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—————————— CACI Products Company - http://www.caciasl.com ——————————————————— COMNET III —————————————— 2-1

Day 2 - Network Traffic, Protocols and Packet Switching

Traffic Source Scheduling

Transport Protocols

Node Parameters

Subnetworks & Transit Networks

Exercise 2 - Interconnection of Networks


Network Traffic Sources


Traffic Source Characteristics

Message Source:

– Datagram or connectionless model of data transport

Session Source:

– Virtual circuit or connection-oriented mode of data transport

Response Source:

– Response messages to Message or Session Sources

Traffic Sources are scheduled by either:

– Iteration time– Received message(s)– Triggering event

Every simulation must have at least one time based Traffic Source in it!


Message Source Scheduling


Response Source Scheduling


Session Source Scheduling


Time Based Source Scheduling

Iteration Time

– time from beginning of one execution to the next scheduled iteration

– may be periodic or statistical

First Arrival

– time the first execution is scheduled– may be a constant or statistical distribution– default of none implies a random start time

– uniformly distributed between 0 and a random variate determined by iteration distribution

Last Arrival

– default is none, which means Source runs until the end of the simulation

– stops scheduling, not execution


Message Based Source Scheduling

Traffic Source is activated when the Received Message List is satisfied

The Received Message List contains one or more message texts

The Source will automatically “read” its received message(s) when it starts

Attributes of first message in list (often referred to as the “original message”) can be used by the Source for determining its own properties

Attributes of the “original message”

– Source of original message– Size of original message– Text of original message


Edit Received Message List


Edit Required Message Text


Select Required Message Text


Received Message List


Wildcards

Uses the “*” character to add additional flexibility in scheduling Sources based on Received Message Texts

May be used:

– alone ( “*” ) matches everything

– at the beginning of text ( *Request ) matches everything that ends in the given text

– at the end of text ( Request* ) matches everything that begins with the given text

– at both the beginning and end of text ( *Request* ) matches any name that in any part contains the given text

This makes the Source sensitive to certain categories of messages only

Different Sources on the same Node may be scheduled by different categories of messages


Wildcard Examples

Matches Does not Match

Request A* Request A1 Request B1

Request ANYTHING RequestA5

Request A REQUEST A5

*Request A MY Request A Request A1

Request A REQUEST

ABCD

*Request A* MY Request A5 MY RequestA5

Request A REQUEST A23

NOTE: Leading and trailing spaces are ignored ( e.g. * Request A * )


Edit Required Message


Enter Required Message Text with Wildcard


Source Scheduled by Wildcard Message Text


Received Message Delay


“ECHO” Messages


“ECHO” Messages (continued)


Triggering Event Scheduling


Triggering Event Reference Model


Node Triggers


Select Advanced Tab


Node Triggered Sources


Triggered Source List


Triggered Source Selections


Multiple Selection in a List Box


Edit Triggered Source


Node Triggering Rules


Select Delay Tab


Triggering Delay


Close Triggering Detail


Link Triggers


Link Triggering Rules


Edit Session Source Properties


Session Source Properties


Session Source Triggers


Triggered Source List


Triggered Source Selections


Multiple Selection in a List Box


Session Source Triggering Rules


Triggering Delay


Close Triggering Detail


Weighted List of Triggered Sources


Enter Probability of Triggered Source


Probabilities Must Sum to 1.0


Packet Switched Operation of Enterprise Wide Networks

WAN


Connectionless Network Operation

Packet switching technique using datagrams (e.g. DECNET)

Datagrams are independently routed packets generated by

– Message sources– Session sources– Response sources

Datagrams from the same message may follow different routes and arrive out of order

Packet sequencing and error handling are the responsibility of the end systems

Data Packets

– Datagram

Acknowledgment Packets

– Flow control– Error control


Packet switching technique analogous to public telephone network (e.g., SNA)

