Transcript Backbone Networks, MAN, WAN

Backbone Networks,
MAN, WAN
PSTN, T-carriers, ATM,
Frame Relay, VPN
Key Concepts
Understand various types of backbones and the
devices they use
Understand VLANs and the devices they use
Understand various MAN and WAN services,
including T-carriers, frame relay, ATM, and
High-speed Ethernet
Be familiar with virtual private network services
Backbone Networks
Backbone networks are high speed networks
that link an organization’s LANs and also
provide connections to other backbones,
MANs, WANs and the Internet.
Network designers view networks as made of
three technology layers:
 The access layer which is the technology
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used in LANs
The distribution layer which is the part of
the backbone that connects the LANs
together
The core layer connects different backbone
networks together, often between buildings
Backbone network design layers
Collapsed Backbones
Collapsed backbones use a star topology, usually
with a high speed switch at the center
Collapsed backbones can use either layer-2 switches
or layer-3 routing switches
The two main advantages are:
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each connection to the switch becomes a separate
point-to-point circuit also giving much higher
performance
the network has far fewer devices and so is much
simpler to manage
Two minor disadvantages are: 1) use more cable
and the cable runs for longer distances, 2) if the
central switch fails, the network goes down
Rack-mounted collapsed backbone architecture
Multi-Switch Ethernet LAN
Switch 2
Port 7 on Switch 2
to Port 4 on Switch 3
Port 5 on Switch 1
to Port 3 on Switch 2
Switch 1
C3-2D-55-3B-A9-4F
Switch 2, Port 5
Switch 3
B2-CD-13-5B-E4-65
Switch 1, Port 7
A1-44-D5-1F-AA-4C
Switch 1, Port 2
D4-55-C4-B6-9F
Switch 3, Port 2
E5-BB-47-21-D3-56
Switch 3, Port 6
Virtual LANs
VLANs are a new type of LAN architecture
using intelligent, high-speed switches
Unlike other LAN types, which physically
connect computers to LAN segments, VLANs
assign computers to LAN segments by
software
VLANs have been standardized as
IEEE802.1q and IEEE802.1p
The two basic designs are:
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Single-switch VLANs
Multiswitch VLANs
Server Broadcasting without VLANS
Frame is Broadcast
Goes to all stations
Creates congestion
Server
Broadcast
Client C
Client B
Client A
Server D
Server E
Server Multicasting with VLANS
Multicasting
(some), not
Broadcasting (all)
Server
Broadcast
Client C
on VLAN1
Client A
on VLAN1
Client B
on VLAN2
Server D
on VLAN2
Server E
on VLAN1
VLANs
Computers can be assigned to VLANs in four
ways:
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Port-based VLANs assign computers according to
the VLAN switch port to which they are attached
MAC-based VLANs assign computers according to
each computer’s data link layer address
IP-based VLANs assign computers using their IPaddress
Application-based VLANs assign computers
depending on the application that the computer
typically uses. This has the advantage of allowing
precise allocation of network capacity
VLANs
Single-Switch or Multiswitch
Main advantages


Simpler to manage the broadcast traffic
Precisely allocate resources to different types
of traffic
Drawbacks

