Chapter 6-7

Question 1

What are BBNs?

Answer 1

BBNs are high speed networks that:
Link an organizations Access Layers (LANs) and;
Provide connections to other BBNs, MANs, WANs and the internet

Question 2

In the structured design approach, BBNs refer to the:

Answer 2

• Distribution layer that connects access layers (or LANs) within a building (and the MAN/WAN/Internet if no core layer needed)
• Core layer connects distribution layers different of different adjacent buildings

Question 3

What are BBNs components?

Answer 3

• Cables: Typically TP in distribution layer, Fiver in core layer
• Intermediary devices: It depends but selection cannot be random, Layer-2 switch (same as device used for access layer or routers or VLAN switch ( aka Layer-3 switch o.e. a combination of switches and routers

Question 4

Where are the physical locations of LAN and BBN devices?

Answer 4

Typically located centrally in main distribution facility
Longer cables needed but easier access when trouble shooting

Question 5

Switched (or collapsed) BBNs

Answer 5

LANs are connected by a layer-2 switch:
- Most common type of distribution layer

Question 6

What are the main advantages of Switched BBN?

Answer 6

Improved performance:
- Full duplex transmissions
- Faster processing
- Easier to manage

Question 7

What are some minor disadvantages of switched BBN?

Answer 7

• No protocol conversion
• No segmentation into broadcast domain

Question 8

Router (or hierarchical) BBNs

Answer 8

Layer 2 switches at distribution layer are connected by routers
- Within the LANs and distribution layers, traffic is based on data link address
- Between distribution layers, message are sent to core layer devices which forwards or routes message based on its network layer address

Question 9

What are limitations of Router (or hierarchical) BBN?

Answer 9

Hardware cost + management cost + processing time

Question 10

What are some benefits of Router (or hierarchical) BBN?

Answer 10

• Segmentation into broadcast domain -security
• routing if needed
• some protocol conversions if needed

Question 11

Virtual LANs (VLANs)

Answer 11

new flexible LAN(BBN architecture that assigns computers to LAN segments (or subnets) by software NOT by hardware

Question 12

Switches that don’t use the VLAN functionality segment networks based on physical location

Answer 12

• 80/20 rule is used as a basis for a network segmentation (see all previous figures)
• Possible exception to the rule: Users in different physical locations need to access to the same LAN resources

Question 13

VLAN switches

Answer 13

Special type of high speed layer-3 switches that enable VLANs which divide LANs in logical rather than physical segmants

Question 14

Single-switch VLANs vs Multi-switch VLANs

Answer 14

Single-switch VLAN: One VLAN switch physically connects all computers and assigns
them to the different VLANs
Multi-switch VLAN use several VLAN switches:
- Each VLAN switch maintains a table that identifies membership with VLAN ID and IP
addresses (Fig. 8-7) and interconnected VLAN switches exchange copies of those tables;
- VLAN trunks are circuits that directly connect the different VLAN switches

Question 15

Virtual LAN switches: Pros and cons

Answer 15

Pros:
- IF justified, they help better manage the flow of traffic the network than the traditional LAN/BBN architecture (which can lead to better performance)
- IF justified, because they create subnets, they filter broadcasts so only members of a VLAN receive broadcast messages (also more flexible subnetting)
- IF justified, VLAN switches are high-speed layer-3 switches with low latency
- IF justified, they support QoS protocols which allows to prioritize traffic
- IF justified, they support ACL

Cons:
- They are more expensive than Layer-2 switches
- They are more complex to manage

Question 16

Best practice BBN design

Answer 16

Architecture:
- Default best practice: Layer-2 switches at the distribution layer and if a core layer is needed, routers or layer-3 switches (without using the VLAN functionality) at the core layer (see Fig. 8-4 and next slide)
- Otherwise, IF a flexible LAN/BBN architecture is required, VLAN(s) i.e., layer-3 switch(es) using the VLAN functionality is the best practice

Question 17

What does Access Control List (ACL) do?

Answer 17

Use devices and software that block unauthorized traffic

Question 18

How do you improve BBN performance?

Answer 18

Increase device performance
- Select faster routing protocols and devices that support them
- Select devices with lower latency i.e., devices with more RAM and/or faster CPU
- Use Layer-3 switches (due to their faster processing, see Slide 6) instead of routers at the core layer IF no routing or protocol conversion is needed (see product specs!)
Increase circuit capacity
- Increase nominal data rates from 100 Mbps to 1000Mbps for example
Reduce demand
- Have a policy on (or restrict) applications that use a lot of network capacity (relevant to
LANs NOT to BBNs)

Question 19

Increase BBN availability:

Answer 19

Redundant devices and cabling (aka fault-tolerance)

Question 20

Key features of leased circuits:

Answer 20

• Create dedicated and permanent “point-to-point” circuits between LANs
• Require a router and CSU-DSU but a multiplexer is optional (see next slide)
• Billed at a flat fee per month

