ITEC 275 Computer Networks Switching, Routing, and WANs Week 3
Robert DAndrea Some slides provide by Priscilla Oppenheimer and
used with permission Accuracy is a measurement of lost packets.
This measurement is achieved by keeping track of lost packets while
measuring response time.
Slide 2
Agenda Review Learning Activities Analyzing an Existing Network
Analyzing Traffic in an Existing Network QoS Introduce homework
problems
Slide 3
Whats the Starting Point? According to Abraham Lincoln: If we
could first know where we are and whither we are tending, we could
better judge what to do and how to do it.
Slide 4
Where Are We? When we characterize the infrastructure of a
network, we develop a set of network maps and locate major devices
and network segments. Developing a network map should involve
understanding traffic flow, performance characteristics of network
segments, and insight into where the users are concentrated and the
level of traffic a network design must support. Everything you can
think of to understand your customers network.
Slide 5
Where Are We? Characterize the existing internetwork in terms
of: Its infrastructure Logical structure (modularity, hierarchy,
topology) Physical structure Addressing and naming Wiring and media
Architectural and environmental constraints Health
Slide 6
How to Start? Characterization can start by using a top- down
approach. Starting with a map or set of maps depicting a high-level
abstraction of informatiom Geographical information WAN WAN to LAN
Buildings and floors Rooms containing servers, routers, mainframes,
and switches Virtual information
Slide 7
How to Start? Characterizing large complex networks should
reflect influence from the OSI reference model. A network map
should depict applications and services used by the network users.
Internal and external web sites Email and external data access
entries Ftp operations Printer and file sharing devices DHCP, DNS,
SNMP Router interface names, firewalls, NAT, IDS, and IPS
Slide 8
Get a Network Map Gigabit Ethernet Eugene Ethernet 20 users
Web/FTP server Grants Pass HQ Gigabit Ethernet FEP (Front End
Processor) IBM Mainframe T1 Medford Fast Ethernet 50 users Roseburg
Fast Ethernet 30 users Frame Relay CIR = 56 Kbps DLCI = 5 Frame
Relay CIR = 56 Kbps DLCI = 4 Grants Pass HQ Fast Ethernet 75 users
Internet T1
Slide 9
Characterize Addressing and Naming IP addressing for major
devices, client networks, server networks, private needing
translation, and so on Any addressing oddities, such as
discontinuous subnets? Any strategies for addressing and naming?
Route summarization reduces routes in a router For example, sites
may be named using airport codes San Francisco = SFO, Oakland =
OAK
Slide 10
Discontiguous Subnets Area 1 Subnets 10.108.16.0 - 10.108.31.0
Area 0 Network 192.168.49.0 Area 2 Subnets 10.108.32.0 -
10.108.47.0 Router ARouter B
Slide 11
Characterize the Wiring and Media Single-mode fiber Multi-mode
fiber Shielded twisted pair (STP) copper Unshielded-twisted-pair
(UTP) copper Coaxial cable Microwave Laser Radio Infra-red
Slide 12
Telecommunications Wiring Closet Horizontal Wiring Work-Area
Wiring Wallplate Main Cross-Connect Room (or Main Distribution
Frame) Intermediate Cross-Connect Room (or Intermediate
Distribution Frame) Building A - HeadquartersBuilding B Vertical
Wiring (Building Backbone) Campus Backbone Campus Network
Wiring
Slide 13
Architectural Constraints Make sure the following are
sufficient Air conditioning Heating Ventilation Power Protection
from electromagnetic interference Doors that can lock
Slide 14
Architectural Constraints ParameterCopper Twisted PairMM
FiberSM FiberWireless DistanceUp to 100 meters Up to 2 kilometers
(Fast Ethernet) Up to 550 m (Gigabit Ethernet) Up to 300 m (10
Gigabit Ethernet) Up to 10 km (Fast Ethernet) Up to 5 km (Gigabit
Ethernet) Up to 80 km (10 Gigabit Ethernet) Up to 500 m at 1 Mbps
Bandwidth Up to 10 Gigabits per second (Gbps) Up to 10 Gbps Up to
10 Gbps or higher Up to 54 Mbps PriceInexpensiveModerate Moderate
to expensive Moderate DeploymentWiring closetInternode or
interbuilding
Slide 15
Architectural Constraints Make sure theres space for: Cabling
conduits Patch panels Equipment racks Work areas for technicians
installing and troubleshooting equipment
Slide 16
Wireless Installation Inspect the architecture and environment
constraints of the site to determining the feasibility of a
wireless transmission. Wireless transmission is RF (radio
frequency) A wireless expert should be hired Network designers can
install access points will be located and where the people
concentration will be located Access point is based on signal loss
between the access point and the user of the access point.