Virtual Circuits are established by Session Setup packets

During data transfer, all packets follow a predetermined route

Multiple virtual circuits can have links and/or nodes in common

Data Packets

– Session information packet

Control Packets

– Session setup packet– Session confirm packet– Acknowledgment packet - Session operation

Flow control Error control

Connection Oriented Network Operation


Circuit Switching

DATA TRANSMISSION TIME

SOURCE NODE 1 NODE 2 DESTINATION

SWITCHING DELAY

PROPAGATION DELAY

TIM

E

CALL SETUP DELAY

Call Request

Call Request

Call Request

Call Connected

Data Message A

Dedicated end-to-end channel between communicating parties

Connection setup required

Well-suited for delay-sensitive traffic with long holding times

(e.g., voice)


Message Switching


SWITCHING DELAY

PROPAGATION DELAY TIM

E

Overhead

Data Message A

Overhead

Data Message A

Store-and-forward from source to destination

No dedicated end-to-end channels

Store-and-forward and queuing delays


Packet Switching


TIM

E

Data Message Abroken into 4 Packets

Message switching with an upper limit on the length of transmitted blocks of data

Pipelining reduces store-and-forward delay

Packets may take different routes


Fast Packet Switching


TIM

E

PACKET OVERHEAD

PACKET PROCESSINGTIME

Packet switching with virtual cut-thru

As the packet overhead and processing times shrink to zero, fast-packet switching begins to approach circuit switching


Define Protocol Parameter Sets


Edit Transport Protocols


Copy a Library Selection or Add a New Protocol


Edit Transport Protocol


Transport Protocol Parameters


Packet Parameters

Name

– Used to apply transport protocol to Traffic Sources

Data bytes

– Datagram or Session information packet size before overhead is added

– Size of packet transmitted from end-to-end

Pad to fill packets

– Always transmit full sized packets (I.e. fractional packets are padded)– Specifically designed for modeling ATM which has fixed size cells– Can be applied to the enhanced flow control methods and “None”

Overhead bytes

– Protocol overhead added to packet size– Overhead remains with packet from end-to-end


Packet Parameters (continued)

Protocol ID

– Identifier used for processing times at packet switches– I.e. Processing times at packet switches are a function of the

Protocol ID

Acknowledgments

– Size and priority of acknowledgment packet for both flow control and error control


Protocol ID


User-defined Protocol ID


Error Control


Error Control Parameters

Retransmit blocked packets

– Check box to specify whether or not to retransmit blocked packets– Automatically turned on without option of turning it off for all flow

control methods except “None”

Model error control ack– Modeling an error control acknowledgment packet is optional– Models additional traffic acknowledging receipt of packet– Also permits modeling acknowledgments when there is no flow

control window

Retransmission time (milliseconds)– Timer for retransmission of blocked packets– Timer starts when packet is transmitted


Flow Control


Flow Control Parameters

Window packets (I.e. Window size)

– Used for flow control– After a fixed number of packets related to window size have

been transmitted, must wait for an acknowledgment before resuming transmission

Flow Control Window

– Handshaking mechanism to regulate the flow of traffic between end systems (I.e. source to destination)

– Enhanced Flow Control Windowing methods have parameter sets


Flow Control Windowing Methods


Basic Flow Control

Sliding Window

– Limit the number of in-transit packets to the window size– Acknowledge each packet

Fixed Window

– Transmit a window of packets– Stop and wait for acknowledgment

SNA Pacing

– Initialize a pacing counter to the window size– Decrement the counter by 1 after each packet is transmitted– Increment the counter by the window size whenever an

acknowledgment is received– Transmit only when the pacing counter is positive– Acknowledge only the first packet in a window

None

– Transmit packets without flow control


Enhanced Flow Control

Enhanced Flow Control used for lossy networks

– Enhanced to include receipt of duplicate packets– Provides more retransmission options

Sliding window (Enhanced) and TCP/IP window

– Allows go-back-N for error control– Options to delay acknowledgments at receiver– Adjust timeout by round-trip time and multiple transmissions– TCP/IP window includes the congestion window algorithm

