Transcript Week_Ten_Network_ppt

ITEC 275
Computer Networks – Switching,
Routing, and WANs
Week 10
Robert D’Andrea
2015
Agenda
• Learning Activities
• PPP
• Cable Modems and DSL
• Leased Lines, SONET, Frame Relay,
Metro Ethernet, ATM
• Selecting a WAN Service Provider
• Metro Ethernet
Enterprise Technologies and Devices
• Remote access networks
• Wide area networks (WANs)
• Devices
– End user remote access devices
– Central site remote access devices
– VPN concentrators
– Routers
Selection Criteria
•
•
•
•
•
•
•
Business requirements and constraints
Cost
Technical goals
Bandwidth requirements
QoS requirements
Network topology
Traffic flow and load
Remote Access Technologies
•
•
•
•
The Point-to-Point Protocol (PPP)
Integrated Services Digital Network (ISDN)
Cable modems
Digital Subscriber Line (DSL)
Point-to-Point Protocol (PPP)
• PPP is used with synchronous, asynchronous,
dial-up, and ISDN links
• Defines an encapsulation scheme for transport
of different network-layer protocols
• Supports authentication:
– Password Authentication Protocol (PAP)
– Challenge Handshake Authentication Protocol
(CHAP). CHAP more secure than PAP
Point-to-Point Protocol (PPP)
• The Internet Engineering Task Force (IETF)
developed PPP as a standard data link layer
protocol for transporting various protocols
across serial, point-to-point links.
• PPP can be used to create point-to-point links
between different vendor’s equipment.
• PPP uses a Network Control Protocol field in
the Data Link header to identify the Network
layer protocol.
Point-to-Point Protocol (PPP)
• PPP can be used to connect a single remote
user to a central office, or to connect a remote
office with many users to a central office.
• PPP is a data-link protocol that can be used
over either asynchronous serial (dial-up) or
synchronous serial (ISDN) media and that uses
the LCP (Link Control Protocol) to build and
maintain data-link connections.
PPP Layers
Network Control Protocol (NCP)
Link Control Protocol (LCP)
Encapsulation based on
High-Level Data-Link Control Protocol (HDLC)
Physical Layer
PPP
Point-to-Point (PPP) is a data link protocol
commonly used in establishing a direct
connection between two networking nodes. It
provides connection authentication, transmission
authentication, and compression.
PPP is used over many types of physical
networks including serial cable, phone line, trunk
line, cellular telephone, and fiber optic links such
as SONET. PPP is also used over the Internet
access connections (broadband).
PPP
Leased Line
PPP, HDLC
Packet Switching
Frame Relay, X.25,
ATM
Circuit Switching
PPP, HDLC
PPP
Metro Ethernet
Ethernet
Broadband
PPPoE, PPPoA,
Ethernet
PPP
Leased lines: ISP is the service provider. PPP protocol.
The user does not want to share the wire or the expense
of leasing a wire with another user.
Packet Switching: Telco is the service provider. Frame
Relay protocol.
The user shares the service with other users to save
money. Frame Relay is an alternate technology to PPP.
Circuit Switching: Pots or ISDN are the service
providers. PPP protocol.
Data is sent encapsulated over the public
telephone network system.
PPP
Metro Ethernet: Telco is the service provider. Ethernet
protocol.
The user wants the data sent at a very high speed.
Broadband: Telco is the service provider. PPPoE,
PPPoA, Ethernet protocols.
PPP
PPP encapsulation includes:
1. Line set up using LCP. The link is established
during this phase.
2. Authentication, encryption and compression
(optional).
2.1 Password Authentication Protocol
(PAP) Avoid using PAP because it sends the password in
ASCII format (clear text).
2.2 Challenge Handshake Authentication
Protocol (CHAP) never sends the password, but sends a
challenged handshake processes.
PPP
3. PPP carries packets from many different
protocol suites using NCP. The NCP sends packets to
negotiate the needed settings.
Is all data encrypted?
No
Encryption is used to simply verify the passwords.
Multilink MPPP
An ordinary dial-up modem connection to the
Internet through an Internet service provider (ISP)
usually uses PPP as its wide area network (WAN) datalink protocol, but there are times when the 56-Kbps
speed provided by V.90 modems is insufficient. MPPP
allows multiple physical dial-up links to be inverse
multiplexed together to form a single high-bandwidth
logical PPP connection between the dial-up client and
the ISP. MPPP works by ordering the data frames from
the client across the multiple PPP channels and
recombining them at the ISP’s termination point, and
vice versa.
