Contents Telektronikk - Telenor

130
LAN Interconnection Traffic Measurements
BY SIGMUND GAAREN
1 Introduction
Interconnection of geographically separated
LANs (Local Area Networks) is expected
to be one of the most important
applications for existing and future pub-
List of abbreviations
and acronyms
ATM Asynchronous Transfer Mode
BPS Bits Per Second
CAD Computer Aided Design
CMIP Communications Management Information
Protocol
CoV Coefficient of Variation
FDDI Fiber Distributed Data Interface
FM Foundation Manager
FTP File Transfer Protocol
IAT InterArrival Time
ICMP Internet Control Message Protocol
IGRP Interior Gateway Routing Protocol
IP Internet Protocol
IPX Internetwork Packet eXchange
ISO International Standards Organization
LAN Local Area Network
LL Leased Lines
LLC Logical Link Control
MAC Medium Access Control
ms milliseconds
NCP Netware Core Protocol
NetBEUI NetBIOS Extended User Interface
NetBIOS Network Basic Input Output System
NFS Network File System
OS Operating System
OSI Open Systems Interconnect
OSPF Open Shortest Path First
PC Personal Computer
PPP Point-to-Point Protocol
RIP Routing Information Protocol
SDLC Synchronous Data Link Control
SMTP Simple Mail Transfer Protocol
SNA System Network Architecture
SNMP Simple Network Management Protocol
SPX Sequenced Packet eXchange
TCP Transmission Control Protocol
TMN Telecommunications Management Network
TR Token Ring
UDP User Datagram Protocol
WAN Wide Area Network
XNS Xerox Network Systems
XWin XWindows
lic data networks. This article presents
the results from LAN interconnections
traffic measurements at a selection of 12
different LANs; nine customers’ sites
and three Telenor sites.
Information about the data traffic flowing
in and out of LANs is needed for optimizing
the WAN (Wide Area Network)
capacity usage, and, hence, reduce customers’
LAN-LAN transmission costs.
The choice of appropriate services and
capacities for LAN interconnections
should be aided by measurements in
order to tell the customer exactly which
product that best suits each specific LAN
communications demand.
Previous LAN traffic analyses have concentrated
on the dynamics of internal
data flow on universities’ and research
laboratories’ local networks. The measurements
in this article were conducted
from January to May 1994, and will provide
information about the data traffic for
the heaviest users of LAN interconnection
services in Norway.
The main objectives for this investigation
of the data traffic characteristics on LAN
interconnections were:
- Identification and description of LAN
categories and their demands for
WAN transmission capabilities
- Recognition of the LAN interconnection
protocols, on OSI layers 3 to 7, in
use; and their per centage occurrences
and frame sizes
- Evaluation of the LAN interconnection
utilization and traffic patterns on different
time scales.
2 Measurement technique
and set-up
This section will provide a brief introduction
to the measurement technicalities
and set-up, and the limitations of the
measurement procedure. For more detailed
information about the measurement
methodology, please consult [2].
2.1 Definitions and
requirements
The LAN as a whole is defined as the
source and sink for the traffic for the traffic
coming in to and going out of the
LAN. In order to understand the LANs as
source and sink for data traffic, information
about applications, usage and location
of shared facilities (e.g. servers)
were obtained by interviews with LAN
managers.
The following metrics were measured:
- bits per second
- frames per second
- frame length in bytes
- frame interarrival time (IAT) in milliseconds
- per centage external traffic relative to
total internal LAN traffic
- per centage occurrence of 24 LANprotocols
on OSI layer 3, 4 and 7
- number of erroneous frames.
The frame interarrival time is defined as
the time gap between arrivals of two
adjacent frames. All the metrics are further
explained in [2]. Figure 4.1 in Section
4.1 contains all detected protocols.
A data traffic file was generated per day
and per direction. WAN-links are offered
with bi-directional data transfer capabilities;
therefore, one file per traffic direction,
LAN incoming and LAN outgoing
traffic, was required. Also, protocol summary
and frame size distribution files
were generated once per day.
The protocol analyser should not corrupt
the transmitted data, generate any traffic,
or lose any frames.
2.2 Tool and observation point
Since the LAN interconnection traffic
data were captured at many different
types of networks for shorter periods of
time, an IP software monitor, e.g. nnstat,
etherfind or tcpdump, was considered
unsuitable for this purpose.
Due to the limitations in OSI layer 4 and
7 decoding, interarrival time detection,
and separation of incoming and outgoing
traffic in available WAN analysers, a
LAN protocol analyser was employed.
The chosen protocol analyser is a Foundation
Manager from ProTools, which is
an OS/2 portable computer, fitted with a
specially designed traffic measurement
software, and Ethernet and Token Ring
interfaces. Figure 2.1 illustrates the
observation point from which the data
traffic was captured at customers’ sites.
Since the external traffic is bound to go
through the router, the LAN interconnection
traffic was extracted by filtering out
all other MAC frames except the frames
to and from the router. All frames with
the router’s MAC address as source is
defined as incoming traffic, depicted as
‘in’ in Figure 2.1. Consequently, all