Backbone Networks, MAN, WAN PSTN, T-carriers, ATM, Frame Relay, VPN.

Backbone Networks, MAN, WAN

PSTN, T-carriers, ATM,

Frame Relay, VPN

Key Concepts

Understand various types of backbones and the devices they useUnderstand VLANs and the devices they useUnderstand various MAN and WAN services, including T-carriers, frame relay, ATM, and High-speed Ethernet Be familiar with virtual private network services

Backbone NetworksBackbone 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

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 switchesThe two main advantages are: 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

Port 5 on Switch 1to Port 3 on Switch 2

C3-2D-55-3B-A9-4FSwitch 2, Port 5

A1-44-D5-1F-AA-4CSwitch 1, Port 2

E5-BB-47-21-D3-56Switch 3, Port 6

D4-55-C4-B6-9FSwitch 3, Port 2

B2-CD-13-5B-E4-65Switch 1, Port 7

Switch 1

Switch 2

Switch 3

Port 7 on Switch 2to Port 4 on Switch 3

Multi-Switch Ethernet LAN

Virtual LANs

VLANs are a new type of LAN architecture using intelligent, high-speed switchesUnlike other LAN types, which physically connect computers to LAN segments, VLANs assign computers to LAN segments by softwareVLANs have been standardized as IEEE802.1q and IEEE802.1pThe two basic designs are: Single-switch VLANs Multiswitch VLANs

Server Broadcasting without VLANS

Client A

Client B

Client C

Server D Server E

ServerBroadcast

Frame is BroadcastGoes to all stationsCreates congestion

Server Multicasting with VLANS

Client Aon VLAN1

Client Bon VLAN2

Client Con VLAN1

Server Don VLAN2

Server Eon VLAN1

ServerBroadcast

Multicasting (some), not Broadcasting (all)

VLANs

Computers can be assigned to VLANs in four ways: 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 IP-

address 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) 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: 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

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

Effective data rates for backbone technologies

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 corporationProvide remote access to individuals who are off-siteInternet access

1. Link Sites 2.RemoteAccess

3.InternetAccess

WANs

WAN Technologies 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

PSDNVPN

Point-to-Point

Telephone Modem Communication

PSTNClient A

Server A Telephone

Telephone33.6kbps

Modem

Binary Data Analog ModulatedSignal

Modem

• Need modem at each end up to 33.6 kbps• For 56 kbps download speed server must have a

digital connection, not a modem

Leased Line Networks

Leased Line 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)


Trunk Line-Based Leased Lines 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 T1 Leased Lines (1.544 Mbps) T3 Leased Lines (44.7 Mbps) SONET Leased Lines operate at

multiples of 51.84 MbpsUse either optical fiber or data-grade copper


Digital Subscriber Lines (DSLs) Broadband speeds over single pair of voice-

grade copper UTP Less expensive than trunk line-based leased

lines

Asymmetric DSL (ADSL) Downstream (to customer): 256 kbps to over

1.5 Mbps Upstream (from customer): 64 kbps or higher

ASDL with Splitter

DataWAN

PSTN

DSLAM

ADSLModem

Splitter

Telephone

SubscriberPremises

Telephone CompanyEnd Office Switch

PC

Data256 kbps

to1.5 Mbps

64 kbps to256 kbps

Ordinary TelephoneService


HDSL (High-rate DSL) Symmetric speed (768 kbps both ways)

over one voice-grade twisted pair Designed for business use with speed

guaranteed

SHDSL (Super High-rate DSL) 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

PCSubscriberPremises

5. CableModem

4. CoaxialCable toPremises

2. OpticalFiber to

Neighborhood

3.Neighborhood

Splitter

ISP

1. CableTelevisionHead End

6. Requires NIC or USB port


Cable Modem 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

T3 LeaseLine

Site C

Site A Site B

OC3 Leased Line

T1 LeasedLine

T1 LeasedLine

Site ESite D

56 kbpsLeased

Line

56 kbpsLeased

Line

56 kbpsLeased

Line

Multisite Leased Line Mesh Network


Public Switched DataNetwork (PSDN)

POPPOP

POPPOP

Site A Site B

Point of Presence

One leasedline per site

Site D Site C Site E

Public Switched Data Network (PSDN)


Leased Line Network Many leased lines Individual leased line spans long

distances Company must plan, buy switching

equipment, and operate the networkPublic Switched Data Network 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

ServiceTypicalSpeeds

Circuit- orPacket-Switched

Reliable orUnreliable

VirtualCircuits?

RelativePrice

X.259,600 kbpsto about40 Mbps

Packet Reliable Yes Moderate

FrameRelay

56 kbpsto about40 Mbps

Packet Unreliable Yes Low

• X.25 (Obsolete): Slow because of reliability

• Frame Relay• Services are offered by all the major carriers


Ethernet10 Gbps and 40 Gbps

Packet Unreliable NoProbablyLow

ATM1 Mbpsto about156 Mbps

Packet Unreliable Yes High




VirtualCircuits?

RelativePrice

• ATM is faster than Frame Relay• grow in demand as corporate demand outgrows FR

• Ethernet MANs are appearing• offer lower prices for comparable speeds





VirtualCircuits?

RelativePrice

ISDN

Two 64 kbpsB channelsOne 16 kbpsD channel

Circuit 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

VPN Server

Corporate Site A

VPN Server

CorporateSite B

2. RemoteCustomer PC

(or site)

3. RemoteCorporate PC

Tunnel

Internet

ExtranetRemote

Access forIntranet

1.Site-to-Site


Virtual Private Network (VPN) Transmission over the Internet with

added security

Why VPNs? PSDNs are not interconnected

Only good for internal corporate communication

But Internet reaches almost all sites in all firms

Low transmission cost per bit transmitted


VPN Problems Latency and Sound Quality

Internet can be congested Creates latency, reduces sound quality Use a single ISP to reduce problems

Security PPTP for remote access is popular IPsec for site-to-site transmission is

popular

ISP-Based PPTP Remote Access VPN

RADIUSServer

PPTPRAS

Internet ISPPPTP

AccessConcentrator

LocalAccess

RemoteCorporate

PCCorporate

Site A

Remote Access VPNs User dials into a remote access server (RAS) RAS often checks with RADIUS server for

user identification information. Allows or rejects connection

Secure Tunnel


Point-to-Point Tunneling Protocol Available in Windows since Windows 95

No need for added software on clients Provided by many ISPs

PPTP access concentrator at ISP access point 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

Tunnel OnlyBetween SitesHosts Need NoExtra Software

SecureTunnel

TunnelMode

IPsecServer

IPsecServer

LocalNetwork

LocalNetwork

No SecurityIn Site Network

No SecurityIn Site Network


IP Security (IPsec) A network layer, so protects information

at higher layers

Transparent: upper layer processes do not have to be modified

Network Layer with IPsec Protection

TCP UDP

HTTP SMTP FTP SNMP

Protected


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 TransmissionsFrom A to B

Security Association (SA2) for TransmissionsFrom B to A

Party B Party A

MAN/WAN Recommendations

For small networks, POTS may still be reasonable alternativeFor moderate volume networks, several choices are popular: 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.

Backbone Networks, MAN, WAN PSTN, T-carriers, ATM, Frame Relay, VPN.

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Transcript of Backbone Networks, MAN, WAN PSTN, T-carriers, ATM, Frame Relay, VPN.