Multilink MPPP
MPPP defines protocols for splitting the data
stream into PPP packets, sequencing the packets,
transmitting them over separate logical data links, and
then recombining them at the receiving station.
Multilink MPPP
Inverse multiplexing speeds up data transmission
by dividing a data stream into multiple concurrent
streams that are transmitted at the same time across
separate channels (such as a T-1 or E-1 lines) and are
then reconstructed at the other end back into the original
data stream. Just the reverse of ordinary multiplexing ,
which combines multiple signals into a single signal,
inverse multiplexing is a technique commonly used
where data in a high-speed local area network (LAN)
flows back and forth into a wide area network (WAN)
across the "bottleneck" of a slower line such as a T-1
(1.544 Mbps).
Multilink MPPP
Various multiplexing methods are possible in
terms of the channel bandwidth and time, and the signal,
in particular the frequency, phase or time. The two basic
methods are:
• Frequency Division Multiplexing (FDM) is derived
from AM techniques in which the signals occupy the
same physical ‘line’ but in different frequency bands.
Each signal occupies its own specific band of
frequencies all the time, i.e. the messages share the
channel bandwidth.
Multilink MPPP
•
Time Division Multiplexing (TDM ) is derived
from sampling techniques in which messages occupy
all the channel bandwidth but for short time intervals
of time, i.e. the messages share the channel time.
Multilink MPPP
Multilink MPPP
• Adds support for channel aggregation fo PPP.
Channel aggregation can be used for load
sharing and providing extra bandwidth. With
channel aggregation, a device can
automatically bring up additional channels as
bandwidth requirements increase.
• MPPP ensures that packets arrive in order at
the receiving device.
Multi-chassis MPPP
Cisco’s enhancement to PPP is MPPP.
MPPP allows WAN administrator to group
multiple access servers into a single stack group.
The user’s traffic can be split and reassembled
across multiple access servers in the stack group.
Multi-chassis Multilink PPP
Stack group
ISDN
Analog
Offload
server
CHAP
CHAP provides a three-way hand-shake.
Provides protection by verifying a remote node
with a three-way hand shake and a variable
challenge value that is unique and unpredictable.
CHAP
Remote Node
Access Server
Connect
Name: 760_1
Password: sfy45
Challenge
Hashed Response
Accept or Deny
Database of
Users and
Passwords
Name: 760_1
Password: sfy45
Name: 760_2
Password: kingsford
ISDN
• Digital data-transport service offered by regional
telephone carriers (Telcos).
• Circuit-switched service that carries voice and data.
• ISDN is a set of digital services that transmits voice
and data over existing phone lines.
• Cost-effective remote-access solution for
telecommuters and remote offices
– Cost of an ISDN circuit is usually based on a
monthly fee plus usage time
• Good choice as a backup link for another type of link,
for example, Frame Relay.
• Channel aggregation is popular with ISDN links.
ISDN Interfaces
Basic Rate Interface (BRI)
2B
64 Kbps
64 Kbps
D
16 Kbps
}
144
Kbps
Primary Rate Interface (PRI)
23B or 30B
D
64 Kbps
64 Kbps
}
1.544 Mbps in U.S.
2.048 Mbps in
Europe
ISDN Components
Non-ISDN
device
(TE2)
R
S/T
ISDN
device
(TE1)
NT1
TA
ISDN
device
(TE1)
U
4-wire
circuit
2-wire
circuit
S/T
U
NT1
S
T
NT2
U
NT1
U
ISDN device (TE1)
with built-in NT1
NT1
To ISDN
service
To ISDN
service
To ISDN
service
To ISDN
service
Cable TV Service
CATV (originally "community antenna television,"
now often "community access television") is more
commonly known as "cable TV." Television programs
were brought to millions of people throughout the world
who were connected to a community antenna, cable TV.
Today, CATV has become an increasingly popular
way to interact with the World Wide Web and other new
forms of multimedia information and entertainment
services.
Cable TV Service
• Operates over the coax cable used by cable TV
providers
• Much faster than analog modems, and usually
much faster than ISDN (depending on how
many users share the cable)
– 25 to 50 Mbps downstream from the head end
– 2 to 3 Mbps upstream from end users
• Standard = Data Over Cable Service Interface
Specification (DOCSIS)
Cable TV Service
• Coax Cable does not require dial-up.
