Information Technology Reference
In-Depth Information
connected devices. The data link layer in Frame Relay establishes connections using a
DTE device such as a router and a DCE device such as a frame switch.
Frame Relay circuits between sites can be either permanent virtual circuits (PVC) or
switched virtual circuits (SVC). PVCs are used more predominantly because of the con-
nections' permanent nature. SVCs, on the other hand, are temporary connections created
for each data t ran sfer s e s s ion.
A point-to-point PVC between two routers or endpoints uses a data-link connection iden-
tifier (DLCI) to identify the local end of the PVC. The DLCI is a locally significant nu-
meric value that can be reused throughout the Frame Relay WAN if necessary.
Frame Relay has been deployed since the late 1980s, but the use of Frame Relay is on the
decline because of the popularity of MPLS.
Time-Division Multiplexing
Time-division multiplexing (TDM) is a type of digital multiplexing in which multiple
channels such as data, voice, and video are combined over one communication medium by
interleaving pulses representing bits from different channels. Basic DS0 channel band-
width is defined at 64 kbps. In North America, a DS1 or T1 circuit provides 1.544 Mbps
of bandwidth consisting of 24 time slots of 64 kbps each and an 8-kbps channel for con-
trol information. In addition, a DS3 or T3 circuit provides 44.736 Mbps of bandwidth.
Other parts of the world, such as Europe, follow E1 standards, which allow for 30 channels
at 2.048 Mbps of bandwidth. Service providers can guarantee or reserve the bandwidth
used on TDM networks. The customers' TDM transmissions are charged for their exclu-
sive access to these circuits. On the other hand, packet-switched networks typically are
shared, thereby allowing the service providers more flexibility in managing their networks
and the services they offer.
Metro Ethernet
Metro Ethernet uses well-known “Ethernet” to deliver low-cost and high-speed
MAN/WAN connectivity for organizations. Many service providers now offer Metro Eth-
ernet solutions to deliver a wide range of converged network services such as data, voice,
and video on the same wire. Metro Ethernet provides enterprise LAN type functionality
out in the MAN and WAN, increasing the throughput available for applications. Metro
Ethernet bandwidths can range from 10Mbps to 1 Gbps, and even higher in some cases,
allowing for support for higher performance and increased QoS requirements. In contrast
to the rigid nature of traditional TDM provisioning, Metro Ethernet services are much
easier to deploy and scale due to the flexible bandwidth increments. Metro Ethernet tech-
nology is appealing to many customers because they are already comfortable using Ether-
net throughout their LAN environments.
Key
To p i c
SONET/SDH
The architecture of SONET/SDH is circuit-based and delivers high-speed services over an
specification, and the International Telecommunications Union (ITU) defines SDH.