Cost and management complexity
FDDI Topology
FDDI operates at 100 Mbps over a fiber optic
cable.
FDDI can attach a maximum of 1000 stations
over a maximum path of 200 km. A repeater is
need every 2 km.
FDDI uses dual counter-rotating rings (called the
primary and secondary). Data normally travels
on the primary ring.
Stations can be attached to the primary ring as
single attachment stations (SAS) or both rings
as dual attachment stations (DAS).
Optical cable topology for an FDDI LAN
FDDI’s Self Healing Rings
Copper Distributed Data Interface (CDDI) is a
related protocol using cat 5 twisted wire pairs.
An important feature of FDDI is its ability to
handle a breaks in the network by forming a
single temporary ring out of the pieces of the
primary and secondary rings.
Once the stations detect the break, traffic is
rerouted through a new ring formed out of the
parts of the primary and secondary rings not
affected by the break.
The network then operates over this temporary
ring until the break can be repaired.
Managing a broken circuit
Asynchronous Transfer Mode (ATM)
ATM was originally designed to carry both
voice and data traffic over WANs. It is
also used in backbone networks.
In the WAN, ATM almost always uses
SONET as its hardware layer.
An ATM gateway is needed to convert
TCP/IP and Ethernet frames into ATM
cells and then converts them back once
they have reached their destination
network. The translation creates significant
delays.
ATM Media Access Control
To handle circuit congestion, ATM prioritizes
transmissions based on Quality of Service
(QoS)
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Real time applications, such as voice, get a
high priority, since it cannot allow delays.
E-mail gets a lower priority, since small delays
don’t matter very much.
ATM in the backbone
Current Backbone Technology Trends
The following trends in backbone technologies have
been taking place in recent years:
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Organizations are moving to collapsed backbones or
VLANs
Gigabit Ethernet use is growing
FDDI seems to be on its way out.
ATM, while still popular in WANs, is losing ground to
Gigabit Ethernet as a backbone technology
Taken together, it appears that Ethernet use will
dominate both the LAN and backbone environments
Effective data rates
for backbone technologies
Technology
Effective Data Rate
Full Duplex 1 GbE
1.8 Gbps
Full Duplex 10 GbE
18 Gbps
FDDI
7-70 Mbps depending on
traffic
ATM (155 Mbps, Full
Duplex)
160 Mbps
ATM (622 Mbps, Full
Duplex)
760 Mbps
Assumes: collapsed backbone connecting Ethernet LANs transmitting mostly large frames
Backbone Recommendations
The best practices are recommended for backbones:
1. Architecture: collapsed backbone or VLAN.
2. Technology: gigabit Ethernet. ATM and FDDI use has
started to fall off over the past year.
3. The ideal network design combines use of layer-2 and
layer-3 Ethernet switches.
4. The access layer (LANs) uses 10/100 layer-2 switches
using cat 5e or cat 6 twisted pair cables (cat 6 is
needed for 1000BaseT).
5. The distribution layer uses layer-3 Ethernet switches
that use 1000BaseT or fiber, Cat 6 or Cat 7 TP.
6. The core layer uses layer-3 Ethernet switches running
10GbE or 40GbE over fiber.
7. Network reliability is increased using redundant
switches and cabling.
MAN & WAN
Metropolitan area networks (MANs) typically
span from 3 to 30 miles and connect
backbone networks (BNs), and LANs.
Wide area networks (WANs) connect BNs
and MANs across longer distances, often
hundreds of miles or more.
Most organizations cannot afford to build
their own MANs and WANs, so they rent or
lease circuits from common carriers such as
AT&T, BellSouth or SBC.
WAN Purposes
Link sites (usually) within the same
corporation
Provide remote access to individuals who are
off-site
Internet access
3.
Internet
Access
1. Link Sites
2.
Remote
Access
WANs
WAN Technologies
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Ordinary telephone line and telephone modem
Point-to-Point Leased lines
Public switched data network (PSDN)
Send your data over the Internet securely,
using Virtual Private Network (VPN) technology
Point-to-Point
PSDN
VPN
Telephone Modem Communication
• Need modem at each end up to 33.6 kbps
• For 56 kbps download speed server must have a
digital connection, not a modem
Binary Data
Client A
Analog Modulated
Signal
33.6 Telephone
kbps
Modem
Telephone
PSTN
Modem
Server A
Leased Line Networks
Leased Line
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Point-to-point connection
Always on
Usually faster (56 kbps or more)
Usually digital instead of analog
Lower cost per bit transmitted than dial-up
service
 But speeds are higher, so higher total cost

Must be provisioned (set up)
Leased Line Networks
Trunk Line-Based Leased Lines
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56 kbps Leased Lines
Fractional T1 lines offer low-speed choices
between 56 kbps and T1, typically:
 128 bps, 256 kbps, 384 kbps, 512 kbps, 768
kbps
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T1 Leased Lines (1.544 Mbps)
T3 Leased Lines (44.7 Mbps)
SONET Leased Lines operate at multiples of
51.84 Mbps
Use either optical fiber or data-grade
copper
Leased Line Networks
Digital Subscriber Lines (DSLs)
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Broadband speeds over single pair of voicegrade copper UTP
Less expensive than trunk line-based leased lines
Asymmetric DSL (ADSL)
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Downstream (to customer): 256 kbps to over 1.5
Mbps
Upstream (from customer): 64 kbps or higher
ASDL with Splitter
Subscriber
Premises
PC
ADSL
Modem
Data
256 kbps to
1.5 Mbps
Telephone Company
End Office Switch
64 kbps to
256 kbps
DSLAM
Splitter
Telephone
Data
WAN
Ordinary Telephone
Service
PSTN
Leased Line Networks
HDSL (High-rate DSL)
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Symmetric speed (768 kbps both ways) over
one voice-grade twisted pair
Designed for business use with speed
guaranteed
SHDSL (Super High-rate DSL)
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Single voice-grade twisted pair; longer
distances than ASDL, HSDL
Symmetric, guaranteed speed
Variable speed ranging from 384 kbps to 2
Mbps
Cable Modem Services
ISP
2. Optical
Fiber to
Neighborhood
4. Coaxial
Cable to
Premises
3.
Neighborhood
Splitter
PC
5. Cable
Modem
Subscriber
Premises
6. Requires NIC or USB port
1. Cable
Television
Head End
Leased Line Networks
Cable Modem
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Delivered by cable television operator
High asymmetric speed
 Up to 10 Mbps downstream
 64 kbps to 256 kbps upstream

