NTIA-REPORT-78-3

ARPAN ET Host to Host Access

and Disengagement Measurements

J.A. Payne

u.s. DEPARTMENT OF COMMERCE

Juanita M. Kreps, Secretary

Henry Geller, Assistant Secretary -Designate

for Communications and Information

May 1978

TABLE OF CONTENTS

LIST OF FIGURES

LIST OF TABLES

GLOSSARY AND ACRONYMS

ABSTRACT

1. INTRODUCTION

2. ARPANET .DESCRIPTION

2.1. Protocols

2.2. Architecture

3. NTIA/ITS HOST DESCRIPTION

4. ACCESS AND DISENGAGEMENT PARAMETERS FROM PROPOSED

STANDARD 1033

5. EXPERIMENT DESIGN FOR ACCESS AND DISENGAGEMENT

PARAMETERS

5.1. Network Events

5.2. Telnet Protocols

5.3. Design of Access Time Measurements

5.4. Design of Disengagement Time Measurements

5.5. Sample Size

6 • MEASUREMENT RESULTS

7. ANALYSIS OF RESULTS

7.1. Access and Disengagement

7.2. Associate Parameters

8. SUMMARY AND CONCLUSIONS

9. RECOMMENDATIONS

10. ACKNOWLEDGMENTS

11. REFERENCES

APPENDIX. MEASUREMENT TABLES

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LIST OF FIGURES

Page.

Figure 1.

Figure 2.

Figure 3.

Figure 4.-

Figure 5.

Figure 6.

Figure 7.

Figure 8.

Figure 9.

ARPANET geographic map from the ARPANET 1977

directory.

ARPANET logical map from the ARPANET 1977

directory.

Conceptual design of the ARPANET.

Sketch of the NTIA/ITS Host connection to the

DOCB TIP.

Illustration of access and disengagement phases

which are measured by the parameters, access,

and disengagement time.

Host-to-Host connection via telnet protocol.

Flow diagram for measuring Host-to-Host access

time via telnet protocol.

Flow diagram for measuring Host-to-Host disengagement time via telnet protocol.

Frequency histogram for "access time between

NTIA/ITS Host and the Rutgers Host; each class

interval represents 65 milliseconds of time.

iv

4

6

9

12

15

19

21

24

27
32

LIST OF TABLES

Page

Table 1. Measurement Values for Connection-Attempt Time

and Close-Attempt Time in Milliseconds Averaged

from Tables A.l Through A.IO 31

Table 2. Measurement Values for Access Time and Disengagement Time Values (in seconds) Derived

fro~ Table 1

Table A.l. Sample Values from Measurements on

August 23, 1977

Table A.2". Sample Values from Measurements on

August 29, 1977

Table A.3. Sample Values from Measurements on

September 2 , 1977

Table A.4. Sample Values from Measurements on

September 6, 1977

Table A.5. Sample Values from Measurements on

September 7, 1977

Table A. 6. Sample Values from Measurements on

September 9, 1977

Table A.7. Sample Values from Measurements on

September 14, 1977

Table A. 8. Sample Values from Measurements on

September 15, 1977

Table A.9. Sample Values from Measurements on

September 20, 1977

Table A.IO. Sample Values from Measurements on

September 21, 1977

46

47

48

49

50

51

52

53

54

55

v
ARPA

Avg

BSC

CR

DEC

DOCB

Elf

EXEC

FTSC

Host

IMP

MHR

modem

NCC

NCP

NTIA/ITS

protocol

Telnet

TIP

VDH

GLOSSARY AND ACRONYMS

Advanced Research Projects Agency

Average of hourly data

Binary synchronous line control pro~ocol

Carriage return

Digital Equipment Corporation

Department of Cormnerce Boulder

Name of PDP-II operating system software

Executive software system

Federal Telecommunications Standards Committee

Computer center

Interface message processor

Minimal hop route

Modulator and demodulator

Network control center

Network control program

National Telecommunications and Information Administration/ Institute for Telecommunication Sciences

In communications, a set of rules governing the

exchange of information

Telnet software system

Terminal interface processor

Very distant Host

vi
ARPANET HOST TO HOST ACCESS AND DISENGAGEMENT MEASUREMENTS

Judd A. Payne*

A set of telecommunications performance parameters

have been developed for proposed Federal Standard 1033.

The measurement of five of these parameters, access time,

incorrect access time, access denial probability, disengagement time and disengagement failure probability

are the subject of this report. The telnet protocol

of the ARPANET is employed to measure the access and

disengagement parameters from a Host to Host connection.

Key words: access, ARPANET, disengagement, Elf operating

system, Host, IMP (interface message processor) ,

NCP (network control program), performance

parameter, protocol, Telnet, TIP (terminal

interface processor)

1. INTRODUCTION

The National Telecommunications and Information Administration, Institute for Telecommunication Sciences (NTIA/ITS) is

engaged in the development of proposed Federal Standard 1033.

This proposed Standard was published in the Federal Register

(1977). The development of the standard was authorized by the

Federal Telecommunication Standards Committee (FTSC). The

purpose of the Standard is to develop digital communication

performance parameters for telecommunication systems from a useroriented approach. As revealed by McManamon et ale (1975), a

sampling of commercial and Federal standards. generated a list of

132 engineering-oriented performance parameters for telecommunication systems. The purpose of proposed Standard 10~3 is to

standardize the description of the performance of telecommunication systems, and to present a set of considerably fewer performance parameters which would enable a user to better understand

the performance of a telecommunication system.

*The author is with the Institute for Telecommunication Sciences,

National Telecommunications and Information Administration,

U.S. Department of Commerce, Boulder, Colorado 80303.
In order to demonstrate the usefulness of the proposed parameters in Federal Standard (FS) 1033 an ARPANET measurement

program was established at ITS. Along with the measurement

program, theoretical studies in support of the proposed standard

have been reported (in papers scheduled for future publication)

by Seitz and McManamon and Kimmett and Seitz.

This report is a sequel to two previous memorandums by Payne

entitled "Access Time Measurements of the ARPA Network" (aT Tech.

Memo. 76-229, 1976) and "Host to Host Disengagement Time on the

ARPANET" (aT Tech. Memo 77-237 (1977). (These reports are available from u.S. Dept. of Commerce, Boulder, CO 80303.) These

previous reports were concerned with the measurements of access

time and disengagement time which are two of the proposed performance parameters in Standard 1033. This report concerns further

measures of access time, disengagement time and initial measures

for incorrect access time, access denial probability and disengagement failure probability.

The measurement of each of the proposed parameters required

designing the experiment, developing the needed hardware and

software, conducting tests and analyz'ing the results.

The contents of the following sections include an ARPANET

description, a description of the NTIA/ITS Host1 , a definition of

measurement parameters, a description of the design and. method of

making the ARPANET measurements, tables of measurement data,

and a discussion of the results of the measurement data..

This report concludes with an assessment of the utility of

the 'proposed performance parameters as applied to· the ARPANET

and some recommendations for further study.

2. ARPANET DESCRIPTION

The ARPANET has been described and studied by many persons

(e.g., Schwartz, 1977; Kleinrock, 1976; Davies and Barber, 1973).

IThe designation "NTIA/ITS Host" is new. The organization name

change to NTIA is recent and all previous literature refers to the

same Host as the "aT/ITS Host." 2
3

Because of the ARPANET's overall success, many computer networks

now or in the future plan to emulate the ARPANET (e.g., TELENET,

AUTODIN II).

This description of the ARPANET will briefly review only

those details necessary for the reader to understand the design

of the experiments discussed in the main body of this report.

The word "ARPANET" refers to the Advanced Research Projects

Agency (ARPA) computer network, which is operated by the u.s.

Defense Communications Agency. In textbooks, the ARPANET's topology is described as a packet-switched, fully distributed computer

network. The ARPANET was proposed by L.G. Roberts (1967).

Figure 1 illustrates the ARPANET geographic map as it

existed in June 1977 (ARPANET Directory, 1977). This,map shows

the interconnected nodes of the ARPANET. The circles represent

an enlarged version of those areas of the u.s. where many nodes

are concentrated in some small geographic area. These nodes

contain mini-computers which, along with their interconnecting

links, form the communications "backbone" of the ARPANET. This

communications backbone or subnet is "described as a "packetswitched" subnet. A packet-switched network is designed to carry

data in the form of packets. A channel is occupied only for the

duration of the packet transmission.

In addition to the subnet, the ARPANET includes a number of

independent computer systems called "Hosts". Each Host is

connected to just one node. The Hosts may vary from a large

computer center to a small (mini-computer) system. Examples of

large systems attached to the networks are Control Data Corporation's model 6600 and 7600 systems 2, IBM's large scale model 360

and 370 systems, Digital Equipment Corporation's PDP-IO and many

others. Arnongthe mini-computer Host systems, the PDP-II is

employed most often because of its available communications

2Certain commercial equipment, instruments, or materials are

identified in this paper to adequately specify the experimental

procedure. In no case does such identification imply recommendation or endorsement by NTIA, .nordoes it imply that the material

or equipment identified is necessarily the best available for the

purpose.
ARPANET GEOGRAPHIC MAP, JUNE 1977

LINCOLN

~IT~"MIT6

RA~ CCA\

RCC5I

RCC49

BBN40

BBN 30

HARVARD

SATELLITE CIRCUIT

o IMP

o TIP

6 PLURIBUS IMP

(NOTE: THIS MAP DOES NOT SHOW ARPA'S EXPERIMENTAL

SATELLITE CONNECTIONS)

NAMES SHOWN ARE IMP NAMES, NOT (NECESSARILY) HOST NAMES

Figure 1. ARPANET geographic map from the ARPANET 1977 directory.
software and hardware interface devices. As of June 1977 the

ARPANET network was composed of 57 nodes and 113 Host systems.

Figure 2 is the ARPANET logical map as shown in the ARPANET 1977

Directory. This map identifies all the Host computers on the

ARPANET and their nodal connections.

The network logical map of Figure 2 is called a logical map

because the message paths between the Hosts are not physical connections, such as a telephone connection between calling parties.

Physical connections exist between nodes (IMPs and TIPs) and between the nodes and attached Hosts. But a connection between two

Hosts is called a logical connection and it is established by a

message sequence protocol. After a connection has been opened between two Hosts, data messages between the two Hosts flow through

the subnet by packet-switched, store-and-forward techniques.

The communication subnet, composed of nodes, provides the

packet-switch capability for the ARPANET. The nodes are Honeywell

mini-computers and they are interconnected by 50 kilobit per

second (kb/s), full-duplex lines. These lines connect each node

to one or more adjacent nodes so the network is considered to be

fully distributed. The nodes are called Interface Message

Processors (IMPs), pluribus IMPs, or Terminal Interface (Message)

Processors (TIPs) depending on their function. As many as four

Host computers can be attached to each IMP, and more than four

can be attached to a pluribus IMP. The primary function of the

IMP is to accept messages from the attached Hosts, to separate

the message into 1000 bit packets, and to route these messages

through the subnet backbone until the messages reach their destination Hosts. TIPs perform the same function as IMPs but also

permit terminal devices such as teletypes and CRTs to be attached

directly to the TIP. All messages flow through the subnet in the

form of packets of data that are switched from node to node.

As of June 1977, 54 of the 113 Host systems were designated

as server Hosts, which means that these particular Hosts will

accept and respond to messages from any other Host on the/network

(i.e., some Hosts provide limited service). The remaining 59

5
ARPANET LOGICAL MAP, JUNE 1977

LONDON

OEC-2050T

PLURIBUS

BELVOIRi-C~0'"'C"'7"'6"0"0'""' COC6600

COC6400

ICL 4/72 GEC40BO

360/195

POP-9

SOAC NORSAR

POP-Il

MITRE

DEC 20/40

POP-10

POP-Il

SPS-41

POP-6

o IMP

o TIP

D. PLURIBUS IMP

/IlIA SATELLITE CIRCUIT

PLEASE NOTE THAT WHILE THIS MAP SHOWS THE HOST POPULATION

OF THE NETWORK ACCORDING TO THE BEST INFORMATION

OBTAINABLE, NO CLAIM CAN BE MADE FOR 'TS ACCURACY

:;.,';,t~~2~,6~TgNW~F1GURATION SUPPLIED BY THE NETWORK

NAMES SHOWN ARE IMP NAMES. NOT I NECESSARILY) HOST NAMES

Figure 2. ARPANET logical map from the ARPANET 1977 directory.
Hosts are known as user Hosts, and normally they can only communicate with other server Hosts although there are some exceptions.