• Cable modem operates more like a LAN.
• Cable-network providers offer hybrid fiber/coax
(HFC) systems that connect CATV networks to
the service provider’s high-speed fiber-optic
network.
• HFC systems allow connections of home PCs
and small LANs to high-speed access to the
Internet or to a private network using VPN.
Cable TV Service
• CATV (Cable Modem Termination System)
provides high-speed connectivity for cable
modems.
• Cable modem solution for remote users or
remote offices is the sharing a single cable and
the types of applications they use.
DSL
• High-speed digital data traffic over ordinary
telephone wires.
• Sophisticated modulation schemes mean
higher speeds than ISDN.
– Speeds range from 1.544 to 9 Mbps
• Actual bandwidth depends on type of DSL
service, DSL modem, and many physical-layer
factors.
• Symmetric communication (SDSL) traffic flow
travels at the same speed up to 1.544 Mbps.
• Asymmetric DSL (ADSL) very popular
– Downstream faster than upstream
PPP and ADSL
Asymmetric DSL (ADSL) uses two
popular PPP implementations.
1. PPP and ATM (PPPoA) the CPE
acts as an Ethernet-to-WAN router and the
PPP session is established between the
CPE and Layer 3 access concentrator in
the service provider’s network.
2. PPP and Ethernet (PPPoE) the
CPE acts as an Ethernet-to-WAN bridge.
PPP and ADSL
PPP and Ethernet (PPPoE) the CPE acts
as an Ethernet-to-WAN bridge. The client
initiates a PPP session by encapsulating PPP
frames in MAC frames and then bridging the
frames over ATM/DSL to a gateway router at
the service provider. From that point, the PPP
session can be established, authenticated, and
achieved. The client receives its IP address
from the service provider, using PPP
negotiation.
Provisioning WAN Bandwidth
• A critical network design is considering
capacity requirements. Selecting the right
amount of capacity for current and future
needs.
• Provisioning requires an analysis of traffic
flows, and analysis of scalability goals.
WAN Technologies
•
•
•
•
Leased lines
Synchronous Optical Network (SONET)
Frame Relay
Asynchronous Transfer Mode (ATM)
Leased Lines
• Dedicated digital, copper circuits that a
customer leases from a carrier for a
predetermined amount of time, usually for
months or years.
• Speeds range from 64 Kbps to 45 Mbps.
• Enterprises use leased lines for both voice
and data traffic.
Leased Lines
• Dedicated connection or Point-to-Point
connection.
• Pre-established WAN communications path
from the Customer Premise Equipment
(CPE) , through the Data Communications
Equipment (DCE) switch, to the CPE of the
remote site, then allowing Data Terminal
Equipment (DTE) networks to communicate
at anytime with no set up procedure before
transmitting data.
DTE and DCE
The end instrument is a piece of
equipment connected to the wires at the end of
a telecommunication link. End instruments
that relate to data terminal equipment (DTE)
include printers, computers, barcode readers,
automated teller machines (ATMs) and the
console ports of routers.
DTE and DCE
The data communication(s) equipment
(DCE) is a device that sits between the DTE
and a data transmission circuit.
The DCE performs functions such as
signal conversion, line clocking, and coding.
The DTE/DCE classification was
introduced by IBM.
Digital Signal (DS)
A channel in the NADH (North
American Digital Hierarchy) is called a digital
signal (DS). Digital signals are multiplexed
together to form high-speed WAN circuits.
DS-1 and DS-3 are the most commonly used
capacities.
The North American Digital
Hierarchy
Synchronous Optical Network (SONET)
Synchronous Optical Network (SONET) is
the American National Standards Institute
standard for synchronous data transmission on
optical
SDH (Synchronous Digital Hierarchy) is a
standard technology for synchronous data
transmission on optical media.
Synchronous Optical Network (SONET)
• Physical-layer specification for high-speed
synchronous transmission of packets or cells
over fiber-optic cabling.
• Service providers and carriers make wide use
of SONET in their internal networks.
• Gaining popularity within private networks.
Synchronous Optical Network (SONET)
Goals of SONET and SDH
1. Define higher speeds than the ones used
by the NADH.
2. Support efficient multiplexing and
de-multiplexing of individual signals.