Speed is shared by people currently
downloading in a neighborhood
 In practice, medium ADSL speed or higher
Leased Line versus Public Switched Data Networks
Multisite Leased Line Mesh Network
Site B
Site A
OC3 Leased Line
T3 Lease
Line
56 kbps
Leased
Line
T1 Leased
Line
Site C
T1 Leased
Line
56 kbps
Leased
Line
Site D
Site E
56 kbps
Leased
Line
Leased Line versus Public Switched Data
Networks
Public Switched Data Network (PSDN)
Site A
Site B
POP
Point of Presence
POP
Public Switched Data
Network (PSDN)
POP
POP
One leased
line per site
Site D
Site C
Site E
Leased Line versus Public Switched Data
Networks
Leased Line Network
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Many leased lines
Individual leased line spans long distances
Company must plan, buy switching equipment,
and operate the network
Public Switched Data Network
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Only need one leased line from each site to a
POP
Few and short-distance leased lines
PSDN carrier provides planning, switching, and
operation of the network
Popular PSDN Services
Typical
Service
Speeds
X.25
Frame
Relay
9,600 kbps
to about
40 Mbps
56 kbps
to about
40 Mbps
Circuit- or
PacketSwitched
Reliable or Virtual
Relative
Unreliable Circuits? Price
Packet
Reliable
Yes
Moderate
Packet
Unreliable
Yes
Low
• X.25 (Obsolete): Slow because of reliability
• Frame Relay
• Services are offered by all the major carriers
Popular PSDN Services
Typical
Speeds
Service
ATM
Ethernet
Circuit- or
PacketSwitched
1 Mbps
to about Packet
156 Mbps
10 Gbps
and
Packet
40 Gbps
Reliable or Virtual
Relative
Unreliable Circuits? Price
Unreliable
Yes
High
Unreliable
No
Probably
Low
• ATM is faster than Frame Relay
• grow in demand as corporate demand outgrows FR
• Ethernet MANs are appearing
• offer lower prices for comparable speeds
Popular PSDN Services
Typical
Service
Speeds
ISDN
Circuit- or
PacketSwitched
Two 64 kbps
B channels
Circuit
One 16 kbps
D channel
Reliable or Virtual
Relative
Unreliable Circuits? Price
Unreliable
No
Moderate
• ISDN
• Expensive for its slow speed
• Has niche in backup connections because Dial-Up, so
only pay for when needed
Virtual Private Network
1.
Site-to-Site
Tunnel
Internet
VPN Server
VPN Server
Corporate
Site B
Corporate
Site A
Extranet
2. Remote
Customer PC
(or site)
Remote
Access for
Intranet
3. Remote
Corporate PC
Virtual Private Network
Virtual Private Network (VPN)

Transmission over the Internet with added
security
Why VPNs?
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PSDNs are not interconnected
 Only good for internal corporate
communication
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But Internet reaches almost all sites in all
firms
Low transmission cost per bit transmitted
Virtual Private Network
VPN Problems

Latency and Sound Quality
 Internet can be congested
 Creates latency, reduces sound quality
 Use a single ISP to reduce problems
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Security
 PPTP for remote access is popular
 IPsec for site-to-site transmission is popular
ISP-Based PPTP Remote Access VPN
Remote Access VPNs
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User dials into a remote access server (RAS)
RAS often checks with RADIUS server for user
identification information. Allows or rejects
connection
Local
Access
Secure Tunnel
RADIUS
Server
PPTP
RAS
Corporate
Site A
Internet
ISP
PPTP
Access
Concentrator
Remote
Corporate
PC
Virtual Private Network
Point-to-Point Tunneling Protocol
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Available in Windows since Windows 95
 No need for added software on clients
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Provided by many ISPs
 PPTP access concentrator at ISP access point
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Some security limitations
 No security between user site and ISP
 No message-by-message authentication of user
 Uses unprotected TCP control channel
IPsec in Tunnel Mode
Local
Network
IPsec
Server
Tunnel
Mode
IPsec
Local
Server
Network
Secure
Tunnel
No Security
In Site Network
Tunnel Only
Between Sites
Hosts Need No
Extra Software
No Security
In Site Network
Virtual Private Network
IP Security (IPsec)
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A network layer, so protects information at
higher layers
Transparent: upper layer processes do not
have to be modified
HTTP
Protected
SMTP
TCP
FTP
SNMP
UDP
Network Layer with IPsec Protection
Virtual Private Network
Security associations:

Agreement on how security options will be
implemented

May be different in the two directions

Governed by corporate policies
Security Association (SA1) for Transmissions
From A to B
Party A
Security Association (SA2) for Transmissions
From B to A
Party B
MAN/WAN Recommendations
For small networks, POTS may still be reasonable
alternative
For moderate volume networks, several choices are
popular:
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VPNs are a good choice when cost is important and
reliability is less of an issue
Frame relay is used when demand is unpredictable
T-Carriers are used if network demand is predictable
For high volume networks Ethernet/IP packet
networks are becoming the dominant choice.
Some organizations also may prefer ATM for their
high volume networks.