There are four basic elements of network architecture that must be considered when designing a network. Each of them must be planned when designing the network. These elements are illustrated below:
Fault tolerance: the mean of fault tolerance is to ensure that the network will function properly even if fails occurs. The fails can occur in many different locations inside the network such as cables, routers, switches, or servers.
The key idea in fault tolerance is to make duplication for the above components such that if as fault occurred in each of them, there will be an alternate one and the network will still be functional. This is a popular component in the internet architecture design.
Scalability: the meaning of scalability is to ensure that the network can grow in the future without changing the design. Thus the administrator of the network can add more users to the network or add even an entire sub network without rebuilding the original network.
This element is very important on the internet because any one can see that the internet is growing continuously and more users are added every day.
Quality of service (QOS): QOS is also an important aspect in any network especially on the internet. QOS enables the admin to classify the services performed by the network from higher to lower. Thus the network performs different from one user to another according to the data he is sending or the type of the user.
Some users transmit voice on the network when making a call while others transmits regular data such as files and emails. Each one of these services requires a different network usage or a class of service. The voice and video must take the highest priority while the files and emails take the lowest priority. This is because voice and videos are delay sensitive and must be transmitted as soon as possible.
Security: when transmitting sensitive data across any network such as the internet, security often is an important aspect to consider. This is because the data to be transmitted may be sensitive or private. This is solved by encrypting the data such that no one can read the data other than the destination. On the internet, a protocol called secure hypertext transfer protocol is used for this purpose.
The sensitive data may be passwords or credit card numbers which needs to be protected. Also when logging into a server, user credentials needs to be defined first at the server. This is called authentication and is another element of security. The two are very important aspects that are used in the internet protocols. Note that the internet is an open network and so security is very important as a part of its architecture.
SONET links can be thought of as highways, as SONET is used in metropolitan and wide area networks. Using this highway analogy, we can say that a SONET transport network is hierarchical, as a collection of small roads, medium-sized roads, and highways for long distance. Unlike highway systems, the typical architecture for SONET is a collection of rings, although point-to-point connections are used as well.
Figure 4-4 illustrates the following three classes of SONET networking equipment:
O-E-O regenerators,
add-drop multiplexers, and
terminal multiplexers.
O-E-O regenerators are used to regenerate optical signals that travel long distances. The most straightforward, although not necessarily the most effective way to regenerate is to convert to the electrical domain and then back to the optical domain, as discussed elsewhere in the book.
SONET O-E-O regenerators might differ from protocol-independent O-E-O regenerators by
Figure 4-4 SONET networking equipment.
implementing additional performance-monitoring functions. To understand performance monitoring, we need to know how a SONET frame is built, which comes later in the chapter. (ADMs) Add- drop multiplexers are the most versatile pieces of SONET networking gear, as they can add or drop any amount of SONET traffic, as desired by the network operations. SONET ADMs are used to create SONET transport networks consisting of SONET rings and point-to-point connections.
Advanced Digital Architectures
(TMs) Terminal multiplexers are a specialized class of ADMs used at the edges of SONET networks. They have the capability to multiplex lower bandwidth signals coming from SONET or non-SONET access networks. Terminal muxes are used
to aggregate lower-bandwidth traffic into higher-bandwidth SONET pipes
for transmission over optical fibers.
An example of SONET transport architecture is shown in Figure 4.3 .
FIGURE 4.3 SONET transport network.
This particular SONET ring consists of fi ve ADMs, which are collecting traffi c from other ADMs and TMs residing outside the ring.
In addition to ADMs, the rings contain O-E-O regenerators which are inserted in the network when the distance between two ADMs becomes too large. SONET regenerators are much simpler and cheaper than ADM regenerators, but unlike ADMs, they have no
ability to branch out traffi c. In addition to O-E-O regenerators, optical amplifi ers can be used in the ring as well. -->
