ANALYSIS AND DESIGN

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24 Οκτ 2013 (πριν από 3 χρόνια και 5 μήνες)

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CIS460


NETWORK
ANALYSIS AND DESIGN

CHAPTER 10

Selecting Technologies and Devices
for Enterprise Networks

Introduction


We are going to look at the technologies for remote
-
access and WAN components of an enterprise
network design


We will talk about physical and data link layer
protocols and enterprise network devices such as
remote
-
access servers, routers and WAN switches


What you select will depend on bandwidth and
quality of service requirements, network topology,
business requirements and constraints and technical
goals


Remote Access Technologies


Have become a more important ingredient
of many network designs


It is important to recognize the location and
number of full and part time telecommuters
and the extent that mobile users need to
access the network


How often and amount of time on the
network will drive what you give them

Point
-
to
-
Point Protocol


Standard data
-
link
-
layer protocol for
transporting various network
-
layer
protocols across serial, point
-
to
-
point links


Can be used for a single user or a group


can be used with ISDN, analog lines, digital
leased line, and other WAN technologies

Point
-
to
-
Point Protocol (Cont’d)


Provides following services: Network
-
layer protocol
multiplexing, link configuration, link quality testing,
link
-
option negotiation, authentication, header
compression and error detection


Four functional layers:


Physical layer


encapsulation of network
-
layer datagrams


Link Control Protocol


Network Control Protocols

Multilink PPP and Multichassis
Multilink PPP


Adds support for channel aggregation to
PPP which can be used for load
-
balancing
and providing extra bandwidth


MPPP ensures packets arrive in order


Multichassis is a Cisco enhancement to
MPPP that allows channel aggregation
across multi
-
remote
-
access servers at a
central site

Multilink PPP and Multichassis
Multilink PPP (Cont’d)


Multichassis MPPP allows multiple access
servers to be grouped into a single stack group


Uses Stack Group Bidding Protocol (SGBP)
to elect a server to handle aggregation for an
application


SGBP can be weighted so that CPU intensive
process are offloaded to routers designated as
offload servers


Password Authentication Protocol and
Challenge Handshake Authentication
Protocol


Supports both PAP and CHAP authentication


CHAP is more secure than PAP. PAP can be
used if remote station does not support CHAP


CHAP is superior. PAP sends password in
plain text. An intruder can use a protocol
analyzer to capture and use it


CHAP uses a connect, challenge, hashed
response and accept/deny reply

Integrated Services Digital
Network


PPP is often used with ISDN since it provides
data encapsulation, link integrity and
authentication for ISDN


Cost effective solution for high transmission
speed and quick connection requirements


Charge is a basic monthly fee and a usage time
charge


MPPP can be used to aggregate ISDN channels

ISDN Components


Terminal equipment type 1 (TE1)(compliant)


Non
-
ISDN terminal equipment Type 2 (TE2)
(non compliant)


NT1 devices (physical
-
layer & connect user)


NT2 devices (Layer 2 and 3 protocols)


Reference point interfaces

Cable Modem Remote Access


Another option that uses coax cable used for
cable TV


Much faster than analog and usually faster
than ISDN


some cable
-
network service providers offer
hybrid fiber/coax (HFC) systems that
connect CATV networks to the service
-
providers high
-
speed fiber
-
optic network

Challenges Associated with
Cable Modem Systems


It’s a new technology and there are many
standards that do not interoperate with each
other


the CATV infrastructure is designed for TV
signals in one direction


Usually more bandwidth is offered
downstream than upstream


Number of users on system

Digital Subscriber Line Remote
Access


Growing in popularity with home users


Have to use a DSL modem or other device


DSL uses sophisticated modulation schemes
to offer much higher speeds than ISDN,
32Mbps for downstream traffic and 15Kbps
to 1.5 Mbps for upstream


Comes in different flavors (ADSL, HDSL,
VDSL, SDSL, RADSL, IDSL, and CDSL)

Asymmetric Digital Subscriber
Line


Has three channels


high
-
speed downstream from 1.5 to 9 Mbps


medium speed duplex from 16 Kbps to 640
Kbps


POTS 64 Kbps channel for voice

High
-
Bit
-
Rate Digital Subscriber
Line


Provides same upstream and downstream


1.544 over 2 wire pair or 2.048 Mbps over 3
wire pairs


Has a 12,000 to 15,000 operating distance
which is shorter than ADSL’s 18,000 feet


Telco can install repeaters for a price

Selecting Devices for Remote
Users


Users using for less than 2 hours a day can
use an analog modem


Before selecting a modem read reviews for
reliability, interoperability with other brands
of modems, interoperability with typical
services, speed and throughput, latency,
ease of setup, support for advanced features
and cost


Selecting Devices for Remote
Users (Cont’d)


Faster access requires cable modems, DSL
or a small router that has an ISDN or other
type of WAN port


for a router look at: protocol support,
support for a remote user or remote LAN,
channel aggregation, ease of configuration,
security, reliability, interoperability and cost


Selecting Devices for the Central
Site


Generally includes remote access servers.
Five types of services


Remote node services
-

various devices


Terminal services
-

Telnet, rlongin X.25, etc


Protocol translation services
-

access hosts


Asynchronous routing services
-

layer 3
routing functionality


Dialout services
-

share access server modems

Selecting Devices for the Central
Site (Cont’d)


Additional criteria


number of ports and type


support for services


configuration flexibility and modularity


support for network address translation (NAT)
or port address translation (PAT) for hosts on
remote networks, Dynamic Host Configuration
Protocol and multimedia features and protocols

