Wide Area Networking - PowerPoint PPT Presentation

Loading...

PPT – Wide Area Networking PowerPoint presentation | free to download - id: 4ff220-MThhM



Loading


The Adobe Flash plugin is needed to view this content

Get the plugin now

View by Category
About This Presentation
Title:

Wide Area Networking

Description:

Wide Area Networking Outline Topics Wide Area Networks Link sites together Carriers and regulation Leased Line Networks Public Switched Data Networks (PSDNs) Virtual ... – PowerPoint PPT presentation

Number of Views:184
Avg rating:3.0/5.0
Slides: 67
Provided by: X458
Learn more at: http://som.csudh.edu
Category:

less

Write a Comment
User Comments (0)
Transcript and Presenter's Notes

Title: Wide Area Networking


1
Wide Area Networking
2
Outline Topics
  • Wide Area Networks
  • Link sites together
  • Carriers and regulation
  • Leased Line Networks
  • Public Switched Data Networks (PSDNs)
  • Virtual Private Networks

3
Wide Area Networks
  • WANs Link Sites (Locations)
  • Usually sites of the same organization
  • Sometimes, sites of different organizations

Site B
Site C
Site A
WAN
4
Carriers
  • You can only install wires on your own property
  • Called your customer premises
  • To send signals between sites or to customers,
    you must use a carrier
  • Carriers transport data and voice traffic between
    customer premises, charging a price for their
    services
  • Receive rights of way from the government to lay
    wires and radio links

Carrier
Customer Premises
5
Carrier Regulation
  • Traditionally, Carriers Have been Regulated
  • Given rights of way
  • Given monopoly protection from competition
  • In return, services normally must be tariffed
  • Tariff specifies exact terms of the service to be
    provided, and
  • Tariff specifies price to be charged
  • Prevents special deals, which would be
    inappropriate for a regulated monopoly
  • Regulators must approve price for reasonableness

6
Carrier Regulation
  • There is a Strong Trend Toward Deregulation
  • Gradual removal of monopoly protections
  • Allows competition, so lower prices and more
    service options
  • Fewer services need to be tariffed, allowing
    price negotiation

7
Carrier Regulation
  • Service Level Agreements (SLAs)
  • Even under competition, carriers may guarantee
    specific levels of service for certain service
    parameters in an SLA
  • Throughput
  • Latency
  • Availability
  • Error Rates, etc.
  • Penalties are paid to customers if carrier fails
    to meet agreed-upon service levels

8
High Cost of Long-Distance
  • LAN Communication is Inexpensive per Bit
    Transmitted
  • So most LANs operate at 10 Mbps to a few gigabits
    per second
  • Long-Distance Communication is Very Expensive per
    Bit Transmitted
  • So Most WANs use low speeds
  • Most WAN demand is 56 kbps to a few Mbps

9
Leased Lines
  • Leased Lines are Circuits
  • Often goes through multiple switches and trunk
    lines
  • Looks to user like a simple direct link
  • Limited to point-to-point communication
  • Limits who you can talk to
  • Carriers offer leased lines at an attractive
    price per bit sent to keep high-volume customers

Switch
Trunk Line
Leased Line
10
Leased Line Meshes
  • If you have several sites, you need a mesh of
    leased lines among sites

Mesh
Leased Line
11
Leased Line Speeds
  • Largest Demand is 56 kbps to a few Mbps
  • 56 kbps (sometimes 64 kbps) digital leased lines
  • DS0 signaling
  • T1 (1.544 Mbps) digital leased lines
  • 24 times effective capacity of 56 kbps
  • Only about 3-5 times cost of 56 kbps
  • DS1 signaling

12
Leased Line Speeds
  • Fractional T1
  • Fraction of T1s speed and price
  • Often 128, 256, 384 kbps
  • T3 is the next step
  • 44.7 Mbps in U.S.
  • Europe has E Series
  • E1 2.048 Mbps
  • E3 34 Mbps
  • SONET/SDH lines offer very high speeds
  • 156 Mbps, 622 Mbps, 2.5 Gbps, 10 Gbps

13
SONET/SDH
  • Created as Trunk Lines for Internal Carrier
    Traffic
  • As were other leased lines
  • The Trunk Line Breakage Problem
  • Problem unrelated construction products often
    break carrier trunk lines, producing service
    disruptions
  • The most common cause of disruptions

X
14
SONET/SDH Uses a Dual Ring
  • Normally, Traffic Travels in One Direction on One
    Ring
  • If Trunk Line Breakage, Ring is Wrapped Still a
    Ring, So Service Continues

Switch
Normal Operation
Wrapped
15
Digital Subscriber Lines (DSLs)
  • Can Use Instead of Traditional Leased Lines
  • Less expensive
  • HDSL (High-Speed DSL)
  • Symmetrical Same speed in each direction
  • HDSL 768 kbps (Half a T1) on a single twisted
    pair
  • HDSL2 1.544 Mbps (T1) on a single twisted pair

