Virtual Leased Line Services
7210 SAS M Services Guide Page 127
Structured DS1/E1 CES without CAS
Structured CES without CAS is configured by choosing cesopsn as the vc-type when creating a
Cpipe service. For n * 64 kb/s structured circuit emulation operation, the framing parameter of the
port must be set to a framed setting (such as ESF for DS1). Each channel group contains n DS0s
(timeslots), where n is between 1 and 24 timeslots for DS1 and between 1 and 31 timeslots for E1.
The packet payload size is configurable (in octets) and must be an integer multiple of the number
of timeslots in the channel group. The minimum payload packet size is 2 octets (based on two
frames per packet and one timeslot per frame). See Table 9 for default and minimum payload size
values. The maximum payload packet size is 1514 octets.
Each DS1 or E1 frame contributes a number of octets to the packet payload. That number is equal
to the number of timeslots configured in the channel group. Thus, a channel group with four
timeslots contributes 4 octets to the payload. The timeslots do not need to be contiguous.
Note that a smaller packet size results in a lower packetization delay; however, it increases the
packet overhead (when expressed as a percentage of the traffic).
Calculation of Payload Size
The payload size (S), in octets, can be calculated using the following formula:
S = N x F
Where:
N = the number of octets (timeslots) collected per received frame (DS1 or E1)
F = the number of received frames (DS1 or E1) that are accumulated in each CESoPSN packet.
For example, assume the packet collects 16 frames (F) and the channel group contains 4 octets
(timeslots) (N). Then the packet payload size (S) is:
S = 4 octets/frame x 16 frames
= 64 octets
Calculation of Packetization Delay
Packetization delay is the time needed to collect the payload for a CESoPSN packet. DS1 and E1
frames arrive at a rate of 8000 frames per second. Therefore, the received frame arrival period is
125 µs.
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