ISO Layer and TCP Fundamentals Rich Carlson Internet2 eVLBI workshop – TCP Fundamentals September...

ISO Layer and TCPFundamentals

Rich CarlsonInternet2

eVLBI workshop – TCP FundamentalsSeptember 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

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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computers must be GOSIP compliant• 1995 – GOSIP requirement rescinded

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7 Layer Reference Model

Physical

Data Link

Network

Transport

Session

Presentation

Application

L1

L2

L3

L4

L5

L6

L7

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Host – to – Host Communications

Physical

Data Link

Network

Transport

Session

Presentation

Application

Physical

Data Link

Network

Transport

Session

Presentation

Application

Ethernet WiFi

Physical

Network

Data Link

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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

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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

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Layer 3 – Network Layer

• Functions and procedures needed to transmit data throughout a global network• Routing functions• Segmentation / reassembly• Global addressing

• Example:• IP addresses

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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

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Layer 5 – Session Layer

• Control sessions between computers• Establish, maintain, terminate connections• Duplex operation (full or half)• Checkpointing and restart procedures

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Layer 6 – Presentation Layer

• Transforms data to/from a common format• Encoding• Compression• Encryption

• Examples:• MIME, XML

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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

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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

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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

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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

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TCP/IP Architecture

Copper, Fiber, Radio

Ethernet, Sonet, ATM

IP

TCP, UDP

Network

Based

Applications

L1

L2

L3

L4

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TCP/IP Architecture



IP

TCP, UDP

Network

Based

Applications

L1

L2

L3

L4

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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

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Architecture Comparison

Physical

Data Link

Network

Transport

Session

Presentation

Application

L1

L2

L3

L4

L5

L6

L7



IP

TCP, UDP

Network

Based

Applications

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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

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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

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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

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Network InfrastructureS

witc

h 1

Switch 2 Switch 3

R1

R3

R4

R2R7

R6R9

R8R5

Switch 4

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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

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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

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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

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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 |+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

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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

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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

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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

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TCP and RTT / Loss

Speed = [C * Pkt Size]/[RTT * Sqrt(loss)]

Distance RTT (msec)

Loss Speed (Mbps)

LAN 1 1 E-8 82,880.0

Metro 8 1 E-8 10,360.0

Transcontinental 70 1 E-8 1,184.0

Transcontinental 70 1 E-3 3.7

Global 500 1 E-6 16.6Uses standard Ethernet Size TCP segment (1480 bytes)

Formula from Mathis et.al.

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TCP and Jumbo Frames

•Speed = [C * Pkt Size]/[RTT * Sqrt(loss)]•Jumbo Frames are a non-standard Ethernet feature

Distance RTT (msec)

Pkt Size (Bytes)

Speed (Mbps)

Transcontinental 70 1500 120.0

Transcontinental 70 9000 720.0

Use 1 E-6 loss rate

Formula from Mathis et.al.

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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

Distance RTT (msec)

Window (Bytes)

Speed (Mbps)

LAN 1 64K 524.3

Metro 8 64K 65.5

Transcontinental 70 64K 7.5

Transcontinental 70 8M 958.7

Global 500 256K 4.2

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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

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TCP Bulk Transfer

http://netflow.internet2.edu/weekly/20060501/#xputs

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TCP Behavior due to Loss

Congestion Window Behavior Throughput Behavior

Cwnd (Bytes) vs Time (msec) Speed (Mbps) vs Time (msec)

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UDP Protocol

• UDP – User Datagram Protocol• Application must provide

• Reliability• Flow Control

• Useful for short messages• DNS• Real Time audio/video

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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

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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

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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

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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

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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

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TCP Behavior due to Loss

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TCP Throughput with Loss

ISO Layer and TCP Fundamentals Rich Carlson Internet2 eVLBI workshop – TCP Fundamentals September...

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