16
Digital Subscriber Line
  • Normal Leased Lines Used Data Grade Wires
  • High-quality, high-cost
  • Two pairs (one in each direction)
  • DSLs Normally Use Voice Grade Copper
  • Not designed for high-speed data
  • So sometimes works poorly
  • Usually one pair (ADSL, HDSL)
  • Sometimes two pairs (HDSL2)

17
Problems of Leased Lines
  • With many sites, meshes are expensive and
    difficult to manage
  • With N sites, N(N-1)/2 leased lines for a mesh
  • May not need all links, but usually use many
  • User firm must handle switching and ongoing
    management
  • Expensive because this requires planning and the
    hiring, training, and retention of a WAN staff

Sites
Lines
5
10
10
45
25
300
18
T1 Leased Lines
  • Voice Requirements
  • Analog voice signal is encoded as a 64 kbps data
    stream
  • 8 bits per sample
  • 8,000 samples per second

19
T1 Leased Lines
  • T1 lines are designed to multiplex 24 voice
    channels of 64 kbps each
  • T1 lines use time division multiplexing (TDM)
  • Time is divided into 8,000 frames per second
  • One frame for each sampling period
  • Each frame is divided into 24 8-bit slots
  • One for each channels sample in that time period
  • (24 x 8) 192 bits
  • Plus one framing bit for 193 bits per frame

20
T1 Leased Lines
  • Speed Calculation
  • 193 bits per frame
  • 8,000 frames per second
  • 1.544 Mbps
  • Framing Bit
  • One per frame
  • 8,000 per second
  • Used to carry supervisory information (in groups
    of 12 or 24 framing bits)

21
PSDNs
  • Public Switched Data Networks
  • Designed for data rather than voice
  • Site-to-site switching is handled for you
  • You merely connect each site to the PSDN cloud
    (No need to know internal details)

22
PSDNs
  • Connect each site to the PSDN using one leased
    line
  • Only one leased line per site
  • With N sites, you only need N leased lines, not
    N (N-1)/2 as with a full mesh

1 LeasedLine
23
PSDNs
  • Access Device Needed at Each Site
  • Connects each site to access line
  • Often a router
  • Sometimes a device specific to a particular PSDN
    Technology

Access Device
24
PSDNs
  • Point of Presence (POP)
  • Place where you connect to the cloud
  • May be several in a city
  • May not have any POP close
  • Need leased line to POP
  • Separate from PSDN charges

POP
LeasedLine
25
PSDNs in Perspective
  • Simpler than Networks of Leased Lines
  • Less staffing
  • Fewer leased lines to support
  • Less Expensive than Networks of Leased Lines
  • Less staffing
  • PSDN prices are very low
  • PSDN is less expensive overall
  • PSDNs are replacing many leased line mesh networks

26
Circuit-Switched PSDNs
  • End-to-End Capacity is Guaranteed
  • If you need it, it is always there
  • When you dont need it, you still pay for it
  • Expensive for data traffic, which usually has
    short bursts and long silences

A bcd efg
27
Packet-Switched PSDNs
  • Messages are divided into small units called
    packets
  • Short packets load switches more effectively than
    fewer long messages

28
Packet-Switched PSDNs
  • Packet-Switched PSDNs Usually Operate at Layer 2
    (Data Link Layer for Single Subnets)
  • Should be called frame-switched networks
  • Still called packet-switched networks

29
Packet Switched PSDNs
  • Packets are multiplexed on trunk lines
  • Cost of trunk lines is shared
  • Packet switching lowers transmission costs
  • Dominates PSDN service today

Multiplexed Trunk Line
30
Packet Switched PSDNs Virtual Circuits
  • All commercial packet switched PSDNs use virtual
    circuits
  • Eliminates forwarding decisions for individual
    packets
  • Reduces switching load, so reduces switching costs

VirtualCircuit
31
Unreliable PSDNs
  • Most commercial PSDNs are Unreliable
  • (Only obsolete X.25 PSDN technology was reliable)
  • No error correction at each hop between switches
  • Reduces costs of switching
  • Note that both virtual circuits and unreliable
    service reduce switching costs

32
PSDN Cost Savings
  • Packet Switching
  • Reduces costs of transmission lines through
    multiplexing
  • Virtual Circuits
  • Reduces costs of switches because they do not
    have to make decisions for each frame
  • Unreliability
  • Reduces costs of switches because they do not
    have to do error correction

33
WAN Products
  • ISDN
  • X.25
  • Frame Relay
  • ATM
  • Virtual Private Networks (VPNs)

34
ISDN
  • Integrated Services Digital Network
  • 2BD Basic Rate Interface (BRI) to the desktop
  • Two 64-kbps B channels
  • Can be bonded for 128 kbps service
  • One 16-kbps D channel, usually for supervisory
    signals

