Repeaters, Hubs, Bridges and Switches

by Johannes Helmig [Published on 19 Dec. 1999 / Last Updated on 19 Dec. 1999]

Networks have the trend to grow, requiring often the need for repeaters ( on 10base2 - Thin-Ethernet ) or multiple hubs (on 10/100baseT Twisted-Pair), where it is required to follow the rules on maximum number of Repeaters/Hubs ( Large Networks: 5-4-3 Rule ).
This includes today also the possibility to connect systems without cables using a
WLAN AccessPoint.

10base2 - Thin Ethernet (Coax):

10baseT - Twisted Pair (TP/UTP):

But these 'cable-extension' method have all a serious limitation
concerning the maximum throughput of the network:
(explanation is visually via the animated GIF below)

Hubs and repeaters are fairly simple, 'non-intelligent' devices:
whatever comes in on one port, gets amplified and send out to ALL other ports, so any network transmission 'fills up/flows into' ALL cable-segments of the network, so only ONE network connection can be active at a time on the complete network !

When multiple system try to communicate at the same time:
(explanation is visually via the animated GIF below)

then the signals 'collide'/corrupt each other, making them invalid, time has been wasted and the system will try after a random delay again to transmit, resulting in network slowdown.

There is a possibility to optimize such network configurations:
In the early days of networking, such a 'intelligent' device called 'Bridge' viewed at the data inside the transmissions, to find out based on the Network-card addresses (MAC), whether it is necessary to transmit the information to a different segment or not. Such Bridges has only 2 connectors, allowing to split large networks into 2 smaller sub-networks.

Switches are also 'intelligent', but are able to handle more than 2 ports and are able to handle more than 2 communications at the same time:
When a transmission comes in on one port, the switch looks at the MAC addresses to determine, onto which port to send it out:

Now a large network can handle MULTIPLE transmissions at the same time:
(explanation is visually via the animated GIF below)

But to be able to get this additional Through-put, careful planing of the network layout is required, looking on the flow of the network traffic:

Singe Server configuration:

Swapping a hub to a Switch in such a configuration will not optimize the network, since the connection from the TP-HUB to the server is still the bottle-neck.

Multi Server configuration:

If most the network traffic is within the workgroups (departments,..) and only few network traffic is between the workgroups, then a Switch is the solution to optimize network utilization.

Optimize 10 Mbit Network using a 100 MBit Server connection:

Blackbox = Hub
if the 'Blackbox' is a hub (even if it is a switching 10/100 Mbit hub), the throughput of the complete network is limited at 10 Mbit (since ALL traffic is transmitted by a hub to ALL connected segmentsand even a 100 Mbit connection
from the hub to the server results to a very limited improvement )

Blackbox = Switch
if the 'Blackbox' is a Switch, then each connected system can communicate at full speed of the 10 Mbit with the server ( because the switch does NOT pass it through to the other 10 MBit segments and the connection of 100 MBit with the server can handle the higher throughput)

In reality, a server is handling multiple network requests at the same time,
which makes the use of a Switch and a 100 Mbit link between the switch and
the server even more efficient:

Since changing of 10 MBit TP-cabling to 100 Mbit/CAT5-cabling is expensive
in offices (where cables run inside walls and across sealings), swapping a
10 Mbit HUB to a 10/100 MBit SWITCH and upgrading the connection to the
server to 100 Mbit is a cost-effective solution to improve network throughput.

See Also

The Author — Johannes Helmig

Dr.Johannes Helmig is working as Director, Technical Knowledge Management in the Belgium office of Gerber Technology where he is involved in Customer Service and internal training, with special interest in Networking.


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