10Base5

1
10Base5

• DIX standard (Digital, Intel, Xerox)
• Early 80s
• Small network model
• Evolution and growth has occurred
• Used thick coax
• Speeds inadequate for todays systems
• CSMA/CD imposed length and speed limitations

2
Early Ethernet Standards

• Repeaters needed because of attenuation
• Designed with 2 ports (one in, one out)
• Half-duplex transmission only since coax uses a
  pair of conductors to send and receive
• Manchester signal encoding used on coax circuits
• Transceivers are converters or filters
• Convert electrical signals into patterns that can
  be used by computer circuits

3
Evolution of Small Networks

• 10Base5
• 10Base2
• 10BaseT
• All are half-duplex bus (broadcast) networks
• No loops allowed
• New installations may take advantage of latest
  technology
• Legacy systems still exist

4
Evolution of small networks

• Limitations of older systems and user demands
  generated new developments
• 10Base2 to 10BaseT and beyond
• 100 Mbps, 1000 Mbps
• Other media (fiber)
• Switching Hubs

5
Expanding to Larger Networks

• 10BaseT bridging (802.1 standards)
• Bridging isolates or connects different LANs
• Bridges use tables of MAC addresses to isolate or
  route network traffic
• 802.1 bridges flood unknown frames
• transmit a frame to all ports to reach all
  segments
• Useful when an address has aged out of the bridge
  table

6
Evolution of Small Ethernet Networks

• Bridging Technology to Switching Hubs
• Switches can learn how to connect computers to
  ports
• mapping source MAC addresses to ports
• Saving info in tables
• Thus eliminating or minimizing collision domains
• Also removes 10BaseT distance limitations

7
Switches

• Hierarchical arrangement
• no loops
• simple forwarding tables (1 port per MAC
  address)
• Spanning tree algorithm eliminates loops
• Also eliminates some vulnerability
• Extra links are initially deactivated
• Upon failure of a link a backup is available for
  spanning

8
Switch Characteristics

• Learning and Unlearning
• Initially switch acts like a hub
• Eventually it captures source MAC addresses and
  maps them to port addresses
• This learned information is stored in a table
• Mappings are dynamic older mappings age out of
  table (are dropped)

9
Switch Characteristics

• Blocking vs Non-Blocking
• Switch capacity exceeded, frames dropped or
  stored in queue
• Non-blocking switches can accommodate maximal
  load, i.e., all stations transmitting
  simultaneously
• 24 port 100BaseTX switch requires 2.4 Gbps (24
  times 100 Mbps) - aggregate throughput to be
  non-blocking

10
Virtual LANs or VLANs

• Logical groups of servers and clients can be set
  to eliminate excessive broadcast traffic

11
Congestion and Latency

• Remedies
• Overprovisioning
• Install more capacity than needed
• Priority
• Use Tag Control Information field
• Quality of Service
• Not offered by Ethernet
• Traffic Shaping
• Limit traffic entering system during peak periods
  (a policy guideline)

12
ATM(Asynchronous Transfer Mode)

• A switching technology
• More sophisticated than Ethernet
• Also more expensive
• Uses fixed length cells
• 53 octets
• 5 octet header and 48 octet payload
• Reduces latency at each switch at the expense of
  overhead

13
ATM Virtual Circuits

• ATM switches can be organized in a mesh to allow
  for alternative routes between end stations
• Forwarding tables
• Contain virtual circuit number
• and port associated with virtual circuit number
• cells actually contain virtual circuit number in
  address field
• switch sends cells to the virtual circuit number
  instead of a port address

14
Quality of Service

• ATM offers 4 Classes of Service (A, B,C,D)
• ATM Forum defines specific Service Categories
• Peak cell rate
• Maximum burst size
• Sustainable cell rate
• Cell delay variation tolerance
• Cell loss ratio
• Forum Service Categories are more extensive than
  ITU Classes

15
Other Technologies

• Routers
• Traditionally routers connect subnets
• More expensive and slower than layer 3 switches
• Can handle multiple protocols
• must be used for transmission over WANs
• Layer 3 switches
• Forward IP packets based upon IP destination
  addresses
• Layer 4 switches
• Read port numbers in TCP and UDP messages
  encapsulated with IP packets