background image
OSI Data Link Layer Functions 97
HDLC includes a meaningless address field because it is used only on point-to-point serial
links. The recipient is implied; if one device sent a frame, the other device is the only possible
intended recipient.
With Frame Relay, there is one physical link that has many logical circuits called virtual circuits
(VCs). (See Chapter 8 for more background on Frame Relay.) The address field in Frame Relay
defines a data-link connection identifier (DLCI), which identifies each VC. For example, in
Figure 3-12, the Frame Relay switch to which router Timbuktu is connected receives frames;
the switch forwards the frame to either Kalamazoo or East Egypt based on the DLCI, which
identifies each VC. So, Timbuktu has one physical connection but multiple logical connections.
Ethernet address, NIC address, LAN
address, Token Ring address, card
address
Other names often used instead of MAC address. These
terms describe the 6-byte address of the LAN interface card.
Burned-in address
The 6-byte address assigned by the vendor making the card.
It is usually burned in to a ROM or EEPROM on the LAN
card and begins with a 3-byte Organizationally Unique
Identifier (OUI) assigned by the IEEE.
Locally administered address
Via configuration, an address that is used instead of the
burned-in address.
Unicast address
Fancy term for a MAC that represents a single LAN
interface.
Broadcast address
An address that means "all devices that reside on this LAN
right now."
Multicast address
Not valid on Token Ring. On Ethernet, a multicast address
implies some subset of all devices currently on the LAN.
Functional address
Not valid on Ethernet. On Token Ring, these addresses are
reserved to represent the device(s) on the ring performing a
particular function. For example, all source-route bridges
supply the ring number to other devices; to do so, they each
listen for the Ring Parameter Server (RPS) functional
address.
Table 3-7
LAN MAC Address Terminology and Features (Continued)
LAN Addressing Terms and
Features
Description
ch03.fm Page 97 Monday, March 20, 2000 4:58 PM