes

• The StepsThe Steps– As they arrive, use the link state messages to build a tree-As they arrive, use the link state messages to build a tree-

shaped map of the network, indicating the shortest path from shaped map of the network, indicating the shortest path from you to the other hosts on the networkyou to the other hosts on the network

– If a new message uncovers a shorter path, fix your treeIf a new message uncovers a shorter path, fix your tree– To route a message, find the host and see which interface To route a message, find the host and see which interface

yields the shortest path, as shown by your treeyields the shortest path, as shown by your tree

• ““Tell everyone about your neighbors”Tell everyone about your neighbors”– Small messages sent to everyoneSmall messages sent to everyone

• The node CARES about who the neighbors areThe node CARES about who the neighbors are

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A final exampleA final example

• Six nodesSix nodes

• Two west, two middle, two eastTwo west, two middle, two east

• Parallel connections north-south on all 3 pairParallel connections north-south on all 3 pair

• Parallel connections acrossParallel connections across– Three westwardThree westward– Two eastwardTwo eastward

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Quality of ServiceQuality of Service

• Elastic vs Inelastic servicesElastic vs Inelastic services– A familiar concept, different termsA familiar concept, different terms

– Possibly elastic/inelastic propertiesPossibly elastic/inelastic properties

• ThroughputThroughput

• DelayDelay

• Delay variationDelay variation

• Packet lossPacket loss

• Differentiated Services (DS)Differentiated Services (DS)– Uses a field in IP packet to identify different handling needsUses a field in IP packet to identify different handling needs

– Can simply be “priority”Can simply be “priority”

• Send it ahead of lower priority trafficSend it ahead of lower priority traffic

• Discard other packets before this one if space is tightDiscard other packets before this one if space is tight

– Routers can provide “guaranteed service” for selected DS settings (at Routers can provide “guaranteed service” for selected DS settings (at UST, CLIC service has a small guaranteed bandwidth)UST, CLIC service has a small guaranteed bandwidth)

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