2.1. Protocols

The process which ena~les incompatible or different types of

Host computers to exchange messages involves a number of layers

or levels of communication protocol (ARPANET Protocol Handbook,

1978) .

These layers of protocol are separated into three levels by

Kleinrock et ale (1976):

(1) Level-O, the protocol which controls the transmission

of packets between adjacent nodes (IMPs and TIPS)3.

(2) Level-I, the protocol which controls the transmission

of messages between source node and destination node.

(3) Level-2, the protocol which controls the transmission

of messages between source Host and destination Host.

In addition to these three basic levels of protocol, there

are higher levels of protocol which are intended for user applications of the ARPANET. All higher level protocols use the

above three protocols. Examples of higher level protocols are:

(1) Telnet - primarily used to allow a human user at

-some Host site to establish a logical connection with

another server Host system and to operate the server

Host in a time-sharing mode.

(2) File Transfer Protocol - allows a user to transfer

files of data between two Host systems.

(3) Remote Job Entry - allows a user at some Host system

to run a batch job on some other server Host system.

The process which allows a specific program in some Host to

communicate with a specific program in another Host is the Network Control Program (NCP) which is the level-2 protocol. The

NCP software is resident in each Host and provides the means of

communication between programs. For example, if a program or

3Although Kleinrock does not distinguish it, there is a Host-IMP/

IMP-Host protocol, Bolt Beranek and Newman (1976).

7
process in the NTIA/ITS Host desires to communicate with another

process in a foreign or distant Host, it does so by calling the

NCP in the NTI~/ITS Host and this NCP then communicates with the

NCP in the foreign Host to establish a logical connection between

the two processes. The NCP acts as the manager for a network

user in arranging and maintaining connections to other Hosts in

the network.

2.2. Architecture

Figure 3, which was obtained from the ARPANET Transition

Plan (1975) and slightly modified, is a conceptual diagram of the

architecture of the ARPANET. This diagram illustrates at least

one approach to defining the architecture of this network. In

this diagram the network is subdivided into three parts: the

communications subnet, the Host computer subnet and the user

subnet. These three subnets are identified in Figure 3 by a

solid line, a dashed line, and a user symbol, respectively.

The communications subnet is composed of the nodes (IMPs and

TIPs) of the network, the Network Control Center (NCC) and the 50

kb/s lines (solid lines) connecting the nodes and the NCC to each

other. The Host subnet consists of the Host computer system and

the communication line connecting the Host to the node. The user

subnet consists of a person, the terminal and the line connecting

the terminal device to the Host computer. In this figure the

user is understood to be a person sending commands to the Host

via a terminal device. The function of the user subnet is to

initiate hardware and software components in the Host subnet

which actually cause the communication subnet to transmit the

data across the network. This three-part separation of the

ARPANET into communications, Hosts, and users subnets;is based on

hardware boundaries or physical objects that can be easily

identified. The boundary separating the communications subnet

from the Host subnet is a special IMP/HOST interface attached to

the IMP, which connects the line from the Host to the IMP. The

boundary between the user subnet and the Host subnet is usually a

8
KEY D-- Communications Subnet

,--,

I :-- - Host Computer Subnet L. __ ..J

o User Subnet

I

,..--, /

lr

_..rOOST" ./ -- L __J

ABBREVIATIONS

IMP: Interface Message Processor

TIP: Terminal Interface Message Processor

NCC: Network Control Center

HOST: Host Computer

Figure 3. Conceptual design of the ARPANET.
serial line interface connecting the line from the terminal to

the Host computer system.

Another approach to defining the network architecture of

the ARPANET is to divide the network into just two parts, a use:r;

system and a communication system. This concept of a user system

is based on the idea that the Host computer subnet and the user

subnet combine actually to perform the task of using the communication subnet. The process of using the communication system

implies that the user system contains the necess~ry hardware and

software components to activate the communication system which

sends data across the network to another ~ser system. The

boundary between the user system and'the communication system

could be the same as the three-part architecture boundary between

Host and communication subnets. Or the boundary might be one of

the three breaks as shown near the user system circle in Figure

3, depending on the particular hardware and software configuration of the user system.

The boundary of interface separating the user system from

the communication system is defined by the PDP-II operating

system known as Elf. A PDP-II operating system is defined in the

DEC software manual as a collection of programs that organize a

set of hardware devices into a working unit such that people can

utilize the computer system.

Elf provides the means for the terminal user to establish

connections and to send messages over the ARPANET. Elf is

described by Retz et ale (1976) as composed of the following

software modules:

(1) kernel,

(2) executive,

(3) network control program (NCP).

The Elf kernel software acts as the primary interface between

system hardware and a program running on the PDP-II. The Elf

executive software acts as the primary interface between system

hardware and persons who operate the system. The NCP software

in each Host serves as the interface between two programs or two

10
processes in separate Hosts. The Telnet software (see Protocol

2.1) serves as a high-level protocol utilizing software which can

establish a connection between two Host systems. Telnet employs

the NCP software via system calls during Host-to-Host communications.

In general, PDP-II operating systems are separated into just

two components: monitor and utility programs. The functions

performed by a PDP-II monitor could include all the functions

performed by the Elf ~ernel and executive. The NCP could be

considered a utility program in that its main function is to

establish and maintain a logical connection between programs or

processes in separate Hosts. In th~s report the NCP is

considered the functional interface or boundary between the user

system and communication system while opening and closing connections between Hosts under Telnet control.

3. NTIA/ITS HOST DESCRIPTION

The NTIA/ITS PDP-II Host mini-computer system (aT Host) was

installed on the ARPANET in March 1975. This Host site is

located in Boulder, Colorado, and is attached to the DOCB (Department of Commerce Boulder) TIP. The DOCB TIP is shown in Figure

2, near the center of the figure interconnecting the University

of Southern California (USC) TIP and the Global Weather Central

(GWC) TIP. The NTIA Host is shown attached to the DQCB TIP.

Figure 4 is a sketch of the NTIA Host connection to the DOCB

TIP. All the necessary hardware and software components required

by the system were obtaineq from known sources of these

components. A PDP-II computer was chosen because an ARPANET

operating system had previously been developed for the PDP-II.

This operating system (OS), known as the Elf as was developed

with ARPA funds. (Currently, Elf is being replaced by the Unix

operating system.) In Figure 4 the connection between the PDP-II

and TIP is called a VDH (very distant Host) connection. The VDH

connection is one of three standard connections used on the

11
TIP SYSTEM NTIA / ITS HOST SYSTEM

,----------------, ,-------------,

I I I

I HONEYWELL 316 I I

I BELL MINICOMPUTER I I 303

I MO DEM (0 node of the I I

I ARPA network) TIP I I

I DOCS (Department of INTERFACE I I

I 30~L Commerce Boulder) (special ~~~L I I

I MODEM TIP (Terminal Inter- interface) MODEM I_~~~i~o~~~i~:' I

I face Messa eProcessor) ,- VDH-c~;;cti~; I ~om456~adio~lding ~~21~dioBui'ding

50 'kilobit lines interconnecting

other nodes on the network

Figure 4. Sketch of the NTIA/ITS Host connection to the DOCB TIP.
network between an IMP or TIP and a Host. The VDH connection

provides error detection and retransmission between the Host and

TIP. A VDH connection is implemented by means of the following

components:

(1) a special interface at each end of the connection;

(2) a special software package in the TIP and Host; and

(3) a 50 kb/s full duplex line connecting the two '

special interfaces.

The two special interfaces are attached directly to the TIP

mini-computer and the PDP-II mini-computer, and these interfaces

provide the hardware which generates the synchronization and"

control characters for the binary synchronous line control (BSC)

protocol. In each mini-computer a special software package is

resident to implement the error detection and retransmission

process for the VDH connection. Each interface plugs directly

into a Bell 303 modem at each end of the connection. The Bell

303 modems are connected by means of two twisted pairs of

shielded cable. The cable extends a distance of almost 1800

feet, within the Radio Building at DOCB.

The 50 kb/s lines which connect the DOCB TIP with adjacent

nodes of the subnet are shown in Figure 4, located on the left

side of the TIP system.

The Elf operating system permits several persons at

terminal devices connected to the NTIA Host to use the network

simultaneously. The network control program (NCP) within Elf

will support simultaneously a number of independent connections

or conversations, each involving a program in the NTIA-Host and

another program in any Host on the network.

4. ACCESS AND DISENGAGEMENT PARAMETERS FROM

PROPOSED STANDARD 1033

This section presents the definitions for the access and

disengagement parameters from proposed Federal Standard 1033.

13
Access time is the average value of elapsed time between the

start of an access attempt and successful access. Unsuccessful

access attempts are not included in the average. The access

phase is the interval of time over which access time is measured.

Successful access or the end of access phase is accomplished when

the first byte (8 bits) of user information is moved by the user

system into the communication system toward some destination

Host, after a connection has been established. In Section 2, the

NCP was identified as the interface between the user system and

the communication system. The access phase is completed when the

first byte of user information passes through the Elf's NCP

(i.e., point B in Fig. 5).

Related to access time are the two parameters incorrect

access probability and access denial probability. Incorrect

access probability is defined as the ratio of access attempts

which result in incorrect access (i.e.; a connection to the wrong

destination Host on the ARPANET), to total access attempts

counted during a measurement period. Access denial probability

is defined as the ratio of access attempts which result in

access denial (system blocking) to total access attempts counted

during a measurement period.

Disengagement time is defined in proposed Federal Standard

1033 as the average value of elapsed time between the start of a

disengagement attempt and successful disengagement. Unsuccessful

disengagement attempts are not included in the average. Disengagement time measures the time span of the disengagement

phase. Disengagement failure probability is defined as the ratio

of disengagement attempts which result in disengagement failure

to total disengagement attempts counted during the measurement

period. The application of these parameters to the ARPANET will

be discussed in Section 5.

14
START

~-----TIME AXIS

END

-'~

I - - - - -l I USERlfR~fiNAlI

IIINfORMAT~g:~RANSfERI I AND OTHER I

COMPLETED I I TERMINALS INVOLVED I

L --.J L ~E~EARE~ --.J

\.. J \. J V y

USER INFORMATION-tDISENGAGEMENT-&

TRANSFER PHASE PHASE 1.

8 C 0

:- SYSTEM ACCESS I

I COMPLETED: I

I USER INfORMATION I

L TRANSfER-.!EGINS ---J

\.. V

r------i

I USER

IINFORMATION TRANSfER I

I NEED ORIGINATION I

L J

"-------y-_J

I-'

\JI t ACCESS . PHASE

A

Figure 5. Illustration of access and disengagement ~hases which a:e

measured by the parameters, access, and dl.sengagement tl.me

(after McManamon and Seitz, 1976).
5. EXPERIMENT DESIGN FOR ACCESS AND

DISENGAGEMENT PARAMETERS

The ARPANET computer network is both experimental and

operational. The ARPANET provides a test bed for experiments

such as the measurements related to proposed Federal" Standard

1033. The five proposed performance parameters, access time,

disengagement time, incorrect access time, access denial probability and disengagement failure probability are suited to

measurement on the ARPANET.

Proposed Standard 1033 was developed for users of Federal

telecommunication systems, where performance between end users

of systems is the measurement objective. For any telecommunication system, one must determine how to apply these performance

parameters to the given system. In the ARPANET case, the Telnet

protocol was selected as a convenient means to demonstrate the

application of the proposed performance parameters. Telnet was

chosen because most persons who,use the ARPANET employ the Telnet

protocol to establish and close connections between Hosts.

