Major Problems Solved with Internetworking Devices


Background.  Three main types of problems to be confronted in internetworking design can be categorized as
  • Delay or media problems
  • Protocol problems
  • Large payloads or latency problems

The decision to use routing, switching or some sort of ultra sophisticated transport approach such as ATM or Gigabit Ethernet can be loosely characterized in the following diagram.



Delay or Media Problems.  Media problems refers to an excessive number of collisions in an Ethernet or a long wait for the token in a Token Ring or FDDI.  Media problems are usually caused by having too many devices sharing the bandwidth of the transport media.  These problems are usually solved by dividing the LAN into more segments using switches.

In general, including and/or making better use of switches in a network results in the following advantages.

  • Higher bandwidth
    • resources not as simultaneously shared
  • Low cost
  • Easy configuration
  • MAC addressing for flatter more direct movement

Protocol Problems.   Protocol problems are usually caused by protocols that do not scale well or do not interact.  These sorts of problems can be solved by either dividing some segments by routers to do things like limit broadcasts or using them to create interactions between stand alone segments.

In general, including and/or making better use of routers in a network offers the following potential services.

  • Broadcast firewalling or filtering
  • Hierarchical addressing
  • Communication between dissimilar LANs
  • Fast convergence
  • Policy routing
  • Quality of Service routing (QoS)
  • Security
  • Redundancy and load balancing
  • Traffic flow management
  • Multimedia group membership

Transport Problems.  Transport problems are usually worst when the network is expected to provide voice and/or video services.  Almost any latency will mess up the signals sufficiently.  These sorts of solutions also require significantly more bandwidth.  These are usually solved using Fast Ethernet or ATM.  Cisco seems to be backing committing to the ATM approach, but doesn't preclude the use of Fast Ethernet.

Switches Versus Routers.  The following table, adapted from Teare, summarizes the issues associated with implementing switching versus routing.


  Routers Switches
Problem Solved Protocol problems
  • Media (LAN Switches)
  • Transport of large payloads (Fast Ethernet and ATM)
Key Features Many including
  • filtering
  • addressing
  • connect dissimilar LANs
  • security
  • load balancing
  • policy routing
  • QoS routing
  • multimedia
Many including
  • higher bandwidth
  • low cost
  • ease of configuration
  • more direct messaging
Reduce broadcast and bandwidth doamins Reduces collision domains