WAN Technologies


Variety of common and established WAN
technologies


Newer technologies are growing such as
Wireless WAN


Low
-
orbit satellite, cellular and radio
-
frequency wireless will probably become
popular option of voice, pager and data
services

Systems for Provisioning WAN
Bandwidth


Must select correct bandwidth
required.Varies depending on location.
Europe uses 30 B
-
channels and 1 d
-
channel
for admin purposes, the U.S. uses 24 b
-
channels and 1 d
-
channel for admin
purposes


the number of digital streams multiplexed
together determine network speed

Leased Lines


A dedicated circuit that a customer leases
from a carrier for a predetermined amount
to time usually for months or years


line is dedicated to that customer


Mature and are proven technology


Dedicated to a single customer


Synchronous Optical Network


Physical layer specification for high
-
speed
synchronous transmission of packets or cells
over fiber
-
optic cabling


can be ATM or packet
-
based networks


provides more sophisticated multiplexing and
demultiplexing of individual signals


4 layer protocol stack
-

photonic layer, section
layer, line layer and path layer


Usually connected in a ring topology

Switched Multimegabit Data
Service


SMDS is a physical and data link layer WAN
technology alternative to leased lines which
runs on fiber or copper media


usually positioned as a high
-
speed, low
-
latency, cost effective solution for connecting
LANs and MANs over a cell relay WAN


can have just one physical connection to the
service provider’s network

Frame Relay


High
-
performance WAN protocol that
operates at the physical and data
-
link layers
of OSI


offers a cost
-
effective method for
connecting remote sites typically at speeds
from 64Kbps to 1.544 Mbps


it is efficient, flexible and has low latency

Frame Relay Hub
-
and
-
Spoke
Topologies and Subinterfaces


Frame relay is often designed in hub and spoke
topology


A central site router can have many logical
connections to remote sites with only one
physical connection to the WAN


One problem is that split horizon can limit
routing. Distance vector routing protocols do
not repeat information out the interface it was
received on

Frame Relay Hub
-
and
-
Spoke Topologies
and Subinterfaces (Cont’d)


A solution to split
-
horizon is to use a full
-
mesh
design with physical circuits between each site


use subinterface which is a logical interface that
is associated with a physical interface. The
router then applies the split horizon rule based
on logical interfaces instead of physical ones


Downside is that router configurations are more
complex

Frame Relay Congestion Control
Mechanisms


A frame relay device has the ability to
transmit data at its physical access rate for
extended periods of time


Includes congestion control mechanisms to
ensure fair bandwidth allocation and
feedback mechanisms


Forward
-
explicit congestion notification


Backward
-
explicit congestion notification


Frame Relay Bandwidth
Allocation


Most frame relay networks provides some
guarantee of band width availability


Committed information rate (CIR) is the
guarantee


At or below CIR will accept it


Leaky bucket


some providers offer zero CIR (inexpensive)
only make a best effort

Frame Relay/ATM Interworking


As ATM gains popularity WANs that use both
ATM and Frame Relay technologies are
becoming more popular


Frame Relay/ATM Interworking is used to
describe the protocols and processes for
connecting ATM and Frame Relay WANs


With network interworking 2 or more frame relay
networks are connected via an ATM core network


With service interworking an ATM network
connects to a Frame Relay network

ATM Wide Area Networks


Support ver high bandwidth requirements


copper cabling T3 or above


Fiber optic
-

speed up to 9.952 Gbps and beyond


Facilitates efficient sharing of bandwidth among
applications with various QoS requirements


Save money spent on monthly tariffs for WAN
circuits

Selecting Devices and Service Providers
for an Enterprise WAN Design


An enterprise WAN design is based on
high
-
performance routers and WAN
switches

Selecting Routers for an
Enterprise WAN Design


High throughput, high availability and
advanced features to optimize the utilization of
expensive WAN circuits


select to support bandwidth requirements,
appropriate packets
-
per
-
second level and
adequate memory and processing power to
forward data and handle routing protocols


Also provide advanced features such as
advanced switching and queuing techniques,
traffic shaping express forwarding


Selecting WAN Switches for an
Enterprise WAN Design


Multiservice WAN switches that handle ATM,
Frame Relay and remote
-
access technologies
are gaining in popularity


support a variety of data types, interfaces and
services and optimize bandwidth utilization


Intelligent queue
-
handling algorithms that take
into account the behavior of different types of
applications


Reallocate buffers as needed

Selecting a WAN Service
Provider


Cost of service but may not be the most
important


extent of services and technologies offered


geographical areas covered


reliability and performance characteristics of
providers internal network


level of security offered


level of technical support

Selecting a WAN Service
Provider (Cont’d)


Characteristics of provider’s network:


physical routing of network links


redundancy


extend relies on other providers for redundancy


level of over subscription


bandwidth allocation mechanisms for QoS

Selecting a WAN Service
Provider (Cont’d)


types of switches and optimization features


frequency and typical causes of outages


security methods from intrusion


security methods for privacy


disaster recovery plans

Selecting a WAN Service
Provider (Cont’d)


Service Level Support Agreements (SLAs)


experience level of installation and support staff


experience with your particular protocols and
applications


dedicated single
-
point of contact


received ISO 9002 certification


How difficult to provision and price new services


Offer a customer training program

Summary


There are many options of LANs and WANs


No single technology or device is the right
answer for all circumstances


The physical design depends on business
objectives, technical requirements, traffic
characteristics, and traffic flows


The physical design builds on the logical
design