Foundation Summary 599
A variety of standards define the types of connectors and physical signaling protocols used on
the interfaces. Table 8-41 summarizes these standards:
Table 8-42 lists a variety of terms associated with Frame Relay.
Table 8-41
WAN Interface Standards
Standard
Standards Body
Number of Pins
on Interface
EIA/TIA 232
Telecommunications Industry Association
25
EIA/TIA 449
Telecommunications Industry Association
37
EIA/TIA 530
Telecommunications Industry Association
25
V.35
International Telecommunications Union
34
X.21
International Telecommunications Union
15
Table 8-42
Frame Relay Terms and Concepts
Virtual circuit (VC)
A VC is a logical concept that represents the path that frames travel
between DTEs. VCs are particularly useful when comparing Frame
Relay to leased physical circuits.
Permanent virtual circuit (PVC)
A PVC is a VC that is predefined. A PVC can be equated to a leased
line in concept.
Switched virtual circuit (SVC)
An SVC is a VC that is set up dynamically. An SVC can be equated
to a dial connection in concept.
Data terminal equipment (DTE)
DTEs are also known as data-circuit termination equipment. For
example, routers are DTEs when connected to a Frame Relay
service from a telecommunication company.
Data communications
equipment (DCE)
Frame Relay switches are DCE devices.
Access link
The access link is the leased line between DTE and DCE.
Access rate (AR)
The access rate is the speed at which the access link is clocked. This
choice affects the price of the connection.
Committed information rate
(CIR)
The CIR is the rate at which the DTE can send data for an
individual VC, for which the provider commits to deliver that
amount of data. The provider will send any data in excess of this
rate for this VC if its network has capacity at the time. This choice
typically affects the price of each VC.
Burst rate
The burst rate is the rate and length of time for which, for a
particular VC, the DTE can send faster than the CIR, and the
provider agrees to forward the data. This choice affects the price of
each VC typically.
continues
ch08.fm Page 599 Monday, March 20, 2000 5:17 PM