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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

*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

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

CALL SETUP DELAY

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

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

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

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

– 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

– 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

PacketProcessing

OutputQueuing

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

OutputQueuing

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

ProcessingElements

PE PE PE

InputQueuing

PacketRoutingDelay

OutputQueuing

InputQueuing

OutputQueuing

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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