Transcript Document

ESE 572
Lectures on Addresses in Networks
Addresses in Communication Networks
What is network address?
Unique identifier for a network destination that enables correct delivery of information
from any source to this destination.
Examples of address that a person can have.
-Postal address
-Phone number (home, office, cellular…)
-Pager of beeper number
-Fax number
-Email address
-Social Security Number
-Drivers ID number
-Student ID number
-Account number (bank, credit card…)
-Finger prints
-Corneal scan
Some Terminologies
Link
Node
Network
Local area network (LAN)
Wide area network(WAN)
Router
Network Layer
Data Link Layer
Network Layer Addresses
Term
A unique global address that enables routing of information from any source to any
destination(s) in the network. As opposed to this term, the Data Link Addresses are
defined on a point-to-point basis, i.e., not necessarily globally.
Address Types
Hierarchical: There is some structure in the addressing scheme that indicates the location
of destination form the address itself (e.g., Postal Address, telephone number, IP address
for workstation). Wide area networks with a large number of subscribers traditionally
have a hierarchical address structure to deal with the complexity. However, this is
changing to accommodate the mobility.
Unstructured or flat: An address is nothing more than an identifier. The location of the
destination must be advertised (frequently) to let others to know how to get to you (e.g.,
Ethernet). This type of address is typical for small networks.
Combination: Some structure complemented by advisement (e.g., wireless telephone).
Example of Hierarchical Addressing: Telephone Number
Numbering plan established for North America in 1947
Designed for
-Subscriber to subscriber call
-Subscriber to telco service (e.g.,directory service)
-Operator to subscriber (e.g.,prearranged call)
-Operator to operator (when direct dialing is unavailable)
Special numbers
-Prefix (e.g.,011 for international, 01 for person to person)
-N11 service code (e.g.,411 for directory assistant, 611 for repair)
-Suffix (e.g., # for end of digit transmission)
10 digit addressing (legend: N=2-9, X=0-9, 0/1=0 or 1)
- It used to be that 3 digit area code must be in the form of N 0/1 X. This resulted in 152
possibilities (why?).
-3 digit central office code (NXX): 800 possibilities
-4 digit line number (XXXX): 10,000 possibilities
Digits are transmitted by
-Dual Tone Multi Frequency (DTMF)
-Dialed Pulse
Call processing
-NXX XXXX calls are processed immediately
-Prefix 0 is used for operator access. 1 is reserved for the toll calls.
-Critical timing issue: When is the dialing completed? E.g., “0” versus “0 N0/1X NXX
XXXX”)
Example of Flat Addressing: Ethernet
One of the IEEE 802 Standard for LANs.
Each device is given a permanent hardware configured address by a manufacturer
Manufacturers obtain a block of Ethernet addresses and use it consecutively to ensure
that no two devices have the same address.
Ethernet device can move to another location without changing its data link layer
address.
Ethernet address is a 48 bit binary number
Ethernet device listens on the link it is attached to and filters out the messages that are
not directed to it.
Non typical addresses
- Broadcast address
- Multicast address
Non typical addresses are configured in firmware. To recognize these addresses, at the
start up, additional addresses must be down loaded to the Ethernet interface to allow
these other types of addresses to be filtered in.
Hierarchical Network Layer Address
There are too many addresses. Partitioning into smaller pieces is required.
(Postal delivery example below.)
-Get
-Get
-Get
-Get
to
to
to
to
the
the
the
the
correct country.
correct state or province.
correct city.
correct destination.
IP (Internet Protocol) Network Layer Address is the best example of this.
However, due to the mobility (via wireless IP devices), the hierarchical
nature of the IP addresses are being modified.
IP Network Layer Address
4 octet address
Address=link ID + host ID
Masking technique is used to distinguish link ID from host ID.
Example: IP Address of a computer is 79.214.192.83. Suppose the 79.214.192.X is
the link ID. Then the mask is 255.255.255.0.
Host ID
Link ID
01001111
11010110
11000000
01010011
Each node must know the mask for the link it is attached to and its
own host ID. Every node attached to the same link must share the
same link portion of the address.
Link ID can be further decomposed into subnets. Link ID=net ID+subnet ID
Masking allows aggregation of links, creating hierarchy of subnets.
R
R
R
4.19.*
R
IP Address Convention
000…0=“this” and 111…1=“all”
First octet.second octet.third octet.fourth octet(e.g., 13.222.13.2)
Multicast address=“1110”+class D address
The current version of IP address is called IP V4.
Now the addressing is going towards 128 bit convention to accommodate the
rapidly increasing ID devices. (IP V6)
Requirements for Communication
1.R1 and R2 need to know the network layer addresses of E1 and E2, for announcing to
the world.
2.R1 and R2 need to know the data link layer addresses of E1 and E2, for packet routing.
3.E1 and E2 need to know the date link layer address pf either R1 or R2 or both.
4.E1 should be able to send a packet directly to E2 without routers.
5.E1 to E3 communication should use R2 not R1.
6.E1 should be able to find the date link layer address of E2 without R1 or R2.
E4
Rest of network
R1
E1
E3
R2
E2
Solutions
If End node is attached via point to point link: Use Neighborhood Greeting
-Use of End-System-Hello (ESH)
E
R
Rest of network
For general network topology:
All devices in the same link share the same mask. By design, routers
know their end nodes data link addresses.
Use of three messages
- Address Resolution Protocol (ARP) query: broadcast from an end node to all
other end nodes.
- ARP response: response to ARP query
- Redirect from a router to end node