Part 5: naming Flashcards
Flat naming
flat names, often referred to as identifiers, are typically random bit strings.
A significant property of such a name is that it does not contain any information on how to locate the access point of its associated entity. [Pages: 256,255]
Simple Solutions for Locating an Entity:
Broadcasting: The identifier of the entity is broadcast to every process in the distributed system. The process that offers an access point for the entity responds by providing an address for that access point. This approach is mainly applicable to local-area networks but has scalability issues in larger networks.
Forwarding Pointers: This is another approach mainly suitable for local-area networks. [Pages: 256,255]
Home-based approaches
Concept of Home Location:
A popular approach to support mobile entities in large-scale networks is to introduce a home location. This home location keeps track of the current location of an entity.
The home location is often chosen to be the place where an entity was created. [Pages: 259]
Usage as a Fall-back Mechanism:
The home-based approach is used as a fall-back mechanism for location services that are based on forwarding pointers.
An example of the home-based approach is found in Mobile IP, where each mobile host uses a fixed IP address. All communication to that IP address is initially directed to the mobile host’s home network. [Pages: 259]
Drawbacks:
One of the main drawbacks of the home-based approach is the need to always contact the home, which may be located far from the entity itself. This can result in increased communication latency.
Another challenge is the use of a fixed home location. Ensuring the home location always exists is crucial; otherwise, contacting the entity becomes impossible. Problems can arise when a long-lived entity decides to move permanently to a different part of the network than where its home is located. In such cases, it would be beneficial if the home could move along with the host. [Pages: 260]
Solution to Moving Home Location:
A potential solution to the problem of a fixed home location is to register the home at a traditional naming service. Clients can first look up the location of the home. Since the home location is relatively stable, its location can be effectively cached after being looked up. [Pages: 260]
Hierarchical approaches
General Approach:
In a hierarchical scheme, a network is divided into a collection of domains.
There is a single top-level domain that spans the entire network. Each domain can be subdivided into multiple, smaller subdomains.
A lowest-level domain, called a leaf domain, typically corresponds to a local-area network in a computer network or a cell in a mobile telephone network. [Pages: 265]
Globe Location Service:
The approach presented is based on the Globe location service, which is a general-purpose location service representative of many hierarchical location services proposed for Personal Communication Systems. [Pages: 265]
Functionality:
In a hierarchical location service, a client wishing to locate an entity issues a lookup request to the directory node of the leaf domain in which the client resides.
If the directory node doesn’t store a location record for the entity (meaning the entity isn’t located in that domain), the request is forwarded to its parent node. This parent node represents a larger domain than its child.
This forwarding continues until a directory node that stores a location record for the entity is reached. [Pages: 266]
Advantages:
Hierarchical approaches can offer scalability and structured organization, making it easier to manage and locate entities in large-scale networks.
Comparison with DHTs:
While Distributed Hash Tables (DHTs) provide a decentralized way to store and retrieve data, hierarchical approaches offer a more structured and organized way to manage entities in a network. Both methods have their own advantages and are suited for different scenarios.
Name Spaces
Introduction:
Flat names are suitable for machines, but they are generally not very convenient for humans to use. As an alternative, naming systems often support structured names that are composed of simple, human-readable names. [Pages: 270,271]
Name Spaces:
Names are commonly organized into what is called a name space. Name spaces for structured names can be represented as a labeled, directed graph with two types of nodes: leaf nodes and directory nodes.
A leaf node represents a named entity and has no outgoing edges. It generally stores information about the entity it represents, such as its address.
In contrast, a directory node has multiple outgoing edges, each labeled with a name. Each node in a naming graph is considered another entity in a distributed system and has an associated identifier. A directory node stores a table in which an outgoing edge is represented as a pair (node identifier, edge label). This table is called a directory table. [Pages: 270,271]
Root Node:
The naming graph can have a node, such as n0, which has only outgoing and no incoming edges. Such a node is called the root node of the naming graph. Many naming systems have only one root node for simplicity. [Pages: 270,271]
Layers in Structured Naming:
The document mentions different layers in structured naming, such as the global layer, administrational layer, and managerial layer. The global layer is formed by directory nodes that are managed by different organizations or groups of organizations. The administrational layer is formed by directory nodes managed within a single organization, representing groups of entities that belong to the same organization or administrative unit. The managerial layer consists of nodes that may change regularly, such as nodes representing hosts in a local network. [Pages: 278,279]
Comparison with Flat Naming:
While flat names are random bit strings without any inherent location information, structured names are organized hierarchically and are more human-friendly. Structured names can be efficiently resolved using hierarchical solutions. [Pages: 254,255]
