Page 216 - Optical Switching And Networking Handbook

09_200023_CH08/Batesx 1/17/01 8:20 AM Page 201

High-Speed Applications 201

Figure 8-13 Upper Layers
5-7
Summary of
protocol layers and 4 TCP Connection oriented, graceful close, retransmission
requests, integrity checking, sequencing
benefits
IP
3 Connectionless, no guaranteed delivery, no integrity
checking, no retransmission, no sequencing
AAL Overhead attached to provide sequencing and Elimination means
integrity checking loss of QoS and
2 need to use a PPP
ATM protocol
Overhead provides for Quality of Service
SONET Elimination loses
1 Provides overhead for OAM&P, plus recovery survivability
Fiber (DWDM) Raw pipe, provides no guarantees, no integrity
checks, no framing and formatting, etc. Point-to-Point

ing statistical gain for bursty services while ensuring that the band-
width and latency requirements of leased-line and time-division
multiplexing (TDM) voice services are also met.
These features enable an OC-12 fiberoptic access ring using ATM
over SONET technology to support over 100 10baseT transparent
LAN services, assuming a 2-Mbps sustainable rate on each service.
Increasing the utilization of access networks enables network oper-
ators to postpone upgrades of these networks to higher rates and
minimizes the need to acquire additional leased access facilities.
Packets can be sent over ATM and then over SONET by going
through several steps of preparation. In Figure 8-14, data must be
sent. The data file can be multimegabytes large. The sequence will
follow as:
1. The multimegabyte file is passed to TCP.
2. TCP segments the data into 64-kB segments.

3. TCP passes the segment to IP.
4. IP creates the default datagrams of 576 bytes (or some other
size).
5. The datagrams are passed to the Asynchronous Transfer Mode
(ATM), ATM Adaption Layer (AAL) (typically AAL5) and broken
down into the segmentation and reassembly (SAR) of 48 bytes.