Figure 5 delimits the three phases that users of telecommunication systems perceive. Access phase is the interval of

time over which aCcess time is measured. Since the Standard

defines access time to include all of the access phase, one must

initiate a data transfer of user information as the last event to

end access phase. Point B of Figure 5 identifies the end of

access phase as the beginning of user information transfer. User

information is defined as non-overhead information provided by a

user or user system that is transferred into the communication

system. User information excludes all overhead information

generated by both high and low levels of ARPANET protocols. The

disengagement phase is the in~erval of time over which disengagement time is measured.

5.1. Network Events

As previously mentioned (Sec. 2) the ARPANET is a packetswitched, fully distributed computer network. Access time and

16
disengagement time are measures of the message transmission

delays that are built into the network. Access and disengagement

are accomplished by the sending and receiving of messages between

two Hosts on the ARPANET.

Some of the factors or events affecting access and disengagement time encompass the following ARPANET packet-switching

delays (Heart et al., 1970):

(1) Propagation time, the electrical propagation time in

the Bell system is estimated to be 30 ms for a coastto-coast connection.

(2) Modem transmission delay, the rate at which bits enter

and leave the modem (50 kb/s).

(3) Queueing delay, the time spent waiting in the IMP's

packet queue while the IMP processes other packets.

(4) IMP processing delay, the time required for the IMP to

process a single packet, estimated at 0.35 ms.

(5) Variable Traffic density, the amount of traffic in the

subnet affects queueing delays and routing.

(6) Variable routes, the routing algorithm resident in each

IMP or TIP can change routes between Hosts.

Flow control delays which affect message delay include:

(1) Flow control procedures between the Host and IMP (or

TIP) which reside in the communications subnet.

(2) The maximum number of messages which a Host is permitted

to have in transit on any connection is eight.

(3) IMPs which serve source and destination Hosts must

exchange control messages which allocate a limited

table space in memory for new connections between

Hosts. See Bolt Beranek and Newman (1976).

Finally, the Telnet server Hosts on the ARPANET are usually

serving local users and simultaneously responding to ARPANET

message traffic. This also introduces variable delay in Host-toHost message response.

17
5.2. Telnet Protocol

The ARPANET Telnet pro t.ocol, was chosen as the user application level protocol for measurement of the performance parameters. The Telnet protocol within the Elf operating system is

used to support user access to the ARPANET. Telnet allows a

person at a terminal connected to some ARPANET Host to access

(using a Telnet connect command) some other foreign Host as

though his terminal were attached to the foreign Host. After the

terminal user has completed his work on the foreign Host he then

issues a disengagement command, a Telnet close command.

Figure 6 is a simplified sketch of how the Elf operating

system software modules interface under the Telnet protocol.

Figure 6 shows the interaction between the NCP·s Telnet user and

server processes and other processes. Access between two ARPANET

Hosts under Telnet requires that the Telnet user process in some

Host call (via the NCP) a Telnet server process in another Host

and eventually establish with messages a full duplex connection

between the two Telnet processes. A socket is used to couple the

NCP to another process within the same Host,' such as a Telnet

process. Disengagement between two ARPANET Hosts under Telnet

requires that a user process hang-up (close) the previously

established connection to the server process. Sometimes the

server closes the connection for reasons of its own choosing.

The NTIA/ITS Host Telnet software was modified to measure

both access time and disengagement time. Elf system macros

(segments of code) were inserted in the Telnet "connect and

close" subroutine code to perform the time interval measurements

for access and disengagement.

5.3. Design of Access Time Measurements

For the ARPANET, access time can be measured as a performance variable. The access phase (Fig. 5) is the interval of

time over which access time is measured.

18
Terminal

User Host

Legend:D . - Software

Com munications

Subnet

Server Host

4 - Socket· Connects the NCP with Another Process

4- -... - ELF Software System Calls

Figure 6. Host-to-Host connection via telnet protocol.
Successful access as illustrated in Figure 5, occurs when

th~ first bit or byte of user information is: moved by the user

system into the communication system. In Section 2.2, the NCP

'was identified as the interface between the user system and

communication system. For this experiment the access phase was

completed when the first byte of user information passed through

the Elf's NCP.

Start of access attempt was chosen as when the CONNECT TO

ABC (CR) command was issued by the operator to Telnet (i.e., when

the first character c is typed from the terminal keyboard, see

Fig. 7). The time intervals to call the Telnet program and to

type the CONNECT TO command were measured and recorded manually.

The Elf telnet program was modified to measure the time period

from the carriage return (CR) following HOST's name to the

passage of the first byte of user information through the -Elf's

NCP. This time period is identified by variable time interval in

Figure 7. The program computed this time interval by time

stamping the above events using the time clock located in the VDH

interface. The time is then printed on the terminal printer in

milliseconds. All events within the variable time interval of

Figure 7 occurred under control of software procedures of the

Telnet user process. The Telnet connection process involves

sending and acknowledging several control messages between Hosts

rcp (initial connection protocol) (Postel, 1971).

The time interval to call the Telnet program is denoted by

TEL CR and a curved arrow in Figure 7. This time inter~al

was not included in the access time interval because once the

Telnet program is installed, a series of connections could be

conducted by the operator without calling Telnet again. One

might question why the connect command (CONNECT TO ABC) time

interval is included in access time, since this is not a function

carried out by the communication system. The answer is that this

operator action is part of the required Telnet connection

process. Access time is variable between any two Hosts because

20
I

~I

I

I User Information

Through the NCP

Connection

Completed

I

I'" ACCESS TIME------~

I

I

CONNECT TO ABC.)

N

.....

CALL

TELNET

4.5 Seconds

START

ACCESS

ATTEMPT

5.5 Seconds Variable Time Interval

A

CONNECTION

ATTEMPT

SUCCESSFUL

ACCESS

TIME

) =Carriage Return

Figure 7. Flow diagram for measuring Host-to-Host access time via

telnet protocol.
of the variable traffic load conditions, variable distances or

routes between Hosts, and variable program load at Host sites

(see Sec. 5.1).

The time interval printed on the PDP-ll terminal includes

both the connection process time, which ends at the point labeled

"connection completed" in Figure 7, and the.. time segment

required to transfer a byte of user information from meIr\0ry

through the Elf NCP, which begins as soon as the connection is

completed. These two time segments are referred to as connect

time and transfer time. Connect time is a variable and transfer

time may also be a variable when the local NTIA/ITS Host has more

than one user logged on the system because Elf is a multi-user

system. However, all measurements were conducted in the single

user, single process mode, and transfer time required about 2 ms.

Assuming that the Telnet process is functioning, the steps

performed to measure access time are as follows:

1. Operator types "CONNECT TO ABC (CR)", where ABC

represents some Host name,

2. Connection attempt begins; if successful, the connect

time plus transfer time are printed on terminal

printer.

In the tables of Appendix and later sections of this report, the

combination of connect time plus transfer time is referred to as

connection-attempt time.

The variable time interval in Figure 7 represents the time

required by the local Telnet software to open successfully a

Host-to-Host connection (connect time) and transfer user

information through NCP (transfer time). During this time

interval (connection-attempt time), the NTIA/ITS Host Elf Telnet

process al$o performs required software housekeeping arrangements.

In Figure 7, the 5.5 seconds needed to type the connect

command represents the operator's typing speed and is not

necessarily a typical value.

22
A

~.

2.

3.

5.4. Design of Disengagement Time Measurements

For the ARPANET, disengagement time can be measured as a

performance variable. The NTIA/ITS Host Telnet software was

modified to measure disengagement time. Disengagement time

measures the time span of the disengagement phase, Figure 5.

This time span as applied to the Telnet protocol is illustrated

in Figure 8.

After a terminal operator using Telnet has opened a connection to some distant ARPANET Host and has finished his interactions with programs in the server Host, then he must close or

disengage the Host-to-Host connection. The operator disengages

from the connection as follows:

1. He issues a CTRL (control) Y. This starts the disengagement attempt shown in Figure 8 which alerts the

Telnet user process in the user Host. The Elf Telnet

software inunediately sends a "prompt" character to

. the operator's terminal. This event is ~ot shown in

Figure 8. The operator's terminal is now connected to

the Telnet user process in the user Host.

The operator then types the letters CLO and carriage

return (CR). In Figure 8, the time to complete these

events is called conunand time. The average conunand

time was 3.3 seconds. The 3.3 seconds represents the

operator's typing speed and should not necessarily be

considered a typical value.

The user Telnet program then begins the process of

telling the Elf NCP to begin the closing process.

This is called "close-attempt time" in Figure 8.

After the connection has been successfully closed, a

"successful-disengagement" message is sent to the

terminal informing the operator that the connection is

closed; see Figure 8.

At this point disengagement is completed. The operator is now

free to open a connection to some other Host on the ARPANET, or

23
I

I

..-1

I

I

Disengagement Time-------__

I

I

I...

CTRL-Y CL~ Connection

Closed

Operator

Interactions

3.3 Seconds

Command Time

Start

Disengagement

Attempt

Variable Time Interval

Close Attempt

Time Successful

Disengagement

Time

) == Carriage Return

Figure 8. Flow diagram for measuring Host-to-Host disengagement time

via telnet protocol.
to call up some process within the user Host or to terminate his

use of the local system.

The variable time interval (close-attempt time) shown in

Figure 8 represents the time required by the user Telnet software

and the server Telnet software to complete the closing of a full

duplex connection between these two software modules. During

this time interval the user Host NCP and server Host NCP exchange

acknowledged close (CLS) commands through the network, and their

respective Telnet software performs housekeeping arrangements,

including a "connection closed" message to, the terminal operator.

This variable time interval was measured by modifying the NTIA/ITS

Telnet software so that it time-stamped the beginning and· end of

"close-attempt time". The difference between the beginning and

end times was calculated and printed on the operator's terminal.

Close-attempt time includes various housekeeping functions that

the Elf Telnet is required to perform and the exchange of two

acknowledged close commands through the network. This time

interval is variable because of the events defined previously in

Section 5.1.

5.5. Sample Size

In Section 4 the definitions of access and disengagement

time specify that these parameters are averages.

From Section 5.1, one observes the various delays present

in the ARPANET which cause these parameters to vary in a random

fashion. The following network events occur during each access

and disengagement attempt: propagation time delay, modem transmission delay, IMP or TIP processing delay for each pa6ket,

variable traffic density in the subnet, variable routes for each

packet assigned by the routing algorithm resident in each IMP or

TIP, and flow-control delays and variable response times by Host

computers in message handling or processing. Most of these

network events are ,independent of each other and this introduces

randomness or variability into access and disengagement times.

25
In addition, each successful access and disengagement

'attempt implies that the above network events were repeated

several times, because successful access and disengagement

requires the exchange of several messages between source and

destination Hosts. Access attempts employ the rep (initial

connection protocol) which involves four or more messages and

their acknowledgments (Acks). Disengagement attempts employ two

messages and their Acks. Therefore, one would expect that

measurements of access and disengagement times would be variable

and that these times should be described with probability relations and statistical averages rather than with deterministic

methods or mathematical equations.

The histogram in Figure 9 was plotted to study to what

extent the above events introduce randomness in measures of

access and disengagement time. The histogram includes the

measurement results of 200 successful access attempts distributed

over an 8-hour interval (8 a.m. to 4 p.m. MDT on June 5, 1976)

from the NTIA/ITS Host to Rutgers-10 Host. These 200 sample

values were placed in ascending order and grouped in 16 equal

class intervals of 65 milliseconds each. All measurement values

were rounded off to the nearest millisecond by the measurement

software. The Y axis displays the frequency count for each class

interval and the X axis displays the equal class intervals of 65

milliseconds. The sample values ranged from 6.479 seconds to

7.513 seconds, with one value in the 27th class interval at 8.229

seconds. The frequency count for each class interval was plotted

in Figure 9. The first class interval represents the time \

interval from 6.450 to 6.515 seconds. The peak and the shape of

the histogram suggests normal or Gaussian distribution properties.

From the above discussion concerning the sum of independent,

variable delay events (Central Limit Theorem), one can assume

that access and disengagement times are normally distributed.

