Internetwork Layers Internetworking

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Internetwork LayersInternetworking TCP/IP
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Coming soon 120 second ET pitch

• What (topic)
• Why should we care
• What we should expect to take away from it

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Agenda

• Transport/network layer
• Protocols
• Segmenting
• Linking to app layer
• Reliable delivery
• Addressing
• Routing
• Types, Protocols, Multicasting

Messy routing of Internet data
Why packet size matters
Why your emails actually arrive
Why You-Tube is fuzzy
Why Bittorrents are unreliable
How lousy sizing can kill a business
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Cocktail Conversation Terms

• Internetwork layers ( USPS analogy)
• Transport layer
• Network layer
• How the app layer (say Firefox) communicates
  w/ISU
• Segmenting of packets?
• Routing?
• What informations needed for routing
• ZIP codes
• Network efficiency
• Reliability
• Unicasting, broadcasting, multicasting?
• Think radio networks

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OverviewThe Network and Transport Layers
Perform encapsulation of message segments from
the application layer
pass them to data link layer
pass them up to app layer
,
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OverviewThe Network and Transport Layers

• Transport layer
• Responsible for
• end-to-end delivery of messages
• setting up virtual circuits
• segmentation (breaking message into smaller
  pieces)
• reassembly (reconstructing original message) into
  a single whole) at the receiving end
• Network layer?addressing and routing of the
  message.

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The Path of an Email?
ISU
?

• A 50-cent Kazaa download from Dallas?
• A You-Tube video from NY?
• A text message on Twitter?
• A Skype message from LA?

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China
ISU
Kzakasthan
Mexico
Peru
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Internetwork Protocols

• Most common protocol suites
• TCP/IP
• IPX/SPX
• by Xerox during in 70s, used by Novell networks
• Dumped for TCP/IP
• X.25
• by ITU-T for use in WANs (European users)
• Minitel.fr
• SNA
• by IBM in 74 for IBM mainframes
• non-standard proprietary IBMs switched to TCP/IP

TCP/IP 1974, part of DoD Arpanet project 70
backbone, MAN, WAN use TCP/IP 1998 TCP/IP
surpassed IPX/SPX for LANs
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Part 1 of 2Transmission Control Protocol

• TASK 1 performs packetization (segmentation)
• breaking up messages into smaller pieces
• numbering the segments 192 bit (24 byte) header
• reassembling them _at_ destination
• TASK 2 ensures reliable delivery
• Header fields include..
• source destination port identifiers
• a packet sequence number used in message
  reassembly

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Part 2 of 2Internet Protocol

• Responsible for addressing and routing of data
  packets
• 2 versions (ZIP and ZIP4)
• IPv4 uses a 160 bit (20 byte) header, and 32 bit
  addresses
• IPv6 uses a 320 bit (40 byte) header and 128 bit
  addresses
• Header fields include..
• source and destination addresses
• packet length
• packet number

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Transport Layer 2 Key Functions

• 1 Linking to the Application Layer
• knowing which application layer program to send
  a message to (why?)
• done using source and destination port numbers
  (2-bytes long)
• located in the first two TCP header fields
• Applications sending outgoing msgs give TCP both
  port numbers
• Incoming messages also provide port numbers
• 2 Segmenting
• breaking large messages into smaller pieces
  (segmentation)
• putting them back together _at_ destination
  (reassembly)
• Decides whether to
• deliver each incoming packets right away (Web
  pages)
• or wait till all arrive (email)

• Standard port numbers
• Web servers 80
• FTP servers 21
• Telnet 23
• SMTP 25

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Transmission Efficiency
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Transmission Efficiency

• Information bytes versus overhead bytes in
  protocol
• Information bytes convey the users meaning
  (URL)
• Overhead bytes carry control data (packets
  header)
• . For example, TCP has 24 bytes of overhead,
  while IPv6 has 40.
• Tx efficiency (info bytes/total bytes) per
  packet

Packet
212 bytes
Tx Eff (15/212) 7
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Optimal packet sizing

• Imagine having to carry 7 boxes of books to my
  office
• How would you move them?
• Why?

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Tradeoffs in Packet Sizing
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Optimal Packet Size

• Throughput BPS, accounting for
• overhead
• need to retransmit flawed packets
• Trade-off between large and small packets
• Small packets less efficient, but less likely to
  contain errors
• Large packets ??? Say 100k
• if errors less costly to retransmit..
• Optimal packet size

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Connection-Oriented Vs. Connectionless Routing

• Connection-Oriented (used in HTTP, SMTP, FTP )
• end-to-end routing by setting up a virtual
  circuit
• all packets in a message follow the same route
  from source?destination
• Requires a special SYN packet (begin) and
  FINish packet (closes virtual circuit)
• Connectionless Routing (UDP User Datagram
  Protocol)
• No virtual circuit used
• each packet sent independently of next
• routed separately can follow different routes
• can arrive at different times
• UDP has a much smaller packet header (8 bytes)so
  what?
• Useful for small control messages (DNS, DHCP,
  RIP)

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Service Reliability

• QoS Quality of Service
• Packet delivery in real time apps (voice vs.
  email)
• QoS defines classes of service each with a
  different priority
• Real-time applications get the highest priority
• a graphical file for a Web page gets a lower
  priority
• E-mail gets the lowest priority
• QoS protocols in TCP/IP protocol suiteuses
  virtual connections
• Resource Reservation Protocol (RSVP) general
  purpose
• Real-Time Streaming Protocol (RTSP) for
  audio-video applications
• Reliable Delivery
• Error detection/correction?packets delivered free
  of errors
• How does error detection work in TCP/IP networks?
• 16 bit checksums in each packet

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Two Techniques for Error Correction

• Stop-and-Wait Error Correction
• acknowledgement (ACK)
• timeout occurs
• the segment is resent
• Downsides?

