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Naming (Intro (What are names? – Description of an Entity, What is it used…
Naming
Intro
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What is it used for?
– Share resources
– Identify Entity in a network or domain uniquely
– Refer to a location of an Entity
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Name – String of characteristic used to refer to an Entity • Entity can be anything in a Distributed System
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Flat Naming
Simple Solution
• Broadcasting
A message containing the identifier of the entity is broadcast to each machine and each machine is requested to check whether it has that entity.
• Forwarding Pointers
When entity moves from A to B, it leaves behind in A reference to its new location at B. As soon as entity has been located, a client can look up the current address by the following chain of forwarding pointers.
Home-based Approach
Single-tiered scheme
Let host’s home location(home agent) keep track of where the host IP address (location). – An entity’s(mobile) home address is registered at a naming service – The home registers the foreign address of the entity – Clients always contact the home first, and then continues with the foreign location
- Client send packet to host’s home location so that it can help to lookup for the host location.
- Sending back the host’s home location(home agent) IP address to client to acknowledge the client where is the location of host’s home location.
- In order to let client send packet successfully to host, host’s home location will create tunnel that wrap data in IP packet and send to care-of address(temporary address) .
- Temporary address of the host will be known by client and that’s why client able to send packet correct host.
Two-tiered scheme
Does not need to go through host’s home location because it will have a record of local register visit OR
The scheme will allow to keep track of the visiting entities:
• Check local visitor register first
• Fall back to home location if local lookup fails
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Distributed Hash Table
Example: Consider the organization of many nodes into a logical ring (Chord)
– Each node is assigned a random m-bit identifier.
– Every entity is assigned a unique m-bit key.
– Entity with key k falls under jurisdiction of node with smallest id k (called its successor).
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Each node p maintains a finger table FTp[] with at most m entries:
FTp[i] = succ(p + 2i−1)
Note: FTp[i] points to the first node succeeding p by at least 2i−1
To look up a key k, node p forwards the request to node with index j satisfying
q = FTp[j] <= k < FTp[j + 1]
If p < k < FTp[1], the request is also forwarded to FTp[1]