64 kbps
BRI 2BD
64 kbps
ISDN Modem
35
ISDN
  • Primary Rate Interface (PRI)
  • Connection between firm and ISDN carrier
  • 23BD (on a T1 line)
  • 30BD (on an E1 line)
  • One 64 kbps D channel for supervision

2BD
23BD
BRI
PRI
36
ISDN
  • Circuit-Switched
  • Dedicated capacity
  • Expensive for data
  • Dial-Up Connection
  • Must connect each time you wish to communicate
  • Other PSDNs are dedicated (always on)
  • Unreliable
  • Only Popular PSDN that is either circuit-switched
    or dial-up

37
ISDN
  • Never achieved strong market use
  • Being overtaken by PSDNs that are both faster and
    less expensive
  • Often, ISDN is spelled out as It still does
    nothing
  • However, there is enough ISDN in use that you
    must know it
  • Also, if connectivity is only needed a short time
    each day, ISDN is still a good choice for
    low-speed transmission

38
X.25
  • First Packet-Switched PSDN Standard
  • Developed in the 1970s
  • Now obsolete
  • But still used, especially in third-world
    countries and Europe
  • Slow Usually 64 kbps or slower
  • Some faster X.25 services are available
  • Reliable, so costs of switches are high
  • So cost of service is high
  • But works even if transmission lines are poor

39
Frame Relay
  • Most Popular PSDN Today
  • Offers speeds of 64 kbps to about 40 Mbps This
    covers the range of greatest corporate demand
  • Most demand is atthe low end of the range
  • Priced aggressively
  • Both reasonsare critical

40
Frame Relay
  • Low-Cost Service
  • Packet-Switched
  • Uses virtual circuits to cut costs
  • Unreliable
  • Relatively low speeds
  • Dedicated Connections
  • Always ready to sendand receive

41
ATM
  • Like Frame Relay
  • Packet switched
  • Virtual circuits
  • Dedicated (Always On) Connections
  • Unlike Frame Relay
  • Much faster top speed
  • 1 Mbps, 25 Mbps, 45 Mbps, 156 kbps, 622 kbps,
    several Gbps
  • May offer quality of service (QoS) guarantees
  • Maximum latency for time-critical applications
  • Exact cell-by-cell timing

42
ATM
  • Very Expensive
  • Complexity because of basic transmission
    mechanisms
  • Complexity because of quality of service
    mechanisms
  • High-speed transmission

43
Frame Relay and ATM
  • Most Vendors Offer Both
  • To cover speeds from 56 kbps to a few gigabits
    per second
  • In general, a smooth price-speed curve across
    the two services
  • At some speed, may offer both
  • If so, usually price them the same

FR
Price
ATM
Speed
44
Frame Relay and ATM
  • Both are widely used
  • Frame Relay is more popular today because it
    serves the range of greatest corporate need (56
    kbps to a few megabits per second) at an
    attractive price
  • As demand for higher-speed links grows, ATM
    should become more widely used
  • Unless other alternatives to ATM appear, such as
    10 Gbps Ethernet for WANs

45
Frame Relay Pricing
  • Frame Relay Access Device (FRAD)
  • Device at each site to connect site network to
    Frame Relay WAN
  • Paid to PSDN carrier or an equipment manufacturer

Access Device
46
Frame Relay Pricing
  • Leased Access Line
  • Usually paid to telephone company rather than
    PSDN
  • PSDN often includes a bundled pricing
    arrangement, but it must pay the telephone
    company if this is the case
  • If POPs are not close, access line charges will
    be high

Access Line
47
Frame Relay Pricing
  • Port Speed
  • At the POP there is a connection port
  • Ports come in different speeds
  • 65 kbps, 1 Mbps are very common
  • Faster ports are more expensive
  • Monthly port speed usually is the most expensive
    component of PSDN cost

Port at POP
48
Frame Relay Pricing
  • Sometimes, Two Port Speeds are Quoted
  • Committed Information Rate (CIR)
  • Frames can be sent continuously at this speed
  • Available Bit Rate (ABR)
  • Higher speed
  • Frames sent above the CIR are on standby
  • If congestion appears, will be discarded first

Port at POP
49
Frame Relay Pricing
  • Port Speed and Access Line Speed
  • Port costs usually are higher than access line
    charges
  • Access line must be as fast as port speed or
    faster to avoid wasting expensive port speed
  • For example, if the port speed is 1 Mbps, you
    should get a T1 (1.544 Mbps) leased access line