With this assumption of normality, the Student t (Bendat

and Piersal, 1966) distribution was used to establish confidence

26
30

25 ••••••••••••

20

To

C

='

0

U

>.

u 15

N C

---.J (l)

='

C"

(l)

1.L 10

5

o

Figure 9.

Class Inte rva Is

Frequency histogram for access ~1me

NTIA/ITS Host and the Rutgers Host;

interval represents 65 milliseconds

between

each class

of time.
intervals which relate to sample size for access and disengagement time measurements.

The arithmetic mean was chosen as the estimator for the true

mean value of these parameters. The arithmetic mean x for sample

N

size N from a random variable x(i) is x= L x(i)/N. For a given

i=l

sample of access or disengagement t~mes between two ARPANET

Hosts, the problem is to determine the sample size N within some

confidence interval.

For the case of a normally distributed random variable with

unknown true mean ~x and unknown true variance 0

x

2 , the Student

t random variable is

t = M(x-0 lis, n=N-l, (1) n x

x is the sample mean and s2 is the sample variance. Here t has

n

a Student t distribution with n=N-I degrees of freedom. To

obtain a confidence interval from the Student t distribution, the

following probability statement applies

prob Tt 1 /2 < (X-ll) IN/s < t -J = I-a, (2) L ni -a x nia/2 '

where t is the value of t at some ·percentage a of the Student niCX

t distribution. A confidence interval can be established for the

true mean value ~- from equation (2). x

[x - (stn i a/2) / IN < ~x -e x + (stn i a/2) / IN] (3)

This equation uses the fact tnil-a/2=-tn;a/2. Equation (3)

utilizes the Student t distribution to obtain a relationship

between the sample size N and a confidence interval about

x

based upon some value of cx. The confidence coefficient associated

with the above interval is I-a.

For example, actual measurement data in milliseconds for

connection-attempt time (Fig. 7) recorded at 0900 at DoCB from

August 24, 1977 to September 17, 1977 between NTIA!ITS Host and the

CMU-I0A (Carnegie-Mellon University) Host are 1998, 2288, 2146,

1954,2518,1857,2123,2211,2244,2092,

x = 21431/10 : 2143.

28
and

The sample variance of this set of data is

2 N - 2

s = l/(N-l) I (X.-x)

i=l 1

s 'V 182 ms.

From the Student t distribution for a=0.05 and N=lO, t /2 nia

becomes t9:0.025=2.26. Substituting_ in equation (3)

12143 - (182x2.26)/3.16 < ~x < ~143 + (182x2.26)/3.16]

becomes [2013 ~x < 2273]. (4)

Equation (4) says that the true mean value 11 falls within

x

the .interval of 2013-2273 milliseconds or 260 milliseconds with

a confidence coefficient of (I-a) xlOO or 9,5%. The confidence coefficient is the degree of trust associated with the confidence

s tra t.ement; of equation (4).

At this point one can only say th~t for a sample size N=lO,

one gets a 95% confidence interval of 260 milliseconds about the

true mean 11 , assuming normally distributed,data. A similar set

x

of measurement data from the NTIAiITS Host to eMU-lOA Host for

close-attempt times in milliseconds included in disengagement

time, are: 1773, 1623, 1536, 1800, 1676, 1717, 1636, 1512, 1498,

1633.

x 1641 milliseconds (ms),

s=3l4 m£lliseconds and from equations (3) and (4) with a=0~05

and N=lO, 11 falls within the interval of 1416-1866 ms with a

x

confidence interval of 450 ms long. These two tests do not

include the values for command time since these values are

constants the confidence intervals are not affected for either

access or disengagement times. Similar confidence intervals were

measured for sample size N=lO and a=0.05 for data recorded

between NTIA/ITS and Harv-lO (Harvard university). The measurements were conducted at the same time and dates as the CMU-IOA

measurements. Connection-attempt time yielded an interval of

23l6~11 <3258 in ms, or 942 ms, 95% confidence interval. Disx

engagement time yielded an interval of 1643~11 <2047 ms or 404 ms, . x

95% confidence interval.

29
In surrrrnary, the values of these four 95% confidence

intervals (260 ms access, 450 ms close, 404 ms close, and 942 ms

access) are not unreasonable when one considers < the magnitude of

the raw data, the small sample size (N=lO) and the value of a.

The author intends to use N=lO as a suitab~e sample size for

measurements of access and disengagement times.

6. MEASUREMENT RESULTS

The sample value measurements are given in the Appendix.

The overall measurement results are shown in Tables land 2.

Column one of each table is the name of the Host computer system

accessed by the NTIA/ITS Host. A list of geographical locations

for the selected Hosts is as follows:

Host Name

USC-ISIB

UCLA-CCN

USC-lSI

CMU-IOA

CMU-IOB

HARV-IO

SU-AI

SUMEX-AIM

NBS-IO

RUTGERS-IO

BB&N

BB&N-B

CCA

SRI-KA

SRI-KL

MIT-DMS

MIT-AJ

LONDON

Location

Marina Del Rey, CA

Los Angeles, CA

Marina Del Rey, CA

Pittsburgh, PA

Pittsburgh, PA

Cambridge, MA

Stanford, CA

Stanford, CA

Gaithersburg, MD

New Brunswick, NJ

Cambridge , MA

Cambridge, MA

Cambridge, MA

Menlo Park, CA

Menlo Park, CA

Cambridge, MA

Cambridge, MA

London, England

30
Table 1. Measurement Values for_Connection-Attempt Time and

Close-Attempt Time in Milliseconds Averaged from

Tables A.l Through A.lO

Host

USC-ISIB

UCLA-CCN

USC-lSI

CMU-I0A

CMU-I0B

HARV-10

SU-AI

SUMEX-AIM

NBS-10

AMES-67

RUTGERS

BB&N

BBN&N-B

CCA

SRI-KL

MIT-DMS

MIT-AI

LONDON

0900

Connect

MHR* Close

2 2820

1665

2 1895

1707

3 3787

1819

3 2207

1608

3 2084

1636

4 2621

1809

4 3128

1605

5 3719

1897

6 2988

1943

6 3828

2631

6 .3126

2012

6 6107

2313

6 6440

2045

7 4813

2215

7 4266

2095

7 4424

2092

7 4516

2005

8 8146

4112

1000

Connect

Close

3152

1701

1950

1779

3413

1691

2086

1646

2114

1648

2612

1883

2799

1749

4091

2027

2832

1949

4722

2940

2767

2002

5331

2094

9563

2069

4846

2114

4858

3688

4152

1992

4377

2043

2020

4060

1100

Connect

Close

3074

1816

1977

2090

3539

1781

2290

1678

2177

1678

2626

1881

3781

2124

3105

1926

4033

2406

2991

2007

5341

2050

5793

1975

4728

2098

4915

2158

4206

1970

4205

2075

7681

3738

0200

Connect

Close

3066

1679

1895

1758

3357

1727

2350

1646

2139

1661

2789

1825

3552

1742

4387

1938

2919

1951

4166

2842

2895

1974

5423

3708

5786

2192

4551

1948

5730

1994

4010

1969

4461

2070

7844

4685

0300

Connect

Close

3000

2861

2350

1837

4518

1719

2194

1691

2176

1663

2831

1867

3369

1666

4046

2046

2809

1910

5444

2823

3279

2070

5206

2329

5918

2396

4781

2156

5178

2142

3942

1940

3676

1741

8235

4090

0400

Connect

Close

2932

1698

1982

1789

3816

1657

2249

1657

2174

1614

2633

1888

4117

1692

4544

2366

2761

1913

4431

2474

2985

1987

5055

1883

5127

2116

5001

1976

4683

2069

4003

2042

4057

2961

7633

3816

0500

Connect

Close

3303

1695

2286

2409

3592

1734

2278

1636

2199

1634

2753

1954

3748

1741

4168

2581

2844

1986

5179

2696

2705

1928

5394

2144

5013

2075

4710

2384

5221

2565

3878

2156

3758

1999

7635

4284

Avg

Connect

Close

3049

1874

2049

1910

3715

1723

2236

1652

2152

1648

2695

1872

3329

1693

4105

2140

2859

1940

4543

2687

2964

1997

5408

2360

6234

2124

4776

2127

4150

2128

7885

4112

*MHR - Minimal Hop Route

**Each Host shown,in the table,above has two lines associated with it. The top line

shows the connectl0n-attempt tlme and the bottom line shows the close-attempt time

for every hour of the day When measurements were made. These measurement values

are averaged for each Host in the far-right column "Avg".

31
Table 2. Measurement Values for Access Time and Disengagement Time Values (in seconds) Derived from

Table 1

Host

USC-ISIB

UCLA-CCN

USC-ISI

CMU-I0A

C~1U-I0B

HARV-10

SU-AI

SUMEX-AIM

NBS-10

AMES-67

RUTGERS

BB&N

BB&N-B

CCA

SRI-KA

SRI-KL

MIT-DMS

MIT-AI

LONDON

0900

Access

MHR* Denga.ge

2 8.3

5.0

2 7.4

5.0

3 9.3

5.1

3 7.7

4.9

3 7.5

4.9

4 8.9

5.1

4 8.6

4.9

5 9.2

5.2

6 8.3

5.2

6 9.3

5.9

6 8.6

5.3

6 11. 6

5.6

6 11. 9

5.3

7 10.3

5.5

7 10.1

5.3

7 9.8

5.4

7 9.9

5.3

7 10.0

5.3

8 13.6

7.4

1000

Access

Den<Jage

8.7

5.0

7.5

5.1

8.9

5.0

7.6

4.9

7.6

4.9

8.1

5.2

8.3

5.0

9.6

5.3

8.3

5.2

10.2

6.3

7.8

5.3

10.8

5.4

15.1

5.4

10.3

5.3

10.3

5.4

9.8

5.3

9.6

5.3

9.9

5.3

13.5

7.3

noo

Access

Dengage

8.6

5.1

7.5

5.4

9.0

5.1

7.8

5.0

7.7

5.0

8.1

5.2

8.1

5.0

9.3

5.3

8.6

5.2

9.5

5.7

8.5

5.3

10.8

5.4

11. 3

5.3

10.2

5.3

10.5

6.9

9.7

5.3

9.7

5.3

9.7

5.4

13.2

7.0

0200

Access

Dengage

8.6

5.0

7.4

5.1

8.9

5.0

7.9

4.9

7.6

5.0

8.3

5.1

9.1

5.0

9.9

5.2

8.4

5.3

9.6

6.1

8.4

5.3

10.9

7.0

11.3

5.5

10.1

5.2

11. 6

5.0

9.5

5.3

9.5

5.3

9.9

5.4

13.3

8.0

0300

Access

Dengage

8.5

8.4

7.9

5.1

10.0

5.0

7.7

5.0

7.7

5.0

8.3

5.2

8.9

5.0

9.5

5.3

8.3

5.2

10.9

6.1

8.8

5.4

10.7

5.6

11.4

5.7

10.3

5.3

10.8

5.8

9.4

5.3

9.5

5.3

9.2

5.0

13.7

7.4

0400

Access

Dengage

8.4

5.0

7.5

5.1

9.3

5.0

7.7

5.0

7.7

4.9

8.1

5.2

9.6

5.0

9.9

5.6

8.3

5.2

9.9

5.8

8.5

5.3

10.6

5.2

10.6

5.4

10.5

5.3

10.2

5.4

9.5

5.3

9.5

5.3

9.6

5.3

13.1

7.1

0500

Access

Dengage

8.8

5.0

7.8

5.7

10.1

5.0

7.8

4.9

7.8

4.9

8.1

5.3

9.2

5.0

9.6

5.9

8.3

5.3

10.6

6.0

8.2

5.2

10.9

5.4

10.5

5.4

10.2

5.7

10.2

5.0

9.4

5.4

9.4

5.5

9.1

5.3

13.1

7.5

Avg

Access

Dengage

8.5

5.2

7.5

5.2

9.2

5.0

7.7

5.0

7.7

4.9

8.2

5.2

8.8

5.0

9.6

5.4

8.4

5.2

10.5

6.0

8.4

5.3

10.9

5.6

11.7

5.4

10.3

5.4

10.5

5.6

9.6

5.3

9.6

5.3

9.7

5.4

13.4

7.4

*MHR - Minimal Hop Route

**Each Host shown in the table above has two lines associated with it. The top line

shows the access time (in seconds) and the bottom line shows the disengagement time

(in seconds) for every hour of the day when measurements were made. These measurements values are averaged for each Host in the far-right column "Avg".

