Internet Protocols

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Internet Protocols

• Midterm is two weeks away ?
• Break is Saturday ?

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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?

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Fetching a Web Page
Home computer
The Internet
www.si.umich.edu
4
Fetching a Web Page
MichNet Modem
Home computer
www.si.umich.edu
The Internet
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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

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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

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Simplified Internet Topology
Routers/Switches
Hosts
Backbone links
Access links
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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

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

• Responsible for routing packets from source to
  destination
• Not responsible for the packets payload
• IP is common
• IPX (Novell Netware) is another
• Next well discuss IP in terms of its
• Service
• Protocol

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IP Service

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

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IP Protocol

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

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IP Protocol Packet Format

• Header
• Source IP address
• Destination IP address
• HopLimit
• Payload length
• Payload
• Actual data

Header
Payload
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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

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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

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Questions
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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
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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

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Routing Changes

• Routers talk to each other (e.g., BGP protocol)
• Advertise routes
• Im now accepting traffic for 141.211.
• Query for route availability
• Is anyone accepting traffic for 141.211.?
• Update entries in own routing table

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Routing Dangers

• Long routes
• Circular routes
• Use HopLimit to limit damage
• Decrement HopLimit at each router
• Discard packet if HopLimit0
• Hijacking routes
• Advertise a route, but dont deliver
• Route flapping
• Frequent updates to routing table

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IP Routing Demonstration 2HopLimit

• Revised routing rules
• Decrement HopLimit (cross out and write next
  smaller number)
• If HopLimit0 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

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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

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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?

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Fetching A Web Page
MichNet Modem
207.75.186.1
Home computer
141.211.0.9
198.108.3.5
c-ugli router
c-ccb2 router
www.si.umich.edu
141.211.203.32
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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
MichNet Modem
207.75.186.1
Home computer
141.211.0.9
198.108.3.5
c-ugli router
c-ccb2 router
www.si.umich.edu
141.211.203.32
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IP As Spanning Layer
Application
Application
TCP or UDP
TCP or UDP
IP
IP
IP
Network 1
Network 2
Host A
Host B
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

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What IP Doesnt 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

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IP over Voice
Public telephone network
?
Computer w/modem
Computer w/modem
Gateway
?
?
Internet
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Voice over IP
Public telephone network
?
Plain old telephone
Gateway
IP telephone or computer running VoIP software
?
?
Internet
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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 doesnt do
• Next time, TCP

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IP over Voice
Public telephone network
?
Computer w/modem
Computer w/modem
Gateway
?
?
Internet
34
Voice over IP
Public telephone network
?
Plain old telephone
Gateway
IP telephone or computer running VoIP software
?
?
Internet