Fixed window (Enhanced) and SNA pacing (Enhanced)

– Allows go-back-N for error control


Rate Control Parameters


Rate Control (continued)

Policing– Mechanism for monitoring burst sizes over an interval to

determine whether or not transmission exceeds burst contract

Rate Control– Regulates the number of packets transmitted in order to

prevent exceeding burst contract


Rate Control Methods


Traffic Policing Methods


Open/Close Sequence Parameters


Accept Transport Protocol Parameters


Close Transport Protocol List


Close Protocol Parameter Sets


Edit Traffic Source


Select Packets Tab


Network Operation Parameters

Transport Protocol

– Packet sizes and traffic constraints for messages

Packetize

– Time to form a packet from this source

Priority

– Priority of packets from this source

Routing Class

– Class of traffic used in routing protocols

Network Service Level

– Maps to data-link or lower-layers services

Apply to all Packet Switched Traffic Sources


Select Transport Protocol


Edit Transport Protocols


Add, Edit, Remove Transport Protocols


Transport Protocols Apply to All Sources of Messages


Packet Switching Nodes


Processing Node Architecture

Propagation Delay

ApplicationSourceQueue

LocalStoragefor Files

PE PE PEProcessingElements

InputQueuing

Delay

PacketProcessing

Delay

OutputQueuing

Delay

Outgoing PacketsIncoming Packets

Transmission Delay


Edit Processing Node Parameters


Add a Processing Node Parameter Set


New Processing Node Parameter Set


Packet Forwarding Parameters

Protocol dependent packet processing times (milliseconds)– protocol dependent time to process a packet regardless of size

Additional Processing/KByte (milliseconds)– size dependent time to process a packet– e.g. Time/Packet = (Processing Time/Kilobyte) * (Packet Size in Kilobytes)

Packet processing uses processor– Off: Without utilization, models non-blocking switching fabrics (I.e. Option

to delay without utilizing the processor– On: With utilization, tasks have to wait for processor

Processing for session setup (milliseconds)– time to process a session source setup packet– typically used for virtual circuit establishment

Session Limit– limits the number of sessions that can use the node


Edit Protocol Dependent Packet Processing Times


Add Packet Processing Time


Packet Processing Time Parameters


Select Routed Protocol ID


Packet Processing Time for Routed Protocol ID


Processing Node Packet Processing Times


Source or Sink Only vs. Virtual Cut-through Nodes


Source or Sink Only vs. Virtual Cut-through Nodes (continued)

Source or sink only

– Traffic can originate and/or terminate only

– Incoming traffic can not be routed to an outgoing link

– “Source or Sink only” specification serves as a constraint in the shortest

path routing calculations

– Group Nodes are always “Source or sink only”

– Switch and Router nodes are never “Source or sink only”

Virtual cut-through

– Cut-through nodes forward packets before the entire packet is received

– Traffic can not originate or terminate at a cut-through node

– Typically applies to a Switch node

– Node may connect only to Point-to-point links of the same speed


Node Processor(s) Parameters


Node Processor(s) Parameters (continued)

Number of processors

– Number of processing elements in node

Application Processing

– Processing Time Per Cycle (microseconds) Used to determine the duration of various kinds of processing e.g. Time/Process = (Processing Time/Cycle) * (Cycles/Process)

