Lecture 5 Flashcards
Why use Ethernet?
- Low Cost
- Performance
- Availability
- Scalability
- Ease of use and management
What are Repeaters?
Physical device
• It merges LAN segment
What are some characteristics of repeaters?
o No Frame Cache
o No logical isolation of segments
o If two stations on different segments send at the same time, the frames are subject to collision
o Only one route across segments and repeaters
between any two stations
Describe a HUB
Special repeaters:
o the hub transmits to all links
o They provide additional network management functionality
Receives bits from a link and transmits these bits to all other links
o The same rate
o without buffering
o Without the use of CSMA/CD (the bits are forwarded without hearing the channel)
What are 2 advantages of a HUB
Advantages:
o If a LAN segment (which has a hub) is not working properly, the backbone hub will detect this and will disconnect the hub from the rest of the LAN.
o The other hubs that are attached to this backbone hub smoothly continue their operation
What are 2 disadvantages of HUBs
o Collisions on a LAN segment will affect the performance of other
LAN segments that are attached to the same backbone hub.
o Hubs cannot communicate in full duplex mode.
What are Bridge/Switching Characteristics?
A local forwarding table(filtering database)
• Stations auto-learning(backward learning)
• Loop detection(spanning tree algorithm)
What is Traffic isolation?
Creates separate LAN subnets
• Packet Filtering
• Frames from the same subnet are not sent to another subnet
• Each subnet is a separate section in the conflict detection mechanism
(collision detection)
What is the Tree spanning Protocol?
The bridges communicating via LANs to determine a tree covered (spanning tree), that is a subset of the original topology without loops
o Once the switches/bridges determine a tree covered:
o They disconnect virtually interfaces to create the tree covered by the original topology.
• If later, one of the links in covered tree failed:
o They can reconnect automatically interfaces, define a new set of interfaces
Switch vs Bridge differences
Switch:
Frame Management in Hardware
Multiple frame
Bridge:
Frame Management in Software
One frame switching
uses store-and forward operation
Which layers are HUBS, BRIDGES, ROUTERS, SWITCHES and REPEATERS?
Physical Layer = Hubs & Repeaters
Data Link Layer = Bridges & Switches
Network Layer = Routers
Why do we need Virtual LANs?
Why we need them o Increased Performance o A single LAN creates too much broadcast traffic o Security o Easy to Manage
What is an ACCESS in a Virtual LAN?
Access
o Send and receives untagged frames
o They are used to connect nodes to the LAN
What is an TRUNK in a Virtual LAN?
Trunk
o Send and receive tagged frames
o Configure switches to support various VLAN-id
