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Frame Relay top speed 1.54 Mbps?
- 05-07-2007
May 7, 2007, 11:16 pm

Im just starting to learn CCNA, go easy on me :)
I keep seeing text stating that "Frame Relay can provide data transfer
rates of up to 1.54 Mbps". Then in the next paragraph it will say:
"Frame Relay can be implemented over a variety of connection lines
including 56K, T1, T3"
My questions: Why would you be running frame relay on a T3 (45Mbps)
if its data transfer speed is limited to 1.544Mbps? Is that really the
top speed for frame relay? 1Would companies typically have multiple
Frame Relay connections? All running on a seperate physical lines? or
through a single T3 perhaps? Im confused!
Any basic/brief info would be appreciated
I keep seeing text stating that "Frame Relay can provide data transfer
rates of up to 1.54 Mbps". Then in the next paragraph it will say:
"Frame Relay can be implemented over a variety of connection lines
including 56K, T1, T3"
My questions: Why would you be running frame relay on a T3 (45Mbps)
if its data transfer speed is limited to 1.544Mbps? Is that really the
top speed for frame relay? 1Would companies typically have multiple
Frame Relay connections? All running on a seperate physical lines? or
through a single T3 perhaps? Im confused!
Any basic/brief info would be appreciated

Re: Frame Relay top speed 1.54 Mbps?

sounds like another old USA tunnel vision Q.
FWIW the typical port speed in Europe was "up to 2 Mbps" (E1) and F/R is
covered by world wide standards - so 1.5 was a USA only answer....

F/R was also available here at E3 34 Mbps as a service from some telcos -
but european telco F/R networks typically used ATM above 2 Mbps.
However - if you ignore the "switching" bit of Frame Relay in the telco
cloud, then from a router perspective F/R is just a serial encapsulation
choice.
And in a Cisco router which supports the interfaces, it works on high speed
serial interfaces such as HSSI (50 Mbps), as well as some others such as E3
/ T3 ports.

--
Regards
stephen_hope@xyzworld.com - replace xyz with ntl

Re: Frame Relay top speed 1.54 Mbps?

starting to learn CCNA, go easy on me :)

telcos -

speed
E3
as long as it is a serial port that support F/R encapsulation, then yes.
we use it at work to do multi VRF to a CE router from MPLS - in this case
there is no switch, just PVCs defined on a CE and a PE to give different sub
interfaces to keep the traffic flows segregated.
fastest one i know about is HSSI, which can do around 50 Mbps - but that
doesnt mean there arent other flavours...

--
Regards
stephen_hope@xyzworld.com - replace xyz with ntl

Re: Frame Relay top speed 1.54 Mbps?

just
transfer
F/R is

(45Mbps)

the
multiple
or
telco
encapsulation
high
such as
case
sub
ATM is a different format "on the wire", but many F/R switches are actually
hybrid F/R + ATM.
If you are using ATM as a data network format, then some frame & ATM formats
are compatible, and you can have a PVC that is F/R at 1 end (maybe for low
bandwidth since ATM isnt used on lines below 2 Mbps), but with ATM into
central site routers.
AFAIR last switches @ work were Alcatel 7670s (these come from the Newbridge
Networks product suite that Alcatel bought up). They are ATM internally, but
support F/R as an interface.
Cisco had a similar set of switches - now obsolete. Lightstream 1010s?
Finally ATM can go a lot faster than 155 Mbps if you had the right kit -
2.4G trunks between the 7670s.....