32
All Hosts were selected arbitrarily from the ARPANET directory

on the basis that they were listed as unl{mited server Hosts.

All tables are formatted into lines that contain two rows of

numbers for each Host. The top-row number relates to access and

the bottom-row number relates to disengagement. These sets ofnumbers are distributed in seven columns with a time of day as

the heading.

Table 1 derived from Tables A.l through A.lO in the

Appendix. The Appendix contains ten tables of sample data for

connection-attempt time and close-attempt time. From Section

5.3, access time is the sum of connection-attempt time (a variable) and operator action time (a constant). From Section 5.4,

disengagement time is the sum of close-attempt time (a variable)

and operator action time (a constant).

Table I was constructed by averaging all values of connection-attempt and close-attempt times for each particular time

slot. There are ten tables so that approximately ten sample

values were used in each sample size as discussed in Section 5.5.

The headings for columns 3 through 8 are the particular times of

the day (Mountain Standard Time) and were chosen arbitrarily.

The samples were measured on dates that ranged from August 23,

1977 to September 21, 1977 (s~e tables). The connection and

close-attempt values were measured and rounded off to the nearest

millisecond. Millisecond accuracy was obtained by using the VDH

timer attached to the PDP-II. This timer or clock is a countdown register which counts at 8 ~s (microsecond) intervals.

The sample values in Table I and the tables in Appendix A

were recorded to the nearest millisecond because of their significance in Host-to-Host network performance. The tables in the

Appendix also record three other events. The letter A denotes

that the access attempt £ailed. This happened when the terminal

operator issued the connect command and the Elf system Telnet

failed to respond. The letter F denotes that the disengagement

attempt failed. This happened when the terminal operator issued

a close command, after a connection was established, and the Elf

33
system Telnet failed to respond. The letter 0 denotes that the

terminal operator issued a connect command to some distant Host

and he received a message from the subnet saying that the

particular Host was not operating on the network. It is not

certain why some of the access and disengagement attempts failed,

but one suspects that there were defects in Elf.

The far-right column headed by the letters "Avg", is the

average for the other seven columns of data. Thesenumbers

represent the average of data in all ten tables in the Appendix

for all hours for each Host.

Tables A.l through A.IO also contain the data needed to

measure the three remaining parameters: incorrect access probability, access denial probability and disengagement failure

probability. These values are obtained from the A, 0, and F

designations explained in Se~tion 7.1.

Table 2 contains the access and disengagement times. These

values were computed from Table 1 with the addition of operator

action times of 5.5 seconds for access and 3.3 seconds for disengagement. The values of Table 1 were rounded to the nearest

tenth of a second and added to their respective operator action

time to produce Table 2.

7. ANALYSIS OF RESULTS

This section examines the measurement results presented in

Section 6 and in the Appendix.

7.1. Access and Disengagement

If one examines the measurement values beginning with the

tables in the Appendix, one can make some performance assessments about the ARPANET. Section 5.1 discusses the packet switch

and flow control delays that are present in the ARPANET. These

delays along with the telnet connect and telnet close processes

combin~ to produce the valuescin all tables. In all cases, the

34
NTIA/ITS Host was the source Host and the destination Hosts are

listed in column I of all tables.

Column 2 of all tables contains a number for each Host.

This number was derived from Figure I and represents the minimum

number of subnet links or the minimum hop route (MHR) between the

NTIA/ITS Host (source mode) and the destination Host (destination

node) listed in column 1. Each access and disengagement attempt

generates several messages between Hosts (Sec. 5.2). Each message

(i.e., these are single packet messages) may travel a different

route depending on the status of the subnet and the routing

decisions by the subnet (Sec. 5.1). Therefore, the MHR is not

necessarily the subhet route used during all measurements.

However, the MHR does offer some insight to ARPANET Host-to-Host

performance.

For example, if one observes the magnitude of the data in

all tables, the magnitude seems to increase as the MHR increases.

This is not true for all Hosts in column 1, but the trend is

apparent. In Table A.l the value at time 1000 for SKI-KL is

17200 ms for close-attempt time and in Table A.6 the value for

BB&N at 0200 for close-attempt time is 14248 ms. These large

values are assumed to be caused by temporary system blocking.

The large values for London, EngLand were attributed to the very

great length of the satellite path, and to an MHR=8.

Another observation from the tables is that connectionattempt time is almost always larger than close-attempt time.

The reason these times are larger can be attributed to the

following:

(a) New connections between Hosts require the source and

destination IMPs which serve the source and destination

Hosts, to exchange special control messages (Sec. 5.1).

This requirement causes additional delay for initial

connection between Hosts.

(b) The Telnet connection-process requires the exchange of

more messages than the Telnet closing process. These

extra exchanges cause additional delays.

35
(c) Another influencing factor could be the priority within

the destination Host operating system for initial

connections. If priority is low this can cause

additional delay.

(d) The-number of local jobs (i.e." the number of active

terminals logged-on plus the number of active processes

in effect) at some destination Host would also influence the initial connection process. If the destination Host is running near capacity, then more delay

will occur.

In Table 1, one cannot separate the Host operating system

delays from the subnet switching delays within the access and

disengagement measure. The reason is that the processes for

Telnet and NCP in each Host and the subnet processes overlap in

time. One can measure part of the Telnet process: the messagetypeout time on the terminal (which requires about 780 ms for

both access and disengagement). All the remaining time for each

measurement value is spent in computer execution and data communication systems activity.

Table 2 shows much the same information that Table 1 shows

except that the rounding of Table 1 values tends to simplify

the difference between destination Host access and disengagement

time values.

Although access time and disengagement time values cannot be

separated into Host operating system delays and subnet switching

delays, one can make some assumptions about these functional

delays and relate these assumptions to ARPANET system performance.

First, assume that the NTIA/ITS system performs ~ts access

or disengagement functions at the same speed each time. This

assumption is valid because the NTIA/ITS system performed all

measurements in single user mode, where all software and hardware

systems performed the same operations for each access or disengagement attempt (i.e., same operation repeated under same

source Host conditions) .

36
Second, assume that when MHR values are equal the packet

switching subnet performs its functions within a tenth of a

second for each attempt. The one exception is the case where (a)

above applies, i.e., where special control messages between

source and destination IMPs (for new connections between Hosts)

cause additional delays. A tenth of a second difference allows

for the variable subnet events presented in Section 5.1. This

becomes a reasonable a~sumption because IMPs can process a packet

in 0.35 ms.

Third, assume that destination Host response times are

variable for connection and closing attempts. The variability of

destination Host response time could be attributed to a large or

small number of local users, program jobs and active terminals

attached to that destination Host. These factors in turn

influence priorities of operating system processes on the

destination Host. For example, Telnet server process priority

could vary according to local user load level.

One applies these three assumptions to the last column of

Table 2. This column, headed "Avg", is the average value for all

access measurements (top value) and disengagement measurements

(bottom value) over all days and hours for that particular

destination Host.

First, the values for London, England are the largest, as

one would expect, because of the satellite-link distances.

Next, the access times for Rutgers and NBS-IO are two to three

~econds smaller than other Hosts with the same MHR value. One

could explain this difference in access times as a combination of

reason (a) above and the fact that these two destination Hosts'

are more readily accessible since there are fewer users. Reason

(a) refers to the fact that source and destination IMPs must

exchange control messages. The control messages allocate a

limited table space within the IMP for each new connection.

Conceivably, the more Hosts there are attached to an IMP (four is

maximum), the more ARPANET connections exist and the more likely

37
IMP table space could become a problem and cause delay. In the

ARPANET directory, Rutgers is one of two Hosts attached to the

Rutgers TIP and NBS-IO is one of two Hosts attached to the NBS

TIP. Therefore it appears that Rutgers and NBS~lO are more

readily accessible because they have fewer ARPANET users or

connections and more IMP table space than other Hosts with the

same·MHR values. Another observation is that CMU-IOA, CMU-IOB

and UCLA-CCN all have small MHR values and seem to offer the

fastest access to the NTIA/ITS Host. These three Hosts provide

the fastest access despite the fact that UCLA-CCN is attached to

a 3-Host node (IMP) and both CMU-IOA and eMU-lOB are attached to

a 4-Host node.

Finally, in the Avg column one notes the uniformity of the

disengagement times compared to access times. With the exception

of London (7.4 seconds) and AMES-67 (6.0 seconds), all Hosts. are

in the 5.0 to 5.6 second range for disengagement time. This

implies that once- the initial connection is established, ARPANET

Hosts respond more uniformly to message exchange. Further, the

uniformity of the disengagement times could offer users a

convenient performance tool. Because if disengagement time is

discovered to be outside the range of 5.0 to 5.6 seconds, then

one could suspect abnormal operations somewhere in the system.

7.2. Associated Parameters

The three other parameters associated with access time and

disengagement time are incorrect access probability, access

denial probability and disengagement failure probability.

Incorrect access probability is defined in Section 4. For

the ARPANET, this parameter is interpreted as a connection to the

wrong destination Host during the access phase. During access

attempt, the NTIA/ITS terminal operator receives a herald from

the destination Host proclaiming the Host name and other information. The herald identif~es the destination Host. In 1221

successful access attempts, the NTIA/ITS operator did not receive

a herald from an incorrect Host. Thus, for incorrect access

38
probability, the measurements yielded an answer of 0/1221=0. An

upper bound probability P for the occurrence of an incorrect

access event can be" computed based on the binomial distribution,

the 1221 independent trials and a confidence coefficient a=0.05.

(l-P) 1221 = ex

P = 0.0025.

Access denial probability is d~fined in Section 4. Although

access denial was probably due to Elf timing problems, the

overall system was blocked and all "A" events were counted to

determine access denial probability. The "0" events were not

included because in these cases the system was not operational

(the destination Host was not on the ARPANET). The total number

of A events was 18 and there were 1239 access attempts. Access

denial probability was 18/1239=0.015.

Disengagement failure probability is defined in Section 4.

The "Fit symbol in TablesA.l through A.IO denotes this event.

From these table~ a total of 1221 disengagement attempts resulted

in 40 failures. Disengagement failure probability was

40/1221=0.033. When disengagement failure occurred during a

disengagement attempt, the Telnet close command timed out after

30 seconds and printed a "timed out" message to the terminal

operator. When access failure occurred during access attempt,

the Telnet connect cornmandgenerated a loop in Elf and the system

had to be halted and re-started.

8. SUMMARY AND CONCLUSIONS

NTIA!ITS is engaged in the development of proposed Federal

Standard 1033. This standard contains several proposed performance parameters, five of which are measured over the ARPANET and

discussed in this report. These five parameters (Sec. 4) are

applied to the ARPANET as follows:

(1) Access time is defined as the average value of

elapsed time between the start of an access attempt and

successful access. For the ARPANET Access time is

39
the time required to complete a Host-to-Host Telnet

connection and call local NTIA/ITS NCP.

(2) Incorrect access probability is defined as the ratio

of access attempts which result in incorrect access

to total access attempts counted during a measurement

period. For the ARPANET Incorrect access probability

is the ratio of access attempts resulting in a connection to the wrong ARPANET destination Host to the

total access attempts to all destination Hosts during

the measurement period.

(3) Access denial probability is defined as the ratio of

access attempts which result in access denial to total

access attempts counted during a measurement period.

For the ARPANET Access denial probability is the ratio

of access attempts to destination Hosts which resulted

in access denial to the total access attempts to all

destination Hosts during the measurement period.

(4) Disengagement time is defined as the average value of

elapsed time between the start of a disengagement'

attempt and successful disengagement. For the ARPANET

Disengagement time is the time required to cLos e a

Host-to-Host Telnet connection.