Selection rules

– Between applications

– Between applications and packets

– Between packet buffers


Computer Group


Computer Group Architecture

TransmissionDelay

Propagation Delay

InputQueuingDelay

PacketProcessing

Delay

OutputQueuing

Delay

Outgoing Packets from SourceIncoming Packets to Destination



PE PE PEProcessingElements


Computer Group Parameters


Add Computer Group Parameter Set


Number in Group


Network Device


Network Device Architecture

Bus N

Bus 1

ProcessingElements



PE PE PE

InputQueuing

Delay

PacketRoutingDelay

OutputQueuing

Delay

InputQueuing

Delay

OutputQueuing

Delay

PacketRoutingDelay

Internal Bus Delay


Edit Network Device Parameters


Copy a Library Selection or Add a New Parameter Set


Edit Network Device Parameter Set


Packet Forwarding Parameters


Network Device Bus Parameters


Link Port


Node Side Port Properties: Line Card ID


Edit Another Link Port


Line Card ID List


Network Device Port Processing Delays


Edit Network Device Parameter Set


Network Device Port Parameters


Edit Port Processing Times


Add Port Processing Time


Port Processing Time Parameters


Select Link Type


Select Routed Protocol ID


Input and Output Port Delays


Special Case Port Processing Times


Port Default Parameters


Node Buffer Parameters


Edit Port Detail


Port Buffer Parameters


Input Port Buffer Parameters


Buffer Ranking Methods


Buffer Policies


Buffer Policies (continued)

Default

– Packets arriving at a full buffer are blocked (I.e. a buffer without enough

room for the arriving packet)

Preemption

– Packets arriving at a full buffer may preempt packets already there

– Which packets to preempt may be based on priority or discard eligibility

– Discard eligibility applies to frame relay and ATM

Threshold

– Packets arriving at a buffer that has exceeded a predetermined

threshold may be dropped

– Drop decision may be based on priority or discard eligibility


Port Processing Parameters


Open New Model


Select Model-1.c3


Save Model to a New File


New Filename for Model


Select All


Cut Selected Objects


Subnetworks


Resize Subnetwork


Resize Subnetwork (continued)


Edit Subnetwork Properties


Subnetwork Properties


Enter Subnetwork


Title Bar


Paste Local Clipboard Contents


Position Contents and Click


Deselect by Clicking on Background


Network Device


Place Network Device in Subnetwork and Edit Properties


Network Device Properties


Access Point


Place Access Point


Select Connection Tool


Connect Access Point and Leave Subnetwork


Clone Subnetwork


Number of Subnetwork Clones


Position Subnetworks


Select and Drag Access Point


Place Access Point


Token Passing Link


Resize Link and Edit Properties


Select Basic FDDI Link Type


Connect Subnetworks to FDDI Backbone


Transit Network Backbone


Enter Transit Network


Transit Network Topology


Exercise 2 - Interconnection of Networks

Four regional offices are connected via the private packet switching network as shown below. Run this model for one replication of 3600 seconds with a 300 second warmup.


Exercise 2 - Regional Subnetwork

The regional offices consist of 4 workstations (modeled as a computer group) and a router connected to a 10BASE5 Ethernet LAN


Exercise 2 - WAN Router Backbone

The WAN Router Backbone consists of 56 Kbps access links to the routers which are connected to each other over T1 lines.


Exercise 2 - Topology

Create a Computer Group parameter set with 4 computers in the group

Create a Router parameter set that has the following characteristics:

– packet processing time of 0.64 milliseconds per IPX packet

– port processing times for input and output based on ability to process 1000 packets/second for all types of links

(1000 packets per second = 1 ms/packet)

– buffer size of 16000 bytes for both input and output

Use the 56 Kbps library parameter set for the router backbone point-to-point access links and the T1 library parameter set for the point-to-point links connecting the routers to each other.

The link from Router A to Router B fails for 1 minute after each minute of operation.


Exercise 2 - Network Traffic & Operation

Change the destination of the E-Mail messages from Random Neighbor

to Random List with all nodes except the routers in the list. (The routers

will automatically route the traffic to its destination!)

The Client Sessions continue to access the server only.

All traffic sources have a user-defined Transport protocol specified as

follows:

– The maximum packet size is 1024 bytes of user data

– The type of packet is IPX

– The IPX packets also carry 50 bytes of overhead per packet

– Fixed Window flow control is used with a window size of 128

– Flow control acknowledgments are 50 bytes


Multiple Select with Shift Key


Replace Processing Node with Computer Group


Copy Computer Group with Traffic Sources


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