--
Regards
stephen_hope@xyzworld.com - replace xyz with ntl

Re: Frame Relay top speed 1.54 Mbps?
ANSWER: The technology of Frame-Relay is not limited to the speed of a =
T1 line.
Take this in the mindset of the OSI model:
(3) Network
(2) Data Link
(1) Physical
Frame-Relay and ATM are both layer 2 data-link technologies, just like =
Ethernet, Token-Ring, PPP, and HDLC. It is common to see WAN =
connections as T1 (a.k.a. DS-1) lines which are 1.5mb/s. This is =
probably the source of the misconception. Seperate the layer 2 =
frame-relay technology from the layer 1 circuit technologu that it =
commonly runs on.
You can have a fractional T-1 with speeds of 256k, 384k, etc...
You can combine T-1 lines with speeds totallying 3m, 4.5m, 6m, etc..
No matter which combination is used, the layer 2 signaling can be PPP, =
HDLC, frame-relay, ATM, etc...
Most of the time, the telco will provide lines at certian speeds. Yes, =
ATM is commonly used for faster lines. Yes, Frame-Relay is usually not =
found above 1.5mb/s.
EXAMPLE:
=20
Situation #1 - PPP
A single T-1 line is run directly between two office =
locations.
=20
RouterA(config)# interface serial 0
RouterA(config-if)# encapsulation ppp
RouterA(config-if)# ip address <ip address/subnet mask>
=20
RouterB(config)# interface serial 0
RouterB(config-if)# encapsulation ppp
RouterB(config-if)# ip address <ip address/subnet mask>
=20
Situation #2 - HDLC
A single T-1 line is run directly between two office =
locations.
=20
RouterA(config)# interface serial 0
RouterA(config-if)# encapsulation hdlc
RouterB(config-if)# ip address <ip address/subnet mask>
=20
RouterB(config)# interface serial 0
RouterB(config-if)# encapsulation hdlc
RouterB(config-if)# ip address <ip address/subnet mask>
=20
Situation #3 - Frame-Relay
Two T-1 lines are run between two office locations with the =
telco providing a frame-relay switch in between.
=20
RouterA(config)# interface serial 0
RouterA(config-if)# encapsulation frame-relay
RouterA(config)# interface serial 0.1
RouterA(config-if)# ip address <ip address/subnet mask>
RouterA(config-if)# frame-relay interface-dlci <DLCI number>
=20
RouterB(config)# interface serial 0
RouterB(config-if)# encapsulation frame-relay
RouterB(config)# interface serial 0.1
RouterB(config-if)# ip address <ip address/subnet mask>
RouterB(config-if)# frame-relay interface-dlci <DLCI number>
Situation #4 - Frame-Relay
Three T-1 line are run between three office locations with the =
telco providing a frame-relay switch in between.
=20
RouterA(config)# interface serial 0
RouterA(config-if)# encapsulation frame-relay
RouterA(config)# interface serial 0.<sub-interface number>
RouterA(config-if)# ip address <ip address/subnet mask>
RouterA(config-if)# frame-relay interface-dlci <DLCI number>
=20
RouterB(config)# interface serial 0
RouterB(config-if)# encapsulation frame-relay
RouterB(config)# interface serial 0.<sub-interface number>
RouterB(config-if)# ip address <ip address/subnet mask>
RouterB(config-if)# frame-relay interface-dlci <DLCI number>
=20
RouterC(config)# interface serial 0
RouterC(config-if)# encapsulation frame-relay
RouterC(config)# interface serial 0.<sub-interface number>
RouterC(config-if)# ip address <ip address/subnet mask>
RouterC(config-if)# frame-relay interface-dlci <DLCI number>
In the first three examples, a T-1 line is provided by the telco to both =
offices. Only in situation 3 and 4 does the company use frame-relay =
which requires that the telco has a frame-relay switch in the middle to =
switch frames to the proper destination circuit.
Frame-Relay allows multiple systems to communicate over the same =
switched frame-relay cloud. PPP and HDLC are intended for only two =
systems to communicate. A T-1 might only have two ends, but multiple =
T-1 lines can come together within the telco company frame-relay switch =
and become a multipoint communication "cloud".
Anyone with three Cisco 2500 series routers and some serial cables could =
configure one to be a frame-relay switch and interconnect the other two =
routers. Whatever the limit is of the serial ports, that is the limit =
of your frame-relay speed. Last I checked, it was 2,000,000 mb/s... =
possibly 4,000,000 mb/s. A HSSI (high speed serial interface) can =
transmit much faster. =20
If you had a T-1 connected to an external CSU/DSU, you would be able to =
use the lower speed 2500 series router serial port. =20
If you had a T-3 connected to an external CSU/DSU, you would need the =
speed of an HSSI, a high-speed serial interface. It can be a card on a =
3600 series, 7200 series, or many other routers.
=3D=3D=3D=3D=3D=3D
Scott Perry
=3D=3D=3D=3D=3D=3D
Indianapolis, Indiana
________________________________________
P.S. The Lightstream 1010 was common for ATM in the LAN, also known as =
LANE and a nightmare to me.

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