Sliding Window Automatic timeout for segments
Faster -- entire segments discarded
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Sliding Windows

• Needs attention to
• Flow control (sender not too fast for receiver)
• Both agree on max of unacknowledged segments
  allowed

Sent
Send after ACK is received
Send after ACK is received
several segments at one time
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Addressing

• 3 types of addresses
• Application layer addresses (domain names)
• www.iastate.edu
• Network layer addresses (IP addresses)
• 129.79.127.4 (? 4 bytes in IPv4 dotted decimal
  notation)
• IPv4 32 bit addresses?1 billion possible
  addresses
• IPv6 128 bit addresses?3.2 x 1038 possible
  addresses
• Data link layer addresses Hardware addresses
  placed on NICs (MAC)00-0C-00-F5-03-5A
• ICANN manages assignment of IP and app layer name
  space
• Servers have permanent addresses, clients usually
  dont.
• Address resolution Translating address from one
  type to another to allow communication

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Subnets Same LAN same prefixISU campus phone
numbers or Ames 515
Subnet masks 255.255.255.473

easier to separate the subnet part of address
from host part
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Finding Servers

• Dynamic Addressing
• Allows efficient use of network IP address space
• Leases an IP address for a fixed time
  (apartments)
• Gives IP addresses to clients when they login to
  the network
• Takes them back when they logout
• Dynamic Host Control Protocol (DHCP)
• a client broadcasts a message requesting an IP
  address
• client sends a new IP address request when lease
  expires
• Server Name Resolution (address resolution)
• application layer address (or domain name) of the
  destination host must first be translated in its
  corresponding IP address
• www.iastate.edu ? 204.71.200.74
• If IP address not in the clients address table
• Must use Domain Name Service (DNS) to resolve the
  address
• Uses name servers (directories of domain names
  and IP addresses)
• phone directories
• DNS uses connectionless routing (UDP)

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Recursive DNS resolution
http//en.wikipedia.org/wiki/Domain_Name_System
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Data Link Layer Address Resolution

• When a data link layer destination address is not
  known, the address resolution protocol (ARP) is
  used to find it
• works by broadcasting a message to all computers
  on a LAN
• will the device with XXX IP address please
  respond
• XXX responds with its data link layer address.
• The sender then stores this data link layer
  address in its address table

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Routing

• Deciding what path to have a packet take through
  nwk
• More than one route possible
• devices that do routing must keep routing tables
• specialized devices routers that maintain
  routing tables
• Two ways to skin a cat
• Centralized Routing decisions made by one
  central computer
• Decentralized (Internet) made independently at
  each routing node
• Static routing Uses fixed routing tables (A?B
  D?F)
• Dynamic Routing decisions made dynamically,
  based on
• routing condition information exchanged b/w
  routing devices

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Dynamic Routing AlgorithmsTwo Types

• Think Driving from ISU to DSM
• Distance Vector Uses the least number of hops to
  route
• Link State Uses a variety of information for
  routing decisions
• Network congestion
• Response time
• Link state preferred better performance

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Routing Protocols

• Exterior between networks focuses on main routes
  only
• Border Gateway Protocol (BGP) ? Internet standard
  
• Interior within a network (an autonomous
  system)
• Routing Information Protocol (RIP) dynamic
  distance vector method
• Computers using RIP broadcast routing tables
  every minute
• Open Shortest Path First (OSPF) link state
  algorithm
• Less network intensive
• Sends updates only, not entire routing tables
• Only communicates with other routers (does NOT
  broadcast)
• Enhanced Interior Gateway Routing Protocol
  (EIGRP) (CISCO)

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Interior
Exterior
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Checking TCP/IP settings

• Run Winipcfg
• View
• Ethernet adapter address
• IP address
• Subnet mask
• IP address of the default gateway
• IP address of the nearest DNS server
• DHCP server
• Hands-on checking tips
• http//support.microsoft.com/kb/169790

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Size matters

• Technical choices, business consequences
• Speed-performance tradeoff has real implications
• Gmails speed slowdown
• Bittorrents unreliable
• You-Tubes poor video quality

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Summary

• Why your emails eventually always arrive
• Transport-network layer functions
• Addressing
• Routing
• Segmenting
• Virtual circuit versus connectionless routing
• Prioritization of packets in protocols
• Addressing
• App layer (URL etc)
• Network layer (IPs)
• Data link layers (hardwired in hardware)
• Address resolution (distributed collaboration)