Packet fragmentation

INET radios ? Do you mean that as in

or do you mean a wireless radio links?

General questions about the operation and construction of wireless links are probably best handled in alt.internet.radio . This newsgroup is fine for specific questions about configuring Cisco wireless devices, but for that purpose it helps to specify the model number and software release.

these are INET radios. They connect to the ethernet port of the router at both ends. What I want to do is run packet fragmentation so i can pass voice traffic over the link using ppp encapsulation.

Thanks

ppp multilink ppp multilink fragment-delay 10 ppp multilink interleave

Flamer.

I seem to be having difficulty in finding a Cisco part number for that?

I do find an archive page linking an european ISP named iNet to Cisco, which references

but that page redirects to some Tektronics test and measuring equipment ??

here is the link

thanks but you can't put this on an ethernet interface and that exactly what i want to do.

router(f0/1)-- radio

-------------------------------------radio(routerf0/1).

I want to be able to do fragmentation as i need voice to go across. Thanks

Those devices do not appear to be manufactured or marketted by Cisco.

It seems I must be a bit more direct:

This is a Cisco-specific newsgroup, not a general newsgroup for discussion of networking-related matters. If your question does not involve Cisco equipment, this is probably not the correct newsgroup for it. If your question *does* involve Cisco equipment, then you need to indicate the model and software revision, and any unusual configuration elements.

thanks but you can't put this on an ethernet interface and that exactly what i want to do.

router(f0/1)-- radio

-------------------------------------radio(routerf0/1).

I want to be able to do fragmentation as i need voice to go across. Thanks

I probably not made myself clear but confused the matter by mentioning the radios. The radios are just the physical layer of the circuit just like a T1 repeater provided by a Telco for a Leased line. My question is how does one configure the etherent interface of a Cisco router to do multilink ppp encapsulation in order for me to do packet fragementation for voice traffic.

thanks

see Cisco doc "VoIP over PPP Links with Quality of Service (LLQ / IP RTP Priority, LFI, cRTP)"

Cisco suggests that you don't bother running Link Fragmentation and Interleaving on a full T1. Its not recommended for link speeds greater than 768kbps. Here's why. A data frame that is 1500 bytes takes less than 10ms to serialize on a full T1. The delay caused by the extra CPU cycles used in fragmenting the data frame can be greater than what you would save through fragmenting it. You probably want to be looking at some other QoS tools-- think Low Latency Queueing to set up a priority queue for your voice traffic.

However, if you want to use LFI, here's a sample config. This method uses Multilink PPP. The other option for use over a Frame Relay connection.

interface Multilink1 ip address 10.1.1.1 255.255.255.252 ppp multilink ppp multilink fragment delay 10 ppp multilink interleave ppp multilink group 1

interface Serial1/0 bandwidth 786 no ip address encapsulation ppp ppp multilink ppp multilink group 1

-- JebediahSpringfield

Cisco suggests that you don't bother running Link Fragmentation and Interleaving on links speeds greater than 768kbps. Here's why. A data frame that is 1500 bytes takes less than 10ms to serialize on a full T1. The delay caused by the extra CPU cycles used in fragmenting the data frame can be greater than the serialization delay of a 1500 byte frame. If you are talking about ethernet speed (10 mbps or greater), you definitely don't need LFI.

However, if you MUST use LFI over ppp, here's a sample config.

interface Multilink1 ip address 10.1.1.1 255.255.255.252 ppp multilink ppp multilink fragment delay 10 ppp multilink interleave ppp multilink group 1

interface Serial1/0 bandwidth 786 no ip address encapsulation ppp ppp multilink ppp multilink group 1

I doubt you can even do that on an ethernet interface and I can't see why you would want to. Think of other QoS mechanisms.... Low Latency Queueing to set up a priority queue for your voice traffic, Traffic policing and WRED on your non-priority traffic classes, etc.

--JebediahSpr> flamer snipped-for-privacy@hotmail.com wrote:

I need to fragment because the link speed is 512Kbps. thanks

Might " ip tcp adjust-mss 500" help? Or see if you can set the interface MTU and let PMTUD do it's thing? Set the MTU/mss values so that your voice gets through without fragmantation.

Your voice is presumably UDP so won't be affected by the tcp adjust-mss bit, If most of your non voice traffic is tcp then this might help a lot.

It is not quite the same thing as MPPP LFI since the full TCP/IP header is on each packet which will reduce the link efficiency a bit compared with LFI, but not by much.

I don't know of a way to get MPPP to run over ethernet. Now that I write it down it seems obvious, would PPPoE work? I have no idea if this is an appropriate deployment for it but it does sound like it should be.

Unfortunately, you have not answered the question as to what model and software revision you are using. You have narrowed down to "Cisco router", and you have tacitly acknowledged some snippets of IOS, but I've lost count of the number of routers Cisco sells these days.

here you go Cisco 2811 running ADV security 12.4.11T on both ends

Do I understand correctly that you want some link-level mechanism which fragments upon sending and reassembles at the router at the other end, making the fragmentation effectively transparent? Is there a particular reason that the existance of the fragmentation must be transparent?

Perhaps something like example 3 in

Loopback interface?

I have my own interest in this.

My understanding is that the OP wishes to use a 512k bps radio link to carry his traffic between two buildings.

The thing is that the radio link terminates in an ethernet port on each router and there are concerns about voice traffic.

I agree that ip tcp adj-mss is a reasonable plan however it does not address the general case of non tcp traffic and will not help with fancy queuing.

So:- Is there a way to run mppp (using only one link) between these two routers?

This will provide as I see it two benefits:-

1 - lfi 2 - Fancy queuing of whatever sort you like. 3 - (can't count) OP has two links, can possibly consider really running mppp with >1 link. Probably not a good idea with radio though due to possible re-ordering and delays.

What about L2TP?

I am interested since I want to do LLQ on dialers and I don't have the co-operation of the ISP. As far as I can determine Fancy Queuing is not supported on Dialers over ADSL unless MPPP is used.

Message "QoS - LLQ on Dialer (ADSL) 3725"

Discusses it further.