With SONET, it is easy to isolate one
channel from a multiplexed circuit. With
plesiochronous systems, like NADH and
European E system, isolating one channel is
more difficult.
Synchronous Optical Network (SONET)
Plesiochronous (pronounced plee-see-AHkrun-us, from Greek plesos, meaning close, and
chronos, meaning time) is an adjective that
describes operations that are almost, but not
quite, in synchronization - in other words, almost
synchronous.
Synchronous Optical Network (SONET)
Terminating multiplexers (implemented in
switches and routers) provide user access to the
SONET network. Terminating multiplexers
convert electrical interfaces into optical signals
and multiplex multiple payloads into STS-N
signals required for optical transport.
SONET Optical Carrier (OC) Levels
aka Synchronous Transport Signal (STS) Levels
STS Rate
OC Level
Speed
STS-1
STS-3
STS-12
STS-24
STS-48
STS-96
STS-192
OC-1
OC-3
OC-12
OC-24
OC-48
OC-96
OC-192
51.84 Mbps
155.52 Mbps
622.08 Mbps
1.244 Gbps
2.488 Gbps
4.976 Gbps
9.952 Gbps
Typical SONET Topology
SONET Multiplexer
Backup Pair
Working Pair
Frame Relay
Frame relay is a telecommunication service designed
for cost-efficient data transmission for intermittent traffic
between local area networks (LANs) and between end-points
in a wide area network (WAN).
Frame relay puts data in a variable-size unit called
a frame and leaves any necessary error correction
(retransmission of data) up to the end-points, which speeds up
overall data transmission. For most services, the network
provides a permanent virtual circuit (PVC), which means that
the customer sees a continuous, dedicated connection without
having to pay for a full-time leased line, while the service
provider figures out the route each frame travels to its
destination and can charge based on usage.
Frame Relay
• Industry-standard data-link-layer protocol
for transporting traffic across wide-area
virtual circuits
• Optimized for efficiency on circuits with
low error rates
• Attractively-priced in most parts of the
world
• Carriers agree to forward traffic at a
Committed Information Rate (CIR)
Frame Relay
To Router B: DLCI
100
To Router A: DLCI
200
Router A
Router B
Virtual Circuit (VC)
Virtual Circuit
What is a virtual circuit?
OSI model used in example. TCP takes large blocks of
information from an application and breaks them into segments.
It numbers and sequences each segment so that the destination ‘s
TCP protocol can put the segments back into the order the
application intended. After the segments are sent, TCP (trans
host) waits for an acknowledgment of the receiving end’s TCP
virtual circuit session, retransmitting those that aren’t
acknowledged.
Before a transmission occurs, a host sends segments down
the OSI model, the sender’s TC protocol contacts the
destination’s TCP protocol to establish a connection. This type of
connection is considered to be connection-oriented. UDP is
connectionless connection.
Frame Relay Hub-and-Spoke Uses
Subinterfaces
hostname central site
Central-Site Router
interface serial 0
encapsulation frame-relay
DLCI 100
DLCI 200
interface serial 0.1
ip address 10.0.1.1 255.255.255.0
frame-relay interface-dlci 100
interface serial 0.2
ip address 10.0.2.1 255.255.255.0
frame-relay interface-dlci 200
X.25
• X.25 was optimized for excellent reliability on
physical circuits with high error rates.
• X.25 was more complex to implement than
Frame Relay.
• X.25 works at the physical, data link, and
network layers.
• X.25 allows computers on different public
networks (CompuServe, TCP/IP) to
communicate through an intermediary
computer at the network layer level.
Split Horizon
A routing technique in which information about
routes is prevented from exiting the router interface
through which that information was received. Split
horizon updates are useful in preventing routing loops.
Use a sub-interface. This is a logical interface that
is associated with a physical interface. The central site
could have five PPP sub-interfaces defined, each
communicating with one of the remotes sites. With this
solution, the central site router applies the split horizon
rule based on logical sub-interfaces, instead of the
physical interface, and includes remote sites in the
routing updates it sends out the WAN interface.
Split Horizon
Split horizon can be eliminated using full
mesh design with physical circuits between each
site.
