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/ addresses –Replicated services Entities might change access points –Laptops get different IP addresses based on their location –New phone number/ 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.