1. Hardware Addressing and Frame Type Identification
the need for addressing
addressing in hardware
static, dynamic and configurable addressing
broadcast addresses and promiscuous mode
frame type and frame format
Ethernet frame format

2. The need for addressing
A LAN provides a physical path from one computer to all others
Most communication is from one computer to one another
addressing allows the source to identify the destination
hardware addressing prevents unnecessary messages being seen by a computer

3. Specifying a recipient
Each station is assigned a unique numerical address on the network called its hardware address or physical address
Each frame transmitted across the network typically includes a destination address field and a source address field
the network hardware in each station decodes each frame and uses the destination address to determine whether to accept it
including the source address field makes it easy to generate a reply

4. LAN hardware and filtering
LAN hardware is typically completely separate from the computer’s CPU and memory

5. Static, dynamic and configurable hardware addresses
Static - the manufacturer assigns the hardware address which never changes
Dynamic - assign the address whenever the station boots up
Configurable - the customer sets the address (usually on installation)

6. Pros and cons
Static - easier for customer, addresses never change and computers can easily move network
Dynamic - easier for vendor, addresses can be smaller, but conflicts can arise
Configurable - allows permanent and smaller addresses

7. Broadcasting
Some applications require that a sender transmits a frame to all stations on the network
Use a special reserved broadcast address
All stations configured to accept packets for their own address and the broadcast address

8. Multicasting Restricted form of broadcasting
Broadcast capability without wasting CPU resources on all computers
E.g. allows some computers to participate in an audio transmission
Extends the addressing scheme by
reserving some addresses for multicast
Extends the network interface to accept an additional set of addresses

9. Promiscuous mode
Network hardware can often be programmed to accept all packets - promiscuous mode
Useful for network analysers (sniffers)
Security implications
Wireless networks can overhear and analyse packets sent within their range
Delay Tolerant Networks -- data couriers
Mobile Ad Hoc networks – opportunistic data transfers
Security: Encryption and/or collaborative reputation

10. Identifying packet contents
Computer may need to know what type a packet is in order to process it
Explicit frame type - network hardware designers specify how type information is included in the frame and may define types
Implicit frame type - the sending and receiving computers must agree how to specify types in software

11. Frame format
Frames typically include a frame header and a frame data area
header has a fixed size
data area varies between a minimum and maximum

12. Example - Ethernet frame format
Ethernet uses a 48 bit static addressing scheme and a 16 bit frame type
Ethernet standards define standard frame types

13. Implicit frame types
Either all computers agree to use a single standard format for data or they negotiate their own type fields (but these are not seen by the network hardware)
IEEE standard to define frame types in software
first component identifies a standards organisation
second component is defined by that organisation

14. Example of Frame Types Used with Ethernet

15. Summary The need for addressing Addressing in hardware
network interface cards
static, dynamic and configurable addressing
broadcast addresses, multicast addresses and promiscuous mode
Frame type and frame format
Ethernet frame format