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ISO Layer and TCP Fundamentals

ISO Layer and TCP Fundamentals. Rich Carlson Internet2 eVLBI workshop – TCP Fundamentals September 17, 2006. Outline. A Brief history of networking The OSI reference model The TCP/IP architecture TCP Fundamentals. Arpanet. 1962 - ARPA pursues new Interactive Computing paradigm

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ISO Layer and TCP Fundamentals

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  1. ISO Layer and TCPFundamentals Rich Carlson Internet2 eVLBI workshop – TCP Fundamentals September 17, 2006

  2. Outline • A Brief history of networking • The OSI reference model • The TCP/IP architecture • TCP Fundamentals

  3. Arpanet • 1962 - ARPA pursues new Interactive Computing paradigm • Focus is on computers as a communications device • Industry focused on computers as arithmetic calculators

  4. IMPs & TIPs • 1969 – A 4 node network is built using Interface Message Processors (IMPs) • UCLA, SRI, UCSB, Univ of Utah • 1971 – BBN develops a Terminal IPM (TIP) supports up to 64 terminals

  5. The Original Arpanet

  6. Networks Proliferate • 1974 – BBN opens Telenet • 1975 – DEC develops DECnet • 1976 – UUCP (Unix-to-Unix CoPy) • 1977 – Tymshare opens Tymnet • 1981 – CUNY develops BITnet

  7. Federal Agencies get in the Act • ARPA - ARPAnet • DOE – MFENet and HEPNet created • NASA – SPAN created • NSF – CSNet created

  8. ISO OSI networks International Organization for Standardization (ISO) • Open Systems Interconnection (OSI) • 1979 - 7 layer reference model defined • 1982 – ISO begins deliberations on specific protocols for each layer • 1990 – U.S. mandates all gov. purchased computers must be GOSIP compliant • 1995 – GOSIP requirement rescinded

  9. Application L7 Presentation L6 Session L5 Transport L4 Network L3 Data Link L2 Physical L1 7 Layer Reference Model

  10. Application Application Presentation Presentation Session Session Transport Transport Network Network Network Data Link Data Link Data Link Physical Physical Physical Host – to – Host Communications Ethernet WiFi

  11. Layer 1 - Physical • Defines the physical, electrical/optical specifications for each network device • Pin layout • Voltages • Optical levels • Modulation scheme • Examples: • Ethernet, SONET, FDDI, IEEE 802.11

  12. Layer 2 – Data Link Layer • Functions and procedures to transmit/receive bits over the physical media. • Media specific addressing • Physical media error detection/recovery • Bridge, Hub, Switch equipment • Examples: • Ethernet CSMA/CD, HDLC, SDLC

  13. Layer 3 – Network Layer • Functions and procedures needed to transmit data throughout a global network • Routing functions • Segmentation / reassembly • Global addressing • Example: • IP addresses

  14. Layer 4 – Transport Layer • Functions to support the transparent transfer of data between end users • Reliability • Error detection and recovery • Flow control • Examples: • TCP, UDP, SCTP

  15. Layer 5 – Session Layer • Control sessions between computers • Establish, maintain, terminate connections • Duplex operation (full or half) • Checkpointing and restart procedures

  16. Layer 6 – Presentation Layer • Transforms data to/from a common format • Encoding • Compression • Encryption • Examples: • MIME, XML

  17. Layer 7 – Application Layer • Program used to interact with computer and data • Specific application for each task • GUI or command line interface • Examples: • SSH, SCP, HTTP, email

  18. OSI Quick Summary • OSI reference model defines modular ‘stack’ that allows multi-vendor interoperations. • Input/output details specified • Internal details left up to individual vendors • Usually implemented by a series of function calls

  19. TCP/P Internet • Direct descendant of ARPAnet • Provides Global packet switched network services • ‘Standard’ protocol shipped by most vendors • Still under active development • IPv6 • TCP modifications

  20. NCP to TCP transition • NCP (Network Control Protocol) a host-to-host protocol for the Arpanet • Handled multiple functions • Separate network and transmission functions into 2 distinct protocols • IP handles addressing and routing functions • TCP handles reliability functions • 1 year transition period • Flag day specified as 1-Jan-1983

  21. Network Based Applications L4 TCP, UDP L3 IP L2 Ethernet, Sonet, ATM L1 Copper, Fiber, Radio TCP/IP Architecture

  22. Network Based Applications L4 TCP, UDP L3 IP L2 Ethernet, Sonet, ATM L1 Copper, Fiber, Radio TCP/IP Architecture

  23. TCP/IP Quick Summary • Grew out of ARPA funded research program • Free wide spread deployment in BSD 4.2 OS • TCP/IP protocols form the Internet

  24. Application L7 Network Based Applications Presentation L6 Session L5 Transport TCP, UDP L4 Network IP L3 Data Link Ethernet, Sonet, ATM L2 Physical Copper, Fiber, Radio L1 Architecture Comparison

  25. IP Protocol • IP is a connectionless datagram delivery service • Unreliable Delivery • No concept of order • No concept of loss • No concept of late • TTL field to ‘Kill Off’ packets • Each packet treated separately • Operates over numerous data-link and physical networks