Slide 17
RF Phenomena Wireless Installations Reflection causes the
signal to bounce back on itself. Absorption occurs as the signal
passes through materials Refraction is when a signal passes through
one medium of one density and then through another medium of
another density. Signal will bend. Diffraction when a signal can
pass in part through a medium more easily in one part than
another
Slide 18
RF Phenomena Wireless Installations A wireless Site Survey
should be performed on the existing network for signal propagation,
strength, and accuracy in different areas. NIC cards ship with
utilities on them to measure signal strength Signal strength can be
determined using a protocol analyzer Access points send beacon
frames every 100 milliseconds (ms). Use a protocol analyzer to
analyze the signal strength being emitted from the different grid
locations of the access points.
Slide 19
RF Phenomena Wireless Installations - Use a protocol analyzer
to capture CRC errors. These errors stem from corruption and
collisions. - Observe if frames are being lost in transmission -
Observe the acknowledgment (ACK) and frame retries after a missing
ACK. ACK is called a control frame. Clients and access points use
them to implement a retransmission mechanism
Slide 20
RF Phenomena Wireless Installations Wired Ethernet Detects
collisions through CSMA/CD (802.11) Ethernet uses CSMA/CA as the
access method to gain access of the wire. An ACK control frame is
returned to a sender for packet received. If a frame does not
receive an ACK, it is retransmitted.
Slide 21
Check the Health of the Existing Internetwork Baseline network
performance with sufficient time and at a typical time Baseline
availability gather information from the customer on MTBF and MTTR
Baseline bandwidth utilization during a specific time frame. This
is usually a percentage of capacity. Accuracy is an upper layer
protocols responsibility. A frame with a bad CRC is dropped and
retransmitted. A good threshold rule for handling errors is that
there should be no more than one bad frame per megabyte of
data.
Slide 22
Check the Health of the Existing Internetwork - Accuracy is a
measurement of lost packets. This measurement is achieved by
keeping track of lost packets while measuring response time.
-Switches have replaced hubs. - There should be fewer than 0.1
percent of frames encounter collisions. - There should be no late
collisions. Indicate bad cabling, cabling longer than 100 meters,
bad NIC, or duplex mismatch.
Slide 23
Check the Health of the Existing Internetwork - Autonegotiation
has received its share of critism in the past for being inaccurate
when setting up a point-to-point link half duplex and full duplex.
- Autonegotiation of speed is usually not a problem. If set up
incorrectly, it does not work. The speeds are 10 Mbps, 100 Mbps, or
1000 Mbps.
Slide 24
Check the Health of the Existing Internetwork - Category 3
cable will support 10MBps, but not 100 MBps and higher. Errors
increase. Efficiency is linked to large frame sizes. Bandwidth
utilization is optimized for efficiency when applications and
protocols are in large sized frames. Change window sizes on clients
and servers. Increasing maximum transmission unit (MTU). Able to
ping and telnet but not be able to send HTTP, and FTP. A hump exist
on the sides of the average transmission. Runt frames (less than 64
bytes) are a result of collisions on the same shared Ethernet
segment.