(5) Disengagement failure probability is defined as the

ratio of disengagement attempts which result in disengagement failure to total disengagement attempts

counted during the measurement period. For the ARPANET

Disengagement failure probability is the ratio of

disengagement attempts to a destination Host which

resulted in disengagement failure to total disengagement attempts to all destination Hosts during the

measurement period.

The Elf (operating system) telnet was modified to measure

access time and aisengagmeent time. These two time intervals

include the sum of two sequential time interva+s:

(1) An operator action time is needed to type a connect

(5.5 seconds) or close (3.3 seconds) command to Telnet.

40
(2) A yariable connection or closing time interval is

required by the Telnet connect and close commands

between two ARPANET Hoat.s , see Table 1.

Access and disengagement times were measured over ARPANET

paths from the NTIA/ITS Host (source) to 19 destination Telnet

server Hosts (see Sec. 6, Tables 1 and 2) selected arbitrarily

from the ARPANET 1977 directory. Approximately ten sample values

of access time and disengagement time were averaged for each

destination Host for each of seven time slots and recorded in

Table 2 (Sec. 6). The overall average for each destination Host

is contained in the last column in Table 2 headed by Avg. The

values in the column headed by Avg (Table 2) were averaged over

all recorded measurement data (about 70 sample values). These

data revealed that Host-to-Host access time is more variable than

disengagement time. This variability is probably caused by

greater delays during the initial connection process at the

destination Host (see Sec. 7.2) and by the exchange of IMP-to-IMP

control messages required for initial connections (see Sec. 5.1).

The uniformity of disengagement times in Table 2 demonstrates

that after initial Host-to-Host connections are established

(access), Host-to-Host message exchanges function in a uniform

manner.

From 1221 successful access attempts the' incorrect access

probability was determined to be zero for Host-to-Host Telnet

connections. An incorrect access probability of zero in 1221

measurements (Hosts) can be interpreted as good Host-to-Host

operational performance. Access denial probability was computed

from Tables A.l through A.IO (Appendix A). In 1239 access

attempts, access denial probability was found to be 0.015. Disengagement failure probability was also computed from Tables A.l

through A.IO (from 1221 disengagement attempts) and found to be

0.033.

The primary conclusion is that the five proposed performance parameters selected for measurement here were applicable to

the ARPANET and that these parameters were measurable.

41
9. RECOMMENDATIONS

The author recommends that measurement experiments be conducte~ which employ many Hosts simultaneously to provide data related to network performance. The network measurements could be

used to test the proposed performance parameters for overall

network performance.

The remaining performance parameters of proposed standard

1033 concerning accuracy, efficiency, and reliability need to be

tested. The author recommends that these parameters be measured

on the ARPANET.

10. ACKNOWLEDGMENTS

The author would like to thank Dr. P.M. McManamon, who

directs the data communication programs at.NTIA/ITS, for his many

helpful comments and Dr. D.L. Retz of the Stanford Research

Institute for his assistance with the measurement software which

runs under Elf. Thanks are also extended to Dr. E.L. Crow of

NTIA/ITS for his helpful comments about statistical matters,

to Mr. Evan Dutton, Mr. Robert Linfield and Evie Gray for their

helpful reviews and to Ms. Pat Sanchez for her superior typing

assistance.

42
11. REFERENCES

ARPANET Directory (1977), prepared for Defense Communications

Agency by Network Information Center, SRI International,

Menlo Park, CA 94025.

ARPANET Protocol Handbook (1978), prepared for Defense Communications Agency by Netrwork Information Center, SRI International, Menlo Park, CA 94025.

ARPANET Transition Plan (1975), pp. 1-5, prepared by Advanced

Research Projects Agency and the Defense Communications

Agency.

Bendat, J., and A. Piersal (1966), Measurement and Analysis of

Random Data (John Wiley & Sons, Inc., New York, New York).

Bolt Beranek and Newman, Inc. (BB&N) (1976), Interface message

processor, Report No. 1822, Developed for the Advanced

Research Projects Agency by BB&N.

Davies, D., and D. Barber (1973), Communication Networks' for

Computers (John Wiley & Sons, Ltd., London, England).

Federal Register (1977), Telecommunications: Digital communication performance parameters, proposed Federal Standard 1033,

published February 22, 1977, Vol. 42, No. 35, pp. 10353-10375.)

Heart, F., R. Kahn, S. Ornstein, W. Crowther, and D. Walden (1970),

The interface message pro,cessorfor the ARPA computer network, Proceedings, 1970 Spring Joint Computer Conference.

Kleinrock, L. (1976), Queueing Systems, Volume 2: Computer

Applications (John Wiley & Sons, Inc., New York, New York).

Kl.e i.nr ock , L., W.c,Naylor, and H. Opderbeck (1976), A study of

line overhead in the ARPANET, Communications of the ACM,

Volume 19, No.1, pp. 3-13, January.

McManamon, P.M., R.K. Rosich, J. Payne, and M. Miles (1975),

Performance criteria for digital data networks, OT Report

75-54. (Available from the National Technical Information

Service, 5285 Port Royal Road, Springfield, VA 22161,

Accession No. COM-75-10779.)

43
Postel, ~. (1971), Official initial connection protocol, Network Information Center, document number 7101, ARPANET

Protocol Handbook, Prepared for Defense Communications

Agency, Code 535.

Retz, D., J. Miller, J. McClurg, and B. Schafer (l976), Elf

programmer's guide (Speech Communication Research Lab, Inc.,

Santa Barbara, CA 93109).

Roberts, L.G. (1967), Multiple computer networks and intercomputer communications, Proceedings of the ACM Symposium

on Operating Systems, Gatlinbur~, Tennessee.

Schwartz, M. (1977), Computer-Communication Network Design and

Analysis (Prentice-Hall, Inc., Englewood Cliffs, N.J.).

44
APPENDIX. MEASUREMENT TABLES

This Appendix contains the raw sample values recorded during

the measurement experiment. These sample values are listed in

the 10 tables (A.l through A.IO). Each table denotes the name of

the Host, the approximate time of day when data were recorded,

the MHR (minimal hop route), a value for connection attempt time

(top value) and a value for close attempt time (bottom value).

The tables also show access attempt failures (A), disengagement

attempt failures (F), and whether or not the destination Host was

operational on the ARPANET (0). The MHR is the smallest number

of links connecting the nodes separating the destination Host

server from theNTIA/ITS Host's DOCB TIP located in Boulder,

Colorado. The MHR data were determined from Figure 1.

45
Table A.1. Sample Values from Measurements on August 23, 1977 (Each

Rectangle Space Contains (top) the Connection Attempt

Time (ms ) and (bottom) the Close Attempt Time (ms) )

0900 1000 1100 0200 0300 0400 0500 .

Connect Connect Connect Connect Connect Connect Connect

Host MHR Close Close Close Close Close· Close Close

USC-ISIB 2 2504 4035 2628 3193 4289 3208 3239

1753 1647 1556 1600 1805 F 1670

UCLA-CCN 2 2090 2016 1914 2318 1920 1992 1906

1700 1993 4535 1898 1759 1864 1850

USC-lSI 3 3173 3643 3353 4881 3792 3762 3451

1705 1783 2143 F 2012 1725 1565

CMU-I0A 3 2244 2420 2130 2328 2182 2151 2166

1512 1667 1689 1624 1773 1618 1602

CMU-10B 3 2529 2079 2293 2208 2850 2247 2091

1734 1831 1590 1628 1973 1674 1596

HARV-I0 4 2672 2444 2679 2659 2812 2622 2674

1611 1882 1846 1819 1797 1932 1770

SU-AI 4 2424 3997 2369 3463 2789 2782 2442

1600 1724 1664 1899 1618 1565 1682

SUMEX-AIM 5 4006 3784 5336 A 4648 5405 5708

1912 2136 2268 2860 2618 8084

NBS-I0 6 3474 3195 2708 3078 2726 2821 2898

2002 F 1775 1993 1984 2053 1998

AMES-67 6 3318 4962 2850 3870 5412 4949 4453

3128 3223 1913 5413 3511 2191 4226

RUTGERS 6 2993 3277 2825 2455 2984 2776 3261

2016 2092 1998 2259 1911 1847 1874

BB&N 6 4876 4642 5853 5383 4492 4328 4534

2180 2259 1905 1985 1917 1941 2380

BBN&N-B 6 6581 4748 5975 6058 4920 5018 3913

1852 1998 1997 2345 2077 2037 1802

CCA 7 6135 4912 5092 5180 3515 5785 8717

2255 2205 1964 2147 2033 1802 2134

SRI-KA 7 4295 4666 4239 3733 5472 4719 4055

2341 2153 1987 2108 2279 2078 1678

SRI-KL 7 4133 5200 5484 5209 4328 5528 4·537

2278 17200 1903 1835 2263 2103 2152

MIT-DMS 7 4309 3908 4338 5353 3970 5385 390-9

2334 2254 2031 1902 2035 2177 2075

MIT-AJ 7 4468 4315 4614 5096 4093 4827 3964

2335 2701 2076 2140 1941 2175 2305

LONDON 8 7733 8010 7981 7164 9397 7838 7936

4273 3873 4084 3804 4089 3772 4672

A - Access Attempt Failed

F - Disengagement Attempt Failed

o - Destination Host Off-net

MHR - Minimal Hop Route

46
Table A.2. Sample Values from Measurements on August 29, 1977 (Each

Rectangle Space Contains (top) the Connection Attempt

Time (ms) and (bottom) the Close Attempt Time (ms ) )

0900 1000 1100 0200 0300 0400 0500

Connect Connect Connect Connect Connect Connect Connect

Host MHR Close Close Close Close Close Close Close

USC-ISIB 2 2935 2494 2756 3104 2547 2620 3256

1513 1737 1606 1475 1312 1511 1639

UCLA-CCN 2 2055 1813 1892 1978 1950 1890 2013

1704 1782 F 1708 F 1875 1759

USC-lSI 3 3160 3363 3568 2919 4052 2742 2439

1741 1916 1725 1668 ] 61 ] 1701 1797

CMU-I0A 3 2518 1777 2153 2157 1895 2052 1842

F 1675 1610 F 1518 1574 J 548

CMU-I0B 3 1855 A 2372 2092 2341 1936 2331

1613 1912 1571 1522 J 525 1586

HARV-I0 4 2511 2409 3017 2664 2822 2721 2688

1834 1899 1996 1718 2035 1823 2024

SU-AI 4 2692 2476 1592 2205 2672 5882 2444

1653 1651 1743 1737 1534 1677 1833

SUMEX-AIM 5 3697 3916 4424 4604 4696 5210 3485

1805 2326 2035 2282 2042 2442 1775

NBS-I0 6 0 2917 3034 2984 2773 2954 3058

1879 1690 2044 1874 1798 1967

AMES-67 6 3010 0 0 6207 6058 7485 3560

2613 3122 2088 2713 1864

RUTGERS 6 3157 3056 2937 2975 5132 2926 2880

2052 2095 1993 2054 2149 1892 1886

BB&N 6 7448 3901 6185 4840 5539 3058 4453

2317 1940 2035 1881 2098 1902 1933

BBN&N-B 6 4034 5000 4482 5112 5092 A 4103

1979 2188 1893 2198 2128 1847

CCA 7 4061 6959 3882 A 4369 4268 3886

2369 1923 1966 1962 1972 1973

SRI-KA 7 5247 5509 4542 5224 4207 4816 5076

2166 2025 s080 1939 1873 2084 2241

SRI-KL 7 0 4056 4447 8839 4802 0 4350

1937 2134 2032 1995 2100

MIT-DMS 7 4167 4324 4375 3531 3262 4198 3536

1995 1940 1934 1912 1814 2372 1787

iv1IT-AJ 7 3864 4244 4025 4404 3615 2706 3774

1991 1881 1796 1987 1849 10061 1916

LONDON 8 8078 8589 8442 8279 7504 8534 7954

4003 3720 4454 4370 F 4285 4297

A - Access Attempt Failed

F - Disengagement Attempt Failed

o - Destination Host Off-net

MHR - Minimal Hop Route

47
Table A.3. Sample Values from Measurements on September 2, 1977 (Each

Rectangle Space Contains (top) the Connection Attempt

Time (ms) and (bottom) the Close Attempt Time (ms ) )