  26. IP Header Field • Fixed size header field (20 Bytes), Variable length options 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |Version| IHL | DSCP |ECN| Total Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Identification |Flags| Fragment Offset | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Time to Live | Protocol | Header Checksum | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Source Address | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Destination Address | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Options | Padding | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

  27. IP Address • 32 bit unsigned number • Network portion used for global routing • Host portion used to identify specific host • Usually expressed in “dot quad” format • 192.168.1.1 specifics specific host • 192.168.1.0/24 specifies subnet of hosts

  28. CIDR Rules • IP address is ANDed with bit mask to extract network portion • Classless Inter-domain Routing (CIDR) • Specifies length of bit mask • Example 192.168.2.10/23 • C0A8020A + FFFFFE00 = C0A80100 • Range is 192.168.1.0 – 192.168.2.255 • First and last addresses in subnet are reserved

  29. Switch 2 Switch 3 R5 R4 R8 R1 R3 R6 Switch 1 R9 R2 R7 Switch 4 Network Infrastructure

  30. IP Fragmentation • Routers may break packets into smaller chunks (fragmentation) • Destination host is responsible for reassembling all fragments into original packet • Performance impact on modern (ASIC based) routers

  31. IP Don’t Fragment • Flag in header to indicate that packet should be discarded instead of fragmented • Basis for Path MTU Discovery protocol • Find the largest packet that can transit the entire end-to-end path • Router may return an ICMP error message when it discards the packet • PMTU black holes can occur

  32. TCP Protocol • TCP provides connection orientated delivery service • Reliable Delivery • In-order guarantee • Loss detection and recovery • Flow control • Error detection • Hides network details from applications

  33. TCP Header • Fixed size header field (20 Bytes), Variable length options 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Source Port | Destination Port | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Sequence Number | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Acknowledgment Number | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Data | |C|E|U|A|P|R|S|F| | | Offset|Reserve|W|C|R|C|S|S|Y|I| Window | | | |R|E|G|K|H|T|N|N| | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Checksum | Urgent Pointer | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Options | Padding | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

  34. TCP Connection Setup • Host in “Listen” state does passive open • Host in “Connect” state does active open • Hosts complete a 3-way handshake to complete open (move to “Established” state • Full Duplex connection established, hosts can transfer data in either direction

  35. TCP Flow Control • Original design relied on TCP Window size to control number of packets entering the network • Real world experience showed that network could experience congestion collapse and new mechanisms were needed • Slow Start after connection is opened • Exponential Growth algorithm • Congestion Avoidance once loss is detected • Linear Growth algorithm

  36. TCP Reno • Most common version of TCP today • Loss based detection to switch from Slow Start to Congestion Avoidance flow control • Transmit and Receive windows to guarantee reliability

  37. TCP and RTT / Loss Speed = [C * Pkt Size]/[RTT * Sqrt(loss)] Uses standard Ethernet Size TCP segment (1480 bytes) Formula from Mathis et.al.

  38. TCP and Jumbo Frames • Speed = [C * Pkt Size]/[RTT * Sqrt(loss)] • Jumbo Frames are a non-standard Ethernet feature Use 1 E-6 loss rate Formula from Mathis et.al.

  39. TCP and BDP • TCP uses a sliding Window to maintain reliability • 16 bit header field for supports 64 KB max window size • Window Scale options increases this up to 1 GByte

  40. TCP modifications • Most changes to TCP’s Congestion Avoidance growth algorithm • Recognized that linear growth is not efficient for Fast Long-Distance Paths • Loss Based Detection • Reno • High Speed • BIC, Cubic • Delay Based Detection • Vegas • Fast

  41. TCP Bulk Transfer http://netflow.internet2.edu/weekly/20060501/#xputs

  42. TCP Behavior due to Loss Throughput Behavior Congestion Window Behavior Speed (Mbps) vs Time (msec) Cwnd (Bytes) vs Time (msec)

  43. UDP Protocol • UDP – User Datagram Protocol • Application must provide • Reliability • Flow Control • Useful for short messages • DNS • Real Time audio/video

  44. Domain Name System • DNS – Domain Name System • Translates Fully Qualified Domain Name (FQDN) into IP address • A Globally distributed database • Hierarchical naming structure • Supports both Authoritative and Caching servers • Requires a minimum of 2 packets and 1 RTT for each resolution

  45. Real-time Transport Protocol • RTP – Real-time Transport Protocol • Carries data with real-time properties • Used for Audio and Video streams • Header contains sequence number and timestamp to provide receiver with pkt info • RTCP – RTP Control Protocol • Carries control information about the stream from receiver back to sender

  46. Unicast vs Multicast • Unicast packets - 1 source & 1 destination • Multicast packets • IP addresses (224.0.0.0 – 239.255.255.255) • Single source, multiple receivers • Multiple sources, multiple receivers • Routers and Switches must support multicast to prevent unwanted packets from flooding the network • Multiple unicast streams can be used to emulate a multicast session

  47. Multicast Traffic • Source starts sending packets using a multicast IP address • Local router/switch uses control messages to advertise traffics availability • Receivers send request-to-join messages • New path from receiver to “merge point” is created and traffic flow begins

  48. Conclusions • Global packet switching began with the ARPAnet • TCP/IP packet switching is the defacto standard for today’s networks • Smart hosts, dumb infrastructure • New and existing applications support end-to-end communications between people

  49. TCP Behavior due to Loss

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