Question 21

T-Line Services

Answer 21

• Most used dedicated circuits
• Commercially available in combinations of nominal data rates varying from 64 Kbps (i.e., 1 channel or DS-0 of a fractional T-1 line) to about 1.5 Mbps (T-1 line equiv. to 24 simultaneous 64-Kbps channels) to about 45 Mbps (T-3 line equivalent to 28 T-1 lines)
• Note: Fractional T-1 provides 64Kbps, 128Kbps, etc. depending on # of channels leased

Question 22

Synchronous Optical Network (SONET)

Answer 22

• Commonly used for MAN with high security and high data rate requirements
• Hierarchy in data rate defined as a multiple of Optical Carrier (OC)-1 and varies from about 50 mbps (OC-1) to about 10 Gbps (OC-192)
• high-speed communication network technology that transmits data over fiber optic cables using a synchronous time-division multiplexing method. It is used for long-distance transmission of data, voice, and video signals in telecommunications networks.

Question 23

Dedicated-circuit networks

Answer 23

Are called point-to-point circuits and circuits is/are permanent and dedicated Devices: Router + CSU/DSU are required, Multiplexer (or MUX) is optional

Question 24

Router

Answer 24

Connects the organizations network to the outside networks

Question 25

CSU/DSU

Answer 25

CSU manages equipment connection, DSU translates between protocols

Question 26

MUX

Answer 26

Allows to carry multiple signals (voice, data and video) over a single circuit

Question 27

Dedicated-circuit topologies for WAN (types of design)

Answer 27

- Ring-based design - Star-based design - Mesh-design - Simple point-to-point design

Question 28

Key advantages/disadvantages of Ring design

Answer 28

**Advantages** - Robust to loss of any one circuit **Disadvantage** - Long routes can cause latency issues

Question 29

Key advantages/disadvantages of Star-based design

Answer 29

**Advantages** - Simpler management - Messages require 1 or 2 hops **Disadvantage** - Susceptible to traffic problems - complete failure if central site fails

Question 30

Key advantages/disadvantages of Mesh design

Answer 30

**Advantages** - Generally short routes - Robust to circuit loss or overload **Disadvantage** - Expensive

Question 31

Key advantages/disadvantages of Mesh design

Answer 31

**Advantages** - Generally short routes - Robust to circuit loss or overload **Disadvantage** - Expensive

Question 32

Packet-switched network

Answer 32

**Organizations connect to a common carrier’s network by leasing:** - Dedicated circuits from their offices to the packet switched network’s point-of- presence (aka POP, i.e., to the local MAN/WAN service provider, see next slide) - Shared virtual circuit(s) (VCs, switched or permanent) between POPs (see next slide) - Device: Router required, packet assembly/ disassembly (PAD) depending on service - Billed at a flat fee for a connection to the carrier plus a fee for the data transmitted ## Footnote **- Computer sends data, data broken down to packets and each sent separately**

Question 33

Packet - swtiched networks

Answer 33

Are called multipoint circuits, include (1) dedicated circuits from LANs to the packet switched networks POP and (2) shared virtual circuits Device: Router required, additional device depending on service

Question 34

Virtual Private Networks (or VPNs)

Answer 34

- VPN device or software encrypts data and encapsulates them in IP packets before it is sent over a VPN - Typical data rates supported vary from 3Mbps to 300Mbps - Advantages: Low cost and service offered anywhere Internet is offered **Problems:** – Unpredictability of the Internet (response time and availability) – Lack of standard: VPN devices or software from different vendors may not be compatible

Question 35

Software-defined Wide Area Network (SDWAN)

Answer 35

**Benefits from SDWAN:** – **Improved performance and availability**: SDWAN provides centralized management (network status information + management of WAN circuits) – **Reduced costs** by balancing traffic between circuits with different costs and capacity – **Improved security** IF SDWAN router has built-in VPN capabilities – **Improved prediction of traffic** future growth IF SDWAN router is a managed router - **is a networking technology that simplifies the management of a Wide Area Network using software and cloud-based technologies. It improves network performance, security, and reduces costs by leveraging multiple WAN connections** ** Application:** See Management Focus 9-3 in p. 260 – Organization signed up for more than 1 service, in this case MPLS and VPN – Organization uses SDWAN to redirect traffic from a service that is close to saturation to the other to improve the performance of the MAN/WAN – Additional benefits: Improved availability and cost management

Question 36

MAN/WAN Recommendations

Answer 36

** For networks with low to moderate data rate requirements (10 Mbps or less):** – VPNs if cost is an issue and predictable availability and/or response time is less of an issue – Ethernet of MPLS otherwise *** For networks with high data rate requirements (10 Mbps to 50Mbps):** – IF traffic is intermittent (burst), Ethernet or MPLS – IF a steady stream of data is required (no burst), T-Carriers (T3) *** For networks with very high data rate requirements (50 Mbps to 100 Gbps):** – SONET if high level of security and a steady stream of data are required – Otherwise Ethernet or MPLS

Question 37

Improve WAN Performance:

Answer 37

– Selecting high performance devices – Improving/upgrading circuit capacity – Reducing network demand: * Use data compression hardware and software * When possible, shift network usage from peak or high-cost time to lower- demand or lower-cost times * Move data closer to users with shift from central to distributed systems and databases