Network Extensions

1
Network Extensions
2
Local Area Networks

• Extending LANs - distance
• Attenuation
• Regenerators /Repeaters
• Too many stations
• Heavy traffic collisions
• ?
• Divide the network to divide the traffic
• Devices?

3
Repeaters

• Operates at the Physical layer
• Can convert from one physical layer spec to
  another
• Recover original information and re-modulate
• Critical placement before signal is very weak
• Extends physical length
• Number of repeaters limited if CSMA/CD

4
Repeaters
5
Repeaters

• Number of repeaters

6
Repeaters

• Network perspective
• One LAN
• All signals forwarded corrupted ?
• One Collision Domain
• Collision information forwarded
• One Broadcast Domain
• All frames are broadcasted
• Any Traffic isolation?

7
Hubs

• Number of repeaters
• Useful for star topology
• One device per leg
• Repeats frames into all legs, but incoming

8
Hubs
Collision Domain? Broadcast Domain? Traffic
isolation?
9
Hub Trees
Collision Domain? Broadcast Domain? Traffic
isolation?
10
Bridges

• Bridges
• Bridging networks with different
• Layer 1, Layer 2
• Support Error and flow control
• Access to the physical address
• Forwards based on the address

11
Bridges

• Intelligent
• Passes only frames belonging to that leg
• Checks frames going by learns
• (transparent bridges)
• Maps addresses to ports
• Maintains a table
• Check destination address and forwards
• First time flood all outgoing legs

12
Bridges

• Frames on same leg discard ?

13
Bridges

• Noise and corrupted frames ignored
• Table entries are timed

14
Bridges

• Collided frames -?
• Corrupted frames -?
• Unicast frames?
• Broadcast frames ?
• Collision Domain
• Broadcast Domain?
• Traffic isolation?

15
Multi-port Bridges

• Bridges connected to more than 2 segments
• Check destination address
• Not known
• Flood to all other legs connected

16
Bridging loops

• Redundancy in Bridges
• Always incoming frame copied to other legs
• Packet looping

17
Bridging Loops

• Spanning tree algorithm
• inter-bridge communications
• Eliminates routing loops
• Source Routing Bridges
• Details of route to follow for the frame

18
Switches

• Can systems talk simultaneously?

19
Switches

• Operates at Layer 2
• Many devices per leg
• Learns MAC address for each leg
• Buffers and forwards packet when link is free
  avoids collision
• May operate on virtual ids
• Switching Fabric

20
Routers

• Interconnect subnets
• Works at Network Layer
• Limits broadcast domain
• Routing decisions
• Identify if packet belongs to this network

21
Multi-homed Hosts

• Hosts connected to many networks
• Increased reliability
• Especially servers
• HOST has multiple addresses
• Difference?