Asynchronous Transfer Mode (ATM)
• Used in service provider internal networks
• Gaining popularity within private networks,
both WANs and sometimes LANs
• Supports very high bandwidth requirements
– Copper cabling: 45 Mbps (T3) or more
– Fiber-optic cabling: OC-192 (9.952
Gbps) and beyond, especially if
technologies such as wavelength-division
multiplexing (WDM) are used
ATM
• Provides efficient sharing of bandwidth among
applications with various Quality of Service
(QoS) requirements
– Cell-based system inherently better for QoS than
frame-based system, because frame-based system,
large frames can monopolize
bandwidth
• ATM is with a connection-oriented technology
• Application can specify upon connection
establishment the QoS it requires
• Peak and minimum cell rates, cell-loss ratio,
and cell-transfer delay
ATM
• A disadvantages of ATM is that ATM
interfaces for routers and switches are
expensive.
ATM Video:
https://www.youtube.com/watch?v=3VAmcN8VmIU
Ethernet over ATM
• ATM router interfaces are expensive
• Some providers allow a customer to use an
Ethernet interface to access the provider’s
ATM WAN
• May require a converter
• Expected to gain popularity because it has
the advantages of both worlds
– Easy-to-use LAN
– QoS-aware WAN
Metro Ethernet
What is Metro Ethernet?
Metro Ethernet makes use of Carrier
Ethernet technology in metropolitan area
networks (MANs).
Carrier Ethernet is the use of highbandwidth Ethernet technology for Internet
access and for communication among
business, academic and government local area
networks (LANs).
Metro Ethernet
Widely available in larger cities, Metro
Ethernet offers efficient and scalable network
services within a specific metropolitan region.
These regions are frequently meshed in fiber
optic networks, making Ethernet more widely
available in the specified metropolitan area.
Comcast Metro Ethernet offers a simple
solution for users that have a complex
network.
Metro Ethernet
• A service offered by providers and carriers
that traditionally only offered WAN services
• Carriers offer Metro Ethernet to customers
who are looking for cost-effective method
to interconnect campus networks and to
access the Internet.
• Metro Ethernet allow users to continue
using 10/100 Mbps Ethernet interfaces.
• Supports copper and fiber optics interfaces.
Metro Ethernet
• Allows providers to offer bandwidth in 1Mbps increments.
Selection Criteria for Remote Access
Devices
•
•
•
•
•
•
Support for VPN features
Support for NAT
Reliability
Cost
Ease of configuration and management
Support for one or more high-speed
Ethernet interfaces
• If desired, wireless support
Selection Criteria for VPN
Concentrators
• Support for:
– Tunneling protocols such as IPsec, PPTP, and L2TP
– Encryption algorithms such as 168-bit Triple DES,
Microsoft Encryption (MPPE), RC4, AES
– Authentication algorithms, including MD5, SHA-1, HMAC
– Network system protocols, such as DNS, RADIUS,
Kerberos, LDAP
– Routing protocols
– Certificate authorities
– Network management using SSH or HTTP with SSL
•
•
•
•
•
•
Selection Criteria for Enterprise
Routers
Number of ports
Processing speed
Media and technologies supported
MTTR and MTBF
Throughput
Optimization features
Selection Criteria for a WAN Service
Provider
• Extent of services and technologies
• Geographical areas covered
• Reliability and performance characteristics of
the provider’s internal network
• The level of security offered by the provider
• The level of technical support offered by the
provider
• The likelihood that the provider will continue
to stay in business
Selecting a Provider
• The provider’s willingness to work with you to
meet your needs
• The physical routing of network links
• Redundancy within the network
• The extent to which the provider relies on other
providers for redundancy
• The level of oversubscription on the network
• QoS support
Summary
• A major task during the physical design phase is
selecting technologies and devices for enterprise
networks
– Remote access networks
– WANs
– Service providers
– Devices
• End user remote access devices
• Central site remote access devices
• VPN concentrators
• Routers
Review Questions
• Compare and contrast technologies for
supporting remote users.
• Compare and contrast WAN technologies.
• What selection criteria can you use when
purchasing internetworking devices for
enterprise network customers?
• What criteria can you use when selecting a
WAN service provider?
This Week’s Outcomes
•
•
•
•
PPP
Frame Relay
Cable Modems and DSL
Leased Lines, SONET, Frame Relay, Metro
Ethernet, ATM
• Selecting a WAN Service Provider
Due this week
• 11-1 – Concept questions 8
Next week
• Read Chapters 12 and 13 in Top-Down
Network Design
• 12-1 – Concept questions 9
• 1-5-3 – Network design project
– New office network
• FranklinLive session 13
Q&A
• Questions, comments, concerns?