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

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

3. 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. 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. 5 The Original Arpanet

6. 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. 7 Federal Agencies get in the Act ARPA - ARPAnet DOE – MFENet and HEPNet created NASA – SPAN created NSF – CSNet created

8. 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 purchased computers must be GOSIP compliant 1995 – GOSIP requirement rescinded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. 9 7 Layer Reference Model Physical Data Link Network Transport Session Presentation Application L1 L2 L3 L4 L5 L6 L7

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

11. 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. 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. 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. 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. 15 Layer 5 – Session Layer Control sessions between computers Establish, maintain, terminate connections Duplex operation (full or half) Checkpointing and restart procedures

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

17. 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. 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. 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. 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. 21 TCP/IP Architecture Copper, Fiber, Radio Ethernet, Sonet, ATM IP TCP, UDP Network Based Applications L1 L2 L3 L4

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

23. 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. 24 Architecture Comparison Physical Data Link Network Transport Session Presentation Application L1 L2 L3 L4 L5 L6 L7 Copper, Fiber, Radio Ethernet, Sonet, ATM IP TCP, UDP Network Based Applications

25. 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. 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. 27 IP Address 32 bit unsigned number Network portionused for global routing Host portionused to identify specific host Usually expressed in “dot quad” format 192.168.1.1specifics specific host 192.168.1.0/24specifies subnet of hosts

28. 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. 29 Network Infrastructure Switch 1 Switch 2 Switch 3 R1 R3 R4 R2 R7 R6 R9 R8 R5 Switch 4

30. 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. 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. 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. 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. 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. 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. 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. 37 TCP and RTT / Loss Speed = [C * Pkt Size]/[RTT * Sqrt(loss)] DistanceRTT (msec) LossSpeed (Mbps) LAN11 E-882,880.0 Metro81 E-810,360.0 Transcontinental701 E-81,184.0 Transcontinental701 E-33.7 Global5001 E-616.6 Uses standard Ethernet Size TCP segment (1480 bytes) Formula from Mathis et.al.

38. 38 TCP and Jumbo Frames Speed = [C * Pkt Size]/[RTT * Sqrt(loss)] Jumbo Frames are a non-standard Ethernet feature DistanceRTT (msec) Pkt Size (Bytes) Speed (Mbps) Transcontinental701500120.0 Transcontinental709000720.0 Use 1 E-6 loss rate Formula from Mathis et.al.

39. 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 DistanceRTT (msec) Window (Bytes) Speed (Mbps) LAN164K524.3 Metro864K65.5 Transcontinental7064K7.5 Transcontinental708M958.7 Global500256K4.2

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

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

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

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

44. 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. 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. 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. 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. 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. 49

50. 50 TCP Behavior due to Loss

51. 51 TCP Throughput with Loss