Slide 25
Check the Health of the Existing Internetwork Response time can
be measured using the round-trip time (RTT)ping command. Observe
response time on a user workstation. Run typical applications to
get a response. Response time for network services protocols, such
as, DHCP and DNS. Status of major routers, switches, and
firewalls
Slide 26
Characterize Availability Enterprise Segment 1 Segment 2
Segment n MTBFMTTR Date and Duration of Last Major Downtime Cause
of Last Major Downtime Fix for Last Major Downtime
Characterize Response Time Node A Node B Node C Node D Node
ANode BNode CNode D X X X X
Slide 32
Check the Status of Major Routers, Switches, and Firewalls Show
buffers Show environment Show interfaces Show memory Show processes
Show running-config Show version
Traffic Flow for Voice over IP The flow associated with
transmitting the audio voice is separate from the flows associated
with call setup and teardown. The flow for transmitting the digital
voice is essentially peer-to-peer. Call setup and teardown is a
client/server flow A phone needs to talk to a server or phone
switch that understands phone numbers, IP addresses, capabilities
negotiation, and so on.
Slide 41
Network Applications Traffic Characteristics Name of
Application Type of Traffic Flow Protocol(s) Used by Application
User Communities That Use the Application Data Stores (Servers,
Hosts, and so on) Approximate Bandwidth Requirements QoS
Requirements
Slide 42
Traffic Load To calculate whether capacity is sufficient, you
should know: The number of stations The average time that a station
is idle between sending frames The time required to transmit a
message once medium access is gained That level of detailed
information can be hard to gather, however.
Slide 43
Size of Objects on Networks Terminal screen: 4 Kbytes Simple
e-mail: 10 Kbytes Simple web page: 50 Kbytes High-quality image:
50,000 Kbytes Database backup: 1,000,000 Kbytes or more
Slide 44
Traffic Behavior Broadcasts All ones data-link layer
destination address FF: FF: FF: FF: FF: FF Doesnt necessarily use
huge amounts of bandwidth But does disturb every CPU in the
broadcast domain Multicasts First bit sent is a one
01:00:0C:CC:CC:CC (Cisco Discovery Protocol) Should just disturb
NICs that have registered to receive it Requires multicast routing
protocol on internetworks
Slide 45
Network Efficiency Frame size Protocol interaction Windowing
and flow control Error-recovery mechanisms
Slide 46
QoS Requirements ATM service specifications Constant bit rate
(CBR) Realtime variable bit rate (rt-VBR) Non-realtime variable bit
rate (nrt-VBR) Unspecified bit rate (UBR) Available bit rate (ABR)
Guaranteed frame rate (GFR)
Slide 47
QoS Requirements per IETF IETF (Internet Engineering Task
Force) IETF integrated services working group specifications
Controlled load service Provides client data flow with a QoS
closely approximating the QoS that same flow would receive on an
unloaded network Guaranteed service Provides firm (mathematically
provable) bounds on end-to-end packet-queuing delays
Slide 48
QoS Requirements per IETF IETF differentiated services working
group specifications RFC 2475 IP packets can be marked with a
differentiated services code point (DSCP) to influence queuing and
packet-dropping decisions for IP datagrams on an output interface
of a router.
Slide 49
Summary Characterize the existing internetwork before designing
enhancements. Helps you verify that a customers design goals are
realistic. Helps you locate where new equipment will be placed.
Helps you cover yourself if the new network has problems due to
unresolved problems in the old network.
Slide 50
Summary Continue to use a systematic, top-down approach Dont
select products until you understand network traffic in terms of:
Flow Load Behavior QoS requirements
Slide 51
Review Questions What factors will help you decide if the
existing internetwork is in good enough shape to support new
enhancements? When considering protocol behavior, what is the
difference between relative network utilization and absolute
network utilization? Why should you characterize the logical
structure of an internetwork and not just the physical structure?
What architectural and environmental factors should you consider
for a new wireless installation?
Slide 52
Review Questions List and describe six different types of
traffic flows. What makes traffic flow in voice over IP networks
challenging to characterize and plan for? Why should you be
concerned about broadcast traffic? How do ATM and IETF
specifications for QoS differ?
Slide 53
This Weeks Outcomes Analyzing an Existing Network Analyzing
Traffic in an Existing Network QoS
Slide 54
Due this week 2-1 Concept questions 2
Slide 55
Next week 3-1 Concept questions 3 FranklinLive session 4 Ensure
you have the VMware View Client installed Examine the MIMIC
simulator software