From: Scott Morris (smorris@ipexpert.com)
Date: Sun Sep 02 2007 - 21:00:53 ART
Typically fragment size is 80 bytes per 64k of line speed.
Now a speed of 480k gives some oddities (64 * 7.5 = 480) so 80 bytes * 7.5
is 600 bytes for a fragment size.
Being that packets are 1500 bytes by standard MTU, I'm going to assume that
"256K" is a typo for fragment size 'cause that would be one BIG frame. :)
VoIP, of course, brings a whole different set of headaches in and things to
think about because of the fragmentation delay and such.
HTH,
Scott Morris, CCIE4 (R&S/ISP-Dial/Security/Service Provider) #4713, JNCIE
#153, CISSP, et al.
CCSI/JNCI-M/JNCI-J
VP - Technical Training - IPexpert, Inc.
IPexpert Sr. Technical Instructor
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smorris@ipexpert.com
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-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
Victor Cappuccio
Sent: Sunday, September 02, 2007 3:46 PM
To: Carlos Trujillo Jimenez; ccielab@groupstudy.com
Cc: ctrujillo@magenta.cl
Subject: RE: CALCULATE FRAGMENT SIZE IN FRAME RELAY is there a formula??
http://www.cisco.com/warp/public/788/vofr/fr_frag.html
Frame-relay fragment is typically not needed for link speeds above 768 kbps.
If CIR is 256k and link speed is 480kbps, frame-relay fragment should be 256
K.
In a VoIP implementation, Frame Relay (Layer 2 protocol) cannot distinguish
between VoIP and data frames. FRF.12 fragments all packets that are larger
than the fragment size setting. Configure the fragmentation size on the DLCI
such that voice frames are not fragmented. You can configure the fragment
size under the Cisco IOS. Software map-class frame-relay command with the
issue of the frame-relay fragment fragment_size command. The fragment size
is in bytes, and the default is 53 B. Many variables determine the size of
the voice packets. For more information on voice packet size, refer to the
document Voice over IP - Per Call Bandwidth Consumption.
56kbps 70 bytes
64 kbps 80 bytes
128 Kbps 160 bytes
Voice packets wont be fragmented.
Default fragment size - 53 bytes
g711 160 bytes (voice payload)
g729 20 bytes (voice payload)
Total size of IP header (IP/UDP/RTP) - (20/8/12) Total g711 packet size =
160 + 40 = 200 bytes Total g729 packet size = 20 + 40 = 60 bytes
A big challenge with voice-data integration is to control the maximum
one-way end-to-end delay for time-sensitive traffic such as voice. For good
voice quality, this delay is less than 150 milliseconds (ms). An important
part of this delay is the serialization delay on the interface, which should
not exceed 20 ms. Serialization delay is the time it takes to actually place
the bits onto an interface.
Serialization Delay = frame size (bits) / link bandwidth (bits per
second
[bps])
For example, a 1500-byte (B) packet takes 187 ms to leave the router over a
64 kbps link. If you send a nonreal-time data packet of 1500 B, real-time
(voice) data packets queue until the transmit of the large data packet. This
delay is unacceptable for voice traffic. If nonreal-time data packets are
fragmented into smaller frames, the frames are interleaved with real-time
(voice) frames.
In this way, both voice and data frames can be carried together on low-speed
links without excessive delay to the real-time voice traffic.
thanks,
Victor Cappuccio.-
- CCSI# 31452
CCBOOTCAMP - A Cisco Sponsored Organization (SO) vcappuccio@ccbootcamp.com
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-----Original Message-----
From: nobody@groupstudy.com on behalf of Carlos Trujillo Jimenez
Sent: Sun 02-Sep-07 11:59 AM
To: ccielab@groupstudy.com
Cc: ctrujillo@magenta.cl
Subject: CALCULATE FRAGMENT SIZE IN FRAME RELAY is there a formula??
Dear partners.
Please I want you to confirm if I am correct or not in the answer of the
following task.
Scenario:
Data and voice packets are traversing the frame relay circuit between RA and
RB.
Enable frame relay traffic shaping in a interface according to the provided
CIR (256 K). and ensure all the shaping intervals are the smallest possible,
and that a single packet cannot take more than one interval to be
transmited.
so in each router I enable frame relay traffic shaping, associating the
following map-class
map-class frame-relay SHAPING
frame relay cir 256000
frame relay bc 2560
frame relay fragment 320
For the last one "FRAME RELAY FRAGMENT 320" what is the formula for
calculating it?? I mean I know that when larga packets exced the 320 size,
they get compressed right?, but how do I get the 320 size?? is there a
formula to calculate it??
I noticed also when I do a "show traffic shape" without enabling
fragmentation it shows me the following response:
Interface Se0/0
Access Target Byte Sustain Excess Interval Increment Adapt
VC List Rate Limit bits/int bits/int (ms) (bytes)
Active
402 256000 320 2560 0 10 320 -
403 256000 320 2560 0 10 320 -
405 256000 320 2560 0 10 320 -
406 256000 320 2560 0 10 320 -
413 256000 320 2560 0 10 320 -
506 256000 320 2560 0 10 320 -
513 256000 320 2560 0 10 320 -
401 256000 320 2560 0 10 320 -
So my question is, for calculating the fragment size, I simply copy the
value of the "byte limit" who shows me the show traffic shape output??
Thanks a lot, and regards.
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