0900 1000 1100 0200 0300 0400 0500

Connect Connect Connect Connect Connect Connect Connect

Host MHR Close Close Close Close Close Close Close

USC-ISIB 2 2648 2896 2688 3130 3008 2629 2914

1688 1748 1965 1510 14337 1498 1772

UCLA-CCN -2 1997 1764 2149 1993 2231 1850 0

F 1758 1863 1637 2036 1865

USC-lSI 3 5014 3203 4616 2851 3140 3485 5737

1849 1644 1645 1550 1673 1585 1885

CMU-I0A 3 1824 1664 2185 2094 2092 1883 2039

1498 1659 1666 1569 F 1633 1599

CMU-I0B_ 3. 2232 2575 2166 2002 2001 2175 2224

1502 1681 1654 1619 1573 1661 1659

HARV-I0 4 2562 3097 2423 2840 2729 0 0

1779 1968 1865 1863 1906

SU-AI 4 2366 2793 2607 2349 2727 2283 2710

1631 1747 1575 1756 1902 1604 1880

SUMEX-AIM 5 5373 5653 5082 5606 3874 2601 4240

.. 1961 2054 1982 1855 1667 1077 F

NBS-I0 6 2688 3138 0 0 0 0 0

1840 1762

AMES-67 6 5758 4505 5690 2989 0 0 9758

4092 4234 3952 1918 4213

RUTGERS 6 3100 3241 2448 3148 2905 2650 3211

1868 2018 2080 1863 1964 1838 1876

BB&N 6 0 0 0 0 0 0 0

BBN&N-B 6 14621 5141 A 5701 5801 5419 6778

1944 2202 1986 2080 2157 2027

CCA 7 4511 4019 5365 4729 6190 4926 3618

2017 2114 1948 1892 2345 1927 1889

SRI-KA 7 4660 4950 4998 4134 4346 4166 4431

2258 2094 2095 1876 1841 2021 2174

SRI-KL 7 3908 4333 4351 4887 5347 4694 5424

2451 1772 1916 2002 2030 1905 7019

MIT-DMS 7 3492 A 4605 4548 4691 3216 3783

2152 1996 1875 F 1907 2151

MIT-AJ 7 4542 3963 4491 4362 2825 4351 4330

2080 1951 2493 1922 2070 2009 2068

LONDON 8 7711 6863 7496 7516 9256 7781 7884

4052 3813 4037 3658 4497 3857 3707

A - Access Attempt Failed

F - Disengagement Attempt Failed

o - Destination Host Off-net

MHR - Minimal Hop Route

48
Table A.4. Sample Values from Measurements on September 6, 1977 (Each

Rectangle Space Contains (top) the Connection Attempt

Time (ms) and (bottom) the Close Attempt Time (ms ) )

0900 1000 1100 0200 0300 0400 0500

Connect Connect Connect- Connect Connect Connect Connect

Host MHR Close Close Close Close 'Close Close Close

USC-ISIB 2 2470 5014 5020 3304 2278 2974 3185

1786 1714 1672 1786 1692 1856 1649

UCLA-CCN 2 2070 1972 1955 2308 7139 2140 2146

1478 1674 1817 1750 1778 1734 1795

USC-lSI 3 2957 A 3312 3946 3661 0 4050

1666 1744 1638 1607 J 731

CMU-I0A 3 2469 2157 1933 2197 1899 2120 2086

F 1817 1588 F 1739 1637 J682

CMU-I0B 3 2146 2072 0 2021 2074 2125 2007

1621 1601 1711 1548 1698 1524

HARV-I0 4 2797 2498 2258 2964 2725 2781 2936

2097 1897 1852 1824 1814 F 1757

SU-AI 4 A 2585 2577 2742 3255 3082 2824

1624 1622 1755 1609 1761 1719

SUMEX-AIM 5 3261 3527 6156 5072 3618 5517 4520

F 1731 1969 2069 1842 1973 2068

NBS-IO 6 0 0 0 f"\ rv v v 0 0

AMES-67 6 2895 4428 3960 4695 8540 5338 3690

1899 2025 2033 1997 2579 F 2134

RUTGERS 6 2886 2764 2881 3231 2728 3403 2848

1992 1831 1884 2035 1950 1922 1718

BB&N 6 5358 4242 4461 6049 4542 4914 5580

2429 1912 1702 2307 2226 1953 2069

BBN&N-B 6 3961 4711 4476 4955 49L~7 4421 4539

1850 1942 1966 2052 2187 2035 2062

CCA 7 3792 4292 4345 4415 3673 6341 3617

2019 18-03 1778 2088 1967 2147 1807

SRI-KA 7 3795 4614 4668 4265 5036 3688 3859·

2110 2108 1973 1977 1996 1872 1934

SRI-KL 7 4424 5031 4813 0 5366 5628 5178

1884 F 2012 2172 2186 2126

MIT-DMS 7 4294 3506 3961 3493 3821 3513 3490

2166 2191 1751 1942 2093 1918 2453

MIT-AJ 7 4596 5814 3677 3954 4363 4452 3945

1945 1880 2140 1933 1938 2224 1775

LONDON 8 8836 7560 8435 8669 8526 6843 7300

4478 4147 4055 F 4223 3655 4860

A Access Attempt Failed

F - Disengagement Attempt Failed

o - Destination Host Off-net

MHR - Minimal Hop Route

49
Table A.5. Sample Values from Measurements on September 7, 1977 (Each

Rectangle Space Contains (top) the Connection Attempt

Time (ms) and (bottom) the Close Attempt Time (ms ) )

0900 1000 1100 0200 0300 0400 0500

Connect Connect Connect Connect Connect Connect Connect

Host MHR Close Close Close Close Close Close Close

USC-ISIB 2 3180 3047 3289 A 2657 A 5155

1750 1612 1365 1819 1778

UCLA-CCN 2 1904 1897 2014 2035 2673 2064 2050

1522 1682 1799 1675 2189 1782 1859

USC-lSI 3 4065 3762 3112 4293 3608 2590 2892

1751 1730 1817 1.800 1513 1679 1905

CMU-I0A 3 2211 0 1896 2354 2146 2377 2207

1636 1675 1715 1735 1762 1630

CMU-I0B 3 2052 1850 2351 1917 2029 2410 2443

1527 1599 1705 1620 1620 1396 2004

HARV-I0 4 2652 2516 2238 2464 4251 2386 2907

1865 1919 1825 1837 1833 1980 1689

SU-AI 4 2452 2584 2485 2502 2238 4279 6386

1569 1923 1747 1631 1618 1694 1690

SUMEX-AIM 5 3292 3248 4102 3567 3976 6596 3611

1725 2025 1900 1832 2167 2933 2104

NBS-I0 6 3042 2683 3154 A 2953 2804 2825

1941 2002 1952 2158 1903 1942

AMES-67 6 3751 3778 6199 A 7357 4616 3388

1949 2189 3862 4884 2025 2737

RUTGERS 6 A 2821 3156 2918 3201 2867 A

1999 1940 1939 3112 F

BB&N 6 5672 7542 4555 4266 7842 A 5486

2304 2167 2131 2481 3240 2014

BBN&N-B 6 4178 5048 8511 4799 10268 5480 4001

1921 1913 1989 2098 3736 2027 2012

CCA 7 4586 4272 4359 3555 4382 5443 4828

2061 2417 F 1690 1996 1960 2297

SR:L-KA 7 4422 4671 5836 6387 7136 4965 4378

1989 2024 1908 1883 1966 1728 1963

SRI-KL 7 4127 4839 4109 3929 5707 4642 4491

2210 1925 2342 2093 1891 F 1875

MIT-DMS 7 4859 4878 4281 3131 4105 4044 4045

1909 1938 1937 2100 1882 1786 2213

MIT-AJ 7 4769 4578 3994 4213 7164 4302 3708

1812 2~31 2089 2301 1975 1994 1933

LONDON 8 0 0 0 0 0 0 0

A - Access Attempt Failed

F - Disengagement Attempt Failed

o - Destination Host Off-net

MHR - Minimal Hop Route

50
Table A.6. Sample Values from Measurements on September 9, 1977 (Each

Rectangle Space Contains (top) the Connection Attempt

Time (ms ) and (bottom) the Close Attempt Time (ms ) )

0900 1000 1100 0200 0300 0400 0500

Connect Connect Connect Connect Connect Connect Connect

Host MHR Close Close Close Close Close Close Close

USC-ISIB 2 3225 2387 2794 3438 3620 2802 3038

1624 1685 F 1665 1399 1824 1685

UCLA-CCN 2 1681 2000 1833 2150 1952 1819 1960

1993 1841 1681 1571 1708 1674 1797

USC-ISI 3 2865 3470 3967 3799 4938 6335 3612

1824 1671 1689 1602 1708 1714 1610

CMU-I0A 3 2123 2166 2800 2021 2113 1883 2148

1717 1518 1670 1673 1615 1562 1684

CMU-I0B 3 2143 1745 1856 2151 2015 2086 2344

1691 1652 1559 1581 1548 1572 1612

HARV-I0 4 0 2590 2444 3156 2447 2411 2477

1955 1688 1881 1767 1712 2443

SU-AI 4 2430 2535 3098 2533 2472 2456 2537

1576 1860 1640 1650 1548 1854 1848

SUMEX-AIM 5 0 0 0 4341 3609 3059 3956

2035 1922 2275 1767

NBS-10 6 2717 2344 2563 2752 2716 2723 2664

F 2032 1730 1899 1939 1861 1940

AMES-67 6 5310 5726 4440 0 6226 3982 10393

2942 4356 1850 2603 2475 2772

RUTGERS 6 32.34 2939 2740 2339 2917 2973 2915

1915 1837 2027 2042 1893 F 2055

BB&N 6 5840 5530 5239 4783 5458 5691 5512

2185 1921 2050 14248 2151 2068 2375

BBN&N-B 6 6720 4295 4508 5521 5316 3393 6051

1929 1961 2129 1976 2071 1890 2249

CCA 7 4691 4203 4596 3962 4390 3406 5002

2071 1935 1951 1920 2166 1968 2144

SRI-KA 7 4756 4551 5234 6347 6125 3670 4482

1893 2254 1979 2067 2103 2215 1915

SRI-KL 7 4200 5429 4378 5544 5253 4407 5445

1956 2017 2160 1814 2306 2045 2015

MIT-DMS 7 4647 3581 4128 3769 3833 3412 3325

1991 1692 2159 1910 2046 1855 2645

MIT-AJ 7 5049 4012 4754 5102 4034 3677 3508

2102 1923 2250 1918 2029 2141 1900

LONDON 8 9941 10507 8618 0 0 0 0

4214 5287 4786

A - Access Attempt Failed

F - Disengagement Attempt Failed

o - Destination Host Off-net

MHR - Minimal Hop Route

51
Table A.7. Sample Values from Measurements on September 14" 1977 (Each

Rectangle Space Contains (top) the Connection Attempt

Time (ms ) and (bottom) the Close Attempt Time (ms ) )

