Internet protocols

Internet Protocols Midterm is two weeks away  Break is Saturday 

Review Given a video file with a message latency of 2 minutes, how much faster will a streamed version of the video start to play if each video segment has a message latency of 4 seconds? Suppose that a video is divided into 2-second segments for a streaming broadcast Does streaming work if each segment has a 1 second transmission time and a 3 second delay? Does streaming work if each segment has a 3 second transmission time and a 1 second delay?

Fetching a Web Page www.si.umich.edu Home computer The Internet

Fetching a Web Page www.si.umich.edu Home computer The Internet MichNet Modem

Overview Of Internet Topics Understand and explain general principles… Layered protocols Indirection in naming Packet routing Local and hierarchical namespaces End-to-end principle … As applied to Internet IP/TCP/HTTP DNS and IP addresses Pressures for Internet evolution Understand structure of ISP industry Diagnose connection troubles

Learning Objectives Understand the Internet protocol stack Understand what IP provides and how it provides it Understand IP addresses & packet routing TCP More advanced topics The end-to-end principle Quality of service Pricing HTTP Web server administration Future sessions

Simplified Internet Topology Hosts Routers/Switches Access links Backbone links

Terminology A network is the collection of routers, communication lines and hosts controlled by a network operator (or an organization or a homeowner) In the diagram, these are the matching yellow ovals and white lines that connect them An internet is a network of networks The Internet is the public network of networks we use all the time

Conceptual Layering of Internet Protocols/Services Internet Protocol (IP) Subnets User Datagram Protocol (UDP) Transmission Control Protocol (TCP) HyperText Transport Protocol (HTTP) Application Real-time Transport Protocol (RTP) Application Layer Transport Layer Network Layer Data Link and Physical Layer Internet Protocol (IP) Last week’s topic Today’s topic Each layer provides services to the layer above, and utilizes service provided by the layer below

Comparing the OSI and TCP/IP Reference Models Data Link Physical Network Transport Presentation Session Application Host-to- Network Transport Application Internet

Network/Internet Layer Responsible for routing packets from source to destination Not responsible for the packet’s payload IP is common IPX (Novell Netware) is another Next we’ll discuss IP in terms of its Service Protocol

IP Service Provides best effort packet delivery Between two hosts Not necessarily sharing a common LAN or subnet How Global addressing Packet forwarding

IP Protocol The IP protocol specifies three things IP packet format IP addresses IP packet routing

IP Protocol: Packet Format Header Source IP address Destination IP address HopLimit Payload length Payload Actual data Header Payload

IP Protocol: Addresses Every host gets a distinct address Can be dynamically assigned IPv4 (currently ubiquitous) Each address 32 bits Divide into 8 bit segments Example: 141.211.203.32 4 billion addresses IPv6 (future widespread adoption?) Each address 128 bits “ 1500 addresses per square foot”

IP Address Assignment Fixed (static) IP address Computer always has same IP address Dynamic IP address Address changes each time computer connects to network Internet Access Provider (U-M, AOL, MSN, etc.) assigns an address from its pool Uses DHCP to allocate addresses All addresses in that pool are routed to the provider Provider forwards on to correct final destination

IP Protocol: Routing Final destination IP address written in packet Not the full route Each router has connections to several hosts Each router keeps a table that indicates where to go based on final destination Reducing table size use wildcards: 141.211.* next hop is X Final Destination Next hop 141.211.203.032 X 207.075.186.001 Y

IP Routing Demonstration #1 Envelope is an IP packet Inside is the payload (a bit string) Outside specifies a destination in the format ( subnet, ID ) If you have two packets, drop the second one Consult your routing table Routers with ID of 0 can pass packets to different subnets All other routers must pass to router at ID 0 if packet needs to reach another subnet Routers send packets on destination subnet to correct ID If destination subnet and ID match your address, open the envelope

Routing Changes Routers talk to each other (e.g., BGP protocol) Advertise routes “I’m now accepting traffic for 141.211.*” Query for route availability “Is anyone accepting traffic for 141.211.*?” Update entries in own routing table

Routing Dangers Long routes Circular routes Use “HopLimit” to limit damage Decrement HopLimit at each router Discard packet if HopLimit=0 Hijacking routes Advertise a route, but don’t deliver Route flapping Frequent updates to routing table

IP Routing Demonstration #2: HopLimit Revised routing rules Decrement HopLimit (cross out and write next smaller number) If HopLimit=0 then drop packet If you have two packets, drop the second one Consult your routing table Routers with ID of 0 can pass packets to different subnets All other routers must pass to router at ID 0 if packet needs to reach another subnet Routers send packets on destination subnet to correct ID If destination subnet and ID match your address, open the envelop

Summary: Why Delivery Not Guaranteed Intermediate host not responding Temporary malfunction Queues full (congestion) Bad routing Reach hop limit because route was too long or circular

Sharing an IP Address? DSL provider gives me one IP address I have several devices on my home network? How many do you have? How does it work?

Fetching A Web Page www.si.umich.edu Home computer MichNet Modem 207.75.186.1 198.108.3.5 141.211.0.9 141.211.203.32 c-ccb2 router c-ugli router

TRACERT SI.UMICH.EDU 1 * Request timed out. 2 140 ms 207.75.186.1 3 140 ms f-umbin.c-ccb2.umnet.umich.edu [198.108.3.5] 4 240 ms f-backbone.c-ugli.umnet.umich.edu [141.211.0.9] 5 141 ms bart.si.umich.edu [141.211.203.32] www.si.umich.edu Home computer MichNet Modem 207.75.186.1 198.108.3.5 141.211.0.9 141.211.203.32 c-ccb2 router c-ugli router

IP As Spanning Layer IP IP IP Network 1 Network 2 TCP or UDP TCP or UDP Host A Host B Application Application Switch or Router Diversity A spanning layer is a common protocol offering consistent services and interfaces to the layers above it that has been implemented on a wide range of underlying networking technologies, such as Ethernet and token ring N 2 N 1

What IP Doesn’t Do Guarantee speed of delivery Guarantee delivery Guarantee order of delivery Maintain conversational context (each packet is independent) Specify a process that should handle the packet at destination

IP over Voice Gateway Public telephone network Internet Computer w/modem    Computer w/modem

Voice over IP Gateway Public telephone network Internet IP telephone or computer running VoIP software Plain old telephone   

Summary The Internet protocol stack defines several protocol layers that work together to deliver Internet traffic IP provides best effort packet delivery using Global addresses Store-and-forward routers IP is a spanning layer Available on a wide range of network architectures, with a variety of applications built on top of it But there are lots of things that IP doesn’t do Next time, TCP…

Internet protocols

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Internet protocols

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