Port at POP
Access Line
50
Frame Relay Pricing
  • Permanent Virtual Circuits (PVCs)
  • Leased line meshes had a leased line to each site
  • PSDNs, usually have PVCs wherever there were
    leased lines between sites in the previous leased
    line network
  • Eases the transition to PSDNs from leased lines
  • PVCs to other sites are multiplexed over a sites
    single leased access line
  • Pay monthly charge per PVC, based on speed

PVC
Leased Access Line
PVC
51
Frame Relay Pricing
  • Permanent Virtual Circuits (PVCs)
  • Leased access line must be fast enough to handle
    all of the PVCs it is multiplexing
  • Example if it multiplexes 15 64 kbps PVCs, the
    access line must be 840 kbps (T1 line needed)

PVC
Leased Access Line
PVC
52
Frame Relay Pricing
  • Other Aspects of Pricing
  • Sometimes only flat fees for access lines, ports,
    etc, but sometimes also charges based on traffic
    volume
  • Ongoing (monthly) fees for leased lines, ports,
    PVCs, etc.
  • Usually also an initial setup or installation
    charge
  • If offer switched virtual circuits (which are set
    up on demand), usually a fee for each set up
  • Many vendors offer managed services that have
    them manage the Frame Relay network instead of
    the customer having to do it

53
Frame Relay Frame Structure
  • Variable Length Frames
  • Start flag (01111110) to signal start of frame
  • Address field has variable length (2-4 octets)
  • Information field to carry data (variable)
  • CRC (Cyclical Redundancy Check) field to detect
    errors (2 octets)
  • If find errors, switch discards the frame
  • Stop flag (01111110) to signal end of frame

54
Frame Relay Frame Structure
  • Address Field of Frame Relay Frame
  • Variable Length 2-4 octets
  • 4-Octet form shown
  • Complex

7
Bits
0
DLCI (6 bits)
C/R
AE
DLCI
FECN
BECN
DE
AE
DLCI
AE
DLCI
AE
55
Frame Relay Frame Structure
  • Congestion Control
  • Traffic shaping
  • The Backward Explicit Congestion Notification
    (BECN) bit is set to tell the station that
    receives the frame to slow down This is easy to
    implement
  • The Forward Explicit Congestion Notification
    (FECN) bit is more complex If a station receives
    this notification in an incoming frame, it should
    tell its communication partner at the other end
    of the Frame Relay network to slow down

56
VPNs
  • Virtual Private Networks
  • Use the Internet for transmission instead of a
    PSDN
  • Sometimes called VPNs if use Frame Relay or ATM
    with added security
  • Why use the Internet?
  • Inexpensive
  • Business partners are already connected to the
    same network (the Internet)
  • May use different PSDNs, but everybody is
    connected to the Internet

Internet
57
VPNs
  • Problems with the Internet
  • Congestion slows transmissions
  • Reliability cannot always connect, sometimes
    fails during transmissions
  • Lack of security

58
VPNs
  • IETF developing IPsec security standards
  • IP security
  • At the internet layer
  • Protects all messages at the transport and
    application layers

E-Mail, WWW, Database, etc.
TCP
UDP
IPsec
59
VPNs
  • IPsec Transport Mode
  • End-to-end security for hosts

Local Network
Internet
Local Network
Secure Communication
60
VPNs
  • IPsec Tunnel Mode
  • IPsec server at each site
  • Secure communication between sites

Local Network
Internet
Local Network
IPsec Server
Secure Communication
61
VPNs
  • IPsec Modes Can be Combined
  • End-to-end transport mode connection
  • Within site-to-site tunnel connection

Local Network
Internet
Local Network
Tunnel Mode
Transport Mode
62
VPNs
  • Another Security System for VPNs is the
    Point-to-Point Tunneling Protocol (PPTP)
  • For dial-up connections, based on PPP
  • Connects user with securely to a remote access
    server at a site

Dial-Up Connection
Local Network
Internet
PPTP Connection
Remote Access Server
63
Virtual Private Networks
  • Other Problems Remain
  • Internet Congestion is Still a Problem
  • Internet throughput tends to be low
  • Internet Reliability is Low
  • Cannot get connections
  • Backbone fails occasionally

64
Virtual Private Networks
  • Alternative
  • Avoid the congested and unreliable backbone!
  • Use one ISP that serves all sites
  • Should offer QoS service level agreement (SLAs)
    for latency and reliability

Site 1
ISP
Site 2
65
Virtual Private Networks
  • Alternative
  • Avoid the congested backbone
  • Use ISPs that peer with one another connect
    with one another not through the Internet
    backbone
  • May offer end-to-end SLAs

Site 1
ISP A
ISP B
Site 2
Peering
66
WANs in Perspective
  • Both Leased Line Networks and PSDNs are widely
    used and will be for several years to come
  • Leased Line Networking is shrinking while PSDN
    networking is growing rapidly
  • VPN technology and standards are still immature
    and use will be very low for several years to come
About PowerShow.com