0900 1000 1100 0200 0300 0400 0500

Connect Connect Connect Connect Connect Connect Connect

Host MHR Close Close Close Close Close- Close Close

USC-ISIB 2 2352 3677 3129 2889 2494 3408 3361

1592 1652 1820 1446 1672 2155 1716

UCLA-CCN 2 1757 2069 2092 1911 1790 2273 1861

1702 F 1784 1732 1436 1697 1779

USC-lSI 3 2757 2964 3606 3097 3255 3780 3933

1607 1727 1641 1827 1746 1447 1882

CMU-I0A 3 2332 1529 1858 1686 1924 2085 2124

1587 1446 1682 1585 1583 1560 1514

CMU-I0B 3 2082 2315 2283 0 1861 2111 2008

1865 1656 1685 1627 1677 1593

HARV-I0 4 2534 2422 2477 2867 2615 2628 2858

1670 1660 1794 1620 1707 2090 2022

SU-AI 4 2449 2986 2543 1878 6627 5075 6373

1586 1668 1568 1753 1877 1763 ] 565

SUMEX-AIM 5 3042 3792 3091 4446 4099 4182 3695

.1746 1973 2551 1714 1847 1930 ]735

NBS-I0 6 3245 3210 3376 2551 2529 2762 2653

2059 2208 2232 F 1860 1828 2094

AMES-67 6 3701 5820 2851 4144 A 2843 5587

1688 3075 1845 3335 2319 2233

RUTGERS 6 2987 3011 3349 2910 3591 A 3029

2124 2028 F 1781 1779 1878

BB&N 6 5015 4572 5891 5939 4767 5774 4760

2267 2157 2281 2908 2834 2224 2130

BBN&N-B 6 5925 5391 4367 11626 4603 0 0

2105 2133 1756 3343 2101

CCA 7 4256 6084 5124 4927 4405 3640 3719

2134 2335 2332 2024 2151 F 2092

SRI-KA 7 3453 4167 5678 11592 4675 4672 3927

1852 1971 20289 1881 1922 1913 1810

SRI-KL 7 4407 5197 4705 A 4597 4281 4792

1942 1972 1958 2023 2287 2127

MIT-DMS 7 0 4287 3626 4280 4019 4697 3665

2208 F 2018 1700 1858 1908

MIT-AJ 7 4120 4562 3564 4030 3456 3780 3370

1861 2008 1808 1931 2056 1891 1734

LONDON 8 0 7522 0 7849 0 0 0

3933 4020

A Access Attempt Failed

F - Disengagement Attempt Failed

o - Destination Host Off-net

MHR - Minimal Hop Route

52
Table A.8. Sample Values from Measurements on September 15, 1977 (Each

Rectangle Space Contains (top) the Connection Attempt

Time (ms) and (bottom) the Close Attempt Time (ms ) )

0900 1000 1100 0200 0300 0400 0500

Connect Connect Connect Connect Connect Connect Connect

Host MHR Close Close Close Close Close Close Close

USC-ISIB 2 2940 2719 2594 2718 2683 3350 3442

1814 1746 2830 1535 1299 1611 1696

UCLA-CCN 2 1840 2070 A 2088 1842 1951 1858

1672 1725 1779 1862 1719 1828

USC-lSI 3 3118 3082 4269 4670 3664 3359 3268

1933 1427 1861 1930 1635 1870 1742

CMU-I0A 3 0 0 0 2097 1857 2052 2561

1633 1678 1881 1856

eMU-lOB 3 1848 2082 1993 2473 1838 2203 2119

1591 1795 1653 1656 1582 1634 1602

HARV-I0 4 0 2592 2717 2996 0 0 0

1834 2248 1871

SU-AI 4 2767 2432 2390 6487 4170 8474 5587

1638 1793 1633 1743 1629 1634 1765

SUMEX-AIM 5 3515 5627 3291 3801 3168 5101 4244

1731 2085 1829 1800 17.34 1794 2022

NBS-I0 6 2797 2699 3868 3297 2632 2691 3000

1819 1885 2239 2103 1647 1695 1963

AMES-67 6 3076 4151 3481 3468 2802 3156 2306

2984 2853 2034 1852 2160 2187 2472

RUTGERS 6 3136 3216 3172 3197 3097 2762 3218

1861 2006 1847 1904 1994 2128 2200

BB&N 6 6578 5745 5041 6418 5355 5327 6423

2007 2468 2070 2024 1938 2517 2366

BBN&N-B 6 5041 5336 5245 4676 8317 5884 4482

1796 2026 2015 1976 3369 1808 2008

CCA 7 4972 4479 5393 5306 4727 5342 5138

2089 2342 2179 1964 1912 1937 2055

SRI-KA 7 4529 4826 5528 7487 5030 6535 4873

2029 2242 2208 2110 7668 2504 1978

SRI-KL 7 4319 4361 6087 0 4165 3572 4054

1940 1837 2508 2662 1911 2175

MIT-DMS 7 4756 4243 4220 3915 3776 3978 4128

2078 1941 1912 2085 1785 2078 2022

MIT-AJ 7 4402 4600 4673 4268 3282 4102 3668

F 2063 2076 2280 1811 1936 2018

LONDON 8 7527 0 0 0 7347 7279 7323

3758 3910 3450 4386

A - Access Attempt Failed

F - Disengagement Attempt Failed

o - Destination Host Off-net

MHR - Minimal Hop Route

53
Table A.9. Sample Values from Measurements on September 20, 1977 (Each

Rectangle Space Contains (top) the Connection Attempt

Time (ms) and (bottom) the Close Attempt Time (ms) )

0900 1000 1100 0200 0300 0400 0500

Connect Connect Connect Connect Connect Connect Connect

Host MHR Close Close Close Close Close Close Close

USC-ISIB 2 3173 2382 2769 2935 2837 2926 2955

1625 1799 1712 1513 1615 1568 1799

UCLA-CCN 2 1717 2061 1965 2097 1896 2151 1913

1893 1757 1663 2043 1936 2024 1723

USC-lSI 3 4265 3774 2992 3160 3107 4557 2901

2267 1647 1531 1741 1968 1707 1700

CMU-10A 3 2146 1954 2092 1990 2021 2241 2030

1536 1800. 1552 1715 1723 1597 1622

CMU-10B 3 1750 0 0 2343 2228 2131 2113

1630 1857 1759 1545 1500

HARV-10 4 0 2943 3195 2511 2591 2546 2734

1930 2014 1834 1871 1808 1977

SU-AI 4 7652 0 3417 0 0 0 0

1558 1684

SUMEX-AIM 5 3869 0 3441 3405 4002 4532 4681

2253 2574 2085 2204 4825 1849

NBS-10 6 2904 2621 3048 2904 3461 2581 2559

1856 1951 1952 1881 F 1987 2024

AMES-67 6 0 4889 4357 3632 3495 4090 4609

2124 2069 3051 1952 2069 2285

RUTGERS 6 3007 2935 3126 3069 3024 2976 3267

1954 214r2 2245 1943 1876 2135 1958

BB&N 6 6240 4871 5727 5232 5470 6705 4443

2546 2097 2158 2127 2499 2364 1895

BBN&N-B 6 4885 4988 5147 4034 4172 6721 5106

2294 2087 1915 1979 2048 3297 2327

CCA 7 5390 4705 2741 3944 4587 4243 4263

2427 2034 2161 2029 2891 1836 2054

SRI-KA 7 5652 5199 5421 5247 6356 5492 7072

1857 2433 1678 2166 2432 2052 2217

SRI-KL 7 4746 5405 4684 0 3307 4709 4671

2099 2332 2126 2066 2044 2270

MIT-DMS 7 4045 4042 4306 4166 3667 4326 4467

2114 1657 2066 1937 2071 2194 2266

MIT-AJ 7 4832 3611 4056 4723 4283 4316 3557

1910 1849 1949 2217 F 2215 2339

LONDON 8 7673 7510 4904 8078 7791 7730 7239

4008 3757 4751 4003 3719 3925 4016

A - Access Attempt Failed

F - Disengagement Attempt Failed

o - Destination Host Off-net

MHR - Minimal Hop Route

54
Table A.I0. Sample Values from Measurements on September 21, 1977 (Each

Rectangle Space Contains (top) the Connection Attempt

Time (ms) and (bottom) the Close Attempt Time (ms.) )

0900 1000 1100 0200 0300 0400 0500

Connect Connect Connect Connect Connect Connect Connect

Host MHR Close Close Close Close Close Close Close

USC-ISIB 2 2768 2872 3075 2879 3591 3389 2486

1505 1612 F 1511 1661 1564 1546

UCLA-CCN 2 1839 1837 1976 2109 2141 1987 4871

1645 1799 1578 1783 1828 1656 7294

USC-lSI 3 6494 3453 2600 3757 11959 3734 3640

1848 1677 2014 1787 1715 1489 1526

CMU-I0A 3 1998 1794 2342 2027 2199 2038 2288

1773 1587 1761 1650 1855 1744 1623

CMU-I0B 3 2200 2194 2105 2048 2468 2312 2310

1583 1369 F 1712 1837 1760 1662

HARV-I0 4 0 0 2799 2772 2490 2971 0

1726 1780 2076 1872

SU-AI 4 2917 0 2828 7811 A 2745 2435

1639 1719 1758 1678 1688

SUMEX-AIM 5 3423 3180 2887 4641 4773 3239 3544

2045 1885 2015 1776 2172 1796 1825

l{BS-IO 6 3040 r"'If"'f""lro. LOO0 3095 2869 2646 2"150 3091

2081 1874 1845 1786 F 2194 1966

AMES-67 6 3642 3239 2473 4425 3662 3417 4044

2387 1987 2098 2044 2809 3810 2028

RUTGERS 6 3637 3311 3273 2718 3212 3533 2745

2330 1970 2047 1916 F 2148 1913

BB&N 6 7941 6941 5125 5904 6234 4641 7358

2586 1928 2120 F 2061 1978 2133

BBN&N-B 6 8453 5970 9424 5373 5741 4676 6145

2782 2241 2118 1962 2158 1675 2341

CCA 7 5739 4570 6384 4937 7571 6619 4310

2711 1986 2605 1780 2137 2235 2391

SRI-KA 7 4432 4372 4110 6596 4768 4295 4739

- 1895 1891 1825 1930 2467 2069 1793

SRI-KL 7 4126 4729 6094 5974 4867 0 9267

2093 2002 2520 2190 2015 1791

MIT-DMS 7 4249 4599 3847 3910 4278 3258 4435

F 2101 1947 2010 2031 2280 2038

MIT-AJ 7 0 0 0 0 ('\ () f"\ v V "v

LONDON 8 7668 7600 7889 7351 7827 7432 7808

F 3951 4133 8259 4105 3770 4047

A - Access Attempt Failed

F _ Disengagement Attempt Failed

o - Destination Host Off-net

MHR - Minimal Hop Route

55

FORM OT-29

(3-73)

U.S. DEPARTMENT OF COMMERCE OFFICE OF TELECOMMUNICATIONS

BIBLIOGRAPHIC DATA SHEET

1. PUBLICATION OR REPORT NO.2. Gov't Accession No.3. Recipient's Accession No.

NTIA Report-78-2

4. TITLE AND SUBTITLE

ARPANET HOST TO HOST ACCESS AND DISENGAGEMENT

MEASUREMENTS

7. AUTHOR(S)

Judd A. Payne

8. PERFORMING ORGANIZATION NAME AND ADDRESS

U.S. Department of Commerce

National Telecommunications & Info. Admin.

Institute for Telecommunication Sciences

325 Broadway, Boulder, CO 80303

11. Sponsoring Organization Name and Address

U.S. Department of Commerce

National Telecommunications & Info. Admin.

1325 G Street, NW

Washington, D.C. 20005

14. SUPPLEMENTARY NOTES

5. Publication Date

May 1978

6. Performing Organization Code

NTIA/ITS

9. Project/Task/Work Unit No.

10. Contract/Grant No.

12. Type 'of Report and Period Covered

13.

15. ABSTRACT (A 200-wordor less factual summary of most significant information. If document includes a significant

bibliogrephy ot literature survey, men ti on it here.)

A set of telecommunications performance parameters have been

developed for proposed Federal Standard 1033. The measurement of

five of these parameters, access time, incorrect access time, access

denial probability, disengagement time and disengagement failure

probability are the subject of this report. The telnet protocol

of the ARPANET is employed to measure the access and disengagement

parameters from a Host to Host connection.

16. Key Words (Alphabetical order, separated by semicolons)

access; ARPANET; disengagement; Elf operating system; Host;

IMP (interface message processor); NCP (network control ·program);

performance parameter; protocol; Telnet; TIP (terminal interface

processor)

17. AVAILABILITY STATEMENT

[K] UNLIMITED.

D FOR OFFICIAL DISTRIBUTION.

18. Securi ty Class (This report)

Unclassified

19. Security Class (This page)

Unclassified

20. Number of pages

63

21. Price:

1rU.S. Government Printing Office: 1978-778-061/356 Region 8 USCOMM-DC 29716-P73