CS455 Sylabus

### Intro to interconnection heterogeneous networks

• Interconnecting heterogeneous networks

• We will now consider the problem of inter-connecting heterogeneous networks.

• Example:

• Problems when we interconnect heterogeneous Networks

• Problems

1. The identification problem:

 Different networks use different network numbers (identification) How can we uniquely identify a node on the entire network: (Computers need to use the same type of identifiers !!!)

2. The heterogeneity problem:

 Different networks use different frame formats (Computers need to use the same format (= code) !!!) How can we make different networks agree on the same encoding ???

3. Scalability (same issue as in a homogeneous network)

• Identification in a homogenous network

• Fact:

 Every Ethernet address is 48 bits Every Ethernet network card that has been made has a unique Ethernet (network) address

• Therefore:

 Nodes on different Ethernet networks have network addresses that are 48 bits long (we know what to use to identify a node) Each node (even on different networks) is uniquely identified by its Ethernet Address

Graphically illustrated:

• Identification in a heterogenous network

• Fact:

 An Ethernet Address is 48 bits A Token bus address is also 48 bits

Claim:

 Even when the address format are identical, we cannot use the Ethernet/Token bus address as identifiers !!!

Reason:

• Two (2) different nodes on the heterogeneous network can have the same address !!!

Example:

An Ethernet/Token bus address is no longer unique !!!

• Analogy:

 The licence plate of a car is unique within one state (e.g., some imaginary Georgia licence plate XXX YYY is unique in Georgia But this is not true for licence plates in two different states

• The hereogeneity (frame format) problem

• In a homogeneous network:

• In homogeneous networks, all frames has the same format:

• In homogeneous networks, node uses the same encoding to interprete meaning:

• The different frame formats used in heterogeneous networks will cause a Babel problem:

• In heterogeneous networks, the fields in the frame can be interpreted incorrectly:

• In heterogeneous networks, the codes in the control field can be interpreted incorrectly:

• Analogy:

• Each type of network "speak" a different language

• The interconnecting device must be smarter than a ordinary bridge because the interconnecting device must perform:

 Protocol translation !!!

• The scalability issue

• Recall: Flooding:

• When an Ethernet switch does not know the location of a destination:

the Ethernet switch will flood all networks:

• Scalability:

 Network operation must minimize the use of flooding !!!

• Summary of the solutions (very brief)

• Summary of solutions:

• Establish a uniform addressing method (and assignment):

 We need a world-wide Social Security Number (identification) system for every computer on the Internet

• Establish a common packet format

 I.e.: we need a network "Esperanto" language spoken by every computer on the Internet !!!

• Minimzie the use of flooding:

 Avoid the use of promiscuous interfaces (which encourage broadcasting) Retain (simplified) forwarding information to all destinations on the Internet

• We will discuss each problem/solution in more details next

(Not neccessary in the order of the problems presented above)