Naming

CSCI 4780/6780

Names & Naming System• Names have unique importance

– Resource sharing– Identifying entities– Location reference

• Name can be resolved to the entity it refers to

• Naming system resolves names

• Naming system in distributed systems can itself be distributed

Names, Entities & Addresses

• Name is a string of bits/characters used to refer to an entity• Entity can resources/users/data/processes

– Web pages, files, hosts, printers, network connections

– Entities permit certain operations (reading/writing files)

• To operate we need to access the entity• Access Point – A special kind of entity

– Host of a server

• Name of access point is called its Address– Hosts IP address and port

• Address of access point is the address of the entity at that access point

More on Entities and Addresses• Entities can have multiple access points

– Multiple telephone numbers/email addresses– Replicated services

• Entities might change access points– Laptops get different IP addresses based on their

location– New phone number/email when switching jobs

• Can we use the address as the name of an entity?– Difficulties in relocation/replication transparency

• Name that is independent of address – Location Independent Names

Identifiers• An name with following properties

– Identifier refers to at most one entity– Entity is referred to by at most one identifier– Identifier always refers to same entity (persistence)

• Facilitates unambiguous reference– Testing equality of identifiers suffices if entities being

referred to are the same

• Addresses cannot be identifiers if they can be re-assigned– Example: Telephone numbers

Flat Naming• Identifiers are random bit strings• No information on how to locate the entity• Simple location resolution strategies

– Broadcasting (E.g. Address Resolution Protocol (ARP))– Multicasting

• Forwarding Pointers– A moving entity leaves behind a reference at its previous

location– Long chains causes inefficiency– Maintenance costs– Vulnerability to broken links

Forwarding Pointers in SSP Chains

Figure 5-1. The principle of forwarding pointers using (client stub, server stub) pairs.

Redirection by Shortcuts

Figure 5-2. Redirecting a forwarding pointer by storing a shortcut in a client stub.

Shortcuts

Figure 5-2. Redirecting a forwarding pointer by storing a shortcut in a client stub.

Home Based Approaches• Each entity has a home location

– Permanent address of the entity

• Obtains temporary address when roaming

• Home location keeps track of the current address of the entity

• Home agent forwards the packet to the entities current location

• Drawbacks?

Home-Based Approaches

Figure 5-3. The principle of Mobile IP.